Comparison of the behavioral effects of phencyclidine, ketamine, d-amphetamine and morphine in the squirrel monkey
Byrd, L.D.
Journal of Pharmacology and Experimental Therapeutics 220(1): 139-144
1982
ISSN/ISBN: 0022-3565 PMID: 7053409 Document Number: 196891
The behavioral effects of phencyclidine, ketamine, d-amphetamine and morphine were studied and compared in squirrel monkeys trained to press a response key under an 8-min fixed-interval (FI) schedule of electric shock presentation with a 30-s timeout after shock presentation. Under nondrug conditions, a pattern of positively accelerated responding was maintained under the FI schedule and mean response rates were 0.39 and 0.25 response/s for each of 2 monkeys. Overall mean rate of responding increased after 0.03-0.17 mg/kg of phenycyclidine and after 0.01-0.1 mg/kg of d-amphetamine and rate decreased after higher doses of either drug. In contrast, ketamine had little effect on responding after 0.3 mg/kg and caused only brief, transient decreases in responding after 1.0 or 3.0 mg/kg. When morphine was administered, mean rate of responding changed little after 0.03 to 1 mg/kg and decreased after higher doses. Increases in mean response rate after phenycyclidine and d-amphetamine were due primarily to increased responding during the first 5-6 min of each FI. Responding either changed little or increased slightly during the last 2-3 min of each FI. Whereas the effects of phencyclidine and d-amphetamine were similar, the effect of ketamine was more like morphine in that the latter 2 drugs decreased responding during the last several minutes of each FI and neither drug reliably increased mean response rate. None of the effects of phencyclidine was shared with morphine. The results extend the response-rate enhancing effects of phencyclidine to shock-maintained behavior and provide additional evidence that phencyclidine can have stimulant-like effects on behavior.