Food restriction and sex differences on concurrent, oral ethanol and water reinforcers in juvenile rhesus monkeys.

The present study assessed the liability of ethanol to be established as an oral reinforcer in 24 juvenile rhesus monkeys. All of the monkeys had a prior oral self-administration history with concurrently available methadone and water. To determine if food restriction and sex differences would contribute to ethanol preference, the monkeys were divided into two groups of 12. Twelve monkeys received 30 biscuits of food each day while the other group received 15 biscuits; six monkeys were male and six were female in each food restriction group. Fluid deliveries (0.5 ml) were provided following contact responses on solenoid-operated drinking spouts. All monkeys were exposed to concurrent water on two spouts and, subsequently, ethanol was available on one spout with water in the alternate spout. Ethanol concentrations (0.25-16 g/l) were doubled weekly. Subsequently, some ethanol concentration exposures were repeated, as was the concurrent water condition. Ethanol (1-2 g/l) served to reinforce responding under most conditions except with the 30-biscuit females; where ethanol so functioned, water responding was reduced. At concentrations less than 1 g/l, ethanol and water were consumed in equal amounts. At 8-16 g/l, ethanol maintained less responding than water. Food restriction amplified ethanol preference in both males and females, although perhaps less in females. A complex set of relations exist among variables that control oral ethanol preference in rhesus monkeys.