title: Central and peripheral mechanisms contribute to the antiemetic actions of delta-9-tetrahydrocannabinol against 5-hydroxytryptophan-induced emesis.
abstract: Delta-9-tetrahydrocannabinol (delta-9-THC) prevents cisplatin-induced emesis via cannabinoid CB(1) receptors. Whether central and/or peripheral cannabinoid CB(1) receptors account for the antiemetic action(s) of delta-9-THC remains to be investigated. The 5-hydroxytryptamine (5-HT=serotonin) precursor, 5-hydroxytryptophan (5-HTP), is an indirect 5-HT agonist and simultaneously produces the head-twitch response (a centrally mediated serotonin 5-HT(2A) receptor-induced behavior) and emesis (a serotonin 5-HT(3) receptor-induced response, mediated by both peripheral and central mechanisms) in the least shrew (Cryptotis parva). The peripheral amino acid decarboxylase inhibitor, carbidopa, prevents the conversion of 5-HTP to 5-HT in the periphery and elevates 5-HTP levels in the central nervous system (CNS). When administered i.p. alone, a 50 mg/kg dose of 5-HTP failed to induce either behaviour while its 100 mg/kg dose produced robust frequencies of both head-twitch response and emesis. Pretreatment with carbidopa (0, 10, 20 and 40 mg/kg) potentiated the ability of both doses of 5-HTP to produce the head-twitch response in a dose-dependent but bell-shaped manner, with maximal potentiation occurring at 20 mg/kg carbidopa. Carbidopa dose-dependently reduced the frequency of 5-HTP (100 mg/kg)-induced emesis, whereas the 10 mg/kg dose potentiated, and the 20 and 40 mg/kg doses suppressed the frequency of vomits produced by the 50 mg/kg dose of 5-HTP. The peripheral and/or central antiemetic action(s) of delta-9-THC (0, 1, 2.5, 5, 10 and 20 mg/kg) against 5-HTP (100 mg/kg)-induced head-twitch response and emesis were investigated in different groups of carbidopa (0, 10 and 20 mg/kg) pretreated shrews. Irrespective of carbidopa treatment, delta-9-THC attenuated the frequency of 5-HTP-induced head-twitch response in a dose-dependent manner with similar ID(50) values. Although delta-9-THC also reduced the frequency of 5-HTP-induced emesis with similar ID(50s), at the 5 mg/kg delta-9-THC dose however, 5-HTP induced significantly less vomits in the 10 and 20 mg/kg carbidopa-treated groups relative to its 0 mg/kg control group. Moreover, increasing doses of carbidopa significantly shifted the inhibitory dose-response effect of delta-9-THC in protecting shrews from 5-HTP-induced emesis to the left. Relatively, a large dose of delta-9-THC (20 mg/kg) was required to significantly reduce the number of vomits produced by direct acting serotonergic 5-HT(3) receptor agonists, serotonin and 2-methylserotonin. Low doses of delta-9-THC (0.1-1 mg/kg) nearly completely prevented 2-methylserotonin-induced, centrally mediated, head-twitch and ear-scratch responses. The results indicate that delta-9-THC probably acts pre- and postsynaptically to attenuate emesis produced by indirect and direct acting 5-HT(3) receptor agonists via both central and peripheral mechanisms. In addition, delta-9-THC prevents 5-HTP-induced head-twitch and emesis via cannabinoid CB(1) receptors since the CB(1) receptor antagonist, SR 141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide], countered the inhibitory actions of an effective dose of delta-9-THC against both behaviours.
authors.affiliation: Department of Pharmacology, Kirksville College of Osteopathic Medicine, A.T. Still University of Health Sciences, 800 West Jefferson Street, Kirksville, MO 63501, USA. ndarmani@atsu.edu
authors.forename: Nissar A
authors.initials: NA
authors.lastname: Darmani
authors.forename: Jane C
authors.initials: JC
authors.lastname: Johnson
mesh_terms: D006916:5-Hydroxytryptophan / Q000037:antagonists & inhibitors*; D000818:Animals; D000932:Antiemetics / Q000494:pharmacology*; D001522:Behavior, Animal / Q000187:drug effects; D002230:Carbidopa / Q000494:pharmacology; D002490:Central Nervous System / Q000187:drug effects*; D015259:Dopamine Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology*; D004639:Emetics / Q000037:antagonists & inhibitors*; D005260:Female; D008297:Male; D017933:Peripheral Nervous System / Q000187:drug effects*; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors / Q000187:drug effects; D000077285:Rimonabant; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D012788:Shrews / Q000502:physiology*
chemical_list: D000932:Antiemetics; D015259:Dopamine Agents; D004639:Emetics; D010880:Piperidines; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; C045918:2-methyl-5-HT; D013759:Dronabinol; D006916:5-Hydroxytryptophan; D002230:Carbidopa; D000077285:Rimonabant