Abstracts

RATIONALE: We are interested in evaluating the time course and distribution of programmed cell death (PCD) that is thought to occur in response to prolonged continuous seizure activity (status epilepticus, SE). Because internucleosomal DNA fragmentation is a reliable marker for the irreversible stages of PCD, the present study examined spatial and temporal characteristics of DNA fragmentation in limbic regions (rhinal and frontal cortices, hippocampus and olfactory bulbs) following varying durations of SE in rats. METHODS: SE was induced in adult male Sprague-Dawley rats by kainic acid (12 mg/kg ip) or by focal infusions of cyclothiazide (1.8 nmol) and bicuculline (180 pmol) into area tempestas (AT); seizures were allowed to continue for either 30, 60, or 120 min before being terminated with diazepam. In rats pretreated with minimal electroshock seizures (ECS), ECS treatment was given daily for 7 days. RESULTS: At 24 hr after either focal or systemically-induced SE lasting for 60 or 120 min, DNA fragmentation was found most prominently in rhinal and frontal cortices, and hippocampus but not in olfactory bulbs. No fragmentation was detected in rats not experiencing SE. A 30 min duration of SE was not sufficient to induce detectable fragmentation in any area. Following a 120 min period of kainic acid-induced SE, DNA fragmentation in frontal and rhinal cortices and hippocampus was not detectable at 8 hr, was significant by 24 hr, and maximum at 48 hr and 72 hr after SE termination. At 72 hr there was a sharp increase in relative amounts of low molecular size DNA fragments (nucleosomal mono-, di-, tri-, and tetramers) as compared to earlier time points, indicative of the final stages of degeneration. Exposure to 7 days of minimal ECS prior to induction of SE dramatically attenuated the DNA fragmentation in hippocampus, rhinal cortex and frontal cortex. CONCLUSIONS: Our results indicate that the terminal stages of PCD occur in specific brain areas between 24 hr and 72 hr after an episode of SE lasting 60 min or longer, and that prior exposure to repeated brief seizures can prevent this response. Supported by NIH grant NS36035.