Behavioral resistance to haloperidol and clozapine.

Using a procedure to assess behavioral resistance to change, the effects of two drugs (haloperidol and clozapine) were compared to each other and to the effect of response-independent food delivered between multiple-schedule components. Using rats as subjects, responding in one component was maintained on a variable-interval 30-s schedule, whereas responding in another component was maintained on a variable-interval 30-s schedule that operated concurrently with a variable-time 30-s schedule. Consistent with previous findings, responding in the component with the greater overall amount of reinforcement displayed the greater resistance to response-independent food delivery. Similarly, increasing the dose of haloperidol or clozapine increased the overall extent of disruption (relative to baseline levels), with the greatest disruption occurring to responding in the component associated with the smaller overall amount of food reinforcement. Thus, as with the disruption caused by alterations in reinforcement conditions, the extent of disruption to reinforced responding caused by haloperidol and clozapine is specifically dependent upon baseline reinforcement conditions rather than baseline response rates.