Abstracts

Rationale: Pilocarpine-induced chronic epilepsy is one of the established animal models mimicking human temporal lobe epilepsy. In this study, we quantified and characterized EEG and seizures in pilocarpine treated rats using long-term video-EEG monitoring. We also performed neuroimaging and pathologic examinations to investigate morphologic and functional brain changes in relation to EEG and behavioral characteristics in various stages of the epileptogenesis.Methods: Sixty three male Sprague-Dawley rats were injected with pilocarpine (250-380 mg/kg) to induce status epilepticus (SE). Diazepam (8.6-28 mg/kg) was administrated depending on the seizure severities after 120 min of initial SE to reduce mortality rate. Continuous video-EEG monitoring (TWIN, Grass-Telefactor, USA) was performed in rats with two epidural (C3, C4) and four depth electrodes (both hippocampi and thalami). Seizure severity was rated as class 1 to 5 by modified Racine classification. Neuroimaging using 7T MRI (MAGNETOM, Siemens, Germany) with high resolution FDG-PET was performed to get anatomical and functional brain images. Animals were sacrificed at 3 hour, 1 day, 3 and 7 days, 4 and 8 weeks after the pilocarpine injection, and immunohistochemistry with neuron-specific nuclear protein (NeuN), terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL), and glial fibrillary acidic protein (GFAP) stainings was performed at each time point. Bromodeoxyuridine (5-bromo-2'-deoxyuridine, BrdU) was injected for 7 days after pilocarpine injection to examine neurogenesis in acute stage after pilocarpine injection.Results: The seizure latency was 4.9 2.5 min for development of initial SE, and the latent period was 3.6 1.3 days for spontaneous recurrent seizures (SRS). MRI revealed abnormal T2 signal change with swelling after 1 day of pilocarpine injection in bilateral hippocampi and peak increase in T2 signal intensity at 7 days with subsequent atrophy afterward. PET results indicated decreased glucose metabolism in both hippocampal regions at 3 and 7 days. Neuropathological examinations showed that neuronal loss and glial changes were peaked at 3 hours and 1 day, subsequently decreased with time, most prominently in both hippocampi. Conclusions: This study indicates that long-term video-EEG recording combined with imaging and pathologic studies can be useful to elucidate relevant changes in acute, subacute, and chronic stages of the epileptogenesis in pilocarpine epilepsy model. Therapeutic application in the future studies in this experimental setting can help us investigate antiepileptic mechanisms and potential development of new therapeutic methods.