Clozapine decreases enkephalin mRNA in rat striatum

Typical antipsychotic drugs (i.e. haloperidol) induce extrapyramidal movement disorders while 'atypical' antipsychotics (i.e. clozapine) do not. In situ hybridization histochemistry followed by film autoradiography showed that clozapine treatment (20 mg/kg i.p. daily for 28 days) decreased the level of labelling for preproenkephalin mRNA in the striatum of the rat while haloperidol treatment (1 mg/kg i.p. daily for 28 days) resulted in no change compared with controls. The results suggest that these typical and atypical antipsychotic drugs exert differential effects on the enkephalin-containing striatal projection to the globus pallidus, a pathway critical for the expression of extrapyramidal movement disorders.