Effects of pimozide on lever pressing behavior maintained on an intermittent reinforcement schedule

Lever pressing for food on a variable interval (2.5 min) schedule was challenged by pretreatment with a 1.0 mg/kg dose of the dopamine receptor blocker pimozide. Large decreases in response rate were recorded even during the first few minutes of the test session before the rats had received any reinforcement. Pimozide also caused extinction-like effects, but it was clear, from comparisons between pimozide-treated rats that were rewarded and pimozide-treated rats that were not rewarded, that the rewarding effects of food were not totally blocked. It is suggested that an important aspect of the pimozide-produced response decrement is its effect on the incentive motivational properties of food-associated apparatus cues known to be important in sustaining responding under extinction and partial reinforcement conditions.