EFFECTS OF FEEDING CONDITION ON ORALLY DELIVERED ETHANOL AS A REINFORCER FOR RHESUS-MONKEYS

Twenty adult male rhesus monkeys could drink either or both an 8%-ethanol (w/v) solution or water during daily 3-h experimental sessions. Subjects were initially tested under ad lib feeding conditions, having received daily access to large amounts of food for approximately 8 months (Phase 1). The ethanol solution was concurrently available with its water vehicle under fixed-ratio schedules of mouth contacts with a drinking spout in which emission of 8 responses produced a liquid delivery (FR 8). Under these conditions ethanol served as a reinforcer for some subjects-it maintained higher response rates than water-but not for others. In the next experimental condition (Phase 2), subjects were again tested for ethanol self-administration under FR 8 schedules with water concurrently available, but while receiving daily food rations that maintained their body weights at less than what they had been under ad lib feeding conditions. Under these conditions all subjects self-administered ethanol at appreciable levels, but water-maintained responding also was at appreciable levels for some subjects. Increases in ethanol self-administration following institution of the reduced-feeding conditions in Phase 2 generally were inversely related to self-administration levels under the free-feeding conditions of Phase 1 (the greatest proportional increases in ethanol intake occurred with those monkeys that self-administered the least amount of ethanol in Phase 1). In Phase 3, the requirements of the concurrently operating fixed-ratio schedules delivering ethanol and water were increased to 16 responses (FR 16). This operation did not markedly alter the rank order of subjects in the amount of ethanol consumed, but did decrease levels of water-maintained responding in those subjects whose water-maintained responding had been high during Phase 2. The importance of feeding condition as a variable affecting the reinforcing effects of ethanol and of other drugs is discussed.