Purpose: Glutamatergic transmission between neurons occurs at chemical synapses. The N-methyl-d-aspartate (NMDA)-receptor subclass of ionotropic glutamate receptors has been implicated in the epileptogenic mechanisms in human cortical dysplasia (CD). NMDA receptors are clustered at the postsynaptic membrane by anchoring to the postsynaptic density protein PSD-95, a putative ion channel-clustering protein. In this study, we quantitatively investigated the coassembly of PSD-95 to NR2B and NR1 in human epileptogenic cortex as compared with nonepileptic cortex.
Methods: We used coimmunoprecipitation and immunoblotting techniques to quantify and compare the numbers of coassembled PSD-95 with NR2B, PSD-95 with NR1, and NR2B with NR1 in the membrane proteins of brain tissues resected from four patients (aged 3.5, 6, 14, and 18 years) with medically intractable neocortical epilepsy associated with CD. The resected cortical tissues were grouped into epileptic and nonepileptic, as determined by prolonged subdural electrode recordings in three patients and direct intraoperative electrocorticographic recording in one patient.
Results: In all patients, the amounts of immunoprecipitated complexes, which reflect the numbers of coassembled PSD-95 proteins to NR2B subunits, were increased in epileptic cortex as compared with nonepileptic cortex.
Conclusions: These results suggest that increased coassembly of NR2B and NR1 with PSD-95 may underlie one of the cellular mechanisms that contribute to the in situ increased hyperexcitability, leading to seizure generation in focal CD.