As an extreme form of abnormally synchronized activity, epilepsy may modify patterns of organization in the nervous system. It is clear that enhanced glutamatergic excitatory synaptic transmission with alterations in the expression of ionotropic glutamate receptors is a mechanism critical for seizure susceptibility and excitotoxicity. However, the exact quomodo and the roles of regulated N-methyl-D-aspartate receptor (NMDAR) composition and expression of a major postsynaptic density (PSD) scaffolding molecule, PSD-95, are as yet unclear. To study protein expression changes after epileptiform discharges in cultured immature rat cortical neurons, we divided cells into three groups which were transiently exposed to regular Neurobasal/B27 (control group), physiological solution (PS group) and magnesium-free physiological solution (MGF group) at cultured day 6. Neurons at three different culture ages (DIV7, DIV12 and DIV17) were collected for immunoblotting analysis. We found a decrease in expression of NR2B NMDAR subunit and PSD-95 (P<0.05) shortly after insult (within 24 h), which may show that brief magnesium-free media treatment of primary cultured rat cortical neurons, an in vitro model of seizure brain injury, has a major influence on the expression of NR2B subunit and PSD-95.