Effects of haloperidol on the biophysical characteristics of operant responding: Implications for motor and reinforcement processes

Food-deprived rats were reinforced with sweetened condensed milk for pressing a force-sensing operandum on a continuous reinforcement basis. Force was continuously recorded (every 0.00195 sec) during each response, and measures derived from the resulting force-time waveforms served as the basis for evaluating neuroleptic challenge in the form of haloperidol (0.04, 0.08, 0.16 mg/kg). Significant dose-related drug effects included a decrease in response rate, an increase in mean emitted peak force, and an increase in overall response duration. Additional quantitative analyses revealed that the drug-induced increase in response duration resulted primarily from a slowing in the animal's paw removal from the force-sensing operandum. The findings are analogous to deficits in Parkinson's disease and suggest a behavioral mechanism that might account for much of the rate attenuating effects of neuroleptics. Implications for motor and reward interpretations of the actions of dopamine antagonists are also discussed.