Three squirrel monkeys received extensive training under a concurrent free-operant avoidance, fixed-ratio escape schedule. The independent effects of D-amphetamine and chlorpromazine were assessed over a range of dose levels. The effects of D-amphetamine (0.03, 0.1, 0.3, and 1.0 mg/kg) on each monkey were dependent upon the subjects' control rates of responding. However, there was a clear rate-increasing effect on a relatively low rate of responding, and a rate-depressant effect on high response rates.
Administration of chlorpromazine characteristically was followed by an overall depression of response rates.
Dose combinations of 0.3 mg/kg chlorpromazine with D-amphetamine (0.1, 0.3, 1.0 mg/kg) illustrated the antagonistic effects of the two drugs. At the lowest amphetamine dosage, the chlorpromazine effect was unimpaired; at the 0.3 mg/kg dosage of each drug it was abolished. The rate-suppressive effect on high response rates of 1.0 mg/kg D-amphetamine was abolished when given together with 0.3 mg/ kg chlorpromazine.
The present experiment demonstrates the phenomenon of amphetamine-chlorpromazine antagonism under conditions in which responding was maintained by the scheduled presentation of aversive stimulation.
Key-Words Amphetamine - Chlorpromazine - Antagonistic Effects - Second-Order Escape Behavior - Squirrel Monkey
Aided by grant # APA-159 to R. Stretch from the National Research Council of Canada. Thanks are due to Mrs. G. Gerber for assistance in the preparation of this manuscript.