Abstracts

Continuous seizures or status epilepticus (SE) endanger vulnerable neurons, with prolonged durations causing cell death. Seizure-evoked oxidative damage, including DNA damage, can contribute to this injury (Crowe et al, AES, 2005), but the threshold duration of seizures to induce DNA damage is not known, nor do we know if DNA damage occurs after seizure durations not causing cell death. Because phosphorylation occurs at sites of DNA double-strand breaks (DSBs), DSBs can be quantified by measuring phosphorylated histone H2AX ([gamma]-H2AX). We examined [gamma]-H2AX in specific brain regions after seizure durations subthreshold for causing neuronal death., Four seizure conditions were studied: 1) acute repeated minimal electroshock seizures (ECS); 2) 30 min of kainic acid (KA)-evoked brief intermittent seizures (prior to the onset of SE); 3) 5 min of continuous seizure (SE) induced by KA; and 4) 120 min of KA-evoked SE in rats pre-exposed to a neuroprotective regimen of ECS for 7 days. Seizures induced by KA (12.5 mg/kg, ip) were terminated with diazepam (30 mg/kg, ip). ECS (200ms, 22-28mA) induced 5-10 sec limbic seizures. A single (acute) ECS session consisted of 3 ECS at 30 min intervals; chronic ECS consisted of daily sessions for 7d. Rats were perfused after seizure termination; brains were cryosectioned for [gamma]-H2AX immunohistochemistry., Neither acute nor chronic ECS changed [gamma]-H2AX immediately or 24h after the last seizure. KA-evoked intermittent seizures (5-7 brief seizures in the first 30 min) caused significant increases in [gamma]-H2AX in neurons in CA1, CA3, and dentate gyrus (hilus and granule cells), amygdala, and entorhinal cortex. Even greater increases were seen following 5 min of SE, although in most areas (except for dentate granule cells) this was not as great as that obtained after 120 min of SE. With ECS preconditioning, the increase in [gamma]-H2AX induced by prolonged (120 min) SE was reduced by at least 80%; the residual increase in [gamma]-H2AX was less than that seen after 5 min SE in rats without preconditioning., Our observation that [gamma]-H2AX increased after seizures that did not cause significant cell death indicates that DSBs are an early sign of cell endangerment. Moreover, the transient increase in [gamma]-H2AX in death-resistant cells (dentate granule cells) suggests that rapid activation of repair processes may contribute to the resistance of these neurons to seizure-evoked injury. Because a single cluster of 5-7 seizures increased [gamma]-H2AX, whereas acute or chronic ECS did not, it appears that isolated seizures do not induce DSBs and that a minimum seizure density is needed to trigger DNA damage. Our data also suggest that 5 min of SE in seizure-naive animals causes substantial DNA damage in the absence of neuronal loss. Thus, early intervention to terminate SE may be necessary to minimize adverse neurological sequelae that can occur without neurodegeneration., (Supported by NIH F31NS461991, R01NS20576, K01MH02040, K07AG019165.)