1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neuroblastic apoptosis in the subventricular zone is caused by 1-methy-4-phenylpiridinium (MPP+) converted from MPTP through MAO-B

Intraperitoneal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration induces apoptosis of subventricular zone (SVZ) doublecortin (Dcx)-positive neural progenitor cells (migrating neuroblasts, A cells). Actually, a metabolite of MPTP, 1-methy-4-phenylpiridinium (MPP⁺), is responsible for neural progenitor cell toxicity. In the present study, to examine whether the MPTP-induced SVZ cell apoptosis is caused directly by MPP⁺ metabolized through monoamine oxidase B (MAO-B), MPTP or MPP⁺ was intracerebroventricularly (icv) injected into C57BL/6 mice. At Day 1 postinjection, many terminal deoxynucleotidyl transferase-mediated dUTP endlabeling (TUNEL)-positive cells were observed in the SVZ of both low (36 μg) and high (162 μg) dose MPTP- and MPP⁺-injected mice. The number of Dcx-positive A cells showed a significant decrease following high dose of MPTP- or MPP⁺-injection on Days 1 and 3, respectively, whereas that of EGFR-positive C cells showed no change in mice with any treatment. In addition, prior icv injection of a MAO-B inhibitor, R(?)-deprenyl (deprenyl), inhibited MPTP-induced apoptosis, but not MPP⁺-induced apoptosis. MAO-B- and GFAP-double positive cells were detected in the ependyma and SVZ in all mice. It is revealed from these results that icv injection of MPTP induces apoptosis of neural progenitor cells (A cells) in the SVZ via MPP⁺ toxicity. In addition, it is suggested that the conversion from MPTP to MPP⁺ is caused mainly by MAO-B located in ependymal cells and GFAP-positive cells in the SVZ.