Activational role of cannabinoids on movement

Cannabinoid's major effect on movement is hypoactivity. Nevertheless, a bip hasic excitatory/inhibitory effect of cannabinoids on movement has been rep eatedly acknowledged. However, the literature is lacking a detailed descrip tion of such an effect. In this study, we performed a dose-response study o f the effects of hg-tetrahydrocannabinol on movement. Immediately after the administration of vehicle or a dose of Delta(9)-tetrahydrocannabinol (0.2, 0.5, 1, 1.5, 2, 2.5, 3, 4, or 5 mg/kg), the animal was placed in an activi ty monitor and observed for 1 h. Several parameters were recorded. The hori zontal and vertical activities were measured as the number of photobeams br oken between the photocells on the walls of an activity monitor. The number of wet dog shakes, scratches with hindpaw, mouth movements, forepaw flutte rs were also recorded, as was the amount of time in minutes that each subje ct spent grooming. The number of fecal boluses was recorded as an index of autonomic activity. Each animal was subsequently tested for catalepsy in th e bar test. A triphasic effect was observed: low doses of the cannabinoid r eceptor agonist Delta(9)-tetrahydrocannabinol (0.2 mg/kg) decreased locomot or activity while higher doses (1-2 mg/kg) dose-dependently stimulated move ment until catalepsy emerged (2.5 mg/kg) accompanied by decreases in activi ty. (C) 2000 Elsevier Science B.V. All rights reserved.