The experimental epileptogenic focus produced by cobalt-gelatine stick implantation in the cerebral cortex of rabbits has been studied by electron microscopy. Since our cobalt focus was latent, the bemegride maneuver was intravenously performed to identify the cobalt lesion of the cortex as an epileptogenic focus. The cobalt lesion comprised three different zones. Of the three zones, the reactive zone showed a glio-mesenchymal scar and prominent ultrastructural changes. The major change of this zone was found in the neurons, neuropils and astrocytes. Electron-lucent neurons deprived of the usual neuropils surrounding them, widening of extracellular spaces and swollen dendrites in neuropils, and proliferating astrocytes were observed constantly throughout the experimental period. These findings may be significant for the genesis of this type of epilepsy.

SUMMARY For the purpose of studying the electrophysiological activity in the apical dendrites during a seizure, changes of dendritic potentials (DPs) in direct cortical responses were investigated during and after electrically induced seizures. As results, during a seizure, either the DPs were not elicited at all or the DPs depressed in amplitude were elicited. Furthermore, the suppression of the DPs was particulary marked when positive seizure discharges were seen in the cortical surface. In conclusion, from reference to the past studies with intracellular recordings, the suppression of the DPs was considered to indicate that a sustained depolarization took place in the apical dendrites during a seizure and greater depression of the DPs during surface‐positive seizure discharges was seemed to suggest that EPSPs arise in the apical dendrites simultaneously with the surface‐positive seizure discharges.

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