Role of TRPV1 and cannabinoid CB1 receptors in AM 404-evoked hypothermia in rats.

AM 404 inhibits endocannabinoid uptake and enhances the cannabinoid CB(1)-mediated effects of endogenous cannabinoids. Accumulating evidence also suggests that AM 404 acts at sites other than the endocannabinoid system. One site is the transient receptor potential vanilloid 1 cation channel (TRPV1). A useful endpoint for discriminating between TRPV1- or CB(1)-mediated effects of AM 404 is hypothermia. This is because TRPV1 or CB(1) receptor activation produces a significant hypothermia in rats. The present study investigated the effects of AM 404 (1, 5, 10 and 20 mg/kg, i.p.) on body temperature in rats and the involvement of TRPV1 and CB(1) receptors in the effects of AM 404. Doses of 10 and 20 mg/kg of AM 404 produced significant hypothermia. Pre-treatment with capsazepine (30 mg/kg, i.p.) blocked the hypothermia caused by 10 and 20 mg/kg of AM 404. Pre-treatment with SB 366791 (2 mg/kg, i.p.), a new TRPV1 antagonist, also abolished the hypothermia evoked by AM 404 (20 mg/kg, i.p.). In contrast, pre-treatment with SR 141716A (Rimonabant), a CB(1) antagonist, or AA-5-HT, a fatty acid amide hydrolase (FAAH) blocker, did not affect AM 404-evoked hypothermia. The present data demonstrate that AM 404 evokes a significant hypothermia in rats that is dependent on TRPV1 receptor activation.