Effects of chronic d-amphetamine on the maintenance and acquisition of schedule-induced polydipsia in rats.

The effects of chronic d-amphetamine on the acquisition of schedule-induced polydipsia and its maintenance by stimuli paired with food were evaluated in three interlocking experiments. In Experiment 1, polydipsia was induced in rats exposed to a response-independent fixed-time schedule in which a food pellet (US) was paired with a stimulus complex of lights and tone (CS) every 45 sec. When food was omitted and only the CS was presented rats drank very little water. Rats were then pretreated with 1 mg/kg d-amphetamine for 15 CS-US sessions and two or three subsequent CS-alone sessions. Animals remained polydipsic during CS-US sessions and drank little water during CS-alone sessions. However, d-amphetamine improved control exerted by the CS over drinking relative to no-drug sessions. In Experiment 2, acquisition of schedule-induced polydipsia during 10 sessions exposure to the periodic CS-US schedule was blocked in rats pretreated with 1 mg/kg d-amphetamine, compared with rats pretreated with buffer. During subsequent CS-alone sessions the temporal control of drinking by the CS was greater in the rats exposed to amphetamine. In Experiment 3, the rats that had not acquired polydipsia while under d-amphetamine in the previous experiment, all became polydipsic when pretreated with buffer. All rats remained polydipsic when re-exposed to amphetamine pretreatment. These results indicate that chronic d-amphetamine administration can facilitate control of licking and drinking by nonfood stimuli paired with food, and can block acquisition of schedule-induced polydipsia.