Abstracts

RATIONALE: A significant component of neuronal degeneration occurring in the aftermath of status epilepticus (SE) is of an apoptotic nature. This is manifest by DNA fragmentation, activation of caspase-3, and by the caspase-3 mediated cleavage of ICAD, an inhibitor of [dsquote]caspase-activated DNase[dsquote] (CAD). In initial studies, we observed that the most robust signs of apoptotic degeneration were associated with slowly evolving SE following injection of intraperitoneal kainate. We therefore directly compared rapid-onset SE with slow-onset SE for the extent of the expression of markers for apoptosis in two vulnerable brain regions.
METHODS: SE was induced in adult male Sprague-Dawley rats by kainic acid injection and seizures were terminated with diazepam. Slow-onset SE was induced by ip administration of kainic acid (12 mg/kg), while rapid-onset SE was induced by intravenous kainic acid (10 mg/kg). Seizures were terminated at 2hr after the onset of SE. At 24, 48, or 72 hr after SE termination, DNA fragmentation was evaluated by autoradiographic detection of radioactively labeled DNA fragments on an agarose gel, in combination with liquid scintillation counting. Levels of ICAD protein were measured in hippocampus and rhinal cortex by Western blotting (after SDS-PAGE) using specific antibodies.
RESULTS: SE induced by ip injection of kainic acid was characterized by a slow onset (60-100 min) and multiple isolated brief seizure episodes preceding SE onset. SE induced by tail vein injection of kainic acid started more rapidly, with an onset between 30 and 60 min and few or no brief isolated seizure episodes. In contrast to the extensive DNA fragmentation and the decrease in ICAD protein obtained in the hippocampus and rhinal cortex of animals with slow-onset SE, there was relatively little DNA fragmentation (70% less than in the slow-onset condition) and no decrease in ICAD protein in the same tissues of animals experiencing rapid-onset of SE.
CONCLUSIONS: Our results suggest that the extent to which apoptotic cell death contributes to the degeneration obtained following SE depends upon the evolution of the state of SE. It appears that the presence of a long latency period, during which multiple brief seizure episodes may occur, favors the occurrence of apoptotic cell death, whereas the relative absence of such a [ssquote]preconditioning[ssquote] period in rapid-onset SE may favor a predominantly necrotic profile. It will be especially interesting to determine whether these two distinct profiles are differentially sensitive to neuroprotective strategies.