ETHANOL AS AN ORAL REINFORCER IN NORMAL-WEIGHT RHESUS-MONKEYS - DOSE-RESPONSE FUNCTIONS

Responding maintained by orally delivered ethanol was studied in three adult male rhesus monkeys with no previous drug-taking histories. The subjects had continuous access to water throughout the study and were fed sufficient food to maintain a positive caloric balance. During da ily 3-h experimental sessions, ethanol solution and water were concurr ently available under fixed-ratio reinforcement schedules from two liq uid delivery systems that were mounted symmetrically on the side of th e monkeys' cages. The positions of the ethanol and water alternated da ily. A range of ethanol doses (1%, 2%, 4%, 5.7%, 8%, 11.3%, 16%, 22.7, and 32% w/v) was tested in ascending and descending order. Changes in concentration were made after six consecutive stable sessions. Genera lly, the number of ethanol deliveries increased and then decreased as the ethanol concentration was raised (an inverted U-shaped function). For two of the monkeys, ethanol deliveries exceeded water deliveries a t concentrations from 1.0% to 5.7% w/v, whereas for a third monkey eth anol solution was preferred to water at concentrations as high as 16% w/v. Ethanol intake (g/kg) tended to increase linearly and then flatte n as the concentration was raised. Blood ethanol levels, measured imme diately following sessions in which 8% w/v ethanol was available, rang ed from 45 to 146 mg/dl. Although no special training or acquisition p rocedures were used to establish responding, ethanol functioned as a r einforcer for each of the monkeys tested.