Cannabinoids inhibit emesis through CB1 receptors in the brainstem of the ferret

Distribution of the Endocannabinoid System in the Central Nervous System

The endocannabinoid system consists of endogenous cannabinoids (endocannabinoids), the enzymes that synthesize and degrade endocannabinoids, and the receptors that transduce the effects of endocannabinoids. Much of what we know about the function of endocannabinoids comes from studies that combine localization of endocannabinoid system components with physiological or behavioral approaches. This review will focus on the localization of the best-known components of the endocannabinoid system for which the strongest anatomical evidence exists.

Anti-Obesity Effect of the CB2 Receptor Agonist JWH-015 in Diet-Induced Obese Mice

The cannabinoid receptor 2 (CB2) is well known for its immune modulatory role. However, recent localisation of CB2 receptors in metabolically active tissue suggests that the CB2 receptor plays a significant role in energy homeostasis. This study was designed to investigate the impact of chronic CB2 receptor stimulation on food intake, body weight and mood. Lean male C57BL/6 mice were injected i.p. with the selective CB2 receptor agonist, JWH-015 (0.0, 1.0, 5.0 and 10.0 mg kg-1) to establish dose response parameters. Mice made obese following exposure to a diet consisting of 19.4 MJ/kg (4641 Kcal/kg) of energy (19.0% protein, 21.0% total fat, 4.7% crude fiber, and 4.7% AD fiber were given either vehicle or 10 mg/kg JWH-015. Impact on mood, food intake, body weight, plasma metabolites, expression of key metabolic proteins in the brown adipose tissue (BAT) and white adipose tissue (WAT), and markers of inflammation were measured. High dose (10 mg/kg) JWH-015 reduced food intake after 1, 2, 4, and 24 h in lean mice. When given to diet induced obese (DIO) mice, a 10 mg/kg dose of JWH-015 significantly reduced body weight compared to vehicle. This dose led to a shift in markers of lipid metabolism and inflammation in WAT consistent with lipolysis and improved immune response. Furthermore, JWH-015 (10 mg/kg) produced a transient reduction in food intake and significant reduction in fat mass and adipocyte cell size. Importantly, JWH-015 produced an anxiolytic response in the elevated plus maze while having no effect on immobility time in the forced swim test. It should be noted that though the 10 mg/kg dose produced positive effects on the obese state, the possibility that these effects are mediated via non-CB2 receptor mechanisms cannot be ruled out. These results demonstrate a role for CB2 receptors in modulating energy homeostasis and obesity associated metabolic pathologies in the absence of any adverse impact on mood.

Endocannabinoid Mechanisms Influencing Nausea

One of the first recognized medical uses of Δ(9)-tetrahydrocannabinol was treatment of chemotherapy-induced nausea and vomiting. Although vomiting is well controlled with the currently available non-cannabinoid antiemetics, nausea continues to be a distressing side effect of chemotherapy and other disorders. Indeed, when nausea becomes conditionally elicited by the cues associated with chemotherapy treatment, known as anticipatory nausea (AN), currently available antiemetics are largely ineffective. Considerable evidence demonstrates that the endocannabinoid system regulates nausea in humans and other animals. In this review, we describe recent evidence suggesting that cannabinoids and manipulations that enhance the functioning of the natural endocannabinoid system are promising treatments for both acute nausea and AN.

Effect of selective inhibition of monoacylglycerol lipase (MAGL) on acute nausea, anticipatory nausea, and vomiting in rats and Suncus murinus

RATIONALE

To determine the role of the endocannabinoid, 2-arachodonyl glycerol (2-AG), in the regulation of nausea and vomiting.

OBJECTIVE

We evaluated the effectiveness of the potent selective monoacylglycerol lipase (MAGL) inhibitor, MJN110, which selectively elevates the endocannabinoid 2-AG, to suppress acute nausea and vomiting, as well as anticipatory nausea in rat and shrew models.

METHODS

The rat gaping models were used to evaluate the potential of MJN110 (5, 10, and 20 mg/kg, intraperitoneally [IP]) to suppress acute nausea produced by LiCl and of MJN110 (10 and 20 mg/kg, IP) to suppress anticipatory nausea elicited by a LiCl-paired context. The potential as well of MJN110 (10 and 20 mg/kg, IP) to suppress vomiting and contextually elicited gaping in the Suncus murinus was evaluated.

RESULTS

MJN110 suppressed acute nausea in rats, LiCl-induced vomiting in shrews and contextually-elicited anticipatory nausea in both rats (accompanied by elevation of 2-AG in the visceral insular cortex) and shrews. These effects were reversed by the CB1 antagonist/inverse agonist, SR141716. The MAGL inhibitor did not modify locomotion at any dose. An activity-based protein profiling analysis of samples of tissue collected from the visceral insular cortex in rats and whole brain tissues in shrews revealed that MJN110 selectively inhibited MAGL and the alternative 2-AG hydrolase, ABHD6.

CONCLUSIONS

MAGL inhibition by MJN110 which selectively elevates endogenous 2-AG has therapeutic potential in the treatment of acute nausea and vomiting as well as anticipatory nausea, a distressful symptom that is resistant to currently available treatments.

Tetrahydrocannabinolic acid reduces nausea-induced conditioned gaping in rats and vomiting in Suncus murinus

BACKGROUND AND PURPOSE

We evaluated the anti-emetic and anti-nausea properties of the acid precursor of Δ(9) -tetrahydrocannabinol (THC), tetrahydrocannabinolic acid (THCA), and determined its mechanism of action in these animal models.

EXPERIMENTAL APPROACH

We investigated the effect of THCA on lithium chloride- (LiCl) induced conditioned gaping (nausea-induced behaviour) to a flavour, and context (a model of anticipatory nausea) in rats, and on LiCl-induced vomiting in Suncus murinus. Furthermore, we investigated THCA's ability to induce hypothermia and suppress locomotion [rodent tasks to assess cannabinoid1 (CB1 ) receptor agonist-like activity], and measured plasma and brain THCA and THC levels. We also determined whether THCA's effect could be blocked by pretreatment with SR141716 (SR, a CB1 receptor antagonist).

KEY RESULTS

In rats, THCA (0.05 and/or 0.5 mg·kg(-1) ) suppressed LiCl-induced conditioned gaping to a flavour and context; the latter effect blocked by the CB1 receptor antagonist, SR, but not by the 5-hydroxytryptamine-1A receptor antagonist, WAY100635. In S. murinus, THCA (0.05 and 0.5 mg·kg(-1) ) reduced LiCl-induced vomiting, an effect that was reversed with SR. A comparatively low dose of THC (0.05 mg·kg(-1) ) did not suppress conditioned gaping to a LiCl-paired flavour or context. THCA did not induce hypothermia or reduce locomotion, indicating non-CB1 agonist-like effects. THCA, but not THC was detected in plasma samples.

CONCLUSIONS AND IMPLICATIONS

THCA potently reduced conditioned gaping in rats and vomiting in S. murinus, effects that were blocked by SR. These data suggest that THCA may be a more potent alternative to THC in the treatment of nausea and vomiting.

An Internet survey of marijuana and hot shower use in adults with cyclic vomiting syndrome (CVS)

Cyclic vomiting syndrome (CVS) is a chronic disorder characterized by episodic nausea and vomiting. A large proportion of patients use marijuana to control their symptoms. Several case reports implicate marijuana as a cause of intractable vomiting with compulsive hot water bathing considered pathognomonic of "cannabinoid hyperemesis." We sought to examine the relationship between marijuana use and CVS. Patients >18 years of age diagnosed by a health care provider were invited to participate in an anonymous internet-based survey. A total of 514 patients participated and 437 completed questions about marijuana use. Mean age was 34 ± 12 years with patients being predominantly female (63%), Caucasian (92%) and from the USA (82%). Nineteen percent never used marijuana and 81% did. Fifty-four percent used marijuana for health issues and 43% for recreational purposes. Users stated that it improved nausea, appetite, general well-being, stress levels and vomiting. Users were more likely to be male and have an associated anxiety disorder. Sixty-seven percent of patients reported taking hot showers/baths for symptom relief, and this was associated with marijuana use. (OR 2.54, CI 1.50-4.31, P = 0.0006). Eighty-one percent of patients with CVS who completed an internet survey reported frequent use of marijuana. With marijuana use, patients noted the greatest improvement with stress levels, appetite and nausea. Marijuana users were more likely to be male and have associated anxiety. Hot showers were not pathognomonic of marijuana use though they were more likely to be associated with its use.

Dexamethasone alleviates motion sickness in rats in part by enhancing the endocannabinoid system

Low-dose dexamethasone has been widely used for the prevention of nausea and vomiting after chemotherapy and surgical procedures and to treat motion sickness due to its minimal adverse effects, but the mechanisms underlying its anti-motion sickness effects are poorly understood. Previous studies have demonstrated that the endocannabinoid system is suppressed by motion sickness but stimulated by dexamethasone. The aim of the present study was to determine whether dexamethasone has an anti-motion sickness effect in rats and to elucidate the mechanism of this action. We used HPLC-MS/MS to measure the plasma concentrations of anandamide and 2-arachidonoylglycerol+1-arachidonoylglycerol, and we employed real-time quantitative PCR (qRT-PCR) and/or Western blot analysis to assay the expression of N-acylphosphatidyl-ethanolamine hydrolyzing phospholipase D, sn-1-selective diacylglycerol lipase, fatty acid hydrolase, monoacylglycerol lipase and endocannabinoid CB1 receptor in the dorsal vagal complex and stomach of rats exposed to a motion sickness protocol. The results showed that dexamethasone lowered the motion sickness index and restored the levels of endogenous cannabinoids and the expression of the endocannabinoid CB1 receptor, which declined after the induction of motion sickness, in the dorsal vagal complex and stomach.

Cannabinoid hyperemesis syndrome

BACKGROUND

The purpose of this review is to describe cannabinoid hyperemesis syndrome (CHS), which is thought to be induced by long-term cannabis use, and provide clinical pharmacists with information to manage the hyperemetic phase of CHS.

METHOD

Published literature was searched and reviewed using PubMed.

RESULTS

CHS is characterized by intractable nausea and vomiting without an obvious organic cause and associated learned compulsive hot water bathing behavior. Patients often seek care in the emergency department (ED) for symptomatic relief.

CONCLUSION

CHS is potentially underrecognized and underdiagnosed in the ED, and it should be considered in the differential diagnosis in long-term cannabis use patients with CHS symptoms to avoid unnecessary extensive diagnostic workup including invasive radiologic imaging. Pharmacists have an important role in CHS recognition, education, and symptom management.

Regulation of nausea and vomiting by cannabinoids and the endocannabinoid system

Nausea and vomiting (emesis) are important elements in defensive or protective responses that animals use to avoid ingestion or digestion of potentially harmful substances. However, these neurally-mediated responses are at times manifested as symptoms of disease and they are frequently observed as side-effects of a variety of medications, notably those used to treat cancer. Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. Here we review recent progress in understanding the regulation of nausea and vomiting by cannabinoids and the endocannabinoid system, and we discuss the potential to utilize the endocannabinoid system in the treatment of these frequently debilitating conditions.

Benzophenanthridine alkaloid, piperonyl butoxide and (S)-methoprene action at the cannabinoid-1 receptor (CB1-receptor) pathway of mouse brain: Interference with [(3)H]CP55940 and [(3)H]SR141716A binding and modification of WIN55212-2-dependent inhibition of synaptosomal l-glutamate release

Benzophenanthridine alkaloids (chelerythrine and sanguinarine) inhibited binding of [(3)H]SR141716A to mouse brain membranes (IC50s: <1µM). Piperonyl butoxide and (S)-methoprene were less potent (IC50s: 21 and 63µM respectively). Benzophenanthridines and piperonyl butoxide were more selective towards brain CB1 receptors versus spleen CB2 receptors. All compounds reduced Bmax of [(3)H]SR141716A binding to CB1 receptors, but only methoprene and piperonyl butoxide increased Kd (3-5-fold). Benzophenanthridines increased the Kd of [(3)H]CP55940 binding (6-fold), but did not alter Bmax. (S)-methoprene increased the Kd of [(3)H]CP55940 binding (by almost 4-fold) and reduced Bmax by 60%. Piperonyl butoxide lowered the Bmax of [(3)H]CP55940 binding by 50%, but did not influence Kd. All compounds reduced [(3)H]SR141716A and [(3)H]CP55940 association with CB1 receptors. Combined with a saturating concentration of SR141716A, only piperonyl butoxide and (S)-methoprene increased dissociation of [(3)H]SR141716A above that of SR141716A alone. Only piperonyl butoxide increased dissociation of [(3)H]CP55940 to a level greater than CP55940 alone. Binding results indicate predominantly allosteric components to the study compounds action. 4-Aminopyridine-(4-AP-) evoked release of l-glutamate from synaptosomes was partially inhibited by WIN55212-2, an effect completely neutralized by AM251, (S)-methoprene and piperonyl butoxide. With WIN55212-2 present, benzophenanthridines enhanced 4-AP-evoked l-glutamate release above 4-AP alone. Modulatory patterns of l-glutamate release (with WIN-55212-2 present) align with previous antagonist/inverse agonist profiling based on [(35)S]GTPγS binding. Although these compounds exhibit lower potencies compared to many classical CB1 receptor inhibitors, they may have potential to modify CB1-receptor-dependent behavioral/physiological outcomes in the whole animal.

Anandamide transport inhibition by ARN272 attenuates nausea-induced behaviour in rats, and vomiting in shrews (Suncus murinus)

BACKGROUND AND PURPOSE

To understand how anandamide transport inhibition impacts the regulation of nausea and vomiting and the receptor level mechanism of action involved. In light of recent characterization of an anandamide transporter, fatty acid amide hydrolase-1-like anandamide transporter, to provide behavioural support for anandamide cellular reuptake as a facilitated transport process.

EXPERIMENTAL APPROACH

The systemic administration of the anandamide transport inhibitor ARN272 ([(4-(5-(4-hydroxy-phenyl)-3,4-diaza-bicyclo[4.4.0]deca-1(6),2,4,7,9-pentaen-2-ylamino)-phenyl)-phenylamino-methanone]) was used to evaluate the prevention of LiCl-induced nausea-induced behaviour (conditioned gaping) in rats, and LiCl-induced emesis in shrews (Suncus murinus). The mechanism of how prolonging anandamide availability acts to regulate nausea in rats was explored by the antagonism of cannabinoid 1 (CB1) receptors with the systemic co-administration of SR141716.

KEY RESULTS

The systemic administration of ARN272 produced a dose-dependent suppression of nausea-induced conditioned gaping in rats, and produced a dose-dependent reduction of vomiting in shrews. The systemic co-administration of SR141716 with ARN272 (at 3.0 mg·kg(-1)) in rats produced a complete reversal of ARN272-suppressed gaping at 1.0 mg·kg(-1). SR141716 alone did not differ from the vehicle solution.

CONCLUSIONS AND IMPLICATIONS

These results suggest that anandamide transport inhibition by the compound ARN272 tonically activates CB1 receptors and as such produces a type of indirect agonism to regulate toxin-induced nausea and vomiting. The results also provide behavioural evidence in support of a facilitated transport mechanism used in the cellular reuptake of anandamide.

Conditioned flavor avoidance and conditioned gaping: rat models of conditioned nausea

Although rats are incapable of vomiting, they demonstrate profound avoidance of a flavor previously paired with an emetic drug. They also display conditioned gaping reactions during re-exposure to the flavor. This robust learning occurs in a single trial and with long delays (hours) between consumption of a novel flavor and the emetic treatment. However, conditioned flavor avoidance learning is not a selective measure of the emetic properties of drugs, because non-emetic treatments (even highly rewarding treatments) produce conditioned avoidance, and anti-emetic treatments are generally ineffective in suppressing conditioned avoidance produced by an emetic drug. On the other hand, conditioned gaping reactions are consistently produced by emetic drugs and are prevented by anti-emetic drugs, indicating that they may be a more selective measure of conditioned malaise in rats. Here we review the literature on the use of conditioned flavor avoidance and conditioned gaping reactions as rat measures of conditioned nausea, as well as the neuropharmacology and neuroanatomy of conditioned gaping reactions in rats.

2-arachidonoylglycerol interferes with lithium-induced vomiting in the house musk shrew, Suncus murinus

The role of the endocannabinoid system in vomiting has been previously studied using several animal species. These investigations have clearly demonstrated an anti-emetic role for the eCB, anandamide, in these animal models; however, research concerning the role of 2-arhachidonoylglycerol (2AG) has been less clear. The aim of the present study was to assess the effects of exogenous 2AG administration in the house musk shrew, Suncus murinus. In Experiment 1, shrews were injected with vehicle or 2AG (1, 2, 5, 10 mg/kg) 15 min prior to behavioral testing in which the frequency of vomiting episodes was observed. In Experiment 2, shrews were pre-treated with 2AG (2, 5 mg/kg) prior to being administered the emetic drug, lithium chloride (LiCl). It was found that 2AG alone did not induce emesis, but interfered with vomiting in response to LiCl administration. The anti-emetic effects of 2AG in Suncus murinus do not appear to be mediated by CB1 receptors, as concomitant pretreatment with the CB1 receptor antagonist, SR141716, did not reverse the suppressive effects of 2AG. These results confirm that manipulations that increase levels of 2AG exert anti-emetic effects in the house musk shrew.

Cannabinoid receptor 1 signaling in cardiovascular regulating nuclei in the brainstem: A review

Cannabinoids elicit complex hemodynamic responses in experimental animals that involve both peripheral and central sites. Centrally administered cannabinoids have been shown to predominantly cause pressor response. However, very little is known about the mechanism of the cannabinoid receptor 1 (CB₁R)-centrally evoked pressor response. In this review, we provided an overview of the contemporary knowledge regarding the cannabinoids centrally elicited cardiovascular responses and the possible underlying signaling mechanisms. The current review focuses on the rostral ventrolateral medulla (RVLM) as the primary brainstem nucleus implicated in CB₁R-evoked pressor response.

The anti-nausea effects of CB1 agonists are mediated by an action at the visceral insular cortex

BACKGROUND AND PURPOSE

Conditioned gaping reactions reflect nausea-induced behaviour in rats. Cannabinoid 1 receptor (CB(1) ) agonists interfere with the establishment of nausea-induced conditioned gaping; however, it is not known if their effects are mediated by an action at peripheral or central CB(1) receptors.

EXPERIMENTAL APPROACH

We utilized the conditioned gaping model of nausea to evaluate the effect of peripheral and central administration of the peripherally restricted CB(1) agonist, CB13, on the establishment of LiCl-induced gaping in rats. We further evaluated the ability of HU-210 administered to the gustatory insular cortex (GIC) or visceral insular cortex (VIC) to interfere with LiCl-induced conditioned gaping and determined if this effect was mediated by CB(1) receptors.

KEY RESULTS

Central, but not peripheral, CB13 suppressed LiCl-induced conditioned gaping. Central administration of the potent CB(1) agonist, HU-210, delivered to the VIC, but not the GIC, suppressed the establishment of LiCl-induced gaping reactions, but not LiCl-induced suppression of hedonic reactions or conditioned taste avoidance. This pattern of results suggests that HU-210 delivered to the VIC prevented LiCl-induced nausea, but not learning per se. The suppression of LiCl-induced conditioned gaping by HU-210 was mediated by CB(1) receptors because it was prevented by co-administration of CB(1) antagonist/inverse agonist, AM-251, into the VIC. A high dose of AM-251 (20 µg) administered alone into the VIC did not produce conditioned gaping reactions.

CONCLUSIONS AND IMPLICATIONS

The nausea-relieving effects of CB(1) agonists, but not the nausea-inducing effects of CB(1) inverse agonists, are mediated, at least in part, by their action at the VIC in rats.

Cannabinoids facilitate the swallowing reflex elicited by the superior laryngeal nerve stimulation in rats

Cannabinoids have been reported to be involved in affecting various biological functions through binding with cannabinoid receptors type 1 (CB1) and 2 (CB2). The present study was designed to investigate whether swallowing, an essential component of feeding behavior, is modulated after the administration of cannabinoid. The swallowing reflex evoked by the repetitive electrical stimulation of the superior laryngeal nerve in rats was recorded before and after the administration of the cannabinoid receptor agonist, WIN 55-212-2 (WIN), with or without CB1 or CB2 antagonist. The onset latency of the first swallow and the time intervals between swallows were analyzed. The onset latency and the intervals between swallows were shorter after the intravenous administration of WIN, and the strength of effect of WIN was dose-dependent. Although the intravenous administration of CB1 antagonist prior to intravenous administration of WIN blocked the effect of WIN, the administration of CB2 antagonist did not block the effect of WIN. The microinjection of the CB1 receptor antagonist directly into the nucleus tractus solitarius (NTS) prior to intravenous administration of WIN also blocked the effect of WIN. Immunofluorescence histochemistry was conducted to assess the co-localization of CB1 receptor immunoreactivity to glutamic acid decarboxylase 67 (GAD67) or glutamate in the NTS. CB1 receptor was co-localized more with GAD67 than glutamate in the NTS. These findings suggest that cannabinoids facilitate the swallowing reflex via CB1 receptors. Cannabinoids may attenuate the tonic inhibitory effect of GABA (gamma-aminobuteric acid) neurons in the central pattern generator for swallowing.

Targeting the endocannabinoid system for gastrointestinal diseases: future therapeutic strategies

Cannabinoids extracted from the marijuana plant (Cannabis sativa) and synthetic cannabinoids have numerous effects on gastrointestinal (GI) functions. Recent experimental data support an important role for cannabinoids in GI diseases. Genetic studies in humans have proven that defects in endocannabinoid metabolism underlie functional GI disorders. Mammalian cells have machinery, the so-called endocannabinoid system (ECS), to produce and metabolize their own cannabinoids in order to control homeostasis of the gut in a rapidly adapting manner. Pharmacological manipulation of the ECS by cannabinoids, or by drugs that raise the levels of endogenous cannabinoids, have shown beneficial effects on GI pathophysiology. This review gives an introduction into the functions of the ECS in the GI tract, highlights the role of the ECS in GI diseases and addresses its potential pharmacological exploitation.

Inhibition of monoacylglycerol lipase attenuates vomiting in Suncus murinus and 2-arachidonoyl glycerol attenuates nausea in rats

BACKGROUND AND PURPOSE

To evaluate the role of 2-arachidonoyl glycerol (2AG) in the regulation of nausea and vomiting using animal models of vomiting and of nausea-like behaviour (conditioned gaping).

EXPERIMENTAL APPROACH

Vomiting was assessed in shrews (Suncus murinus), pretreated with JZL184, a selective monoacylglycerol lipase (MAGL) inhibitor which elevates endogenous 2AG levels, 1 h before administering the emetogenic compound, LiCl. Regulation of nausea-like behaviour in rats by exogenous 2AG or its metabolite arachidonic acid (AA) was assessed, using the conditioned gaping model. The role of cannabinoid CB(1) receptors, CB(2) receptors and cyclooxygenase (COX) inhibition in suppression of vomiting or nausea-like behaviour was assessed.

KEY RESULTS

JZL184 dose-dependently suppressed vomiting in shrews, an effect prevented by pretreatment with the CB(1) receptor inverse agonist/antagonist, AM251. In shrew brain tissue, JZL184 inhibited MAGL activity in vivo. In rats, 2AG suppressed LiCl-induced conditioned gaping but this effect was not prevented by AM251 or the CB(2) receptor antagonist, AM630. Instead, the COX inhibitor, indomethacin, prevented suppression of conditioned gaping by 2AG or AA. However, when rats were pretreated with a high dose of JZL184 (40 mg·kg(-1) ), suppression of gaping by 2AG was partially reversed by AM251. Suppression of conditioned gaping was not due to interference with learning because the same dose of 2AG did not modify the strength of conditioned freezing to a shock-paired tone.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that manipulations that elevate 2AG may have anti-emetic or anti-nausea potential.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Cannabidiol, a non-psychotropic component of cannabis, attenuates vomiting and nausea-like behaviour via indirect agonism of 5-HT(1A) somatodendritic autoreceptors in the dorsal raphe nucleus

BACKGROUND AND PURPOSE

To evaluate the hypothesis that activation of somatodendritic 5-HT(1A) 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 APPROACH

The potential of systemic and intra-DRN administration of 5-HT(1A) 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-HT(1A) receptors and to modify the ability of the 5-HT(1A) agonist, 8-OH-DPAT, to stimulate [(35) S]GTPγS binding in rat brainstem membranes.

KEY RESULTS

CBD suppressed nicotine-, lithium chloride (LiCl)- and cisplatin (20 mg·kg(-1) , but not 40 mg·kg(-1) )-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 [(35) S]GTPγS binding to rat brainstem membranes in vitro. Systemically administered CBD and 8-OH-DPAT synergistically suppressed LiCl-induced conditioned gaping.

CONCLUSIONS AND IMPLICATIONS

These results suggest that CBD produced its anti-emetic/anti-nausea effects by indirect activation of the somatodendritic 5-HT(1A) autoreceptors in the DRN.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Localization of mGluR5, GABAB, GABAA, and cannabinoid receptors on the vago-vagal reflex pathway responsible for transient lower esophageal sphincter relaxation in humans: an immunohistochemical study

BACKGROUND

  Transient lower esophageal sphincter relaxations (TLESRs) are the predominant mechanisms underlying gastro-esophageal reflux. TLESRs are mediated by a vago-vagal reflex, which can be blocked by interaction with metabotropic Glutamate Receptor 5 (mGluR5), γ-aminobutyric acid type B (GABA(B)), γ-aminobutyric acid type A (GABA(A)), and cannabinoid (CB) receptors. However, the distribution of these receptors in the neural pathway underlying the triggering of TLESRs has not been evaluated in humans.

METHODS

  Using immunohistochemistry, we investigated the distribution of mGluR5, GABA(A), GABA(B), CB1, and CB2 receptors in the human nodose ganglion, the brain stem, and the myenteric plexus of the esophagus.

KEY RESULTS

  MGluR5, GABA(B), CB1, and CB2 receptors are abundantly expressed in neurons of the myenteric plexus of the LES, nodose ganglion cell bodies and nerve fibers, the dorsal motor nucleus, and nucleus of the solitary tract in the brain stem. GABA(A) receptors are expressed in the same regions except in the nodose ganglion and myenteric plexus of the LES.

CONCLUSIONS & INFERENCES

  Human mGluR5, GABA(A,B), and CB(1,2) receptors are abundantly expressed along the vago-vagal neural pathway and involved in the triggering of TLESRs. These findings are not only in line with the central side effects observed during treatment with reflux inhibitors such as GABA(B) receptor agonists and mGluR5 antagonists, but also suggest that peripherally acting compounds may be effective.

Dietary conditions and highly palatable food access alter rat cannabinoid receptor expression and binding density

Endogenous cannabinoid signaling, mediated predominately by CB1 receptor activation, is involved in food intake control and body weight regulation. Despite advances in determining the role of the CB1 receptor in obesity, its involvement in the driven nature of eating pathologies has received little attention. The present study examined CB1 receptor alterations as a consequence of dietary-induced binge eating in female Sprague Dawley rats. Four control groups were used to control for calorie restriction and highly palatable food variables characterizing this behavioral model. All groups were kept on their respective feeding schedules for 6-weeks and were given a uniform 33% calorie restriction (~22 h food deprivation) prior to sacrifice. Our findings indicate that regional CB1 mRNA and density were influenced by dietary conditions, but were not specific to the dietary-induced binge eating paradigm used. An increase of approximately 50% (compared with naive controls) in CB1 receptor mRNA levels in the nucleus of the solitary tract as measured by in situ hybridization was found in animals receiving continuous access to a highly palatable food (i.e., vegetable shortening with 10% sucrose). This group also had a significant increase in body weight and adiposity. An approximate 20% reduction in CB1 mRNA was observed in the cingulate cortex (areas 1 and 2) in animals exposed to an intermittent schedule of feeding, compared with groups that had ad libitum feeding schedules (i.e., continuous access and naive controls). Receptor density as measured by [(3)H]CP55,940 autoradiography, was reduced by approximately 30% in the nucleus accumbens shell region in groups receiving repeated access to the highly palatable food. Taken together, these findings indicate that dietary conditions can differentially influence CB1 receptors in forebrain and hindbrain regions.

Alternative targets within the endocannabinoid system for future treatment of gastrointestinal diseases

Many beneficial effects of herbal and synthetic cannabinoids on gut motility and inflammation have been demonstrated, suggesting a vast potential for these compounds in the treatment of gastrointestinal disorders. These effects are based on the so-called 'endocannabinoid system' (ECS), a cooperating network of molecules that regulate the metabolism of the body's own and of exogenously administered cannabinoids. The ECS in the gastrointestinal tract quickly responds to homeostatic disturbances by de novo synthesis of its components to maintain homeostasis, thereby offering many potential targets for pharmacological intervention. Of major therapeutic interest are nonpsychoactive cannabinoids or compounds that do not directly target cannabinoid receptors but still possess cannabinoid-like properties. Drugs that inhibit endocannabinoid degradation and raise the level of endocannabinoids are becoming increasingly promising alternative therapeutic tools to manipulate the ECS.

Regulation of nausea and vomiting by cannabinoids

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. CB(1) agonism suppresses vomiting, which is reversed by CB(1) antagonism, and CB(1) 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 (Δ(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 CB(1) 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-HT(1A) 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.

Interaction between non-psychotropic cannabinoids in marihuana: effect of cannabigerol (CBG) on the anti-nausea or anti-emetic effects of cannabidiol (CBD) in rats and shrews

RATIONALE

The interaction between two non-psychotropic cannabinoids, cannabidiol (CBD) and cannabigerol (CBG), which have been reported to act as a 5-hydroxytryptamine 1A (5-HT(1A)) agonist and antagonist, respectively, was evaluated.

OBJECTIVE

To evaluate the potential of CBG to reverse the anti-nausea, anti-emetic effects of CBD.

MATERIALS AND METHODS

In experiment 1, rats were pre-treated with CBG (0.0, 1, 5, and 10 mg/kg, ip), 15 min prior to being treated with CBD (experiment 1a: VEH or 5 mg/kg, ip) or 8-OH-DPAT (experiment 1b: VEH or 0.01 mg/kg, ip). Thirty minutes later, all rats received a pairing of 0.1% saccharin solution and LiCl (20 ml/kg of 0.15 M, ip). Seventy-two hours later, the rats received a drug-free taste reactivity test with saccharin to evaluate the effects of the treatments on the establishment of conditioned gaping reactions (a model of nausea). As well, conditioned saccharin avoidance was measured. In experiment 2, Suncus murinus were injected with CBG (5 mg/kg, ip) or VEH 15 min prior to CBD (5 mg/kg) or VEH and 30 min later were injected with LiCl (60 ml/kg of 0.15 M, i.p.), and the number of vomiting episodes were measured.

RESULTS

CBD (5 mg/kg) suppressed conditioned gaping in rats and vomiting in shrews, which were reversed by pre-treatment with all doses of CBG. CBG also prevented the anti-nausea effects of 8-OH-DPAT.

CONCLUSIONS

Interactions between moderate doses of CBG and CBD may oppose one another at the 5-HT(1A) receptor in the regulation of nausea and vomiting.

Is there a legitimate role for the therapeutic use of cannabinoids for symptom management in chronic kidney disease?

Chronic pain is a common and debilitating symptom experienced in the context of numerous other physical and emotional symptoms by many patients with chronic kidney disease (CKD). Management of pain with opioids in CKD can be problematic given the prominence of adverse effects of opioids in CKD, which may exacerbate symptoms, such as nausea, anorexia, pruritus, and insomnia, all of which impact negatively on patients' health-related quality of life. Novel therapeutic approaches for pain and symptom management in CKD are required. Recent research in the area of cannabinoids (CBs) is legitimizing the use of cannabis-based medicine. In this review, we describe the symptom burden borne by patients with CKD and review some of the key basic science and clinical literature to evaluate the potential use of CBs for the management of overall symptom burden in CKD.

Review article: the clinical relevance of transient lower oesophageal sphincter relaxations in gastro-oesophageal reflux disease

BACKGROUND

Transient lower oesophageal sphincter relaxations (TLOSR) are considered the physiological mechanism that enables venting of gas from the stomach and appear as sphincter relaxations that are not induced by swallowing. It has become increasingly clear that most reflux episodes occur during TLOSRs and therefore play a key role in gastro-oesophageal reflux disease (GERD).

AIM

To describe the current knowledge about TLOSRs and its clinical implications.

METHODS

Search of the literature published in English using the PubMed database and relevant abstracts presented at international conventions.

RESULTS

Several factors influence the rate of TLOSRs including anti-reflux surgery, meal, body position, nutrition, lifestyle and a wide array of neurotransmitters. Ongoing insights in the neurotransmitters responsible for the modulation of TLOSRs, as well as the neural pathways involved in TLOSR induction, have lead to novel therapeutic targets. These therapeutic targets can serve as an add-on therapy in patients with an unsatisfactory response to proton pump inhibitor by inhibiting TLOSRs and its associated reflux events. However, the TLOSR-inhibiting drugs that are currently available still have significant side effects.

CONCLUSION

It is likely that in the future, selected GERD patients may benefit from transient lower oesophageal sphincter relaxation inhibition when compounds are found without significant side effects.

Effect of rimonabant on oesophageal motor function in man

BACKGROUND

Cannabinoid type 1 (CB1) receptors are implicated in the control of transient lower oesophageal sphincter relaxations (TLESRs) in animals. In man, it is unclear whether CB1 receptors are involved in the control of oesophageal function.

AIM

To study the effects of the CB1 receptor antagonist rimonabant on fasting and postprandial LES function in healthy subjects.

METHODS

Twelve healthy volunteers underwent two oesophageal manometry studies with administration of wet swallows and a meal after 3 days' premedication with placebo or rimonabant 20 mg.

RESULTS

Rimonabant did not significantly alter preprandial LES pressure (21.1±4.0 vs. 17.3±3.0 mmHg, N.S.), but postprandial LES pressures were significantly enhanced (9.9±1.9 vs.17.1±2.7 mmHg in the first and 10.0±1.4 vs. 19.3±3.6 mmHg in the second postprandial hour, both P<0.05). Swallow-induced relaxations and amplitude of peristaltic contractions were not altered, but rimonabant significantly increased the duration of peristaltic contractions at all time points (e.g. 5.0±0.3 vs. 8.0±0.3s preprandially and 5.0±0.2 vs. 8.2±0.3s at 60 min postprandially, both P<0.01). The number of postprandial TLESRs (3.1±0.5 vs. 1.2±0.5, P<0.05) and acid reflux episodes (1.4±0.2 vs. 0.3±0.1, P<0.05) were significantly lower after rimonabant.

CONCLUSION

The CB1 receptor antagonist rimonabant enhances postprandial LES pressure and decreases TLESRs in healthy subjects.

Inverse agonism of cannabinoid CB1 receptors potentiates LiCl-induced nausea in the conditioned gaping model in rats

BACKGROUND AND PURPOSE

Cannabinoid CB(1) receptor antagonists/inverse agonists, potentiate toxin-induced nausea and vomiting in animal models. Here, we sought to determine if this potentiated nausea was mediated by inverse agonism or neutral antagonism of the CB(1) receptor, and if the potentiated nausea would be produced by intracerebroventricular (icv) administration of an inverse agonist.

EXPERIMENTAL APPROACH

The conditioned gaping model of nausea in rats was used to compare the CB(1) receptor antagonist/inverse agonist, AM251, and the CB(1) receptor neutral antagonists, AM6527 (centrally and peripherally active) and AM6545 (peripherally active), in potentiating conditioned gaping produced by lithium chloride (LiCl) solution. The effect of icv (lateral ventricle and 4th ventricle) administration of AM251 on LiCl-induced gaping in this model was also evaluated.

KEY RESULTS

At a dose that did not produce conditioned gaping on its own, systemically administered AM251 (1.25 mg.kg(-1)) potentiated LiCl-induced conditioned gaping and reduced sucrose palatability; however, even doses as high as 8 mg.kg(-1) of AM6545 and AM6527 neither potentiated LiCl-induced conditioned gaping nor reduced sucrose palatability. Infusions of AM251 into the lateral ventricles (1.25, 12.5 and 125 microg) or the 4th ventricle (2.5, 12.5 and 125 microg) did not potentiate LiCl-induced conditioned gaping reactions, but all doses attenuated saccharin palatability during the subsequent test.

CONCLUSIONS AND IMPLICATIONS

Inverse agonism, but not neutral antagonism, of CB(1) receptors potentiated toxin-induced nausea. This effect may be peripherally mediated or may be mediated centrally by action on CB(1) receptors, located distal to the cerebral ventricles.

Local pretreatment with the cannabinoid CB1 receptor antagonist AM251 attenuates methamphetamine intra-accumbens self-administration

The endocannabinoid system is a potential target for therapeutic intervention of substance abuse. Cannabinoid CB1 receptor antagonist decreases intravenous methamphetamine self-administration in animal models. This study examined whether the nucleus accumbens (NAcc) is a site of interaction between methamphetamine and the CB1 receptor antagonist AM251. Male Sprague-Dawley rats were trained to lever press and then were surgically implanted with a guide cannula into the right NAcc. Rats were allowed one week to recover and then AM251 (0.1 or 1.0 μg/μL) was reverse dialyzed directly into the NAcc prior to methamphetamine (10 μg/μL) intra-accumbens self-administration. AM251 (1.0 μg/μL) reduced methamphetamine self-administration while AM251 (0.1 μg/μL) had an intermediary effect. The mechanism of self-administration attenuation is not known but could be mediated by AM251 affecting the negative feedback from the NAcc to the ventral tegmental area (VTA). This study provides evidence that the endocannabinoid system is involved with rewarding effects of methamphetamine and suggests a possible therapeutic intervention for methamphetamine abuse.

Cannabinoid-induced reduction in antral pacemaker frequency: a telemetric study in the ferret

BACKGROUND

The gastric myoelectric activity (GMA) is the electrical pacesetter potential, which drives gastric motility. Cannabinoids have broad-spectrum antiemetic and antinauseant activity. Paradoxically, they inhibit intestinal peristalsis and reduce gastric motility but their effect on GMA remains unknown.

METHODS

Ferrets were surgically implanted with radiotelemetry transmitters to record GMA, body temperature and heart rate. The effect of WIN 55,212-2 (1 mg kg(-1), i.p.), an agonist at the cannabinoid type 1 and 2 receptors was examined in conscious, unrestrained ferrets. WIN 55,212-2 was also compared to the anandamide upregulator URB 597 (5 mg kg(-1), i.p.) for a potential to modulate the emetic response and behavioral changes induced by apomorphine (0.25 mg kg(-1), s.c.).

KEY RESULTS

WIN 55,212-2 decreased GMA frequency (8.1 ± 0.4 cpm, compared to 9.6 ± 0.1 cpm in vehicle-treated animals, n = 6, P < 0.01). Apomorphine induced 9.0 ± 1.6 emetic episodes, WIN 55,212-2 inhibited the emetic response (3.3 ± 1.0 episodes, n = 6, P < 0.05) but URB 597 had no effect (9.0 ± 1.5 episodes). Apomorphine-induced hyperactivity in vehicle-treated animals (6.5 ± 3.6-16.6 ± 4.9 active behavior counts, n = 6, P < 0.01), which was reduced by WIN 55,212-2 (5.0 ± 1.5 counts, n = 6, P < 0.05).

CONCLUSIONS & INFERENCES

WIN 55,212-2 demonstrated clear antiemetic efficacy, which extends the broad-spectrum antiemetic efficacy of cannabinoids to dopamine receptor agonists in the ferret. Our results, however, suggest a more limited spectrum of action for URB 597. WIN 55,212-2 decreased the frequency of the antral electrical pacemaker, which reveals new insights into the mechanism regulating the decrease in motility induced by cannabinoids.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

Expression of cannabinoid CB1 receptors by vagal afferent neurons: kinetics and role in influencing neurochemical phenotype

The intestinal hormone cholecystokinin (CCK) inhibits food intake via stimulation of vagal afferent neurons (VAN). Recent studies suggest that CCK also regulates the expression of some G protein-coupled receptors and neuropeptide transmitters in these neurons. The aim of the present study was to characterize the expression of cannabinoid (CB)1 receptors in VAN and to determine whether stimulation of these receptors plays a role in regulating neurochemical phenotype. Expression of CB1 in rat VAN was detectable by in situ hybridization or immunohistochemistry after 6 h of fasting and increased to a maximum after 24 h when approximately 50% of neurons in the mid and caudal regions expressed the receptor. Melanin-concentrating hormone (MCH)1 receptors also increased with fasting, but the changes were delayed compared with CB1; in contrast Y2 receptors (Y2R) exhibited reciprocal changes in expression to CB1. Administration of CCK8s (10 nmol ip) to fasted rats decreased expression of CB1 with a t(1/2) of approximately 1 h compared with 3 h for MCH1. The action of CCK8s was inhibited by ghrelin and orexin-A. The CB1 agonist anandamide (intraperitoneally) reversed the effect of CCK8s on CB1, MCH1, and Y2 receptor expression. In contrast, in rats fasted for 18 h, administration of a CB1 antagonist/inverse agonist (AM281 ip) downregulated CB1 expression and increased Y2 receptor expression. Activation of vagal CB1 receptors therefore influences the neurochemical phenotype of these neurons, indicating a new and hitherto unrecognized role for endocannabinoids in gut-brain signaling.

Naphthalen-1-yl-(4-pentyloxynaphthalen-1-yl)methanone (SAB378), a peripherally restricted cannabinoid CB1/CB2 receptor agonist, inhibits gastrointestinal motility but has no effect on experimental colitis in mice

The endocannabinoid system is involved in the regulation of gastrointestinal (GI) motility and inflammation. Using the peripherally restricted cannabinoid (CB)(1)/CB(2) receptor agonist naphthalen-1-yl-(4-pentyloxynaphthalen-1-yl)methanone (SAB378), we investigated the role of peripheral cannabinoid receptors in the regulation of GI motility and the development of colitis in mice. The actions of SAB378 on whole gut transit, upper GI transit, colonic propulsion, and locomotor activity were investigated in C57BL/6N, CB(1) receptor knockout, and CB(2) receptor knockout mice. The potential for SAB378 to modify inflammation was studied by using dextran sulfate sodium (DSS) and 2,4,6-trinitrobenzene sulfonic acid (TNBS) models of experimental colitis. SAB378 did not modify locomotor activity. SAB378 slowed all parameters of GI motility, and these effects were significantly reduced by the CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide (AM251), but not by the CB(2) receptor antagonist 6-iodo-2-methyl-1-[2-(4-morpholinyl)ethyl]-1H- indol-3-yl](4-methoxyphenyl)methanone (AM630). SAB378 did not inhibit GI transit or colonic propulsion in CB(1) receptor knockout mice, whereas its effects were observed in CB(2) receptor knockout mice. SAB378 did not reduce the degree of colitis induced by DSS or TNBS. The actions of SAB378 on GI motility are mediated by peripherally located CB(1) receptors. SAB378 was not effective against two models of experimental colitis, which may indicate that peripheral cannabinoid receptor stimulation alone may not be sufficient to mediate the anti-inflammatory effects of cannabinoids.

Motion sickness, stress and the endocannabinoid system

Background

A substantial number of individuals are at risk for the development of motion sickness induced nausea and vomiting (N&V) during road, air or sea travel. Motion sickness can be extremely stressful but the neurobiologic mechanisms leading to motion sickness are not clear. The endocannabinoid system (ECS) represents an important neuromodulator of stress and N&V. Inhibitory effects of the ECS on N&V are mediated by endocannabinoid-receptor activation.

Methodology/Principal Findings

We studied the activity of the ECS in human volunteers (n = 21) during parabolic flight maneuvers (PFs). During PFs, microgravity conditions (<10⁻² g) are generated for approximately 22 s which results in a profound kinetic stimulus. Blood endocannabinoids (anandamide and 2-arachidonoylglycerol, 2-AG) were measured from blood samples taken in-flight before start of the parabolic maneuvers, after 10, 20, and 30 parabolas, in-flight after termination of PFs and 24 h later. Volunteers who developed acute motion sickness (n = 7) showed significantly higher stress scores but lower endocannabinoid levels during PFs. After 20 parabolas, blood anandamide levels had dropped significantly in volunteers with motion sickness (from 0.39±0.40 to 0.22±0.25 ng/ml) but increased in participants without the condition (from 0.43±0.23 to 0.60±0.38 ng/ml) resulting in significantly higher anandamide levels in participants without motion sickness (p = 0.02). 2-AG levels in individuals with motion sickness were low and almost unchanged throughout the experiment but showed a robust increase in participants without motion sickness. Cannabinoid-receptor 1 (CB1) but not cannabinoid-receptor 2 (CB2) mRNA expression in leucocytes 4 h after the experiment was significantly lower in volunteers with motion sickness than in participants without N&V.

Conclusions/Significance

These findings demonstrate that stress and motion sickness in humans are associated with impaired endocannabinoid activity. Enhancing ECS signaling may represent an alternative therapeutic strategy for motion sickness in individuals who do not respond to currently available treatments.

Cannabinoids and the gut: new developments and emerging concepts

Cannabis has been used to treat gastrointestinal (GI) conditions that range from enteric infections and inflammatory conditions to disorders of motility, emesis and abdominal pain. The mechanistic basis of these treatments emerged after the discovery of Delta(9)-tetrahydrocannabinol as the major constituent of Cannabis. Further progress was made when the receptors for Delta(9)-tetrahydrocannabinol were identified as part of an endocannabinoid system, that consists of specific cannabinoid receptors, endogenous ligands and their biosynthetic and degradative enzymes. Anatomical, physiological and pharmacological studies have shown that the endocannabinoid system is widely distributed throughout the gut, with regional variation and organ-specific actions. It is involved in the regulation of food intake, nausea and emesis, gastric secretion and gastroprotection, GI motility, ion transport, visceral sensation, intestinal inflammation and cell proliferation in the gut. Cellular targets have been defined that include the enteric nervous system, epithelial and immune cells. Molecular targets of the endocannabinoid system include, in addition to the cannabinoid receptors, transient receptor potential vanilloid 1 receptors, peroxisome proliferator-activated receptor alpha receptors and the orphan G-protein coupled receptors, GPR55 and GPR119. Pharmacological agents that act on these targets have been shown in preclinical models to have therapeutic potential. Here, we discuss cannabinoid receptors and their localization in the gut, the proteins involved in endocannabinoid synthesis and degradation and the presence of endocannabinoids in the gut in health and disease. We focus on the pharmacological actions of cannabinoids in relation to GI disorders, highlighting recent data on genetic mutations in the endocannabinoid system in GI disease.

Food restriction, refeeding, and gastric fill fail to affect emesis in musk shrews

Nausea and emesis are common side effects of gastrointestinal disease. Reports indicate that ghrelin and endocannabinoids, agents that stimulate appetite, also reduce emesis evoked by chemotherapy treatment, which suggests that stimulation of feeding inhibits the emetic system. In the following study we conducted a more direct test of this hypothesis by determining the impact of manipulating the motivation to eat on emesis, using food restriction and refeeding. Emesis was induced in musk shrews, a commonly used animal model for emesis research, using the cancer chemotherapy agent cisplatin (20 mg/kg ip), nicotine (2 mg/kg sc), or motion (1 Hz, horizontal, 4-cm displacement), because these treatments are known to target separate emetic pathways: gut vagal afferents, area postrema, and vestibular pathways, respectively. Twenty-four hours of food restriction was sufficient to stimulate food intake, and 1 h of refeeding filled the stomach. The results indicate that food restriction, refeeding, and gastric fill had no significant effects on the amount of emesis produced by any of the emetic treatments tested here. This suggests that, although activation of the emetic system might have prominent effects on food intake, neural controls for feeding behavior do not significantly affect the neural pathways for emesis. These results may have implications for how we treat patients who experience a constellation of side effects, including nausea and emesis, since stimulating appetite may not necessarily inhibit emetic pathways.

Constitutive activity at the cannabinoid CB(1) receptor and behavioral responses

The cannabinoid receptor type 1, found mainly on cells of the central and peripheral nervous system, is a major component of the endogenous cannabinoid system. Constitutive and endogenous activity at cannabinoid receptor type 1 regulates a diverse subset of biological processes including appetite, mood, motor function, learning and memory, and pain. The complexity of cannabinoid receptor type 1 activity is not limited to the constitutive activity of the receptor: promiscuity of ligands associated with and the capability of this receptor to instigate G protein sequestration also complicates the activity of cannabinoid receptor type 1. The therapeutic use of cannabinoid receptor type 1 agonists is still a heavily debated topic, making research on the mechanisms underlying the potential benefits and risks of cannabinoid use more vital than ever. Elucidation of these mechanisms and the quest for agonists and antagonists with greater specificity will allow a greater control of the side effects and risks involved in utilizing cannabinoids as therapeutic agents. In this chapter, we review a small subset of techniques used in the pharmacological application of and the behavioral effects of molecules acting at the paradoxical cannabinoid receptor type 1.

Opportunities for the replacement of animals in the study of nausea and vomiting

Nausea and vomiting are among the most common symptoms encountered in medicine as either symptoms of disease or side effects of treatments. Developing novel anti-emetics and identifying emetic liability in novel chemical entities rely on models that can recreate the complexity of these multi-system reflexes. Animal models (especially the ferret and dog) are the current gold standard; however, the selection of appropriate models is still a matter of debate, especially when studying the subjective human sensation of nausea. Furthermore, these studies are associated with animal suffering. Here, following a recent workshop held to review the utility of animal models in nausea and vomiting research, we discuss the limitations of some of the current models in the context of basic research, anti-emetic development and emetic liability detection. We provide suggestions for how these limitations may be overcome using non-animal alternatives, including greater use of human volunteers, in silico and in vitro techniques and lower organisms.

Analysis of endocannabinoids, their congeners and COX-2 metabolites

Since the discovery of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) in the early 1990s, the endocannabinoid system has been implicated in a wide array of physiological processes, such as control of food intake and energy balance, fertility and obesity. As the importance of this system becomes apparent, there is a tremendous need for robust, sensitive and efficient analytical methodology for the examination of the endocannabinoids, their congeners and putative metabolites. This review will summarize quantitative analytical methodology as reported in the literature from 1992 to present for the analysis of endocannabinoids and related compounds.

The FAAH inhibitor URB-597 interferes with cisplatin- and nicotine-induced vomiting in the Suncus murinus (house musk shrew)

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 CB(1) 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.