1-Methyl-4-phenylpyridine (MPP+) is toxic to mesencephalic dopamine neurons in culture.

1-Methyl-4-phenylpyridine (MPP+) is the product of oxidative metabolism by monoamine oxidase of the Parkinson-inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPP+ was tested for neurotoxicity on the dopaminergic neurons of embryonic rat midbrain in culture. Compared with MPTP, MPP+ was a more potent neurotoxin for the cultured dopamine (DA) neurons as determined by decrease in [3H]DA uptake by the cultures and decrease in endogenous levels of DA and homovanillic acid. Catecholamine histofluorescence demonstrated the loss of fluorescing fibers after exposure to MPP+. The reduced analogue of MPTP, namely 1-methyl-4-phenylpiperidine, had no significant neurotoxic action on the dopaminergic neurons in culture.