Parvalbumin and somatostatin interneurons contribute to the generation of hippocampal gamma oscillations

Abstract

c-frequency oscillations (30-120 Hz) in cortical networks influence neuronal encoding and information transfer, and are disrupted in multiple brain disorders. While synaptic inhibition is important for synchronization across the c-frequency range, the role of distinct interneuronal subtypes in slow (,60 Hz) and fast c states remains unclear. Here, we used optogenetics to examine the involvement of parvalbumin-expressing (PV1) and somatostatin-expressing (SST1) interneurons in c oscillations in the mouse hippocampal CA3 ex vivo, using animals of either sex. Disrupting either PV1 or SST1 interneuron activity, via either photoinhibition or photoexcitation, led to a decrease in the power of cholinergically induced slow c oscillations. Furthermore, photoexcitation of SST1 interneurons induced fast c oscillations, which depended on both synaptic excitation and inhibition. Our findings support a critical role for both PV1 and SST1 interneurons in slow hippocampal c oscillations, and further suggest that intense activation of SST1 interneurons can enable the CA3 circuit to generate fast c oscillations.