Astrocytic GAT-3 Regulates Synaptic Transmission and Memory Formation in the Dentate Gyrus.

GABAergic network activity plays a crucial role in a wide array of physiological processes and is implicated in various pathological conditions. While extensive research has been conducted on how GABAergic network activity modulates both excitatory and inhibitory synaptic transmission in the CA1 region, the mechanisms by which it influences synaptic transmission in the entorhinal cortex-dentate gyrus (EC-DG) circuits are still largely unexplored. Using a combination of whole-cell patch-clamp recordings, optogenetics, immunohistochemistry, and behavioral assays, we demonstrate that activation of GABA transporter 3 (GAT-3) in astrocytes triggers an increase in intracellular Ca²⁺ via the reverse Na⁺/Ca²⁺ exchanger. Intriguingly, inhibiting GAT-3 impedes the GABA-induced elevation of astrocytic Ca²⁺ levels, thereby curtailing the subsequent enhancement of synaptic transmission. Additionally, we show that endogenously released GABA from interneurons also modulates synaptic transmission through GAT-3 in the DG. Crucially, by selectively diminishing astrocytic calcium signals, we observed a concomitant decrease in the GABA-induced enhancement of synaptic transmission, underscoring the crucial role of astrocytes in this regulatory pathway. Moreover, we found that the activation of GAT-3 enhances excitatory transmission via presynaptic GluN2B-containing N-methyl-D-aspartate receptors (GluN2B-NMDARs) in the DG. Finally, our in vivo experiments demonstrate that inhibiting GAT-3 adversely affects the formation of contextual fear memory, highlighting its pivotal role in cognitive processing. These findings underscore the significance of astrocytic GAT-3 in cognitive functions and offer valuable insights into potential therapeutic targets for cognitive impairments, opening new avenues for the treatment of related disorders.