Abstract
Contextual learning requires strengthening at both AMPA receptor-mediated excitatory synapses and GABA(A) receptor-mediated inhibitory synapses in CA1 neurons. However, the precise mechanisms underlying learning-induced strengthening at inhibitory synapses have remained unclear. To address this, we developed a novel cell-permeable peptide (Tat-pep β(3)-SS) that inhibits phosphorylation of the GABA(A) receptor β(3) subunit at Ser(408-409), using an HIV-Tat-tagged sequence. In behavioral experiments, bilateral microinjection of Tat-pep β(3)-SS into the CA1 region 60 min prior to inhibitory avoidance (IA) training significantly impaired contextual learning performance without affecting sensory, motor, and emotional functions. Western blot analysis revealed that Tat-pep β(3)-SS, but not the mutant control peptide (Tat-pep β(3)-AA), suppressed training-induced rapid phosphorylation at Ser(408-409). Patch-clamp recordings from FITC-labeled CA1 neurons showed that Tat-pep β(3)-SS blocked learning-induced enhancement of postsynaptic Cl⁻ currents mediated by GABA(A) receptors. Furthermore, histological analysis demonstrated a reduction in membrane-associated GABA(A) receptor clusters in Tat-pep β(3)-SS-positive neurons compared to Tat-pep β(3)-AA controls. These findings provide novel evidence that rapid phosphorylation of the GABA(A) receptor β(3) subunit at Ser(408-409) is essential for training-dependent inhibitory synaptic strengthening and contextual memory formation.