Tranylcypromine, but not moclobemide, prolongs the inhibitory action of dopamine on midbrain dopaminergic neurons: An in vitro electrophysiological study

The degradation of dopamine by monoamine oxidase (MAO) enzymes plays an imp ortant role in the function of dopamine receptors in the central nervous sy stem. Accordingly, it has already been reported that the blockade of MAO by specific inhibitors prolongs the effects of dopamine on its receptors. By using intracellular electrophysiological recordings, here we report that th e irreversible MAO A and B inhibitor tranylcypromine, but not the reversibl e MAO A inhibitor moclobemide, potentiates DA responses in rat midbrain dop aminergic neurones maintained in vitro. Moclobemide was not effective even when the MAO B enzymes were additionally blocked by the MAOI deprenyl. Thus , our electrophysiological findings confirm that the degradation DA is very important to control the effects of this catecholamine at a cellular level . Furthermore, they demonstrate that tranylcypromine potentiates DB neurotr ansmission while moclobemide is devoid of dopaminergic action in an in vitr o condition. The phenomena reported above support the hypothesis that part of the antidepressant and antiparkinsonian effects of tranylcypromine depen d on an action on DB transmission. Synapse 37:216-221, 2000. (C) 2000 Wiley -Liss, Inc.