Considerable evidence demonstrates that manipulation of the endocannabinoid system regulates nausea and vomiting in humans and other animals. The anti-emetic effect of cannabinoids has been shown across a wide variety of animals that are capable of vomiting in response to a toxic challenge. CB1 agonism suppresses vomiting, which is reversed by CB1 antagonism, and CB1 inverse agonism promotes vomiting. Recently, evidence from animal experiments suggests that cannabinoids may be especially useful in treating the more difficult to control symptoms of nausea and anticipatory nausea in chemotherapy patients, which are less well controlled by the currently available conventional pharmaceutical agents. Although rats and mice are incapable of vomiting, they display a distinctive conditioned gaping response when re-exposed to cues (flavours or contexts) paired with a nauseating treatment. Cannabinoid agonists (D 9 -THC, HU-210) and the fatty acid amide hydrolase (FAAH) inhibitor, URB-597, suppress conditioned gaping reactions (nausea) in rats as they suppress vomiting in emetic species. Inverse agonists, but not neutral antagonists, of the CB1 receptor promote nausea, and at subthreshold doses potentiate nausea produced by other toxins (LiCl). The primary non-psychoactive compound in cannabis, cannabidiol (CBD), also suppresses nausea and vomiting within a limited dose range. The anti-nausea/anti-emetic effects of CBD may be mediated by indirect activation of somatodendritic 5-HT1A receptors in the dorsal raphe nucleus; activation of these autoreceptors reduces the release of 5-HT in terminal forebrain regions. Preclinical research indicates that cannabinioids, including CBD, may be effective clinically for treating both nausea and vomiting produced by chemotherapy or other therapeutic treatments. LINKED ARTICLESThis article is part of a themed issue on Cannabinoids in Biology and Medicine. To view the other articles in this issue visit http://dx.doi. org/10.1111/bph.2011.163.issue-7 Abbreviations 2-AG, 2-arachidonolylglycerol; 5-HT, 5-hydroxytryptamine; 5-HT3, 5-hydroxytryptamine receptor 3; 5-HT1A, 5-hydroxytryptamine receptor 1A; 5-HTP, 5-hydroxytryptophan; 5,7-DHT, 5,7-dihydroxytryptamine; 8-OH-DPAT, 8-hydroxy-N,N-dipropyl-2-aminotetralin; D 9-THC, D 9 -tetrahydrocannabinol; AN, anticipatory nausea; AP, area postrema; CB1,cannabinoid receptor 1; CB2, cannabinoid receptor 2; CBD, cannabidiol; DMNX, doral motor nucleus of the vagus; DRN, dorsal raphe nucleus; DVC, dorsal vagal complex; FAAH, fatty acid amide hydrolase; Gi, inhibitory G protein subunit; LiCl, lithium chloride; MAGL, monoacylglycerol-lipase; M6G, morphine-6-glucuronide; MRN, medial raphe nucleus; NADA, n-arachidonoyl-dopamine; NTS, nucleus of the solitary tract; S. murinus, Suncus murinus; TRPV1, transient receptor potential vanilloid 1 IntroductionA major advance in the control of acute emesis in chemotherapy treatment was the finding that blockade of one subtype of the 5-hydroxytryptamine (5-HT) receptor, the 5-HT3 receptor, could suppress the ...

BACKGROUND AND PURPOSETo evaluate the hypothesis that activation of somatodendritic 5-HT1A autoreceptors in the dorsal raphe nucleus (DRN) produces the anti-emetic/anti-nausea effects of cannabidiol (CBD), a primary non-psychoactive cannabinoid found in cannabis. EXPERIMENTAL APPROACHThe potential of systemic and intra-DRN administration of 5-HT1A receptor antagonists, WAY100135 or WAY100635, to prevent the anti-emetic effect of CBD in shrews (Suncus murinus) and the anti-nausea-like effects of CBD (conditioned gaping) in rats were evaluated. Also, the ability of intra-DRN administration of CBD to produce anti-nausea-like effects (and reversal by systemic WAY100635) was assessed. In vitro studies evaluated the potential of CBD to directly target 5-HT1A receptors and to modify the ability of the 5-HT1A agonist, 8-OH-DPAT, to stimulate [ KEY RESULTSCBD suppressed nicotine-, lithium chloride (LiCl)-and cisplatin (20 mg·kg )-induced vomiting in the S. murinus and LiCl-induced conditioned gaping in rats. Anti-emetic and anti-nausea-like effects of CBD were suppressed by WAY100135 and the latter by WAY100635. When administered to the DRN: (i) WAY100635 reversed anti-nausea-like effects of systemic CBD, and (ii) CBD suppressed nausea-like effects, an effect that was reversed by systemic WAY100635. CBD also displayed significant potency (in a bell-shaped dose-response curve) at enhancing the ability of 8-OH-DPAT to stimulate [ CONCLUSIONS AND IMPLICATIONSThese results suggest that CBD produced its anti-emetic/anti-nausea effects by indirect activation of the somatodendritic 5-HT1A autoreceptors in the DRN.

Compared with cannabidiol, CBDA displays significantly greater potency at inhibiting vomiting in shrews and nausea in rats, and at enhancing 5-HT(1A) receptor activation, an action that accounts for its ability to attenuate conditioned gaping in rats. Consequently, CBDA shows promise as a treatment for nausea and vomiting, including anticipatory nausea for which no specific therapy is currently available.

CBDA or THC alone, as well as very low doses of combined CBDA and THC, has anti-inflammatory and anti-hyperalgesia effects in this animal model of acute inflammation.

Considerable evidence implicates the endocannabinoid system as a neuromodulator of nausea and vomiting. The action of anandamide (AEA) can be prolonged by inhibiting its degradation, through the use of URB597 (URB), a Fatty Acid Amide Hydrolase (FAAH) enzyme inhibitor. Here we present evidence that the FAAH inhibitor, URB, interferes with cisplatin- and nicotine -induced vomiting in the Suncus murinus. In Experiment 1, shrews were injected with URB (0.9 mg/kg) or vehicle 120 min prior to the behavioral testing. They received a second injection of AEA (5 mg/kg) or vehicle 15 min prior to being injected with cisplatin (20 mg/kg) or saline and the number of vomiting episodes were counted for 60 min. In Experiment 2, shrews were injected with vehicle or URB (0.9 mg/kg) 120 min prior to receiving an injection of nicotine (5 mg/kg) or saline and the number of vomiting episodes were counted for 15 min. Experiment 3 evaluated the potential of the CB1 antagonist, SR141716, to reverse the effect of URB on nicotine-induced vomiting. URB attenuated vomiting produced by cisplatin and nicotine and the combination of URB+AEA suppressed vomiting produced by cisplatin. The effect of URB on nicotine-induced vomiting was reversed by SR141716. These data suggest that the EC system plays a tonic role in the regulation of toxin-induced vomiting.

Rationale Anticipatory nausea (AN) experienced by chemotherapy patients is resistant to current anti-nausea treatments. In this study, the effect of manipulation of the endocannabinoid (EC) system on a rat model of nausea (conditioned gaping) was determined. Objective The potential of cannabidiol (CBD) and the fatty acid amide hydrolase (FAAH) inhibitor, URB597 (URB) to reduce conditioned gaping in rats were evaluated. Materials and methods In each experiment, rats received four conditioning trials in which they were injected with lithium chloride immediately before placement in a distinctive odor-laced context. During testing, in experiment 1, rats were injected with vehicle (VEH), 1, 5 or 10 mg/kg CBD 30 min before placement in the context previously paired with nausea and in experiment 2, rats were injected with VEH, 0.1 or 0.3 mg/kg URB 2 h before placement in the context. Additional groups evaluated the ability of the CB 1 antagonist/inverse agonist, SR141716A, to reverse the suppressive effects of URB. Experiment 3 measured the potential of URB to interfere with the establishment of conditioned gaping.Results When administered before testing, CBD (1 and 5, but not 10 mg/kg) and URB (0.3, but not 0.1 mg/kg) suppressed conditioned gaping. The effect of URB was reversed by pre-treatment with the CB 1 antagonist/inverse agonist, SR141716A. When administered before conditioning, URB also interfered with the establishment of conditioned gaping. Conclusions Manipulations of the EC system may have therapeutic potential in the treatment of AN.

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BACKGROUND AND PURPOSEThe aim of this study was to compare the abilities of cannabidiolic acid methyl ester (HU-580) and cannabidiolic acid (CBDA) to enhance 5-HT 1A receptor activation in vitro and produce 5-HT 1A -mediated reductions in nausea and anxiety in vivo. EXPERIMENTAL APPROACHWe investigated the effects of HU-580 and CBDA on (i) activation by 8-hydroxy-2-(di-n-propylamino)tetralin of human 5-HT 1A receptors in CHO cell membranes, using [35 S]-GTPγS binding assays, (ii) gaping by rats in acute and anticipatory nausea models, and (iii) stress-induced anxiety-like behaviour, as indicated by exit time from the light compartment of a light-dark box of rats subjected 24 h earlier to six tone-paired foot shocks. KEY RESULTSHU-580 and CBDA increased the E max of 8-hydroxy-2-(di-n-propylamino) tetralin in vitro at 0.01-10 and 0.1-10 nM, respectively, and reduced signs of (i) acute nausea at 0.1 and 1 μg·kg À1 i.p. and at 1 μg·kg À1 i.p., respectively, and (ii) anticipatory nausea at 0.01 and 0.1 μg·kg À1 , and at 0.1 μg·kg À1 i.p. respectively. At 0.01 μg·kg À1 , HU-580, but not CBDA, increased the time footshocked rats spent in the light compartment of a light-dark box. The anti-nausea and anti-anxiety effects of 0.01 or 0.1 μg·kg À1 HU-580 were opposed by the 5-HT 1A antagonist, WAY100635 (0.1 mg·kg À1 i.p.). CONCLUSIONS AND IMPLICATIONSHU-580 is more potent than CBDA at enhancing 5-HT 1A receptor activation, and inhibiting signs of acute and anticipatory nausea, and anxiety. Consequently, HU-580 is a potential medicine for treating some nausea and anxiety disorders and possibly other disorders ameliorated by enhancement of 5-HT 1A receptor activation. Abbreviations