EFFECTS OF d-AMPHETAMINE ON PERFORMANCE UNDER SEVERAL PARAMETERS OF MULTIPLE FIXED-RATIO, FIXED-INTERVAL SCHEDULES

¹ Department of Pharmacology, State University of New York, Downstate Medical Center, Brooklyn, New York

The effects of d-amphetamine in the pigeon were studied on the rate and pattern of responding under a fixed-ratio (FR) 30-response, fixed-interval (FI) 5-min schedule of food presentation. Each component of the schedule was available for only a limited time period (limited hold). The low rates of responding under the FI 5 component were increased by low doses of d-amphetamine and were decreased by high doses at limited hold durations of both 20 and 160 sec. The high rates of responding under the FR 30 component were not affected at low doses of d-amphetamine and were decreased at high doses at the same limited hold durations. These data indicated that the duration of the limited hold was not an important determinant of the drug effect. To determine whether the drug effects were dependent primarily upon the schedule of food presentation maintaining the behavior or upon the rate of responding generated by the schedule, the number of responses in the FR component was increased to 150 and later to 250 to decrease the rate of responding and the FI component was shortened to 60 sec to increase the rate of responding. The low rates of responding under the FR 250 component were increased by low doses of d-amphetamine and were decreased by high doses. The high rates of responding under the FI 60-sec component were decreased by high doses of d-amphetamine. These data show that the drug effects are more closely related to the control rate of responding than to the schedule of reinforcement. Further support for a dose-rate dependency came from an analysis of the patterns of responding within the schedule components.