The effect of deprenyl (selegiline) on intra- and extraneuronal dopamine oxidation

It was found that in the rat striatum DA was oxidized extrasynaptosomally to 11% by MAO-A and to 3% by MAO-B. The corresponding intrasynaptosomal oxidations were 84% and 2%, respectively. Those figures were virtually unchanged even if the rat brain MAO-B was selectively inhibited to 87% by deprenyl. In the human brain extrasynaptosomal oxidation was 16% and 66%, respectively, by MAO-A and -B. Intrasynaptosomally the corresponding figures were 12% and 6%, respectively. Selective inhibition of human caudate MAO-B was calculated to give a total reduction of DA oxidation of 63%. The differences between man and rat are due to the proportionately greater oxidation of DA by MAO-B in man, which is a consequence of a higher ratio of concentration of MAO-A/-B in the rat.