Abstract

Marijuana and other cannabinoid (CB) compounds are widely used by cocaine users. Preclinical animal studies suggest that these compounds can increase the reinforcing effects of cocaine under some schedules of cocaine self-administration and reinstatement, but not in all cases. To date, no studies have used a food-cocaine concurrent choice procedure, which allows for assessment of drug effects on response allocation, not just changes in cocaine self-administration. The goal of the present study was to examine the effects of compounds differing in their efficacy at the CB receptor (CBR) on cocaine self-administration using a food-drug choice procedure in monkeys. Four adult male rhesus monkeys were trained to self-administer cocaine in the context of an alternative food (1.0-g banana-flavored pellets) reinforcer, such that complete cocaine dose-response curves (0, 0.003-0.1 mg/kg/injection) were determined each session. Monkeys were tested acutely with the CBR full agonist CP 55,940 (0.001-0.01 mg/kg), the CBR partial agonist Δ9-THC (0.03-0.3 mg/kg mg/kg), which is also the primary active ingredient in marijuana, and the CBR antagonist rimonabant (0.3-3.0 mg/kg mg/kg). Cocaine choice increased in a dose-dependent manner. Acute treatment with CP 55,940 decreased cocaine choice, while THC and rimonabant enhanced the reinforcing effects of cocaine. Chronic (7-day) treatment with CP 55,940 resulted in tolerance to the decreases in cocaine choice. These findings with Δ9-THC provide support for a potential mechanism for co-abuse of marijuana and cocaine. Additional research with chronic treatment with full CBR agonists on attenuating the reinforcing strength of cocaine is warranted.