Methamphetamine induces fos expression in the striatum and the substantia nigra pars reticulata in a rat model of Parkinson's disease.

In rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion in the nigrostriatal pathway, methamphetamine (3 mg/kg, i.p.) induced Fos-like immunoreactivity (FLI) not only in the striatum on the intact side but also in the substantia nigra pars reticulata (SNr) on the lesioned side. The methamphetamine-induced hyperexpression of FLI in the SNr on the lesioned side was suppressed by pretreatment with either dopamine D1 receptor antagonist SCH-23390 (0.5 mg/kg, i.p.), D2 receptor antagonist raclopride (2 mg/kg, i.p.) or N-methyl-d-aspartate receptor antagonist MK-801 (1 mg/kg, i.p.), which was concomitant with inhibition of the methamphetamine-induced rotational behavior of each antagonist. However, the hyperexpression of FLI in the SNr was not suppressed by intrastriatal grafts of fetal ventral mesencephalon which could suppress the methamphetamine-induced rotation completely. These results indicate that opposite hemispheric asymmetries in FLI are induced by methamphetamine in the striatum and the SNr in the 6-OHDA rats. It is suggested that the FLIs in the two discrete sites are activated independently by different mechanisms, and furthermore, different neuronal pathways are involved in the methamphetamine-induced rotation and Fos expression in the SNr of 6-OHDA rats.