5-HT_2A receptor activation normalizes stress-induced dysregulation of GABAergic signaling in the ventral tegmental area.

Abstract

Stress is known to alter GABAergic signaling in the ventral tegmental area (VTA), and this inhibitory plasticity is associated with increased alcohol self-administration. In humans, serotonin 2A receptor (5-HT_2AR) agonists can treat stress- and alcohol-related disorders, but the neural substrates are ill-defined. Thus, we reasoned that 5-HT_2AR pharmacotherapies may ameliorate the stress-induced dysregulated inhibitory VTA circuitry that contributes to subsequent alcohol abuse. We found that acute stress exposure in mice compromised GABA-mediated inhibition of VTA GABA neurons corresponding with increased ethanol-induced GABAergic transmission. This stress-induced inhibitory plasticity was reversible by applying the 5-HT_2AR agonist TCB-2 ex vivo via functional enhancement of the potassium-chloride cotransporter KCC2. The signaling pathway linking 5-HT_2AR activation and normalization of KCC2 function was dependent on protein kinase C signaling and phosphorylation of KCC2 at serine 940 (S940), as mutation of S940 to alanine prevented restoration of chloride transport function by TCB-2. Through positive modulation of KCC2, TCB-2 also reduced elevated ethanol-induced GABAergic signaling after stress exposure that has previously been linked to increased ethanol consumption. Collectively, these findings provide mechanistic insights into the therapeutic action of 5-HT_2AR agonists at the neuronal and circuit levels of brain reward circuitry.