Abstracts

Status epilepticus (SE) is a life-threatening condition charecterized by continuous seizure activity. Our previous studies have suggested that the calcium stimulated phosphatase, calcineurin (CaN), is involved in the pathology of SE. This study investigated the temporal profile of changes in CaN during the early stages of induction and expression of SE. Pilocarpine injection (350 mg/kg, i.p.) was used to induce seizure activity in adult male Wistar rats. Electrographic and behavioral charecteriztics were monitored by video-EEG. At specfic time points after the initiation of discrete seizure activity, brain tissue was harvested and tested for CaN activity. CaN activity was assayed in homogenates and specific subcellular fractions via pNPP dephosphorylation. Enzyme concentration in subcellular fractions was determined by western analysis. Both hippocampal and cortical synaptoplasmic membrane (SPM) fractions showed an approximate doubling in CaN concentration at a time point corresponding to the initiation of SE. This increase in SPM CaN concentration remained present at all subsequent time points. However, no alteration of CaN activity was detected in cortical or hippocampal homogenates within the first 10 min of SE. At 20 min of SE, basal CaN activity was elevated to 203.5% of control in cortical, and 209.7% of control in hippocampal homogenates (n=5, p [lt] 0.001). Basal CaN activity remained elevated in both cortical and hippocampal homogenates at all subsequent time points. Maximal CaN activity in both cortical and hippocampal homogenates was indistinguishable from control at onset of SE and 10 min of SE. At 20 min of SE, maximal CaN activity in cortical homogenates increased by 53.1% compared with control, and 57.2% in hippocampal homogenates (n=5, p [lt] 0.01). Maximal activity remained elevated at all subsequent time points in homogenates from both brain regions. Similar to the whole cell activity, basal and maximal CaN activity in both hippocampal and cortical crude synaptoplasmic membrane fractions (SPM) was not altered initially, but became significantly elevated at the 20 min time point and remained elevated at all subsequent time points. The data demonstrate differential, early modulation of CaN activity and subcellular distribution. The late increase in CaN activity may represent a protective mechanism or may be involved in secondary pathologies, such as epileptogenesis. (Supported by R01-NS39770 (SBC), This project was supported by the Epilepsy Foundation through the support of the Centers for Disease Control and Prevention (SBC), the American Epilepsy Society, and the Lennox Trust Fund (JEK).)