Inhibition by Somatostatin Interneurons in Olfactory Cortex.

Adam M Large,Nicholas A Kunz,Samantha L Mielo,Anne-Marie M Oswald

doi:10.3389/fncir.2016.00062

Adam M Large, Nicholas A Kunz + Show 2 more

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https://doi.org/10.3389/fncir.2016.00062

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Abstract

Inhibitory circuitry plays an integral role in cortical network activity. The development of transgenic mouse lines targeting unique interneuron classes has significantly advanced our understanding of the functional roles of specific inhibitory circuits in neocortical sensory processing. In contrast, considerably less is known about the circuitry and function of interneuron classes in piriform cortex, a paleocortex responsible for olfactory processing. In this study, we sought to utilize transgenic technology to investigate inhibition mediated by somatostatin (SST) interneurons onto pyramidal cells (PCs), parvalbumin (PV) interneurons, and other interneuron classes. As a first step, we characterized the anatomical distributions and intrinsic properties of SST and PV interneurons in four transgenic lines (SST-cre, GIN, PV-cre, and G42) that are commonly interbred to investigate inhibitory connectivity. Surprisingly, the distributions SST and PV cell subtypes targeted in the GIN and G42 lines were sparse in piriform cortex compared to neocortex. Moreover, two-thirds of interneurons recorded in the SST-cre line had electrophysiological properties similar to fast spiking (FS) interneurons rather than regular (RS) or low threshold spiking (LTS) phenotypes. Nonetheless, like neocortex, we find that SST-cells broadly inhibit a number of unidentified interneuron classes including putatively identified PV cells and surprisingly, other SST cells. We also confirm that SST-cells inhibit pyramidal cell dendrites and thus, influence dendritic integration of afferent and recurrent inputs to the piriform cortex. Altogether, our findings suggest that SST interneurons play an important role in regulating both excitation and the global inhibitory network during olfactory processing.

Highlights

Throughout the cortex, inhibitory interneurons that express somatostatin (SST) have been implicated in numerous aspects of sensory processing including gain control and/or tuning (Adesnik et al, 2012; Wilson et al, 2012; Stryker, 2014; Seybold et al, 2015; Sturgill and Isaacson, 2015)
Our initial goal was to cross SST-cre mice with G42 mice to investigate the inhibitory connectivity between SST and PV interneurons
These transgenic lines have not been previously characterized in piriform cortex, so we first investigated the anatomical distributions and electrophysiological properties of interneurons targeted in these lines

Summary

Introduction

Throughout the cortex, inhibitory interneurons that express somatostatin (SST) have been implicated in numerous aspects of sensory processing including gain control and/or tuning (Adesnik et al, 2012; Wilson et al, 2012; Stryker, 2014; Seybold et al, 2015; Sturgill and Isaacson, 2015). SST interneurons inhibit excitatory pyramidal cells (PCs; Fino and Yuste, 2011; Pfeffer et al, 2013) as well as inhibitory interneurons, including parvalbumin (PV) cells (Pfeffer et al, 2013; Xu et al, 2013; Jiang et al, 2015). We investigate SST-cell properties and inhibitory connectivity in the piriform cortex to gain insight into the roles these interneurons play in olfactory processing

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