Neuronal Excitability Abnormal UP/DOWN Membrane Potential Dynamics Coupled with the Neocortical Slow Oscillation in Dentate Granule Cells during the Latent Phase of Temporal Lobe Epilepsy 1,2,3 David W. Ouedraogo, 1,2,3 Pierre-Pascal Lenck-Santini 1,2,3,4 , Geoffrey Marti 1,2,3,5 , David Robbe, 1,2,3 Valérie Crépel, 1,2,3 and Jérôme Epsztein 1,2,3 DOI:http://dx.doi.org/10.1523/ENEURO.0017-16.2016 1 Institut National de la Santé et de la Recherche Médicale U901, 13273 Marseille, France, 2 Unité Mixte de Recherche 901, Aix-Marseille University, 13273 Marseille, France, 3 Institut de neurobiologie de la méditerranée, 13273 Marseille, France, 4 Department of Neurological Sciences, University of Vermont, Burlington, Vermont 05405, 5 Centre National de la Recherche Scientifique, Institut des Sciences du Mouvement, Unité Mixte de Recherche 7287, Aix-Marseille University, 13288 Marseille, France Visual Abstract Dentate Granule Cells Cont Post-SE Parietal Cortex Silent UP/DOWN states Vm LFP Whole-cell Local Field Potentials Patch-clamp and firing The dentate gyrus, a major entry point to the hippocampus, gates (or filters) incoming information from the cortex. During sleep or anesthesia, the slow-wave oscillation (SWO) or- chestrates hippocampus–neocortex communication, which is important for memory formation. The dentate gate is altered in temporal lobe epi- lepsy (TLE) early during epileptogen- esis, which favors the propagation of pathological activities. Yet, whether the gating of physiological SWO by dentate granule cells (DGCs) is altered in TLE has remained unexplored. We combined intracellular recordings of membrane potential (V m ) of DGCs and local field potential recordings of the SWO in parietal cortex in anesthetized rats early during epileptogenesis [post-status epilepticus (SE) rats]. As expected, in control rats, the V m of DGCs weakly and rarely oscillated in the SWO frequency range. In contrast, in post-SE rats, the V m of DGCs displayed strong and long-lasting SWO. In Significance Statement Communication between cortex and hippocampus during sleep, orchestrated by the neocortical slow-wave oscillation (SWO), is important for memory consolidation. Whether this communication is affected in temporal lobe epilepsy (TLE), a disease with profound memory impairments, is not known. In control rats, dentate granule cells (DGCs), at the gate of the hippocampus, filter incoming information from the cortex. This relative independence of hippocampal neurons from SWO allows the replay of hippocampus-specific information independently from the neocortex. Here, using in vivo whole-cell patch-clamp recordings of DGCs and field recordings in the neocortex, we report an abnormally strong influence of neocortical SWO on the membrane potential and firing of DGCs in TLE rats. This could profoundly alter hippocampus– neocortex dialogue during sleep and associated cognitive functions. New Research May/June 2016, 3(3) e0017-16.2016 1–18