Theta-Gamma-Modulated Synaptic Currents in Hippocampal Granule Cells In Vivo Define a Mechanism for Network Oscillations

Summary

Theta-gamma network oscillations are thought to represent key reference signals for information processing in neuronal ensembles, but the underlying synaptic mechanisms remain unclear. To address this question, we performed whole-cell (WC) patch-clamp recordings from mature hippocampal granule cells (GCs) in vivo in the dentate gyrus of anesthetized and awake rats. GCs in vivo fired action potentials at low frequency, consistent with sparse coding in the dentate gyrus. GCs were exposed to barrages of fast AMPAR-mediated excitatory postsynaptic currents (EPSCs), primarily relayed from the entorhinal cortex, and inhibitory postsynaptic currents (IPSCs), presumably generated by local interneurons. EPSCs exhibited coherence with the field potential predominantly in the theta frequency band, whereas IPSCs showed coherence primarily in the gamma range. Action potentials in GCs were phase locked to network oscillations. Thus, theta-gamma-modulated synaptic currents may provide a framework for sparse temporal coding of information in the dentate gyrus.

Highlights

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  Granule cells in vivo fire action potentials sparsely but often in bursts

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  Granule cells are exposed to barrages of fast excitatory postsynaptic currents

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  Granule cells receive theta-coherent excitation but gamma-coherent inhibition

Abstract

Pernía-Andrade and Jonas characterize the synaptic mechanisms underlying network oscillations and temporal coding in the dorsal hippocampus in awake rats. Theta-gamma-modulated synaptic currents may provide a framework for sparse temporal coding of information in the dentate gyrus.