Effects of pimozide on emitted force, duration and rate of operant response maintained at low and high levels of required force

Abstract

The behavioral effects of pimozide (0.25, 0.5, and 1.0 mg/kg) were assessed in two separate experiments in which session mean peak force, maximum peak force, and response duration served as the dependent variables complementing operant response rate. In the first experiment, two groups of water-deprived rats were trained on a continuous reinforcement (CRF) schedule for reaching out and pressing downward on a force transducer with peak forces of at least 4 g (low-force group) or 40 g (high-force group). In the second experiment a pull-type response topography and fixed ratio 20 were used, and force requirements were 4 g for the low-force group and 100 g for the high-force condition. Under these conditions pimozide decreased response rate and increased response duration irrespective of response topography, required force, or schedule of reinforcement. Neither mean peak force nor maximum peak force were significantly decreased by the drug, and in the low-force CRF condition a small but significant dose-related rise in mean peak force was observed. It was hypothesized that neuroleptics exert their motor-impairing effects primarily in the temporal domain of behavior but do not appreciably affect the force dimension of performance capacity. And these temporal domain effects may be reflected in differences in the kinetic requirements for the overall behavior and not just the response itself. Additionally, the possibility that some of the observed effects could be accounted for by "anhedonia" was addressed.