Characteristic behavioral seizures and abnormal signal asymmetry of magnetic resonance imaging in an electrogenic rat model of chronic epilepsy.

Chronic tetani (60 Hz, 2 s, 0.4~0.6 mA) were administered to the dorsal hippocampus (DHPC) or the medial temporal lobe neocortex (MTNC) of rats, to study the role of the entorhinal cortex (EC)-hippocampal loop in temporal lobe epileptogenesis. This was repeated once a day for 7 or 10 days. Magnification of hyper-intensity was induced by tetanization of the HPC or the MTNC, as detected by contralateral T(2) weighed magnetic resonance imaging (T(2)-WI). The effects were associated with an enlarged volume of the lateral ventricle (LV), which was verified histologically. T(2)-WI hper-intensities, contralateral to the tetanized hemispheres, were observed with high frequency primary wet dog shakes (WEDS) in the DHPC-stimulated rats and with low frequency WEDS in the MTNC-stimulated rats. It seems likely that the same neural mechanisms are shared by chronic tetanization of the right HPC and the righ MTNC, involving the closed EC-HPC loop. Poor correlation between contralateral T(2)-WI hper-intensities and light primary behavioral seizures in the MTNC-stimulated rats might be attributed to a controlled information flow into or out of this loop because of potential EC gating. In addition, asymmetric T(2)-WI hyper-intensities in the LV area reflected a hemispheric dependence, contralateral to the electrogenic focus in our model of rat epilepsy.