Selegiline and the prophylaxis of Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration causes a Parkinson's disease like syndrome in man and primates, with selective degeneration of the substantia nigra. This discovery has raised the possibility that some environmental or endogenous toxin causes idiopathic Parkinson's disease. MPTP is oxidised to its neurotoxic metabolite, 1-methyl-4-phenylpyridinium (MPP+) by monoamine oxidase B (MAO B). MPTP toxicity is prevented by pretreatment with the MAO B inhibitor selegiline ((-)-deprenyl). We have screened a range of structural analogues of MPTP as possible alternative substrates for the enzyme. All compounds which were found to be substrates for MAO B were tetrahydropyridines, some with substituents on the phenyl ring. The most interesting substrate, ethyl-MTP-carboxylate, did not have a phenyl ring. The precise histochemical localisation of MAO B within the rat and marmoset brain has been established. There was substantial activity within the nigrostriatal pathway of the marmoset; in comparison, the rat had only a low background MAO B level. These results may partially explain why the marmoset is more susceptible to the action of MPTP than the rat.