Partial inhibition of catecholamine activity and enhanced responsiveness to NMDA after sustained administration of vortioxetine

Vortioxetine is a multimodal drug that blocks serotonin (5-HT) reuptake and directly modulates 5-HT receptors. The effects of subacute and long-term administration of vortioxetine on various aspects of catecholamine and glutamate systems were investigated using single-unit extracellular recordings and microiontophoresis in the rat brain. The firing rate of dopamine (DA) neurons was significantly decreased (26%) after 14, but not 4 days of vortioxetine administration (vortioxetine-containing chow, 1.8 g/kg vortioxetine). Same 14- and 4-day regimens of vortioxetine decreased the firing activity of norepinephrine (NE) neurons (by 27% and 41%, respectively). For DA and NE neurons, 14-day vortioxetine exposure also decreased the number of bursts per minute, without changing the number of spikes per burst, percentage of spike firing in burst and the number of spontaneously active neurons per track. However, this vortioxetine-induced suppression of DA and NE neuronal activity is less than that obtained in previous studies with the selective 5-HT reuptake inhibitor (SSRI) escitalopram. In the CA3 region of the hippocampus, 14 days of vortioxetine exposure did not change the sensitivity of postsynaptic α2-adrenoceptors nor did it increase the tonic activation of α1-and α2-adrenoceptors. Vortioxetine administration for 14 days increased the N-methyl-d-aspartate (NMDA)-, but not α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-evoked responses of CA3 pyramidal neurons. Taken together, the results of the current study suggest that vortioxetine might produce a lesser inhibition of DA and NE neuronal activity when compared to those induced by escitalopram as reported in previous studies.