Rapid antidepressants stimulate the decoupling of [GABA.sub.B] receptors from GIRK/Kir3 channels through increased protein stability of 14-3-3η

A single injection of N-methyl-D-aspartate receptor (NMDAR) antagonists produces a rapid antidepressant response. Lasting changes in the synapse structure and composition underlie the effectiveness of these drugs. We recently discovered that rapid antidepressants cause a shift in the y-aminobutyric acid receptor ([GABA.sub.B]R) signaling pathway, such that [GABA.sub.B]R activation shifts from opening inwardly rectifiying potassium channels (Kir/GIRK) to increasing resting dendritic calcium signal and mammalian Target of Rapamycin activity. However, little is known about the molecular and biochemical mechanisms that initiate this shift. Herein, we show that [GABA.sub.B]R signaling to Kir3 (GIRK) channels decreases with NMDAR blockade. Blocking NMDAR signaling stabilizes the adaptor protein 14-3-3η, which decouples [GABA.sub.B]R signaling from Kir3 and is required for the rapid antidepressant efficacy. Consistent with these results, we find that key proteins involved in [GABA.sub.B]R signaling bidirectionally change in a depression model and with rapid antidepressants. In socially defeated rodents, a model for depression, [GABA.sub.B]R and 14-3-3η levels decrease in the hippocampus. The NMDAR antagonists AP5 and Ro-25-6981, acting as rapid antidepressants, increase [GABA.sub.B]R and 14-3-3η expression and decrease Kir3.2. Taken together, these data suggest that the shift in [GABA.sub.B]R function requires a loss of [GABA.sub.B]R-Kir3 channel activity mediated by 14-3-3η. Our findings support a central role for 14-3-3η in the efficacy of rapid antidepressants and define a critical molecular mechanism for activity-dependent alterations in [GABA.sub.B]R signaling. Molecular Psychiatry (2015) 20, 298-310; doi: 10.1038/mp.2014.165; published online 6 January 2015