Functional role of the endocannabinoid system and AMPA/kainate receptors in 5-HT2A receptor-mediated wet dog shakes

These experiments sought to determine the influence of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors and the endocannabinoid system in the functional expression of the serotonin (5-HT) type 2A receptor-mediated wet dog shake response. Male Long-Evans rats were pretreated with either 1 mg/kg i.p. of the 5-HT(2A/2C) receptor antagonist ketanserin; 1, 10 or 30 mg/kg i.p. of the AMPA/kainate antagonist 6,7-dinitroquinnoxaline-2,3-dione (DNQX); 1, 5 or 10 mg/kg i.p. of the endocannabinoid uptake inhibitor AM404; or 1, 5 or 10 mg/kg i.p. of the cannabinoid CB(1) receptor antagonist AM 251 prior to injection of the 5-HT(2A/2C) receptor agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI, 1 mg/kg i.p.). Results demonstrated that 10 mg/kg of AM404 significantly reduced the expression of DOI-induced wet dog shakes, but lower doses were ineffective. Administration of AM251 did not induce wet dog shakes behavior when administered alone, but significantly potentiated DOI-induced wet dog shaking behavior at a dose of 10 mg/kg. Pretreatment with DNQX significantly reduced the expression of DOI-induced wet dog shakes at all doses tested. These data suggest that AMPA/kainate receptors play a role in the mediation of 5-HT(2A) receptor activity, whereas the endocannabinoid system may act as a regulatory buffer system during periods of elevated activity, but not under basal conditions.