title: Anxiety does not affect the antinociceptive effect of Delta 9-THC in mice: participation of cannabinoid and opioid receptors.
abstract: Cannabinoid receptor agonists significantly inhibit nociceptive responses in a large number of animal models. The present study examined whether mice displaying different basal levels of anxiety in the plus-maze test of anxiety might differ in terms of responsiveness to the antinociceptive effects of Delta(9)-tetrahydrocannabinol (Delta(9)-THC). Further, the involvement of the cannabinoid and/or opioid receptors in Delta(9)-THC-induced antinociception was investigated by using SR 141716A and naloxone, respectively, cannabinoid and opioid receptor antagonists. Delta(9)-THC-induced antinociception was evaluated in the formalin test that involves a biphasic response with an early and a late phase of high paw-licking activity. This characteristic biphasic response was observed in all control animals selected as "anxious" and "nonanxious." Delta(9)-THC (0.5-5 mg/kg i.p.) caused a dose-dependent antinociceptive effect in both groups of mice during the early and late phases. This response was fully reversed by SR 141716A (1 mg/kg i.p.) and partially reversed by naloxone (2 mg/kg i.p.). These findings suggest that mice selected for differences in anxiety-related behavior show similar responses to the antinociceptive action of Delta(9)-THC and that this action involves predominantly cannabinoid mechanisms.
authors.affiliation: Departamento de Farmacologia, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, R. Ferreira Lima 82, Florianópolis, Brazil. takahashi@farmaco.ufsc.br
authors.forename: Reinaldo N
authors.initials: RN
authors.lastname: Takahashi
authors.forename: Geraldo A
authors.initials: GA
authors.lastname: Ramos
authors.forename: Fabrício L
authors.initials: FL
authors.lastname: Assini
mesh_terms: D000818:Animals; D001007:Anxiety / Q000188:drug therapy / Q000523:psychology; D063387:Cannabinoid Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D013759:Dronabinol / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D051379:Mice; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists; D010147:Pain Measurement / Q000187:drug effects* / Q000379:methods; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043882:Receptors, Cannabinoid / Q000502:physiology*; D011957:Receptors, Opioid / Q000502:physiology*; D000077285:Rimonabant
chemical_list: D063387:Cannabinoid Receptor Antagonists; D009292:Narcotic Antagonists; D010880:Piperidines; D011720:Pyrazoles; D043882:Receptors, Cannabinoid; D011957:Receptors, Opioid; D009270:Naloxone; D013759:Dronabinol; D000077285:Rimonabant