WNT-5A SIGNALING PROMOTES AMPA RECEPTOR INSERTION AND CONVERTS SILENT SYNAPSES INTO FUNCTIONAL CONNECTIONS IN THE DEVELOPING HIPPOCAMPUS

Silent synapses are prevalent during early brain development and their conversion into functional synapses is essential for circuit maturation. We investigated whether the Wnt ligand Wnt-5a drives the unsilencing of glutamatergic synapses in the neonatal hippocampus. Whole-cell patch-clamp recordings were obtained from CA1 pyramidal neurons in acute rat hippocampal slices using minimal stimulation to monitor single-synapse responses. Wnt-5a application increased both α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) mediated excitatory postsynaptic currents, converting silent synapses into functional ones. This effect was mimicked by the Wnt-5a-derived peptide Foxy-5 and blocked by the soluble Wnt antagonist secreted frizzled-related protein-2 (sFRP-2), confirming pathway specificity. Potentiation of NMDAR currents resulted from increased synaptic potency followed by enhanced release probability and occurred even in the presence of AMPAR blockade, indicating coordinated pre- and postsynaptic mechanisms. Pharmacological inhibition of NMDARs prevented conversion in most synapses; however, a subset became functional independently of NMDAR activation, suggesting the engagement of distinct calcium-dependent pathways. Collectively, these findings demonstrate that Wnt-5a signaling promotes AMPAR insertion, synaptic unsilencing, and the emergence of nascent synapses during early hippocampal development. Our results identify Wnt signaling as a key regulator of synaptic maturation and connectivity in developing neural circuits.