A new experimental model of focal seizures in the entorhinal cortex

Purpose: Despite intensive studies, our understanding of the cellular and molecular mechanisms underlying epileptogenesis remains largely unsatisfactory. Our defective knowledge derives in part from the lack of adequate experimental models of the distinct phases that characterize the epileptic event, that is, initiation, propagation, and cessation. The aim of our study is the development of a new brain slice model in which a focal seizure can be repetitively evoked at a precise and predictable site. Methods: Epileptiform activities were studied by fast Ca²(+) imaging coupled with simultaneous single and double patch-clamp or extracellular recordings from neurons of entorhinal cortex (EC) slices from Wistar rats and C57BL6J mice at postnatal days 13-17. Results: In the presence of 4-aminopyridine (4-AP) and low Mg²(+) , activation of layer V-VI neurons by local N-methyl-d-aspartate (NMDA) applications evolved into an ictal discharge (ID) that propagated to the entire EC. NMDA-evoked IDs were similar to spontaneous events. IDs with similar pattern and duration could be repetitively triggered from the same site by successive NMDA stimulations. The high ID reproducibility is an important feature of the model that allowed testing of the effects of currently used antiepileptic drugs (AEDs) on initiation, propagation, and cessation of focal ictal events. Conclusions: By offering the unique opportunity to repetitively evoke an ID from the same restricted site, this model represents a powerful approach to study the cellular and molecular events at the basis of initiation, propagation, and cessation of focal seizures.