Progression of neuronal damage after status epilepticus and during spontaneous seizures in a rat model of temporal lobe epilepsy

Abstract

The present study was designed to address the question of whether recurrent spontaneous seizures cause progressive neuronal damage in the brain. Epileptogenesis was triggered by status epilepticus (SE) induced by electrically stimulating the amygdala in rat. Spontaneous seizures were continuously monitored by video-EEG for up to 6 months. The progression of damage in individual rats was assessed with serial magnetic resonance imaging (MRI) by quantifying the markers of neuronal damage (T2, T1 rho, and Dav) in the amygdala and hippocampus. The data indicate that SE induces structural alterations in the amygdala and the septal hippocampus that progressively increased for approximately 3 weeks after SE. T2, T1 rho, and Dav did not normalize during the 50 days of follow-up after SE, suggesting ongoing neuronal death due to spontaneous seizures. Consistent with these observations, Fluoro-Jade B-stained preparations revealed damaged neurons in the hippocampus of spontaneously seizing animals that were sacrificed up to 62 days after SE. The presence of Fluoro-Jade B-positive neurons did not, however, correlate with the number of spontaneous seizures, but rather with the time interval from SE to perfusion. Further, there were no Fluoro-Jade B-positive neurons in frequently seizing rats that were perfused for histology 6 months after SE. Also, the number of lifetime seizures did not correlate with the severity of neuronal loss in the hilus of the dentate gyrus assessed by stereologic cell counting. The methodology used in the present experiments did not demonstrate a clear association between the number or occurrence of spontaneous seizures and the severity of hilar cell death. The ongoing hippocampal damage in these epileptic animals detected even 2 month after SE was associated with epileptogenic insult, that is, SE rather than spontaneous seizures.