MAOB and Parkinson disease: As DA is a substrate of both forms of MAO, and because levodopa (L-DOPA, L-3,4 dihydroxyphenylalanine), the immediate DA precursor, is still the main medication to treat PD [72], a lot of investigations have been devoted to the effect of MAO A and MAO B inhibitors on the metabolism of intrinsic DA and DA derived from levodopa.