Electroencephalographic characterization of an adult rat model of radiation-induced cortical dysplasia

Purpose: Cortical dysplasia (CD) is a frequent cause of medically intractab le focal epilepsy. The mechanisms of CD-induced epileptogenicity remain unk nown. The difficulty in obtaining and testing human tissue warrants the ide ntification and characterization of animal model(s) of CD that share most o f the clinical, electroencephalographic (EEG), and histopathologic characte ristics of human CD. In this study, we report on the in vivo EEG characteri zation of the radiation-induced model of CD. Methods: Timed-pregnant Sprague-Dawley rats were irradiated on E17 using a single dose of 145 cGy or left untreated. Their litters were identified and implanted with bifrontal epidural and hippocampal depth electrodes for pro longed continuous EEG recordings. After prolonged EEG monitoring, animals w ere killed and their brains sectioned and stained for histologic studies. Results: In utero-irradiated rats showed frequent spontaneous interictal ep ileptiform spikes and spontaneous seizures arising independently from the h ippocampal or the frontal neocortical structures. No epileptiform or seizur e activities were recorded from age-matched control rats. Histologic studie s showed the presence of multiple cortical areas of neuronal clustering and disorganization. Moreover, pyramidal cell dispersion was seen in the CA1CA 3 areas of the hippocampal formations. Conclusions: Our results further characterize the in vivo EEG characteristi cs of the in utero radiation model of CD using long-term EEG monitoring. Th is model may be used to study the molecular and cellular changes in epilept ogenic CD and to test the efficacy of newer antiepileptic medications.