High frequency oscillations in the dentate gyrus of rat hippocampal slices induced by tetanic stimulation.

Tetanic stimulation induces high-frequency network oscillations in area CA1 and in the subiculum of rat hippocampal slices. Here, we describe the effects of similar tetanic stimulation in the molecular layer of the dentate gyrus. We found field potential oscillations in the dentate granule cell layer which shared several properties with tetanically induced oscillations in CA1, including delayed onset, duration, progressive slowing of frequency within the oscillations and sensitivity to blockers of GABA(A) receptors, NMDA receptors and metabotropic glutamate receptors. However, the mean frequency of the oscillations in the dentate is approximately 100 Hz, much higher than tetanic oscillations in CA1 and, in contrast to CA1, dentate high-frequency oscillations are sensitive to antagonists of AMPA-receptors. Oscillation frequency was decreased by metabotropic glutamate receptor antagonists and increased by antagonists of AMPA-receptors as well as the gap junction blocker carbenoxolone. The oscillations can be observed in the whole dentate gyrus-CA3-network and are tightly correlated between the dentate gyrus and area CA3. Thus, tetanic stimulation in the dentate elicits a new pattern of network oscillations with coherence in the dentate-CA3-network which may affect the processing of afferent information in the hippocampus.