Spectral analysis of bilateral or alternate-site kindling-induced afterdischarges in the rabbit hippocampi.

Kindling is one of the popular animal models of temporal lobe epilepsy. In the present study following the previous results obtained using unilateral hippocampal kindling (UK), we performed spectral analysis of bilateral or alternate-site kindling-induced afterdischarges (ADs) in the rabbit hippocampi. Eight and ten adult rabbits were used for bilateral kindling (BK) and alternate-site kindling (AK), respectively. Kindling stimuli consisted of a train of biphasic pulses (1ms duration each) of 50Hz for 1s, with suprathreshold intensity for AD. The stimulations were applied simultaneously to the bilateral hippocampi in the BK and were delivered to the right and left hippocampus once every 24h in the AK. Motor responses were classified into five stages according to the conventional criteria. All animals in BK as well as AK developed stage 5 convulsions. This contrasts to the result of UK (kindled: 50%; incomplete: 50%). We normalized power spectral density (PSD) and monitored the changes in the proportion of lower frequency band component (LFB: 0-9Hz) and the higher frequency band (HFB: 12-30Hz). BK animals showed a significantly large decrement (0.5 times, p<0.01) in LFB component at the final stage compared to the initial stage, but a very large increment (4.7 times) in HFB component. Likewise, AK animals exhibited a significantly large decrement (0.6 times, p<0.01) in LFB component at the final stage, but a very large increment (3.6 times) in HFB component. Correlation analyses were performed between the HFB component and AD duration, interictal discharge frequency, and behavioral stages during kindling progression. Very strong positive correlations were found in both kindling animals. Chronological spectral analysis of seizure discharges, resulting in a pattern of LFB decrement accompanied by HFB increment, is a convenient tool to investigate epileptic disorders and diagnose epileptic states.