Dendritic Spikes Induce Ripples in Parvalbumin Interneurons during Hippocampal Sharp Waves

Chiovini, Balázs and Turi, Gergely F. and Katona, Gergely and Kaszás, Attila and Pálfi, Dénes and Maák, Pál and Szalay, Gergely and Szabó, Mátyás Forián and Szabó, Gábor and Szadai, Zoltán and Káli, Szabolcs and Rózsa, Balázs (2014) Dendritic Spikes Induce Ripples in Parvalbumin Interneurons during Hippocampal Sharp Waves. NEURON, 82 (4). pp. 908-924. ISSN 0896-6273

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Abstract

Sharp-wave ripples are transient oscillatory events in the hippocampus that are associated with the reactivation of neuronal ensembles within specific circuits during memory formation. Fast-spiking, parvalbumin-expressing interneurons (FS-PV INs) are thought to provide fast integration in these oscillatory circuits by suppressing regenerative activity in their dendrites. Here, using fast 3D two-photon imaging and a caged glutamate, we challenge this classical view by demonstrating that FS-PV IN dendrites can generate propagating Ca2+ spikes during sharp-wave ripples. The spikes originate from dendritic hot spots and are mediated dominantly by L-type Ca2+ channels. Notably, Ca2+ spikes were associated with intrinsically generated membrane potential oscillations. These oscillations required the activation of voltage-gated Na+ channels, had the same frequency as the field potential oscillations associated with sharp-wave ripples, and controlled the phase of action potentials. Furthermore, our results demonstrate that the smallest functional unit that can generate ripple-frequency oscillations is a segment of a dendrite.

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