The effects of food deprivation and satiation on oral pentobarbital self-administration in rhesus monkeys.

The effects of food deprivation and satiation on oral pentobarbital self-administration were studied in four rhesus monkeys. Pentobarbital (1.0 mg/ml) or water was available during alternate daily 3-hr session; between sessions, water was freely available. Lip contacts on a drinking spout activated a solenoid operated liquid delivery system. Liquid deliveries (0.56 ml) occurred after a fixed number of lip contact responses were emitted; that is, liquids were delivered according to fixed-ratio (FR) schedules. Under food deprivation conditions, pentobarbital-maintained behavior exceeded water-maintained behavior. Thus, pentobarbital functioned as a reinforcer. Abrupt unlimited access to food resulted in decreased pentobarbital intake. Pentobarbital-maintained behavior increased to previous levels when food intake was again restricted. In a second experiment, the effects of pentobarbital availability on water-maintained behavior were studied. Access to pentobarbital during alternate sessions produced elevated levels of water drinking during intervening sessions. Water drinking decreased to low levels when pentobarbital access was terminated and water was present for consecutive sessions. When pentobarbital was again available during alternate sessions, high levels of water drinking recurred. In the third experiment, water and pentobarbital (1.0 mg/ml) were concurrently available via separate drinking spouts. All three monkeys drank much more pentobarbital solution than water.