Abstracts

Rationale: The spontaneously epileptic rat (SER) exhibits both tonic convulsion and absence-like seizures from the age of 8 weeks. The antiepileptic profiles of conventional antiepileptic drugs for SER parallel those in human epilepsy. Hippocampal CA3 neurons show an abnormal firing in SER when a single stimulus is delivered to the mossy fibers in slice preparations due to the activation of voltage dependent Ca²⁺ channel. Histologicaly, decrease of CA3 neurons and sprouting of mossy fiber were observed in mature SER. Levetiracetam (LEV) inhibits both seizures observed in SER, and low dose-application of LEV to SER that does not exhibits spontaneous seizure, reduces the seizures at 5-weeks after termination of the administration. LEV inhibits and sometimes totally suppresses the abnormal excitement of CA3 neurons induced by the stimulation of mossy fiber. This examination is planned to evaluate the inhibitory effect of LEV on the acquisition of excitability following generalized seizure using hippocampal tissue in SER.Methods: LEV (420 mg/ml) or physiological saline was given to SER aged 4 weeks prior to appearance of epileptic seizures. They were administered for 28days using alzet osmotic mini-pump at 2.5μl/hr. At 11-12 weeks of age, SER were sacrificed. H-E staining, Timm staining, and immunostaining with anti-SV2A, anti-synaptophysin antibody, anti-BDNF antibody, and anticaspase-3 antibody were performed. Quantification of cell density of hippocampus was performed with a 1cm² microscopic grid. Sprouting of mossy fiber was evaluated according the sprouting score, and the immunoreactivity of SV2A, synaptophysin and BDNF was expressed as optical density using Image J software (NIH). The value was obtained from the average of serial 3 neurons from each 5-6 rats.Results: Serum concentration of LEV were 16.72-37.32μg/ml in LEV treated SER (SER-LEV). LEV leaded to nearly 50 % reduction of tonic-clonic convulsion in SER-LEV, compared to sham-operated SER (SER-sham). LEV administration prior to epileptic seizure significantly reduced the decrease of CA3 neurons (SER-sham 29.5±1.2, SER-LEV 24.8±2.4; mean±SD). Treatment of LEV inhibited mild sprouting observed in mature SER (SER-sham: 1.80±0.45, SER-LEV: 0.83±0.75). Caspase-3 positive neuron was slightly observed in CA3 of SER-sham (0.78±0.75), but not observed in SER-LEV. Treatment of LEV decreased the expression of BDNF on the distribution of mossy fiber (Fig 1). Expression of SV2A and synaptophysin showed the tendency that the density of both antibodies in SER-sham was higher in dentate, hilus, and CA3 than that in SER-LEV. Density of SV2A was significantly higher in frontal cortex of SER-LEV (Fig 2).Conclusions: Hippocampal findings in SER suggest LEV has a cell protective effect and inhibits the histological change after repeated seizures. Higher expression of synaptic markers in SER-sham seems to be related to a sprouting of mossy fiber. Lower distribution of SV2A in frontal cortex may contribute to the seizure expression in SER, and LEV may inhibit such findings that are related to an epileptogenesity in SER.