Effects of Ethanol on Cocaine Self‐administration in Monkeys under a Fixed‐interval Schedule or Food‐Drug Choice Procedure

As many as 90% of cocaine abusers also drink ethanol (EtOH), suggesting that EtOH enhances sensitivity to the reinforcing effects of cocaine. However, little is known about the interaction of these drugs. In the present studies we determined the effects of acute i.v. administration of EtOH (0.5‐2.0 g/kg over 10 minutes) on cocaine self‐adminstraiton using two paradigms in male nonhuman primates. In one set of studies, rhesus monkeys (n=4) self‐administered cocaine (0.003‐0.3 mg/kg/injection) under a 300‐sec fixed‐interval schedule. The second set of studies used a food‐cocaine choice procedure in socailly housed cynomolgus monkeys (n=8) in which a complete dose‐effect curve for cocaine (0.0, 0.003, 0.01, 0.03, 0.1 mg/kg/injection) was generated daily. Use of socially housed monkeys permitted an assessment of the effects of environmental enrichment (in dominant‐ranked monkeys) and chronic social stress (in subordinate‐ranked monkeys) on EtOH/cocaine interactions. In rhesus monkeys, 1.0 g/kg EtOH decreased self‐administration of low cocaine doses but was without effect on self‐administration of higher cocaine doses. In dominant monkeys, 1.5‐2.0 g/kg EtOH increased cocaine choice but no EtOH dose significantly affected cocaine choice in subordinate monkeys. Taken together, the results suggest that acute administraiton of EtOH can potentiate the relative reinforcing effects of low cocaine doses under a food‐cocaine choice procedure, but higher doses are necessary to alter self‐administration under a simple schedule of reinforcement. Surprisingly, conditions modeling social stress (subordination) did not lead to greater sensitivity to EtOH's effects on cocaine reinforcement. Support: DA10584, DA21658.