Selective suppression of type B monoamine oxidase immunoreactivity in the raphe nuclei following MPTP administration in the cat

Abstract

Using immunohistochemistry, we investigated in the cat the effects of MPTP, a Parkinsonian syndrome-inducing substance, on brain type B monoamine oxidase (MAO-B) which is responsible for the conversion of MPTP to its neurotoxic product (MPP+). Intraperitoneal administration of MPTP (5 mg kg-1 daily for 5 days) caused a selective suppression of MAO-B in neurones of the raphe nuclei without affecting hypothalamic MAO-B. Since these effects were accompanied by loss of nigral dopaminergic cells but not of raphe cell bodies or 5-HT immunoreactivity, we suggest that MPTP suppresses raphe MAO-B without destroying its presumed host serotoninergic neurones and that raphe MAO-B does not appear to be crucial in the MPTP-induced nigral lesion. In addition, the MPTP-induced paradoxical sleep suppression might be related to this raphe MAO-B loss.