The presence and function of CB2 receptors in central nervous system (CNS) neurons are controversial. We report the expression of CB2 receptor messenger RNA and protein localization on brainstem neurons. These functional CB2 receptors in the brainstem were activated by a CB2 receptor agonist, 2-arachidonoylglycerol, and by elevated endogenous levels of endocannabinoids, which also act at CB1 receptors. CB2 receptors represent an alternative site of action of endocannabinoids that opens the possibility of nonpsychotropic therapeutic interventions using enhanced endocannabinoid levels in localized brain areas.

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1 The biological effects of cannabinoids (CB) are mediated by CB 1 and CB 2 receptors. The role of CB 2 receptors in the gastrointestinal tract is uncertain. In this study, we examined whether CB 2 receptor activation is involved in the regulation of gastrointestinal transit in rats. 2 Basal and lipopolysaccharide (LPS)-stimulated gastrointestinal transit was measured after instillation of an Evans blue-gum Arabic suspension into the stomach, in the presence of specific CB 1 and CB 2 agonists and antagonists, or after treatment with inhibitors of mediators implicated in the transit process. 3 In control rats a CB 1 (ACEA; 1 mg kg À1 ), but not a CB 2 (JWH-133; 1 mg kg À1 ), receptor agonist inhibited basal gastrointestinal transit. The effects of the CB 1 agonist were reversed by the CB 1 antagonist AM-251, which alone increased basal transit. LPS treatment increased gastrointestinal transit. This increased transit was reduced to control values by the CB 2 , but not the CB 1 , agonist. This inhibition by the CB 2 agonist was dose dependent and prevented by a selective CB 2 antagonist (AM-630; 1 mg kg À1 ). 4 By evaluating the inhibition of LPS-enhanced gastrointestinal transit by different antagonists, the effects of the CB 2 agonist (JWH-133; 1 mg kg À1 ) were found to act via cyclooxygenase, and to act independently of inducible nitric oxide synthase (NOS) and platelet-activating factor. Interleukin-1b and constitutive NOS isoforms may be involved in the accelerated LPS transit. 5 The activation of CB 2 receptors in response to LPS is a mechanism for the re-establishment of normal gastrointestinal transit after an inflammatory stimulus.

Enhanced intestinal transit due to lipopolysaccharide (LPS) is reversed by cannabinoid (CB)2 receptor agonists in vivo, but the site and mechanism of action are unknown. We have tested the hypothesis that CB2 receptors are expressed in the enteric nervous system and are activated in pathophysiological conditions. Tissues from either saline- or LPS-treated (2 h; 65 microg/kg ip) rats were processed for RT-PCR, Western blotting, and immunohistochemistry or were mounted in organ baths where electrical field stimulation was applied in the presence or absence of CB receptor agonists. Whereas the CB2 receptor agonist JWH133 did not affect the electrically evoked twitch response of the ileum under basal conditions, in the LPS-treated tissues JWH133 was able to reduce the enhanced contractile response in a concentration-dependent manner. Rat ileum expressed CB2 receptor mRNA and protein under physiological conditions, and this expression was not affected by LPS treatment. In the myenteric plexus, CB2 receptors were expressed on the majority of neurons, although not on those expressing nitric oxide synthase. LPS did not alter the distribution of CB2 receptor expression in the myenteric plexus. In vivo LPS treatment significantly increased Fos expression in both enteric glia and neurons. This enhanced expression was significantly attenuated by JWH133, whose action was reversed by the CB2 receptor antagonist AM630. Taking these facts together, we conclude that activation of CB2 receptors in the enteric nervous system of the gastrointestinal tract dampens endotoxin-induced enhanced intestinal contractility.

The aim of this study was to investigate the efficacy, receptor specificity, and site of action of Delta9-tetrahydrocannabinol (THC) as an antiemetic in the ferret. THC (0.05-1 mg/kg ip) dose-dependently inhibited the emetic actions of cisplatin. The ED50 for retching was approximately 0.1 mg/kg and for vomiting was 0.05 mg/kg. A specific cannabinoid (CB)1 receptor antagonist SR-141716A (5 mg/kg ip) reversed the effect of THC, whereas the CB2 receptor antagonist SR-144528 (5 mg/kg ip) was ineffective. THC applied to the surface of the brain stem was sufficient to inhibit emesis induced by intragastric hypertonic saline. The site of action of THC in the brain stem was further assessed using Fos immunohistochemistry. Fos expression induced by cisplatin in the dorsal motor nucleus of the vagus (DMNX) and the medial subnucleus of the nucleus of the solitary tract (NTS), but not other subnuclei of the NTS, was significantly reduced by THC rostral to obex. At the level of the obex, THC reduced Fos expression in the area postrema and the dorsal subnucleus of the NTS. The highest density of CB1 receptor immunoreactivity was found in the DMNX and the medial subnucleus of the NTS. Lower densities were observed in the area postrema and dorsal subnucleus of the NTS. Caudal to obex, there was moderate density of staining in the commissural subnucleus of the NTS. These results show that THC selectively acts at CB1 receptors to reduce neuronal activation in response to emetic stimuli in specific regions of the dorsal vagal complex.

Cannabinoid (CB) agonists suppress nausea and vomiting (emesis). Similarly, transient receptor potential vanilloid-1 (TRPV1) receptor agonists are anti-emetic. Arvanil, N-(3-methoxy-4-hydroxy-benzyl)-arachidonamide, is a synthetic 'hybrid' agonist of CB1 and TRPV1 receptors. Anandamide and N-arachidonoyl-dopamine (NADA) are endogenous agonists at both these receptors. We investigated if arvanil, NADA and anandamide were anti-emetic in the ferret and their mechanism of action. All compounds reduced the episodes of emesis in response to morphine 6 glucuronide. These effects were attenuated by AM251, a CB1 antagonist that was pro-emetic per se, and TRPV1 antagonists iodoresiniferatoxin and AMG 9810, which were without pro-emetic effects. Similar sensitivity to arvanil and NADA was found for prodromal signs of emesis. We analysed the distribution of TRPV1 receptors in the ferret brainstem and, for comparison, the co-localization of CB1 and TRPV1 receptors in the mouse brainstem. TRPV1 immunoreactivity was largely restricted to the nucleus of the solitary tract of the ferret, with faint labeling in the dorsal motor nucleus of the vagus and sparse distribution in the area postrema. A similar distribution of TRPV1, and its extensive co-localization with CB1, was observed in the mouse. Our findings suggest that CB1 and TRPV1 receptors in the brainstem play a major role in the control of emesis by agonists of these two receptors. While there appears to be an endogenous 'tone' of CB1 receptors inhibiting emesis, this does not seem to be the case for TRPV1 receptors, indicating that endogenously released endocannabinoids/endovanilloids inhibit emesis preferentially via CB1 receptors.

Sixty single afferent fibers with endings in the stomach wall were isolated from the cervical vagus of urethan-anesthetized Sprague-Dawley rats. All the fibers, most of which were spontaneously active, increased their discharge after gastric distension or during spontaneous contractions of the stomach. Because of this and the characteristic dynamic and static features of their response to inflation and deflation, they were identified as in-series tension receptors. Certain features of their responses, previously suspected from studies on reflex modulation of vagal efferent fibers or brain stem neurons, were directly confirmed. These included a broad range of mechanical thresholds and spontaneous firing frequencies that were correlated and a sensitivity only to dynamic stretch and active contraction in the highest threshold endings. The tension receptors could also be activated by circulating cholecystokinin, an effect unrelated to changes in intraluminal pressure and hence gastric wall tension, suggesting that there may be humoral modulation of visceral sensory signals that might be relevant to several behavioral situations, such as food intake regulation.

Marijuana has been used for thousands of years to affect human health. Dissecting the peripheral effects from the central psychotropic effects has revealed a complex interplay between cannabinoids, endocannabinoids and their receptors. This review examines recent advances in understanding the expression, regulation and utilization of the CB(2) receptor. Here we highlight the molecular aspects of the CB(2) receptor, CB(2) receptor signaling and new ligands for this receptor. We focus in the rest of the review on recent findings in the immune system, the gastrointestinal tract and liver, the brain and the cardiovascular system and airways as examples of areas where new developments in our understanding of the CB(2) receptor have occurred. Early studies focused on expression of this receptor under baseline physiologic conditions; however, perturbations such as those that occur during inflammation, ischemia/reperfusion injury and cancer are revealing a critical role for the CB(2) receptor in regulating these disease processes amongst others. As a result, the CB(2) receptor is an appealing therapeutic target as well as a useful tool for shedding new light on physiological regulatory processes throughout the body.