Medial septum mediates the increase in post-ictal behaviors and hippocampal gamma waves after an electrically induced seizure

Abstract

Hippocampal EEG and behavior of freely moving rats were studied before and after a hippocampal afterdischarge (AD), with or without reversible inactivation of the medial septum (MS) by muscimol. Muscimol suppressed the normal hippocampal EEG, including theta (5–10 Hz) and gamma (30–70 Hz) waves. After a hippocampal AD, hippocampal gamma waves were decreased for about 2 min and then increased at 3–10 min, while power of EEG of <30 Hz was decreased at ≤3 min and showed no increase after an AD. Muscimol injection in the MS before the AD blocked the post-ictal increase of the gamma waves. In rats injected with vehicle in the MS, post-ictal increase in gamma waves was accompanied by an increase in horizontal locomotion, rearings, face washes, and wet dog shakes. In rats injected with muscimol in the MS before the AD, both the post-ictal increase in gamma waves and behaviors were completely suppressed. Muscimol injection in the MS after the AD significantly suppressed both gamma waves and post-ictal behaviors, as compared to vehicle-injected rats, but to a lesser degree than rats injected with muscimol in the MS before the AD. Hippocampal AD duration was not significantly affected by muscimol injection in the MS. We conclude that the MS is responsible for the maintenance of the normal and the post-ictal gamma waves. We suggest that the post-ictal gamma waves in the hippocampus may drive post-ictal behaviors, and in previous studies, we showed that this may occur through the nucleus accumbens.