c-JUN expression and apoptotic cell death in kainate-induced temporal lobe epilepsy

Following kainate (KA)-induced epilepsy, rat hippocampal neurons strongly express immediate early gene (IEG) products, i.e., c-FOS and c-JUN, and neural stress protein, HSP72. Prolonged expression of c-JUN and c-FOS 48 hr after cerebral ischemia has been underwent delayed neuronal death. However, it is not yet clear whether IEGs actually assume the essential roles in the cell death process or simply as a by-product due to external stimuli because of the prolonged expression of c-FOS, more than one week, on intact CA2 neurons of the hippocampus in a KA-induced epilepsy model. This study investigated the relationships between prolonged expression of c-JUN and hippocampal neuronal apoptosis in a KA-induced epilepsy model. Epileptic seizure was induced in rats by a single microinjection of KA (1 microgram/microL) into the left amygdala. Characteristic seizures and hippocampal neuronal injury were developed. The expression of c-JUN was evaluated by immunohistochemistry, and neuronal apoptosis by in situ end labeling. The seizures were associated with c-JUN expression in the hippocampal neurons, of which the level showed a positive correlation with that of apoptosis. Losses of hippocampal neurons, especially in the CA3 region, were partly caused by apoptotic cell death via a c-JUN-mediated signaling pathway. This is thought to be an important component in the pathogenesis of hippocampal neuronal injury via KA-induced epilepsy.