Abstracts

In kindling epileptogenesis, a model of mesial temporal lobe epilepsy, repetitive stimulation of the perforant path leads to increased after-discharges as measured by EEG and an enduring seizure-prone state. Stimulus-induced glutamate release is thought to participate in rearrangements of neuronal circuitry favoring a permanent hyper-excitable state, often associated with mossy fiber sprouting. But the molecular mechanisms by which repetitive stimuli evoke these long-lasting changes in synaptic strength are unknown. We hypothesize that during seizures, glutamate-receptor activation turns on protein signaling cascades, possible via 1-[italic]O[/italic]-alkyl-2-acetyl-glycero-3-phosphocholine (PAF), which lead to long-term changes in neuronal circuitry through alterations in gene transcription. In the current study, we set out to determine the role of the stress-activated MAPK, c-jun N-terminal kinase (JNK) and the newly-discovered JNK scaffold-regulating proteins in kindling. Adult, male Wistar rats were stereotaxically implanted in the right ventral hippocampus with stimulatory and recording electrodes and underwent a rapid kindling protocol. The progression of kindling was verfied behaviorally, by scoring seizures according to Racine[rsquo]s scale and electrophysiologically, by recording after-discharges. Immunoblot analysis of Thr183/ Tyr185-phosphorylated JNK-1, -2, and -3 was employed as indication of the JNK activation state in the dentate gyrus, CA3, and CA1 sub-regions of the hippocampus as well as in the cortex. Immunofluorescent analysis was performed to confirm this region-specific localization of phosphorylated JNK and to examine the distribution of the JIP proteins in kindled animals. Finally, brain sections from fully kindled animals were processed with a Nissl stain to assess the distribution of neuronal injury. Preliminary results indicate that kindled animals experiencing severe stimulus-induced seizures (stage 5 on Racine[rsquo]s scale) not only exhibit an increased mean number of spikes on EEG recordings but also display marked JNK phosphorylation in the hippocampus and the cortex compared to their na[iuml]ve counterparts. Immunofluorescence analysis of phosphorylated JNK confirms this region-specific pattern of JNK activation in the cortex and the hippocampus. In addition, JNK activation, which has been implicated in neuronal death under many pathological conditions in the CNS, coincides with neuronal damage as seen with Nissl stain. These data suggest that decreasing thresholds for JNK activation may play a critical role in the progression of kindling by promoting death of neurons, possibly inhibitory interneurons, and/or by phosphorylating substrates which may act to modulate synaptic strength during kindling epileptogenesis. (Supported by NIH NS 23002.)