Central and peripheral mechanisms contribute to the antiemetic actions of delta-9-tetrahydrocannabinol against 5-hydroxytryptophan-induced emesis

The Role of Cannabinoids and the Endocannabinoid System in the Treatment and Regulation of Nausea and Vomiting

Despite using the recommended anti-emetic treatments, control of nausea and vomiting is still an unmet need for cancer patients undergoing chemotherapy treatment. Few properly controlled clinical trials have evaluated the potential of exogenously administered cannabinoids or manipulations of the endogenous cannabinoid (eCB) system to treat nausea and vomiting. In this chapter, we explore the pre-clinical and human clinical trial evidence for the potential of exogenous cannabinoids and manipulations of the eCB system to reduce nausea and vomiting. Although there are limited high-quality human clinical trials, pre-clinical evidence suggests that cannabinoids and manipulations of the eCB system have anti-nausea/anti-emetic potential. The pre-clinical anti-nausea/anti-emetic evidence highlights the need for further evaluation of cannabinoids and manipulations of eCBs and other fatty acid amides in clinical trials.

Ultra-low doses of methamphetamine suppress 5-hydroxytryptophan-induced head-twitch response in mice during aging

The head-twitch response (HTR) in mice is considered a behavioral assay for activation of 5-HT 2A receptors in rodents. It can be evoked by direct-acting 5-HT 2A receptor agonists such as (±)-2,5-dimethoxy-4-iodoamphetamine, 5-hydroxytryptamine precursors [e.g. 5-hydroxytryptophan (5-HTP)], and selective 5-hydroxytryptamine releasers (e.g. d -fenfluramine). The nonselective monoamine releaser methamphetamine by itself does not produce the HTR but can suppress both (±)-2,5-dimethoxy-4-iodoamphetamine- and d -fenfluramine-evoked HTRs across ages via concomitant activation of the inhibitory serotonergic 5-HT 1A or adrenergic α 2 receptors. Currently, we investigated: (1) the ontogenic development of 5-HTP-induced HTR in 20-, 30-, and 60-day-old mice; (2) whether pretreatment with ultra-low doses of methamphetamine (0.1, 0.25, and 0.5 mg/kg, intraperitoneally) can suppress the frequency of 5-HTP-induced HTR at different ages; and (3) whether the inhibitory serotonergic 5-HT 1A or adrenergic α 2 receptors may account for the potential inhibitory effect of methamphetamine on 5-HTP-induced HTR. In the presence of a peripheral decarboxylase inhibitor (carbidopa), 5-HTP produced maximal frequency of HTRs in 20-day-old mice which rapidly subsided during aging. Methamphetamine dose-dependently suppressed 5-HTP-evoked HTR in 20- and 30-day-old mice. The selective 5-HT 1A -receptor antagonist WAY 100635 reversed the inhibitory effect of methamphetamine on 5-HTP-induced HTR in 30-day-old mice, whereas the selective adrenergic α 2 -receptor antagonist RS 79948 failed to reverse methamphetamine's inhibition at any tested age. These findings suggest an ontogenic rationale for methamphetamine's inhibitory 5-HT 1A receptor component of action in its suppressive effect on 5-HTP-induced HTR during development which is not maximally active at a very early age.

NHS-Reimbursed Cannabis Flowers for Cancer Palliative Care and the Management of Chemotherapy-Induced Nausea and Vomiting: An Autobiographical Case Report

Chemotherapy-induced nausea and vomiting (CINV) is a debilitating side effect of cancer treatment, affecting many patients. Cannabinoid agonists, such as nabilone and Δ9-tetrahydrocannabinol (THC), the main psychoactive component of Cannabis sativa L., have shown efficacy as antiemetics. Here, we report the case of Michael Roberts (MR), who we believe is the first British patient reimbursed by the National Health Service (NHS) England for the cost of medicinal cannabis flowers to manage CINV. Medical data were obtained from NHS records and individual funding request (IFR) forms. Patient-reported outcome measures (PROMs) were collected using validated questionnaires as part of the standard of care at the specialized private clinics where the prescription of medicinal cannabis was initiated. The patient presented with rectosigmoid adenocarcinoma with lung metastases. He received FOLFIRI (folinic acid, fluorouracil, and irinotecan) chemotherapy and underwent an emergency Hartmann's procedure with subsequent second-line FOLFOX (folinic acid, fluorouracil, and oxaliplatin) chemotherapy and lung ablation. MR reported severe nausea and vomiting associated with the initial FOLFIRI treatment. Antiemetics metoclopramide and aprepitant demonstrated moderated efficacy. Antiemetics ondansetron, levomepromazine, and nabilone were associated with intolerable side effects. Inhalation of THC-predominant cannabis flowers in association with standard medication improved CINV, anxiety, sleep quality, appetite, overall mood, and quality of life. Our results add to the available evidence suggesting that medicinal cannabis flowers may offer valuable support in cancer palliative care integrated with standard-of-care oncology treatment. The successful individual funding request in this case demonstrates a pathway for other patients to gain access to these treatments, advocating for broader awareness and integration of cannabis-based medicinal products in national healthcare services.

5-HT3a receptor contributes to neuropathic pain by regulating central sensitization in a rat with brachial plexus avulsion

PURPOSE

As a frequently occurring complication resulting from brachial plexus avulsion (BPA), neuropathic pain significantly impacts the quality of life of patients and places a substantial burden on their families. Recent reports have suggested that the 5-HT3a receptor may play a role in the development and regulation of neuropathic pain. The current study aimed to explore the involvement of the 5-HT3a receptor in neuropathic pain resulting from BPA in rats.

METHODS

A rat model of neuropathic pain was induced through brachial plexus avulsion (BPA). The pain thresholds of the rats were measured after BPA. The spinal dorsal horn (SDH) of rats was collected at day 14 after surgery, and the expression and distribution of the 5-HT3a receptor were analyzed using immunohistochemistry and western blotting. The expression levels of various factors related to central sensitization were measured by western blot, including c-Fos, GFAP, IBA-1, IL-1β and TNF-α. The effects of 5-HT3a receptor antagonists on hyperalgesia were assessed through behavioral tests after intrathecal administration of ondansetron. Additionally, at 120 min postinjection, the SDH of rats was acquired, and the change of expression levels of protiens related to central sensitization were measured by western blot.

RESULTS

BPA induced mechanical and cold hypersensitivity in rats. The 5-HT3a receptor was increased and mainly distributed on neurons and microglia in the SDH after BPA, and the level of central sensitization and expression of inflammatory factors, such as c-Fos, GFAP, IBA-1, IL-1β and TNF-α, were also increased markedly. Ondansetron, which is a selective 5-HT3a receptor antagonist, reversed the behavioral changes caused by BPA. The antagonist also decreased the expression of central sensitization markers and inflammatory factors.

CONCLUSION

The results suggested that the 5-HT3a receptor is involved in neuropathic pain by regulating central nervous system sensitization in a rat brachial plexus avulsion model. Targeting the 5-HT3a receptor may be a promising approach for treating neuropathic pain after brachial plexus avulsion.

Chemotherapy-induced gastrointestinal toxicity: Pathogenesis and current management

Chemotherapy is the most common treatment for malignant tumors. However, chemotherapy-induced gastrointestinal toxicity (CIGT) has been a major concern for cancer patients, which reduces their quality of life and leads to treatment intolerance and even cessation. Nevertheless, prevention and treatment for CIGT are challenging, due to the prevalence and complexity of the condition. Chemotherapeutic drugs directly damage gastrointestinal mucosa to induce CIGT, including nausea, vomiting, anorexia, gastrointestinal mucositis, and diarrhea, etc. The pathogenesis of CIGT involves multiple factors, such as gut microbiota disorders, inflammatory responses and abnormal neurotransmitter levels, that synergistically contribute to its occurrence and development. In particular, the dysbiosis of gut microbiota is usually linked to abnormal immune responses that increases inflammatory cytokines' expression, which is a common characteristic of many types of CIGT. Chemotherapy-induced intestinal neurotoxicity is also a vital concern in CIGT. Currently, modern medicine is the dominant treatment of CIGT, however, traditional Chinese medicine (TCM) has attracted interest as a complementary and alternative therapy that can greatly alleviate CIGT. Accordingly, this review aimed to comprehensively summarize the pathogenesis and current management of CIGT using PubMed and Google Scholar databases, and proposed that future research for CIGT should focus on the gut microbiota, intestinal neurotoxicity, and promising TCM therapies, which may help to develop more effective interventions and optimize managements of CIGT.

Effects of low-doses of methamphetamine on d-fenfluramine-induced head-twitch response (HTR) in mice during ageing and c-fos expression in the prefrontal cortex

BACKGROUND

The head-twitch response (HTR) in mice is considered a behavioral model for hallucinogens and serotonin 5-HT_2A receptor function, as well as Tourette syndrome in humans. It is mediated by 5-HT_2A receptor agonists such as ( ±)- 2,5-dimethoxy-4-iodoamphetamine (DOI) in the prefrontal cortex (PFC). The 5-HT_2A antagonist EMD 281014, can prevent both DOI-induced HTR during ageing and c-fos expression in different regions of PFC. Moreover, the nonselective monoamine releaser methamphetamine (MA) suppressed DOI-induced HTR through ageing via concomitant activation of inhibitory 5-HT_1A receptors, but enhanced DOI-evoked c-fos expression. d-Fenfluramine is a selective 5-HT releaser and induces HTR in mice, whereas MA does not. Currently, we investigated whether EMD 281014 or MA would alter: (1) d-fenfluramine-induced HTR frequency in 20-, 30- and 60-day old mice, (2) d-fenfluramine-evoked c-fos expression in PFC, and (3) whether blockade of inhibitory serotonergic 5-HT_1A- or adrenergic ɑ₂-receptors would prevent suppressive effect of MA on d-fenfluramine-induced HTR.

RESULTS

EMD 281014 (0.001-0.05 mg/kg) or MA (0.1-5 mg/kg) blocked d-fenfluramine-induced HTR dose-dependently during ageing. The 5-HT_1A antagonist WAY 100635 countered the inhibitory effect of MA on d-fenfluramine-induced HTR in 30-day old mice, whereas the adrenergic ɑ₂ antagonist RS 79948 reversed MA's inhibitory effect in both 20- and 30- day old mice. d-Fenfluramine significantly increased c-fos expressions in PFC regions. MA (1 mg/kg) pretreatment significantly increased d-fenfluramine-evoked c-fos expression in different regions of PFC. EMD 281014 (0.05 mg/kg) failed to prevent d-fenfluramine-induced c-fos expression, but significantly increased it in one PFC region (PrL at - 2.68 mm).

CONCLUSION

EMD 281014 suppressed d-fenfluramine-induced HTR but failed to prevent d-fenfluramine-evoked c-fos expression which suggest involvement of additional serotonergic receptors in the mediation of evoked c-fos. The suppressive effect of MA on d-fenfluramine-evoked HTR is due to well-recognized functional interactions between stimulatory 5-HT_2A- and the inhibitory 5-HT_1A- and ɑ₂-receptors. MA-evoked increases in c-fos expression in PFC regions are due to the activation of diverse monoaminergic receptors through increased synaptic concentrations of 5-HT, NE and/or DA, which may also account for the additive effect of MA on d-fenfluramine-evoked changes in c-fos expression. Our findings suggest potential drug receptor functional interaction during development when used in combination.

Molecular networks underlying cannabinoid signaling in skeletal muscle plasticity

The cannabinoid system is ubiquitously present and is classically considered to engage in neural and immunity processes. Yet, the role of the cannabinoid system in the whole body and tissue metabolism via central and peripheral mechanisms is increasingly recognized. The present review provides insights in (i) how cannabinoid signaling is regulated via receptor-independent and -dependent mechanisms and (ii) how these signaling cascades (might) affect skeletal muscle plasticity and physiology. Receptor-independent mechanisms include endocannabinoid metabolism to eicosanoids and the regulation of ion channels. Alternatively, endocannabinoids can act as ligands for different classic (cannabinoid receptor 1 [CB₁ ], CB₂ ) and/or alternative (e.g., TRPV1, GPR55) cannabinoid receptors with a unique affinity, specificity, and intracellular signaling cascade (often tissue-specific). Antagonism of CB₁ might hold clues to improve oxidative (mitochondrial) metabolism, insulin sensitivity, satellite cell growth, and muscle anabolism, whereas CB₂ agonism might be a promising way to stimulate muscle metabolism and muscle cell growth. Besides, CB₂ ameliorates muscle regeneration via macrophage polarization toward an anti-inflammatory phenotype, induction of MyoD and myogenin expression and antifibrotic mechanisms. Also TRPV1 and GPR55 contribute to the regulation of muscle growth and metabolism. Future studies should reveal how the cannabinoid system can be targeted to improve muscle quantity and/or quality in conditions such as ageing, disease, disuse, and metabolic dysregulation, taking into account challenges that are inherent to modulation of the cannabinoid system, such as central and peripheral side effects.

Cannabis and Cannabis Derivatives for Abdominal Pain Management in Inflammatory Bowel Disease

For centuries, cannabis and its components have been used to manage a wide variety of symptoms associated with many illnesses. Gastrointestinal (GI) diseases are no exception in this regard. Individuals suffering from inflammatory bowel disease (IBD) are among those who have sought out the ameliorating properties of this plant. As legal limitations of its use have eased, interest has grown from both patients and their providers regarding the potential of cannabis to be used in the clinical setting. Similarly, a growing number of animal and human studies have been undertaken to evaluate the impact of cannabis and cannabinoid signaling elements on the natural history of IBD and its associated complications. There is little clinical evidence supporting the ability of cannabis or related products to treat the GI inflammation underlying these disorders. However, 1 recurring theme from both animal and human studies is that these agents have a significant impact on several IBD-related symptoms, including abdominal pain. In this review, we discuss the role of cannabis and cannabinoid signaling in visceral pain perception, what is currently known regarding the efficacy of cannabis and its derivatives for managing pain, related symptoms and inflammation in IBD, and what work remains to effectively utilize cannabis and its derivatives in the clinical setting.

Mechanisms of Nausea and Vomiting: Current Knowledge and Recent Advances in Intracellular Emetic Signaling Systems

Nausea and vomiting are common gastrointestinal complaints that can be triggered by diverse emetic stimuli through central and/or peripheral nervous systems. Both nausea and vomiting are considered as defense mechanisms when threatening toxins/drugs/bacteria/viruses/fungi enter the body either via the enteral (e.g., the gastrointestinal tract) or parenteral routes, including the blood, skin, and respiratory systems. While vomiting is the act of forceful removal of gastrointestinal contents, nausea is believed to be a subjective sensation that is more difficult to study in nonhuman species. In this review, the authors discuss the anatomical structures, neurotransmitters/mediators, and corresponding receptors, as well as intracellular emetic signaling pathways involved in the processes of nausea and vomiting in diverse animal models as well as humans. While blockade of emetic receptors in the prevention of vomiting is fairly well understood, the potential of new classes of antiemetics altering postreceptor signal transduction mechanisms is currently evolving, which is also reviewed. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide potential answers.

Cyclic Vomiting Syndrome in Children

Cyclic Vomiting Syndrome (CVS) is an underdiagnosed episodic syndrome characterized by frequent hospitalizations, multiple comorbidities, and poor quality of life. It is often misdiagnosed due to the unappreciated pattern of recurrence and lack of confirmatory testing. CVS mainly occurs in pre-school or early school-age, but infants and elderly onset have been also described. The etiopathogenesis is largely unknown, but it is likely to be multifactorial. Recent evidence suggests that aberrant brain-gut pathways, mitochondrial enzymopathies, gastrointestinal motility disorders, calcium channel abnormalities, and hyperactivity of the hypothalamic-pituitary-adrenal axis in response to a triggering environmental stimulus are involved. CVS is characterized by acute, stereotyped and recurrent episodes of intense nausea and incoercible vomiting with predictable periodicity and return to baseline health between episodes. A distinction with other differential diagnoses is a challenge for clinicians. Although extensive and invasive investigations should be avoided, baseline testing toward identifying organic causes is recommended in all children with CVS. The management of CVS requires an individually tailored therapy. Management of acute phase is mainly based on supportive and symptomatic care. Early intervention with abortive agents during the brief prodromal phase can be used to attempt to terminate the attack. During the interictal period, non-pharmacologic measures as lifestyle changes and the use of reassurance and anticipatory guidance seem to be effective as a preventive treatment. The indication for prophylactic pharmacotherapy depends on attack intensity and severity, the impairment of the QoL and if attack treatments are ineffective or cause side effects. When children remain refractory to acute or prophylactic treatment, or the episode differs from previous ones, the clinician should consider the possibility of an underlying disease and further mono- or combination therapy and psychotherapy can be guided by accompanying comorbidities and specific sub-phenotype. This review was developed by a joint task force of the Italian Society of Pediatric Gastroenterology Hepatology and Nutrition (SIGENP) and Italian Society of Pediatric Neurology (SINP) to identify relevant current issues and to propose future research directions on pediatric CVS.

Antiemetic Effects of Cannabinoid Agonists in Nonhuman Primates

Attenuating emesis elicited by both disease and medical treatments of disease remains a critical public health challenge. Although cannabinergic medications have been used in certain treatment-resistant populations, Food and Drug Administration-approved cannabinoid antiemetics are associated with undesirable side effects, including cognitive disruption, that limit their prescription. Previous studies have shown that a metabolically stable analog of the endocannabinoid anandamide, methanandamide (mAEA), may produce lesser cognitive disruption than that associated with the primary psychoactive constituent in cannabis, Δ9-tetrahydrocannabinol (Δ9-THC), raising the possibility that endocannabinoids may offer a therapeutic advantage over currently used medications. The present studies were conducted to evaluate this possibility by comparing the antiemetic effects of Δ9-THC (0.032-0.1 mg/kg) and mAEA (3.2-10.0 mg/kg) against nicotine- and lithium chloride (LiCl)-induced emesis and prodromal hypersalivation in squirrel monkeys. Pretreatment with 0.1 mg/kg Δ9-THC blocked nicotine-induced emesis and reduced hypersalivation in all subjects and blocked LiCl-induced emesis and reduced hypersalivation in three of four subjects. Pretreatment with 10 mg/kg mAEA blocked nicotine-induced emesis in three of four subjects and LiCl-induced emesis in one of four subjects and reduced both nicotine- and LiCl-induced hypersalivation. Antiemetic effects of Δ9-THC and mAEA were reversed by rimonabant pretreatment, providing verification of cannabinoid receptor type 1 mediation. These studies systematically demonstrate for the first time the antiemetic effects of cannabinoid agonists in nonhuman primates. Importantly, although Δ9-THC produced superior antiemetic effects, the milder cognitive effects of mAEA demonstrated in previous studies suggest that it may provide a favorable treatment option under clinical circumstances in which antiemetic efficacy must be balanced against side effect liability. SIGNIFICANCE STATEMENT: Emesis has significant evolutionary value as a defense mechanism against ingested toxins; however, it is also one of the most common adverse symptoms associated with both disease and medical treatments of disease. The development of improved antiemetic pharmacotherapies has been impeded by a paucity of animal models. The present studies systematically demonstrate for the first time the antiemetic effects of the phytocannabinoid Δ9-tetrahydrocannabinol and endocannabinoid analog methanandamide in nonhuman primates.

Neuroprotective constituents from the aerial parts of Cannabis sativa L. subsp. sativa

Five new compounds including three new cannabinoids, cannabisativas A-C (1-3), two new phenolic acids, (7Z,9Z)-cannabiphenolic acid A (4) and (8S,9Z)-cannabiphenolic acid B (5), together with twelve known compounds (6-17), were isolated from the aerial parts of Cannabis sativa L. subsp. sativa. The structures of 1-5 were established on the basis of extensive 1D, 2D NMR and HRESIMS analysis. The absolute configurations were determined by comparison between their experimental and calculated spectra of electronic circular dichroism (ECD) or the modified Mosher's method. The neuroprotective effects of the compounds 1-17 were evaluated on PC 12 cells. Compounds 12, 13 and 15 showed potential protective effects against H2O2-induced damage.

Δ9-THC and related cannabinoids suppress substance P- induced neurokinin NK1-receptor-mediated vomiting via activation of cannabinoid CB1 receptor

Δ⁹-THC suppresses cisplatin-induced vomiting through activation of cannabinoid CB₁ receptors. Cisplatin-evoked emesis is predominantly due to release of serotonin and substance P (SP) in the gut and the brainstem which subsequently stimulate their corresponding 5-HT₃-and neurokinin NK₁-receptors to induce vomiting. Δ⁹-THC can inhibit vomiting caused either by the serotonin precursor 5-HTP, or the 5-HT₃ receptor selective agonist, 2-methyserotonin. In the current study, we explored whether Δ⁹-THC and related CB₁/CB₂ receptor agonists (WIN55,212-2 and CP55,940) inhibit vomiting evoked by SP (50 mg/kg, i.p.) or the NK₁ receptor selective agonist GR73632 (5 mg/kg, i.p.). Behavioral methods were employed to determine the antiemetic efficacy of cannabinoids in least shrews. Our results showed that administration of varying doses of Δ⁹-THC (i.p. or s.c.), WIN55,212-2 (i.p.), or CP55,940 (i.p.) caused significant suppression of SP-evoked vomiting in a dose-dependent manner. When tested against GR73632, Δ⁹-THC also dose-dependently reduced the evoked emesis. The antiemetic effect of Δ⁹-THC against SP-induced vomiting was prevented by low non-emetic doses of the CB₁ receptor inverse-agonist/antagonist SR141716A (<10 mg/kg). We also found that the NK₁ receptor antagonist netupitant can significantly suppress vomiting caused by a large emetic dose of SR141716A (20 mg/kg). In sum, Δ⁹-THC and related cannabinoids suppress vomiting evoked by the nonselective (SP) and selective (GR73632) neurokinin NK₁ receptor agonists via stimulation of cannabinoid CB₁ receptors.

Suppression of Cisplatin-Induced Vomiting by Cannabis sativa in Pigeons: Neurochemical Evidences

Cannabis sativa (CS, family Cannabinaceae) has been reported for its anti-emetic activity against cancer chemotherapy-induced emesis in animal models and in clinics. The current study was designed to investigate CS for potential effectiveness to attenuate cisplatin-induced vomiting in healthy pigeons and to study the impact on neurotransmitters involved centrally and peripherally in the act of vomiting. High-performance liquid chromatography system coupled with electrochemical detector was used for the quantification of neurotransmitters 5-hydroxytryptamine (5HT), dopamine (DA) and their metabolites; Di-hydroxy Phenyl Acetic acid (Dopac), Homovanillic acid (HVA), and 5-hydroxy indole acetic acid (5HIAA) centrally in specific brain areas (area postrema and brain stem) while, peripherally in small intestine. Cisplatin (7 mg/kg i.v.) induce emesis without lethality across the 24 h observation period. CS hexane fraction (CS-HexFr; 10 mg/kg) attenuated cisplatin-induced emesis ∼ 65.85% (P < 0.05); the reference anti-emetic drug, metoclopramide (MCP; 30 mg/kg), produced ∼43.90% reduction (P < 0.05). At acute time point (3^rd h), CS-HexFr decreased (P < 0.001) the concentration of 5HT and 5HIAA in the area postrema, brain stem and intestine, while at 18^th h (delayed time point) CS-HexFr attenuated (P < 0.001) the upsurge of 5HT caused by cisplatin in the brain stem and intestine and dopamine in the area postrema. CS-HexFr treatment alone did not alter the basal neurotransmitters and their metabolites in the brain areas and intestine except 5HIAA and HVA, which were decreased significantly. In conclusion the anti-emetic effect of CS-HexFr is mediated by anti-serotonergic and anti-dopaminergic components in a blended manner at the two different time points, i.e., 3^rd and 18^th h in pigeons.

A case of pancreatic cancer with severe vomiting treated by endoscopic ultrasound-guided celiac ganglia neurolysis

A 50-year-old man with advanced pancreatic cancer was admitted for intractable severe vomiting 5-6 times a day, continuing over a week. He had been treated for advanced pancreatic cancer with chemotherapy for 6 months, and had undergone self-expandable metalic stent placement for obstructive jaundice due to the pancreatic cancer 4 months before admission. No abnormal findings suggesting gastrointestinal obstruction or brain metastasis were revealed on diagnostic imaging. We performed endoscopic ultrasound-guided celiac ganglia neurolysis twice by injecting ethanol into the celiac ganglion. After the treatments, the vomiting disappeared, and his eating habits gradually returned to normal. The patient died 7 months after treatment due to the advanced pancreatic cancer without recurrence of the vomiting.

Can You Pass the Acid Test? Critical Review and Novel Therapeutic Perspectives of Δ9-Tetrahydrocannabinolic Acid A

Δ⁹-tetrahydrocannabinolic acid A (THCA-A) is the acidic precursor of Δ⁹-tetrahydrocannabinol (THC), the main psychoactive compound found in Cannabis sativa. THCA-A is biosynthesized and accumulated in glandular trichomes present on flowers and leaves, where it serves protective functions and can represent up to 90% of the total THC contained in the plant. THCA-A slowly decarboxylates to form THC during storage and fermentation and can further degrade to cannabinol. Decarboxylation also occurs rapidly during baking of edibles, smoking, or vaporizing, the most common ways in which the general population consumes Cannabis. Contrary to THC, THCA-A does not elicit psychoactive effects in humans and, perhaps for this reason, its pharmacological value is often neglected. In fact, many studies use the term “THCA” to refer indistinctly to several acid derivatives of THC. Despite this perception, many in vitro studies seem to indicate that THCA-A interacts with a number of molecular targets and displays a robust pharmacological profile that includes potential anti-inflammatory, immunomodulatory, neuroprotective, and antineoplastic properties. Moreover, the few in vivo studies performed with THCA-A indicate that this compound exerts pharmacological actions in rodents, likely by engaging type-1 cannabinoid (CB1) receptors. Although these findings may seem counterintuitive due to the lack of cannabinoid-related psychoactivity, a careful perusal of the available literature yields a plausible explanation to this conundrum and points toward novel therapeutic perspectives for raw, unheated Cannabis preparations in humans.

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.

Role of central vagal 5-HT3 receptors in gastrointestinal physiology and pathophysiology

Vagal neurocircuits are vitally important in the co-ordination and modulation of GI reflexes and homeostatic functions. 5-hydroxytryptamine (5-HT; serotonin) is critically important in the regulation of several of these autonomic gastrointestinal (GI) functions including motility, secretion and visceral sensitivity. While several 5-HT receptors are involved in these physiological responses, the ligand-gated 5-HT3 receptor appears intimately involved in gut-brain signaling, particularly via the afferent (sensory) vagus nerve. 5-HT is released from enterochromaffin cells in response to mechanical or chemical stimulation of the GI tract which leads to activation of 5-HT3 receptors on the terminals of vagal afferents. 5-HT3 receptors are also present on the soma of vagal afferent neurons, including GI vagal afferent neurons, where they can be activated by circulating 5-HT. The central terminals of vagal afferents also exhibit 5-HT3 receptors that function to increase glutamatergic synaptic transmission to second order neurons of the nucleus tractus solitarius within the brainstem. While activation of central brainstem 5-HT3 receptors modulates visceral functions, it is still unclear whether central vagal neurons, i.e., nucleus of the tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMV) neurons themselves also display functional 5-HT3 receptors. Thus, activation of 5-HT3 receptors may modulate the excitability and activity of gastrointestinal vagal afferents at multiple sites and may be involved in several physiological and pathophysiological conditions, including distention- and chemical-evoked vagal reflexes, nausea, and vomiting, as well as visceral hypersensitivity.

Isolation and Pharmacological Evaluation of Minor Cannabinoids from High-Potency Cannabis sativa

Seven new naturally occurring hydroxylated cannabinoids (1-7), along with the known cannabiripsol (8), have been isolated from the aerial parts of high-potency Cannabis sativa. The structures of the new compounds were determined by 1D and 2D NMR spectroscopic analysis, GC-MS, and HRESIMS as 8α-hydroxy-Δ(9)-tetrahydrocannabinol (1), 8β-hydroxy-Δ(9)-tetrahydrocannabinol (2), 10α-hydroxy-Δ(8)-tetrahydrocannabinol (3), 10β-hydroxy-Δ(8)-tetrahydrocannabinol (4), 10α-hydroxy-Δ(9,11)-hexahydrocannabinol (5), 9β,10β-epoxyhexahydrocannabinol (6), and 11-acetoxy-Δ(9)-tetrahydrocannabinolic acid A (7). The binding affinity of isolated compounds 1-8, Δ(9)-tetrahydrocannabinol, and Δ(8)-tetrahydrocannabinol toward CB1 and CB2 receptors as well as their behavioral effects in a mouse tetrad assay were studied. The results indicated that compound 3, with the highest affinity to the CB1 receptors, exerted the most potent cannabimimetic-like actions in the tetrad assay, while compound 4 showed partial cannabimimetic actions. Compound 2, on the other hand, displayed a dose-dependent hypolocomotive effect only.

L-type calcium channels contribute to 5-HT3-receptor-evoked CaMKIIα and ERK activation and induction of emesis in the least shrew (Cryptotis parva)

Activation of serotonergic 5-HT3 receptors by its selective agonist 2-methyl serotonin (2-Me-5-HT) induces vomiting, which is sensitive to selective antagonists of both 5-HT3 receptors (palonosetron) and L-type calcium channels (LTCC) (amlodipine or nifedipine). Previously we demonstrated that 5-HT3 receptor activation also causes increases in a palonosetron-sensitive manner in: i) intracellular Ca(2+) concentration, ii) attachment of calmodulin (CaM) to 5-HT3 receptor, and iii) phosphorylation of Ca(2+)/calmodulin-dependent protein kinase IIα (CaMKIIα) and extracellular-signal-regulated kinase 1/2 (ERK1/2). Here, we investigate the role of the short-acting LTCC blocker nifedipine on 2-Me-5-HT-evoked intracellular Ca(2+) increase and on downstream intracellular emetic signaling, which have been shown to be coupled with 2-Me-5-HT׳s emetic effects in the least shrew. Using the cell-permeant Ca(2+) indicator fluo-4 AM, here we present evidence for the contribution of Ca(2+) influx through LTCCs (sensitive to nifedipine) in 2-Me-5-HT (1µM) -evoked rise in cytosolic Ca(2+) levels in least shrew brainstem slices. Nifedipine pretreatment (10mg/kg, s.c.) also suppressed 2-Me-5-HT-evoked interaction of 5-HT3 receptors with CaM as well as phosphorylation of CaMKIIα and ERK1/2 in the least shrew brainstem, and 5-HT3 receptors -CaM colocalization in jejunum of the small intestine. In vitro exposure of isolated enterochromaffin cells of the small intestine to 2-Me-5-HT (1µM) caused CaMKIIα phosphorylation, which was also abrogated by nifedipine pretreatment (0.1µM). In addition, pretreatment with the CaMKII inhibitor KN62 (10mg/kg, i.p.) suppressed emesis and also the activation of CaMKIIα, and ERK in brainstem caused by 2-Me-5-HT (5mg/kg, i.p.). This study provides further mechanistic explanation for our published findings that nifedipine can dose-dependently protect shrews from 2-Me-5-HT-induced vomiting.

Mechanism of gastrointestinal abnormal motor activity induced by cisplatin in conscious dogs

AIM: To investigate whether 5-hydroxytryptamine (serotonin; 5-HT) is involved in mediating abnormal motor activity in dogs after cisplatin administration.

METHODS: After the dogs had been given a 2-wk recovery period, all of them were administered cisplatin, and the motor activity was recorded using strain gauge force transducers. Blood and intestinal fluid samples were collected to measure 5-HT for 24 h. To determine whether 5-HT in plasma or that in intestinal fluids is more closely related to abnormal motor activity we injected 5-HT into the bloodstream and the intestinal tract of the dogs.

RESULTS: Cisplatin given intravenously produced abnormal motor activity that lasted up to 5 h. From 3 to 4 h after cisplatin administration, normal intact dogs exhibited retropropagation of motor activity accompanied by emesis. The concentration of 5-HT in plasma reached the peak at 4 h, and that in intestinal fluids reached the peak at 3 h. In normal intact dogs with resection of the vagus nerve that were administered kytril, cisplatin given intravenously did not produce abnormal motor activity. Intestinal serotonin administration did not produce abnormal motor activity, but intravenous serotonin administration did.

CONCLUSION: After the intravenous administration of cisplatin, abnormal motor activity was produced in the involved vagus nerve and in the involved serotonergic neurons via another pathway. This study was the first to determine the relationship between 5-HT and emesis-induced motor activity.

Cannabinoid type 1 and type 2 receptor antagonists prevent attenuation of serotonin-induced reflex apneas by dronabinol in Sprague-Dawley rats

The prevalence of obstructive sleep apnea (OSA) in Americans is 9% and increasing. Increased afferent vagal activation may predispose to OSA by reducing upper airway muscle activation/patency and disrupting respiratory rhythmogenesis. Vagal afferent neurons are inhibited by cannabinoid type 1 (CB₁) or cannabinoid type 2 (CB₂) receptors in animal models of vagally-mediated behaviors. Injections of dronabinol, a non-selective CB₁/CB₂ receptor agonist, into the nodose ganglia reduced serotonin (5-HT)-induced reflex apneas. It is unknown what role CB₁ and/or CB₂ receptors play in reflex apnea. Here, to determine the independent and combined effects of activating CB₁ and/or CB₂ receptors on dronabinol’s attenuating effect, rats were pre-treated with CB₁ (AM251) and/or CB₂ (AM630) receptor antagonists. Adult male Sprague-Dawley rats were anesthetized, instrumented with bilateral electrodes to monitor genioglossus electromyogram (EMGgg) and a piezoelectric strain gauge to monitor respiratory pattern. Following intraperitoneal treatment with AM251 and/or AM630, or with vehicle, serotonin was intravenously infused into a femoral vein to induce reflex apnea. After baseline recordings, the nodose ganglia were exposed and 5-HT-induced reflex apneas were again recorded to confirm that the nerves remained functionally intact. Dronabinol was injected into each nodose ganglion and 5-HT infusion was repeated. Prior to dronabinol injection, there were no significant differences in 5-HT-induced reflex apneas or phasic and tonic EMGgg before or after surgery in the CB₁, CB₂, combined CB₁/CB₂ antagonist, and vehicle groups. In the vehicle group, dronabinol injections reduced 5-HT-induced reflex apnea duration. In contrast, dronabinol injections into nodose ganglia of the CB₁, CB₂, and combined CB₁/CB₂ groups did not attenuate 5-HT-induced reflex apnea duration. However, the CB₁ and CB₂ antagonists had no effect on dronabinol’s ability to increase phasic EMGgg. These findings underscore the therapeutic potential of dronabinol in the treatment of OSA and implicate participation of both cannabinoid receptors in dronabinol’s apnea suppression effect.

Broad-spectrum antiemetic potential of the L-type calcium channel antagonist nifedipine and evidence for its additive antiemetic interaction with the 5-HT(3) receptor antagonist palonosetron in the least shrew (Cryptotis parva)

Cisplatin-like chemotherapeutics cause vomiting via release of multiple neurotransmitters (dopamine, serotonin (5-HT), or substance P (SP)) from the gastrointestinal enterochromaffin cells and/or the brainstem via a calcium dependent process. Diverse channels in the plasma membrane allow extracellular Ca(2+) entry into cells for the transmitter release process. Agonists of 5-HT3 receptors increase calcium influx through both 5-HT3 receptors and L-type Ca(2+) channels. We envisaged that L-type calcium agonists such as FPL 64176 should cause vomiting and corresponding antagonists such as nifedipine would behave as broad-spectrum antiemetics. Administration of FPL 64176 did cause vomiting in the least shrew in a dose-dependent fashion. Nifedipine and the 5-HT3 receptor antagonist palonosetron, potently suppressed FPL 64176-induced vomiting, while a combination of ineffective doses of these antagonists was more efficacious. Subsequently, we investigated the broad-spectrum antiemetic potential of nifedipine against diverse emetogens including agonists of serotonergic 5-HT3- (e.g. 5-HT or 2-Me-5-HT), SP tachykinin NK1- (GR73632), dopamine D2- (apomorphine or quinpirole), and cholinergic M1- (McN-A-343) receptors, as well as the non-specific emetogen, cisplatin. Nifedipine by itself suppressed vomiting in a potent and dose-dependent manner caused by the above emetogens except cisplatin. Moreover, low doses of nifedipine potentiated the antiemetic efficacy of non-effective or semi-effective doses of palonosetron against vomiting caused by either 2-Me-5-HT or cisplatin. Thus, our findings demonstrate that activation of L-type calcium channels causes vomiting, whereas blockade of these ion channels by nifedipine-like antagonists not only provides broad-spectrum antiemetic activity but can also potentiate the antiemetic efficacy of well-established antiemetics such as palonosetron. L-type calcium channel antagonists should also provide antiemetic activity against drug-induced vomiting as well as other emetogens including bacterial and viral proteins.

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.

Serotonin 5-HT3 receptor-mediated vomiting occurs via the activation of Ca2+/CaMKII-dependent ERK1/2 signaling in the least shrew (Cryptotis parva)

Stimulation of 5-HT₃ receptors (5-HT₃Rs) by 2-methylserotonin (2-Me-5-HT), a selective 5-HT₃ receptor agonist, can induce vomiting. However, downstream signaling pathways for the induced emesis remain unknown. The 5-HT₃R channel has high permeability to extracellular calcium (Ca²⁺) and upon stimulation allows increased Ca²⁺ influx. We examined the contribution of Ca²⁺/calmodulin-dependent protein kinase IIα (Ca²⁺/CaMKIIα), interaction of 5-HT₃R with calmodulin, and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling to 2-Me-5-HT-induced emesis in the least shrew. Using fluo-4 AM dye, we found that 2-Me-5-HT augments intracellular Ca²⁺ levels in brainstem slices and that the selective 5-HT₃R antagonist palonosetron, can abolish the induced Ca²⁺ signaling. Pre-treatment of shrews with either: i) amlodipine, an antagonist of L-type Ca²⁺ channels present on the cell membrane; ii) dantrolene, an inhibitor of ryanodine receptors (RyRs) Ca²⁺-release channels located on the endoplasmic reticulum (ER); iii) a combination of their less-effective doses; or iv) inhibitors of CaMKII (KN93) and ERK1/2 (PD98059); dose-dependently suppressed emesis caused by 2-Me-5-HT. Administration of 2-Me-5-HT also significantly: i) enhanced the interaction of 5-HT₃R with calmodulin in the brainstem as revealed by immunoprecipitation, as well as their colocalization in the area postrema (brainstem) and small intestine by immunohistochemistry; and ii) activated CaMKIIα in brainstem and in isolated enterochromaffin cells of the small intestine as shown by Western blot and immunocytochemistry. These effects were suppressed by palonosetron. 2-Me-5-HT also activated ERK1/2 in brainstem, which was abrogated by palonosetron, KN93, PD98059, amlodipine, dantrolene, or a combination of amlodipine plus dantrolene. However, blockade of ER inositol-1, 4, 5-triphosphate receptors by 2-APB, had no significant effect on the discussed behavioral and biochemical parameters. This study demonstrates that Ca²⁺ mobilization via extracellular Ca²⁺ influx through 5-HT₃Rs/L-type Ca²⁺ channels, and intracellular Ca²⁺ release via RyRs on ER, initiate Ca²⁺-dependent sequential activation of CaMKIIα and ERK1/2, which contribute to the 5-HT₃R-mediated, 2-Me-5-HT-evoked emesis.

Looking beyond 5-HT(3) receptors: a review of the wider role of serotonin in the pharmacology of nausea and vomiting

The concept that 5-hydroxytryptamine (5-HT; serotonin) is involved in the emetic reflex was revealed using drugs that interfere with its synthesis, storage, release and metabolism ahead of the discovery of selective tools to modulate specific subtypes of receptors. This review comprehensively examines the fundamental role of serotonin in emesis control and highlights data indicating association of 5-HT1-4 receptors in the emetic reflex, whilst leaving open the possibility that 5-HT5-7 receptors may also be involved. The fact that each receptor subtype may mediate both emetic and anti-emetic effects is discussed in detail for the first time. These discussions are made in light of known species differences in emesis control, which has sometimes affected the perception of the translational value of data in regard to the development of novel anti-emetic for use in man.

The role of vagal neurocircuits in the regulation of nausea and vomiting

Nausea and vomiting are among the most frequently occurring symptoms observed by clinicians. While advances have been made in understanding both the physiological as well as the neurophysiological pathways involved in nausea and vomiting, the final common pathway(s) for emesis have yet to be defined. Regardless of the difficulties in elucidating the precise neurocircuitry involved in nausea and vomiting, it has been accepted for over a century that the locus for these neurocircuits encompasses several structures within the medullary reticular formation of the hindbrain and that the role of vagal neurocircuits in particular are of critical importance. The afferent vagus nerve is responsible for relaying a vast amount of sensory information from thoracic and abdominal organs to the central nervous system. Neurons within the nucleus of the tractus solitarius not only receive these peripheral sensory inputs but have direct or indirect connections with several other hindbrain, midbrain and forebrain structures responsible for the co-ordination of the multiple organ systems. The efferent vagus nerve relays the integrated and co-ordinated output response to several peripheral organs responsible for emesis. The important role of both sensory and motor vagus nerves, and the available nature of peripheral vagal afferent and efferent nerve terminals, provides extensive and readily accessible targets for the development of drugs to combat nausea and vomiting.

Additive antiemetic efficacy of low-doses of the cannabinoid CB(1/2) receptor agonist Δ(9)-THC with ultralow-doses of the vanilloid TRPV1 receptor agonist resiniferatoxin in the least shrew (Cryptotis parva)

Previous studies have shown that cannabinoid CB1/2 and vanilloid TRPV1 agonists (delta-9-tetrahydrocannabinol (Δ(9)-THC) and resiniferatoxin (RTX), respectively) can attenuate the emetic effects of chemotherapeutic agents such as cisplatin. In this study we used the least shrew to demonstrate whether combinations of varying doses of Δ(9)-THC with resiniferatoxin can produce additive antiemetic efficacy against cisplatin-induced vomiting. RTX by itself caused vomiting in a bell-shaped dose-dependent manner with maximal vomiting at 18 μg/kg when administered subcutaneously (s.c.) but not intraperitoneally (i.p.). Δ(9)-THC up to 10 mg/kg provides only 80% protection of least shrews from cisplatin-induced emesis with an ID50 of 0.3-1.8 mg/kg. Combinations of 1 or 5 μg/kg RTX with varying doses of Δ(9)-THC completely suppressed both the frequency and the percentage of shrews vomiting with ID50 dose values 5-50 times lower than Δ(9)-THC doses tested alone against cisplatin. A less potent TRPV1 agonist, capsaicin, by itself did not cause emesis (i.p. or s.c.), but it did significantly reduce vomiting induced by cisplatin given after 30 min but not at 2 h. The TRPV1-receptor antagonist, ruthenium red, attenuated cisplatin-induced emesis at 5mg/kg; however, another TRPV1-receptor antagonist, capsazepine, did not. In summary, we present evidence that combination of CB1/2 and TRPV1 agonists have the capacity to completely abolish cisplatin-induced emesis at doses that are ineffective when used individually.

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.

Intranodose ganglion injections of dronabinol attenuate serotonin-induced apnea in Sprague-Dawley rat

Obstructive sleep apnea represents a significant public health concern. Afferent vagal activation is implicated in increased apnea susceptibility by reducing upper airway muscle tone via activation of serotonin receptors in the nodose ganglia. Previous investigations demonstrated that systemically administered cannabinoids can be used therapeutically to decrease the apnea/hypopnea index in rats and in humans. However, cannabinoids have effects on both the central and peripheral nervous systems, and the exact mechanism of decreased apnea/hypopnea index with cannabinoids is unknown. Here, we hypothesized that intranodose ganglion injections of a cannabinoid will attenuate 5-HT-induced reflex apnea and increase upper airway muscle tone. We show that dronabinol injected locally into the nodose ganglia suppresses 5-HT-induced reflex apnea, and increases phasic, but not tonic, activation of the genioglossus. These data support the view that dronabinol stabilizes respiratory pattern and augments upper airway muscles by acting at the nodose ganglia. These findings underscore a therapeutic potential of dronabinol for the treatment of obstructive sleep apnea.

Animal models of the serotonin syndrome: a systematic review

The serotonin syndrome (SS) is a potentially life-threatening disorder in humans which is induced by ingestion of an overdose or by combination of two or more serotonin (5-HT)-enhancing drugs. In animals, acute administration of direct and indirect 5-HT agonists also leads to a set of behavioral and autonomic responses. In the current review, we provide an overview of the existing versions of the animal model of the SS. With a focus on studies in rats and mice, we analyze the frequency of behavioral and autonomic responses following administration of 5-HT-enhancing drugs and direct 5-HT agonists administered alone or in combination, and we briefly discuss the receptor mediation of these responses. Considering species differences, we identify a distinct set of behavioral and autonomic responses that are consistently observed following administration of direct and indirect 5-HT agonists. Finally, we discuss the importance of a standardized assessment of SS responses in rodents and the utility of animal models of the SS in translational studies, and provide suggestions for future research.

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.

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.

Cisplatin causes over-expression of tachykinin NK(1) receptors and increases ERK1/2- and PKA- phosphorylation during peak immediate- and delayed-phase emesis in the least shrew (Cryptotis parva) brainstem

Scant information is available regarding the effects of cisplatin on the expression profile of tachykinin NK(1) receptors and downstream signaling during cisplatin-induced emesis. Cisplatin causes peak early- and delayed-phase emesis in the least shrew at 1-2 and 33 h post-injection. To investigate the expression profile of NK(1) receptor during both emetic phases, we cloned the cDNA corresponding to a ~700 base pairs of mRNA flanked by two stretches of nucleotides conserved among different species and demonstrated that the shrew NK(1) receptor nucleotide sequence shares ~90% sequence identity with the human NK(1) receptor. Of the 12 time-points tested, significant increases in expression levels of NK(1) receptor mRNA in the shrew brainstem occurred at 2 and 28 h post-cisplatin injection, whereas intestinal NK(1) receptor mRNA was increased at 28 h. Shrew brainstem and intestinal substance P mRNA levels also tended to increase during the two phases. Furthermore, expression levels of NK(1) receptor protein were significantly increased in the brainstem at 2, 8, and 33 h post-cisplatin. No change in brainstem 5-HT(3) receptor protein expression was observed. The temporal enhancements in NK(1) receptor protein expression were mirrored by significant increases in the phosphorylation status of the brainstem ERK1/2 at 2, 8, and 33 h post-cisplatin. Phosphorylation of PKA significantly increased at 33rd and 40th hour. Our results indicate associations between cisplatin's peak immediate- and delayed-phase vomiting frequency with increased: (1) expression levels of NK(1) receptor mRNA and its protein level, and (2) downstream NK(1) receptor-mediated phosphorylation of ERK1/2 and PKA signaling.

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.

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.

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.

Cannabinoid-Induced Hyperemesis: A Conundrum-From Clinical Recognition to Basic Science Mechanisms

Cannabinoids are used clinically on a subacute basis as prophylactic agonist antiemetics for the prevention of nausea and vomiting caused by chemotherapeutics. Cannabinoids prevent vomiting by inhibition of release of emetic neurotransmitters via stimulation of presynaptic cannabinoid CB₁ receptors. Cannabis-induced hyperemesis is a recently recognized syndrome associated with chronic cannabis use. It is characterized by repeated cyclical vomiting and learned compulsive hot water bathing behavior. Although considered rare, recent international publications of numerous case reports suggest the contrary. The syndrome appears to be a paradox and the pathophysiological mechanism(s) underlying the induced vomiting remains unknown. Although some traditional hypotheses have already been proposed, the present review critically explores the basic science of these explanations in the clinical setting and provides more current mechanisms for the induced hyperemesis. These encompass: (1) pharmacokinetic factors such as long half-life, chronic exposure, lipid solubility, individual variation in metabolism/excretion leading to accumulation of emetogenic cannabinoid metabolites, and/or cannabinoid withdrawal; and (2) pharmacodynamic factors including switching of the efficacy of Δ⁸-THC from partial agonist to antagonist, differential interaction of Δ⁸-THC with Gs and Gi signal transduction proteins, CB₁ receptor desensitization or downregulation, alterations in tissue concentrations of endocannabinoid agonists/inverse agonists, Δ⁸-THC-induced mobilization of emetogenic metabolites of the arachidonic acid cascade, brainstem versus enteric actions of Δ⁸-THC, and/or hypothermic versus hyperthermic actions of Δ⁸-THC. In addition, human and animal findings suggest that chronic exposure to cannabis may not be a prerequisite for the induction of vomiting but is required for the intensity of emesis.

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.

Receptor-selective agonists induce emesis and Fos expression in the brain and enteric nervous system of the least shrew (Cryptotis parva)

Research on the mechanisms of emesis has implicated multiple neurotransmitters via both central (dorsal vagal complex) and peripheral (enteric neurons and enterochromaffin cells) anatomical substrates. Taking advantage of advances in receptor-specific agonists, and utilizing Fos expression as a functional activity marker, this study demonstrates a strong, but incomplete, overlap in anatomical substrates for a variety of emetogens. We used cisplatin and specific agonists to 5-HT(3) serotonergic, D(2)/D(3) dopaminergic, and NK(1) tachykininergic receptors to induce vomiting in the least shrew (Cryptotis parva), and quantified the resulting Fos expression. The least shrew is a small mammal whose responses to emetic challenges are very similar to its human counterparts. In all cases, the enteric nervous system, nucleus of the solitary tract, and dorsal motor nucleus of the vagus demonstrated significantly increased Fos immunoreactivity (Fos-IR). However, Fos-IR induction was notably absent from the area postrema following the dopaminergic and NK(1) receptor-specific agents. Two brain nuclei not usually discussed regarding emesis, the dorsal raphe nucleus and paraventricular thalamic nucleus, also demonstrated increased emesis-related Fos-IR. Taken together, these data suggest the dorsal vagal complex is part of a common pathway for a variety of distinct emetogens, but there are central emetic substrates, both medullary and diencephalic, that can be accessed without directly stimulating the area postrema.

Ablation of least shrew central neurokinin NK1 receptors reduces GR73632-induced vomiting

The neurocircuitry mediating the emetic reflex is still incompletely understood, and a key question is the degree to which central and/or peripheral components contribute to the overall vomiting mechanism. Having previously found a significant peripheral component in neurokinin NK-receptor mediated emesis, the authors undertook this study to examine the putative central component. Adult least shrews were injected intracerebroventricularly (icv) with saline or the blood-brain barrier impermeable toxin, stable substance P-saporin (SSP-SAP), which ablates cells expressing NK receptors. After 3 days, shrews were challenged intraperitoneally with the emetogenic NK agonist GR73632 at different doses, and vomiting and scratching behaviors were quantified. Ablation of NK1-bearing cells was verified immunohistochemically. Although SSP-SAP injection reduced emesis at GR73632 doses of 2.5 and 5 mg/kg, no injections completely eliminated emesis. These data demonstrate that there is both a major central nervous system component and a minor peripheral nervous system component to tachykinin-mediated vomiting. Side effects of the current generation of antiemetics could potentially be reduced by improving bioavailability of the drugs in the more potent central nervous system compartment while reducing bioavailability in the less potent peripheral compartment.

Delta 9-tetrahydrocannabinol suppresses vomiting behavior and Fos expression in both acute and delayed phases of cisplatin-induced emesis in the least shrew

Cisplatin chemotherapy frequently causes severe vomiting in two temporally separated clusters of bouts dubbed the acute and delayed phases. Cannabinoids can inhibit the acute phase, albeit through a poorly understood mechanism. We examined the substrates of cannabinoid-mediated inhibition of both the emetic phases via immunolabeling for serotonin, Substance P, cannabinoid receptors 1 and 2 (CB(1), CB(2)), and the neuronal activation marker Fos in the least shrew (Cryptotis parva). Shrews were injected with cisplatin (10mg/kg i.p.), and one of vehicle, Delta(9)-THC, or both Delta(9)-THC and the CB(1) receptor antagonist SR141716A (2mg/kg i.p.), and monitored for vomiting. Delta(9)-THC-pretreatment caused concurrent decreases in the number of shrews expressing vomiting and Fos-immunoreactivity (Fos-IR), effects which were blocked by SR141716A-pretreatment. Acute phase vomiting induced Fos-IR in the solitary tract nucleus (NTS), dorsal motor nucleus of the vagus (DMNX), and area postrema (AP), whereas in the delayed phase Fos-IR was not induced in the AP at all, and was induced at lower levels in the other nuclei when compared to the acute phase. CB(1) receptor-IR in the NTS was dense, punctate labeling indicative of presynaptic elements, which surrounded Fos-expressing NTS neurons. CB(2) receptor-IR was not found in neuronal elements, but in vascular-appearing structures. All areas correlated with serotonin- and Substance P-IR. These results support published acute phase data in other species, and are the first describing Fos-IR following delayed phase emesis. The data suggest overlapping but separate mechanisms are invoked for each phase, which are sensitive to antiemetic effects of Delta(9)-THC mediated by CB(1) receptors.