Unilateral intranigral administration of the oxidative metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenyl-dihydropyridine (MPDP+) or 1-methyl-4-phenylpyridine (MPP+) produced dose-dependently a depletion of dopamine in the ipsilateral striatum of rats two weeks following treatment. d-Amphetamine and apomorphine induced circling toward the lesioned side in these unilaterally treated animals. No contralateral circling behavior was observed after challenging with apomorphine. This dopamine lesioning effect of MPP+ was not blocked by pretreatment of animals with a dopamine uptake blocker, GBR 12909. Furthermore, MPP+ increased the 45Ca accumulation into cells at the site of injection and produced "nonspecific" cell membrane and/or cytotoxic damage seen by histological procedures. These results indicate that MPDP+ and MPP+ produced localized cytotoxic damage to nigrostriatal neurons, caused a decrease in striatal dopamine, and disrupted the nigrostriatal system's functioning following intranigral administration to rats. It is postulated that the cationic surfactant properties of MPDP+ and MPP+ might contribute to its neurotoxic effects.

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