MODIFICATION OF THE EFFECTS OF CHLORPROMAZINE ON BEHAVIOR IN THE CHIMPANZEE

¹ Laboratory of Psychobiology, Department of Psychiatry, Harvard Medical School, at the New England Regional Primate Research Center, Southborough, Massachusetts

During daily two-hour sessions, key-pressing behavior in the chimpanzee was maintained under a multiple schedule comprising a 10-minute fixed-interval schedule and a 30-response fixed-ratio schedule of food delivery. Water was freely available in the chimpanzee's living area and in the experimental chamber, and schedule-related drinking occurred regularly during the session. Chlorpromazine had dose-dependent effects on key pressing and on water intake during the session. The drug increased mean response rates under the fixed-interval schedule at doses of 0.03 to 0.3 mg/kg i.m. and decreased responding at 1.0 to 3.0 mg/kg. The high rates of responding engedered under the fixed-ratio schedule were not affected by the lower doses, but were decreased by doses of 1.0 to 3.0 mg/kg. Water intake was also unaffected by doses below 1.0 mg/kg, but decreased at doses of 1.0 to 3.0 mg/kg. Presentation of a brief (20 msec) auditory stimulus after each response during the fixed-interval and fixed-ratio schedules poteniated the enhancing effect of chlorpromazine on responding under the fixed-interval schedule. Presentation of the brief stimulus did not alter the effects of chlorpromazine on responding under the fixed-ratio schedule and on water intake, however. These results show that 1) chlorpromazine can enhance schedule-controlled responding in the chimpanzee. 2) the enhancing effect of chlorpromazine can be potentiated when each response produces a brief change in environmental stimuli and 3) chlorpromazine only affects water intake at doses that also disrupt responding.