Endogenous MPTP-Like Amines in the Brain: Isoquinolines

The discovery of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a parkinsonism-producing neurotoxin (Davis et al., 1979; Langston et al., 1983) has greatly contributed to the pathogenesis of Parkinson’s disease. Efforts have been made to find MPTP-like neurotoxins in the brain of parkinsonian patients. MPTP is a precursor neurotoxin, and the oxidized form, by monoamine oxidase type B, N-methyl-4-phenylpyridinium ion (MPP+), is the active neurotoxin (Chiba et al., 1984). It is assumed, therefore, that if any hypothetical MPTP-like neurotoxins exist in the parkinsonian brain they might be oxidized by monoamine oxidase to active neurotoxins.