Differential attenuation of some effects of haloperidol in rats given scopolamine.

In a series of pharmacological tests the ability of 0.6 mg/kg of the anticholinergic scopolamine to decrease the effectiveness of the neuroleptic heloperidol varied widely. Most severely attenuated was production of catalepsy followed in order of decreasing interference by inhibition of amphetamine-induced rotation, inhibition of amphetamine- or apomorphine-induced stereotyped behavior, inhibition of conditioned avoidance responding and lastly attenuation of the haloperidol-induced increase in striatal HVA. By use of such a relatively low dose of scopolamine the behavioral effects of heloperidol were dissociated from effects on dopamine turnover in the striatum. If behavioral tests in animals can be related to the clinical effects of neuroleptic drugs, those effects of haloperidol severely reduced by scopolamine may be related to extrapyramidal effects.