Voltage imaging in the olfactory bulb using transgenic mouse lines expressing the genetically encoded voltage indicator ArcLight

Jelena Platisa,Lawrence B Cohen,Hongkui Zeng,Vincent A Pieribone,Linda Madisen,Douglas A Storace

doi:10.1038/s41598-021-04482-3

Abstract

Genetically encoded voltage indicators (GEVIs) allow optical recordings of membrane potential changes in defined cell populations. Transgenic reporter animals that facilitate precise and repeatable targeting with high expression levels would further the use of GEVIs in the in vivo mammalian brain. However, the literature on developing and applying transgenic mouse lines as vehicles for GEVI expression is limited. Here we report the first in vivo experiments using a transgenic reporter mouse for the GEVI ArcLight, which utilizes a Cre/tTA dependent expression system (TIGRE 1.0). We developed two mouse lines with ArcLight expression restricted to either olfactory receptor neurons, or a subpopulation of interneurons located in the granule and glomerular layers in the olfactory bulb. The ArcLight expression in these lines was sufficient for in vivo imaging of odorant responses in single trials using epifluorescence and 2-photon imaging. The voltage responses were odor-specific and concentration-dependent, which supported earlier studies about perceptual transformations carried out by the bulb that used calcium sensors of neural activity. This study demonstrates that the ArcLight transgenic line is a flexible genetic tool that can be used to record the neuronal electrical activity of different cell types with a signal-to-noise ratio that is comparable to previous reports using viral transduction.

Highlights

Encoded voltage indicators (GEVIs) can report changes in membrane potential from defined cell types
The transgenic offspring of these lines were crossed to create a triple transgenic mouse line Ai86 x Camk2a-tTA x Emx1-Cre with ArcLight expression targeted to the granule cell layer and a small population of interneurons located in the glomerular layer in the olfactory bulb
A second triple transgenic line with ArcLight targeted to the olfactory receptor neurons was created by crossing Ai86 x Camk2a-tTA and OMP-Cre (Jax Stock # 006668) lines, yielding Ai86 x Camk2atTA x OMP-Cre. 11 out of the 45 offspring resulting from this cross were transgenic (24.4%)

Summary

Introduction

Encoded voltage indicators (GEVIs) can report changes in membrane potential from defined cell types. Most mammalian in vivo approaches have driven expression using in utero electroporation[12,17] or injection of a viral vector (e.g., adeno-associated viruses, AAVs)[10,11]. These protocols complicate the experiment by requiring additional surgical procedures, and in some instances, available viruses have limited transduction capacity for particular cell types (e.g., olfactory receptor neurons)[18]. We took advantage of a novel transgenic reporter mouse, Ai86(TITL-ArcLight)[24,26], that can be used to selectively drive the expression of the GEVI ArcLight[7] in specific cell types. We report a novel transgenic line with ArcLight expression localized to either olfactory receptor neurons (OMP-ArcLight) or olfactory bulb interneurons (Emx1-ArcLight) and demonstrate their ability to report odor-evoked signals in vivo

Methods

Results

Conclusion