Abstracts

Rationale: Electroencephalographic (EEG) events in epileptogenesis have been rigorously pursued in animal models in an effort to prevent epileptogenesis. For the first time, we have shown that C57BL6/J can become epileptic after kainate-induced status epilepticus (SE). We have characterized different types of spontaneous recurrent non-convulsive and convulsive motor seizures (SR-NCS/SR-CMS) in 18wk continuous long study. We have identified maximum number of SR-CMS episodes during the first month, therefore this is an "early-onset C57BL6/J mouse seizure model" of TLE. Past studies have not clearly characterized the EEG events that lead to SR-CMS during the epileptogenesis. Methods: We used 13 male C57BL6/J mice that were implanted with radio-telemetry device for this study. The electrodes were positioned epidurally for continuous video-EEG monitoring. After a 48h baseline, mice were administered with low dose of kainate (5mg/kg intraperitoneally at 30min intervals) to induce SE of varying severity. The SE was observed for 2h (2h SE) starting from first stage-5 episode in severe seizure group (SSG) and first stage-3 episode in mild seizure group (MSG). Behavioral and electrographic severity of seizures was calculated based on the exact duration of stage-specific epileptiform spike episode (stage 1-5) during the 2h SE. At the end of 2h SE, diazepam was given (10mg/kg, i.p.) to stop the behavioral seizures. Later, the mice were continuously monitored to observe EEG events of epileptogenesis and the development of SR-CMS. Results: Although diazepam controlled behavioral seizures, it did not prevent EEG spiking during epileptogenesis. The spike frequency reduced 24-72h post-SE to form inter-ictal spikes (0.2 to 1Hz) that consisted of stage-1 spikes (amplitude 200-300uV) and stage-2 spikes (amplitude 300-1500uV). The inter-ictal spikes lead to the formation of NCS spike episodes namely; stage-1 type (2-5Hz); stage-2 type (0.8-1.2Hz) and stage-2 with high frequency trigger (HFT) patterns (0.8-1.2Hz). When stage-1 and stage-2 NCS spike episodes intermixed, led to the development of SR-CMS episodes that lasted for a minimum of 30s. In the SSG, SR-CMS episodes were observed within first 5-7d while, these events were considerably prolonged in MSG. The SR-CMS types observed were stage-3 type (consisting stage 1-3 spikes), stage-4 type (stage 1-4 spikes) and stage-5 type (stage1-5 spikes). The stage-5 CMS showed three behavioral signatures associated with lateral recumbence/rigidity, wild running and jumping. The development of SR-CMS during epileptogenesis also coincided with reactive astrogliosis and microgliosis in hippocampus, aberrant migration of neuroblasts in dentate gyrus at 7d post-SE. Conclusions: Overall, the real-time EEG events coupled with neurobiological markers of epileptogenesis provide convincing evidence for early-onset of SRS in C57BL/6J mouse. Because of very early onset of SRS in our model, compared to rat models, it reduces the duration of experiments, the amount of drugs and overall cost of experiments.