Contextual and behavioral control of antipsychotic sensitization induced by haloperidol and olanzapine.

Repeated administration of haloperidol (HAL) and olanzapine (OLZ) causes a progressively enhanced disruption of the conditioned avoidance response (CAR) and a progressively enhanced inhibition of phencyclidine (PCP)-induced hyperlocomotion in rats (termed antipsychotic sensitization). Both actions are thought to reflect intrinsic antipsychotic activity. The present study examined the extent to which antipsychotic-induced sensitization in one model (e.g. CAR) can be transferred or maintained in another (e.g. PCP hyperlocomotion) as a means of investigating the contextual and behavioral controls of antipsychotic sensitization. Well-trained male Sprague-Dawley rats were first repeatedly tested in the CAR or the PCP (3.2 mg/kg, subcutaneously) hyperlocomotion model under HAL or OLZ for 5 consecutive days. Then they were switched to the other model and tested for the expression of sensitization. Finally, all rats were switched back to the original model and retested for the expression of sensitization. Repeated HAL or OLZ treatment progressively disrupted avoidance responding and decreased PCP-induced hyperlocomotion, indicating a robust sensitization. When tested in a different model, rats previously treated with HAL or OLZ did not show a stronger inhibition of CAR-induced or PCP-induced hyperlocomotion than those treated with these drugs for the first time; however, they did show such an effect when tested in the original model in which they received repeated antipsychotic treatment. These findings suggest that the expression of antipsychotic sensitization is strongly influenced by the testing environment and/or selected behavioral response under certain experimental conditions. Distinct contextual cues and behavioral responses may develop an association with unconditional drug effects through a Pavlovian conditioning process. They may also serve as occasion setters to modulate the expression of sensitized responses. As antipsychotic sensitization mimics the clinical effects of antipsychotic treatment, understanding the neurobiological mechanisms of antipsychotic sensitization and its contextual control would greatly enhance our understanding of the psychological and neurochemical nature of antipsychotic treatment in the clinic.