Haloperidol blocks the response-reinstating effects of food reward: A methodology for separating neuroleptic effects on reinforcement and motor processes

Abstract

To test the hypothesis that dopamine antagonist drugs attenuate the reinforcing properties of foods, rats previously trained to traverse a straight runway for food reward subsequently underwent extinction sessions. After running speeds had substantially decreased, rats received a single food-rewarded trial either in the presence or absence of haloperidol (0, 0.15 or 0.30 mg/kg IP). Twenty-four hours later, animals were tested for reinstatement of the running response during a drug-free test trial. Animals that were nondrugged during the food-rewarded trial showed increases in running speed on the test trial relative to extinction baseline speeds. In contrast, animals under the influence of haloperidol during the food-rewarded trial failed to show test day increases in running speed. Additional control groups ruled out the possibility that the haloperidol results were due to either motor or state-dependent learning effects. The findings support the view that dopamine systems play a role in the neural substrates underlying food reinforcement. In addition, the study demonstrates a simple and effective methodology for separating neuroleptic effects on motor and reinforcement processes.