Repeated seizures cause a generalized increase in excitability in the hippocampus.

Changes in excitability within the hippocampus were examined by recording in CA3 and in CA1 or the dentate gyrus and stimulating in the angular bundle (fiber bundle connecting the entorhinal cortex with the dentate gyrus) before and after 36 electrographic seizures in urethane anesthetized rats. The responses recorded in CA3 or CA1 to stimulation of the angular bundle every 30 s were unchanged after repeated seizures, while the responses in the dentate gyrus were augmented. When the angular bundle was stimulated every 200 ms, population spikes appeared in CA3 and CA1, with CA1 producing multiple population spikes before CA3. The results indicate that after repeated seizures there is a general enhancement of excitability throughout the hippocampus.