Fast Network Oscillations in the Rat Dentate Gyrus In Vitro

1 School of Biomedical Sciences, University of Leeds, Leeds LS2 9NQ; 2 Medical Research Council Anatomical Neuropharmacology Unit, University of Oxford, Oxford OX1 3TH, United Kingdom; and 3 Department of Physiology and Pharmacology, SUNY Health Science Center, Brooklyn, New York 11203 Towers, Stephen K., Fiona E. N. LeBeau, Tengis Gloveli, Roger D. Traub, Miles A. Whittington, and Eberhard H. Buhl. Fast Network Oscillations in the Rat Dentate Gyrus In Vitro. J. Neurophysiol. 87: 1165-1168, 2002. The dentate gyrus is a prominent source of gamma frequency activity in the hippocampal formation in vivo. Here we show that transient epochs of gamma frequency network activity (67 ± 12 Hz) can be generated in the dentate gyrus of rat hippocampal slices, following brief pressure ejections of a high-molarity potassium solution onto the molecular layer. Oscillatory activity remains synchronized over distances >300 µm and is accompanied by a modest rise in [K + ] o . Gamma frequency oscillations were abolished by a GABA A receptor antagonist demonstrating their dependence on rhythmic inhibition. However, in many cases, higher frequency oscillations (>80 Hz) remained in the absence of synaptic transmission, thus demonstrating that nonsynaptic factors may underlie fast oscillatory activity.