Modification of dopamine release by selective inhibitors of MAO-B.

Chronic low dose deprenyl treatment in rats causes an increase in striatal extracellular dopamine level, without significant reduction in deaminated metabolite formation. This effect could be the result of increased endogenous levels of the MAO-B substrate beta-phenylethylamine, which is both a releaser of dopamine as well as an inhibitor of the neuronal membrane active dopamine uptake. In guinea pigs, however, striatal extracellular dopamine was not increased either by deprenyl or by clorgyline. Local infusion of the dopamine uptake inhibitor GBR-12909 caused a greater increase in striatal dopamine in microdialysate in rats than in guinea pigs. Intra-species differences in synaptic architecture or in density of dopamine transporter expression may account for these differences.