The effects of d-amphetamine and scopolamine on drinking induced by a multiple schedule

Three food-deprived rats obtained food pellets on a multiple fixed-interval fixed-time schedule. During fixed-interval components a 45 mg pellet was made available for a lever-press every minute (FI 1 min). When the fixed-time component was in operation the lever was retracted and a pellet was delivered every minute (FT 1 min) independent of behaviour. A water bottle was available to each subject and similar levels of schedule-induced drinking developed during the two schedule components. The effects of several doses (0.25, 0.5, 1.0, 2.0 mg/kg) of d-amphetamine and scopolamine were assessed on lever-pressing and drinking maintained by this procedure. Both drugs increased rates of lever-pressing at lower doses and reduced levels of licking and water intake at all doses. The patterning of fixed-interval lever pressing was altered by both drugs increasing the proportion of responses emitted during early parts of the intervals. d-Amphetamine also increased the proportion of licks that occurred during early segments of the interfood intervals, while scopolamine had variable effects on patterns of licking. There were no consistent differences in the effects of the drugs on licking induced by the two schedules.