Acute and chronic effects on rats of (−)δ¹-trans-tetrahydrocannabinol on unlearned motor tasks

Abstract

Eighty-eight rats were either injected with. 5 mg/kgδ ¹-THC, 4 mg/kgδ ¹-THC, corresponding volumes of propylene glycol or were handled and/or pierced prior to being tested on five tasks; an open field, rotating rod, balance beam, black-white choice, and swimming. Each task was characterized by being self motivating and requiring only one trial, thus minimizing state-dependent effects. The number of drug administrations preceeding testing was either less than five (acute condition) or more than 25 (chronic condition). Under the acute conditions, doses of 4 mg/kgδ ¹-THC significantly impaired all the measured motor skills, whereas doses of .5 mg/kg had little effect except on the open field. However, those rats receiving 25 administrations of 4 mg/kg were equal or superior to control groups in the motor tasks and both the high and low chronicδ ¹-THC groups demonstrated a shift of preference from black to white. General reactivity, as measured by defecation, speed of swimming, open field behaviour and aggressiveness was increased following multiple injections.