Differential effects of typical and atypical antipsychotic drugs on striosome and matrix compartments of the striatum

Administration of typical antipsychotic drugs (APDs) is often accompanied by extrapyramidal side-effects (EPS). Treatment with atypical APDs has a lower incidence of motor side-effects and atypical APDs are superior to typical APDs in treating the negative symptoms of schizophrenia. Although typical APDs strongly induce the immediate-early gene c-fos in the striatum while atypical APDs do so only weakly, it is possible that the effects of atypical APDs are more pronounced within certain regions of the striatum. The striatum contains two histochemically defined compartments, the striosome (patch) and the matrix. These compartments have been well characterized anatomically but their functional attributes are unclear. We therefore examined the effects of typical and atypical APDs on Fos expression in the striosome and matrix of the rat. Typical and atypical APDs were distinguished by the pattern of striatal compartmental activation they induced: the striosome : matrix ratio of Fos-li neurons was greater in rats treated with atypical APDs. Pretreating animals with selective antagonists of receptors that atypical APDs target with high affinity did not increase the striosome : matrix Fos ratio of typical APD-treated rats and thus did not mimic the ratio seen in response to atypical APDs. However, pretreatment with the atypical APD clozapine did recapitulate the characteristic compartmental Fos pattern seen in response to typical APDs. These data suggest that some characteristics of atypical APDs, such as the lower EPS liability and greater reduction of negative symptoms, may be linked to the coordinate regulation of the striatal striosome and matrix.