Abstracts

Human medial temporal lobe epilepsy (MTLE) is characterized clinically by the progressive development of spontaneous recurrent seizures from temporal lobe foci. Electroencephalographic (EEG) studies in these patients often revealed interictal epileptiform discharges from the temporal lobes and EEG seizures of secondary generalization often starts with an electrodecremental event lasting a few seconds that is bilaterally followed by rhythmic fast activity. A rat model of chronic limbic epilepsy (CLE) was developed following a period of status epilepticus induced by continuous hippocampal stimulation. Spontaneous recurrent seizures occurred after a silent period of 4-6 weeks. The aim of this study was to examine whether the EEG changes in this model resemble those of human temporal lobe epilepsy. 330 micron stainless steel monopolar electrodes were stereotaxically implanted in bilateral hippocampus and frontal cortex. Neuronal activity was recorded at 200Hz. Time-locked continuous video/EEG (VEEG) recordings were collected over the course of two months from a chronically seizing animal model of limbic epilepsy. EEG and behavior seizures were visually identified from time-locked continuous video/EEG recordings. VEEG recordings from 24 animals with spontaneous recurrent seizures were reviewed. These EEGs were obtained from bilateral hippocampal depth electrodes and bilateral frontal cortical electrodes after the first spontaneous recurrent seizures and continued for 2-3 months. The interictal spikes and sharp waves were observed in the hippocampus ipsilateral to the stimulation site in majority of animals, and bilateral interictal spikes were observed in about 30% of animals. Prior to the onset of each spontaneous recurrent seizures, EEGs showed sudden onset of electrodecrements bilaterally for 1-2 seconds, followed by generalized bursts of sharp waves and buildup of rhythmic theta activity that accompanied the behavioral seizures. Postictal EEG showed a mixture of slow waves and attenuation of background activities. These EEG patterns were rather stereotypic and seen in the majority of animals. The pattern of interictal, ictal and post-ictal EEG changes in the rat CLE model resemble those observed in human MTLE. These results support the notion that the spontaneous limbic epilepsy rat model is a realistic model of human MLTE. (Supported by National Institutes of Health, National Science Foundation, Children[apos]s Miracle Network)