Mechanism of resistance to NO-induced neurotoxicity in cultured rat dopaminergic neurons

We previously reported that mesencephalic dopaminergic neurons are resistant to cytotoxicity induced by nitric oxide (NO). This study investigated the intracellular mechanism that protects dopaminergic neurons against NO toxicity in rat mesencephalic cultures. Peroxynitrite anion, an active metabolite of NO, caused significant cytotoxic effects against dopaminergic and nondopaminergic neurons, but NO caused cytotoxic effects restricted to nondopaminergic neurons. In addition, we studied the effects of ascorbate, an anti-oxidant, on NO-induced neurotoxicity against dopaminergic neurons and found that coadministration of ascorbate failed to affect resistance against NO-induced neurotoxicity. These findings suggest that the protecting mechanism from NO neurotoxicity in dopaminergic neurons is based on inhibition of conversion of NO to peroxynitrite anion, is independent of the NO redox state, and is possibly due to suppression of superoxide anion production. Furthermore, we investigated NO-induced neurotoxicity with or without pretreatment with sublethal doses of methylphenylpyridium ion (MPP+). Following pretreatment with 1 microM MPP+, which did not show significant cytotoxic effects against dopaminergic neurons, NO demonstrated significant cytotoxicity. Therefore, MPP+ may inhibit the protecting systems from NO neurotoxicity in dopaminergic neurons.