Role of nitric oxide synthase against MPTP neurotoxicity in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes nigrostriatal dopaminergic pathway injury similar to that observed in Parkinson's disease. Many hypotheses have been proposed to explain the mechanisms underlying MPTP neurotoxicity. Previous work showed that the inhibitor of neuronal nitric oxide synthase (nNOS) might produce protection against MPTP-induced dopaminergic toxicity. To exactly test the role of NO in MPTP neurotoxicity, we examined the effect of nNOS inhibitor 7-nitroindazole, in comparison with that of nonselective NOS inhibitor (L-NAME), immunosuppressant (FK-506), monoamine oxidase (MAO) inhibitors (clorgyline and pargyline), N-methyI methyl-D-aspartate receptor antagonist (MK-801) and Ca²⁺ antagonist (amlodipine). Among seven compounds, 7-nitroindazole produced dose-dependent protection against MPTP-induced depletion of striatal dopamine and its metabolite 3,4-dihydroxyphenyl acetic acid (DOPAC) in mice. Clorgyline and pargyline also showed a significant effect on MPTP-induced dopamine depletion in the mouse striatum. However, both compounds did not protect against MPTP-induced depletion of striatal DOPAC. Our immunohistological study with tyrosine hydroxylase (TH) and microtuble-associated protein 2 (MAP 2) showed that 7-nitroindazole or pargyline can protect against MPTP-induced depletion of TH and MAP 2 immunostained neurons in the substantia nigra. Furthermore, these compounds reduced a marked increase in GFAP-positive astrocytes of the mouse striatum after MPTP treatments. The present study demonstrates that nNOS inhibitor 7-nitroindazole as well as MAO inhibitors clorgyline and pargyline can produce dose-dependent neuroprotection against the dopaminergic neurotoxicity of MPTP. However, nonselective NOS inhibitor L-NAME, immunosuppressant FK-506, NMDA receptor antagonist MK-801 and Ca²⁺ antagonist amlodipine did not show a beneficial effect on MPTP neurotoxicity.