Abstracts

Rationale: Recent evidence of key synchrony dynamics between hippocampi and thalamus in an acute limbic epilepsy model in rats has been reported from our laboratory. However, the relevance of this newfound dynamic to a chronic model of epilepsy that might more closely model clinical cases of limbic epilepsy has not yet been demonstrated.Methods: Electrodes were implanted in the CA3 region of both hippocampi and in the anteromedial nucleus of the right thalamus in young adult male Sprague-Dawley rats. In the acute model, kainic acid (KA; 5nmol) was injected through a microcannula directly into the right hippocampus. Recordings were made in acute animals under general sedation within 8 hours of KA injection. In contrast, chronic animals were induced by i.p. injections of pilocarpine (10mg/kg) following pretreatment with LiCl and allowed to undergo status epilepticus for 90 min before diazepam i.p. injection (10mg/kg). Following a latency period and subsequent onset of spontaneous seizures, intracranial electrode activity was recorded during and between seizures in awake, freely-moving animals.Results: In the chronic animals, low frequency (25-35Hz) synchrony was repeatedly observed between hippocampus and thalamus at or before onset of full spontaneous seizures. High frequency (130-145Hz) synchrony was seen between these brain sites as seizures naturally terminated. This behavior of strong coherence in electrical activity between these structures was shown to occur at nearly identical frequency ranges as that of acute models during the same stages in seizure evolution.Conclusions: These findings of similarity in electrophysiological behavior during seizures between two significantly different models of limbic epilepsy suggest that this may be a critical component of the mechanisms by which seizures arise and naturally resolve. This information may provide important insight into how seizures might be disrupted or prevented using electrical or other perturbations to the brain.