Abstracts

Status epilepticus (SE) results in cell death in vulnerable neuronal populations. By increasing oxidative stress in the brain, SE may lead to oxidative-DNA damage. Oxidative DNA double-strand breaks (DSBs) have not been examined following SE even though they are the most lethal DNA lesion. DSBs can be quantified by immunocytochemical detection of the phosphorylated form of histone H2AX ([gamma]-H2AX); this phosphorylation occurs at the sites of DSBs. Using this marker, we investigated whether injurious durations of continuous seizures are required to provoke DSB formation. Moreover, we examined whether neuroprotective preconditioning with minimal electroconvulsive seizures (ECS) would prevent [gamma]-H2AX formation following SE. Continuous seizures were induced by kainic acid (12.5 mg/kg, i.p.) and terminated after 15, 30, or 120 min with diazepam (30 mg/kg, i.p.). Rats were perfused immediately following seizure termination, and their brains were removed for cryosectioning. [gamma]-H2AX was measured immunohistochemically. Minimal ECS was applied via corneal electrodes (200 msec, 22-28 mA) to induce minimal limbic motor seizures lasting 5-10 sec. Control (sham) animals received the same handling and contact with the electrodes, but no current was passed. Each ECS session consisted of 3 ECS seizures within 1 hr. One session was given daily for 7 days; kainic acid was administered on day 8, and SE was terminated at 120 min. Continuous seizures with durations as short as 15 min resulted in significant increases in [gamma]-H2AX in the CA1, CA3, and dentate gyrus (hilus and granule cell layer) of the hippocampus; thalamus; and entorhinal, perirhinal, piriform, and retrosplenial cortices. [gamma]-H2AX increased with seizure duration in all regions. ECS preconditioning attenuated the increase in [gamma]-H2AX induced by severe (120 min) SE. ECS alone did not significantly increase [gamma]-H2AX. Our observation that [gamma]-H2AX increased after non-injurious durations of continuous seizures (15 min) indicates that DSBs can occur in response to cell endangerment insufficient to cause cell death. This may explain the increase in [gamma]-H2AX in death-resistant cell populations (dentate granule cells) following injurious seizure durations (120 min of SE). Thus, molecular injury caused by continuous seizures of durations too short to cause brain damage may have long-term adverse sequelae. The reduction of [gamma]-H2AX following severe SE in animals preconditioned with ECS suggests that brief seizures are protective not only against cell death but also against molecular injury. (Supported by F31NS 461991(SC), R01NS 20576(KG), K01MH 02040(AK), and K07AG019165(AK) from NIH.)