Effects of marihuana extract on the operant behavior of chimpanzees.

Abstract

Six chimpanzees were trained to panel push under a food reinforcement baseline in which three operant schedules, each associated with a different stimulus, were presented successively. The fixed ratio (FR) reinforcement schedule required the emission of 40 responses for reinforcement. Reinforcement under the differential reinforcement of low rate (DRL) schedule was delivered only when successive responses were spaced by at least 10 sec. During the extinction or time out from positive reinforcement schedule (TO), no responses were reinforced. In Experiment 1, amounts of marihuana extract containing from 0.2 to 4.0 mg/kg (−)-Δ9-trans-tetrahydrocannabinol (Δ9-THC) were orally administered 1 h prior to experimentation. In Experiment 2, 1.0 mg/kg Δ9-THC was orally administered between 1 and 23 h prior to experimental sessions. No disruption of stimulus control or drug effects during TO were observed. Both DRL and FR response suppression occurred at the highest drug dose. Lower Δ9-THC doses produced facilitation of DRL responding up to 12 h following drug administration. Although FR responding was less sensitive, Δ9-THC stimulated FR behavior from 2 to 5 h following drug administration. It was concluded that marihuana has a biphasic effect on food reinforcement schedule controlled operant behavior.