Abstracts

Status Epilepticus (SE) is a life-threatening, clinical emergency. One hallmark of SE is that seizure activity does not self-terminate. This study investigated the early cellular changes during the induction and expression of seizure activity in the rat pilocarpine model. The study focused on the alteration of CaM kinase II activity, which has been shown to modulate membrane excitability in numerous studies. Characterizing the early modulation of this enzyme system may elucidate the mechanisms of seizure induction that differentiate SE from discrete seizure activity. Seizure activity was induced by pilocarpine injection (350 mg/kg, i.p.) . Electrographic and behavioral activity were tracked and characterized by video-EEG monitoring. At specific time points following initiation of discrete seizure activity, brain tissue was harvested and tested for CaM kinase II activity. Enzyme activity was analyzed in hippocampal and cortical homogenates and specific subcellular fractions. Phosphate incorporation into Autocamtide II was measured to determine CaM kinase II activity. Enzyme translocation was measured by western analyses of subcellular fractions. The induction of discrete seizure activity and status epilepticus was similar to previously describe studies. No alteration of basal kinase activity was observed at any time point, or in any subcellular fraction tested. However, significant modulation of calcium-stimulate CaM kinase II activity was observed coincident with the induction of SE. Homogenate fractions isolated from SE animals displayed significant inhibition in both cortical (18% inhibition, P [lt] 0.05, n = 9) and hippocampal structures (30% inhibition, p [lt] 0.001, n = 9). No inhibition of kinase activity was observed in rats that exhibited seizure activity but did not develop SE. Contrary to whole cell homogenate activity, an initial increase in synaptic kinase activity was observed with the induction of SE. A significant initial increase in kinase activity was observed in crude synaptic membrane fractions from the cortex (21% increase, p [lt] 0.05). Kinase activity showed a similar, but insignificant increase in crude synaptic membrane isolated from hippocampal structures (11% increase, p [gt] 0.05). The initial increase in kinase activity was associated with a significant increase in enzyme concentration at the synaptic level. However, as SE progresses, significant inhibition of CaM kinase II activity was observed. The data suggest that alteration of CaM kinase II activity may be involved in the switch between discrete seizures and initiation of continuous seizure activity in SE. (Supported by RO1-NS39770.)