Effect of chronic binge-like ethanol consumption on subsequent cocaine reinforcement in rhesus monkeys

Abstract

BackgroundAlthough most individuals with cocaine use disorder also abuse alcohol, little is known about the behavioral and pharmacological mechanisms that promote co-abuse. For example, it is unclear whether prior experience with alcohol renders individuals more sensitive to cocaine when it is subsequently experienced. MethodsThis study examined the effects of chronic ethanol consumption on subsequent cocaine reinforcement in rhesus monkeys. Six monkeys consumed 2.0 g/kg ethanol in a binge-drinking paradigm and 6 monkeys drank a non-alcoholic solution 5 days per week. After 9 months, each monkey’s sensitivity to acquiring cocaine self-administration was determined. Monkeys performed an operant response resulting in food pellet delivery under a fixed-ratio 30 schedule of reinforcement. Saline, then ascending doses of cocaine, were substituted for food pellets until a cocaine dose was reached at which the number of cocaine injections delivered differed significantly from saline injections delivered. Following acquisition, a complete cocaine dose-effect curve was generated to determine whether ethanol consumption altered the reinforcing potency of cocaine determined by calculating the ED50 of the ascending limb of each subject’s curve. ResultsAlthough individual variability was observed, the cocaine dose which initially served as a reinforcer did not differ between ethanol-drinking and control groups and, within the ethanol-drinking group, was not related to the amount of ethanol consumed. Moreover, the reinforcing potency of cocaine did not differ between groups. ConclusionTaken together, the data suggest that a history of binge-like alcohol consumption does not affect sensitivity to cocaine when it is subsequently first experienced.