Chronic Alcohol Exposure Alters Expression of GluN3A-NMDA Receptors in Adult VTA DA Neurons.

N-methyl-D-aspartate receptor (NMDAR) neurotransmission plays a central role in the neurophysiological and behavioral adaptations produced by chronic alcohol (EtOH) exposure and withdrawal. Although alcohol-induced changes in canonical NMDAR subtypes have been extensively studied, the mechanisms by which prolonged alcohol exposure remodels NMDAR function remain incompletely understood. To investigate the impact of chronic voluntary alcohol consumption on glutamatergic signaling, adult C57BL/6J mice were exposed to 20% EtOH using the intermittent two-bottle choice (I2BC) approach for 8 weeks and NMDAR function was examined in ventral tegmental area (VTA) dopamine (DA) neurons using whole-cell electrophysiology. Chronic EtOH exposure reduced NMDA-evoked currents, an effect that became more pronounced during withdrawal. Withdrawal also reduced NMDAR outward current rectification, indicating that chronic alcohol exposure altered the biophysical properties of NMDAR-mediated signaling. These unexpected observations led us to investigate the contribution of GluN3A-containing NMDARs. Pharmacological analyses revealed a significant increase in the proportion of VTA DA neurons expressing functional GluN3A-containing receptors following chronic EtOH exposure, with all tested neurons expressing these receptors during withdrawal. Glycine activation directly depolarized VTA DA neurons and increased action potential firing, demonstrating that the recruited receptors function as excitatory NMDARs. Moreover, the alcohol-induced changes in NMDAR currents, receptor pharmacology, and glycine responsiveness were absent in GluN3A null mice. Together, these findings identify functional recruitment of GluN3A-containing NMDARs as a previously unrecognized neuroadaptation through which chronic alcohol remodels glutamatergic signaling in the adult VTA.