The effect of thioridazine on haloperidol induced behavioral hypersensitivity.

Behavioral Hypersensitivity (BH) to dopamine agonists occurs following chronic treatment with most neuroleptics including haloperidol. In the present study we observed that the concurrent administration of thioridazine and haloperidol prevented the development of BH. In contrast, another neuroleptic, fluphenazine, coadministered with haloperidol, potentiated the degree of BH relative to animals treated with haloperidol only. In rats already made hypersensitive by chronic treatment with haloperidol, a 4 week subsequent treatment with normal saline, thioridazine alone of thioridazine in combination with haloperidol, produced normal behavioral responsiveness. These results suggest that thioridazine prevents the development of BH and can reverse the expression of haloperidol-induced BH.