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The subunit composition of glutamate receptors affects their functional properties, and could contribute to abnormal electrophysiology in pediatric cortical dysplasia (CD). We examined electrophysiological responses and subunit assembly of N-methyl-D-aspartate (NMDA) receptors in acutely dissociated normal-appearing pyramidal and cytomegalic neurons from CD tissue and normal-appearing pyramidal neurons from non-CD tissue. In most cytomegalic and ∼30% of normal-appearing pyramidal neurons from CD tissue, NMDA currents showed decreased Mg2+ sensitivity compared with neurons from non-CD tissue. Ifenprodil had less effect in CD compared with non-CD neurons, indicating a functional loss of NR2B subunits. NMDA-evoked current density was decreased in cytomegalic compared with normal-appearing neurons. Single-cell reverse transcriptase polymerase chain reaction showed that all non-CD neurons expressed NR2B subunit mRNA. By comparison, 22% of pyramidal neurons in CD tissue lacked NR2B mRNA. Immunofluorescence showed a decrease in NR2B subunit expression in cytomegalic neurons and a subset of normal-appearing pyramidal neurons from CD tissue. Taken together, these results demonstrate the presence of NMDA receptors with altered subunit composition and Mg2+ sensitivity that could contribute to functional abnormalities in CD.