Abstracts

RATIONALE: Status epilepticus (SE) induced neuronal death in selected populations of neurons in hippocampus and rhinal cortex involves caspase-3-dependent mechanisms despite the fact that the adult brain has very low expression levels of caspase-3. Moreover, caspase-3 activation can be elicited by apoptotic protease-activating factor-1 (APAF-1), a factor that is constitutively expressed at extremely low levels in the adult brain. We therefore reasoned that both caspase-3 and APAF-1 would be upregulated by SE.
METHODS: SE was induced in adult male Sprague-Dawley rats by kainic acid (12 mg/kg ip) and terminated after a 2 hr duration with diazepam (30 mg/kg ip). Total RNA was extracted from rhinal cortex at 2, 4, 8, 24, and 48 hr after termination of SE and analyzed by semi-quantitative RT-PCR for mRNA encoding caspase-3, caspase-9, and APAF-1.
RESULTS: A significant increase in caspase-3 mRNA levels was found at 4, 8, 24, and 48 hr after SE termination as compared with control animals, with maximum levels reached by 24 hr. APAF-1 mRNA levels were also significantly elevated, with maximum at 48 hr post-SE. In contrast, caspase-9 mRNA levels remained unchanged at all time points examined.
CONCLUSIONS: These results demonstrate that prolonged injurious seizure activity induces both caspase-3 and APAF-1 genes, allowing for the initiation of a caspase-dependent apoptotic cascade. Interestingly, these genes are highly downregulated in the adult brain, as compared with the immature brain (prior to postnatal day 7 in rat). This raises the possibility that SE-induced injury reengages the cellular machinery characteristic of programmed cell death during development.
[Supported by: NIH grants NS 20576, NS 38941, NS041231, MH 02040 and by the Epilepsy Foundation]