MICROGLIA-MEDIATED, P<SUB >2</SUB>Y<SUB>12</SUB>-DEPENDENT REMODELING OF INHIBITORY SYNAPSES BY MAGNETIC INTERMITTENT THETA-BURST STIMULATION IN ORGANOTYPIC SLICE CULTURES

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique widely used in the treatment of neuropsychiatric disorders, yet the cellular mechanisms underlying its therapeutic efficacy remain incompletely understood. Here, we investigated whether microglia contribute to inhibitory synaptic plasticity induced by magnetic intermittent theta-burst stimulation (iTBS). Using magnetic iTBS applied to mouse entorhino-hippocampal organotypic slice cultures, we performed whole-cell patch-clamp recordings from pyramidal neurons to assess inhibitory synaptic transmission. In hippocampal CA1 pyramidal neurons, iTBS with 900 pulses (iTBS900) significantly reduced the amplitude of GABA_A-mediated miniature inhibitory postsynaptic currents (mIPSCs), while event frequency remained unchanged. Consistent with these functional changes, immunohistochemical analyses revealed a selective reduction of the inhibitory postsynaptic scaffold protein gephyrin within the pyramidal cell layer, but not in the stratum radiatum, indicating compartment-specific remodeling of (peri)somatic inhibition. Depletion of microglia using the CSF1R inhibitor pexidartinib (PLX3397, 50 nM) abolished iTBS-induced inhibitory synaptic plasticity. Similarly, pharmacological blockade of the microglial purinergic receptor P₂Y₁₂ with the selective antagonist PSB0739 (2 µM) prevented iTBS-dependent changes in inhibitory synaptic strength. Together, these findings identify microglia-mediated, P₂Y₁₂-dependent signaling as an essential mechanism underlying magnetic iTBS-induced, compartment-specific inhibitory plasticity, providing mechanistic insights into cellular pathways relevant for the therapeutic actions of TMS.