Despite the large amount of neuropharmacological data concerning catecholamine (CA) mechanisms of the mammalian brain, little is known yet about the effects of MAO-inhibitors on single neurons. The present series of experiments aim to elucidate these specific neurochemical attributes of forebrain cells. Single neuron activity was recorded by means of multi-barreled microelectrodes in the caudate nucleus, globus pallidus, and amygdala of both anesthetized rats and anesthetized or alert monkeys during microelectrophoretic application of the MAO-B blocker L-deprenyl (DEPR).  CAs (dopamine and noradrenaline), glutamate, GABA, and acetylcholine were also applied.  Nearly the half (46%) of all forebrain neurons tested responded, exclusively with inhibition, to L-deprenyl, and the CA-sensitive cells were especially responsive to the MAO-B inhibitor.  The time course of L-deprenyl-induced neuronal suppression was short. In some cases, amphetamine (AMPH) and clorgyline (CLOR) were also applied microelectrophoretically. AMPH elicited similar activity changes to those seen after L-deprenyl administrations, whereas CLOR applications were less effective. Our results provide evidence that L-deprenyl can effectively modulate the activity of CA-sensitive neurons in the three different forebrain regions of two different species.  On the basis of this data, the possible neurochemical mechanisms of L-deprenyl action are discussed.

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