ALTERED AMPA RECEPTOR SUBUNIT CONFIGURATION DRIVES HYPEREXCITABILITY IN BCNU MODEL OF FOCAL CORTICAL DYSPLASIA (FCD)

Focal Cortical Dysplasia (FCD) is a major cause of drug-resistant epilepsy, yet its molecular drivers remain poorly defined. AMPA receptor (AMPAR) subunit composition plays a key role in synaptic excitability and may be altered in FCD. To investigate whether dysregulated expression of AMPA receptor subunits, specifically GluA1 and GluA4, contributes to the enhanced excitatory synaptic activity observed in a histopathologically validated BCNU (1,3-bis(2-chloroethyl)-1-nitrosourea) rat model of FCD. BCNU-model recapitulates key features of human FCD and it is ethically infeasible to obtain age- and sex-matched human cortical brain samples. At postnatal day 30, somatosensory cortex samples were analysed using qPCR and immunohistochemistry for GluA1, GluA4, and GluN2B. Whole-cell patch clamp recordings of spontaneous EPSCs (sEPSCs) were performed, with APV (2-amino-5-phosphonovalerate) and CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) used for pharmacological dissection. GluA1 expression was significantly reduced in FCD tissue at both mRNA and protein levels (p<0.05), while GluA4 (L- and S-isoforms) showed significant upregulation (p<0.01). GluN2B levels remained unchanged. Functionally, FCD neurons displayed increased sEPSC amplitude (p=0.0022) and frequency (p=0.045), with a leftward shift in interevent intervals (p=0.0002). CNQX + APV application almost suppressed all sEPSCs confirming their glutamatergic nature. APV alone did not show any significant reduction in peak amplitude or frequency, suggesting altered AMPAR kinetics. Power spectrum analysis further supported a distinct glutamatergic signature in FCD. Upregulation of the GluA4 subunit with concomitant downregulation of GluA1 likely shifts AMPAR-mediated synaptic transmission toward hyperexcitability in FCD, with altered AMPAR channel dynamics reflecting modified subunit interactions that represent potential targets for subunit-specific pharmacotherapy.