Classification of Cannabinoid Receptors

Thread starter #1
A. C. Howlett7,
F. Barth1,
T. I. Bonner2,
G. Cabral4,
P. Casellas1,
W. A. Devane5,
C. C. Felder6,
M. Herkenham3,
K. Mackie8,
B. R. Martin5,
R. Mechoulam9 and
R. G. Pertwee10

- Author Affiliations

1Sanofi-Synthelabo Recherche, Montpellier, Cedex, France (F.B., P.C.); 2Laboratory of Genetics (T.I.B.) and 3Section on Functional Neuroanatomy (M.H.), National Institute of Mental Health, Bethesda, Maryland; Departments of 4Microbiology and Immunology (G.C.) and5Pharmacology and Toxicology (W.A.D., B.R.M.), Virginia Commonwealth University, Richmond, Virginia; 6Eli Lilly & Co. Ltd., Lilly Research Centre, Windlesham, Surrey, United Kingdom (C.C.F.); 7Neuroscience of Drug Abuse Program, Julius L. Chambers Biomedical/Biotechnology Research Institute, North Carolina Central University, Durham, North Carolina (A.H.); 8Department of Anesthesiology, University of Washington, Seattle, Washington (K.M.); 9Department of Natural Products, Hebrew University, Medical Faculty, El Kerem Campus, Jerusalem, Israel (R.M.); and 10Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, United Kingdom (R.G.P.)

+ Navigate This Article

Next Section
Abstract

Two types of cannabinoid receptor have been discovered so far, CB1 (2.1: CBD:1:CB1:), cloned in 1990, and CB2(2.1:CBD:2:CB2:), cloned in 1993. Distinction between these receptors is based on differences in their predicted amino acid sequence, signaling mechanisms, tissue distribution, and sensitivity to certain potent agonists and antagonists that show marked selectivity for one or the other receptor type. Cannabinoid receptors CB1 and CB2 exhibit 48% amino acid sequence identity. Both receptor types are coupled through G proteins to adenylyl cyclase and mitogen-activated protein kinase. CB1 receptors are also coupled through G proteins to several types of calcium and potassium channels. These receptors exist primarily on central and peripheral neurons, one of their functions being to inhibit neurotransmitter release. Indeed, endogenous CB1 agonists probably serve as retrograde synaptic messengers. CB2 receptors are present mainly on immune cells. Such cells also express CB1receptors, albeit to a lesser extent, with both receptor types exerting a broad spectrum of immune effects that includes modulation of cytokine release. Of several endogenous agonists for cannabinoid receptors identified thus far, the most notable are arachidonoylethanolamide, 2-arachidonoylglycerol, and 2-arachidonylglyceryl ether. It is unclear whether these eicosanoid molecules are the only, or primary, endogenous agonists. Hence, we consider it premature to rename cannabinoid receptors after an endogenous agonist as is recommended by the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification. Although pharmacological evidence for the existence of additional types of cannabinoid receptor is emerging, other kinds of supporting evidence are still lacking.
Previous SectionNext Section
I. Introduction: Overview of the Cannabinoid Receptors

Cannabinoid receptors received their name as those receptors that respond to cannabinoid drugs, such as Δ9-tetrahydrocannabinol (Δ9-THC1; Fig. 1), derived from Cannabis sativa and its biologically active synthetic analogs. As detailed under Section II., synthetic agonists that bind to cannabinoid receptors include Δ9-THC-like analogs and aminoalkylindole compounds typified byR-(+)-WIN55212. Several endogenous ligands for cannabinoid receptors have also been identified, most notably arachidonoylethanolamide (anandamide), 2-arachidonoylglycerol, and 2-arachidonylglyceryl ether (noladin ether) (Section II.). However, because it is not yet clear whether these eicosanoid molecules are the only, or primary, endogenous agonists, we continue to call the receptors cannabinoid receptors rather than prematurely renaming them after an endogenous agonist as is recommended by the NC-IUPHAR. Cannabinoid receptor types are denoted by the abbreviation CB and numbered in the order of their discovery by a subscript (CB1, CB2). At present, two cannabinoid receptor types have been determined, the distinction between them being based on differences in their predicted amino acid sequence, their signaling mechanisms, and their tissue distribution. It has also proved possible to develop potent agonists and antagonists with marked selectivity for CB1 or CB2 receptors (Section II.) as well as CB1, CB2, and CB1/CB2 knockout mice (Section VI.).
Figure 1
View larger version:

In this page
In a new window

Figure 1

The structures of four constituents of cannabis: Δ9-THC, Δ8-THC, cannabinol, and cannabidiol.

The CB1 cannabinoid receptor (2.1:CBD:1:CB1:) has been cloned from rat, mouse, and human tissues and exhibits 97 to 99% amino acid sequence identity across species (Section V.). Its structure is that of a seven-transmembrane domain receptor, consistent with biochemical and cellular determinations of signal transduction via G proteins (Section IV.). CB1 receptor mRNA and protein are found primarily in brain and neuronal tissue (Section VII.). The CB2 cannabinoid receptor (2.1:CBD:2:CB2:) exhibits 48% homology with the CB1 cannabinoid receptor (Section V.). Expressed CB2receptor protein binds Δ9-THC-like, aminoalkylindole, and eicosanoid ligands (Section II.) and signals a response (Section IV.), thereby defining this receptor as being of the cannabinoid receptor class. The mouse CB2 receptor has been cloned and has an 82% sequence identity to the hCB2 receptor (Section V.). CB2 receptor mRNA is found primarily in immune tissue and is notably absent from normal nervous tissue (Section VII.). Any novel type(s) of cannabinoid receptor will be defined based on multiple criteria of primary structure homology, pharmacological characteristics in biological systems, and signal transduction mechanisms. Although some preliminary pharmacological evidence for the existence of additional types of cannabinoid receptor has already emerged (Section XI.), other kinds of evidence are still lacking.

The CB1 cannabinoid receptor has been extensively characterized for biological responses, and information about the structure-activity relationships of ligands for interaction with this receptor is extensive (Section II.). Claimed central nervous system responses to Δ9-THC and other cannabinoid receptor agonists include therapeutically beneficial effects of analgesia, attenuation of the nausea and vomiting in cancer chemotherapy, reduction of intraocular pressure, appetite stimulation in wasting syndromes, relief from muscle spasms/spasticity in multiple sclerosis, and decreased intestinal motility (for reviews, see Pertwee, 2000b; 2001a,b, 2002; Piomelli et al., 2000). Untoward side effects accompanying these therapeutic responses include alterations in cognition and memory, dysphoria/euphoria, and sedation (see Abood and Martin, 1992 for a review). Animal models that distinguish cannabinoid receptor activity include drug discrimination paradigms in rodents, pigeons, and nonhuman primates, a typical static ataxia in dogs, and a tetrad of responses in rodents (hypothermia, analgesia, hypoactivity, and catalepsy; reviewed under Section III.). Nerve-muscle tissue preparations (e.g., mouse vas deferens and guinea pig small intestine) respond to CB1 cannabinoid receptor agonists with an inhibition of electrically evoked contraction, believed to be the result of diminished release of neurotransmitter (Section III.). CB2mRNA has been found primarily in cells of the immune system (Sections VII. and IX.). However, because CB1 receptor transcripts have also been found in immune cells and tissues, it cannot be assumed that immune responses are solely regulated by the CB2 cannabinoid receptor. Therapeutic applications or untoward effects of cannabinoid receptor agonists in the immune system remain unclear. CB1 and CB2 cannabinoid receptors are both coupled to pertussis toxin-sensitive Gi/o proteins to inhibit adenylyl cyclase activity and to initiate the mitogen-activated protein kinase and immediate early gene signaling pathway(s) (Section IV.). In addition, CB1 receptors are coupled through Gi/o proteins to various types of potassium and calcium channels (Section IV.).

As to endogenous cannabinoid receptor agonists (endocannabinoids), it is likely that anandamide and 2-arachidonoylglycerol both function as neurotransmitters or neuromodulators and that one of their roles may be to serve as retrograde synaptic messengers (Section VIII.). Thus, there is evidence that they are synthesized by neurons “on demandâ€, that they can undergo depolarization-induced release from neurons, and that after their release, they are rapidly removed from the extracellular space by a membrane transport process yet to be fully characterized (Di Marzo et al., 1998; Maccarrone et al., 1998; Di Marzo, 1999; Piomelli et al., 1999; Hillard and Jarrahian, 2000). Once within the cell, anandamide is hydrolyzed to arachidonic acid and ethanolamine by the microsomal enzyme, fatty acid amide hydrolase (FAAH) (Di Marzo et al., 1998; Maccarrone et al., 1998; Di Marzo, 1999;Ueda et al., 2000). 2-Arachidonoylglycerol can also be hydrolyzed enzymically, both by FAAH and by other hydrolases yet to be characterized (Di Marzo et al., 1998; Di Marzo, 1999; Khanolkar and Makriyannis, 1999). Mechanisms underlying the release and fate of noladin ether remain to be identified.

This review summarizes the main features of the structure, pharmacology, and function of cannabinoid receptors that provide the basis for the classification of these receptors. Because it does not set out to be a comprehensive review of the literature, readers seeking more detail should refer to the many relevant reviews in the field (Table 1).
View this table:

In this window
In a new window

Table 1

Recent reviews on cannabinoid receptors or endogenous cannabinoids
Previous SectionNext Section
II. Classification of Ligands That Bind to Cannabinoid Receptors
A. Cannabinoid Receptor Agonists
1. Classical Cannabinoids.

This group of cannabinoids consists of ABC-tricyclic dibenzopyran derivatives that are either compounds occurring naturally in the plant, C. sativa, or synthetic analogs of these compounds. The most investigated of the classical cannabinoids have been Δ9-THC (Fig. 1), Δ8-THC (Fig. 1), 11-hydroxy-Δ8-THC-dimethylheptyl (HU-210) (Fig. 2), and desacetyl-l-nantradol (Fig. 2). Of these, Δ9-THC is the main psychotropic constituent of cannabis. Δ8-THC is also a psychotropic plant cannabinoid, whereas HU-210 and desacetyl-l-nantradol are synthetic cannabinoids. All these cannabinoids have been demonstrated to elicit cannabimimetic responses both in vivo and in vitro (Johnson and Melvin, 1986; Howlett et al., 1988; Martin et al., 1991; Martin et al., 1995; Pertwee, 1999).
Figure 2
View larger version:

In this page
In a new window

Figure 2

The structures of the synthetic classical cannabinoid receptor agonists, HU-210 and desacetyl-l-nantradol, and of HU-211, the (+)-enantiomer of HU-210.

Δ9-THC was first isolated from C. sativa in pure form by Gaoni and Mechoulam (1964), who also elucidated its structure. Its absolute stereochemistry was subsequently shown to be (6aR,10aR) (Mechoulam and Gaoni, 1967). Δ9-THC undergoes significant binding to cannabinoid receptors at submicromolar concentrations, with similar affinities for CB1 and CB2receptors (Table 2). At CB1 receptors, it behaves as a partial agonist, the size of its maximal effect in several CB1receptor-containing systems falling well below that of cannabinoid receptor agonists with higher relative intrinsic activity, such as CP55940 and R-(+)-WIN55212 (Gérard et al., 1991;Breivogel et al., 1998; Griffin et al., 1998; Pertwee, 1999). The relative intrinsic activity of Δ9-THC at CB2 receptors is even less than its relative intrinsic activity at CB1 receptors (Bayewitch et al., 1996; Pertwee, 1999). Indeed, in one set of experiments with CHO cells transfected with hCB2 receptors, in which the cyclic AMP assay was used, Δ9-THC failed to show any agonist activity at all, behaving instead as a CB2 receptor antagonist (Bayewitch et al., 1996). Δ9-THC has also been reported to behave as an antagonist at CB1 receptors both in the [35S]GTPγS assay performed with rat cerebellar membranes (Sim et al., 1996; Griffin et al., 1998) and when the measured response was cannabinoid-induced inhibition of glutamatergic synaptic transmission in rat cultured hippocampal neurons (Shen and Thayer, 1999).
View this table:

In this window
In a new window

Table 2

Ki values of certain ligands for the in vitro displacement of [3H]CP55940, [3H]R-(+)-WIN55212, or [3H]HU-243 from CB1- and CB2-specific binding sites

Δ8-THC has affinities for CB1 and CB2 receptors that are similar to those of Δ9-THC (Table 2) and also resembles Δ9-THC in behaving as a partial agonist at CB1 receptors (Matsuda et al., 1990;Gérard et al., 1991). However, its synthetic analog, HU-210, has relative intrinsic activities at CB1 and CB2 receptors that match those of the high-efficacy agonists, CP55940 and (+)-WIN55212 (Slipetz et al., 1995;Song and Bonner, 1996; Burkey et al., 1997; Griffin et al., 1998). HU-210 also has affinities for CB1 and CB2 receptors that exceed those of these other cannabinoids (Table 2). As a result, it is a particularly potent cannabinoid receptor agonist. Its pharmacological effects in vivo are also exceptionally long lasting. The enhanced affinity and relative intrinsic activity shown by HU-210 at cannabinoid receptors can be largely attributed to the replacement of the pentyl side chain of Δ8-THC with a dimethylheptyl group (see also below).

Like THC and HU-210, most classical cannabinoids that bind to CB1 have affinity for CB2as well, without major selectivity for either of these receptors. Thus, Δ9-THC-dimethylheptyl, 5′-F-Δ8-THC, 11-OH-cannabinol, 11-OH-cannabinol-dimethylheptyl, and cannabinol-dimethylheptyl-11-oic acid bind to both CB1 and CB2 receptors without major differences in theirKi values, although there are significant differential levels of potency between the various compounds (Showalter et al., 1996; Rhee et al., 1997). For example, theKi for Δ9-THC is about 40 nM for either receptor, whereas that for HU-210 is about 100 times lower (Showalter et al., 1996). Because binding values differ due to experimental conditions, data from different laboratories may vary considerably, but the general trend is apparently retained (Table2).

The first SAR determinations based on the Δ9-THC structure were summarized by Edery et al. (1971), and numerous reviews on this topic have since appeared (Mechoulam and Edery, 1973; Pars et al., 1977; Razdan, 1986; Mechoulam et al., 1987; Mechoulam et al., 1992; Martin et al., 1995). Most of the originally proposed SARs have withstood the erosion of time, although exceptions have been noted and certain refinements have had to be made. The SARs for classical cannabinoids at CB1receptors are summarized below (see Mechoulam et al., 1992 for references). They were established by animal experimentation (overt behavior in rhesus monkeys or baboons, dog static ataxia, the mouse ring test, spontaneous activity in rats and mice, and drug discrimination in THC-trained rats and pigeons, etc.; see Section III.). These tests are all presumed to involve CB1 receptor-mediated activity, and, indeed, a good correlation has been established between some of the above animal data and CB1 binding (Compton et al., 1993). However, since receptor binding is only the first step in a signal transduction pathway, lack of activation at some other point of the mechanistic cascade may result in a discrepancy between binding and activity. Thus, for example, Δ8-THC-11-oic-dimethylheptyl acid binds well to the CB1 receptor, but its inhibition of adenylyl cyclase is poor (Rhee et al., 1997). Current SAR information about classical cannabinoids is summarized below.

A dihydrobenzopyran-type structure with a hydroxyl group at the C-1 aromatic position and an alkyl group on the C-3 aromatic position seems to be a requirement. Opening of the pyran ring generally leads to complete loss of activity if both phenolic groups are present and are not substituted. Thus, (−)-cannabidiol (Fig. 1) has markedly less affinity for CB1 or CB2 receptors than Δ8- or Δ9-THC (Tables 2 and3).

The aromatic hydroxyl group has to be free or esterified for significant CB1 activity. Blocking of the hydroxyl group as an ether inactivates the molecule. It is possible that the esters are actually inactive but undergo hydrolysis to the free phenols in vivo. Thus, Δ9-THC acetate, when tested in vitro, shows negligible activity in biochemical reactions in which Δ9-THC is active (Banerjee et al., 1975).

The length of the chain on C-3 is of major importance. Some activity may be noted with propyl or butyl substitution; Δ9-THC has a pentyl group. A 1′,1′-dimethylheptyl or 1′,2′-dimethyl heptyl side chain strongly potentiates the cannabimimetic activity of compounds that have low activity in the n-pentyl series. An all carbon side chain on C-3 is not an absolute requirement. The side chain may contain an etheric oxygen (Loev et al., 1973).

11-Hydroxy THCs, which are major metabolites of classical cannabinoids, are potent cannabimimetics. Monohydroxylation on other positions of the terpene ring also usually leads to active derivatives. Dihydroxylation generally causes loss of activity. Further oxidation of the C-11 hydroxyl group to a carboxyl group causes inactivation.

Hydroxylation of C-1 of the side chain on C-3 abolishes activity. Hydroxylation at the other C-3 side chain carbons retains activity, with hydroxylation on C-3 of the side chain potentiating activity. Some of these hydroxylated compounds have been detected as major metabolites.

Alkylation of the C-2 aromatic position retains activity; alkylation on the C-4 position eliminates activity. Electronegative groups, such as carbonyl or carboxyl, at either C-2 or C-4 eliminate activity.

The methyl group on C-9 is not an absolute requirement for activity; 9-nor-Δ9-THC and 9-nor-Δ8-THC are active in the dog static ataxia test (Martin et al., 1975).

The double bond in the terpene ring is not essential for activity (Mechoulam and Edery, 1973; Mechoulam et al., 1980), and, indeed, this ring may be exchanged by some heterocyclic systems (Pars et al., 1977;Lee et al., 1983).

View this table:

In this window
In a new window

Table 3

CB1 and CB2 Ki values of stereoisomers of cannabidiol and of two cannabidiol analogs

Changes in the stereochemistry at various carbons of THC-type molecules may cause significant changes in pharmacological activity. The following tentative SARs have been proposed (Mechoulam et al., 1992):

The stereochemistry at 6a,10a in the natural active cannabinoids is trans(6aR,10aR). A few cis isomers have been tested and have shown very low activity. However, ciscompounds have not been studied over a wide range of tests. (6aS,10aS) THCs are either completely inactive or show very low activity both in animal tests and in binding assays. Thus, although the 6aR,10aR analog HU-210 is a highly potent cannabinoid, its 6aS,10aSenantiomer (HU-211), when well purified, has been shown to be less active by more than three orders of magnitude (Järbe et al., 1989; Howlett et al., 1990; Mechoulam et al., 1991; Felder et al., 1992; Pertwee et al., 1992). With Δ8- and Δ9-THC, the picture is less clear. In the original publications, the synthetic (+)-enantiomers of these cannabinoids were apparently not completely separated from the corresponding (−)-enantiomers, such that activity was determined to be about 5 to 10% of the (−) compounds (Mechoulam et al., 1992). For Δ9-THC, careful purification led to a (+)-enantiomer with activity less than 1% of the (−)-enantiomer (Herkenham et al., 1990; Matsuda et al., 1990; Felder et al., 1992;Pertwee, 1997).

Reduction of Δ9-THC leads to hexahydrocannabinol epimers that are both active, the equatorial epimer being considerably more active than the axial one (Mechoulam and Edery, 1973; Mechoulam et al., 1980). The same relationship is observed with the 11-hydroxyhexahydrocannabinols (Mechoulam et al., 1991). Thus, it seems that an equatorial substitution (i.e., one in which the C-9 methyl or hydroxymethyl group is in the plane of the cyclohexane ring) is preferable to an axial one.

Several hydroxylated metabolites of Δ9-THC and Δ8-THC are known in both epimeric forms. For example, 8α- and 8β-hydroxy-Δ9-THC and 7α- and 7β-hydroxy-Δ8-THC have been identified as relatively minor metabolites, and slight differences in activity between the epimers in each pair have been observed (Mechoulam and Edery, 1973; Razdan, 1986).

Recent experiments have shown that stereochemical changes can also affect the pharmacological activity of cannabidiol-type molecules (Bisogno et al., 2001). More specifically, (+)-CBD, (+)-5′-dimethylheptyl-CBD, and (+)-7-OH-5′-dimethylheptyl-CBD each has significantly greater affinity for CB1 and CB2 receptors than its corresponding (−)-enantiomer (Table 3). Unexpectedly, these findings indicate that the stereochemical prerequisites for binding to CB1 and CB2 receptors are not the same in the cannabidiol series in which the (+) (3S,4S) enantiomers show the greater cannabinoid receptor affinity as in the THC series in which the (−) (6aR,10aR) enantiomers show the greater cannabinoid receptor affinity. It is also noteworthy that both (+)- and (−)-CBD behave as vanilloid receptor agonists. Interestingly, these two enantiomers are equipotent at vanilloid receptors, each having an EC50 in the low micromolar range (Bisogno et al., 2001).

Despite the lack of CB1/CB2selectivity shown by the first generation of classical cannabinoids, it has proved possible to develop CB2-selective agonists from this series by making relatively minor changes to the THC molecule (Gareau et al., 1996; Huffman et al., 1996; Hanus et al., 1999). More specifically, Huffman et al. (1996) discovered that removal of the phenolic OH group from HU-210 to form 1-deoxy-11-OH-Δ8-THC-dimethylheptyl (JWH-051; Fig. 3) greatly enhanced affinity for CB2 receptors without significantly affecting CB1 affinity (Table 2). More remarkable still is the high degree of CB2 selectivity shown in binding experiments by JWH-133, JWH-139, and HU-308 (Fig. 3) and by the Merck Frosst compounds L-759633 and L-759656 (Fig. 3) (Merck Frosst Canada Ltd., Kirkland, QC, Canada), all of which bind to CB2 receptors at concentrations in the low nanomolar range (Table 2). L-759633 and L-759656 are both equipotent and equiefficacious with the high relative intrinsic activity agonist CP55940 at inhibiting forskolin-stimulated cyclic AMP accumulation in CHO cells expressing recombinant CB2 receptors (Ross et al., 1999a). It has also been found that L-759656 (10 μM) is inactive at CB1 receptors and that L-759633 behaves as a weak agonist at these receptors, with an EC50 of about 10 μM (Ross et al., 1999a). Similarly, HU-308 and JWH-133 are much more potent inhibitors of forskolin-stimulated cyclic AMP production by CB2- than by CB1-transfected CHO cells (Hanus et al., 1999;Pertwee, 2000a).
Figure 3
View larger version:

In this page
In a new window

Figure 3

The structures of the CB2-selective cannabinoid receptor agonists, HU-308, L-759633, L-759656, JWH-133, JWH-139, and JWH-051.
2. Nonclassical Cannabinoids.

During the course of their extensive SAR studies on the analgesic activity of classical cannabinoids, researchers at Pfizer synthesized new analogs lacking the dihydropyran ring of THC. CP47497 (Fig.4) represents the prototypical compound of this series of AC-bicyclic and ACD-tricyclic cannabinoid analogs (Melvin et al., 1984; Melvin et al., 1993). Further developments ultimately led to the bicyclic analog, CP55940 (Fig. 4), which has become one of the major cannabinoid agonists. Less lipophilic than THC, [3H]CP55940 has allowed the discovery and characterization of the CB1 cannabinoid receptor (Devane et al., 1988), and it is still the most used radiolabeled cannabinoid ligand. It binds to CB1and CB2 receptors with similar affinity (Table 2) and displays high activity in vivo as well, being 10 to 50 times more potent than Δ9-THC in the mouse tetrad model (Johnson and Melvin, 1986; Little et al., 1988). CP55940 behaves as a full agonist for both receptor types, its maximal effects in CB1 and CB2 receptor assay systems often matching or exceeding the maximal effects of several other cannabinoid receptor agonists (Pacheco et al., 1993; Slipetz et al., 1995; Burkey et al., 1997; Griffin et al., 1998; MacLennan et al., 1998; Pertwee, 1999). One potent ACD-tricyclic nonclassical cannabinoid is CP55244 (Fig. 4), which also displays signs of high affinity and high relative intrinsic activity, at least for CB1 receptors (Howlett et al., 1988; Little et al., 1988; Herkenham et al., 1990; Gérard et al., 1991; Griffin et al., 1998). Indeed, CP55244 seems to have even higher CB1 affinity and relative intrinsic activity than CP55940. It seems likely that other nonclassical cannabinoids share the ability of CP55940 to interact with CB2receptors; however, this remains to be established. Like classical cannabinoids, nonclassical cannabinoids with chiral centers exhibit significant stereoselectivity, those compounds with the same absolute stereochemistry as (−)-Δ9-THC at 6aand 10a (6aR,10aR) exhibiting the greater pharmacological activity (Little et al., 1988; Herkenham et al., 1990; Melvin et al., 1993).
Figure 4
View larger version:

In this page
In a new window

Figure 4

The structures of the (−)-enantiomers of three nonclassical cannabinoid receptor agonists: CP55940, CP47497, and CP55244.
3. Aminoalkylindoles.

Until the early 1990s, all the compounds known to act as cannabimimetics were structurally derived from THC. The situation changed when Sterling Winthrop researchers reported a new family of aminoalkylindoles possessing cannabimimetic properties. This discovery resulted from the development of structurally constrained analogs of pravadoline (Bell et al., 1991;Pacheco et al., 1991), a series of compounds with reduced ability to behave as nonsteroidal anti-inflammatory agents that inhibit cyclooxygenase but increased ability to bind to the CB1 receptor (D'Ambra et al., 1992; Eissenstat et al., 1995). R-(+)-WIN55212 (Fig.5) is the most highly studied, commercially available compound of the series. It displays high affinity for both cannabinoid receptors, with moderate selectivity in favor of the CB2 receptor (Table 2), and exhibits high relative intrinsic activity at both CB1 and CB2 receptors (Bouaboula et al., 1997; Griffin et al., 1998; Tao and Abood, 1998; Pertwee, 1999). In vivo, it produces the full spectrum of pharmacological effects of THC and substitutes totally for other cannabinoids in discriminative stimulus tests, whereas its S-(−)-enantiomer, WIN55212-3, lacks activity both in vivo and in vitro (Martin et al., 1991; Compton et al., 1992a;Pacheco et al., 1993; Slipetz et al., 1995; Wiley et al., 1995b;Pertwee, 1997; Pertwee, 1999). A [3H]R-(+)-WIN55212 assay has been developed, which has been used to characterize and map cannabinoid receptors in rat brain (Jansen et al., 1992; Kuster et al., 1993). There is evidence that R-(+)-WIN55212 binds differently to the CB1 receptor than classical or nonclassical cannabinoids, albeit in a manner that still permits displacement byR-(+)-WIN55212 of other known types of cannabinoid from CB1 binding sites (Petitet et al., 1996; Song and Bonner, 1996; Pertwee, 1997; Chin et al., 1998; Tao and Abood, 1998; see also Section V.).
Figure 5
View larger version:

In this page
In a new window

Figure 5

The structures of three aminoalkylindole cannabinoid receptor agonists: R-(+)-WIN55212, JWH-015, and L-768242.

A number of cannabinoid receptor agonists based on the aminoalkylindole structure have been prepared (see Huffman, 1999). As a result, it has been possible to demonstrate that activity is retained when the aminoalkyl substituent is replaced by simple n-alkyl chains (Huffman et al., 1994) or when the indole nucleus is replaced by a pyrrole ring (Lainton et al., 1995; Wiley et al., 1998) or an indene ring (Kumar et al., 1995). Interestingly, some of these newer aminoalkylindoles have been found to display significant selectivity for the CB2 receptor. Among these are JWH-015 (Fig. 5) and a series of Merck Frosst compounds that includes L-768242 (Fig. 5) (Gallant et al., 1996; Showalter et al., 1996) (see also Table 2).
4. Eicosanoids.

The prototypic member of the eicosanoid group of cannabinoid receptor agonists is anandamide, which belongs to the 20:4, n-6 series of fatty acid amides (Fig.6). This is the first of five endogenous cannabinoid receptor agonists to have been discovered in mammalian brain and certain other tissues (Devane et al., 1992b), the other compounds being homo-γ-linolenoylethanolamide and docosatetraenoylethanolamide (Hanus et al., 1993), 2-arachidonoylglycerol (Mechoulam et al., 1995; Sugiura et al., 1995), and noladin ether (Fig. 6) (Hanus et al., 2001). Of these endocannabinoids, the most investigated to date have been anandamide and 2-arachidonoylglycerol.
Figure 6
View larger version:

In this page
In a new window

Figure 6

The structures of five endogenous cannabinoids.

Anandamide resembles Δ9-THC in behaving as a partial agonist at CB1 receptors and in exhibiting less relative intrinsic activity at CB2 than CB1 receptors (Bayewitch et al., 1995; Rinaldi-Carmona et al., 1996a; Griffin et al., 1998; Pertwee, 1999). In line with this classification as a CB2 receptor partial agonist, it shares the ability of Δ9-THC (Section II.A.1.) to attenuate CB2receptor-mediated responses to an agonist with higher relative intrinsic activity (2-arachidonoylglycerol) (Gonsiorek et al., 2000). The anandamide molecule does not contain any chiral centers; however, some of its synthetic analogs do, one example being methanandamide, theR-(+)-isomer, which has nine times greater affinity for CB1 receptors than the S-(−)-isomer (Abadji et al., 1994). Structural modification of the anandamide molecule, which itself displays marginally higher affinity for CB1 than CB2 receptors, has led to the development of the first generation of CB1-selective agonists. Notable examples areR-(+)-methanandamide (Khanolkar et al., 1996; Lin et al., 1998), arachidonyl-2′-chloroethylamide (ACEA), arachidonylcyclopropylamide (ACPA) (Hillard et al., 1999), and O-1812 (Fig. 7) (Di Marzo et al., 2001a). The CB1 selectivity ofR-(+)-methanandamide stems from the introduction of a methyl group on the 1′ carbon of anandamide, a structural change that also confers greater resistance to the hydrolytic action of FAAH. Neither ACEA nor ACPA show any sign of reduced susceptibility to enzymic hydrolysis by FAAH, presumably because they lack a methyl substituent. Indeed, the addition of a methyl group to the 1′-carbon of ACEA markedly decreases the susceptibility of this compound to FAAH-mediated hydrolysis (Jarrahian et al., 2000). However, another consequence of this addition is a reduction of about 14-fold in CB1 receptor affinity. O-1812 also possesses a 1′-methyl substituent, and it too appears to lack significant susceptibility to hydrolysis by FAAH (Di Marzo et al., 2001a). Compared with anandamide, O-1812 exhibits higher affinity for the CB1 receptor, greater CB1/CB2 selectivity, and higher in vivo potency as a CB1 receptor agonist.
Figure 7
View larger version:

In this page
In a new window

Figure 7

The structures of the CB1-selective synthetic cannabinoid receptor agonists, methanandamide, ACEA, ACPA, and O-1812.

The following SARs have been proposed by Martin et al. (1999) for the production of CB1-like effects by the anandamide series of compounds (see Di Marzo et al., 1999; Palmer et al., 2000 for other recent reviews on the anandamide SAR).

Monosubstitution of the amide is a requirement for activity. Substitution by an alkyl, fluoroalkyl, or hydroxyalkyl increases activity, with a two- or three-carbon chain being optimal. Branching of the chain (methyl is optimal) retains activity.

Substitution of the hydroxyl in anandamide by a methyl ether, phenyl ether, or forming a phosphate derivative of anandamide decreases activity, whereas introduction of an amino or a carboxyl group eliminates activity.

Highest potencies are observed when structural changes are carried out in both the arachidonoyl and ethanolamide moieties of anandamide.

The introduction of an alkyl substituent (methyl is optimal) on the carbon α to the carbonyl or on the carbon adjacent to the nitrogen increases metabolic stability.

The SAR of the end pentyl chain (C-16 to C-20) in anandamide is very similar to that of classical cannabinoids; however, by branching the chain, the effect on pharmacological measures is not as dramatic in the anandamide series as in the classical series.

As a requirement for activity in the 20:x, n-6 series, x has to be three or four; however, activity is strongly reduced when n-6 is changed to n-3.

Activity is retained by increasing the chain length of anandamide by two methylenes (i.e., 22:4 and n-6) but is dramatically reduced or eliminated if the chain length is decreased by two methylenes.

Interpretation of SAR data for anandamide is complicated by evidence firstly, that this fatty acid amide is also an agonist for non-CB1, non-CB2 receptors, and secondly, that some of its metabolites also have pharmacological activity (Adams et al., 1998; Craib et al., 2001; Pertwee and Ross, 2002).

Turning now to 2-arachidonoylglycerol, there is evidence that this compound is an agonist for both CB1 and CB2 receptors (Stella et al., 1997; Sugiura et al., 1997b; Ben-Shabat et al., 1998) and that it exhibits higher relative intrinsic activity than anandamide at both CB1 and CB2 receptors (Pertwee, 1999; Gonsiorek et al., 2000; Savinainen et al., 2001). Like anandamide, 2-arachidonoylglycerol has marginally higher affinity for CB1 than CB2 receptors, its affinity for each of these receptors matching that of anandamide when the latter is protected from enzymic hydrolysis by phenylmethylsulfonyl fluoride (Table 2). Rather few structure-activity experiments have been performed with analogs of 2-arachidonoylglycerol thus far. The available data suggest that 1(3)-arachidonoylglycerol has similar CB1 and CB2 binding properties to 2-arachidonoylglycerol (Mechoulam et al., 1998) and that it is about three times more potent than 2-arachidonoylglycerol as a CB1 receptor agonist in vitro (Stella et al., 1997). There is also evidence that 2-palmitoylglycerol and 2-linoleoylglycerol lack significant affinity for CB1 or CB2 receptors (Mechoulam et al., 1995, 1998; Ben-Shabat et al., 1998) and that 1(3)-palmitoylglycerol and 1(3)-stearoylglycerol (10 μM) do not share the ability of 1(3)- and 2-arachidonoylglycerol to behave as CB1 receptor agonists in vitro (Stella et al., 1997).

As yet, few pharmacological experiments have been performed with noladin ether. These have generated data indicating that in contrast to anandamide and 2-arachidonoylglycerol, noladin ether has much higher affinity for CB1 receptors than for CB2 receptors (Hanus et al., 2001; Table 2). It also appears to have less relative intrinsic activity at CB1 receptors than 2-arachidonoylglycerol (Savinainen et al., 2001). As expected for a CB1receptor agonist, noladin ether produces hypokinesia, antinociception, catalepsy, and hypothermia in mice (Hanus et al., 2001).
B. Cannabinoid Receptor Antagonists/Inverse Agonists
1. Diarylpyrazoles.

The prototypic members of this series of compounds are the Sanofi compounds SR141716A, a potent CB1-selective ligand, and SR144528, a potent CB2-selective ligand (Fig.8). These ligands readily prevent or reverse effects mediated respectively by CB1 and CB2 receptors (Rinaldi-Carmona et al., 1994,1998). There are many reports that, by themselves, SR141716A and SR144528 can act on CB1 or CB2 receptors to produce effects that are converse to those produced by cannabinoid receptor agonists (Pertwee, 1999). Although these effects of the arylpyrazole antagonists may be attributable to the inhibition of endogenously produced agonists in the biological preparation, there is evidence that SR141716A and SR144528 can evoke inverse agonist responses (Bouaboula et al., 1997; MacLennan et al., 1998; Pan et al., 1998; Rinaldi-Carmona et al., 1998; Portier et al., 1999; Ross et al., 1999a; Coutts et al., 2000; Sim-Selley et al., 2001). This notion rests on the ability of the CB1 and CB2 receptors to exhibit signal transduction activity in the absence of endogenous or exogenous agonists (constitutive activity). As such, arylpyrazoles can behave as “inverse agonists†to reduce the constitutive activity of these signal transduction pathways. In some experiments, SR141716A has been found to be more potent in blocking the actions of CB1 receptor agonists than in eliciting inverse cannabimimetic responses by itself (Gessa et al., 1997, 1998a;Schlicker et al., 1997; Acquas et al., 2000; Sim-Selley et al., 2001).Sim-Selley et al. (2001) have obtained evidence that this may be because SR141716A binds with relatively low affinity to a site on the CB1 receptor that is distinct from the agonist binding site for which it has higher affinity. Their data also suggest that it is this lower affinity site that is responsible for the inverse agonist properties of SR141716A.
Figure 8
View larger version:

In this page
In a new window

Figure 8

The structures of the cannabinoid receptor antagonists/inverse agonists, SR141716A, AM251, AM281, SR144528, and LY320135.

Two analogs of SR141716A that have also been used to block CB1 receptor-mediated effects are AM251 and AM281 (Fig. 8). AM281 has 350 times greater affinity for CB1 than CB2 receptors (Table 2), and both analogs share the ability of SR141716A to attenuate responses to established cannabinoid receptor agonists (Gifford et al., 1997b; Al-Hayani and Davies, 2000; Cosenza et al., 2000; Izzo et al., 2000; Huang et al., 2001; Maejima et al., 2001; Simoneau et al., 2001;Wilson and Nicoll, 2001). There are also reports that like SR141716A, AM281 behaves as an inverse agonist when administered alone (Gifford et al., 1997b; Cosenza et al., 2000; Izzo et al., 2000). Current information about the SARs for SR141716A-like compounds can be summarized as follows.

Disubstitution of the amide nitrogen of SR141716A strongly decreases CB1 affinity (Lan et al., 1999b).

Replacement of the amide function by ketone, alcohol, or ether also greatly decreases CB1 binding affinity (Wiley et al., 2001). Interestingly, some of the ether or alkylamide derivatives display partial agonist activity in mice in vivo. The highly hindered endo-fenchyl amide was used to design the CB2 receptor antagonist SR144528 (Rinaldi-Carmona et al., 1998).

Although the 2,4-dichlorophenyl substituent at the 1-position of the pyrazole ring seems to be optimal (Barth and Rinaldi-Carmona, 1999), its replacement by a 1-(5-isothiocyanato)-pentyl group decreases CB1 affinity only by a factor 4 (Howlett et al., 2000). The phenyl group has been replaced by a 4-methylbenzyl group in SR144528 (Rinaldi-Carmona et al., 1998).

In the 3-position of the pyrazole ring of SR141716A, replacement of theN-aminopiperidine substituent by the related 5- or 7-membered rings or by cyclohexyl does not alter CB1 binding affinity, whereas replacement by aminomorpholine or linear alkyl chains leads to a reduction in CB1 affinity (Lan et al., 1999b; Wiley et al., 2001).

Compounds with methyl, bromine, or iodine in the 4-position of the pyrazole ring are approximately equipotent, whereas replacement of methyl with hydrogen at this position results in a 12-fold decrease in CB1 affinity (Wiley et al., 2001). Methyl has been replaced by hydrogen at the 4-position of the pyrazole ring in SR144528.

In the 5-position of the pyrazole ring, replacement of the 4-chloro substituent of the phenyl group by other halogen or alkyl groups does not alter CB1 binding affinity (Thomas et al., 1998; Lan et al., 1999b). However, replacement by nitro or amino groups or displacement from the 4-(para) position to the 2-position of the phenyl group leads to poor CB1 receptor ligands, and replacement of the aromatic ring by alkyl groups abolishes CB1 affinity (Lan et al., 1999b).

A particularly potent compound in the SR141716A series is AM251 (Fig.8). This contains a para-iodophenyl group at the 5-position, a piperidinyl carboxamide at the 3-position, and a 2,4-dichlorophenyl group at the 1-position of the pyrazole ring (Lan et al., 1999b).

2. Other Chemical Series.

The most notable members of these series are the substituted benzofuran, LY320135, and the aminoalkylindole, 6-iodopravadoline (AM630) (Fig.9). LY320135, developed by Eli Lilly, shares the ability of SR141716A to bind with much higher affinity to CB1 than CB2 receptors (Table 2). However, it has less affinity for CB1receptors than SR141716A and, at concentrations in the low micromolar range, also binds to muscarinic and 5-HT2receptors (Felder et al., 1998). Like SR141716A, LY320135 not only blocks the effects of CB1 receptor agonists (Felder et al., 1998; Coruzzi et al., 1999; Holland et al., 1999;Molderings et al., 1999; Christopoulos et al., 2001) but also exhibits inverse agonist activity at some signal transduction pathways of the CB1 receptor (Felder et al., 1998; Christopoulos et al., 2001).
Figure 9
View larger version:

In this page
In a new window

Figure 9

The structures of the pravadoline analogs, AM630, WIN56098, and WIN54461 (6-bromopravadoline).

AM630 is a CB2-selective antagonist/inverse agonist. Thus, experiments with hCB2-transfected CHO cell preparations have shown that it potently reverses CP55940-induced inhibition of forskolin-stimulated cyclic AMP production (EC50 = 128.6 nM) and that when administered by itself, it enhances forskolin-stimulated cyclic AMP production (EC50 = 230.4 nM) and inhibits [35S]GTPγS binding (EC50 = 76.6 nM) (Ross et al., 1999a). The inverse agonist activity of AM630 at CB2receptors appears to be less than that of SR144528 (Ross et al., 1999b). As to the ability of AM630 to interact with CB1 receptors, results from several investigations, when taken together, suggest that this ligand has mixed agonist-antagonist properties and that it is a low-affinity partial CB1 agonist (Pertwee et al., 1996; Hosohata et al., 1997a,b; Pertwee, 1999; Ross et al., 1999a). There is also one report that it can behave as a low-potency inverse agonist at CB1 receptors (Landsman et al., 1998). The ability of AM630 to behave as a cannabinoid receptor antagonist was first noted in experiments with the mouse isolated vas deferens, which yielded dissociation constant (KB) values for AM630 against Δ9-THC and CP55940 of 14.0 and 17.3 nM, respectively (Pertwee et al., 1995a). The pharmacological properties of AM630 in vivo have yet to be investigated. Two other aminoalkylindoles that have been found to attenuate responses to cannabinoids in the mouse isolated vas deferens are the Sterling Winthrop compounds, WIN56098 and WIN54461 (Fig.9). WIN56098 is the weaker antagonist, itsKB value for antagonism of Δ9-THC being 1.85 μM (Pacheco et al., 1991). Corresponding potency values for WIN54461 againstR-(+)-WIN55212 and Δ9-THC have been reported to be 159 and 251 nM, respectively (Eissenstat et al., 1995). The IC50 value of WIN54461 for displacement of [3H]R-(+)-WIN55212 from rat cerebellar membranes has been reported to be 515 nM by Eissenstat et al. (1995). However, they also found WIN54461 to lack detectable antagonist properties in vivo.

One compound that is close to being a CB1/CB2 receptor antagonist that lacks any agonist or inverse agonist activity is the classical cannabinoid 6′-azidohex-2′-yne-Δ8-THC (O-1184) (Fig. 10). In addition to a terminal N3 group, the C-3 alkyl side chain of this ligand contains a carbon-carbon triple bond, a structural modification that decreases relative intrinsic activity at CB1 and CB2 receptors without affecting CB1 or CB2 affinity (Ross et al., 1999b). At CB1 receptors, O-1184 behaves as a high-affinity, low-efficacy agonist, whereas at CB2 receptors, it behaves as a high-affinity, low-efficacy inverse agonist (Ross et al., 1998, 1999b). O-1238 (Fig.10), in which the carbon-carbon triple bond of O-1184 is replaced by a carbon-carbon double bond, has higher efficacy than O-1184 at CB1 receptors and behaves as a high-affinity, low-efficacy partial agonist at CB2 receptors (Ross et al., 1999b).
Figure 10
View larger version:

In this page
In a new window

Figure 10

The structures of O-1184 and O-1238.
Previous SectionNext Section
III. Bioassay
A. In Vivo Bioassay Systems
1. Introduction.

Cannabinoids produce a complex array of behavioral effects that have been characterized in numerous animal species as well as in humans. Although the diverse behavioral effects of cannabinoids provide ample opportunity for quantitating the pharmacological actions of this class of compounds, they provide a challenge to the elucidation of mechanism of action. A major focus of cannabinoid research has been the identification of pharmacological effects that are receptor-mediated. Until the recent development of a specific CB1 receptor antagonist, SARs provided the only in vivo approach for implicating receptor mechanisms. A major goal of cannabinoid research is elucidating the mechanisms responsible for the behavioral “highâ€. Of course, the psychotomimetic effects can only be assessed in humans, which imposes severe restrictions on SAR studies. Few cannabinoid analogs have sufficient toxicological histories to qualify for human experimentation. The difficulties with human studies have necessitated close examination of pharmacological effects in several animal species, many of which vary in their response to cannabinoids. However, it has now been established that numerous pharmacological effects are mediated via the cannabinoid receptor. There are several fundamental principles that have guided this undertaking. One of the most critical aspects of the choice is whether the pharmacological measure in animals is representative of cannabinoid effects in humans. Equally important is the characterization of behavioral effects that are unique to cannabinoids (i.e., mediated through cannabinoid receptors). Finally, there are the practical aspects of selecting pharmacological effects that can be quantitated and readily obtained. Using these criteria, several pharmacological effects in vivo can be attributed to the activation of cannabinoid receptors.
2. Dog Static Ataxia.

Walton et al. (1937) described the effects of cannabinoids in dogs, which represented one of the first animal models that was highly unique for this class of compounds. These effects include sedation, catalepsy, motor incoordination, and hyperexcitability; however, it is the combination of these effects that causes dogs to weave to and fro while remaining fixed in one spot that led to the somewhat anomalous term “static ataxiaâ€. Again, the primary advantage of this model is that these behaviors describe a highly specific profile for cannabinoids that is not confused with that produced by other behaviorally active compounds. These behaviors can also be semiquantitated, and extensive SAR studies have revealed both dramatic changes in potency with modest changes in structure (Walton et al., 1937; Martin et al., 1975; Beardsley et al., 1987) and enantioselectivity (Dewey et al., 1984; Little et al., 1989). The strength of this model is that the results obtained correlate well with psychoactivity. These findings strongly suggest that cannabinoid-induced static ataxia is receptor-mediated. Moreover, the CB1 receptor antagonist, SR141716A, antagonizes the effects of Δ9-THC in this model, a finding that strongly supports CB1 involvement (Lichtman et al., 1998).
3. Overt Behavior in Monkeys.

Mechoulam and colleagues (Edery et al., 1971) synthesized a large number of cannabinoid analogs that allowed them to develop the first framework for describing the structural features that were critical for cannabinoid pharmacological activity. Their model was based on the gross observation of overt behavioral effects in monkeys. The cannabinoids produced sedation, ptosis, body sag, etc., which was reasonably selective for cannabinoids and could be rated in a semiquantitative fashion. They described a SAR that also included enantioselectivity (Edery et al., 1971); however, there have been no reports of reversal of these effects by the CB1 receptor antagonist, SR141716A.
4. Rat Drug Discrimination.

Drug discrimination is considered one of the most reliable means of predicting whether test drugs produce subjective effects similar to those of a known drug. Initially, an animal is trained to press a lever for food reward and then subsequently trained to press a specific lever for this reward when under the influence of Δ9-THC and another lever when any other drug is administered. Therefore, on test days, which lever the animal chooses tells the experimenter whether the test compound is perceived as THC-like or not. Much of the early rat drug discrimination literature for the cannabinoids was generated by Järbe's laboratory (Järbe and Ohlin, 1977; Järbe and McMillan, 1979, 1980; Järbe et al., 1989; Järbe and Mathis, 1992). Rats have also been trained to discriminate between CP55940, a potent cannabinoid agonist, and vehicle (Gold et al., 1992). These animals perceived Δ9-THC as being like CP55940. Furthermore, the Δ9-THC-discriminative cue has been shown to be selective for cannabinoids (Barrett et al., 1995).

SAR data have been obtained in drug discrimination experiments conducted with the aminoalkylindoles (Compton et al., 1992a), various other structurally dissimilar cannabinoids (Wiley et al., 1995b), and anandamide (Wiley et al., 1995a). The results from all of these studies are consistent with receptor affinity for the CB1receptor. In addition, SR141716A was shown to block the discriminative properties of rats trained on CP55940 (Wiley et al., 1995b) and on Δ9-THC (Wiley et al., 1995c). Therefore, the discriminative properties of cannabinoids appear to be mediated through CB1 receptors. More importantly, there is an excellent correlation between drugs that engender cannabinoid responding in the drug discrimination paradigm and psychoactivity in humans (Balster and Prescott, 1992).
5. Monkey Drug Discrimination.

The above description of drug discrimination in rats applies to monkeys; however, it has been argued that primates may provide a more accurate reflection of cannabinoid behavioral effects in humans. This model has provided reassuring data that novel cannabinoids, such as CP55940 (Gold et al., 1992),R-(+)-WIN55212 (Compton et al., 1992a), and the endogenous ligand anandamide (Wiley et al., 1997), are likely to produce cannabinoid behavioral effects in humans. Establishing this fact is particularly crucial since these compounds are being used widely as cannabinoid probes. As with the rat drug discrimination, SR141716A was shown to block the discriminative properties of Δ9-THC (Wiley et al., 1995c), thereby implicating CB1 receptors.
6. Mouse Tetrad Model.

As mentioned earlier, cannabinoids are known to produce a wide range of pharmacological effects that include hyperstimulation, sedation, catalepsy, and several other depressant properties. Individually, none of these effects can be considered unique for cannabinoids, since all of these properties are shared by numerous classes of centrally active agents. Several years ago, it was discovered that i.v. administration of cannabinoids in mice produced sedation, hypothermia, antinociception, and catalepsy in the same dose range and within the same time frame, so that all four behaviors could be determined in the same animal for each injection (Martin et al., 1987). Compounds active in this composite model also produce effects in models that we traditionally consider to be highly predictive of cannabinoid effects, such as drug discrimination (Compton et al., 1993). Furthermore, the SAR studies in the mouse tetrad model are consistent with affinity for the CB1 receptor for CP55940 and related analogs (Little et al., 1988; Compton et al., 1992b), enantiomers of dimethylheptyl analogs of THC (Little et al., 1989), aminoalkylindoles (Compton et al., 1992a; Huffman et al., 1994), and endocannabinoids (Adams et al., 1998). It has also been shown that SR141716A is highly effective in blocking the effects of most cannabinoid analogs in the mouse tetrad model (Rinaldi-Carmona et al., 1994; Compton et al., 1996), confirming the involvement of CB1 receptors. The one exception has been the endocannabinoids (Adams et al., 1998). Although SR141716A fails to block the effects of anandamide, it is capable of blocking the effects of metabolically stable anandamide analogs (Adams et al., 1998). However, some anandamide analogs are effective in the mouse tetrad and apparently bind with little affinity for the CB1receptor (Di Marzo et al., 2001a). There are several possible explanations for these discrepancies, one of which is that the mouse tetrad may not be selective for cannabinoids. If future studies reveal that false positives can occur in this model, then it will be necessary to verify the results in this model with antagonism studies using a CB1-selective antagonist.
7. Memory Models.

The naturally occurring cannabinoids, as well as a wide range of synthetic compounds, have been demonstrated to impair learning and memory in rodents (Carlini et al., 1970), nonhuman primates (Ferraro and Grilly, 1973), and humans (Abel, 1971). Δ9-THC has been found to disrupt memory as assessed in the delayed match-to-sample task (Heyser et al., 1993), Lashley III maze (Carlini et al., 1970), and the eight-arm radial maze (Nakamura et al., 1991). Δ9-THC, CP55940, andR-(+)-WIN55212 all impaired working memory in rats in the eight-arm radial maze and the delayed nonmatch-to-sample task. Lichtman and Martin (1996) also found that Δ9-THC, CP55940, and R-(+)-WIN55212, administered systemically, impaired spatial memory in rats as assessed by the eight-arm radial maze and retarded completion time. Direct injection of CP55940 into the hippocampus impaired memory, which appeared specific to cognition since no other pharmacological effects were produced (Lichtman et al., 1995). The effects of cannabinoid on memory in rats are also blocked by SR141716A, providing strong evidence that these effects are mediated through CB1 receptors (Lichtman and Martin, 1996). Furthermore, the eight-arm radial maze has also been modified to evaluate agents for their potential to enhance memory performance. Under these conditions, SR141716A administration improved the performance of rats (Lichtman, 2000). Another learning and memory paradigm that has become increasingly popular in recent years is the Morris water maze. Reference memory can be assessed by requiring a well trained rat or mouse to navigate to a hidden platform that always remains in the same location, whereas working memory is assessed by requiring the animal to learn a new platform location each session. In this model, Δ9-THC disrupts working memory at doses much lower than those required to interfere with reference memory (Varvel et al., 2001). Additionally, SR141716A reverses the effects of Δ9-THC, demonstrating CB1-mediated effects. This model is ideal for assessing the SARs of cannabinoid agonists and antagonists.
8. Human Assays.

Cannabinoids that have been evaluated in humans include the active constituents in marihuana, their metabolites, and some agents with therapeutic potential (Razdan, 1986). Some of the earlier studies demonstrated that SAR could be conducted in humans (Perez-Reyes et al., 1972; Hollister, 1974). These evaluations in humans provided the basis for correlating psychotomimetic potency to potency in animal models. For the more than 20 cannabinoids that have been evaluated in humans, an excellent correlation exists between the cannabinoid subjective effects in humans and drug discrimination in laboratory animals (Balster and Prescott, 1992). Since CB1 receptors have been implicated in mediating drug discrimination, as discussed above, it seems most plausible that the behavioral effects in humans are mediated through the CB1 receptor. More conclusive evidence came from recent studies demonstrating that SR141716A blocks cannabinoid subjective effects as well as cannabinoid-induced tachycardia in humans (Huestis et al., 2001).
B. In Vitro Bioassay Systems
1. Binding Assays.

As detailed elsewhere (Pertwee, 1997,1999), the most widely used radiolabeled cannabinoid receptor probe is [3H]CP55940. Because CP55940 has approximately equal affinity for CB1 and CB2 binding sites (Table 2), displacement assays with [3H]CP55940 that are directed at characterizing the binding properties of novel unlabeled ligands are generally performed with membranes that are known to contain either CB1 or CB2 receptors but not both receptor types. These membranes are often obtained from cells transfected with CB1 or CB2receptors. An alternative practice has been to use tissues that express dense populations of CB1 or CB2 receptors naturally, usually brain tissue for CB1 receptors and spleen tissue for CB2 receptors. However, although brain tissue is largely populated with CB1 receptors, some CB2 receptors may also be present on microglia (Kearn and Hillard, 1999; see also Section VII.B.). Similarly, although most cannabinoid receptors in the spleen are CB2, some CB1 receptors are expressed by this tissue as well (Bouaboula et al., 1993;Galiègue et al., 1995; Ishac et al., 1996). The possibility also exists that brain and/or spleen express types of cannabinoid receptor yet to be identified. Indeed, there is already some evidence that mammalian brain, spinal cord, and peripheral nervous system can express additional types of cannabinoid receptor (Section XI.).

Other commercially available probes with high affinity for cannabinoid receptors are [3H]SR141716A, which is CB1-selective (Rinaldi-Carmona et al., 1996b; Table 2), [3H]HU-243, which binds more or less equally well to both CB1 and CB2 receptor (Devane et al., 1992a; Bayewitch et al., 1995), and [3H]R-(+)-WIN55212, which has marginally greater affinity for CB2than CB1 binding sites (Slipetz et al., 1995;Song and Bonner, 1996; see also Pertwee, 1999). Tritiated 11-hydroxy-Δ9-THC-1′,1′-dimethylheptyl has also been synthesized and used in cannabinoid binding assays (Thomas et al., 1992). However, this ligand is not generally available. Three other radiolabeled ligands have been developed as potential probes for human single photon emission computed tomography or positron emission tomography experiments. These are 123I-labeled analogs of AM251 and AM281 (Lan et al., 1996; Gatley et al., 1997;Gatley et al., 1998) and an 18F-labeled analog of SR141716A (SR144385) (Barth, 1998). Particularly promising single photon emission computed tomography results have been obtained from animal experiments with [123I]AM281 (Gatley et al., 1998).
2. Inhibition of Cyclic AMP Production.

The ability of cannabinoid CB1 and CB2receptor agonists to inhibit basal or drug-induced cyclic AMP production is widely exploited for the quantitative, functional bioassay of cannabinoids in vitro (see Pertwee, 1997, 1999). Although many types of receptor are negatively coupled to adenylyl cyclase, it is still possible to achieve selectivity by using a CB1 or CB2 receptor antagonist or by performing assays with cells transfected with CB1 or CB2 receptors. Preparations that are particularly sensitive to the inhibitory effect of cannabinoids on cyclic AMP production are cultured cells transfected with CB1 or CB2 receptors, certain cultured cell lines that express CB1receptors naturally, and CB1 receptor-containing membrane preparations obtained from the brain (see Pertwee, 1997,1999). Cells expressing CB2 receptors naturally (e.g., mouse spleen cells and human lymphocytes) are relatively insensitive to cannabinoid-induced inhibition of cyclic AMP production (Pertwee, 1997).
3. [35S]Guanosine-5′-O-(3-thiotriphosphate) Binding Assay.

This bioassay exploits the coupling of CB1 and CB2 receptors to G proteins. It relies on the increase in G protein affinity for GTP (and hence [35S]GTPγS) that is triggered by the occupation by agonist molecules of CB1 or CB2 receptors, the measured response being net agonist-stimulated [35S]GTPγS binding to G protein. The assay can be performed with the same range of tissue preparations that are used for the cyclic AMP assay, again in the presence or absence of selective CB1 or CB2 antagonists. In addition, [35S]GTPγS is sometimes used in autoradiography experiments with tissue sections (Sim et al., 1995;Selley et al., 1996; Breivogel et al., 1997). To minimize [35S]GTPγS binding that occurs in the absence of the agonist and so maximize agonist-induced stimulation of binding, high amounts of GDP and sodium chloride are usually added to the bioassay system (Sim et al., 1995; Selley et al., 1996; Breivogel et al., 1998). Since GDP decreases basal binding of [35S]GTPγS to a greater extent than agonist-stimulated binding, the overall consequence of adding GDP is an increase in net agonist-stimulated [35S]GTPγS binding (Breivogel et al., 1998). The extent to which net agonist-stimulated [35S]GTPγS binding can be enhanced in this way is limited by the concentration-related inhibitory effect that GDP has on absolute levels of both basal and agonist-stimulated binding. Thus, as GDP concentrations are progressively raised, a point is eventually reached at which [35S]GTPγS binding has fallen to a level that is too low to be measured reproducibly (Selley et al., 1996). The optimal GDP concentration appears to be higher for the assay of agonists with high than with low relative intrinsic activities, such that the ability of an agonist with low relative intrinsic activity to increase [35S]GTPγS binding above basal levels may be completely abolished when the concentration of GDP is increased (Breivogel et al., 1998; Griffin et al., 1998).

The [35S]GTPγS assay is less sensitive than the cyclic AMP and isolated tissue assays described underSections III.B.2. or III.B.4. Presumably, this is because the measured responses in these other bioassays are located further along the signaling cascade than G protein, so that there is greater signal amplification. The [35S]GTPγS assay should be independent of any variations that may exist between tissues in the relative contribution made by different G protein-coupled effector mechanisms. This is because it provides a total measure of G protein-mediated cannabinoid receptor activation rather than a measure of the activation of just one particular cannabinoid receptor effector mechanism as in the cyclic AMP assay. However, the [35S]GTPγS assay will be affected by both the type and the relative abundance of G protein α subunits. For example, if more Goα is expressed than Giα, the Goα response will dominate. Also, some G protein α subunits, such as Gq/11, are difficult to detect in the [35S]GTPγS assay.
4. Inhibition of Electrically Evoked Contractions of Isolated Smooth Muscle Preparations.

Smooth muscle preparations most often used for the bioassay of cannabinoids are the mouse isolated vas deferens and the myenteric plexus-longitudinal muscle preparation of guinea pig small intestine. These bioassays, which are particularly sensitive, rely on the ability of cannabinoid receptor agonists to act through CB1 receptors to inhibit electrically evoked contractions (Pertwee et al., 1992; Pertwee, 1997, Pertwee, 2001a). The CB1 receptors are located on prejunctional neurons and mediate inhibition of electrically evoked contractile transmitter release (Coutts and Pertwee, 1997; Pertwee, 1997; Schlicker and Kathmann, 2001). It is also possible that CB2-like receptors (see Section XI.) share the ability of CB1receptors to mediate inhibition of evoked contractions of the mouse vas deferens (Griffin et al., 1997). Several types of noncannabinoid receptor can mediate inhibition of evoked contractions of the mouse vas deferens or myenteric plexus-longitudinal muscle preparation. Consequently, to achieve selectivity, it is necessary to establish the susceptibility of agonists to antagonism by a selective CB1 antagonist, such as SR141716A (Pertwee et al., 1995b, 1996).
C. Practical Difficulties

One practical difficulty associated with the bioassay of cannabinoids both in vivo and in vitro is the high lipophilicity and low water solubility of these compounds, as this necessitates the use of nonaqueous vehicles. Indeed, it was this difficulty that prompted the development of the water-soluble cannabinoid receptor agonist O-1057 (Pertwee et al., 2000). Commonly used vehicles for the in vivo or in vitro administration of cannabinoid receptor agonists and antagonists include ethanol, dimethyl sulfoxide, polyvinylpyrrolidone, Tween 80, Cremophor, Emulphor, and bovine serum albumin (BSA). These are used singly or in combination, either by themselves or mixed with water or saline. Results obtained using such vehicles should be interpreted with caution because the vehicles may themselves produce pharmacological changes, for example, by perturbing membrane phospholipids. Consequently, vehicle control experiments are vital. These vehicles may also affect the apparent potencies of cannabinoid receptor ligands. Indeed, as detailed elsewhere (Pertwee, 1997), there are reports that [3H]CP55940 binding to CB1-containing membranes can be markedly influenced by the concentration of BSA used for cannabinoid solubilization. For example, in binding experiments with rat brain sections, Herkenham et al. (1991) found the apparent dissociation constant of [3H]CP55940 to be 2.6 nM in the presence of 1% BSA but 15 nM in the presence of 5% BSA. For endocannabinoids, a second practical difficulty is that they are substrates both of membrane transporters and of hydrolytic enzymes such as FAAH (Section I.). It is for this reason that experiments with anandamide are often performed in the presence of a FAAH inhibitor, such as the general protease inhibitor phenylmethylsulfonyl fluoride (see Pertwee, 1997). Alternative strategies have been to perform experiments with FAAH−/− mice (Cravatt et al., 2001) or with analogs that are more resistant than anandamide to enzymic hydrolysis, for example, R-(+)-methanandamide (Section II.).
Previous SectionNext Section
IV. Cellular Signal Transduction

Agonist stimulation of CB1 and CB2 cannabinoid receptors activates a number of signal transduction pathways via the Gi/o family of G proteins (see reviews by Howlett, 1995a; Pertwee, 1997, 1999). CB1 receptor signaling through G proteins has been demonstrated by [35S]GTPγS binding using rat brain membranes and brain slices (see Section III.B. for references). For CB1 receptor-stimulated [35S]GTPγS binding, anandamide andR-(+)-methanandamide are partial agonists compared withR-(+)-WIN55212, levonantradol, CP55940, 2-arachidonoylglycerol, and desacetyl-l-nantradol (see Howlett and Mukhopadhyay, 2000 for review and original references). In CHO cells expressing recombinant hCB2 receptors, [35S]GTPγS binding was stimulated by anandamide as a partial agonist compared with HU-210, whereas 2-arachidonoylglycerol was a full agonist (Hillard et al., 1999;Gonsiorek et al., 2000). Inverse agonist activity exhibited by SR141716A and analogs has been most clearly demonstrated by a decrement in [35S]GTPγS binding to G proteins in brain preparations (Landsman et al., 1997; Meschler et al., 2000).

Free Giα proteins regulate adenylyl cyclase, leading to an inhibition of cyclic AMP production. The consequent damping of phosphorylation by protein kinase A may modulate signaling pathways, such as that of ion channels and focal adhesion kinase. It is believed that free βγ dimers mediate the regulation of ion channels, mitogen-activated protein kinase (MAPK), and phosphatidylinositol-3-kinase (PI3K). However, it is not clear which Gi/oα subtypes might be associated with the βγ dimers in heterotrimers responsible for those responses. It should be noted that values of potency and relative intrinsic activity may differ for the various signal transduction pathways. The relative intrinsic activities of various cannabinoid receptor agonists to evoke a response via G proteins has been discussed by Breivogel et al. (1998)and Kearn et al. (1999). This section will summarize the most well characterized signaling pathways for cannabinoid receptors.
A. Regulation of Adenylyl Cyclase

Inhibition of adenylyl cyclase has been characterized in brain tissue and neuronal cells expressing CB1 and in human lymphocytes and mouse spleen cells expressing CB2 receptors (see Howlett and Mukhopadhyay, 2000and Pertwee, 1997, 1999 for review). The finding that cultured cell lines that express recombinant CB1 or CB2 receptors lead to inhibition of cyclic AMP production is supportive evidence that these receptor types can initiate this response (Matsuda et al., 1990; Felder et al., 1992;Vogel et al., 1993; Slipetz et al., 1995). CB1and CB2 receptor-mediated inhibition of adenylyl cyclase is a pertussis toxin-sensitive cellular event, indicating the requirement for Gi/o proteins (Howlett et al., 1986; Felder et al., 1992; Pacheco et al., 1993; Vogel et al., 1993). Adenylyl cyclase activity in N18TG2 membranes possessing endogenous CB1 receptors was inhibited by anandamide,R-(+)-methanandamide, and 2-arachidonoylglycerol, with relative intrinsic activities similar to desacetyl-l-nantradol, R-(+)-WIN55212, or CP55940 (Childers et al., 1994; Pinto et al., 1994; Howlett and Mukhopadhyay, 2000). In CHO cells expressing CB2receptors, anandamide and R-(+)-methanandamide partially inhibited forskolin-stimulated cyclic AMP accumulation at high concentrations (Felder et al., 1995; Hillard et al., 1999; Gonsiorek et al., 2000). The data suggest that anandamide is an agonist with low relative intrinsic activity for CB2 receptor- compared with CB1 receptor-mediated cyclic AMP production. 2-Arachidonoyl-glycerol has been found to behave as a full agonist when the measured effect is inhibition of forskolin-stimulated cyclic AMP accumulation in CHO cells expressing recombinant CB2 receptors (Gonsiorek et al., 2000).

Stimulation of adenylyl cyclase has been reported in pertussis toxin-treated cells, suggesting that in the absence of functional Gi/o coupling, the CB1receptor can activate Gs (Glass and Felder, 1997). The isoform of adenylyl cyclase expressed in cells is predicted to be a major determinant of the outcome of cannabinoid receptor activation, as demonstrated by studies in Vogel's laboratory (Rhee et al., 1998). These researchers found that expression of CB1 or CB2 cannabinoid receptors in a host cell coexpressing adenylyl cyclase isoforms 1, 3, 5, 6, or 8 resulted in inhibition of cyclic AMP accumulation. However, coexpression of either cannabinoid receptor type with adenylyl cyclase isoforms 2, 4, or 7 resulted in stimulation of cyclic AMP accumulation.
B. Regulation of Ion Channels
1. Ion Channel Modulation by Protein Kinase A.

CB1 cannabinoid receptors activate A-type potassium currents in rat hippocampal cells (Childers and Deadwyler, 1996). This response is due to the modulation of the intracellular cyclic AMP concentrations, thereby regulating the net phosphorylation of ion channel proteins by protein kinase A.
2. K+ Channel Activation.

Exogenously expressed CB1 receptors couple to the inwardly rectifying Kir channels in AtT-20 pituitary tumor cells in a pertussis toxin-sensitive manner, indicating that Gi/o proteins serve as transducers of the response (Henry and Chavkin, 1995; Mackie et al., 1995). Anandamide was a full agonist compared with R-(+)-WIN55212 in theKir current activation in the AtT-20 cell model (Mackie et al., 1995); however, it was a partial agonist inXenopus laevis oocytes coexpressing the CB1 receptor and G protein-coupled inwardly rectifying potassium channel 1 and G protein-coupled inwardly rectifying potassium channel 4 channels (McAllister et al., 1999).
3. Inhibition of Voltage-Gated L, N, P, and Q Ca2+Channels.

L-type Ca2+ channels were inhibited by anandamide and R-(+)-WIN55212 in cat brain arterial smooth muscle cells, which express mRNA for the CB1 receptor (Gebremedhin et al., 1999). The cannabinoid-evoked inhibition of L-type Ca2+currents was blocked by pertussis toxin and SR141716A and was pharmacologically correlated with vascular relaxation in cat cerebral arterial rings (Gebremedhin et al., 1999).

The CB1 receptor inhibits N-type voltage-gated Ca2+ channels in neuronal cells through Gi/o protein (Caulfield and Brown, 1992; Mackie and Hille, 1992; Felder et al., 1993; Mackie et al., 1993; Pan et al., 1996). Anandamide was a partial agonist compared withR-(+)-WIN55212 or CP55940 (Mackie et al., 1993). 2-Arachidonoylglycerol and analogs inhibited the depolarization-evoked rise in intracellular Ca2+ as detected by Fura-2 in differentiated NG108-15 cells (Sugiura et al., 1997b). Anandamide was a partial agonist, and arachidonic acid was without effect.

R-(+)-WIN55212 and anandamide were both full agonists to inhibit Q-type Ca2+ currents in AtT-20 pituitary cells expressing recombinant CB1 receptors (Mackie et al., 1995). This response was pertussis toxin-sensitive, implicating Gi/o proteins as transducers. Anandamide inhibited P/Q-type Ca2+ fluxes (i.e., blocked by ω-agatoxin-IVa) as detected by Fura-2 fluorescence in rat cortical and cerebellar brain slices (Hampson et al., 1998). This response was blocked by SR141716A and pertussis toxin, indicating mediation by CB1 receptors and Gi/o proteins. Neither R-(+)-WIN55212 nor anandamide were able to inhibit Q-type Ca2+currents in AtT-20 cells expressing CB2receptors, indicating that the CB2 receptor fails to couple to this current (Felder et al., 1995).
C. Regulation of Intracellular Ca2+ Transients

Cannabinoid agonists evoked a rapid, transient increase in intracellular free Ca2+ in undifferentiated N18TG2 neuroblastoma and NG108-15 neuroblastoma-glioma hybrid cells (Sugiura et al., 1996, 1997a). This response was blocked by SR141716A, confirming mediation by the CB1receptor (Sugiura et al., 1996, 1999). For this response, HU-210, CP55940, Δ9-THC, anandamide, andR-(+)-methanandamide behaved as partial agonists compared with 2-arachidonoylglycerol or 1(3)-arachidonoylglycerol (Sugiura et al., 1996, 1997a, 1999). The 2-arachidonoylglycerol-evoked intracellular Ca2+ transient was blocked by pertussis toxin and by a phospholipase C inhibitor, suggesting a mechanism whereby a receptor-mediated release of Gi/o βγ subunits might activate phospholipase Cβ, leading to inositol-1,4,5-triphosphate (IP3) release (Sugiura et al., 1996, 1997a). An interaction between CB1 cannabinoid receptors and phospholipase C was shown in cultured cerebellar granule neurons, in which cannabinoid agonists augmented the Ca2+signal in response to NMDA receptor stimulation or K+ depolarization (Netzeband et al., 1999). The response was antagonized by SR141716A, pertussis toxin, and the phospholipase C inhibitor 1-[6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (Netzeband et al., 1999). The source of the released Ca2+ was a caffeine-sensitive and IP3 receptor-sensitive pool. In contrast, studies of CHO cells expressing recombinant CB1 or CB2 receptors were unable to detect release of IP3 or phosphatidic acid in response to anandamide or R-(+)-WIN55212, under conditions in which other exogenously expressed receptors coupled to phospholipases C could evoke IP3 release (Felder et al., 1992, 1995). This suggests that the cellular milieu may be a factor in this CB1 receptor signal transduction pathway.
D. Regulation of Focal Adhesion Kinase, Mitogen-Activated Protein Kinase, Phosphatidylinositol-3-Kinase, and Ceramide Metabolism
1. Signal Transduction via Focal Adhesion Kinase.

Cannabinoid agonists stimulatedtyr-phosphorylation of focal adhesion kinase (FAK) (pp125) in hippocampal slices (Derkinderen et al., 1996). The response could be blocked with SR141716A and pertussis toxin as evidence for mediation by CB1 receptors and Gi/o. Thetyr-phosphorylation of FAK in brain slices was reversed by 8-Br-cyclic AMP and mimicked by protein kinase A inhibitors, suggesting that Gi-mediated inhibition of adenylyl cyclase is integral to this pathway (Derkinderen et al., 1996). FAK is important for integrating cytoskeletal changes with signal transduction events, perhaps playing a role in synaptic plasticity.
2. Signal Transduction via Mitogen-Activated Protein Kinase and Phosphatidylinositol-3-Kinase.

MAPK (p38) was activated in CHO cells expressing recombinant CB1 receptors (Rueda et al., 2000) and in human umbilical vein endothelial cells possessing endogenous CB1 receptors (Liu et al., 2000). MAPK (p42/p44) was activated via CB1 receptors in U373MG astrocytic cells and in host cells expressing recombinant CB1 receptors (Bouaboula et al., 1995b). In C6 glioma and primary astrocyte cultures, Δ9-THC and HU-210 activated MAPK (p42/p44) (Sánchez et al., 1998;Guzmán and Sánchez, 1999). These effects were mediated by CB1 receptors and Gi/oproteins inasmuch as they were blocked by SR141716A and pertussis toxin. In WI-38 fibroblasts, anandamide promotedtyr-phosphorylation of extracellular signal-regulated kinase 2 and increased MAPK activity (Wartmann et al., 1995). In some cells, CB1 receptor signaling via MAPK was blocked by wortmannin (Bouaboula et al., 1995b; Wartmann et al., 1995), implicating PI3K as a mediator along this pathway. Δ9-THC promoted Raf-1 translocation to the membrane and phosphorylation in cortical astrocytes (Sánchez et al., 1998). From these studies, one could envisage a pathway whereby CB1 receptor-mediated Gi/orelease of βγ subunits leads to activation of PI3K, resulting in tyrosine phosphorylation and activation of Raf-1, and subsequent MAPK phosphorylation. Regarding functions regulated by the MAPK pathway, CP55940-stimulated MAPK activity led to activation of the Na+/H+ exchanger in CHO cells stably expressing the CB1 receptor (Bouaboula et al., 1999). Anandamide-stimulated MAPK activity was associated with phosphorylation of cytoplasmic phospholipase A2, release of [3H]arachidonic acid, and subsequent synthesis of prostaglandin E2 in WI-38 cells (Wartmann et al., 1995).

In C6 glioma and primary astrocyte cultures, Δ9-THC and HU-210 increased glucose metabolism and glycogen synthesis (Guzmán and Sánchez, 1999). The activation of Gi/o and PI3K by cannabinoid agonists led to activation of protein kinase B/Akt (isoform IB) in U373MG astrocytic cells and in CHO cells expressing recombinant CB1 receptors (Gómez del Pulgar et al., 2000). Protein kinase B phosphorylation and inhibition of glycogen synthase kinase-3 could account for increased glycogen synthase activity and increased glycolysis in responsive cells.

MAPK was activated in cultured human promyelocytic HL-60 cells possessing endogenous CB2 receptors and in CHO cells expressing recombinant CB2 receptors (Bouaboula et al., 1996). However, cannabinoid drugs failed to activate protein kinase B in HL-60 cells, suggesting that a PI3K mechanism may not be regulated by CB2 receptors in this model (Gómez del Pulgar et al., 2000).
3. Signal Transduction via Ceramide.

Studies with primary astrocyte cultures showed that anandamide, Δ9-THC, and HU-210 increased glucose metabolism, phospholipid synthesis, and glycogen synthesis via an SR141716A-inhibitable but pertussis toxin-resistant mechanism (see reviews by Guzmán and Sánchez, 1999 and Guzmán et al., 2001 for commentary and original references). Data supported a pathway that utilizes the adaptor protein Fan (factorassociated with neutral sphingomyelinase) to couple CB1 receptor stimulation to sphingomyelinase activation, release of ceramide, and subsequent activation of the Raf-1/MAPK cascade (Sánchez et al., 2001). In a second mechanism, ceramide activated carnitine palmitoyltransferase I within astrocyte mitochondrial membranes to stimulate ketogenesis and fatty acid oxidation (Blázquez et al., 1999).

Prolonged (days) elevation of intracellular ceramide has been associated with events leading to decreased proliferation and apoptosis in glioma cells (see Guzmán et al., 2001 for review). This response was initiated by chronic stimulation of both CB1 and CB2 receptors on a susceptible C6 glioma strain and involves increased ceramide synthesis via serine palmitoyltransferase, Raf-1 activation, and MAPK (p42/44) activation.
E. Immediate Early Gene Expression and Protein Synthesis Regulation

MAPK activation can be linked to expression of immediate early genes, as has been demonstrated for Krox-24 expression mediated by CB1 receptors in U373MG human astrocytoma cells (Bouaboula et al., 1995a). Krox-24 expression was stimulated via CB2 receptors in HL-60 promyelocytes (Bouaboula et al., 1996). Intracerebroventricular injection of anandamide evoked an increase in c-FOS immunoreactive protein in rat brain (Patel et al., 1998). Cannabinoid receptor agonists activated c-Jun N-terminal kinase (JNK1 and JNK2) in CHO cells expressing recombinant CB1 receptors (Rueda et al., 2000). The pathway for JNK activation involves Gi/o proteins, PI3K, and Ras (Rueda et al., 2000).

The suppression of prolactin receptor and trk nerve growth factor receptor synthesis by anandamide in human breast cancer MCF-7 cells may be due to a CB1 receptor-mediated decrease in protein kinase A and increase in MAPK activities (De Petrocellis et al., 1998; Melck et al., 1999). This CB1-mediated response ultimately led to an antiproliferative effect on the cells.
F. Regulation of Nitric Oxide Synthase

Nitric oxide (NO) production was stimulated by anandamide in rat median eminence fragments (Prevot et al., 1998) and by anandamide or CP55940 in leech or muscle ganglia (Stefano et al., 1997a,b; 1998). Responses in these tissues were blocked by SR141716A, implicating the involvement of a CB1-like receptor. Antagonism byNG-nitro-l-arginine methyl ester suggests that a signal transduction pathway must lead to regulation of NOS (Prevot et al., 1998). Because both anandamide and the NO-generating agentS-nitroso-N-acetyl-penicillamine could inhibit the release of preloaded radiolabeled dopamine from invertebrate ganglia, a role for NO in mediating the effects of anandamide on neurotransmitter release was implied (Stefano et al., 1997a).

Anandamide and HU-210 stimulated NO production in human saphenous vein segments (Stefano et al., 1998), cultured human arterial endothelial cells (Fimiani et al., 1999; Mombouli et al., 1999), cultured human umbilical vein endothelial cells (Maccarrone et al., 2000), and human monocytes (Stefano et al., 1996). These responses were blocked by SR141716A, implicating CB1 receptors. In cultured human arterial endothelial cells, NO generation was preceded by a rapid increase in intracellular Ca2+ concentration (Fimiani et al., 1999; Mombouli et al., 1999), consistent with the stimulation of a Ca2+-regulated constitutive NOS. In saphenous vein endothelia, the generation of NO required Ca2+ in the perfusate, suggesting that an extracellular source of Ca2+ might be required for NOS activation (Stefano et al., 1998). In human vein arterial cells, generation of NO and peroxynitrite was associated with activation of the anandamide transporter (Maccarrone et al., 2000).

Anandamide inhibited induction of inducible NOS (iNOS) by lipopolysaccharide plus interferon-γ in saphenous vein endothelium (Stefano et al., 1998) and neonatal mouse astrocytes (Molina-Holgado et al., 1997). The modulation of iNOS induction by anandamide required NO production, and this was blocked by SR141716A, implicating the CB1 receptor. The response could be mimicked byS-nitrosyl-N-acetyl-penicillamine, suggesting that transient NO production (presumably via a constitutive type of NOS) regulated the induction of iNOS (Stefano et al., 1998). Because both anandamide andS-nitrosyl-N-acetyl-penicillamine diminished the cyclic AMP accumulation evoked by lipopolysaccharide plus interferon-γ, these authors suggested that the mechanism for suppression of iNOS induction involved the inhibition of cyclic AMP production by NO (Stefano et al., 1998). It is well recognized that NO reversibly inhibits adenylyl cyclase isoforms 5 and 6 by acys-nitrosylation mechanism (Tao et al., 1998; McVey et al., 1999), providing a basis for postulating this mechanism.

The attenuation of iNOS induction by Δ9-THC in RAW 264.7 cells implicated the CB2 receptor and a mechanism involving a decrement in cyclic AMP (Jeon et al., 1996). In mouse peritoneal macrophages, the attenuation of iNOS induction by a series of cannabinoid drugs exhibited a relative order of potency that did not resemble the expected profile for CB1 or CB2 receptors (Coffey et al., 1996).
Previous SectionNext Section
V. Molecular Biology of Cannabinoid Receptors

Although the existence of cannabinoid receptors was known before their cloning, the receptors presently known as CB1 and CB2 cannabinoid receptors were cloned as part of strategies based on conserved sequence motifs to clone G protein-coupled receptors in general rather than specifically trying to clone cannabinoid receptors. It was only after extensive screening of an expressed rat brain cDNA clone that it was identified as the CB1 cannabinoid receptor (Matsuda et al., 1990). Human (Gérard et al., 1990, 1991) and mouse homologues (Chakrabarti et al., 1995) have since been reported. They encode proteins of 472 (human) or 473 (rat, mouse) amino acids, including a rather long and well conserved amino terminal extracellular domain of 116 to 117 residues (Fig.11). Overall, these three receptors have 97 to 99% amino acid sequence identity. A recent sequence-based phylogenetic study of placental mammals (Murphy et al., 2001) included partial sequences from 60 placental mammals covering amino acids 53 to 381 of the rat or mouse sequence (i.e., from the middle of the amino terminal domain to the beginning of the seventh transmembrane domain). There are 24 positions of 329 where more than one sequence differs from the consensus (Table 4). Seven are highly variable positions (67–68, 75–79, and 94) where more than 25% of the sequences differ from the consensus, all of which occur in the amino terminal domain. Except for positions 75 to 79, where the variation is concentrated in Rodentia and Lagomorpha, these variations are broadly distributed across phylogenetic groups. Of potentially greater pharmacological significance are four positions (176, 187, 259, and 271) at which humans and three of the four most closely related primates share common alterations. Except for position 176, where there is a conservative isoleucine for valine substitution at the extracellular end of helix 1, these are highly nonconservative changes located in extracellular loops close to helices 3 to 5, where they might affect binding of large ligands.
Figure 11
View larger version:

In this page
In a new window

Figure 11

Amino acid sequence alignment of human, rat, and mouse CB1 and CB2 receptors. Consensus matches are boxed and shaded with darker shading for identities and lighter shading for conservative substitutions. Numbering corresponds to the rat/mouse CB1 sequence. Underlines indicate the positions of the seven transmembrane helices. Helix 3 spans two lines as indicated by the arrowheads on the underline. The rat CB2sequence is a consensus of GenBank accession nos. AF286721 and AF176350together with edited trace data from the rat genome sequencing project (http://www.ncbi.nlm.nih.gov/genome/seq/RnBlast.html). The rat CB2 residue at alignment position 310 appears to be polymorphic [i.e., either Ala (as shown) or Thr].
View this table:

In this window
In a new window

Table 4

Amino acid sequence variations in CB1 among 60 placental mammals

The CB1 coding sequence is contained in a single exon (see, for example, the human gene sequence in GenBank accession no. U73304), but the available cDNA sequences indicate that there must be at least one additional exon containing only 5′-untranslated sequence. However, an alternatively spliced form of the human receptor has been reported (Shire et al., 1995), in which a 167 base portion of the coding exon is spliced out of the human mRNA leading to the predicted substitution of a different 28-residue sequence for the first 90 amino acids. This shorter mRNA appears to be relatively rare by reverse transcription-polymerase chain reaction analysis: 1 to 20% of the message in most brain areas, according to the original report, although it now appears that these are substantial overestimates due to overexposure of the autoradiograms. Moreover, the invariant GT of the splice donor site becomes a GA in both the rat and mouse genes, which implies that this alternative splicing should not occur in these species. Although a similarly spliced form of the rat receptor was also reported (Shire et al., 1995), it now appears that it does not exist in either rat (Shire et al., 1996b) or mouse (Ho and Zhao, 1996). Most importantly, the short isoform is likely to be inefficiently translated because it initiates at the second AUG of the mRNA and has a T rather than the highly preferred A or G at the critical −3-position (i.e., three bases before the AUG) (Kozak, 1994). The question of whether the shorter protein is expressed in significant quantities is presently unanswered; however, if it were to be expressed in significant quantities, the guidelines of the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification would dictate that the short isoform be referred to as CB1(b) and the major (i.e., larger) isoform should be CB1(a). To date, the short isoform has been referred to as CB1A (Shire et al., 1995). The CB1 mRNA is typically 5.5 to 6 kb, but an alternatively polyadenylated cDNA sequence was reported (Matsuda et al., 1990), which is 2.6-kb shorter in the rat. This species is not usually detected on Northern blots, but the predominant mRNA in human testis is only 4 kb and might represent a similar alternatively polyadenylated mRNA (T. I. Bonner, unpublished observations).

There was no substantial evidence for a second cannabinoid receptor until the hCB2 cDNA was cloned from HL-60 cells (Munro et al., 1993). Its 360-amino acid sequence is quite different from that of CB1, especially in its much shorter amino terminal domain where there is no significant conservation (Fig.11). Between transmembrane domains 1 and 7, the CB2 protein is only 48% identical to that of CB1, substantially less than the 70 to 80% usually seen between different types of G protein-coupled receptors, but enough to have led to its identification as a cannabinoid receptor. It is reported to be expressed primarily in spleen (Fig.12). The mouse CB2 gene has been cloned (Shire et al., 1996a) and is only 82% identical in amino acid sequence to the human receptor and is 13 amino acids shorter at the carboxyl terminal. The rat gene (Griffin et al., 2000) is similar to the mouse gene, except that it is 13 amino acids longer at the carboxyl terminal. It should be noted that this rat receptor is in fact a hybrid mouse-rat receptor with the first and last six amino acids derived from mouse sequence used as polymerase chain reaction primers. As with the CB1 gene, the coding sequence is contained in a single exon of the mouse gene (see GenBank accession no. U21681), but available cDNA sequence indicates that there is at least one additional exon containing only 5′-untranslated sequence.
Figure 12
View larger version:

In this page
In a new window

Figure 12

Autoradiographs show cannabinoid receptor binding (a, f, g) and CB1 (b, d) and CB2 (c, e) mRNA expression in sections from the mouse (sagittal) and human brain (coronal) and mouse spleen (M. Herkenham and A. Hohmann, unpublished observations). Receptor binding of [3H]CP55940, a high-affinity agonist, shows high levels of receptors in the basal ganglia, cerebellum, hippocampus (hipp), and cerebral cortex (a). Cells expressing CB1 mRNA are shown in a similar plane of section (b). Lack of detectable CB2 expression in brain (c) indicates that the binding is to the CB1 type. In contrast, spleen has the opposite relative abundance of CB1 (d) versus CB2 mRNA (e) expression. The human brain has a distribution of cannabinoid receptors that closely matches that of the mouse, with high levels expressed in the basal ganglia, intermediate levels in the amygdala and hypothalamus, and low levels in the thalamus (f, g). The high levels of binding in many areas [cerebellar molecular layer, globus pallidus (GP, GPe), entopeduncular nucleus (Ep, GPi), substantia nigra pars reticulata (SNR), and dentate gyrus molecular layer] are on axons of cells expressing mRNA in afferent areas, such as the caudate putamen (CPu). Some cells in cortex and hippocampus express extremely high levels of CB1 message (arrows in b). Bars measure 1 mm for mouse and 1 cm for human.

Although the amino terminal domain of the CB1receptor is uncommonly long and well conserved, it appears to play no major role in ligand recognition, as deletion of the first 89 amino acids of the hCB1 receptor has no effect on CP55940 binding affinity (Rinaldi-Carmona et al., 1996a). Similarly, the altered amino terminal sequence presented by the CB1(b) isoform has little effect (0- to 3-fold) on the pharmacological properties of several agonists and only a 5- to 10-fold effect on the properties of the SR141716A antagonist.

Site-directed mutagenesis has only recently begun to define which residues constitute the agonist binding sites. Mutation of lysine 192 of the hCB1 receptor to an alanine demonstrated that this lysine is critical for the binding of several agonists (CP55940, HU-210, and anandamide), whereas the mutation has no appreciable effect on either binding or receptor activation byR-(+)-WIN55212 (Song and Bonner, 1996). Clearly, the agonist binding site is not precisely the same for all agonists. This lysine is located at the extracellular end of helix three in both the CB1 and CB2 receptors, a region commonly implicated in agonist binding in other G protein-coupled receptors. This result was extended (Chin et al., 1998) to show that the conservative substitution of an arginine for the lysine had little effect, whereas potentially much more disruptive substitutions of glutamine or glutamic acid eliminated binding of CP55940 but had little effect on binding of R-(+)-WIN55212. However, when the corresponding mutations of the hCB2 receptor at lysine 109 were tested, both the arginine and the alanine substitutions had little effect (Tao et al., 1999). Molecular modeling of the two alanine-substituted receptors (CB1K192A and CB2K109A) indicated that the CB2 receptor still could bind CP55940 via hydrogen bonds to serine 112 that were absent in CB1 at the corresponding residue, glycine 195. When the CB2K109A receptor was altered to also change Ser112 to Gly112, its properties recapitulated those of the CB1K192A receptor, thus confirming the modeling prediction. More recently, mutation of the CB1receptor to change Gly195 to Ser195, analogous to the CB2 receptor, has been shown to increase affinity for R-(+)-WIN55212 4-fold (Chin et al., 1999). Thus, there are two residues that are adjacent on the same face of helix 3, which play a critical role in binding of agonists other thanR-(+)-WIN55212 but a minor role in binding ofR-(+)-WIN55212. A complementary situation occurs in helix 5, where the corresponding residues Val282 in CB1and Phe197 in CB2 confer the selectivity ofR-(+)-WIN55212 for CB2 (Song et al., 1999). Substitution of phenylalanine for Val282 in CB1 results in an increase in affinity forR-(+)-WIN55212 to the CB2 value, whereas the converse mutation, replacing Phe197 of CB2 with a valine, results in a decrease ofR-(+)-WIN55212 affinity to the CB1value. Neither substitution affects affinities for CP55940, HU-210, or anandamide.

A number of other mutations have been reported that alter residues that are highly conserved throughout the rhodopsin family of G protein-coupled receptors, such as the aspartic acid in helix 2 (Tao and Abood, 1998; Roche et al., 1999), the DRY motif at the intracellular end of helix 3 (Rhee et al., 2000b), the tryptophan in the middle of helix 4 (Rhee et al., 2000a), and the tyrosine near the intracellular end of helix 7 (Feng and Song, 2001). These mutations generally give the same results as observed with the analogous mutations in other receptors. Given the highly conserved nature of these residues and their positions generally near the intracellular ends of the helices, it is likely that they are not so much a part of the agonist binding site as they are important for conformations that play a role in transmitting the binding signal to the G proteins. Of more interest for the agonist binding sites is the tryptophan at the extracellular end of helix 4. Conservative mutations of Trp172 in hCB2 to phenylalanine or tyrosine had little effect, but removal of the aromatic side chain by substitution of alanine or leucine eliminated binding of HU-210, CP55940, andR-(+)-WIN55212. The implications of these results are not clear, but it is worth noting that Trp172 is part of a GWNC motif shared (with some deviations from the G and N) by the sphingosine-1 phosphate and lysophosphatidic acid receptors and a small group of orphan receptors, GPR3, GPR6, and GPR12. All of these receptors have a cysteine at the extracellular end of helix 4 instead of the cysteine that is commonly found at the extracellular end of helix 3 and thought to participate in disulfide bonding that constrains the ends of helix 3 and 5. Similar loss of binding has been reported for the CB2 receptor when nearby Cys174 is replaced with serine (Shire et al., 1996a).

Studies with chimeric CB1/CB2 receptors (Shire et al., 1996a) demonstrate that the selectivity of the antagonist SR141716A for CB1 is provided about equally by the portions of the receptor on either side of the beginning of helix 5. Substitution of helices 4 through 5 of the CB2receptor into CB1 resulted in loss of SR141716A binding without altering CP55940 binding, which, together with chimeras substituting only the loop between the two helices, suggests that the specificity lies within helices 4 and 5. However, the critical chimera in which helices 4 and 5 from CB1 might have been expected to confer high-affinity antagonist binding on a CB2 receptor failed to bind either ligand. More recent mutations of the hCB2 receptor aimed at defining the selectivity of SR144528 for CB2identified three mutations in or adjacent to helix 4, S161A, S165A, and C175S, which eliminated SR144528 binding but had little effect on CP55940 or R-(+)-WIN55212 binding or activity (Gouldson et al., 2000). A molecular model was presented that accounted for the role of the two serine residues but did not account for the Cys175 residue. The complementary mutations of the CB1 receptor that might have been expected to gain SR144528 binding were not attempted. Nevertheless, this is yet another case where mutations have been identified that have dramatic effects on the binding of one ligand but not others.

No significant genetic polymorphism has been reported for the cannabinoid receptor genes. A silent mutation in the coding sequence of the CB1 gene, 1259G → A in codon 453 (Thr), has been reported (Gadzicki et al., 1999) to be common in the German population, but since this does not alter the amino acid sequence of the receptor, it is of little pharmacological significance. Another study that determined the coding sequence from 21 individuals, seven of whom exhibited extreme responses to cannabis, found no amino acid-changing mutations (Hoehe et al., 2000).
Previous SectionNext Section
VI. Cannabinoid Receptor Knockout Mice

The relatively recent creation both of transgenic mice bearing a genetic deletion of the CB1 or CB2 receptor and of CB1/CB2 double knockouts has provided additional avenues for probing cannabinoid receptor function in both the CNS and periphery. Through gene targeting and homologous recombination in embryonic stem cells, two independent laboratories have generated CB1 receptor knockout mice (Ledent et al., 1999; Zimmer et al., 1999). After implantation in pseudopregnant females, homozygous offspring (CB1−/−) lacked expression of the wild-type CB1 receptor both in the CNS and periphery. Using identical techniques, mice were bred lacking the CB2 receptor (CB2−/−) (Buckley et al., 2000). CB1/CB2double-knockout mice have been obtained with the expected mendelian frequency by mating mice heterozygous for both receptors (CB1+/−/CB2+/−) (N. E. Buckley and A. Zimmer, personal communication).

CB1 knockout mice bred on a C57BL/6J background showed a variety of spontaneous phenotypes, including hypoactivity, reduced locomotion and rearing, supraspinal hypoalgesia, and increased mortality (Zimmer et al., 1999). Subsequent studies revealed a spontaneous reduction in feeding behavior (Di Marzo et al., 2001b) and change in male hormone balance (Paria et al., 2001). In contrast, mice bred on a CD1 background showed increased locomotor and exploratory activity when newly exposed to an arena but no change in supraspinal hypoalgesia or mortality (Ledent et al., 1999). CB1 null mice showed an increase in long-term potentiation (Böhme et al., 2000) and improvements in memory scores (Reibaud et al., 1999), supporting a role for this receptor in cognitive function. Both CB1 receptor knockout mouse lines demonstrated complete loss of cannabinoid agonist-induced behaviors, such as hypolocomotion, hypothermia, spinal and supraspinal analgesia, and bradycardia, consistent with a central role for CB1 receptors in these phenotypes. Moreover, these mice demonstrated less responsiveness to the reinforcing properties of opiates but not other drugs of dependence, suggesting a role for CB1 receptors in specific addictive behaviors (Ledent et al., 1999; Mascia et al., 1999; Cossu et al., 2001). For the most part, results observed in mice treated with selective CB1 receptor antagonists mimic the findings observed in the transgenic animals. However, developmental changes may have occurred in brain architecture to compensate for the lack of CB1 receptors, as has been suggested from studies of neuropeptide expression (Steiner et al., 1999). These findings suggest that studies with CB1 receptor knockout mice, as with other knockout mice, should be interpreted with caution and should be supported with pharmacological experiments.

One of the most promising uses of receptor knockout mice is to uncover new receptor types (see also Section XI.). Studies with CB1 receptor knockout mice have revealed non-CB1receptor-mediated responses to cannabinoid agonists in the CNS (see also Section XI.).R-(+)-WIN55212-mediated reduction in excitatory postsynaptic currents occurred in both wild-type and CB1receptor null mice, suggesting that the γ-aminobutyric acid (GABA)ergic currents are modulated by an unknown cannabinoid receptor (Hájos et al., 2001). Anandamide showed analgesic and hypolocomotor effects of similar magnitude in both wild-type and CB1 receptor knockout mice, again indicating the expression of an anandamide-sensitive non-CB1, non-CB2 receptor in brain tissue (Di Marzo et al., 2000b). Radioligand binding studies and functional GTPγS binding assays using anandamide and R-(+)-WIN55212 indicate the presence of a non-CB1 or -CB2 receptor in brain tissue (Breivogel et al., 2001). Similar non-CB1 receptor-mediated regulation of mesenteric vasodilation was observed in CB1, CB2, and CB1/CB2 double-knockout mice (Járai et al., 1999).

Few studies have revealed a role for the CB2receptors using the CB2 knockout mice. To date, one study has shown a role for CB2 receptors in cannabinoid agonist-mediated inhibition of helper T cell activation, in which the response was lost in CB2 null mice but not in their wild-type controls (Buckley et al., 2000). A study detailing the phenotype of the CB1/CB2 double receptor knockout mice has not been published to date.
Previous SectionNext Section
VII. Tissue Distribution of Cannabinoid Receptors
A. Neuronal Distribution of Cannabinoid Receptors

The distribution of CB1 cannabinoid receptors has been investigated in considerable detail. Studies have used quantitative autoradiography, in situ hybridization, and immunocytochemistry, yielding complementary information. Investigations of CB2 cannabinoid receptor distribution are fewer. These indicate that this receptor is primarily localized on cells in structures associated with the immune system.

Autoradiographic studies of CB1 receptors are noteworthy for several reasons. They preceded the cloning of the receptor, indicated that the receptor was expressed in regions predicted from the behavioral effects of cannabinoids, and also established that cannabinoid receptors are expressed at high levels compared with other G protein-coupled receptors. Historically, autoradiography studies with [3H]CP55940 helped to establish the existence of a high-affinity cannabinoid receptor. As shown in Fig. 12, cannabinoid receptors were found to be particularly enriched in cerebral cortex, hippocampus, basal ganglia, and cerebellum, regions that were predicted from the behavioral effects of cannabinoids. Lower levels were found in hypothalamus and spinal cord. CB1 receptor binding was almost absent from the respiratory centers of the brainstem, consistent with the clinical observation of the low lethality of cannabis overdose (Robson, 2001).

Detailed autoradiographic studies have been conducted in several species, including human, monkey, and rat (Herkenham et al., 1990,1991; Glass et al., 1997). Qualitatively, all species have similar distributions; however, subtle differences are seen. For example, in humans, CB1 receptors are more highly expressed in amygdala and cingulate cortex compared with rat or monkey (Herkenham et al., 1990). Differences like these may explain interspecies differences in the behavioral effects of cannabinoids. In contrast to other anatomical techniques, the autoradiographic studies can give a quantitative measure of the density of cannabinoid receptors. These studies often found levels of expression greater than 1 pmol/mg tissue. These densities are greater than those of most other G protein-coupled receptors and are comparable with levels found for common ionotropic receptors (Greenamyre et al., 1984; Bowery et al., 1987). Comprehensive anatomical surveys have also been conducted with tritiatedR-(+)-WIN55212 and with SR141716A. These compounds gave a similar distribution as [3H]CP55940 (Jansen et al., 1992; Rinaldi-Carmona et al., 1996b). However, with the recent demonstration of physiological effects of R-(+)-WIN55212 in CB1 knockout mice (Section XI.), reexamination of these latter studies is in order.

Soon after the cloning of the CB1 receptor, several in situ hybridization studies were conducted (Mailleux et al., 1992; Matsuda et al., 1993). The results of these studies generally agreed with the results of the preceding autoradiographic studies, taking into account that in situ hybridization will identify CB1 receptor mRNA in cell bodies, whereas autoradiography will label receptors throughout the neuron. An important finding from the in situ studies was the corroboration of the impression from the autoradiographic studies that CB1 receptors are often found on axons and probably their terminals (Fig. 12). Another interesting finding from the in situ studies was that cannabinoid receptor expressing neurons have two general patterns of distribution (Mailleux et al., 1992;Matsuda et al., 1993). In some regions, they are expressed broadly and uniformly. For example, in cerebellum, almost all granule cells express CB1. In contrast, in the hippocampus, despite intense labeling of the pyramidal cell layer in the autoradiographic studies, most neurons do not express appreciable levels of CB1 mRNA. Instead, a few neurons express very high levels. A similar pattern is found in the cerebral cortex.

Once antibodies were developed against the CB1receptor, immunocytochemical studies were possible. Several of these have been conducted using distinct antibodies (Fig.13). Two comprehensive surveys of CB1 receptor expression in rat brain have been undertaken (Tsou et al., 1998a; Egertová and Elphick, 2000). In both of these studies, cannabinoid receptors were found in the regions predicted from the earlier autoradiographic and in situ hybridization studies. These surveys emphasized the high levels of CB1 receptor expressed on axonal fibers, especially at their terminals. Detailed electron microscope (EM) studies in rat and human hippocampus found that cell-surface CB1 receptors were found almost exclusively on presynaptic terminals (Hájos et al., 2000; Katona et al., 2000). EM gold studies suggest that hippocampal CB1receptors are expressed on the membrane of the entire presynaptic bouton, with the exception of the active zone. In contrast, EM studies in striatum suggest that CB1 receptors may be expressed more widely. This report found CB1labeling of postsynaptic elements and even perivascular astroglia (Rodrı́guez et al., 2001).
Figure 13
View larger version:

In this page
In a new window

Figure 13

Electron micrograph of consecutive rat brain hippocampal sections stained with the C terminus-CB1antibody showing that inhibitory terminals presynaptically express CB1 cannabinoid receptors in the hippocampus. Serial sections have been cut through a CB1-immunoreactive axon terminal forming a symmetrical (GABAergic) synapse (thick arrow) on a dendrite in the stratum radiatum of the CA1 region. Gold particle labeling (small arrows) is restricted to the inner surface of the bouton, where the intracellular carboxy terminus epitope of CB1 is located. A small arrowhead indicates a dense core vesicle. In contrast, the complete lack of staining in axon terminals (★), forming an asymmetrical synapse (large arrowhead), suggests that glutamatergic axons do not contain CB1 receptors. Scale bar is 0.2 μm. Courtesy of I. Katona and T. F. Freund.

The anatomical localization of cannabinoid receptors has also given additional insight into their function. For example, CB1 receptors are often expressed on synaptic terminals that release both GABA and cholecystokinin (CCK) (Katona et al., 1999; Marsicano and Lutz, 1999; Tsou et al., 1999; see also Fig.13). Thus, inhibition of neurotransmission by CB1receptor activation will cause not only a decrease in GABA release but also a decrease in CCK release (Section VIII.). Another interesting feature is the reciprocal nature of the localization of CB1 receptors and the endocannabinoid hydrolyzing enzyme (FAAH). In at least some brain regions, CB1 receptors and FAAH appear to be localized on opposing neurons (Egertová et al., 1998; Tsou et al., 1998b). For example, hippocampal pyramidal neurons and cerebellar Purkinje neurons both express high levels of FAAH and few CB1receptors. Conversely, FAAH expression is low in hippocampal interneurons and cerebellar granule cells, which synapse onto pyramidal neurons and Purkinje neurons, respectively.

In addition to the CNS, CB1 receptors are widely expressed in the peripheral nervous system, both on sensory nerve fibers and in the autonomic nervous system (e.g., Pertwee et al., 1992). Although detailed comparative anatomical studies have not been conducted on CB1 receptor expression in the autonomic nervous system, the physiological experiments suggest significant interspecies differences (e.g., Benowitz et al., 1979; Lake et al., 1997). CB1 receptors are also found in moderate levels in the testis (Gérard et al., 1991; Wenger et al., 2001); their function there is unknown. CB1receptors are also expressed in some immune cells, but their level of expression is considerably lower than that of CB2receptors (Section VII.B.).

As discussed in greater detail elsewhere (Pertwee, 1997, 2001b), CB1 receptor expression levels are highest in the CNS, particularly in brain regions associated with higher cognitive functions. Functionally significant levels of CB1receptors are also expressed in pain pathways and the autonomic nervous system. Often, CB1 receptors are expressed on nerve terminals. One consequence of their activation is to decrease calcium entry through voltage-dependent calcium channels decreasing neurotransmitter release (Sections IV. andVIII.). As detailed in the next section, CB2 receptors are primarily found on immune cells, particularly mature B cells, and, to a lesser degree, on macrophages.
B. Immune Distribution of Cannabinoid Receptors

Current knowledge about the immune distribution of CB1 and CB2 cannabinoid receptors is summarized in Table 5. Cannabinoid CB1 receptor mRNA is found primarily in neural tissue but can be found to a lower extent in peripheral tissues, including the adrenal gland, bone marrow, heart, lung, prostate, testis, thymus, tonsils, and spleen (Kaminski et al., 1992;Bouaboula et al., 1993; Galiègue et al., 1995; Noe et al., 2000). Messenger RNA for CB1 can be found at low levels in neonatal rat brain cortical microglia (Waksman et al., 1999;Carlisle et al., 2002) and in select immune cell lines, including human THP-1 monocytic cells, human Raji B-cells, murine NKB61A2 natural killer-like cells, and murine CTLL2 IL-2-dependent T cells (Daaka et al., 1995).
View this table:

In this window
In a new window

Table 5

Detection of cannabinoid receptors in immune cells and tissues

Both in situ hybridization studies and autoradiographic studies suggest expression of CB2 receptors in multiple lymphoid organs (Lynn and Herkenham, 1994; Buckley et al., 1998). Cannabinoid CB2 receptor mRNA is found in spleen (Fig. 12), thymus, tonsils, bone marrow, pancreas, splenic macrophage/monocyte preparations, mast cells, peripheral blood leukocytes, and in a variety of cultured immune cell models, including the myeloid cell line U937 and undifferentiated and differentiated granulocyte-like or macrophage-like HL-60 cells (Bouaboula et al., 1993; Munro et al., 1993; Facci et al., 1995; Galiègue et al., 1995; Condie et al., 1996; Pettit et al., 1996; Schatz et al., 1997). Valk et al. (1997)reported the presence of CB2 receptor mRNA in 45 of 51 cell lines of distinct hematopoietic lineages, including myeloid, macrophage, mast, B-lymphoid, T-lymphoid, and erythroid cells. In spleen and tonsils, CB2 mRNA content is equivalent to that of CB1 mRNA in the central nervous system. However, the distribution pattern of CB2 mRNA displays major variation in human blood cell populations, with a rank order of B lymphocytes > natural killer cells ≫ monocytes > polymorphonuclear neutrophils > T8 lymphocytes > T4 lymphocytes (Galiègue et al., 1995). A rank order for CB2 mRNA content similar to that noted for primary human cell types has been recorded for human cell lines belonging to the myeloid, monocytic, and lymphoid lineages (Galiègue et al., 1995). Lee et al. (2001) have reported a similar pattern of CB2 mRNA distribution in murine immune cell subpopulations. CB2 mRNA was most abundant in splenic B cells, followed by macrophages and T cells. Messenger RNA for CB2 has been identified also in neonatal rat brain cortical microglia maintained in vitro at levels that exceed those for CB1 (Carlisle et al., 2002).

Cannabinoid receptor protein has been localized in a variety of immune cell types and tissues. Ligand binding assays have allowed for the assessment of cannabinoid receptor protein in rat lymph nodes, Peyer's patches, and spleen (Lynn and Herkenham, 1994). Cannabinoid receptor binding was confined to B lymphocyte: enriched areas such as the marginal zone of the spleen, cortex of the lymph nodes, and nodular corona of Peyer's patches. Specific binding was absent in T lymphocyte-enriched areas, such as the thymus and periarteriolar lymphatic sheaths of the spleen, and certain macrophage-enriched areas, such as the liver and lung. Binding assay also has permitted quantitation of cannabinoid receptors on membranes of a variety of immune cell types and lines. Bouaboula et al. (1993) used [3H]CP55940 as a ligand for characterizing cannabinoid receptors in human myelomonocytic U937 cells. AKd of 0.1 nM and aBmax of 525 fmol/mg protein was determined from Scatchard analysis for membranes of these cells.

In addition, CB1- and CB2-specific antibodies have been used to identify cannabinoid receptors in immune cells. Cannabinoid CB1 receptor protein has been identified in the human Jurkat T cell line (Daaka et al., 1996), in Daudi human B-lymphoblastoid cells and macrophage-like cells from rat brain tissue (Sinha et al., 1998), and in cortical microglia cultured from neonatal rat brain (Waksman et al., 1999). Galiègue et al. (1995) used an anti-hCB2 IgG to localize CB2 receptors within B lymphocyte-enriched areas of the mantle of secondary lymphoid follicles in sections of human tonsil. Carayon et al. (1998) employed immunopurified polyclonal antibody to investigate the expression of CB2receptors in leukocytes and showed that peripheral blood and tonsillar B cells were the leukocyte subsets expressing the highest amount of CB2 receptor proteins. Dual-color confocal microscopy performed on human tonsillar tissues demonstrated a marked expression of CB2 receptors in mantle zones of secondary follicles, whereas germinal centers were weakly stained, suggesting a modulation of this receptor during the differentiation stages from virgin B lymphocytes to memory B cells.

Changes in levels of cannabinoid receptors or their mRNAs after treatment with a variety of immune modulators or activators have been reported. Levels of CB2 mRNA have been detected in peritoneal macrophages at differential levels in relation to cell activation state. Lee et al. (2001) and Carlisle et al. (2002)determined that CB2 mRNA was present in thioglycollate-elicited murine peritoneal macrophages but not in resident peritoneal macrophages. In addition to these studies on receptor expression at basal activity, CB2 mRNA expression was studied following immune cell activation. Bacterial lipopolysaccharide stimulation down-regulated CB2mRNA expression in splenocyte cultures in a dose-response manner, whereas stimulation through cluster of differentiation 40 (CD40) using anti-CD40 antibody up-regulated the response and costimulation with IL-4 attenuated the anti-CD40 response. Daaka et al. (1995) have indicated that lipopolysaccharide-stimulated Raji and PMA-stimulated THP-1 human acute monocytic leukemia cell lines show increased levels of CB1 cannabinoid receptor mRNA. It was demonstrated also that increases in CB1 mRNA were linked to comparable increases in cognate protein expression. Mitogen activation of Jurkat cells showed an increase in specific binding of [3H]CP55940, and Western analysis indicated the presence of immunoreactive proteins on membranes from mitogen-activated Jurkat cells but not on membranes of unstimulated cells. Noe et al. (2000) reported that anti-CD40, anti-CD3, and IL-2 stimulation induced contrasting changes in CB1 mRNA expression in mouse splenocytes. Splenocytes stimulated with the T cell mitogens PMA/Io and anti-CD3 showed a decrease in CB1message, whereas cultures stimulated with the B-cell mitogen, anti-CD40 antibody, showed an increase in message. In addition, cotreatment with mitogens and IL-2 uniformly caused an increase in CB1 mRNA. These observations suggest that signaling pathways activated by T cell mitogens lead to decreased CB1 gene activation, whereas pathways activated by B-cell mitogens and IL-2 lead to increased CB1. Collectively, these reports suggest that cannabinoid receptors have biological relevance in lymphoid and myeloid cells during defined stages of cell activation.

Changes in levels of rat spleen cannabinoid receptors have been reported also after chronic cannabinoid administration. Massi et al. (1997) assessed the effect of chronic in vivo administration of CP55940 on the expression of cannabinoid receptors. Spleen coronal sections processed for receptor binding autoradiography with [3H]CP55940 in the absence or presence of unlabeled CP55940 and subjected to densitometric analysis of the autoradiograms showed significant loss of [3H]CP55940 binding for chronic cannabinoid-treated, tolerant rats.
Previous SectionNext Section
VIII. Effects on Neurotransmission

As detailed in Table 6, there is good evidence that the activation of presynaptic CB1 receptors can lead to inhibition of the evoked release of a number of different excitatory or inhibitory neurotransmitters both in the brain and in the peripheral nervous system. This evidence has been obtained from experiments in which release has been monitored either through the direct measurement of transmitter levels in vivo or in vitro (acetylcholine, noradrenaline, dopamine, 5-hydroxytryptamine, d-aspartate, cholecystokinin, and GABA) or indirectly using electrophysiological techniques (glutamate, glycine, and GABA). R-(+)-WIN55212 and Δ9-THC have been reported to inhibit GABA uptake into tissue obtained from rat globus pallidus (Maneuf et al., 1996a,b) or substantia nigra (Romero et al., 1998), albeit at a rather high concentration (50 μM). Even so, the main effect of cannabinoids on GABAergic transmission in rat hippocampus seems to be inhibitory in nature (Paton et al., 1998; Hoffman and Lupica, 2000). Although there are some electrophysiological data that support CB1 receptor-mediated inhibition of GABA release in rat substantia nigra (Table 6), it has not proved possible to detect any cannabinoid-induced inhibition of spontaneous or evoked release of [3H]GABA from fragments of rat substantia nigra preloaded with this radioisotope (Romero et al., 1998) or, indeed, from slices of globus pallidus (Maneuf et al., 1996a). Although there is little doubt that CB1 receptors play a major role in modulating neurotransmitter release, evidence has recently emerged from experiments with CB1 knockout mice that inhibition of hippocampal glutamate release is mediated by presynaptic,R-(+)-WIN55212-sensitive, non-CB1receptors (Section XI.).
View this table:

In this window
In a new window

Table 6

Cannabinoid-induced inhibition of central and peripheral neurotransmitter release

Although the primary effect of CB1 receptor agonists on neurotransmitter release seems to be one of inhibition, this may sometimes result in enhanced neurotransmitter release at some point downstream of the initial inhibitory effect. For example, there is evidence that cannabinoids enhance dynorphin release within the spinal cord and that this effect depends on CB1receptor-mediated inhibition of tonically active neurons that exert an inhibitory influence on dynorphinergic neurons (see Pertwee, 2001b). There is also evidence from experiments both with whole animals (Chen et al., 1990a,b; 1991; French, 1997; French et al., 1997; Tanda et al., 1997; Gessa et al., 1998b; Melis et al., 2000) and with brain slices (Cheer et al., 2000) that CB1 receptor agonists can stimulate dopamine release in the nucleus accumbens, and it is likely that this effect stems from a cannabinoid receptor-mediated inhibition of glutamate release from extrinsic glutamatergic fibers. These are large fibers that form synapses in the nucleus accumbens with GABAergic neurons that project to the ventral tegmental area to exert an inhibitory effect on dopaminergic mesoaccumbens neurons (Robbe et al., 2001). It is possible that cannabinoid receptor-mediated disinhibition of dopamine release in the nucleus accumbens gives rise to increases in acetylcholine release in the prefrontal cortex that have recently been observed in microdialysis experiments with rats in response to intravenous injections of low doses of Δ9-THC, HU-210, or R-(+)-WIN55212 (Acquas et al., 2000, 2001). Thus, GABAergic neurons project from the nucleus accumbens to the prefrontal cortex, and it is thought that dopamine released in the nucleus accumbens may act on these neurons to disinhibit acetylcholine release in the cortex (Moore et al., 1999). Results from microdialysis experiments with rats have indicated that at low doses, intravenously administered cannabinoids can also act through CB1 receptors to increase acetylcholine release in the hippocampus (Acquas et al., 2000, 2001), whereas data from in vivo electrophysiological experiments suggest that systemically administered cannabinoids can enhance dopamine release from mesoprefrontal cortical neurons that project from the ventral tegmental area to the prefrontal cortex (Diana et al., 1998). This stimulatory effect on cortical dopamine release may result from inhibition of GABA release mediated by CB1 receptors that are presumed to be located on the terminals of prefrontal cortical GABAergic interneurons that modulate the activity of pyramidal neurons (Pistis et al., 2001). These prefrontal cortical pyramidal neurons project to the ventral tegmental area, where they form excitatory synapses on mesoprefrontal dopaminergic neurons that release GABA from the prefrontal cortical GABAergic interneurons that have been postulated to express CB1 receptors.

One apparently anomalous finding, obtained from microdialysis experiments with unanaesthetized rats, is thatR-(+)-WIN55212 can act through cannabinoid receptors in the cerebral cortex to enhance calcium-dependent glutamate release (Ferraro et al., 2001). The same investigation also provided evidence thatR-(+)-WIN55212 can produce cannabinoid receptor-mediated increases in spontaneous, calcium-dependent glutamate release in primary cultures of rat cerebral cortex. The reason for the apparent discrepancy between these glutamate release data and previous electrophysiological data that indicate an inhibitory effect of cannabinoids on glutamate release (Table 6) remains to be elucidated. It is possible that when administered in vivo, CB1 receptor agonists have dose-dependent biphasic effects on cortical and hippocampal acetylcholine release: a stimulant effect at low doses and an inhibitory effect at higher doses. This hypothesis has been put forward by Acquas et al. (2001) to explain why, in some microdialysis experiments with rats, cannabinoids increase acetylcholine release in prefrontal cortex and hippocampus (Acquas et al., 2000, 2001), whereas in other microdialysis experiments, they decrease acetylcholine release in these same brain areas (Table 6).

Results from a number of recent investigations suggest that endocannabinoids may act through presynaptic cannabinoid receptors to function as fast retrograde synaptic messengers. More specifically, there is evidence to suggest that the biosynthesis and nonvesicular release of endocannabinoid molecules can be rapidly triggered by intense activity at glutamatergic synapses in the hippocampus and cerebellum. In the hippocampus, such release seems to take place from pyramidal cells (Ohno-Shosaku et al., 2001; Wilson and Nicoll, 2001). These cells receive synaptic inputs from both (excitatory) glutamatergic neurons and (inhibitory) GABAergic neurons. It has been proposed that pyramidal cells produce and release endocannabinoid molecules in response to elevations in intracellular calcium levels induced by the synaptic release of glutamate, and that the endocannabinoid molecules so produced then act through CB1 receptors on GABAergic neurons to inhibit calcium influx, thus decreasing GABA release onto the pyramidal cells (depolarization-induced suppression of inhibition). In the cerebellum, glutamate released onto Purkinje cells appears to be capable of triggering endocannabinoid production and release both by transiently increasing calcium levels within these cells and by acting on postsynaptic metabotropic glutamate receptors (mGluR subtype 1) to activate G proteins without producing any elevation of intracellular calcium (Kreitzer and Regehr, 2001a; Maejima et al., 2001). Once released from the Purkinje cells, the endocannabinoid molecules are thought to act through cannabinoid receptors that are present on the terminals of climbing fibers and of parallel fibers of cerebellar granule cells to inhibit the ongoing glutamate release (depolarization-induced suppression of excitation) (Kreitzer and Regehr, 2001a; Maejima et al., 2001). There is also evidence that cerebellar depolarization-induced suppression of inhibition results from the release of endocannabinoid molecules from Purkinje cells onto presynaptic CB1 receptors that are present on GABAergic basket and stellate cell terminals (Diana et al., 2002;Kreitzer and Regehr, 2001b). Although depolarization-induced suppression of excitation should provide a negative feedback mechanism for damping down high synaptic activity, depolarization-induced suppression of inhibition will have more complex effects. The identity of endocannabinoid(s) that serve as fast retrograde synaptic messengers remains to be established. In the meantime, it is noteworthy that results from experiments with primary cultures of rat cortical neurons have indicated that glutamate and NMDA stimulate the formation of 2-arachidonoylglycerol and that anandamide formation can be stimulated by the simultaneous activation of nicotinic and NMDA receptors with glutamate and carbachol although not by either of these agents alone (Stella and Piomelli, 2001). There are also reports firstly, that high-frequency in vivo electrical stimulation of rat Schaffer collaterals (excitatory hippocampal CA1 afferents) provokes increased calcium-dependent release of 2-arachidonoylglycerol but not of anandamide (Stella et al., 1997) and secondly, that striatal concentrations of anandamide but not of 2-arachidonoylglycerol can be increased in rats in vivo by local perfusion with a depolarizing concentration of potassium chloride or with the D2-like receptor agonist quinpirole (Giuffrida et al., 1999). In addition, it has been found that anandamide release in the periaqueductal gray area of rat brain can be induced both by direct electrical stimulation of this brain area and by subcutaneous injection of a chemical irritant into the hindpaw (Walker et al., 1999).
Previous SectionNext Section
IX. Immunological Effects

The identification of peripheral cannabinoid receptor mRNA and protein in a variety of immune cell types, and the recognition that cannabinoids inhibit adenylyl cyclase in immune cells through a pertussis toxin-sensitive mode (Kaminski et al., 1992, 1994; Kaminski, 1998), suggest a role for cannabinoid receptors in the modulation of immune cell functions. Kaminski et al. (1992) demonstrated that suppression of the humoral immune response by cannabinoids was mediated partially through inhibition of adenylyl cyclase by a pertussis toxin-sensitive G protein-coupled mechanism. Δ9-THC and the synthetic nonclassical bicyclic cannabinoid CP55940 inhibited the lymphocyte proliferative and the sheep erythrocyte IgM antibody-forming cell responses of murine splenocytes to PMA plus the calcium ionophore ionomycin. More direct evidence for a functional linkage of cannabinoid receptors to modulation of immune functional activities has been obtained through the use of CB1- and CB2-selective antagonists.

Select functional activities of macrophages and macrophage-like cells have been reported to be affected by cannabinoids through cannabinoid receptors. McCoy et al. (1995, 1999) demonstrated that Δ9-THC modulated the capacity of macrophages to process antigens that are necessary for the activation of CD4+ T lymphocytes. Δ9-THC was reported to inhibit the processing of intact lysozyme in a dose-dependent fashion, and this inhibition was blocked by the CB2-selective antagonist SR144528, indicating that the inhibitory effect was mediated, at least in part, through the CB2receptor. The CB1-selective antagonist SR141716A did not reverse the suppression caused by Δ9-THC, consistent with no functional linkage of this receptor to this event. These observations were confirmed using CB2 receptor knockout mice (Buckley et al., 2000). Δ9-THC inhibited helper T cell activation through macrophages derived from wild type, but not from knockout mice, consistent with alterations in antigen processing being mediated by the CB2 receptor.

Sacerdote et al. (2000) reported that in vivo and in vitro treatment with the synthetic cannabinoid CP55940 decreased the in vitro migration of macrophages in the rat and that this effect involved both CB1 and CB2 receptors. Spontaneous migration and formyl-methionyl-leucine-phenylalanine-induced chemotaxis assessed by the use of Boyden-modified microchemotaxis chambers were affected. Both SR141716A and SR144528 were able to block the CP55940-induced inhibition of spontaneous migration, although the CB2 antagonist was more potent, and only the CB2 antagonist was able to reverse the effect of CP55940 on formyl-methionyl-leucine-phenylalanine-induced chemotaxis. The CB1 receptor has also been reported to mediate inhibition of iNOS production by neonatal rat microglial cells (Waksman et al., 1999). The potent cannabinoid agonist CP55940 effected a dose-dependent inhibition of iNOS that was reversed by SR141716A. However, no data were provided regarding a role for the CB2 receptor in this process. On the other hand,Stefano et al. (2000) have reported that the endocannabinoid 2-arachidonoylglycerol stimulated constitutive nitric oxide release from human monocytes and vascular tissues and immunocytes of the invertebrate Mytilus edulis and that this effect is mediated through the CB1 receptor in human cells and through an apparent cannabinoid receptor in the invertebrate immunocytes. Furthermore, in both the monocytes and the immunocytes, NO release elicited in response to 2-arachidonoylglycerol exposure was blocked by a CB1 antagonist but not by a CB2 antagonist. Inhibition of lipopolysaccharide-induced iNOS expression by murine RAW 264.7 macrophage-like cells by cannabinoids and the putative cannabinoid CB2-like receptor agonist palmitoylethanolamide (Section XI.) also has been reported (Gross et al., 2000). The inhibition of nitric oxide production byR-(+)-WIN55212 but not palmitoylethanolamide was attenuated significantly by the CB2 receptor antagonist SR144528. These results suggested that inhibition of RAW 264.7 cell lipopolysaccharide-induced iNOS expression byR-(+)-WIN55212, but not palmitoylethanolamide, is mediated by the CB2 receptor.

Gross et al. (2000) suggested an involvement of the CB1 cannabinoid receptor in infection of macrophages by the intracellular pathogen Brucella suis, a Gram-negative bacterium. The influence of the CB1and CB2 receptor antagonists, SR141716A and SR144528, and the nonselective CB1/CB2 cannabinoid receptor agonists, CP55940 and R-(+)-WIN55212, on macrophage infection by B. suis was examined. The intracellular multiplication of Brucella was dose-dependently inhibited in cells treated with SR141716A but not with SR144528, CP55940, orR-(+)-WIN55212. The agonists CP55940 andR-(+)-WIN55212 reversed the SR141716A-induced effect, implicating an involvement of the CB1 receptor in this process.

The involvement of both CB1 and CB2 receptors in Δ9-THC-induced inhibition of natural killer activity has been reported (Massi et al., 2000). In vivo administration of Δ9-THC to mice significantly inhibited natural killer cytolytic activity without affecting concanavalin A-induced splenocyte proliferation. Pretreatment with the CB1 and CB2 cannabinoid receptor antagonists SR141716 and SR144528 partially reversed the inhibition of natural killer cytolytic activity by Δ9-THC. However, the CB1receptor antagonist was more effective than the CB2 receptor antagonist. The parallel measurement of interferon γ (IFN-γ) revealed that Δ9-THC significantly reduced production of this cytokine. The CB1 and CB2receptor antagonists completely reversed the IFN-γ reduction induced by Δ9-THC. Thus, both cannabinoid receptor types were involved in the complex network mediating natural killer cytolytic activity.

Sugiura et al. (2000) examined the effect of 2-arachidonoylglycerol on the intracellular free Ca2+ concentrations in human HL-60 promyelocytic leukemia cells that express the CB2 receptor. It was found that 2-arachidonoylglycerol induced a rapid transient increase in intracellular free Ca2+ concentrations. The Ca2+ transient induced by 2-arachidonoylglycerol was blocked by pretreatment of the cells with the CB2 receptor-specific antagonist SR144528 but not with the CB1 receptor-specific antagonist SR141716A, indicating the involvement of the CB2receptor but not the CB1 receptor in this cellular response. Two other putative endogenous cannabinoid receptor ligands, anandamide and palmitoylethanolamide, were found to be a weak partial agonist and an inactive ligand, respectively.

Carayon et al. (1998) reported that CB2 receptor expression is down-regulated at the mRNA and protein levels during B-cell differentiation. The lowest expression was observed in germinal center proliferating centroblasts of tonsillar tissues. The cannabinoid agonist CP55940 enhanced CD40-mediated proliferation of both virgin and germinal center B-cell subsets. This enhancement was blocked by the CB2 receptor antagonist SR144528 but not by the CB1 receptor antagonist SR141716. It was also observed that CB2 receptors were up-regulated in both B-cell subsets during the first 24 h of CD40-mediated activation. In addition, SR144528 was shown to antagonize the stimulating effects of CP55940 on human tonsillar B-cell activation evoked by cross-linking of surface immunoglobulins (IC50 = 20 nM) (Rinaldi-Carmona et al., 1998). These results suggest a functional involvement of CB2 cannabinoid receptors during B-cell differentiation.

A possible explanation for the capacity of cannabinoids to act through cannabinoid receptors so as to exert a broad spectrum of immune function effects is that these compounds exert differential expression of cytokine profiles. Δ9-THC and other cannabinoid agonists have been reported to augment the expression of immune inhibitory Th2-type cytokines while inhibiting that of Th1-type immune stimulatory cytokines. Δ9-THC has been reported to inhibit antitumor immunity by a CB2receptor-mediated, cytokine-dependent pathway (Zhu et al., 2000). It suppressed host immune reactivity against lung cancer using two different weakly immunogenic murine lung cancer models. Δ9-THC decreased tumor immunogenicity, as indicated by the limited capacity for tumor-immunized, Δ9-THC-treated mice to withstand tumor rechallenge. The immune inhibitory Th2 cytokines, IL-10 and transforming growth factor, were augmented, whereas the immune stimulatory Th1 cytokine, IFN-γ, was down-regulated at both the tumor site and in the spleens of Δ9-THC-treated mice. In vivo administration of the CB2-selective antagonist SR144528 blocked the effects of Δ9-THC. These findings suggest the Δ9-THC promotes tumor growth by inhibiting antitumor immunity by a CB2 receptor-mediated, cytokine-dependent pathway. Δ9-THC treatment of BALB/c mice also suppressed immunity and early IFN-γ, IL-12, and IL-12 receptor β2 responses to Legionella pneumophila(Klein et al., 2000). Levels of IL-12 and IFN-γ, cytokines that promote the development of Th1 cells as well as resistance to a challenge infection, were suppressed by Δ9-THC. Results obtained with selective cannabinoid receptor antagonists indicated that both the CB1 and CB2 receptors were involved in this process.
Previous SectionNext Section
X. Anandamide Is a Vanilloid Receptor Agonist

There are several reports that the endocannabinoid anandamide can act on rat or human vanilloid receptors transfected into cultured cells to produce membrane currents or increase intracellular calcium (Zygmunt et al., 1999; Smart et al., 2000, 2001; Ross et al., 2001). Anandamide also acts on naturally expressed vanilloid receptors in neonatal rat dorsal root ganglia to produce membrane currents (Tognetto et al., 2001) and in rat or guinea pig isolated arterial strips to trigger both release of calcitonin-gene-related peptide from perivascular sensory nerves and relaxation of precontracted tissues (Zygmunt et al., 1999). Results from experiments with transfected rat vanilloid receptors suggest that anandamide has markedly less relative intrinsic activity at these receptors than capsaicin (Ross et al., 2001). Methanandamide activates vanilloid receptors even less potently or effectively than anandamide (Zygmunt et al., 1999; Ralevic et al., 2000; Ross et al., 2001), whereas the CB1/CB2receptor agonists 2-arachidonoylglycerol and HU-210 lack significant activity at these receptors altogether (Zygmunt et al., 1999).

CB1 receptors are negatively coupled to calcium channels, whereas vanilloid receptors open cation channels. Consequently, some experiments have been directed at exploring the consequences of simultaneously activating both receptor types. These have been performed with rat cultured dorsal root ganglion neurons that are known to coexpress CB1 and vanilloid receptors to a very high degree (Ahluwalia et al., 2000). The results obtained indicate that capsaicin-induced increases in intracellular calcium can be opposed by CB1 receptor activation (Millns et al., 2001) and that CB1receptor-mediated inhibition of electrically evoked calcium mobilization and calcitonin-gene-related peptide release can be opposed by the activation of vanilloid receptors (Tognetto et al., 2001). Anandamide was found to be considerably more potent in inhibiting calcium mobilization than in activating vanilloid receptors. There is evidence that in the mouse isolated vas deferens, inhibition of electrically evoked contractions can be mediated both by presynaptic CB1 receptors through reduction of contractile transmitter release and by vanilloid receptors that trigger the release of neuropeptide molecules, which then presumably inhibit contractile transmitter release (Pertwee, 1997; Ross et al., 2001). Anandamide appears to act through both CB1 and vanilloid receptors to inhibit electrically evoked contractions of this tissue preparation, whereas the inhibitory effect of R-(+)-WIN55212 seems to be mediated solely by CB1 receptors (Ross et al., 2001).

The finding that anandamide is an agonist for both cannabinoid and vanilloid receptors prompted the development of the anandamide/capsaicin hybrid molecule, arvanil, which has anandamide-like CB1 affinity, less relative intrinsic activity than anandamide at CB1receptors, and greater potency than anandamide as a vanilloid receptor agonist (De Petrocellis et al., 2000; Di Marzo et al., 2000a). AM404 is another anandamide analog that activates vanilloid receptors (Jerman et al., 2000; Zygmunt et al., 2000; Ross et al., 2001), albeit at concentrations no higher than those at which it inhibits anandamide membrane transport (Beltramo et al., 1997; Piomelli et al., 1999).
Previous SectionNext Section
XI. Preliminary Pharmacological Evidence for Non-CB1, Non-CB2 Cannabinoid Receptors
A. A Putative CB2-Like Cannabinoid Receptor

It has been found by Calignano et al. (1998, 2001) that the endogenous fatty acid amide, palmitoylethanolamide, induces antinociceptive effects that are attenuated by the CB2-selective antagonist SR144528 but not by the CB1-selective antagonist SR141716A. These results were obtained in the mouse formalin paw test after intraplantar injection of palmitoylethanolamide and in the mouse abdominal stretch test after intraperitoneal injection of this compound (Calignano et al., 1998, 2001). The same investigators also found that in these bioassays, anandamide can be antagonized by SR141716A but not SR144528, and that palmitoylethanolamide and anandamide act synergistically. Palmitoylethanolamide lacks significant affinity for CB1 or CB2 receptors (Devane et al., 1992b; Felder et al., 1993; Showalter et al., 1996;Sheskin et al., 1997; Lambert et al., 1999). Consequently, Calignano et al. (1998, 2001) have proposed the existence of an SR144528-sensitive, non-CB2 cannabinoid receptor (“CB2-like†receptor). This putative receptor is thought not to be a vanilloid receptor, because palmitoylethanolamide does not share the ability of anandamide or capsazepine to suppress paw-licking behavior when coadministered with capsaicin into mouse hindpaw (Calignano et al., 2001). Evidence for the existence of CB2-like receptors has also been obtained in experiments with the mouse vas deferens (Griffin et al., 1997). Unlike anandamide or other established CB1receptor agonists, palmitoylethanolamide does not show antinociceptive activity in the mouse hot plate test, suggesting that it does not interfere directly with neuronally mediated transmission of pain signals to the central nervous system (Calignano et al., 2001).
B. A Putative SR141716A-Sensitive, Non-CB1, Non-CB2 Cannabinoid Receptor

There is some evidence that mesenteric arteries of mice and rats express receptors that can be activated by anandamide and methanandamide but not by other established CB1/CB2 receptor agonists and that are both non-CB1, non-CB2, and nonvanilloid. More specifically, anandamide and methanandamide can both induce a concentration-related relaxation of rat or mouse precontracted mesenteric arteries, whereas Δ9-THC, HU-210,R-(+)-WIN55212, and 2-arachidonoylglycerol cannot (Járai et al., 1999; Wagner et al., 1999). Other agonists for this putative novel receptor are the cannabidiol analogs, abnormal cannabidiol and O-1602 (Fig. 14), neither of which exhibits significant affinity for rat brain CB1 receptors (Járai et al., 1999). Anandamide, methanandamide, and abnormal cannabidiol also relax precontracted mesenteric arteries obtained from CB1 receptor knockout (CB1−/−) mice or from CB1−/−/CB2−/−double-knockout mice, confirming a lack of involvement of either CB1 or CB2 receptors in this effect (Járai et al., 1999).
Figure 14
View larger version:

In this page
In a new window

Figure 14

The structures of abnormal cannabidiol and O-1602.

The proposed mesenteric non-CB1, non-CB2 receptors can be blocked by SR141716A, albeit less potently than CB1 receptors. Thus, the relaxant effects of anandamide, abnormal cannabidiol, and O-1602 in precontracted mesenteric arteries obtained from rats or from CB1+/+ or CB1−/− mice have been found to be attenuated by SR141716A at 0.5, 1, or 5 μM (Járai et al., 1999; Wagner et al., 1999). At 10 μM, the nonpsychotropic plant cannabinoid, cannabidiol (Fig. 1), also attenuates the relaxation of rat or CB1−/− mouse precontracted mesenteric arteries induced by anandamide or abnormal cannabidiol (Járai et al., 1999; Wagner et al., 1999). This cannabinoid exhibits at least some degree of selectivity in that it does not attenuate relaxation induced in such vessels by acetylcholine, bradykinin, or sodium nitroprusside (Járai et al., 1999). The relaxant effect of abnormal cannabidiol in rat precontracted mesenteric arteries has been found to be unaffected by a concentration of capsazepine (5 μM) that can attenuate the relaxant effect of capsaicin, ruling out any major involvement of vanilloid receptors (Járai et al., 1999). SR141716A (1 μM) does not attenuate capsaicin-induced relaxation of rat precontracted mesenteric arteries (Járai et al., 1999).

Anandamide-induced vasorelaxation is detectable both in endothelium-intact and in endothelium-denuded precontracted mesenteric arteries of rats (Wagner et al., 1999; Kunos et al., 2000). However, SR141716A only attenuates this vasorelaxant effect of anandamide in the presence of endothelium, and the relaxant effects of abnormal cannabidiol and O-1602 in rat precontracted mesenteric arteries are also largely endothelium-dependent (Járai et al., 1999). It seems likely, therefore, that there are at least two mechanisms by which anandamide relaxes precontracted mesenteric arteries, and that the SR141716A-sensitive, non-CB1, non-CB2 receptors for anandamide proposed byKunos and colleagues (2000) are present on the endothelium but not on mesenteric smooth muscle.
C. A Putative Receptor for Anandamide and R-(+)-WIN55212

Evidence has emerged for the existence in mouse brain of a G protein-coupled receptor that can be activated by anandamide andR-(+)-WIN55212 but not by other CB1/CB2 agonists (Di Marzo et al., 2000b; Breivogel et al., 2001). More specifically, it has been found that [35S]GTPγS binding can be activated in brain membranes from CB1−/− mice by anandamide (EC50 = 3.6 μM) and R-(+)-WIN55212 (EC50 = 1.8 μM) but not by Δ9-THC, HU-210, or CP55940. These properties of this possible new cannabinoid receptor distinguish it from the CB2 receptor for which Δ9-THC, HU-210, and CP55940 are all established agonists. They also distinguish it both from the SR141716A-sensitive, anandamide-sensitive, R-(+)-WIN55212-insensitive receptor that George Kunos' group has postulated to be present in mesenteric arteries (Kunos et al., 2000; Section XI.B.) and from the vanilloid receptor, which is not coupled to G proteins and is unresponsive to R-(+)-WIN55212 (Zygmunt et al., 1999). Activation of [35S]GTPγS binding by anandamide and R-(+)-WIN55212 was detected in membranes from CB1−/− whole brain and from CB1−/− cerebral cortex, midbrain, hippocampus, diencephalon, and brain stem but not in membranes from CB1−/−caudate-putamen/globus pallidus or cerebellum, brain areas that are well populated with CB1 receptors in wild-type animals (Breivogel et al., 2001). Near maximal concentrations of anandamide and R-(+)-WIN55212 were not fully additive in their effects on [35S]GTPγS binding, supporting the hypothesis that these two agents act through a common mechanism (Breivogel et al., 2001). Membranes from CB1−/− cerebral cortex, hippocampus, and brain stem were found to contain specific binding sites for [3H]R-(+)-WIN55212 but not [3H]CP55940 (Breivogel et al., 2001). However, neither of these tritiated ligands exhibited detectable specific binding in membranes from CB1−/− diencephalon, midbrain, caudate-putamen/globus pallidus, cerebellum, or spinal cord. Membranes from some CB1−/− brain areas (brain stem, cortex, midbrain, and spinal cord) but not others (basal ganglia, cerebellum, diencephalon, and hippocampus) also contained specific binding sites for [3H]SR141716A. Even so, it is unlikely that this compound is a ligand for the proposedR-(+)-WIN55212/anandamide receptor, as the distribution patterns of [3H]R-(+)-WIN55212 and [3H]SR141716A binding sites in CB1−/− brain are different. Moreover, although concentrations of SR141716A above 1 μM were found to attenuate the stimulatory effects of anandamide andR-(+)-WIN55212 on [35S]GTPγS binding to CB1−/− membranes, this attenuation could be attributed entirely to the inhibition of [35S]GTPγS binding that was produced by SR141716A in the same concentration range (Breivogel et al., 2001).

Other evidence for the presence of anR-(+)-WIN55212-sensitive non-CB1receptor in mouse brain was obtained recently by Hájos et al. (2001) in electrophysiological experiments with hippocampal slices obtained from CB1−/− or wild-type mice. Their results suggest that althoughR-(+)-WIN55212 probably acts through presynaptic CB1 receptors in the CA1 region of the hippocampus to inhibit GABA release, it acts through presynaptic non-CB1 receptors to inhibit glutamate release in this brain region. This conclusion is consistent with previous reports that CB1 immunostaining cannot be reliably detected in hippocampal axon terminals forming glutamatergic synapses (Katona et al., 1999, 2000; Hájos et al., 2000). It is noteworthy that the inhibitory effect of R-(+)-WIN55212 on glutamatergic transmission observed by Hájos et al. (2001) in hippocampal tissue from CB1−/−mice could be reversed by 1 μM SR141716A.
D. Other Putative Types of Mammalian Cannabinoid Receptor

Results obtained by Sandra Welch's group in experiments with rats and mice have prompted the hypothesis that there may be more than one subtype of CB1 receptor in the spinal cord. Thus,Welch et al. (1998) have found that the potency of intraperitoneal SR141716A against antinociception in the mouse tail-flick test induced by intrathecal administration of certain established cannabinoid receptor agonists is agonist-dependent. SR141716A was most potent against CP55940, less potent against Δ9-THC and Δ8-THC, and least potent against anandamide. As detailed elsewhere (Pertwee, 2001b), Welch's group also found that, in mice, intrathecal morphine interacts synergistically with intrathecal Δ9-THC but not with intrathecal anandamide or CP55940. In addition, there is some evidence for signaling differences between the mechanisms mediating the antinociceptive effects of intrathecal Δ9-THC and anandamide in mice (Welch et al., 1995; Pertwee, 2001b). There is also evidence from rat experiments that although intrathecal Δ9-THC triggers spinal release of dynorphins A and B, intrathecal CP55940 increases the release of dynorphin B but not dynorphin A and intrathecal anandamide fails to affect the release of either peptide (see Houser et al., 2000; Pertwee, 2001b). Signs of differences between cannabinoid receptor populations in mouse spinal cord and brain have also been reported by Welch's group (Pertwee, 2001b).
Previous SectionNext Section
XII. Conclusions

Genes for two types of cannabinoid receptor, CB1 and CB2, have been characterized, and the existence of endogenous agonists for these receptors has also been conclusively demonstrated. The use of cloned receptors expressed in cell lines has greatly facilitated elucidation of the coupling characteristics of CB1 and CB2 receptors and the development and validation of selective ligands for these receptors. The availability of highly selective and potent CB1 and CB2 agonists and antagonists/inverse agonists has assisted in the characterization of the pharmacological properties of naturally expressed cannabinoid receptors, and the development of selective antibodies has allowed detailed localization of cannabinoid receptors, particularly of the CB1 receptor. Some CB1 receptors are present on nerve terminals, and these mediate inhibition of transmitter release when activated by agonists for these receptors that are either released endogenously or administered exogenously. Less is known about the physiological roles of CB2 receptors, which most likely include modulation of cytokine release from immune cells. There is some pharmacological evidence that supports the existence of additional types or subtypes of cannabinoid receptor, the characterization of which is being aided by the availability of CB1, CB2, and CB1/CB2 knockout mice. However, critical evidence in the form of genes encoding receptors with the appropriate pharmacology is currently lacking. Given the rather low sequence similarity between CB1 and CB2, it may be difficult to identify candidate receptors with more divergent pharmacology. If such genes are identified, it will be important to define their endogenous agonists fully to determine how broadly the cannabinoid receptor family should be defined.
Previous SectionNext Section
Footnotes

Address correspondence to: Professor R. G. Pertwee, Co-Chair of the NC-IUPHAR Subcommittee on Cannabinoid Receptors, Department of Biomedical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland, UK. E-mail: rgp@aberdeen.ac.uk
Abbreviations:

Δ9-THC
Δ9-tetrahydrocannabinol
THC
tetrahydrocannabinol
NC-IUPHAR
International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification
ACEA
arachidonyl-2′-chloroethylamide
ACPA
arachidonylcyclopropylamide
anandamide
arachidonoylethanolamide
CBD
cannabidiol
CCK
cholecystokinin
CD40
cluster of differentiation 40
CHO
Chinese hamster ovary
FAAH
fatty acid amide hydrolase
FAK
focal adhesion kinase
GABA
γ-aminobutyric acid
HU-210
6aR,10aR analog of 11-hydroxy-Δ8-THC-dimethylheptyl
HU-211
6aS,10aS analog of 11-hydroxy-Δ8-THC-dimethylheptyl
IFN-γ
interferon γ
IL
interleukin
NOS
nitric-oxide synthase
iNOS
inducible NOS
IP3
inositol-1,4,5-triphosphate
MAPK
mitogen-activated protein kinase
NMDA
N-methyl-d-aspartate
NO
nitric oxide
PI3K
phosphatidylinositol-3-kinase
PMA
phorbol 12-myristate 13-acetate
PMA/Io
PMA plus calcium ionophore
R-(+)-WIN55212
(R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo-[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanonemesylate (WIN55212-2)
SAR
structure-activity relationship
[35S]GTPγS
[35S]guanosine-5′-O-(3-thiotriphosphate)
JWH-051
1-deoxy-11-OH-Δ8-THC-dimethylheptyl
BSA
bovine serum albumin
CNS
central nervous system
EM
electron microscope
AM281
N-(morpholin-4-yl)-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-1H-pyrazole-3-carboxamide
AM251
N-(piperidin-1-yl)-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-1H-pyrazole-3-carboxamide
CP55940
(1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol
CP55244
(−)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxy-propyl)cyclohexan-1-ol
AM630
6-iodo-2-methyl-1-[2-(4-morpholinyl) ethyl]-1H-indol-3-yl](4-methoxyphenyl)methanone (6-iodopravadoline)
RT-PCR
reverse transcription-polymerase chain reaction
SR141716A
N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride
5-HT
5-hydroxytryptamine
JNK
c-Jun N-terminal kinase
kb
kilobase(s)
L-759633
(6aR,10aR)-3-(1,1-dimethylheptyl)-1-methoxy-6,6,9-trimethyl-6a,7,10,10a-tetrahydro-6H-benzo[c]chromene
L-759656
(6aR,10aR)-3-(1,1-dimethylheptyl)-1-methoxy-6,6-dimethyl-9-methylene-6a,7, 8,9,10,10a-hexahydro-6H-benzo[c]chromene
JWH-015
(2-methyl- 1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone
JWH-133
3-(1,1-dimethylbutyl)-6,6,9-trimethyl-6a,7,10,10a-tetrahydro-6H-benzo[c]chromene
JWH-139
3-(1,1-dimethylpropyl)-6,6,9-trimethyl-6a,7,10,10a-tetrahydro-6H-benzo[c]chromene
HU-308
{4-[4-(1,1-dimethylheptyl)-2,6-dimethoxy-phenyl]-6,6-dimethyl-bicyclo[3.1.1] hept-2-en-2-yl}-methanol
CP47497
5-(1,1-dimethylheptyl)-2-(3-hydroxy-cyclohexyl)-phenol
L-768242
(2,3-dichloro-phenyl)-[5-methoxy-2-methyl-3-(2-morpholin-4-yl-ethyl)-indol-1-yl]-methanone
WIN54461
6-bromo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl](4-methoxyphenyl)methanone
WIN56098
anthracen-9-yl-[2-methyl-1-(2-morpholin-4-yl-ethyl)-1H-indol-3-yl]-methanone

U.S. Government

Previous Section

References


Abadji V,
Lin S,
Taha G,
Griffin G,
Stevenson LA,
Pertwee RG,
Makriyannis A
(1994) (R)-Methanandamide: a chiral novel anandamide possessing higher potency and metabolic stability. J Med Chem 37:1889–1893.
CrossRefMedline

Abel EL
(1971) Retrieval of information after use of marihuana. Nature (Lond) 231:58.
CrossRefMedline

Abood ME,
Martin BR
(1992) Neurobiology of marijuana abuse. Trends Pharmacol Sci 13:201–206.
CrossRefMedline

Acquas E,
Pisanu A,
Marrocu P,
Di Chiara G
(2000) Cannabinoid CB1 receptor agonists increase rat cortical and hippocampal acetylcholine release in vivo. Eur J Pharmacol 401:179–185.
CrossRefMedline

Acquas E,
Pisanu A,
Marrocu P,
Goldberg SR,
Di Chiara G
(2001) Δ9-Tetrahydrocannabinol enhances cortical and hippocampal acetylcholine release in vivo: a microdialysis study. Eur J Pharmacol 419:155–161.
CrossRefMedline

Adams IB,
Compton DR,
Martin BR
(1998) Assessment of anandamide interaction with the cannabinoid brain receptor: SR 141716A antagonism studies in mice and autoradiographic analysis of receptor binding in rat brain. J Pharmacol Exp Ther 284:1209–1217.
Abstract/FREE Full Text

Ahluwalia J,
Urban L,
Capogna M,
Bevan S,
Nagy I
(2000) Cannabinoid 1 receptors are expressed in nociceptive primary sensory neurons. Neuroscience 100:685–688.
CrossRefMedline

Al-Hayani A,
Davies SN
(2000) Cannabinoid receptor mediated inhibition of excitatory synaptic transmission in the rat hippocampal slice is developmentally regulated. Br J Pharmacol 131:663–665.
CrossRefMedline

Ameri A
(1999) The effects of cannabinoids on the brain. Prog Neurobiol 58:315–348.
CrossRefMedline

Auclair N,
Otani S,
Soubrié P,
Crepel F
(2000) Cannabinoids modulate synaptic strength and plasticity at glutamatergic synapses of rat prefrontal cortex pyramidal neurons. J Neurophysiol 83:3287–3293.
Abstract/FREE Full Text

Balster RL,
Prescott WR
(1992) Δ9-Tetrahydrocannabinol discrimination in rats as a model for cannabis intoxication. Neurosci Biobehav Rev 16:55–62.
CrossRefMedline

Banerjee SP,
Snyder SH,
Mechoulam R
(1975) Cannabinoids: influence on neurotransmitter uptake in rat brain synaptosomes. J Pharmacol Exp Ther 194:74–81.
Abstract/FREE Full Text

Barrett RL,
Wiley JL,
Balster RL,
Martin BR
(1995) Pharmacological specificity of Δ9-tetrahydrocannabinol discrimination in rats. Psychopharmacology 118:419–424.
CrossRefMedline

Barth F
(1998) Cannabinoid receptor agonists and antagonists. Exp Opin Ther Patents 8:301–313.
CrossRef

Barth F,
Rinaldi-Carmona M
(1999) The development of cannabinoid antagonists. Curr Med Chem 6:745–755.
Medline

Bayewitch M,
Avidor-Reiss T,
Levy R,
Barg J,
Mechoulam R,
Vogel Z
(1995) The peripheral cannabinoid receptor: adenylate cyclase inhibition and G protein coupling. FEBS Lett 375:143–147.
CrossRefMedline

Bayewitch M,
Rhee M-H,
Avidor-Reiss T,
Breuer A,
Mechoulam R,
Vogel Z
(1996) (−)-Δ9-tetrahydrocannabinol antagonizes the peripheral cannabinoid receptor-mediated inhibition of adenylyl cyclase. J Biol Chem 271:9902–9905.
Abstract/FREE Full Text

Beardsley PM,
Scimeca JA,
Martin BR
(1987) Studies on the agonistic activity of Δ9–11-tetrahydrocannabinol in mice, dogs and rhesus monkeys and its interactions with Δ9-tetrahydrocannabinol. J Pharmacol Exp Ther 241:521–526.
Abstract/FREE Full Text

Begg M,
Molleman A,
Parsons M
(2002) Modulation of the release of endogenous γ-aminobutyric acid by cannabinoids in the guinea pig ileum. Eur J Pharmacol 434:87–94.
CrossRefMedline

Beinfeld MC,
Connolly K
(2001) Activation of CB1 cannabinoid receptors in rat hippocampal slices inhibits potassium-evoked cholecystokinin release, a possible mechanism contributing to the spatial memory defects produced by cannabinoids. Neurosci Lett 301:69–71.
CrossRefMedline

Bell MR,
D'Ambra TE,
Kumar V,
Eissenstat MA,
Herrmann JL,
Wetzel JR,
Rosi D,
Philion RE,
Daum SJ,
Hlasta DJ,
et al.
(1991) Antinociceptive (aminoalkyl)indoles. J Med Chem 34:1099–1110.
CrossRefMedline

Beltramo M,
Stella N,
Calignano A,
Lin SY,
Makriyannis A,
Piomelli D
(1997) Functional role of high-affinity anandamide transport, as revealed by selective inhibition. Science (Wash DC) 277:1094–1097.
Abstract/FREE Full Text

Ben-Shabat S,
Fride E,
Sheskin T,
Tamiri T,
Rhee M-H,
Vogel Z,
Bisogno T,
De Petrocellis L,
Di Marzo V,
Mechoulam R
(1998) An entourage effect: inactive endogenous fatty acid glycerol esters enhance 2-arachidonoyl-glycerol cannabinoid activity. Eur J Pharmacol 353:23–31.
CrossRefMedline

Benowitz NL,
Rosenberg J,
Rogers W,
Bachman J,
Jones RT
(1979) Cardiovascular effects of intravenous delta-9-tetrahydrocannabinol: autonomic nervous mechanisms. Clin Pharmacol Ther 25:440–446.
Medline

Berdyshev EV
(2000) Cannabinoid receptors and the regulation of immune response. Chem Phys Lipids 108:169–190.
CrossRefMedline

Bisogno T,
Hanus L,
De Petrocellis L,
Tchilibon S,
Ponde DE,
Brandi I,
Schiano Moriello A,
Davis JB,
Mechoulam R,
Di Marzo V
(2001) Molecular targets for cannabidiol and its synthetic analogues: effect on vanilloid VR1 receptors and on the cellular uptake and enzymatic hydrolysis of anandamide. Br J Pharmacol 134:845–852.
CrossRefMedline

Blázquez C,
Sánchez C,
Daza A,
GalveRoperh I,
Guzmán M
(1999) The stimulation of ketogenesis by cannabinoids in cultured astrocytes defines carnitine palmitoyltransferase I as a new ceramide-activated enzyme. J Neurochem 72:1759–1768.
CrossRefMedline

Böhme GA,
Laville M,
Ledent C,
Parmentier M,
Imperato A
(2000) Enhanced long-term potentiation in mice lacking cannabinoid CB1 receptors. Neuroscience 95:5–7.
Medline

Bouaboula M,
Bianchini L,
McKenzie FR,
Pouyssegur J,
Casellas P
(1999) Cannabinoid receptor CB1 activates the Na+/H+ exchanger NHE-1 isoform via Gi-mediated mitogen activated protein kinase signaling transduction pathways. FEBS Lett 449:61–65.
CrossRefMedline

Bouaboula M,
Bourrié B,
Rinaldi-Carmona M,
Shire D,
Le Fur G,
Casellas P
(1995a) Stimulation of cannabinoid receptor CB1 induces krox-24 expression in human astrocytoma cells. J Biol Chem 270:13973–13980.
Abstract/FREE Full Text

Bouaboula M,
Perrachon S,
Milligan L,
Canat X,
Rinaldi-Carmona M,
Portier M,
Barth F,
Calandra B,
Pecceu F,
Lupker J,
et al.
(1997) A selective inverse agonist for central cannabinoid receptor inhibits mitogen-activated protein kinase activation stimulated by insulin or insulin-like growth factor 1. Evidence for a new model of receptor/ligand interactions. J Biol Chem 272:22330–22339.
Abstract/FREE Full Text

Bouaboula M,
Poinot-Chazel C,
Bourrié B,
Canat X,
Calandra B,
Rinaldi-Carmona M,
Le Fur G,
Casellas P
(1995b) Activation of mitogen-activated protein kinases by stimulation of the central cannabinoid receptor CB1. Biochem J 312:637–641.

Bouaboula M,
Poinot-Chazel C,
Marchand J,
Canat X,
Bourrié B,
Rinaldi-Carmona M,
Calandra B,
Le Fur G,
Casellas P
(1996) Signaling pathway associated with stimulation of CB2 peripheral cannabinoid receptor: involvement of both mitogen-activated protein kinase and induction of Krox-24 expression. Eur J Biochem 237:704–711.
Medline

Bouaboula M,
Rinaldi M,
Carayon P,
Carillon C,
Delpech B,
Shire D,
Le Fur G,
Casellas P
(1993) Cannabinoid-receptor expression in human leukocytes. Eur J Biochem 214:173–180.
Medline

Bowery NG,
Hudson AL,
Price GW
(1987) GABAA and GABAB receptor site distribution in the rat central nervous system. Neuroscience 20:365–383.
CrossRefMedline

Breivogel CS,
Griffin G,
Di Marzo V,
Martin BR
(2001) Evidence for a new G protein-coupled cannabinoid receptor in mouse brain. Mol Pharmacol 60:155–163.
Abstract/FREE Full Text

Breivogel CS,
Selley DE,
Childers SR
(1998) Cannabinoid receptor agonist efficacy for stimulating [35S]GTPγS binding to rat cerebellar membranes correlates with agonist-induced decreases in GDP affinity. J Biol Chem 273:16865–16873.
Abstract/FREE Full Text

Breivogel CS,
Sim LJ,
Childers SR
(1997) Regional differences in cannabinoid receptor/G-protein coupling in rat brain. J Pharmacol Exp Ther 282:1632–1642.
Abstract/FREE Full Text

Breivogel CS,
Walker JM,
Huang S,
Childers SR
(1999) Cannabinoid signaling in cultured rat cerebellar granule cells. 1999 Symposium on the Cannabinoids; 1999 Jun 18–20; Acapulco, Mexico. (International Cannabinoid Research Society, Burlington, Vermont), p 10.

Buckley NE,
Hansson S,
Harta G,
Mezey É
(1998) Expression of the CB1 and CB2 receptor messenger RNAs during embryonic development in the rat. Neuroscience 82:1131–1149.
CrossRefMedline

Buckley NE,
McCoy KL,
Mezey É,
Bonner T,
Zimmer A,
Felder CC,
Glass M,
Zimmer A
(2000) Immunomodulation by cannabinoids is absent in mice deficient for the cannabinoid CB2 receptor. Eur J Pharmacol 396:141–149.
CrossRefMedline

Burkey TH,
Quock RM,
Consroe P,
Ehlert FJ,
Hosohata Y,
Roeske WR,
Yamamura HI
(1997) Relative efficacies of cannabinoid CB1 receptor agonists in the mouse brain. Eur J Pharmacol 336:295–298.
CrossRefMedline

Busch-Petersen J,
Hill WA,
Fan P,
Khanolkar A,
Xie X-Q,
Tius MA,
Makriyannis A
(1996) Unsaturated side chain β-11-hydroxyhexahydrocannabinol analogs. J Med Chem 39:3790–3796.
CrossRefMedline

Cabral GA
(2001) Marijuana and cannabinoids: effects on infections, immunity and AIDS. J Cannabis Ther 1:61–85.

Cadogan A-K,
Alexander SPH,
Boyd EA,
Kendall DA
(1997) Influence of cannabinoids on electrically evoked dopamine release and cyclic AMP generation in the rat striatum. J Neurochem 69:1131–1137.
Medline

Calignano A,
La Rana G,
Giuffrida A,
Piomelli D
(1998) Control of pain initiation by endogenous cannabinoids. Nature (Lond) 394:277–281.
CrossRefMedline

Calignano A,
La Rana G,
Piomelli D
(2001) Antinociceptive activity of the endogenous fatty acid amide, palmitylethanolamide. Eur J Pharmacol 419:191–198.
CrossRefMedline

Carayon P,
Marchand J,
Dussossoy D,
Derocq J-M,
Jbilo O,
Bord A,
Bouaboula M,
Galiègue S,
Mondière P,
Pénarier G,
et al.
(1998) Modulation and functional involvement of CB2 peripheral cannabinoid receptors during B-cell differentiation. Blood 92:3605–3615.
Abstract/FREE Full Text

Carlini EA,
Hamaoui A,
Bieniek D,
Korte F
(1970) Effects of (−)-Δ9-trans-tetrahydrocannabinol and a synthetic derivative on maze performance of rats. Pharmacology 4:359–368.
Medline

Carlisle SJ,
Marciano-Cabral F,
Staab A,
Ludwick C,
Cabral GA
(2002) Differential expression of the CB2 cannabinoid receptor by rodent macrophages and macrophage-like cells in relation to cell activation. Int Immunopharmacol 2:69–82.
CrossRefMedline

Carta G,
Nava F,
Gessa GL
(1998) Inhibition of hippocampal acetylcholine release after acute and repeated Δ9-tetrahydrocannabinol in rats. Brain Res 809:1–4.
CrossRefMedline

Caulfield MP,
Brown DA
(1992) Cannabinoid receptor agonists inhibit Ca current in NG108-15 neuroblastoma cells via a pertussis toxin-sensitive mechanism. Br J Pharmacol 106:231–232.
Medline

Chakrabarti A,
Onaivi ES,
Chaudhuri G
(1995) Cloning and sequencing of a cDNA encoding the mouse brain-type cannabinoid receptor protein. DNA Sequence 5:385–388.
Medline

Chan PKY,
Chan SCY,
Yung W-H
(1998) Presynaptic inhibition of GABAergic inputs to rat substantia nigra pars reticulata neurones by a cannabinoid agonist. Neuroreport 9:671–675.
Medline

Chan PKY,
Yung W-H
(1998) Occlusion of the presynaptic action of cannabinoids in rat substantia nigra pars reticulata by cadmium. Neurosci Lett 249:57–60.
CrossRefMedline

Chaperon F,
Thiébot M-H
(1999) Behavioral effects of cannabinoid agents in animals. Crit Rev Neurobiol 13:243–281.
Medline

Cheer JF,
Marsden CA,
Kendall DA,
Mason R
(2000) Lack of response suppression follows repeated ventral tegmental cannabinoid administration: an in vitro electrophysiological study. Neuroscience 99:661–667.
CrossRefMedline

Chen JP,
Paredes W,
Li J,
Smith D,
Lowinson J,
Gardner EL
(1990a) Δ9-Tetrahydrocannabinol produces naloxone-blockable enhancement of presynaptic basal dopamine efflux in nucleus accumbens of conscious, freely-moving rats as measured by intracerebral microdialysis. Psychopharmacology 102:156–162.
CrossRefMedline

Chen J,
Paredes W,
Lowinson JH,
Gardner EL
(1990b) Δ9-Tetrahydrocannabinol enhances presynaptic dopamine efflux in medial prefrontal cortex. Eur J Pharmacol 190:259–262.
CrossRefMedline

Chen J,
Paredes W,
Lowinson JH,
Gardner EL
(1991) Strain-specific facilitation of dopamine efflux by Δ9-tetrahydrocannabinol in the nucleus accumbens of rat: an in vivo microdialysis study. Neurosci Lett 129:136–140.
CrossRefMedline

Childers SR,
Deadwyler SA
(1996) Role of cyclic AMP in the actions of cannabinoid receptors. Biochem Pharmacol 52:819–827.
CrossRefMedline

Childers SR,
Sexton T,
Roy MB
(1994) Effects of anandamide on cannabinoid receptors in rat brain membranes. Biochem Pharmacol 47:711–715.
CrossRefMedline

Chin C,
Lucas-Lenard J,
Abadji V,
Kendall DA
(1998) Ligand binding and modulation of cyclic AMP levels depend on the chemical nature of residue 192 of the human cannabinoid receptor 1. J Neurochem 70:366–373.
Medline

Chin CN,
Murphy JW,
Huffman JW,
Kendall DA
(1999) The third transmembrane helix of the cannabinoid receptor plays a role in the selectivity of aminoalkylindoles for CB2, peripheral cannabinoid receptor. J Pharmacol Exp Ther 291:837–844.
Abstract/FREE Full Text

Christopoulos A,
Coles P,
Lay L,
Lew MJ,
Angus JA
(2001) Pharmacological analysis of cannabinoid receptor activity in the rat vas deferens. Br J Pharmacol 132:1281–1291.
CrossRefMedline

Coffey RG,
Yamamoto Y,
Snella E,
Pross S
(1996) Tetrahydrocannabinol inhibition of macrophage nitric oxide production. Biochem Pharmacol 52:743–751.
CrossRefMedline

Compton DR,
Aceto MD,
Lowe J,
Martin BR
(1996) In vivo characterization of a specific cannabinoid receptor antagonist (SR141716A): inhibition of Δ9-tetrahydrocannabinol-induced responses and apparent agonist activity. J Pharmacol Exp Ther 277:586–594.
Abstract/FREE Full Text

Compton DR,
Gold LH,
Ward SJ,
Balster RL,
Martin BR
(1992a) Aminoalkylindole analogs: cannabimimetic activity of a class of compounds structurally distinct from Δ9-tetrahydrocannabinol. J Pharmacol Exp Ther 263:1118–1126.
Abstract/FREE Full Text

Compton DR,
Johnson MR,
Melvin LS,
Martin BR
(1992b) Pharmacological profile of a series of bicyclic cannabinoid analogs: classification as cannabimimetic agents. J Pharmacol ExpTher 260:201–209.
Abstract/FREE Full Text

Compton DR,
Rice KC,
de Costa BR,
Razdan RK,
Melvin LS,
Johnson MR,
Martin BR
(1993) Cannabinoid structure-activity relationships: correlation of receptor binding and in vivo activities. J Pharmacol Exp Ther 265:218–226.
Abstract/FREE Full Text

Condie R,
Herring A,
Koh WS,
Lee M,
Kaminski NE
(1996) Cannabinoid inhibition of adenylate cyclase-mediated signal transduction and interleukin 2 (IL-2) expression in the murine T-cell line, EL4.IL-2. J Biol Chem 271:13175–13183.
Abstract/FREE Full Text

Coruzzi G,
Adami M,
Coppelli G,
Frati P,
Soldani G
(1999) Inhibitory effect of the cannabinoid receptor agonist WIN 55,212-2 on pentagastrin-induced gastric acid secretion in the anaesthetized rat. Naunyn-Schmiedeberg's Arch Pharmacol 360:715–718.
CrossRefMedline

Cosenza M,
Gifford AN,
Gatley SJ,
Pyatt B,
Liu Q,
Makriyannis A,
Volkow ND
(2000) Locomotor activity and occupancy of brain cannabinoid CB1 receptors by the antagonist/inverse agonist AM281. Synapse 38:477–482.
CrossRefMedline

Cossu G,
Ledent C,
Fattore L,
Imperato A,
Böhme GA,
Parmentier M,
Fratta W
(2001) Cannabinoid CB1 receptor knockout mice fail to self-administer morphine but not other drugs of abuse. Behav Brain Res 118:61–65.
CrossRefMedline

Coutts AA,
Brewster N,
Ingram T,
Razdan RK,
Pertwee RG
(2000) Comparison of novel cannabinoid partial agonists and SR141716A in the guinea-pig small intestine. Br J Pharmacol 129:645–652.
CrossRefMedline

Coutts AA,
Pertwee RG
(1997) Inhibition by cannabinoid receptor agonists of acetylcholine release from the guinea-pig myenteric plexus. Br J Pharmacol 121:1557–1566.
CrossRefMedline

Craib SJ,
Ellington HC,
Pertwee RG,
Ross RA
(2001) A possible role of lipoxygenase in the activation of vanilloid receptors by anandamide in the guinea-pig bronchus. Br J Pharmacol 134:30–37.
CrossRefMedline

Cravatt BF,
Demarest K,
Patricelli MP,
Bracey MH,
Giang DK,
Martin BR,
Lichtman AH
(2001) Supersensitivity to anandamide and enhanced endogenous cannabinoid signaling in mice lacking fatty acid amide hydrolase. Proc Natl Acad Sci USA 98:9371–9376.
Abstract/FREE Full Text

D'Ambra TE,
Estep KG,
Bell MR,
Eissenstat MA,
Josef KA,
Ward SJ,
Haycock DA,
Baizman ER,
Casiano FM,
Beglin NC,
et al.
(1992) Conformationally restrained analogues of pravadoline: nanomolar potent enantioselective, (aminoalkyl)indole agonists of the cannabinoid receptor. J Med Chem 35:124–135.
CrossRefMedline

Daaka Y,
Friedman H,
Klein TW
(1996) Cannabinoid receptor proteins are increased in Jurkat, human T-cell line after mitogen activation. J Pharmacol Exp Ther 276:776–783.
Abstract/FREE Full Text

Daaka Y,
Klein TW,
Friedman H
(1995) Expression of cannabinoid receptor mRNA in murine and human leukocytes. in The Brain Immune Axis and Substance Abuse, eds Sharp BM, Eisenstein TK, Madden JJ, Friedman H (Plenum Press, New York), pp 91–96.

De Petrocellis L,
Bisogno T,
Davis JB,
Pertwee RG,
Di Marzo V
(2000) Overlap between the ligand recognition properties of the anandamide transporter and the VR1 vanilloid receptor: inhibitors of anandamide uptake with negligible capsaicin-like activity. FEBS Lett 483:52–56.
CrossRefMedline

De Petrocellis L,
Melck D,
Palmisano A,
Bisogno T,
Laezza C,
Bifulco M,
Di Marzo V
(1998) The endogenous cannabinoid anandamide inhibits human breast cancer cell proliferation. Proc Natl Acad Sci USA 95:8375–8380.
Abstract/FREE Full Text

Derkinderen P,
Toutant M,
Burgaya F,
Lebert M,
Siciliano JC,
Defranciscis V,
Gelman M,
Girault JA
(1996) Regulation of a neuronal form of focal adhesion kinase by anandamide. Science (Wash DC) 273:1719–1722.
Abstract/FREE Full Text

Devane WA,
Breuer A,
Sheskin T,
Järbe TUC,
Eisen MS,
Mechoulam R
(1992a) A novel probe for the cannabinoid receptor. J Med Chem 35:2065–2069.
CrossRefMedline

Devane WA,
Dysarz FA,
Johnson MR,
Melvin LS,
Howlett AC
(1988) Determination and characterization of a cannabinoid receptor in rat brain. Mol Pharmacol 34:605–613.
Abstract

Devane WA,
Hanus L,
Breuer A,
Pertwee RG,
Stevenson LA,
Griffin G,
Gibson D,
Mandelbaum A,
Etinger A,
Mechoulam R
(1992b) Isolation and structure of a brain constituent that binds to the cannabinoid receptor. Science (Wash DC) 258:1946–1949.
Abstract/FREE Full Text

Dewey WL,
Martin BR,
May EL
(1984) Cannabinoid stereoisomers: pharmacological effects. in Handbook of Stereoisomers: Drugs in Psychopharmacology, ed Smith DF (CRC Press, Boca Raton, FL), pp 317–326.

Di Marzo V
(1999) Biosynthesis and inactivation of endocannabinoids: relevance to their proposed role as neuromodulators. Life Sci 65:645–655.
CrossRefMedline

Di Marzo V,
Bisogno T,
De Petrocellis L,
Brandi I,
Jefferson RG,
Winckler RL,
Davis JB,
Dasse O,
Mahadevan A,
Razdan RK,
et al.
(2001a) Highly selective CB1 cannabinoid receptor ligands and novel CB1/VR1 vanilloid receptor “hybrid†ligands. Biochem Biophys Res Commun 281:444–451.
CrossRefMedline

Di Marzo V,
Bisogno T,
De Petrocellis L,
Melck D,
Martin BR
(1999) Cannabimimetic fatty acid derivatives: the anandamide family and other endocannabinoids. Curr Med Chem 6:721–744.
Medline

Di Marzo V,
Breivogel C,
Bisogno T,
Melck D,
Patrick G,
Tao Q,
Szallasi A,
Razdan RK,
Martin BR
(2000a) Neurobehavioral activity in mice of N-vanillyl-arachidonyl-amide. Eur J Pharmacol 406:363–374.
CrossRefMedline

Di Marzo V,
Breivogel CS,
Tao Q,
Bridgen DT,
Razdan RK,
Zimmer AM,
Zimmer A,
Martin BR
(2000b) Levels, metabolism and pharmacological activity of anandamide in CB1 cannabinoid receptor knockout mice: evidence for non-CB1, non-CB2 receptor-mediated actions of anandamide in mouse brain. J Neurochem 75:2434–2444.
CrossRefMedline

Di Marzo V,
Goparaju SK,
Wang L,
Liu J,
Bátkai S,
Járai Z,
Fezza F,
Miura GI,
Palmiter RD,
Sugiura T,
Kunos G
(2001b) Leptin-regulated endocannabinoids are involved in maintaining food intake. Nature (Lond) 410:822–825.
CrossRefMedline

Di Marzo V,
Melck D,
Bisogno T,
De Petrocellis L
(1998) Endocannabinoids: endogenous cannabinoid receptor ligands with neuromodulatory action. Trends Neurosci 21:521–528.
CrossRefMedline

Diana MA,
Levenes C,
Mackie K,
Marty A
(2002) Short-term retrograde inhibition of GABAergic synaptic currents in rat Purkinje cells is mediated by endogenous cannabinoids. J Neurosci 22:200–208.
Abstract/FREE Full Text

Diana M,
Melis M,
Gessa GL
(1998) Increase in meso-prefrontal dopaminergic activity after stimulation of CB1 receptors by cannabinoids. Eur J Neurosci 10:2825–2830.
CrossRefMedline

Edery H,
Grunfeld Y,
Ben-Zvi Z,
Mechoulam R
(1971) Structural requirements for cannabinoid activity. Ann NY Acad Sci 191:40–53.
CrossRef

Egertová M,
Elphick MR
(2000) Localisation of cannabinoid receptors in the rat brain using antibodies to the intracellular C-terminal tail of CB1. J Comp Neurol 422:159–171.
CrossRefMedline

Egertová M,
Giang DK,
Cravatt BF,
Elphick MR
(1998) A new perspective on cannabinoid signalling: complementary localization of fatty acid amide hydrolase and the CB1 receptor in rat brain. Proc R Soc Lond B Biol Sci 265:2081–2085.
Medline

Eissenstat MA,
Bell MR,
D'Ambra TE,
Alexander EJ,
Daum SJ,
Ackerman JH,
Gruett MD,
Kumar V,
Estep KG,
Olefirowicz EM,
et al.
(1995) Aminoalkylindoles: structure-activity relationships of novel cannabinoid mimetics. J Med Chem 38:3094–3105.
CrossRefMedline

Elphick MR,
Egertová M
(2001) The neurobiology and evolution of cannabinoid signalling. Philos Trans R Soc Lond B Biol Sci 356:381–408.
Abstract/FREE Full Text

Facci L,
Dal Toso R,
Romanello S,
Buriani A,
Skaper SD,
Leon A
(1995) Mast cells express a peripheral cannabinoid receptor with differential sensitivity to anandamide and palmitoyl ethanolamide. Proc Natl Acad Sci USA 92:3376–3380.
Abstract/FREE Full Text

Felder CC,
Briley EM,
Axelrod J,
Simpson JT,
Mackie K,
Devane WA
(1993) Anandamide, an endogenous cannabimimetic eicosanoid, binds to the cloned human cannabinoid receptor and stimulates receptor-mediated signal transduction. Proc Natl Acad Sci USA 90:7656–7660.
Abstract/FREE Full Text

Felder CC,
Glass M
(1998) Cannabinoid receptors and their endogenous agonists. Annu Rev Pharmacol Toxicol 38:179–200.
CrossRefMedline

Felder CC,
Joyce KE,
Briley EM,
Glass M,
Mackie KP,
Fahey KJ,
Cullinan GJ,
Hunden DC,
Johnson DW,
Chaney MO,
et al.
(1998) LY320135, a novel cannabinoid CB1 receptor antagonist, unmasks coupling of the CB1 receptor to stimulation of cAMP accumulation. J Pharmacol Exp Ther 284:291–297.
Abstract/FREE Full Text

Felder CC,
Joyce KE,
Briley EM,
Mansouri J,
Mackie K,
Blond O,
Lai Y,
Ma AL,
Mitchell RL
(1995) Comparison of the pharmacology and signal transduction of the human cannabinoid CB1 and CB2 receptors. Mol Pharmacol 48:443–450.
Abstract

Felder CC,
Veluz JS,
Williams HL,
Briley EM,
Matsuda LA
(1992) Cannabinoid agonists stimulate both receptor- and non-receptor-mediated signal transduction pathways in cells transfected with and expressing cannabinoid receptor clones. Mol Pharmacol 42:838–845.
Abstract

Feng WK,
Song ZH
(2001) Functional roles of the tyrosine within the NP(X)nY motif and the cysteines in the C-terminal juxtamembrane region of the CB2 cannabinoid receptor. FEBS Lett 501:166–170.
CrossRefMedline

Ferraro DP,
Grilly DM
(1973) Lack of tolerance to Δ9-tetrahydrocannabinol in chimpanzees. Science (Wash DC) 179:490–492.
Abstract/FREE Full Text

Ferraro L,
Tomasini MC,
Gessa GL,
Bebe BW,
Tanganelli S,
Antonelli T
(2001) The cannabinoid receptor agonist WIN 55,212-2 regulates glutamate transmission in rat cerebral cortex: an in vivo and in vitro study. Cereb Cortex 11:728–733.
Abstract/FREE Full Text

Fimiani C,
Mattocks D,
Cavani F,
Salzet M,
Deutsch DG,
Pryor S,
Bilfinger TV,
Stefano GB
(1999) Morphine and anandamide stimulate intracellular calcium transients in human arterial endothelial cells: coupling to nitric oxide release. Cell Signal 11:189–193.
CrossRefMedline

French ED
(1997) Δ9-Tetrahydrocannabinol excites rat VTA dopamine neurons through activation of cannabinoid CB1 but not opioid receptors. Neurosci Lett 226:159–162.
CrossRefMedline

French ED,
Dillon K,
Wu X
(1997) Cannabinoids excite dopamine neurons in the ventral tegmentum and substantia nigra. Neuroreport 8:649–652.
Medline

Gadzicki D,
Müller-Vahl K,
Stuhrmann M
(1999) A frequent polymorphism in the coding exon of the human cannabinoid receptor (CNR1) gene. Mol Cell Probes 13:321–323.
CrossRefMedline

Galiègue S,
Mary S,
Marchand J,
Dussossoy D,
Carrière D,
Carayon P,
Bouaboula M,
Shire D,
Le Fur G,
Casellas P
(1995) Expression of central and peripheral cannabinoid receptors in human immune tissues and leukocyte subpopulations. Eur J Biochem 232:54–61.
Medline

Gallant M,
Dufresne C,
Gareau Y,
Guay D,
Leblanc Y,
Prasit P,
Rochette C,
Sawyer N,
Slipetz DM,
Tremblay N,
et al.
(1996) New class of potent ligands for the human peripheral cannabinoid receptor. Bioorg Med Chem Lett 6:2263–2268.
CrossRef

Gaoni Y,
Mechoulam R
(1964) Isolation, structure and partial synthesis of an active constituent of hashish. J Am Chem Soc 86:1646–1647.
CrossRef

Gareau Y,
Dufresne C,
Gallant M,
Rochette C,
Sawyer N,
Slipetz DM,
Tremblay N,
Weech PK,
Metters KM,
Labelle M
(1996) Structure activity relationships of tetrahydrocannabinol analogues on human cannabinoid receptors. Bioorg Med Chem Lett 6:189–194.

Gatley SJ,
Lan R,
Pyatt B,
Gifford AN,
Volkow ND,
Makriyannis A
(1997) Binding of the non-classical cannabinoid CP 55,940 and the diarylpyrazole AM251 to rodent brain cannabinoid receptors. Life Sci 61:pL191–PL197.
CrossRef

Gatley SJ,
Lan R,
Volkow ND,
Pappas N,
King P,
Wong CT,
Gifford AN,
Pyatt B,
Dewey SL,
Makriyannis A
(1998) Imaging the brain marijuana receptor: development of a radioligand that binds to cannabinoid CB1 receptors in vivo. J Neurochem 70:417–423.
Medline

Gebremedhin D,
Lange AR,
Campbell WB,
Hillard CJ,
Harder DR
(1999) Cannabinoid CB1 receptor of cat cerebral arterial muscle functions to inhibit L-type Ca2+ channel current. Am J Physiol 276:H2085–H2093.

Gérard C,
Mollereau C,
Vassart G,
Parmentier M
(1990) Nucleotide sequence of a human cannabinoid receptor cDNA. Nucleic Acids Res 18:7142.
FREE Full Text

Gérard CM,
Mollereau C,
Vassart G,
Parmentier M
(1991) Molecular cloning of a human cannabinoid receptor which is also expressed in testis. Biochem J 279:129–134.

Gerdeman G,
Lovinger DM
(2001) CB1 cannabinoid receptor inhibits synaptic release of glutamate in rat dorsolateral striatum. J Neurophysiol 85:468–471.
Abstract/FREE Full Text

Gessa GL,
Casu MA,
Carta G,
Mascia MS
(1998a) Cannabinoids decrease acetylcholine release in the medial-prefrontal cortex and hippocampus, reversal by SR 141716A. Eur J Pharmacol 355:119–124.
CrossRefMedline

Gessa GL,
Mascia MS,
Casu MA,
Carta G
(1997) Inhibition of hippocampal acetylcholine release by cannabinoids: reversal by SR141716A. Eur J Pharmacol 327:R1–R2.
CrossRefMedline

Gessa GL,
Melis M,
Muntoni A,
Diana M
(1998b) Cannabinoids activate mesolimbic dopamine neurons by an action on cannabinoid CB1 receptors. Eur J Pharmacol 341:39–44.
CrossRefMedline

Gifford AN,
Ashby CR
(1996) Electrically evoked acetylcholine release from hippocampal slices is inhibited by the cannabinoid receptor agonist, WIN 55212-2 and is potentiated by the cannabinoid antagonist, SR 141716A. J Pharmacol Exp Ther 277:1431–1436.
Abstract/FREE Full Text

Gifford AN,
Bruneus M,
Gatley SJ,
Volkow ND
(2000) Cannabinoid receptor-mediated inhibition of acetylcholine release from hippocampal and cortical synaptosomes. Br J Pharmacol 131:645–650.
CrossRefMedline

Gifford AN,
Bruneus M,
Lin S,
Goutopoulos A,
Makriyannis A,
Volkow ND,
Gatley SJ
(1999) Potentiation of the action of anandamide on hippocampal slices by the fatty acid amide hydrolase inhibitor, palmitylsulphonyl fluoride (AM 374). Eur J Pharmacol 383:9–14.
CrossRefMedline

Gifford AN,
Samiian L,
Gatley SJ,
Ashby CR
(1997a) Examination of the effect of the cannabinoid receptor agonist, CP 55,940, on electrically evoked transmitter release from rat brain slices. Eur J Pharmacol 324:187–192.
CrossRefMedline

Gifford AN,
Tang Y,
Gatley SJ,
Volkow ND,
Lan R,
Makriyannis A
(1997b) Effect of the cannabinoid receptor SPECT agent, AM 281, on hippocampal acetylcholine release from rat brain slices. Neurosci Lett 238:84–86.
CrossRefMedline

Giuffrida A,
Parsons LH,
Kerr TM,
Rodrı́guez de Fonseca F,
Navarro M,
Piomelli D
(1999) Dopamine activation of endogenous cannabinoid signaling in dorsal striatum. Nat Neurosci 2:358–363.
CrossRefMedline

Glass M,
Dragunow M,
Faull RLM
(1997) Cannabinoid receptors in the human brain: a detailed anatomical and quantitative autoradiographic study in the fetal, neonatal and adult human brain. Neuroscience 77:299–318.
CrossRefMedline

Glass M,
Felder CC
(1997) Concurrent stimulation of cannabinoid CB1 and dopamine D2 receptors augments cAMP accumulation in striatal neurons: evidence for a Gs linkage to the CB1 receptor. J Neurosci 17:5327–5333.
Abstract/FREE Full Text

Göbel I,
Trendelenburg AU,
Cox SL,
Meyer A,
Starke K
(2000) Electrically evoked release of [3H]noradrenaline from mouse cultured sympathetic neurons: release-modulating heteroreceptors. J Neurochem 75:2087–2094.
CrossRefMedline

Gold LH,
Balster RL,
Barrett RL,
Britt DT,
Martin BR
(1992) A comparison of the discriminative stimulus properties of Δ9-tetrahydrocannabinol and CP 55,940 in rats and rhesus monkeys. J Pharmacol Exp Ther 262:479–486.
Abstract/FREE Full Text

Gómez del Pulgar T,
Velasco G,
Guzmán M
(2000) The CB1 cannabinoid receptor is coupled to the activation of protein kinase B/Akt. Biochem J 347:369–373.
CrossRefMedline

Gonsiorek W,
Lunn C,
Fan X,
Narula S,
Lundell D,
Hipkin RW
(2000) Endocannabinoid 2-arachidonyl glycerol is a full agonist through human type 2 cannabinoid receptor: antagonism by anandamide. Mol Pharmacol 57:1045–1050.
Abstract/FREE Full Text

Gouldson P,
Calandra B,
Legoux P,
Kernéis A,
Rinaldi-Carmona M,
Barth F,
Le Fur G,
Ferrara P,
Shire D
(2000) Mutational analysis and molecular modelling of the antagonist SR 144528 binding site on the human cannabinoid CB2 receptor. Eur J Pharmacol 401:17–25.
CrossRefMedline

Greenamyre JT,
Young AB,
Penney JB
(1984) Quantitative autoradiographic distribution of l-[3H]glutamate-binding sites in rat central nervous system. J Neurosci 4:2133–2144.
Abstract

Griffin G,
Atkinson PJ,
Showalter VM,
Martin BR,
Abood ME
(1998) Evaluation of cannabinoid receptor agonists and antagonists using the guanosine-5′-O-(3-[35S]thio)-triphosphate binding assay in rat cerebellar membranes. J Pharmacol Exp Ther 285:553–560.
Abstract/FREE Full Text

Griffin G,
Fernando SR,
Ross RA,
McKay NG,
Ashford MLJ,
Shire D,
Huffman JW,
Yu S,
Lainton JAH,
Pertwee RG
(1997) Evidence for the presence of CB2-like cannabinoid receptors on peripheral nerve terminals. Eur J Pharmacol 339:53–61.
CrossRefMedline

Griffin G,
Tao Q,
Abood ME
(2000) Cloning and pharmacological characterization of the rat CB2 cannabinoid receptor. J Pharmacol Exp Ther 292:886–894.
Abstract/FREE Full Text

Gross A,
Terraza A,
Marchant J,
Bouaboula M,
Ouahrani-Bettache S,
Liautard J-P,
Casellas P,
Dornand J
(2000) A beneficial aspect of a CB1 cannabinoid receptor antagonist: SR141716A is a potent inhibitor of macrophage infection by the intracellular pathogen Brucella suis. J Leukocyte Biol 67:335–344.
Abstract

Guzmán M,
Galve-Roperh I,
Sánchez C
(2001) Ceramide: a new second messenger of cannabinoid action. Trends Pharmacol Sci 22:19–22.
Medline

Guzmán M,
Sánchez C
(1999) Effects of cannabinoids on energy metabolism. Life Sci 65:657–664.
CrossRefMedline

Hájos N,
Katona I,
Naiem SS,
Mackie K,
Ledent C,
Mody I,
Freund TF
(2000) Cannabinoids inhibit hippocampal GABAergic transmission and network oscillations. Eur J Neurosci 12:3239–3249.
CrossRefMedline

Hájos N,
Ledent C,
Freund TF
(2001) Novel cannabinoid-sensitive receptor mediates inhibition of glutamatergic synaptic transmission in the hippocampus. Neuroscience 106:1–4.
CrossRefMedline

Hampson AJ,
Bornheim LM,
Scanziani M,
Yost CS,
Gray AT,
Hansen BM,
Leonoudakis DJ,
Bickler PE
(1998) Dual effects of anandamide on NMDA receptor-mediated responses and neurotransmission. J Neurochem 70:671–676.
Medline

Hanus L,
Abu-Lafi S,
Fride E,
Breuer A,
Vogel Z,
Shalev DE,
Kustanovich I,
Mechoulam R
(2001) 2-Arachidonyl glyceryl ether, an endogenous agonist of the cannabinoid CB1 receptor. Proc Natl Acad Sci USA 98:3662–3665.
Abstract/FREE Full Text

Hanus L,
Breuer A,
Tchilibon S,
Shiloah S,
Goldenberg D,
Horowitz M,
Pertwee RG,
Ross RA,
Mechoulam R,
Fride E
(1999) HU-308: a specific agonist for CB2, a peripheral cannabinoid receptor. Proc Natl Acad Sci USA 96:14228–14233.
Abstract/FREE Full Text

Hanus L,
Gopher A,
Almog S,
Mechoulam R
(1993) Two new unsaturated fatty acid ethanolamides in brain that bind to the cannabinoid receptor. J Med Chem 36:3032–3034.
CrossRefMedline

Henry DJ,
Chavkin C
(1995) Activation of inwardly rectifying potassium channels (GIRK1) by co-expressed rat brain cannabinoid receptors in Xenopus oocytes. Neurosci Lett 186:91–94.
CrossRefMedline

Herkenham M,
Lynn AB,
Johnson MR,
Melvin LS,
de Costa BR,
Rice KC
(1991) Characterization and localization of cannabinoid receptors in rat brain: a quantitative in vitro autoradiographic study. J Neurosci 11:563–583.
Abstract

Herkenham M,
Lynn AB,
Little MD,
Johnson MR,
Melvin LS,
de Costa BR,
Rice KC
(1990) Cannabinoid receptor localization in brain. Proc Natl Acad Sci USA 87:1932–1936.
Abstract/FREE Full Text

Heyser CJ,
Hampson RE,
Deadwyler SA
(1993) Effects of delta-9-tetrahydrocannabinol on delayed match to sample performance in rats: alterations in short-term memory associated with changes in task specific firing of hippocampal cells. J Pharmacol Exp Ther 264:294–307.
Abstract/FREE Full Text

Hillard CJ,
Jarrahian A
(2000) The movement of N-arachidonoylethanolamine (anandamide) across cellular membranes. Chem Phys Lipids 108:123–134.
CrossRefMedline

Hillard CJ,
Manna S,
Greenberg MJ,
Dicamelli R,
Ross RA,
Stevenson LA,
Murphy V,
Pertwee RG,
Campbell WB
(1999) Synthesis and characterization of potent and selective agonists of the neuronal cannabinoid receptor (CB1). J Pharmacol Exp Ther 289:1427–1433.
Abstract/FREE Full Text

Ho BY,
Zhao JC
(1996) Determination of the cannabinoid receptors in mouse x rat hybridoma NG108-15 cells and rat GH4C1 cells. Neurosci Lett 212:123–126.
CrossRefMedline

Hoehe MR,
Rinn T,
Flachmeier C,
Heere P,
Kunert HJ,
Timmermann B,
Kopke K,
Ehrenreich H
(2000) Comparative sequencing of the human CB1 cannabinoid receptor gene coding exon: no structural mutations in individuals exhibiting extreme responses to cannabis. Psychiat Genet 10:173–177.
Medline

Hoffman AF,
Lupica CR
(2000) Mechanisms of cannabinoid inhibition of GABAA synaptic transmission in the hippocampus. J Neurosci 20:2470–2479.
Abstract/FREE Full Text

Hoffman AF,
Lupica CR
(2001) Direct actions of cannabinoids on synaptic transmission in the nucleus accumbens: a comparison with opioids. J Neurophysiol 85:72–83.
Abstract/FREE Full Text

Holland M,
Challiss RAJ,
Standen NB,
Boyle JP
(1999) Cannabinoid CB1 receptors fail to cause relaxation, but couple via Gi/Go to the inhibition of adenylyl cyclase in carotid artery smooth muscle. Br J Pharmacol 128:597–604.
CrossRefMedline

Hollister LE
(1974) Structure-activity relationships in man of Cannabis constituents and homologs and metabolites of Δ9-tetrahydrocannabinol. Pharmacology 11:3–11.
CrossRefMedline

Hosohata K,
Quock RM,
Hosohata Y,
Burkey TH,
Makriyannis A,
Consroe P,
Roeske WR,
Yamamura HI
(1997a) AM630 is a competitive cannabinoid receptor antagonist in the guinea pig brain. Life Sci 61:pL115–PL118.
CrossRefMedline

Hosohata Y,
Quock RM,
Hosohata K,
Makriyannis A,
Consroe P,
Roeske WR,
Yamamura HI
(1997b) AM630 antagonism of cannabinoid-stimulated [35S]GTPγS binding in the mouse brain. Eur J Pharmacol 321:R1–R3.
CrossRefMedline

Houser SJ,
Eads M,
Embrey JP,
Welch SP
(2000) Dynorphin B and spinal analgesia: induction of antinociception by the cannabinoids CP55,940, Δ9-THC and anandamide. Brain Res 857:337–342.
CrossRefMedline

Howlett AC
(1995a) Cannabinoid compounds and signal transduction mechanisms. in Cannabinoid Receptors, ed Pertwee RG (Academic Press, London), pp 167–204.

Howlett AC
(1995b) Pharmacology of cannabinoid receptors. Annu Rev Pharmacol Toxicol 33:607–634.
CrossRef

Howlett AC,
Champion TM,
Wilken GH,
Mechoulam R
(1990) Stereochemical effects of 11-OH-Δ8-tetrahydrocannabinol-dimethylheptyl to inhibit adenylate cyclase and bind to the cannabinoid receptor. Neuropharmacology 29:161–165.
CrossRefMedline

Howlett AC,
Johnson MR,
Melvin LS,
Milne GM
(1988) Non-classical cannabinoid analgetics inhibit adenylate cyclase: development of a cannabinoid receptor model. Mol Pharmacol 33:297–302.
Abstract

Howlett AC,
Mukhopadhyay S
(2000) Cellular signal transduction by anandamide and 2-arachidonoylglycerol. Chem Phys Lipids 108:53–70.
CrossRefMedline

Howlett AC,
Qualy JM,
Khachatrian LL
(1986) Involvement of Gi in the inhibition of adenylate cyclase by cannabimimetic drugs. Mol Pharmacol 29:307–313.
Abstract

Howlett AC,
Wilken GH,
Pigg JJ,
Houston DB,
Lan R,
Liu Q,
Makriyannis A
(2000) Azido- and isothiocyanato-substituted aryl pyrazoles bind covalently to the CB1 cannabinoid receptor and impair signal transduction. J Neurochem 74:2174–2181.
CrossRefMedline

Huang C-C,
Lo S-W,
Hsu K-S
(2001) Presynaptic mechanisms underlying cannabinoid inhibition of excitatory synaptic transmission in rat striatal neurons. J Physiol 532:731–748.
Abstract/FREE Full Text

Huestis MA,
Gorelick DA,
Heishman SJ,
Preston KL,
Nelson RA,
Moolchan ET,
Frank RA
(2001) Blockade of effects of smoked marijuana by the CBl-selective cannabinoid receptor antagonist SR141716. Arch Gen Psychiat 58:322–328.
Abstract/FREE Full Text

Huffman JW
(1999) Cannabimimetic indoles, pyrroles and indenes. Curr Med Chem 6:705–720.
Medline

Huffman JW,
Dai D,
Martin BR,
Compton DR
(1994) Design, synthesis and pharmacology of cannabimimetic indoles. Bioorg Med Chem Lett 4:563–566.
CrossRef

Huffman JW,
Liddle J,
Yu S,
Aung MM,
Abood ME,
Wiley JL,
Martin BR
(1999) 3-(1′,1′-dimethylbutyl)-1-deoxy-Δ8-THC and related compounds: synthesis of selective ligands for the CB2 receptor. Bioorg Med Chem 7:2905–2914.
CrossRefMedline

Huffman JW,
Yu S,
Liddle J,
Wiley JL,
Abood M,
Martin BR,
Aung MM
(1998) 1-Deoxy-1′,1′-dimethylalkyl-Δ8-THC derivatives: selective ligands for the CB2 receptor. 1999 Symposium on the Cannabinoids; 1999 Jun 18–20; Acapulco, Mexico. (International Cannabinoid Research Society, Burlington, Vermont), p 10.

Huffman JW,
Yu S,
Showalter V,
Abood ME,
Wiley JL,
Compton DR,
Martin BR,
Bramblett RD,
Reggio PH
(1996) Synthesis and pharmacology of a very potent cannabinoid lacking a phenolic hydroxyl with high affinity for the CB2 receptor. J Med Chem 39:3875–3877.
CrossRefMedline

Irving AJ,
Caldwell D,
Rae M,
Bewick G,
Coutts AA
(2001) Functional expression of cell surface CB1 receptors at synaptic terminals in cultured cerebellar granule cells. 2001 Symposium on the Cannabinoids; 2001 Jun 28–30; San Lorenzo de El Escorial, Spain; (International Cannabinoid Research Society, Burlington, Vermont), p 61.

Irving AJ,
Coutts AA,
Harvey J,
Rae MG,
Mackie K,
Bewick GS,
Pertwee RG
(2000) Functional expression of cell surface cannabinoid CB1 receptors on presynaptic inhibitory terminals in cultured rat hippocampal neurons. Neuroscience 98:253–262.
CrossRefMedline

Ishac EJN,
Jiang L,
Lake KD,
Varga K,
Abood ME,
Kunos G
(1996) Inhibition of exocytotic noradrenaline release by presynaptic cannabinoid CB1 receptors on peripheral sympathetic nerves. Br J Pharmacol 118:2023–2028.
Medline

Izzo AA,
Mascolo N,
Tonini M,
Capasso F
(2000) Modulation of peristalsis by cannabinoid CB1 ligands in the isolated guinea-pig ileum. Br J Pharmacol 129:984–990.
CrossRefMedline

Jansen EM,
Haycock DA,
Ward SJ,
Seybold VS
(1992) Distribution of cannabinoid receptors in rat brain determined with aminoalkylindoles. Brain Res 575:93–102.
CrossRefMedline

Járai Z,
Wagner JA,
Varga K,
Lake KD,
Compton DR,
Martin BR,
Zimmer AM,
Bonner TI,
Buckley NE,
Mezey É,
et al.
(1999) Cannabinoid-induced mesenteric vasodilation through an endothelial site distinct from CB1 or CB2 receptors. Proc Natl Acad Sci USA 96:14136–14141.
Abstract/FREE Full Text

Järbe TUC,
Hiltunen AJ,
Mechoulam R
(1989) Stereospecificity of the discriminative stimulus functions of the dimethylheptyl homologs of 11-hydroxy-Δ8-tetrahydrocannabinol in rats and pigeons. J Pharmacol Exp Ther 250:1000–1005.
Abstract/FREE Full Text

Järbe TUC,
Mathis DA
(1992) Dissociative and discriminative stimulus functions of cannabinoids/cannabimimetics. in Marijuana/Cannabinoids Neurobiology and Neurophysiology, eds Murphy L, Bartke A (CRC Press, Boca Raton, FL), pp 425–458.

Järbe TUC,
McMillan DE
(1979) Discrimination stimulus properties of tetrahydrocannabinols and related drugs in rats and pigeons. Neuropharmacology 18:1023–1024.
CrossRefMedline

Järbe TUC,
McMillan DE
(1980) Δ9-THC as a discriminative stimulus in rats and pigeons: generalization to THC metabolites and SP-111. Psychopharmacology 71:281–289.
CrossRefMedline

Järbe TUC,
Ohlin GC
(1977) Stimulus effects of Δ9-THC and its interaction with naltrexone and catecholamine blockers in rats. Psychopharmacology 54:193–195.
CrossRefMedline

Jarrahian A,
Manna S,
Edgemond WS,
Campbell WB,
Hillard CJ
(2000) Structure-activity relationships among N-arachidonylethanolamine (anandamide) head group analogues for the anandamide transporter. J Neurochem 74:2597–2606.
CrossRefMedline

Jennings EA,
Vaughan CW,
Christie MJ
(2001) Cannabinoid actions on rat superficial medullary dorsal horn neurons in vitro. J Physiol 534:805–812.
Abstract/FREE Full Text

Jeon YJ,
Yang KH,
Pulaski JT,
Kaminski NE
(1996) Attenuation of inducible nitric oxide synthase gene expression by Δ9-tetrahydrocannabinol is mediated through the inhibition of nuclear factor-κB/Rel activation. Mol Pharmacol 50:334–341.
Abstract

Jerman JC,
Brough SJ,
Davis JB,
Middlemiss DN,
Smart D
(2000) The anandamide transport inhibitor AM404 is an agonist at the rat vanilloid receptor (VR1). Br J Pharmacol 129:73P.
CrossRef

Johnson MR,
Melvin LS
(1986) The discovery of nonclassical cannabinoid analgetics. in Cannabinoids As Therapeutic Agents, ed Mechoulam R (CRC Press, Boca Raton, FL), pp 121–145.

Kaminski NE
(1998) Inhibition of the cAMP signaling cascade via cannabinoid receptors: a putative mechanism of immune modulation by cannabinoid compounds. Toxicol Lett (Shannon) 102–103:59–63.

Kaminski NE,
Abood ME,
Kessler FK,
Martin BR,
Schatz AR
(1992) Identification of a functionally relevant cannabinoid receptor on mouse spleen cells that is involved in cannabinoid-mediated immune modulation. Mol Pharmacol 42:736–742.
Abstract

Kaminski NE,
Koh WS,
Yang KH,
Lee M,
Kessler FK
(1994) Suppression of the humoral immune response by cannabinoids is partially mediated through inhibition of adenylate cyclase by a pertussis toxin-sensitive G-protein coupled mechanism. Biochem Pharmacol 48:1899–1908.
CrossRefMedline

Kathmann M,
Bauer U,
Schlicker E,
Göthert M
(1999a) Cannabinoid CB1 receptor-mediated inhibition of NMDA- and kainate-stimulated noradrenaline and dopamine release in the brain. Naunyn-Schmiedeberg's Arch Pharmacol 359:466–470.
CrossRefMedline

Kathmann M,
Nakazi M,
Bauer U,
Schlicker E
(1999b) WIN 55212-2 inhibits serotonin release in the mouse brain cortex via presynaptic cannabinoid CB1 receptors. 1999 Symposium on the Cannabinoids; 1999 Jun 18–20; Acapulco, Mexico. (International Cannabinoid Research Society, Burlington, Vermont), p 51.

Kathmann M,
Weber B,
Schlicker E
(2001a) Cannabinoid CB1 receptor-mediated inhibition of acetylcholine release in the brain of NMRI, CD-1 and C57BL/6J mice. Naunyn-Schmiedeberg's Arch Pharmacol 363:50–56.
CrossRefMedline
Kathmann M,
Weber B,
Zimmer A,
Schlicker E
(2001b) Enhanced acetylcholine release in the hippocampus of cannabinoid CB1 receptor-deficient mice. Br J Pharmacol 132:1169–1173.
CrossRefMedline

Katona I,
Rancz EA,
Acsády L,
Ledent C,
Mackie K,
Hájos N,
Freund TF
(2001) Distribution of CB1 cannabinoid receptors in the amygdala and their role in the control of GABAergic transmission. J Neurosci 21:9506–9518.
Abstract/FREE Full Text

Katona I,
Sperlágh B,
Maglóczky Z,
Sántha E,
Köfalvi A,
Czirják S,
Mackie K,
Vizi ES,
Freund TF
(2000) GABAergic interneurons are the targets of cannabinoid actions in the human hippocampus. Neuroscience 100:797–804.
CrossRefMedline

Katona I,
Sperlágh B,
Sı́k A,
Käfalvi A,
Vizi ES,
Mackie K,
Freund TF
(1999) Presynaptically located CB1 cannabinoid receptors regulate GABA release from axon terminals of specific hippocampal interneurons. J Neurosci 19:4544–4558.
Abstract/FREE Full Text

Kearn CS,
Greenberg MJ,
DiCamelli R,
Kurzawa K,
Hillard CJ
(1999) Relationships between ligand affinities for the cerebellar cannabinoid receptor CB1 and the induction of GDP/GTP exchange. J Neurochem 72:2379–2387.
CrossRefMedline

Kearn CS,
Hillard C
(1999) A model for the study of cannabinoid actions in microglia. 1999 Symposium on the Cannabinoids; 1999 Jun 18–20; Acapulco, Mexico. (International Cannabinoid Research Society, Burlington, Vermont), p 44.

Khanolkar AD,
Abadji V,
Lin S,
Hill WAG,
Taha G,
Abouzid K,
Meng Z,
Fan P,
Makriyannis A
(1996) Head group analogs of arachidonylethanolamide, the endogenous cannabinoid ligand. J Med Chem 39:4515–4519.
CrossRefMedline

Khanolkar AD,
Makriyannis A
(1999) Structure-activity relationships of anandamide, an endogenous cannabinoid ligand. Life Sci 65:607–616.
CrossRefMedline

Klein TW,
Newton CA,
Nakachi N,
Friedman H
(2000) Δ9-Tetrahydrocannabinol treatment suppresses immunity and early IFN-γ, IL-12 and IL-12 receptor β2 responses to Legionella pneumophila infection. J Immunol 164:6461–6466.
Abstract/FREE Full Text

Kozak M
(1994) Determinants of translational fidelity and efficiency in vertebrate mRNAs. Biochimie (Paris) 76:815–821.
Medline

Kreitzer AC,
Regehr WG
(2001a) Retrograde inhibition of presynaptic calcium influx by endogenous cannabinoids at excitatory synapses onto Purkinje cells. Neuron 29:717–727.
CrossRefMedline

Kreitzer AC,
Regehr WG
(2001b) Cerebellar depolarization-induced suppression of inhibition is mediated by endogenous cannabinoids. J Neurosci 21:RC174, (1–5)..
Abstract/FREE Full Text

Kumar V,
Alexander MD,
Bell MR,
Eissenstat MA,
Casiano FM,
Chippari SM,
Haycock DA,
Luttinger DA,
Kuster JE,
Miller MS,
et al.
(1995) Morpholinoalkylindenes as antinociceptive agents: novel cannabinoid receptor agonists. Bioorg Med Chem Lett 5:381–386.

Kunos G,
Járai Z,
Bátkai S,
Goparaju SK,
Ishac EJN,
Liu J,
Wang L,
Wagner JA
(2000) Endocannabinoids as cardiovascular modulators. Chem Phys Lipids 108:159–168.
CrossRefMedline

Kurihara J,
Nishigaki M,
Suzuki S,
Okubo Y,
Takata Y,
Nakane S,
Sugiura T,
Waku K,
Kato H
(2001) 2-Arachidonoylglycerol and anandamide oppositely modulate norepinephrine release from the rat heart sympathetic nerves. Jpn J Pharmacol 87:93–96.
CrossRefMedline

Kuster JE,
Stevenson JI,
Ward SJ,
D'Ambra TE,
Haycock DA
(1993) Aminoalkylindole binding in rat cerebellum: selective displacement by natural and synthetic cannabinoids. J Pharmacol Exp Ther 264:1352–1363.
Abstract/FREE Full Text

Lainton JAH,
Huffman JW,
Martin BR,
Compton DR
(1995) 1-Alkyl-3-(1-naphthoyl)pyrroles: a new class of cannabinoid. Tetrahedron Lett 36:1401–1404.
CrossRef

Lake KD,
Martin BR,
Kunos G,
Varga K
(1997) Cardiovascular effects of anandamide in anesthetized and conscious normotensive and hypertensive rats. Hypertension 29:1204–1210.
Abstract/FREE Full Text

Lambert DM,
DiPaolo FG,
Sonveaux P,
Kanyonyo M,
Govaerts SJ,
Hermans E,
Bueb J-L,
Delzenne NM,
Tschirhart EJ
(1999) Analogues and homologues of N-palmitoyl ethanolamide, a putative endogenous CB2 cannabinoid, as potential ligands for the cannabinoid receptors. Biochim Biophys Acta 1440:266–274.
Medline

Lan R,
Gatley J,
Lu Q,
Fan P,
Fernando SR,
Volkow ND,
Pertwee R,
Makriyannis A
(1999a) Design and synthesis of the CB1 selective cannabinoid antagonist AM281: a potential human SPECT ligand. AAPS PharmSci 1:E4.
CrossRefMedline

Lan R,
Gatley SJ,
Makriyannis A
(1996) Preparation of iodine-123 labeled AM251: a potential SPECT radioligand for the brain cannabinoid CB1 receptor. J Lab Comps Radiopharmaceut 38:875–881.
CrossRef

Lan R,
Liu Q,
Fan P,
Lin S,
Fernando SR,
McCallion D,
Pertwee R,
Makriyannis A
(1999b) Structure-activity relationships of pyrazole derivatives as cannabinoid receptor antagonists. J Med Chem 42:769–776.
CrossRefMedline

Landsman RS,
Burkey TH,
Consroe P,
Roeske WR,
Yamamura HI
(1997) SR141716A is an inverse agonist at the human cannabinoid CB1 receptor. Eur J Pharmacol 334:R1–R2.
CrossRefMedline

Landsman RS,
Makriyannis A,
Deng H,
Consroe P,
Roeske WR,
Yamamura HI
(1998) AM630 is an inverse agonist at the human cannabinoid CB1 receptor. Life Sci 62:pL109–PL113.
CrossRefMedline

Ledent C,
Valverde O,
Cossu G,
Petitet F,
Aubert J-F,
Beslot F,
Böhme GA,
Imperato A,
Pedrazzini T,
Roques BP,
et al.
(1999) Unresponsiveness to cannabinoids and reduced addictive effects of opiates in CB1 receptor knockout mice. Science (Wash DC) 283:401–404.
Abstract/FREE Full Text

Lee C-M,
Zaugg HE,
Michaels RJ,
Dren AT,
Plotnikoff NP,
Young PR
(1983) New azacannabinoids highly active in the central nervous system. J Med Chem 26:278–280.
CrossRefMedline

Lee SF,
Newton C,
Widen R,
Friedman H,
Klein TW
(2001) Differential expression of cannabinoid CB2 receptor mRNA in mouse immune cell subpopulations and following B cell stimulation. Eur J Pharmacol 423:235–241.
CrossRefMedline

Lévénès C,
Daniel H,
Soubrié P,
Crépel F
(1998) Cannabinoids decrease excitatory synaptic transmission and impair long-term depression in rat cerebellar Purkinje cells. J Physiol 510:867–879.
Abstract/FREE Full Text

Lichtman AH
(2000) SR 141716A enhances spatial memory as assessed in a radial-arm maze task in rats. Eur J Pharmacol 404:175–179.
CrossRefMedline

Lichtman AH,
Dimen KR,
Martin BR
(1995) Systemic or intrahippocampal cannabinoid administration impairs spatial memory in rats. Psychopharmacology 119:282–290.
CrossRefMedline

Lichtman AH,
Martin BR
(1996) Δ9-Tetrahydrocannabinol impairs spatial memory through a cannabinoid receptor mechanism. Psychopharmacology 126:125–131.
CrossRefMedline

Lichtman AH,
Wiley JL,
LaVecchia KL,
Neviaser ST,
Arthur DB,
Wilson DM,
Martin BR
(1998) Effects of SR 141716A after acute or chronic cannabinoid administration in dogs. Eur J Pharmacol 357:139–148.
CrossRefMedline

Lin SY,
Khanolkar AD,
Fan P,
Goutopoulos A,
Qin C,
Papahadjis D,
Makriyannis A
(1998) Novel analogues of arachidonylethanolamide (anandamide): affinities for the CB1 and CB2 cannabinoid receptors and metabolic stability. J Med Chem 41:5353–5361.
CrossRefMedline

Little PJ,
Compton DR,
Johnson MR,
Melvin LS,
Martin BR
(1988) Pharmacology and stereoselectivity of structurally novel cannabinoids in mice. J Pharmacol Exp Ther 247:1046–1051.
Abstract/FREE Full Text

Little PJ,
Compton DR,
Mechoulam R,
Martin BR
(1989) Stereochemical effects of 11-OH-Δ8-THC-dimethylheptyl in mice and dogs. Pharmacol Biochem Behav 32:661–666.
CrossRefMedline

Liu J,
Gao B,
Mirshahi F,
Sanyal AJ,
Khanolkar AD,
Makriyannis A,
Kunos G
(2000) Functional CB1 cannabinoid receptors in human vascular endothelial cells. Biochem J 346:835–840.

Loev B,
Bender PE,
Dowalo F,
Macko E,
Fowler PJ
(1973) Cannabinoids. Structure-activity studies related to 1,2-dimethylheptyl derivatives. J Med Chem 16:1200–1206.
CrossRefMedline

Lynn AB,
Herkenham M
(1994) Localization of cannabinoid receptors and nonsaturable high-density cannabinoid binding sites in peripheral tissues of the rat: implications for receptor-mediated immune modulation by cannabinoids. J Pharmacol Exp Ther 268:1612–1623.
Abstract/FREE Full Text

Maccarrone M,
Bari M,
Lorenzon T,
Bisogno T,
Di Marzo V,
Finazzi-Agro A
(2000) Anandamide uptake by human endothelial cells and its regulation by nitric oxide. J Biol Chem 275:13484–13492.
Abstract/FREE Full Text

Maccarrone M,
van der Stelt M,
Rossi A,
Veldink GA,
Vliegenthart JFG,
Fina Iagrzzò A
(1998) Anandamide hydrolysis by human cells in culture and brain. J Biol Chem 273:32332–32339.
Abstract/FREE Full Text

Mackie K,
Devane WA,
Hille B
(1993) Anandamide, an endogenous cannabinoid, inhibits calcium currents as a partial agonist in N18 neuroblastoma cells. Mol Pharmacol 44:498–503.
Abstract/FREE Full Text

Mackie K,
Hille B
(1992) Cannabinoids inhibit N-type calcium channels in neuroblastoma-glioma cells. Proc Natl Acad Sci USA 89:3825–3829.
Abstract/FREE Full Text

Mackie K,
Lai Y,
Westenbroek R,
Mitchell R
(1995) Cannabinoids activate an inwardly rectifying potassium conductance and inhibit Q-type calcium currents in AtT20 cells transfected with rat brain cannabinoid receptor. J Neurosci 15:6552–6561.
Abstract/FREE Full Text

MacLennan SJ,
Reynen PH,
Kwan J,
Bonhaus DW
(1998) Evidence for inverse agonism of SR141716A at human recombinant cannabinoid CB1 and CB2 receptors. Br J Pharmacol 124:619–622.
CrossRefMedline

Maejima T,
Hashimoto K,
Yoshida T,
Aiba A,
Kano M
(2001) Presynaptic inhibition caused by retrograde signal from metabotropic glutamate to cannabinoid receptors. Neuron 31:463–475.
CrossRefMedline

Mailleux P,
Parmentier M,
Vanderhaeghen J-J
(1992) Distribution of cannabinoid receptor messenger RNA in the human brain: an in situ hybridization histochemistry with oligonucleotides. Neurosci Lett 143:200–204.
CrossRefMedline

Maneuf YP,
Crossman AR,
Brotchie JM
(1996a) Modulation of GABAergic transmission in the globus pallidus by the synthetic cannabinoid WIN 55,212-2. Synapse 22:382–385.
CrossRefMedline

Maneuf YP,
Nash JE,
Crossman AR,
Brotchie JM
(1996b) Activation of the cannabinoid receptor by Δ9-tetrahydrocannabinol reduces γ-aminobutyric acid uptake in the globus pallidus. Eur J Pharmacol 308:161–164.
CrossRefMedline

Mang CF,
Erbelding D,
Kilbinger H
(2001) Differential effects of anandamide on acetylcholine release in the guinea-pig ileum mediated via vanilloid and non-CB1 cannabinoid receptors. Br J Pharmacol 134:161–167.
CrossRefMedline

Manzoni OJ,
Bockaert J
(2001) Cannabinoids inhibit GABAergic synaptic transmission in mice nucleus accumbens. Eur J Pharmacol 412:R3–R5.
CrossRefMedline

Marsicano G,
Lutz B
(1999) Expression of the cannabinoid receptor CB1 in distinct neuronal subpopulations in the adult mouse forebrain. Eur J Neurosci 11:4213–4225.
CrossRefMedline

Mascia MS,
Obinu MC,
Ledent C,
Parmentier M,
Böhme GA,
Imperato A,
Fratta W
(1999) Lack of morphine-induced dopamine release in the nucleus accumbens of cannabinoid CB1 receptor knockout mice. Eur J Pharmacol 383:R1–R2.
CrossRefMedline

Martin BR,
Compton DR,
Little PJ,
Martin TJ,
Beardsley PM
(1987) Pharmacological evaluation of agonistic and antagonistic activity of cannabinoids. in Structure-Activity Relationships of the Cannabinoids, eds Rapaka RS, Makriyannis A (NIDA Research Monograph 79, Govt. Printing Office, Washington, DC), pp 108–122.

Martin BR,
Compton DR,
Thomas BF,
Prescott WR,
Little PJ,
Razdan RK,
Johnson MR,
Melvin LS,
Mechoulam R,
Ward SJ
(1991) Behavioral, biochemical and molecular modeling evaluations of cannabinoid analogs. Pharmacol Biochem Behav 40:471–478.
CrossRefMedline

Martin BR,
Dewey WL,
Harris LS,
Beckner J
(1975) Marihuana-like activity of new synthetic tetrahydrocannabinols. Pharmacol Biochem Behav 3:849–853.
CrossRefMedline

Martin BR,
Lichtman AH
(1998) Cannabinoid transmission and pain perception. Neurobiol Dis 5:447–461.
CrossRefMedline

Martin BR,
Mechoulam R,
Razdan RK
(1999) Discovery and characterization of endogenous cannabinoids. Life Sci 65:573–595.
CrossRefMedline

Martin BR,
Thomas BF,
Razdan RK
(1995) Structural requirements for cannabinoid receptor probes. in Cannabinoid Receptors, ed Pertwee RG (Academic Press, London), pp 35–85.

Massi P,
Fuzio D,
Viganò D,
Sacerdote P,
Parolaro D
(2000) Relative involvement of cannabinoid CB1 and CB2 receptors in the Δ9-tetrahydrocannabinol-induced inhibition of natural killer activity. Eur J Pharmacol 387:343–347.
CrossRefMedline

Massi P,
Patrini G,
Rubino T,
Fuzio D,
Parolaro D
(1997) Changes in rat spleen cannabinoid receptors after chronic CP-55,940: an autoradiographic study. Pharmacol Biochem Behav 58:73–78.
CrossRefMedline

Matsuda LA
(1997) Molecular aspects of cannabinoid receptors. Crit Rev Neurobiol 11:143–166.
Medline

Matsuda LA,
Bonner TI,
Lolait SJ
(1993) Localization of cannabinoid receptor messenger RNA in rat brain. J Comp Neurol 327:535–550.
CrossRefMedline

Matsuda LA,
Lolait SJ,
Brownstein MJ,
Young AC,
Bonner TI
(1990) Structure of a cannabinoid receptor and functional expression of the cloned cDNA. Nature (Lond) 346:561–564.
CrossRefMedline

McAllister SD,
Griffin G,
Satin LS,
Abood ME
(1999) Cannabinoid receptors can activate and inhibit G protein-coupled inwardly rectifying potassium channels in a Xenopus oocyte expression system. J Pharmacol Exp Ther 291:618–626.
Abstract/FREE Full Text

McCoy KL,
Gainey D,
Cabral GA
(1995) Δ9-Tetrahydrocannabinol modulates antigen processing by macrophages. J Pharmacol Exp Ther 273:1216–1223.
Abstract/FREE Full Text

McCoy KL,
Matveyeva M,
Carlisle SJ,
Cabral GA
(1999) Cannabinoid inhibition of the processing of intact lysozyme by macrophages: evidence for CB2 receptor participation. J Pharmacol Exp Ther 289:1620–1625.
Abstract/FREE Full Text

McVey M,
Hill J,
Howlett AC,
Klein C
(1999) Adenylyl cyclase, a coincidence detector for nitric oxide. J Biol Chem 274:18887–18892.
Abstract/FREE Full Text

Mechoulam R,
Ben-Shabat S,
Hanus L,
Ligumsky M,
Kaminski NE,
Schatz AR,
Gopher A,
Almog S,
Martin BR,
Compton DR,
et al.
(1995) Identification of an endogenous 2-monoglyceride, present in canine gut, that binds to cannabinoid receptors. Biochem Pharmacol 50:83–90.
CrossRefMedline

Mechoulam R,
Devane WA,
Breuer A,
Zahalka J
(1991) A random walk through a cannabis field. Pharmacol Biochem Behav 40:461–464.
CrossRefMedline

Mechoulam R,
Devane WA,
Glaser R
(1992) Cannabinoid geometry and biological activity. in Marijuana/Cannabinoids Neurobiology and Neurophysiology, eds Murphy L, Bartke A (CRC Press Inc. Boca Raton, FL), pp 1–33.

Mechoulam R,
Edery H
(1973) Structure-activity relationships in the cannabinoid series. in Marijuana, ed Mechoulam R (Academic Press, New York), pp 101–136.

Mechoulam R,
Fride E,
Di Marzo V
(1998) Endocannabinoids. Eur J Pharmacol 359:1–18.
CrossRefMedline

Mechoulam R,
Gaoni Y
(1967) The absolute configuration of Δ1-tetrahydrocannabinol, the major active constituent of hashish. Tetrahedron Lett 12:1109–1111.
Medline

Mechoulam R,
Lander N,
Varkony TH,
Kimmel I,
Becker O,
Ben-Zvi Z,
Edery H,
Porath G
(1980) Stereochemical requirements for cannabinoid activity. J Med Chem 23:1068–1072.
CrossRefMedline

Mechoulam R,
Lander N,
Srebnik M,
Breuer A,
Segal M,
Feigenbaum JJ,
Järbe TUC,
Consroe P
(1987) Stereochemical requirements for cannabimimetic activity. in Structure-Activity Relationships of the Cannabinoids, eds Rapaka RS, Makriyannis A (NIDA Research Monograph 79, Govt. Printing Office, Washington, DC), pp 15–30.

Melck D,
Rueda D,
Galve Roperh I,
De Petrocellis L,
Guzmán M,
Di Marzo V
(1999) Involvement of the cAMP/protein kinase A pathway and of mitogen-activated protein kinase in the anti-proliferative effects of anandamide in human breast cancer cells. FEBS Lett 463:235–240.
CrossRefMedline

Melis M,
Gessa GL,
Diana M
(2000) Different mechanisms for dopaminergic excitation induced by opiates and cannabinoids in the rat midbrain. Prog Neuropsychopharmacol Biol Psychiatry 24:993–1006.
CrossRefMedline

Melvin LS,
Johnson MR,
Harbert CA,
Milne GM,
Weissman A
(1984) A cannabinoid derived prototypical analgesic. J Med Chem 27:67–71.
CrossRefMedline

Melvin LS,
Milne GM,
Johnson MR,
Subramaniam B,
Wilken GH,
Howlett AC
(1993) Structure-activity relationships for cannabinoid receptor-binding and analgesic activity: studies of bicyclic cannabinoid analogs. Mol Pharmacol 44:1008–1015.
Abstract

Meschler JP,
Kraichely DM,
Wilken GH,
Howlett AC
(2000) Inverse agonist properties of N-(piperidin-1-yl)-5-(4- chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3- carboxamide HCl (SR141716A) and 1-(2-chlorophenyl)-4-cyano-5-(4-methoxypheny-1H-pyrazole-3-carboxylic acid phenylamide (CP-272871) for the CB1 cannabinoid receptor. Biochem Pharmacol 60:1315–1323.
CrossRefMedline

Millns PJ,
Chapman V,
Kendall DA
(2001) Cannabinoid inhibition of the capsaicin-induced calcium response in rat dorsal root ganglion neurones. Br J Pharmacol 132:969–971.
CrossRefMedline

Misner DL,
Sullivan JM
(1999) Mechanism of cannabinoid effects on long-term potentiation and depression in hippocampal CA1 neurons. J Neurosci 19:6795–6805.
Abstract/FREE Full Text

Molderings GJ,
Likungu J,
Göthert M
(1999) Presynaptic cannabinoid and imidazoline receptors in the human heart and their potential relationship. Naunyn-Schmiedeberg's Arch Pharmacol 360:157–164.
CrossRefMedline

Molina-Holgado F,
Lledó A,
Guaza C
(1997) Anandamide suppresses nitric oxide and TNF-α responses to Theiler's virus or endotoxin in astrocytes. Neuroreport 8:1929–1933.
Medline

Mombouli J-V,
Schaeffer G,
Holzmann S,
Kostner GM,
Graier WF
(1999) Anandamide-induced mobilization of cytosolic Ca2+ in endothelial cells. Br J Pharmacol 126:1593–1600.
CrossRefMedline

Moore H,
Fadel J,
Sarter M,
Bruno JP
(1999) Role of accumbens and cortical dopamine receptors in the regulation of cortical acetylcholine release. Neuroscience 88:811–822.
CrossRefMedline

Morisset V,
Urban L
(2001) Cannabinoid-induced presynaptic inhibition of glutamatergic EPSCs in substantia gelatinosa neurons of the rat spinal cord. J Neurophysiol 86:40–48.
Abstract/FREE Full Text

Munro S,
Thomas KL,
Abu-Shaar M
(1993) Molecular characterization of a peripheral receptor for cannabinoids. Nature (Lond) 365:61–65.
CrossRefMedline

Murphy WJ,
Eizirik E,
Johnson WE,
Zhang YP,
Ryder OA,
O'Brien SJ
(2001) Molecular phylogenetics and the origins of placental mammals. Nature (Lond) 409:614–618.
CrossRefMedline

Nakamura EM,
da Silva EA,
Concilio GV,
Wilkinson DA,
Masur J
(1991) Reversible effects of acute and long-term administration of Δ9-tetrahydrocannabinol (THC) on memory in the rat. Drug Alcohol Depend 28:167–175.
CrossRefMedline

Nakazi M,
Bauer U,
Nickel T,
Kathmann M,
Schlicker E
(2000) Inhibition of serotonin release in the mouse brain via presynaptic cannabinoid CB1 receptors. Naunyn-Schmiedeberg's Arch Pharmacol 361:19–24.
CrossRefMedline

Nava F,
Carta G,
Battasi AM,
Gessa GL
(2000) D2 dopamine receptors enable Δ9-tetrahydrocannabinol induced memory impairment and reduction of hippocampal extracellular acetylcholine concentration. Br J Pharmacol 130:1201–1210.
CrossRefMedline

Nava F,
Carta G,
Colombo G,
Gessa GL
(2001) Effects of chronic Δ9-tetrahydrocannabinol treatment on hippocampal extracellular acetylcholine concentration and alternation performance in the T-maze. Neuropharmacology 41:392–399.
CrossRefMedline

Netzeband JG,
Conroy SM,
Parsons KL,
Gruol DL
(1999) Cannabinoids enhance NMDA-elicited Ca2+ signals in cerebellar granule neurons in culture. J Neurosci 19:8765–8777.
Abstract/FREE Full Text

Noe SN,
Newton C,
Widen R,
Friedman H,
Klein TW
(2000) Anti-CD40, anti-CD3 and IL-2 stimulation induce contrasting changes in CB1 mRNA expression in mouse splenocytes. J Neuroimmunol 110:161–167.
CrossRefMedline

Ohno-Shosaku T,
Maejima T,
Kano M
(2001) Endogenous cannabinoids mediate retrograde signals from depolarized postsynaptic neurons to presynaptic terminals. Neuron 29:729–738.
CrossRefMedline

Onaivi ES,
Chakrabarti A,
Chaudhuri G
(1996) Cannabinoid receptor genes. Prog Neurobiol 48:275–305.
CrossRefMedline

Pacheco M,
Childers SR,
Arnold R,
Casiano F,
Ward SJ
(1991) Aminoalkylindoles: actions on specific G-protein-linked receptors. J Pharmacol Exp Ther 257:170–183.
Abstract/FREE Full Text

Pacheco MA,
Ward SJ,
Childers SR
(1993) Identification of cannabinoid receptors in cultures of rat cerebellar granule cells. Brain Res 603:102–110.
CrossRefMedline

Palmer SL,
Khanolkar AD,
Makriyannis A
(2000) Natural and synthetic endocannabinoids and their structure-activity relationships. Curr Pharm Design 6:1381–1397.
CrossRefMedline

Pan X,
Ikeda SR,
Lewis DL
(1996) Rat brain cannabinoid receptor modulates N-type Ca2+ channels in a neuronal expression system. Mol Pharmacol 49:707–714.
Abstract

Pan X,
Ikeda SR,
Lewis DL
(1998) SR 141716A acts as an inverse agonist to increase neuronal voltage-dependent Ca2+ currents by reversal of tonic CB1 cannabinoid receptor activity. Mol Pharmacol 54:1064–1072.
Abstract/FREE Full Text

Paria BC,
Song H,
Wang X,
Schmid PC,
Krebsbach RJ,
Schmid HHO,
Bonner TI,
Zimmer A,
Dey SK
(2001) Dysregulated cannabinoid signaling disrupts uterine receptivity for embryo implantation. J Biol Chem 276:20523–20528.
Abstract/FREE Full Text

Pars HG,
Razdan RK,
Howes JF
(1977) Potential therapeutic agents derived from the cannabinoid nucleus. Adv Drug Res 11:97–189.
Medline

Patel NA,
Moldow RL,
Patel JA,
Wu G,
Chang SL
(1998) Arachidonylethanolamide (AEA) activation of FOS proto-oncogene protein immunoreactivity in the rat brain. Brain Res 797:225–233.
CrossRefMedline

Paton GS,
Pertwee RG,
Davies SN
(1998) Correlation between cannabinoid mediated effects on paired pulse depression and induction of long term potentiation in the rat hippocampal slice. Neuropharmacology 37:1123–1130.
CrossRefMedline

Perez-Reyes M,
Timmons MC,
Lipton MA,
Davis KH,
Wall ME
(1972) Intravenous injection in man of Δ9-tetrahydrocannabinol and 11-OH-Δ9-tetrahydrocannabinol. Science (Wash DC) 177:633–635.
Abstract/FREE Full Text

Pertwee RG
(1997) Pharmacology of cannabinoid CB1 and CB2 receptors. Pharmacol Ther 74:129–180.
CrossRefMedline

Pertwee RG
(1999) Pharmacology of cannabinoid receptor ligands. Curr Med Chem 6:635–664.
Medline

Pertwee RG
(2000a) Cannabinoid receptor ligands: clinical and neuropharmacological considerations, relevant to future drug discovery and development. Exp Opin Invest Drugs 9:1553–1571.

Pertwee RG
(2000b) Neuropharmacology and therapeutic potential of cannabinoids. Addict Biol 5:37–46.

Pertwee RG
(2001a) Cannabinoids and the gastrointestinal tract. Gut 48:859–867.
Abstract/FREE Full Text

Pertwee RG
(2001b) Cannabinoid receptors and pain. Prog Neurobiol 63:569–611.
CrossRefMedline


Pertwee RG,
Fernando SR,
Nash JE,
Coutts AA
(1996) Further evidence for the presence of cannabinoid CB1 receptors in guinea-pig small intestine. Br J Pharmacol 118:2199–2205.
Medline

Pertwee RG,
Gibson TM,
Stevenson LA,
Ross RA,
Banner WK,
Saha B,
Razdan RK,
Martin BR
(2000) O-1057, a potent water-soluble cannabinoid receptor agonist with antinociceptive properties. Br J Pharmacol 129:1577–1584.
CrossRefMedline

Pertwee R,
Griffin G,
Fernando S,
Li X,
Hill A,
Makriyannis A
(1995a) AM630, a competitive cannabinoid receptor antagonist. Life Sci 56:1949–1955.
CrossRefMedline

Pertwee RG,
Griffin G,
Lainton JAH,
Huffman JW
(1995b) Pharmacological characterization of three novel cannabinoid receptor agonists in the mouse isolated vas deferens. Eur J Pharmacol 284:241–247.
CrossRefMedline


Pertwee RG,
Stevenson LA,
Elrick DB,
Mechoulam R,
Corbett AD
(1992) Inhibitory effects of certain enantiomeric cannabinoids in the mouse vas deferens and the myenteric plexus preparation of guinea-pig small intestine. Br J Pharmacol 105:980–984.
Medline

Petitet F,
Marin L,
Doble A
(1996) Biochemical and pharmacological characterization of cannabinoid binding sites using [3H]SR141716A. Neuroreport 7:789–792.
Medline

Pettit DA,
Anders DL,
Harrison MP,
Cabral GA
(1996) Cannabinoid receptor expression in immune cells. Adv Exp Med Biol 402:119–129.
Medline

Pinto JC,
Potie F,
Rice KC,
Boring D,
Johnson MR,
Evans DM,
Wilken GH,
Cantrell CH,
Howlett AC
(1994) Cannabinoid receptor binding and agonist activity of amides and esters of arachidonic acid. Mol Pharmacol 46:516–522.
Abstract

Piomelli D,
Beltramo M,
Glasnapp S,
Lin SY,
Goutopoulos A,
Xie X-Q,
Makriyannis A
(1999) Structural determinants for recognition and translocation by the anandamide transporter. Proc Natl Acad Sci USA 96:5802–5807.
Abstract/FREE Full Text

Piomelli D,
Giuffrida A,
Calignano A,
Rodrı́guez de Fonseca F
(2000) The endocannabinoid system as a target for therapeutic drugs. Trends Pharmacol Sci 21:218–224.
CrossRefMedline

Pistis M,
Porcu G,
Melis M,
Diana M,
Gessa GL
(2001) Effects of cannabinoids on prefrontal neuronal responses to ventral tegmental area stimulation. Eur J Neurosci 14:96–102.
CrossRefMedline

Porter AC,
Felder CC
(2001) The endocannabinoid nervous system: unique opportunities for therapeutic intervention. Pharmacol Ther 90:45–60.
CrossRefMedline

Portier M,
Rinaldi-Carmona M,
Pecceu F,
Combes T,
Poinot-Chazel C,
Calandra B,
Barth F,
Le Fur G,
Casellas P
(1999) SR 144528, an antagonist for the peripheral cannabinoid receptor that behaves as an inverse agonist. J Pharmacol Exp Ther 288:582–589.
Abstract/FREE Full Text

Prevot V,
Rialas CM,
Croix D,
Salzet M,
Dupouy J-P,
Poulain P,
Beauvillain J-C,
Stefano GB
(1998) Morphine and anandamide coupling to nitric oxide stimulates GnRH and CRF release from rat median eminence: neurovascular regulation. Brain Res 790:236–244.
CrossRefMedline

Ralevic V,
Kendall DA,
Randall MD,
Zygmunt PM,
Movahed P,
Högestätt ED
(2000) Vanilloid receptors on capsaicin-sensitive sensory nerves mediate relaxation to methanandamide in the rat isolated mesenteric arterial bed and small mesenteric arteries. Br J Pharmacol 130:1483–1488.
CrossRefMedline

Razdan RK
(1986) Structure-activity relationships in cannabinoids. Pharmacol Rev 38:75–149.
Medline

Reggio PH
(1999) Ligand-ligand and ligand-receptor approaches to modeling the cannabinoid CB1 and CB2 receptors: achievements and challenges. Curr Med Chem 6:665–683.
Medline

Reggio PH,
Traore H
(2000) Conformational requirements for endocannabinoid interaction with the cannabinoid receptors, the anandamide transporter and fatty acid amidohydrolase. Chem Phys Lipids 108:15–35.
CrossRefMedline

Reibaud M,
Obinu MC,
Ledent C,
Parmentier M,
Böhme GA,
Imperato A
(1999) Enhancement of memory in cannabinoid CB1 receptor knock-out mice. Eur J Pharmacol 379:R1–R2.
CrossRefMedline

Rhee M-H,
Bayewitch M,
Avidor-Reiss T,
Levy R,
Vogel Z
(1998) Cannabinoid receptor activation differentially regulates the various adenylyl cyclase isozymes. J Neurochem 71:1525–1534.
Medline

Rhee MH,
Nevo I,
Bayewitch ML,
Zagoory O,
Vogel Z
(2000a) Functional role of tryptophan residues in the fourth transmembrane domain of the CB2 cannabinoid receptor. J Neurochem 75:2485–2491.
CrossRefMedline

Rhee MH,
Nevo I,
Levy R,
Vogel Z
(2000b) Role of the highly conserved Asp-Arg-Tyr motif in signal transduction of the CB2 cannabinoid receptor. FEBS Lett 466:300–304.
CrossRefMedline

Rhee M-H,
Vogel Z,
Barg J,
Bayewitch M,
Levy R,
Hanus L,
Breuer A,
Mechoulam R
(1997) Cannabinol derivatives: binding to cannabinoid receptors and inhibition of adenylylcyclase. J Med Chem 40:3228–3233.
CrossRefMedline

Rinaldi-Carmona M,
Barth F,
Héaulme M,
Shire D,
Calandra B,
Congy C,
Martinez S,
Maruani J,
Néliat G,
Caput D,
Ferrara P,
Soubrié P,
Brelière JC,
Le Fur G
(1994) SR141716A, a potent and selective antagonist of the brain cannabinoid receptor. FEBS Lett 350:240–244.
CrossRefMedline

Rinaldi-Carmona M,
Barth F,
Millan J,
Derocq J-M,
Casellas P,
Congy C,
Oustric D,
Sarran M,
Bouaboula M,
Calandra B,
et al.
(1998) SR 144528, the first potent and selective antagonist of the CB2 cannabinoid receptor. J Pharmacol Exp Ther 284:644–650.
Abstract/FREE Full Text

Rinaldi-Carmona M,
Calandra B,
Shire D,
Bouaboula M,
Oustric D,
Barth F,
Casellas P,
Ferrara P,
Le Fur G
(1996a) Characterization of two cloned human CB1 cannabinoid receptor isoforms. J Pharmacol Exp Ther 278:871–878.
Abstract/FREE Full Text

Rinaldi-Carmona M,
Pialot F,
Congy C,
Redon E,
Barth F,
Bachy A,
Brelière J-C,
Soubrié P,
Le Fur G
(1996b) Characterization and distribution of binding sites for [3H]-SR141716A, a selective brain (CB1) cannabinoid receptor antagonist, in rodent brain. Life Sci 58:1239–1247.
CrossRefMedline

Robbe D,
Alonso G,
Duchamp F,
Bockaert J,
Manzoni OJ
(2001) Localization and mechanisms of action of cannabinoid receptors at the glutamatergic synapses of the mouse nucleus accumbens. J Neurosci 21:109–116.
Abstract/FREE Full Text

Robson P
(2001) Therapeutic aspects of cannabis and cannabinoids. Br J Psychiatry 178:107–115.
Abstract/FREE Full Text

Roche JP,
Bounds S,
Brown S,
Mackie K
(1999) A mutation in the second transmembrane region of the CB1 receptor selectively disrupts G protein signaling and prevents receptor internalization. Mol Pharmacol 56:611–618.
Abstract/FREE Full Text

Rodrı́guez JJ,
Mackie K,
Pickel VM
(2001) Ultrastructural localization of the CB1 cannabinoid receptor in μ-opioid receptor patches of the rat caudate putamen nucleus. J Neurosci 21:823–833.
Abstract/FREE Full Text

Romero J,
de Miguel R,
Ramos JA,
Fernández Ruiz JJ
(1998) The activation of cannabinoid receptors in striatonigral GABAergic neurons inhibited GABA uptake. Life Sci 62:351–363.
Medline

Ross RA,
Brockie HC,
Fernando SR,
Saha B,
Razdan RK,
Pertwee RG
(1998) Comparison of cannabinoid binding sites in guinea-pig forebrain and small intestine. Br J Pharmacol 125:1345–1351.
CrossRefMedline

Ross RA,
Brockie HC,
Stevenson LA,
Murphy VL,
Templeton F,
Makriyannis A,
Pertwee RG
(1999a) Agonist-inverse agonist characterization at CB1 and CB2 cannabinoid receptors of L759633, L759656 and AM630. Br J Pharmacol 126:665–672.
CrossRefMedline

Ross RA,
Gibson TM,
Brockie HC,
Leslie M,
Pashmi G,
Craib SJ,
Di Marzo V,
Pertwee RG
(2001) Structure-activity relationship for the endogenous cannabinoid, anandamide and certain of its analogues at vanilloid receptors in transfected cells and vas deferens. Br J Pharmacol 132:631–640.
CrossRefMedline

Ross RA,
Gibson TM,
Stevenson LA,
Saha B,
Crocker P,
Razdan RK,
Pertwee RG
(1999b) Structural determinants of the partial agonist-inverse agonist properties of 6′-azidohex-2′-yne-Δ8-tetrahydrocannabinol at cannabinoid receptors. Br J Pharmacol 128:735–743.
CrossRefMedline

Rueda D,
Galve-Roperh I,
Haro A,
Guzmán M
(2000) The CB1 cannabinoid receptor is coupled to the activation of c-Jun N-terminal kinase. Mol Pharmacol 58:814–820.
Abstract/FREE Full Text

Sacerdote P,
Massi P,
Panerai AE,
Parolaro D
(2000) In vivo and in vitro treatment with the synthetic cannabinoid CP55,940 decreases the in vitro migration of macrophages in the rat: involvement of both CB1 and CB2 receptors. J Neuroimmunol 109:155–163.
CrossRefMedline

Sánchez C,
Galve Roperh I,
Rueda D,
Guzmán M
(1998) Involvement of sphingomyelin hydrolysis and the mitogen-activated protein kinase cascade in the Δ9-tetrahydrocannabinol-induced stimulation of glucose metabolism in primary astrocytes. Mol Pharmacol 54:834–843.
Abstract/FREE Full Text

Sánchez C,
Rueda D,
Ségui B,
Galve-Roperh I,
Levade T,
Guzmán M
(2001) The CB1 cannabinoid receptor of astrocytes is coupled to sphingomyelin hydrolysis through the adaptor protein Fan. Mol Pharmacol 59:955–959.
Abstract/FREE Full Text

Savinainen JR,
Jarvinen T,
Laine K,
Laitinen JT
(2001) Despite substantial degradation, 2-arachidonoylglycerol is a potent full efficacy agonist mediating CB1 receptor-dependent G-protein activation in rat cerebellar membranes. Br J Pharmacol 134:664–672.
CrossRefMedline

Schatz AR,
Lee M,
Condie RB,
Pulaski JT,
Kaminski NE
(1997) Cannabinoid receptors CB1 and CB2: a characterization of expression and adenylate cyclase modulation within the immune system. Toxicol Appl Pharmacol 142:278–287.
CrossRefMedline

Schlicker E,
Kathmann M
(2001) Modulation of transmitter release via presynaptic cannabinoid receptors. Trends Pharmacol Sci 22:565–572.
CrossRefMedline

Schlicker E,
Timm J,
Göthert M
(1996) Cannabinoid receptor-mediated inhibition of dopamine release in the retina. Naunyn-Schmiedeberg's Arch Pharmacol 354:791–795.
CrossRefMedline

Schlicker E,
Timm J,
Zentner J,
Göthert M
(1997) Cannabinoid CB1 receptor-mediated inhibition of noradrenaline release in the human and guinea-pig hippocampus. Naunyn-Schmiedeberg's Arch Pharmacol 356:583–589.
CrossRefMedline

Selley DE,
Stark S,
Sim LJ,
Childers SR
(1996) Cannabinoid receptor stimulation of guanosine-5′-O-(3-[35S]thio)triphosphate binding in rat brain membranes. Life Sci 59:659–668.
CrossRefMedline

Shen M,
Piser TM,
Seybold VS,
Thayer SA
(1996) Cannabinoid receptor agonists inhibit glutamatergic synaptic transmission in rat hippocampal cultures. J Neurosci 16:4322–4334.
Abstract/FREE Full Text

Shen M,
Thayer SA
(1998a) The cannabinoid agonist Win55,212-2 inhibits calcium channels by receptor-mediated and direct pathways in cultured rat hippocampal neurons. Brain Res 783:77–84.
CrossRefMedline

Shen M,
Thayer SA
(1998b) Cannabinoid receptor agonists protect cultured rat hippocampal neurons from excitotoxicity. Mol Pharmacol 54:459–462.
Abstract/FREE Full Text

Shen M,
Thayer SA
(1999) Δ9-Tetrahydrocannabinol acts as a partial agonist to modulate glutamatergic synaptic transmission between rat hippocampal neurons in culture. Mol Pharmacol 55:8–13.
Abstract/FREE Full Text

Sheskin T,
Hanus L,
Slager J,
Vogel Z,
Mechoulam R
(1997) Structural requirements for binding of anandamide-type compounds to the brain cannabinoid receptor. J Med Chem 40:659–667.
CrossRefMedline

Shire D,
Calandra B,
Rinaldi-Carmona M,
Oustric D,
Pessègue B,
Bonnin-Cabanne O,
Le Fur G,
Caput D,
Ferrara P
(1996a) Molecular cloning, expression and function of the murine CB2 peripheral cannabinoid receptor. Biochim Biophys Acta 1307:132–136.
Medline

Shire D,
Carillon C,
Kaghad M,
Calandra B,
Rinaldi-Carmona M,
Le Fur G,
Caput D,
Ferrara P
(1995) An amino-terminal variant of the central cannabinoid receptor resulting from alternative splicing. J Biol Chem 270:3726–3731.
Abstract/FREE Full Text

Shire D,
Carillon C,
Kaghad M,
Calandra B,
Rinaldi-Carmona R,
Le Fur G,
Caput D,
Ferrera P
(1996b) Erratum: an amino-terminal variant of the central cannabinoid receptor resulting from alternative splicing. J Biol Chem 271:33706.
Abstract/FREE Full Text

Showalter VM,
Compton DR,
Martin BR,
Abood ME
(1996) Evaluation of binding in a transfected cell line expressing a peripheral cannabinoid receptor (CB2): identification of cannabinoid receptor subtype selective ligands. J Pharmacol Exp Ther 278:989–999.
Abstract/FREE Full Text

Sim LJ,
Hampson RE,
Deadwyler SA,
Childers SR
(1996) Effects of chronic treatment with Δ9-tetrahydrocannabinol on cannabinoid-stimulated [35S]GTPγS autoradiography in rat brain. J Neurosci 16:8057–8066.
Abstract/FREE Full Text

Sim LJ,
Selley DE,
Childers SR
(1995) In vitro autoradiography of receptor-activated G proteins in rat brain by agonist-stimulated guanylyl 5′-[γ-[35S]thio]triphosphate binding. Proc Nat Acad Sci USA 92:7242–7246.
Abstract/FREE Full Text

Sim-Selley LJ,
Brunk LK,
Selley DE
(2001) Inhibitory effects of SR141716A on G-protein activation in rat brain. Eur J Pharmacol 414:135–143.
CrossRefMedline

Simoneau II,
Hamza MS,
Mata HP,
Siegel EM,
Vanderah TW,
Porreca F,
Makriyannis A,
Malan TP
(2001) The cannabinoid agonist WIN55,212-2 suppresses opioid-induced emesis in ferrets. Anesthesiology 94:882–887.
CrossRefMedline

Sinha D,
Bonner TI,
Bhat NR,
Matsuda LA
(1998) Expression of the CB1 cannabinoid receptor in macrophage-like cells from brain tissue: immunochemical characterization by fusion protein antibodies. J Neuroimmunol 82:13–21.
CrossRefMedline

Slipetz DM,
O'Neill GP,
Favreau L,
Dufresne C,
Gallant M,
Gareau Y,
Guay D,
Labelle M,
Metters KM
(1995) Activation of the human peripheral cannabinoid receptor results in inhibition of adenylyl cyclase. Mol Pharmacol 48:352–361.
Abstract

Smart D,
Gunthorpe MJ,
Jerman JC,
Nasir S,
Gray J,
Muir AI,
Chambers JK,
Randall AD,
Davis JB
(2000) The endogenous lipid anandamide is a full agonist at the human vanilloid receptor (hVR1). Br J Pharmacol 129:227–230.
CrossRefMedline

Smart D,
Jerman JC,
Gunthorpe MJ,
Brough SJ,
Ranson J,
Cairns W,
Hayes PD,
Randall AD,
Davis JB
(2001) Characterisation using FLIPR of human vanilloid VR1 receptor pharmacology. Eur J Pharmacol 417:51–58.
CrossRefMedline

Song ZH,
Bonner TI
(1996) A lysine residue of the cannabinoid receptor is critical for receptor recognition by several agonists but not WIN55212-2. Mol Pharmacol 49:891–896.
Abstract

Song ZH,
Slowey C-A,
Hurst DP,
Reggio PH
(1999) The difference between the CB1 and CB2 cannabinoid receptors at position 5.46 is crucial for the selectivity of WIN55212-2 for CB2. Mol Pharmacol 56:834–840.
Abstract/FREE Full Text

Stefano GB,
Bilfinger TV,
Rialas CM,
Deutsch DG
(2000) 2-Arachidonyl-glycerol stimulates nitric oxide release from human immune and vascular tissues and invertebrate immunocytes by cannabinoid receptor 1. Pharmacol Res 42:317–322.
CrossRefMedline

Stefano GB,
Liu Y,
Goligorsky MS
(1996) Cannabinoid receptors are coupled to nitric oxide release in invertebrate immunocytes, microglia and human monocytes. J Biol Chem 271:19238–19242.
Abstract/FREE Full Text

Stefano GB,
Salzet M,
Magazine HI,
Bilfinger TV
(1998) Antagonism of LPS and IFN-γ induction of iNOS in human saphenous vein endothelium by morphine and anandamide by nitric oxide inhibition of adenylate cyclase. J Cardiovasc Pharmacol 31:813–820.
CrossRefMedline

Stefano GB,
Salzet B,
Rialas CM,
Pope M,
Kustka A,
Neenan K,
Pryor S,
Salzet M
(1997a) Morphine- and anandamide-stimulated nitric oxide production inhibits presynaptic dopamine release. Brain Res 763:63–68.
CrossRefMedline

Stefano GB,
Salzet B,
Salzet M
(1997b) Identification and characterization of the leech CNS cannabinoid receptor: coupling to nitric oxide release. Brain Res 753:219–224.
CrossRefMedline

Steiner H,
Bonner TI,
Zimmer AM,
Kitai ST,
Zimmer A
(1999) Altered gene expression in striatal projection neurons in CB1 cannabinoid receptor knockout mice. Proc Natl Acad Sci USA 96:5786–5790.
Abstract/FREE Full Text

Stella N,
Piomelli D
(2001) Receptor-dependent formation of endogenous cannabinoids in cortical neurons. Eur J Pharmacol 425:189–196.
CrossRefMedline

Stella N,
Schweitzer P,
Piomelli D
(1997) A second endogenous cannabinoid that modulates long-term potentiation. Nature (Lond) 388:773–778.
CrossRefMedline

Sugiura T,
Kodaka T,
Kondo S,
Nakane S,
Kondo H,
Waku K,
Ishima Y,
Watanabe K,
Yamamoto I
(1997a) Is the cannabinoid CB1 receptor a 2-arachidonoylglycerol receptor? Structural requirements for triggering a Ca2++ transient in NG108-15 cells. J Biochem 122:890–895.
Abstract/FREE Full Text

Sugiura T,
Kodaka T,
Kondo S,
Tonegawa T,
Nakane S,
Kishimoto S,
Yamashita A,
Waku K
(1996) 2-Arachidonoylglycerol, a putative endogenous cannabinoid receptor ligand, induces rapid, transient elevation of intracellular free Ca2+ in neuroblastoma x glioma hybrid NG108-15 cells. Biochem Biophys Res Commun 229:58–64.
CrossRefMedline

Sugiura T,
Kodaka T,
Kondo S,
Tonegawa T,
Nakane S,
Kishimoto S,
Yamashita A,
Waku K
(1997b) Inhibition by 2-arachidonoylglycerol, a novel type of possible neuromodulator, of the depolarization-induced increase in intracellular free calcium in neuroblastoma x glioma hybrid NG108-15 cells. Biochem Biophys Res Commun 233:207–210.
CrossRefMedline

Sugiura T,
Kodaka T,
Nakane S,
Miyashita T,
Kondo S,
Suhara Y,
Takayama H,
Waku K,
Seki C,
Baba N,
et al.
(1999) Evidence that the cannabinoid CB1 receptor is a 2-arachidonoylglycerol receptor: structure-activity relationship of 2-arachidonoylglycerol ether-linked analogues and related compounds. J Biol Chem 274:2794–2801.
Abstract/FREE Full Text

Sugiura T,
Kondo S,
Kishimoto S,
Miyashita T,
Nakane S,
Kodaka T,
Suhara Y,
Takayama H,
Waku K
(2000) Evidence that 2-arachidonoylglycerol but not N-palmitoylethanolamine or anandamide is the physiological ligand for the cannabinoid CB2 receptor: comparison of the agonistic activities of various cannabinoid receptor ligands in HL-60 cells. J Biol Chem 275:605–612.
Abstract/FREE Full Text

Sugiura T,
Kondo S,
Sukagawa A,
Nakane S,
Shinoda A,
Itoh K,
Yamashita A,
Waku K
(1995) 2-Arachidonoylglycerol: a possible endogenous cannabinoid receptor ligand in brain. Biochem Biophys Res Commun 215:89–97.
CrossRefMedline

Sullivan JM
(1999) Mechanisms of cannabinoid-receptor-mediated inhibition of synaptic transmission in cultured hippocampal pyramidal neurons. J Neurophysiol 82:1286–1294.
Abstract/FREE Full Text

Szabo B,
Dörner L,
Pfreundtner C,
Nörenberg W,
Starke K
(1998) Inhibition of GABAergic inhibitory postsynaptic currents by cannabinoids in rat corpus striatum. Neuroscience 85:395–403.
CrossRefMedline

Szabo B,
Wallmichrath I,
Mathonia P,
Pfreundtner C
(2000) Cannabinoids inhibit excitatory neurotransmission in the substantia nigra pars reticulata. Neuroscience 97:89–97.
CrossRefMedline

Takahashi KA,
Linden DJ
(2000) Cannabinoid receptor modulation of synapses received by cerebellar Purkinje cells. J Neurophysiol 83:1167–1180.
Abstract/FREE Full Text

Tanda G,
Pontieri FE,
Di Chiara G
(1997) Cannabinoid and heroin activation of mesolimbic dopamine transmission by a common μ1 opioid receptor mechanism. Science (Wash DC) 276:2048–2050.
Abstract/FREE Full Text

Tao Q,
Abood ME
(1998) Mutation of a highly conserved aspartate residue in the second transmembrane domain of the cannabinoid receptors, CB1 and CB2, disrupts G-protein coupling. J Pharmacol Exp Ther 285:651–658.
Abstract/FREE Full Text

Tao Q,
McAllister SD,
Andreassi J,
Nowell KW,
Cabral GA,
Hurst DP,
Bachtel K,
Ekman MC,
Reggio PH,
Abood ME
(1999) Role of a conserved lysine residue in the peripheral cannabinoid receptor (CB2): evidence for subtype specificity. Mol Pharmacol 55:605–613.
Abstract/FREE Full Text

Tao Y-P,
Najafi L,
Shipley S,
Howlett A,
Klein C
(1998) Effects of nitric oxide on adenylyl cyclase stimulation in N18TG2 neuroblastoma cells. J Pharmacol Exp Ther 286:298–304.
Abstract/FREE Full Text

Tersigni TJ,
Rosenberg HC
(1996) Local pressure application of cannabinoid agonists increases spontaneous activity of rat substantia nigra pars reticulata neurons without affecting response to iontophoretically-applied GABA. Brain Res 733:184–192.
CrossRefMedline

Thomas BF,
Gilliam AF,
Burch DF,
Roche MJ,
Seltzman HH
(1998) Comparative receptor binding analyses of cannabinoid agonists and antagonists. J Pharmacol Exp Ther 285:285–292.
Abstract/FREE Full Text

Thomas BF,
Wei X,
Martin BR
(1992) Characterization and autoradiographic localization of the cannabinoid binding site in rat brain using [3H]11-OH-Δ9-THC-DMH. J Pharmacol Exp Ther 263:1383–1390.
Abstract/FREE Full Text

Tognetto M,
Amadesi S,
Harrison S,
Creminon C,
Trevisani M,
Carreras M,
Matera M,
Geppetti P,
Bianchi A
(2001) Anandamide excites central terminals of dorsal root ganglion neurons via vanilloid receptor-1 activation. J Neurosci 21:1104–1109.
Abstract/FREE Full Text

Trendelenburg AU,
Cox SL,
Schelb V,
Klebroff W,
Khairallah L,
Starke K
(2000) Modulation of 3H-noradrenaline release by presynaptic opioid, cannabinoid and bradykinin receptors and β-adrenoceptors in mouse tissues. Br J Pharmacol 130:321–330.
CrossRefMedline

Tsou K,
Brown S,
Sañudo-Peña MC,
Mackie K,
Walker JM
(1998a) Immunohistochemical distribution of cannabinoid CB1 receptors in the rat central nervous system. Neuroscience 83:393–411.
CrossRefMedline

Tsou K,
Mackie K,
Sañudo-Peña MC,
Walker JM
(1999) Cannabinoid CB1 receptors are localized primarily on cholecystokinin-containing GABAergic interneurons in the rat hippocampal formation. Neuroscience 93:969–975.
CrossRefMedline

Tsou K,
Nogueron MI,
Muthian S,
Sañudo-Peña MC,
Hillard CJ,
Deutsch DG,
Walker JM
(1998b) Fatty acid amide hydrolase is located preferentially in large neurons in the rat central nervous system as revealed by immunohistochemistry. Neurosci Lett 254:137–140.
CrossRefMedline

Ueda N,
Puffenbarger RA,
Yamamoto S,
Deutsch DG
(2000) The fatty acid amide hydrolase (FAAH). Chem Phys Lipids 108:107–121.
CrossRefMedline

Valk P,
Verbakel S,
Vankan Y,
Hol S,
Mancham S,
Ploemacher R,
Mayen A,
Löwenberg B,
Delwel R
(1997) Anandamide, a natural ligand for the peripheral cannabinoid receptor is a novel synergistic growth factor for hematopoietic cells. Blood 90:1448–1457.
Abstract/FREE Full Text

Varvel SA,
Hamm RJ,
Martin BR,
Lichtman AH
(2001) Differential effects of Δ9-THC on spatial reference and working memory in mice. Psychopharmacology 157:142–150.
CrossRefMedline

Vaughan CW,
Connor M,
Bagley EE,
Christie MJ
(2000) Actions of cannabinoids on membrane properties and synaptic transmission in rat periaqueductal gray neurons in vitro. Mol Pharmacol 57:288–295.
Abstract/FREE Full Text

Vaughan CW,
McGregor IS,
Christie MJ
(1999) Cannabinoid receptor activation inhibits GABAergic neurotransmission in rostral ventromedial medulla neurons in vitro. Br J Pharmacol 127:935–940.
CrossRefMedline

Vizi ES,
Katona I,
Freund TF
(2001) Evidence for presynaptic cannabinoid CB1 receptor-mediated inhibition of noradrenaline release in the guinea pig lung. Eur J Pharmacol 431:237–244.
CrossRefMedline

Vogel Z,
Barg J,
Levy R,
Saya D,
Heldman E,
Mechoulam R
(1993) Anandamide, a brain endogenous compound, interacts specifically with cannabinoid receptors and inhibits adenylate cyclase. J Neurochem 61:352–355.
Medline

Wagner JA,
Varga K,
Járai Z,
Kunos G
(1999) Mesenteric vasodilation mediated by endothelial anandamide receptors. Hypertension 33:429–434.
Abstract/FREE Full Text

Waksman Y,
Olson JM,
Carlisle SJ,
Cabral GA
(1999) The central cannabinoid receptor (CB1) mediates inhibition of nitric oxide production by rat microglial cells. J Pharmacol Exp Ther 288:1357–1366.
Abstract/FREE Full Text

Walker JM,
Huang SM,
Strangman NM,
Tsou K,
Sañudo-Peña MC
(1999) Pain modulation by release of the endogenous cannabinoid anandamide. Proc Nat Acad Sci USA 96:12198–12203.
Abstract/FREE Full Text

Walton RP,
Martin LF,
Keller JH
(1937) The relative activity of various purified products obtained from American grown hashish. J Pharmacol Exp Ther 62:239–251.

Wartmann M,
Campbell D,
Subramanian A,
Burstein SH,
Davis RJ
(1995) The MAP kinase signal transduction pathway is activated by the endogenous cannabinoid anandamide. FEBS Lett 359:133–136.
CrossRefMedline

Welch SP,
Dunlow LD,
Patrick GS,
Razdan RK
(1995) Characterization of anandamide- and fluoroanandamide-induced antinociception and cross-tolerance to Δ9-THC after intrathecal administration to mice: blockade of Δ9-THC-induced antinociception. J Pharmacol Exp Ther 273:1235–1244.
Abstract/FREE Full Text

Welch SP,
Huffman JW,
Lowe J
(1998) Differential blockade of the antinociceptive effects of centrally administered cannabinoids by SR141716A. J Pharmacol Exp Ther 286:1301–1308.
Abstract/FREE Full Text

Wenger T,
Ledent C,
Csernus V,
Gerendai I
(2001) The central cannabinoid receptor inactivation suppresses endocrine reproductive functions. Biochem Biophys Res Commun 284:363–368.
CrossRefMedline

Wiley J,
Balster R,
Martin B
(1995a) Discriminative stimulus effects of anandamide in rats. Eur J Pharmacol 276:49–54.
CrossRefMedline

Wiley JL,
Barrett RL,
Lowe J,
Balster RL,
Martin BR
(1995b) Discriminative stimulus effects of CP 55,940 and structurally dissimilar cannabinoids in rats. Neuropharmacology 34:669–676.
CrossRefMedline

Wiley JL,
Compton DR,
Dai D,
Lainton JAH,
Phillips M,
Huffman JW,
Martin BR
(1998) Structure-activity relationships of indole- and pyrrole-derived cannabinoids. J Pharmacol Exp Ther 285:995–1004.
Abstract/FREE Full Text

Wiley JL,
Golden KM,
Ryan WJ,
Balster RL,
Razdan RK,
Martin BR
(1997) Evaluation of cannabimimetic discriminative stimulus effects of anandamide and methylated fluoroanandamide in rhesus monkeys. Pharmacol Biochem Behav 58:1139–1143.
CrossRefMedline

Wiley JL,
Jefferson RG,
Grier MC,
Mahadevan A,
Razdan RK,
Martin BR
(2001) Novel pyrazole cannabinoids: insights into CB1 receptor recognition and activation. J Pharmacol Exp Ther 296:1013–1022.
Abstract/FREE Full Text

Wiley JL,
Lowe JA,
Balster RL,
Martin BR
(1995c) Antagonism of the discriminative stimulus effects of Δ9-tetrahydrocannabinol in rats and rhesus monkeys. J Pharmacol Exp Ther 275:1–6.
Abstract/FREE Full Text

Wilson RI,
Nicoll RA
(2001) Endogenous cannabinoids mediate retrograde signalling at hippocampal synapses. Nature (Lond) 410:588–592.
CrossRefMedline

Zhu LX,
Sharma S,
Stolina M,
Gardner B,
Roth MD,
Tashkin DP,
Dubinett SM
(2000) Δ-9-Tetrahydrocannabinol inhibits antitumor immunity by a CB2 receptor-mediated, cytokine-dependent pathway. J Immunol 165:373–380.
Abstract/FREE Full Text

Zimmer A,
Zimmer AM,
Hohmann AG,
Herkenham M,
Bonner TI
(1999) Increased mortality, hypoactivity and hypoalgesia in cannabinoid CB1 receptor knockout mice. Proc Natl Acad Sci USA 96:5780–5785.
Abstract/FREE Full Text

Zygmunt PM,
Chuang H,
Movahed P,
Julius D,
Högestätt ED
(2000) The anandamide transport inhibitor AM404 activates vanilloid receptors. Eur J Pharmacol 396:39–42.
CrossRefMedline

Zygmunt PM,
Petersson J,
Andersson DA,
Chuang H,
SφrgÃ¥rd M,
Di Marzo V,
Julius D,
Högestätt ED
(1999) Vanilloid receptors on sensory nerves mediate the vasodilator action of anandamide. Nature (Lond) 400:452–457.


Source: International Union of Pharmacology. XXVII. Classification of Cannabinoid Receptors