Intra-visceral insular cortex 2-arachidonoylglycerol, but not N-arachidonoylethanolamide, suppresses acute nausea-induced conditioned gaping in rats

Endocannabinoid signaling in stress, nausea, and vomiting

BACKGROUND

Classical antiemetics that target the serotonin system may not be effective in treating certain nausea and vomiting conditions like cyclic vomiting syndrome (CVS) and cannabinoid hyperemesis syndrome (CHS). As a result, there is a need for better therapies to manage the symptoms of these disorders, including nausea, vomiting, and anxiety. Cannabis is often used for its purported antiemetic and anxiolytic effects, given regulation of these processes by the endocannabinoid system (ECS). However, there is considerable evidence that cannabinoids can also produce nausea and vomiting and increase anxiety in certain instances, especially at higher doses. This paradoxical effect of cannabinoids on nausea, vomiting, and anxiety may be due to the dysregulation of the ECS, altering how it maintains these processes and contributing to the pathophysiology of CVS or CHS.

PURPOSE

The purpose of this review is to highlight the involvement of the ECS in the regulation of stress, nausea, and vomiting. We discuss how prolonged cannabis use, such as in the case of CHS or heightened stress, can dysregulate the ECS and affect its modulation of these functions. The review also examines the evidence for the roles of ECS and stress systems' dysfunction in CVS and CHS to better understand the underlying mechanisms of these conditions.

Spontaneous and Naloxone-Precipitated Withdrawal Behaviors From Chronic Opiates are Accompanied by Changes in N-Oleoylglycine and N-Oleoylalanine Levels in the Brain and Ameliorated by Treatment With These Mediators

Rationale: The endocannabinoidome mediators, N-Oleoylglycine (OlGly) and N-Oleoylalanine (OlAla), have been shown to reduce acute naloxone-precipitated morphine withdrawal affective and somatic responses.

Objectives: To determine the role and mechanism of action of OlGly and OlAla in withdrawal responses from chronic exposure to opiates in male Sprague-Dawley rats.

Methods: Opiate withdrawal was produced: 1) spontaneously 24 h following chronic exposure to escalating doses of morphine over 14 days (Experiments 1 and 2) and steady-state exposure to heroin by minipumps for 12 days (Experiment 3), 2) by naloxone injection during steady-state heroin exposure (Experiment 4), 3) by naloxone injection during operant heroin self-administration (Experiment 5).

Results: In Experiment 1, spontaneous morphine withdrawal produced somatic withdrawal reactions. The behavioral withdrawal reactions were accompanied by suppressed endogenous levels of OlGly in the nucleus accumbens, amygdala, and prefrontal cortex, N-Arachidonylglycerol and OlAla in the amygdala, 2-arachidonoylglycerol in the nucleus accumbens, amygdala and interoceptive insular cortex, and by changes in colonic microbiota composition. In Experiment 2, treatment with OlAla, but not OlGly, reduced spontaneous morphine withdrawal responses. In Experiment 3, OlAla attenuated spontaneous steady-state heroin withdrawal responses at both 5 and 20 mg/kg; OlGly only reduced withdrawal responses at the higher dose of 20 mg/kg. Experiment 4 demonstrated that naloxone-precipitated heroin withdrawal from steady-state exposure to heroin (7 mg/kg/day for 12 days) is accompanied by tissue-specific changes in brain or gut endocannabinoidome mediator, including OlGly and OlAla, levels and colonic microbiota composition, and that OlAla (5 mg/kg) attenuated behavioural withdrawal reactions, while also reversing some of the changes in brain and gut endocannabinoidome and gut microbiota induced by naloxone. Experiment 5 demonstrated that although OlAla (5 mg/kg) did not interfere with operant heroin self-administration on its own, it blocked naloxone-precipitated elevation of heroin self-administration behavior.

Conclusion: These results suggest that OlAla and OlGly are two endogenous mediators whose brain concentrations respond to chronic opiate treatment and withdrawal concomitantly with changes in colon microbiota composition, and that OlAla may be more effective than OlGly in suppressing chronic opiate withdrawal responses.

The CSF-Contacting Nucleus Receives Anatomical Inputs From the Cerebral Cortex: A Combination of Retrograde Tracing and 3D Reconstruction Study in Rat

Objective

This study aimed to investigate the direct monosynaptic projections from cortical functional regions to the cerebrospinal fluid (CSF)-contacting nucleus for understanding the functions of the CSF-contacting nucleus.

Methods

The Sprague-Dawley rats received cholera toxin B subunit (CB) injections into the CSF-contacting nucleus. After 7-10 days of survival time, the rats were perfused, and the whole brain and spinal cord were sliced under a freezing microtome at 40 μm. All sections were treated with the CB immunofluorescence reaction. The retrogradely labeled neurons in different cortical areas were revealed under a confocal microscope. The distribution features were further illustrated under 3D reconstruction.

Results

The retrogradely labeled neurons were identified in the olfactory, orbital, cingulate, insula, retrosplenial, somatosensory, motor, visual, auditory, association, rhinal, and parietal cortical areas. A total of 12 functional areas and 34 functional subregions showed projections to the CSF-contacting nucleus in different cell intensities.

Conclusion

According to the connectivity patterns, we conclude that the CSF-contacting nucleus participates in cognition, emotion, pain, visceral activity, etc. The present study firstly reveals the cerebral cortex→CSF-contacting nucleus connections, which implies the multiple functions of this special nucleus in neural and body fluid regulations.

Role of the stress response and the endocannabinoid system in Δ9-tetrahydrocannabinol (THC)-induced nausea

RATIONALE

Dysregulation of the endocannabinoid (eCB) system by high doses of Δ⁹-tetrahydrocannabinol (THC) is hypothesized to generate a dysfunctional hypothalamic-pituitary-adrenal (HPA) axis contributing to cannabinoid hyperemesis syndrome (CHS).

OBJECTIVES AND METHODS

Using the conditioned gaping model of nausea, we aimed to determine if pre-treatments that interfere with stress, or an anti-emetic drug, interfere with THC-induced nausea in male rats. The corticotropin-releasing hormone (CRH) antagonist, antalarmin, was given to inhibit the HPA axis during conditioning. Since eCBs inhibit stress, MJN110 (which elevates 2-arachidonylglycerol (2-AG)) and URB597 (which elevates anandamide (AEA)) were also tested. Propranolol (β-adrenergic antagonist) and WAY-100635 (5-HT_1A antagonist) attenuate HPA activation by cannabinoids and, therefore, were assessed. In humans, CHS symptoms are not alleviated by anti-emetic drugs, such as ondansetron (5-HT₃ antagonist); however, benzodiazepines are effective. Therefore, ondansetron and chlordiazepoxide were tested. To determine if HPA activation by THC is dose-dependent, corticosterone (CORT) was analyzed from serum of rats treated with 0.0, 0.5, or 10 mg/kg THC.

RESULTS

Antalarmin (10 and 20 mg/kg), MJN110 (10 mg/kg), URB597 (0.3 mg/kg), propranolol (2.5 and 5 mg/kg), WAY-100635 (0.5 mg/kg), and chlordiazepoxide (5 mg/kg) interfered with THC-induced conditioned gaping, but the anti-emetic ondansetron (0.1 and 0.01 mg/kg) did not. THC produced significantly higher CORT levels at 10 mg/kg than at 0.0 and 0.5 mg/kg THC.

CONCLUSIONS

Treatments that interfere with the stress response also inhibit THC-induced conditioned gaping, but a typical anti-emetic drug does not, supporting the hypothesis that THC-induced nausea, and CHS, is a result of a dysregulated stress response.

Endocannabinoid regulation of homeostatic feeding and stress-induced alterations in food intake in male rats

BACKGROUND AND PURPOSE

Stress is known to reduce food intake. Many aspects of the stress response and feeding are regulated by the endocannabinoid system, but the roles of anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) in stress-induced anorexia are unclear.

EXPERIMENTAL APPROACH

Effects of acute restraint stress on endocannabinoids were investigated in male Sprague-Dawley rats. Systemic and central pharmacological inhibition of fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MAGL) was used to assess the effects of elevated AEA and 2-AG on homeostatic feeding and on food consumption after stress. Animals were pretreated with the FAAH inhibitor, PF-04457845, or the MAGL inhibitor, MJN110, before 2 h acute restraint stress or 2 h homecage period without food.

KEY RESULTS

Restraint stress decreased hypothalamic and circulating AEA, with no effect in the gastrointestinal tract, while 2-AG content in the jejunum (but not duodenum) was reduced. PF-04457845 (30 μg), given i.c.v., attenuated stress-induced anorexia via CB₁ receptors, but reduced homeostatic feeding in unstressed animals through an unknown mechanism. On the other hand, systemic administration of MJN110 (10 mg·kg^-1 ) reduced feeding, regardless of stress or feeding status and inhibited basal intestinal transit in unstressed rats. The ability of MAGL inhibition to reduce feeding in combination with stress was independent of CB₁ receptor signalling in the gut as the peripherally restricted CB₁ receptor antagonist, AM6545 did not block this effect.

CONCLUSIONS AND IMPLICATIONS

Our data reveal diverse roles for 2-AG and AEA in homeostatic feeding and changes in energy intake following stress.

LINKED ARTICLES

This article is part of a themed section on 8^th European Workshop on Cannabinoid Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.10/issuetoc.

Cannabinoid CB1 Discrimination: Effects of Endocannabinoids and Catabolic Enzyme Inhibitors

An improved understanding of the endocannabinoid system has provided new avenues of drug discovery and development toward the management of pain and other behavioral maladies. Exogenous cannabinoid type 1 (CB1) receptor agonists such as Δ9-tetrahydrocannabinol are increasingly used for their medicinal actions; however, their utility is constrained by concern regarding abuse-related subjective effects. This has led to growing interest in the clinical benefit of indirectly enhancing the activity of the highly labile endocannabinoids N-arachidonoylethanolamine [AEA (or anandamide)] and/or 2-arachidonoylglycerol (2-AG) via catabolic enzyme inhibition. The present studies were conducted to determine whether such actions can lead to CB1 agonist-like subjective effects, as reflected in CB1-related discriminative stimulus effects in laboratory subjects. Squirrel monkeys (n = 8) that discriminated the CB1 full agonist AM4054 (0.01 mg/kg) from vehicle were used to study, first, the inhibitors of fatty acid amide hydrolase (FAAH) or monoacylglycerol lipase (MGL) alone or in combination [FAAH (URB597, AM4303); MGL (AM4301); FAAH/MGL (JZL195, AM4302)] and, second, the ability of the endocannabinoids AEA and 2-AG to produce CB1 agonist-like effects when administered alone or after enzyme inhibition. Results indicate that CB1-related discriminative stimulus effects were produced by combined, but not selective, inhibition of FAAH and MGL, and that these effects were nonsurmountably antagonized by low doses of rimonabant. Additionally, FAAH or MGL inhibition revealed CB1-like subjective effects produced by AEA but not by 2-AG. Taken together, the present data suggest that therapeutic effects of combined, but not selective, enhancement of AEA or 2-AG activity via enzyme inhibition may be accompanied by CB1 receptor-mediated subjective effects.

Elevation of 2-AG by monoacylglycerol lipase inhibition in the visceral insular cortex interferes with anticipatory nausea in a rat model

Anticipatory nausea (AN) is a conditioned nausea reaction experienced by chemotherapy patients upon returning to the clinic. Currently, there are no specific treatments for this phenomenon, with the classic antiemetic treatments (e.g., ondansetron) providing no relief. The rat model of AN, contextually elicited conditioned gaping reactions in rats, provides a tool for assessing potential treatments for this difficult to treat disorder. Systemically administered drugs which elevate the endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG), by interfering with their respective degrading enzymes, fatty acid amide hydrolase (FAAH) and monoacyl glycerol lipase (MAGL) interfere with AN in the rat model. We have shown that MAGL inhibition within the visceral insular cortex (VIC) interferes with acute nausea in the gaping model (Sticht et al., 2015). Here we report that bilateral infusion of the MAGL inhibitor, MJN110 (but neither the FAAH inhibitor, PF3845, nor ondansetron) into the VIC suppressed contextually elicited conditioned gaping, and this effect was reversed by coadministration of the CB1 antagonist, AM251. These findings suggest that 2-AG within the VIC plays a critical role in the regulation of both acute nausea and AN. Because there are currently no specific therapeutics for chemotherapy patients that develop anticipatory nausea, MAGL inhibition by MJN110 may be a candidate treatment. (PsycINFO Database Record

The gastrointestinal tract - a central organ of cannabinoid signaling in health and disease

BACKGROUND

In ancient medicine, extracts of the marijuana plant Cannabis sativa were used against diseases of the gastrointestinal (GI) tract. Today, our knowledge of the ingredients of the Cannabis plant has remarkably advanced enabling us to use a variety of herbal and synthetic cannabinoid (CB) compounds to study the endocannabinoid system (ECS), a physiologic entity that controls tissue homeostasis with the help of endogenously produced CBs and their receptors. After many anecdotal reports suggested beneficial effects of Cannabis in GI disorders, it was not surprising to discover that the GI tract accommodates and expresses all the components of the ECS. Cannabinoid receptors and their endogenous ligands, the endocannabinoids, participate in the regulation of GI motility, secretion, and the maintenance of the epithelial barrier integrity. In addition, other receptors, such as the transient receptor potential cation channel subfamily V member 1 (TRPV1), the peroxisome proliferator-activated receptor alpha (PPARα) and the G-protein coupled receptor 55 (GPR55), are important participants in the actions of CBs in the gut and critically determine the course of bowel inflammation and colon cancer.

PURPOSE

The following review summarizes important and recent findings on the role of CB receptors and their ligands in the GI tract with emphasis on GI disorders, such as irritable bowel syndrome, inflammatory bowel disease, and colon cancer.

The Role of the Endocannabinoid System in the Brain-Gut Axis

The actions of cannabis are mediated by receptors that are part of an endogenous cannabinoid system. The endocannabinoid system (ECS) consists of the naturally occurring ligands N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol (2-AG), their biosynthetic and degradative enzymes, and the cannabinoid (CB) receptors CB1 and CB2. The ECS is a widely distributed transmitter system that controls gut functions peripherally and centrally. It is an important physiologic regulator of gastrointestinal motility. Polymorphisms in the gene encoding CB1 (CNR1) have been associated with some forms of irritable bowel syndrome. The ECS is involved in the control of nausea and vomiting and visceral sensation. The homeostatic role of the ECS also extends to the control of intestinal inflammation. We review the mechanisms by which the ECS links stress and visceral pain. CB1 in sensory ganglia controls visceral sensation, and transcription of CNR1 is modified through epigenetic processes under conditions of chronic stress. These processes might link stress with abdominal pain. The ECS is also involved centrally in the manifestation of stress, and endocannabinoid signaling reduces the activity of hypothalamic-pituitary-adrenal pathways via actions in specific brain regions, notably the prefrontal cortex, amygdala, and hypothalamus. Agents that modulate the ECS are in early stages of development for treatment of gastrointestinal diseases. Increasing our understanding of the ECS will greatly advance our knowledge of interactions between the brain and gut and could lead to new treatments for gastrointestinal disorders.

Cannabinoids As Potential Treatment for Chemotherapy-Induced Nausea and Vomiting

Despite the advent of classic anti-emetics, chemotherapy-induced nausea is still problematic, with vomiting being somewhat better managed in the clinic. If post-treatment nausea and vomiting are not properly controlled, anticipatory nausea—a conditioned response to the contextual cues associated with illness-inducing chemotherapy—can develop. Once it develops, anticipatory nausea is refractive to current anti-emetics, highlighting the need for alternative treatment options. One of the first documented medicinal uses of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) was for the treatment of chemotherapy-induced nausea and vomiting (CINV), and recent evidence is accumulating to suggest a role for the endocannabinoid system in modulating CINV. Here, we review studies assessing the therapeutic potential of cannabinoids and manipulations of the endocannabinoid system in human patients and pre-clinical animal models of nausea and vomiting.

Double Dissociation of Monoacylglycerol Lipase Inhibition and CB1 Antagonism in the Central Amygdala, Basolateral Amygdala, and the Interoceptive Insular Cortex on the Affective Properties of Acute Naloxone-Precipitated Morphine Withdrawal in Rats

Both CB1 receptor antagonism and agonism, in particular by 2-arachidonyl glycerol (2-AG), have been shown to reduce somatic symptoms of morphine withdrawal (MWD). Here we evaluated the effects of both systemic pretreatment with the monoacylglycerol lipase (MAGL) inhibitor MJN110 (which selectively elevates 2-AG) and central administration of both MJN110 and the CB1 antagonist (AM251) on the affective properties of MWD. Acute MWD induced place aversion occurs when naloxone is administered 24 h following a single exposure to a high dose of morphine. Systemic pretreatment with the MAGL inhibitor, MJN110, prevented the aversive effects of acute MWD by a CB1 receptor-dependent mechanism. Furthermore, in a double dissociation, AM251 infusions into the central amygdala, but MJN110 infusions into the basolateral amygdala, interfered with the naloxone-precipitated MWD induced place aversion. As well, MJN110, but not AM251, infusions into the interoceptive insular cortex (a region known to be activated in acute MWD) also prevented the establishment of the place aversion by a CB1 mechanism of action. These findings reveal the respective sites of action of systemically administered MJN110 and AM251 in regulating the aversive effects of MWD.

A comparison of novel, selective fatty acid amide hydrolase (FAAH), monoacyglycerol lipase (MAGL) or dual FAAH/MAGL inhibitors to suppress acute and anticipatory nausea in rat models

RATIONALE

Drugs that block fatty acid amide hydrolase (FAAH, which elevates anandamide [AEA]) and drugs which block monoacylglycerol (MAGL, which elevates 2-arachidonyl glycerol [2-AG]) have promise in treating both acute and anticipatory nausea in human patients.

OBJECTIVE

This study aims to evaluate the relative effectiveness of dual MAGL/FAAH inhibition with either alone to reduce acute and anticipatory nausea in rat models.

MATERIALS AND METHODS

AM4302, a new dual MAGL/FAAH inhibitor, was compared with a new selective MAGL inhibitor, AM4301, and new selective FAAH inhibitor, AM4303, for their potential to reduce acute nausea (gaping in taste reactivity) and anticipatory nausea (contextually elicited conditioned gaping) in two rat models.

RESULTS

Our in vitro studies indicate that AM4302 blocks human and rat FAAH: IC50 60 and 31 nM, respectively, with comparable potencies against human MAGL (IC50 41 nM) and rat MAGL (IC50 200 nM). AM4301 selectively blocks human and rat MAGL (IC50 8.9 and 36 nM, respectively), while AM4303 selectively inhibits human and rat FAAH (IC50 2 and 1.9 nM), respectively. Our in vivo studies show that the MAGL inhibitor, AM4301, suppressed acute nausea in a CB1-mediated manner, when delivered systemically or into the interoceptive insular cortex. Although the dual FAAH/MAGL inhibitor, AM4302, was equally effective as the FAAH inhibitor or MAGL inhibitor in reducing acute nausea, it was more effective than both in suppressing anticipatory nausea.

CONCLUSIONS

Dual FAAH and MAGL inhibition with AM4302 may be an especially effective treatment for the very difficult to treat symptom of anticipatory nausea.

Cannabinoid Regulation of Acute and Anticipatory Nausea

Chemotherapy-induced nausea is one of the most distressing symptoms reported by patients undergoing treatment, and even with the introduction of newer antiemetics such as ondansetron and aprepitant, nausea remains problematic in the clinic. Indeed, when acute nausea is not properly managed, the cues of the clinic can become associated with this distressing symptom resulting in anticipatory nausea for which no effective treatments are available. Clinical trials exploring the potential of exogenous or endogenous cannabinoids to reduce chemotherapy-induced nausea are sparse; therefore, we must rely on the data from pre-clinical rat models of nausea. In this review, we explore the human and pre-clinical animal literature examining the potential for exogenous and endogenous cannabinoid treatments to regulate chemotherapy-induced nausea. The pre-clinical evidence points to a compelling need to evaluate the antinausea potential of cannabidiol, cannabidiolic acid, and treatments that boost the functioning of the endocannabinoid system in human clinical trials.

Cannabinoid Receptors in Regulating the GI Tract: Experimental Evidence and Therapeutic Relevance

Cannabinoid receptors are fundamentally involved in all aspects of intestinal physiology, such as motility, secretion, and epithelial barrier function. They are part of a broader entity, the so-called endocannabinoid system which also includes their endocannabinoid ligands and the ligands' synthesizing/degrading enzymes. The system has a strong impact on the pathophysiology of the gastrointestinal tract and is believed to maintain homeostasis in the gut by controlling hypercontractility and by promoting regeneration after injury. For instance, genetic knockout of cannabinoid receptor 1 leads to inflammation and cancer of the intestines. Derivatives of Δ⁹-tetrahydrocannabinol, such as nabilone and dronabinol, activate cannabinoid receptors and have been introduced into the clinic to treat chemotherapy-induced emesis and loss of appetite; however, they may cause many psychotropic side effects. New drugs that interfere with endocannabinoid degradation to raise endocannabinoid levels circumvent this obstacle and could be used in the future to treat emesis, intestinal inflammation, and functional disorders associated with visceral hyperalgesia.

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.

Endocannabinoid regulation of nausea is mediated by 2-arachidonoylglycerol (2-AG) in the rat visceral insular cortex

Cannabinoid (CB) agonists suppress nausea in humans and animal models; yet, their underlying neural substrates remain largely unknown. Evidence suggests that the visceral insular cortex (VIC) plays a critical role in nausea. Given the expression of CB1 receptors and the presence of endocannabinoids in this brain region, we hypothesized that the VIC endocannabinoid system regulates nausea. In the present study, we assessed whether inhibiting the primary endocannabinoid hydrolytic enzymes in the VIC reduces acute lithium chloride (LiCl)-induced conditioned gaping, a rat model of nausea. We also quantified endocannabinoid levels during an episode of nausea, and assessed VIC neuronal activation using the marker, c-Fos. Local inhibition of monoacylglycerol lipase (MAGL), the main hydrolytic enzyme of 2-arachidonylglycerol (2-AG), reduced acute nausea through a CB1 receptor mechanism, whereas inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of anandamide (AEA), was without effect. Levels of 2-AG were also selectively elevated in the VIC during an episode of nausea. Inhibition of MAGL robustly increased 2-AG in the VIC, while FAAH inhibition had no effect on AEA. Finally, we demonstrated that inhibition of MAGL reduced VIC Fos immunoreactivity in response to LiCl treatment. Taken together, these findings provide compelling evidence that acute nausea selectively increases 2-AG in the VIC, and suggests that 2-AG signaling within the VIC regulates nausea by reducing neuronal activity in this forebrain region.

Interference with acute nausea and anticipatory nausea in rats by fatty acid amide hydrolase (FAAH) inhibition through a PPARα and CB1 receptor mechanism, respectively: a double dissociation

RATIONALE

Fatty acid amide hydrolase (FAAH) inhibition elevates anandamide (AEA), which acts on cannabinoid (CB1 and CB2) receptors, as well as N-palmitoylethanolamide (PEA) and N-oleoylethanolamine (OEA), which act on peroxisome proliferator-activated receptor alpha (PPARα). Here, we determine the mechanism of action of FAAH inhibition on acute and anticipatory nausea (AN).

OBJECTIVE

We compared the effectiveness and mechanism of action of two FAAH inhibitors, URB597 and PF-3845, to reduce acute nausea and AN in rodent models of conditioned gaping.

MATERIALS AND METHODS

For assessment of acute nausea, rats were pretreated with vehicle (VEH), URB597 (0.3 and 10 mg/kg, experiment 1a) or PF-3845 (10 mg/kg, experiment 1b) 120 min prior to a saccharin-lithium chloride (LiCl) pairing. To assess the CB1 receptor or PPARα mediation of the effect of PF-3845 on acute nausea, rats were also pretreated with rimonabant or MK886, respectively. For assessment of AN, following four pairings of a novel context with LiCl, rats received a pretreatment of VEH, URB597 (0.3 mg/kg, experiment 2a), or PF-3845 (10, 20 mg/kg, experiment 2b) 120 min prior to placement in the AN context. To assess the CB1 receptor or PPARα mediation of the effect, rats were also pretreated with rimonabant or MK886, respectively.

RESULTS

PF-3845 (10 mg/kg, but not URB597 0.3 or 10 mg/kg) suppressed acute nausea via PPARα, but not CB1 receptors. URB597 (0.3 and 10 mg/kg) or PF-3845 (10 and 20 mg/kg) reduced AN via CB1 receptors, but not PPARα.

CONCLUSIONS

FAAH inhibition reduces acute nausea and AN through PPARα and CB1 receptor mediated effects, respectively.