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Chemical probes are powerful reagents with increasing impacts on biomedical research. However, probes of poor quality or that are used incorrectly generate misleading results. To help address these shortcomings, we will create a community-driven wiki resource to improve quality and convey current best practice.

The roles of endocannabinoid signaling during central nervous system development are unknown. We report that CB(1) cannabinoid receptors (CB(1)Rs) are enriched in the axonal growth cones of gamma-aminobutyric acid-containing (GABAergic) interneurons in the rodent cortex during late gestation. Endocannabinoids trigger CB(1)R internalization and elimination from filopodia and induce chemorepulsion and collapse of axonal growth cones of these GABAergic interneurons by activating RhoA. Similarly, endocannabinoids diminish the galvanotropism of Xenopus laevis spinal neurons. These findings, together with the impaired target selection of cortical GABAergic interneurons lacking CB(1)Rs, identify endocannabinoids as axon guidance cues and demonstrate that endocannabinoid signaling regulates synaptogenesis and target selection in vivo.

We investigated the pharmacology of three novel compounds, Org 27569 (5-chloro-3-ethyl-1H-indole-2-carboxylic acid [2-(4-piperidin-1-yl-phenyl)-ethyl]-amide), Org 27759 (3-ethyl-5-fluoro-1H-indole-2-carboxylic acid [2-94-dimethylamino-phenyl)-ethyl]-amide), and Org 29647 (5-chloro-3-ethyl-1H-indole-2-carboxylic acid (1-benzyl-pyrrolidin-3-yl)-amide, 2-enedioic acid salt), at the cannabinoid CB 1 receptor. In equilibrium binding assays, the Org compounds significantly increased the binding of the CB 1 receptor agonist, indicative of a positively cooperative allosteric effect. The same compounds caused a significant, but incomplete, decrease in the specific binding of the CB 1 receptor inverse agonist studies also validated the allosteric nature of the Org compounds, because they all significantly decreased radioligand dissociation. These data suggest that the Org compounds bind allosterically to the CB 1 receptor and elicit a conformational change that increases agonist affinity for the orthosteric binding site. In contrast to the binding assays, however, the Org compounds behaved as insurmountable antagonists of receptor function; in the reporter gene assay, the guanosine 5Ј-O-(3-[35 S]thio)triphosphate binding assay and the mouse vas deferens assay they elicited a significant reduction in the E max value for CB 1 receptor agonists. The data presented clearly demonstrate, for the first time, that the cannabinoid CB 1 receptor contains an allosteric binding site that can be recognized by synthetic small molecule ligands.Mammalian tissues express at least two types of cannabinoid receptor, CB 1 and CB 2 , both G protein-coupled (for review, see Howlett et al., 2002). CB 1 receptors are found predominantly at central and peripheral nerve terminals where they mediate inhibition of transmitter release. Endogenous ligands for these receptors also exist. These "endocannabinoids" are all eicosanoids, prominent examples including arachidonoylethanolamide (anandamide) and 2-arachidonoyl glycerol, both of which are synthesized on demand, removed from their sites of action by tissue uptake processes and metabolized by intracellular enzymes (Pertwee and Ross,

Background and purpose: A nonpsychoactive constituent of the cannabis plant, cannabidiol has been demonstrated to have low affinity for both cannabinoid CB 1 and CB 2 receptors. We have shown previously that cannabidiol can enhance electrically evoked contractions of the mouse vas deferens, suggestive of inverse agonism. We have also shown that cannabidiol can antagonize cannabinoid receptor agonists in this tissue with a greater potency than we would expect from its poor affinity for cannabinoid receptors. This study aimed to investigate whether these properties of cannabidiol extend to CB 1 receptors expressed in mouse brain and to human CB 2 receptors that have been transfected into CHO cells. Experimental approach: The [ 35 S]GTPgS binding assay was used to determine both the efficacy of cannabidiol and the ability of cannabidiol to antagonize cannabinoid receptor agonists (CP55940 and R-( þ )-WIN55212) at the mouse CB 1 and the human CB 2 receptor. Key results: This paper reports firstly that cannabidiol displays inverse agonism at the human CB 2 receptor. Secondly, we demonstrate that cannabidiol is a high potency antagonist of cannabinoid receptor agonists in mouse brain and in membranes from CHO cells transfected with human CB 2 receptors. Conclusions and implications:This study has provided the first evidence that cannabidiol can display CB 2 receptor inverse agonism, an action that appears to be responsible for its antagonism of CP55940 at the human CB 2 receptor. The ability of cannabidiol to behave as a CB 2 receptor inverse agonist may contribute to its documented anti-inflammatory properties.

A large body of evidence now exists to substantiate that the endocannabinoid, anandamide, activates TRPV1 receptors. It is a low intrinsic efficacy TRPV1 agonist that behaves as a partial agonist in tissues with a low receptor reserve, while in tissues with high receptor reserve and in circumstances associated with certain disease states, it behaves as a full agonist. The efficacy of anandamide as a TRPV1 agonist is influenced by a succession of factors including receptor reserve, phosphorylation, metabolism and uptake, CB 1 receptor activation, voltage, temperature, pH and bovine serum albumin. There are indications that the endocannabinoid system may play a role in the modulation of TRPV1 receptor activation. The activation of TRPV1 receptors by anandamide has potential implications in the treatment of inflammatory, respiratory and cardiovascular disorders. The relative importance of anandamide as a physiological and/or pathophysiological TRPV1 receptor agonist in comparison to other potential candidates has yet to be revealed.

Two cannabinoid receptors have been identified: CB1, present in the central nervous system (CNS) and to a lesser extent in other tissues, and CB2, present outside the CNS, in peripheral organs. There is evidence for the presence of CB2-like receptors in peripheral nerve terminals. We report now that we have synthesized a CB2-specific agonist, code-named HU-308. This cannabinoid does not bind to CB1 (Ki > 10 M), but does so efficiently to CB2 (Ki ‫؍‬ 22.7 ؎ 3.9 nM); it inhibits forskolin-stimulated cyclic AMP production in CB2-transfected cells, but does so much less in CB1-transfected cells. HU-308 shows no activity in mice in a tetrad of behavioral tests, which together have been shown to be specific for tetrahydrocannabinol (THC)-type activity in the CNS mediated by CB1. However, HU-308 reduces blood pressure, blocks defecation, and elicits anti-inflammatory and peripheral analgesic activity. The hypotension, the inhibition of defecation, the anti-inflammatory and peripheral analgesic effects produced by HU-308 are blocked (or partially blocked) by the CB2 antagonist SR-144528, but not by the CB1 antagonist SR-141716A. These results demonstrate the feasibility of discovering novel nonpsychotropic cannabinoids that may lead to new therapies for hypertension, inflammation, and pain.

The endogenous phospholipid l-alpha-lysophosphatidylinositol (LPI) was recently identified as a novel ligand for the orphan G protein-coupled receptor 55 (GPR55). In this study we define the downstream signaling pathways activated by LPI in a human embryonic kidney (HEK) 293 cell line engineered to stably express recombinant human GPR55. We find that treatment with LPI induces marked GPR55 internalization and stimulates a sustained, oscillatory Ca(2+) release pathway, which is dependent on Galpha13 and requires RhoA activation. We then establish that this signaling cascade leads to the efficient activation of NFAT (nuclear factor of activated T cells) family transcription factors and their nuclear translocation. Analysis of cannabinoid ligand activity at GPR55 revealed no clear effect of the endocannabinoids anandamide and 2-arachidonoylglycerol; however, the classical CB(1) antagonist AM251 evoked GPR55-mediated Ca(2+) signaling. Thus, LPI is a potent and efficacious ligand at GPR55, which is likely to be a key plasma membrane mediator of LPI-mediated signaling events and changes in gene expression.