In vitro ictogenesis and parahippocampal networks in a rodent model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is a chronic epileptic disorder involving the hippocampal formation. Details onthe interactions between the hippocampus proper and parahippocampal networks during ictogenesisremain, however, unclear. In addition, recent findings have shown that epileptic limbic networks maintainedin vitro are paradoxically less responsive than non-epileptic control (NEC) tissue to application of theconvulsant drug 4-aminopyridine (4AP). Field potential recordings allowed us to establish here the effects of4AP in brain slices obtained from NEC and pilocarpine-treated epileptic rats; these slices included thehippocampus and parahippocampal areas such as entorhinal and perirhinal cortices and the amygdala. First,we found that both types of tissue generate epileptiform discharges with similar electrographiccharacteristics. Further investigation showed that generation of robust ictal-like discharges in the epilepticrat tissue is (i) favored by decreased hippocampal output (ii) reinforced by EC–subiculum interactions and(iii) predominantly driven by amygdala networks. We propose that a functional switch to alternativesynaptic routes may promote network hyperexcitability in the epileptic limbic system.