Firing-phase coupling is preserved in the hippocampus of epileptic mice

Abstract

Event Abstract Back to Event Firing-phase coupling is preserved in the hippocampus of epileptic mice Antje Kilias1, 2, 3*, Ulrich P. Froriep1, 2, 3, Ute Häussler4, Arvind Kumar2, 3, Carola A. Haas3, 4 and Ulrich Egert1, 3 1 University of Freiburg, Department of Microsystems Engineering - IMTEK, Faculty of Engineering, Germany 2 University of Freiburg, Faculty of Biology, Germany 3 University of Freiburg, Bernstein Center Freiburg, Germany 4 University of Freiburg, Department of Neurosurgery, Germany Structural changes in the hippocampal network associated with mesial temporal lobe epilepsy (MTLE) very likely contribute to seizure susceptibility. These changes should not only be reflected in epileptic seizures but also affect ongoing brain activity. Recent findings in mice suggest that the theta and gamma rhythms in ongoing activity are indeed altered in the epileptic hippocampus. In particular, the cross-structural coupling of theta activity between the dentate gyrus and the medial entorhinal cortex as well as the cross-frequency coupling between theta and gamma rhythms within the dentate gyrus has been shown to be shifted [1]. The mechanisms underlying these shifts, however, are unknown, as are their possible contributions to the generation of epileptic activity. Importantly, theta and gamma band activity of the local field potentials (LFPs) are associated with preferential phase-coupled firing of single cells but it is unclear whether this coupling is preserved in epileptic animals. To address this, we investigated the firing of hippocampal neurons with respect to theta and gamma rhythms using the intrahippocampal kainate mouse model, which reproduces key features of MTLE. We implanted custom-made multi-site silicon probes [2] to record simultaneously single-unit activity and LFPs at several positions in the hippocampal formation. We find that the phase-coupled firing of single cells to theta and gamma band activity is preserved in hippocampal and parahippocampal areas in epileptic mice. Since theta band activity is shifted between entorhinal cortex and hippocampus [1], these data indicate that this is associated with a shift of single cell firing. Acknowledgements This work was supported by the German Federal Ministry of Education and Research (FKZ 01GQ0420 and 01GQ0830) and by the Deutsche Forschungsgemeinschaft (SFB TR3 and SFB 780).