Abstracts

Rationale: Kindling is a widely used animal model of intractable temporal lobe epilepsy. We reported fast Fourier transformation (FFT) analysis on the afterdischarge (AD) induced by unilateral hippocampal kindling of the rabbit, where the kindled animals showed a significant enhancement of the high frequency band (HFB: 12-30 Hz) component (K. Tsuchiya et al., Epilepsy Res, 2011;95:144-151). In the present study, we examined FFT analysis on ADs, spontaneous seizures and background EEGs induced by alternate-site kindling (AK) of the rabbit hippocampi to reveal the underlying mechanism of kindling-induced epileptogenesis.Methods: We performed all experiments under appropriate conditions in accordance with the Declaration of Helsinki and the Guide for Animal Experimentation at Soka University. Ten adult rabbits were used. Under pentobarbital (PTB) anesthesia, we stereotaxically implanted two pairs of bipolar stainless steel electrodes coated with polyurethane into the dorsal hippocampi. The electrodes were used for stimulating as well as recording. Daily kindling stimulations consisted of a 1-s of 50 pulses, with pulse duration of 1 ms, at 80 200 ?A, which was higher than the afterdischarge (AD) threshold. Concurrent alternating stimulations were delivered to the right and the left hippocampus once every 24 h. Conventional behavioral criteria were used.FFT analysis was performed with sampling frequency of 1 kHz by Power Lab (Chart, ADInstrument).Results: All animals developed stage 5 behavioral responses. The power spectral density ratios of the lower frequency band (LFB: 0-9 Hz), the middle frequency band (MFB: 9-12Hz) and HFB components against total PSD were calculated. FFT analysis on AD showed the peak frequency at LFB during early phase of kindling, but two peaks at LFB and HFB during late phase. Standardizing each ratio in the initial stage as 1.00, the ratio of LFB component significantly decreased to 0.62 while the ratio of HFB increased to 3.93 (p<0.01). Nine animals showed spontaneous seizures. FFT analysis on spontaneous seizures revealed that they have similar frequency characteristics with those of ADs induced in late phase. In background EEG, all frequency bands gradually increased with kindling procedure advanced.Conclusions: Frequency analyses on AK-induced AD and spontaneous seizure provided that enhancement of higher frequency component leads to kindled stage. As epileptogenesis proceeded, the LFB component decreased while the HFB component increased. It is suggested that FFT analysis on stimulus-induced or spontaneous seizure discharge and background EEG is useful for progression of epileptic disorders. We will discuss domain of these high frequency components and circuit suspected focus of epileptogenesis in hippocampus.