Abstracts

The contribution of hyperthermia [italic]per se[/italic] to status epilepticus (SE)-induced neuronal damage in the immature brain is not well understood. In adult animals, hyperthermia can aggravate seizure-induced neuronal damage (Liu [italic]et al.[/italic], 1993; Lundgren [italic]et al.[/italic], 1994). However, published reports did not show any additional damage caused by hyperthermic when compared to normothermic seizures in immature brain (Bender [italic]et al.[/italic], 2003; Sarkisian [italic]et al.[/italic], 1999; Toth [italic]et al.[/italic], 1998). To study this problem, we developed a model of lithium-pilocarpine SE in rats at post-natal day 10 (P10), in which we were able to obtain seizures of very similar intensity at a body temperature of 35[deg]C (normothermia) vs 39[deg]C (hyperthermia)., SE was induced in P10 rats with lithium (3mEq/kg, i.p.), and pilocarpine (60 mg/kg, s.c., 24 hours later). Their body temperature was maintained during 30 min of SE at 39[plusmn]1[deg]C (hyperthermic animals, HT+SE) or at 35[plusmn]1[deg]C (normothermic animals, NT+SE). Several measures showed seizure severity to be similar in both experimental groups. SE was terminated by diazepam (0.5 mg/kg, i.p.). Control animals received lithium and diazepam in presence of hyperthermia or normothermia. Anesthetized animals were perfused with 4% phosphate-buffered paraformaldehyde 24 hours after induction of SE. Each brain was embedded in paraffin and sectioned to 10 uM. The distribution of neuronal injury was evaluated by using Fluoro-jade B staining, whereas the expression of death markers (the active forms of initiator caspase-9 and executioner caspase-3) was assessed by fluorescence immunohistochemistry in adjacent sections. Mode of death (necrotic or apoptotic) from HT+SE and NT+SE animals was defined by electron microscopy., Fluoro-jade B staining showed neuronal injury in CA1, medial amygdala, dentate gyrus inner granule cell layer and cingulate cortex from HT+SE animals. NT+SE animals displayed very mild damage in CA1 and granule cell layer, none in amygdala. No damage was detected in controls. Electron microscopy showed a mixed population of apoptotic and necrotic neurons in CA1 from HT+SE and NT+SE groups. Active caspase-3 immunoreactive neurons were seen in CA1, granule cell layer and cingulate cortex from HT+SE animals, but active caspase-9 staining was limited to granule cell layer and cingulate cortex. Caspase-3 or -9 were not activated in NT+SE animals., Hyperthermia markedly aggravated the severity and the extent of SE-induced neuronal injury through a caspase-3 and/or -9-dependent mechanism., (Supported by Grant NS13515 from NINDS, National Institutes of Health, by UC Mexus grant, and by the Research Service of the Veterans Health Administration.)