DECREASED RESISTANCE TO EXTINCTION AFTER HALOPERIDOL - IMPLICATIONS FOR THE ROLE OF DOPAMINE IN REINFORCEMENT

Previous experiments have noted that the reduction in operant behavior following treatment with neuroleptic drugs resembles an extinction curve. From this it has been argued that neuroleptic drugs disrupt operant responding by blocking the hedonic properties of primary reinforcers. The present series of experiments challenge this interpretation on several grounds. Rats were trained to bar-press either for food or for brain-stimulation reward on a variable interval (VI-60 sec) schedule. They were subsequently put into a condition of non-reward (i.e. extinction) and the effects of haloperidol (0.1 mg/kg) on the rate of responding during extinction were examined. According to the anhedonia hypothesis haloperidol should not further reduce responding during extinction. Contrary to the prediction it was found that the rate of responding during haloperidol and extinction was greatly reduced compared to that measured during extinction alone. Furthermore, the anhedonia hypothesis has maintained that following neuroleptic treatment, response patterns change only after the animal has been reinforced on several occasions. However, in the third experiment of the present study which employed a VI-4 min schedule of food reinforcement, the response rate often was attenuated prior to the first reinforcement. These data indicate that the effects of neuroleptics on operant behavior cannot be accounted for in terms of unitary actions such as specific motor impairments or blockade of primary reinforcement. Rather these drugs appear to have multiple behavioral effects. © 1979.