Increased NMDA responses and dendritic degeneration in human epileptic hippocampal neurons in slices

To investigate physiological properties of epileptogenic neurons in relation to epileptic pathology, intracellular recording and intracellular dye injection after the recording were obtained in dentate granule cells in slices prepared from excised human epileptic hippocampus in which selective cell degeneration has been documented. Markedly prolonged excitatory postsynaptic potentials (EPSPs) were recorded in 67% of the total neurons sampled during perforant path stimulation. Such EPSPs were voltage dependent and sensitive to the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid. Neurons that generated the increased N-methyl-D-aspartate (NMDA) responses were accompanied by abnormal dendritic morphology, i.e. loss of dendritic spines and development of beaded shafts. These findings suggest that an NMDA receptor-mediated toxic process that impinges specifically on dendritic components might take place in intractable epilepsy.