Effects of d-amphetamine on temporal distributions of schedule-induced polydipsia

Food-deprived rats were divided into four groups according to the equal interval and time durations of a multiple fixed-interval, fixed-time schedule (15, 30, 60, and 120 s). Fixed-time components were signaled by a tone and lever withdrawal. d-Amphetamine (0.25-4.0 mg/kg) produced similar dose-dependent reductions in the drinking and ticking induced by fixed-interval and fixed-time schedules. These dose-dependent decrements were a function of the interfood interval length. More licks occurred early in the interfood intervals with doses of d-amphetamine. Dose-dependent shifts to the left were observed in the distribution of licking, and there were dose-dependent decreases in the quarter-life, which were a function of fixed-interval and fixed-time lengths. The maximum lick rate within interfood intervals occurred at about the same absolute time in schedules up to 60 s; therefore, the effects of d-amphetamine were not mediated by its effects on temporal discrimination. (C) 1997 Elsevier Science Inc.