Characterization of the electrophysiological properties of triple reuptake inhibitors on monoaminergic neurons

Triple reuptake inhibitors represent a potential new class of antidepressant drugs that block norepinephrine (NE), dopamine (DA) and serotonin [5-hydroxytryptamine (5-HT)] transporters. The present in-vivo electrophysiological study was undertaken to determine the effects of the triple reuptake inhibitors SEP-225289 and DOV216303 on the neuronal activities of locus coeruleus (LC) NE, ventral tegmental area (VTA) DA and dorsal raphe (DR) 5-HT neurons. Administered acutely, SEP-225289 and DOV216303 dose-dependently decreased the spontaneous firing rate of LC NE, VTA DA and DR 5-HT neurons through the activation of α₂, D₂ and 5-HT(₁A) autoreceptors, respectively. Both compounds predominantly inhibited the firing rate of LC NE neurons while producing only a partial decrease in VTA DA and DR 5-HT neuronal discharge. SEP-225289 was equipotent at inhibiting 5-HT and NE transporters since it prolonged to the same extent the time required for a 50% recovery (RT₅₀) of the firing activity of dorsal hippocampus CA3 pyramidal neurons from the inhibition induced by microiontophoretic application of 5-HT and NE. Finally, in the presence of WAY100635, a 5-HT(₁A) receptor antagonist, SEP-225289 activated 5-HT neurons at doses that normally did not inhibit them. Taken together, the present results indicate that reciprocal interactions among NE, DA and 5-HT inputs need to be considered to anticipate the net effect of triple reuptake inhibitors on the enhancement of brain monoamine transmission. The results also suggest that the therapeutic action of triple reuptake inhibitors may be potentiated by antagonizing the cell body 5-HT(₁A) autoreceptors.