Adult-born neurons facilitate olfactory bulb pattern separation during task engagement.

Wankun L Li,Yusuke Suzuki,Itaru Imayoshi,Monica W Chu,Takaki Komiyama,An Wu

doi:10.7554/elife.33006

Wankun L Li, Yusuke Suzuki + Show 4 more

Open Access

https://doi.org/10.7554/elife.33006

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Journal: eLife	Publication Date: Mar 13, 2018
Citations: 63	License type: CC BY 4.0

Affiliation: Kyoto University, University of California, San Diego

Abstract

The rodent olfactory bulb incorporates thousands of newly generated inhibitory neurons daily throughout adulthood, but the role of adult neurogenesis in olfactory processing is not fully understood. Here we adopted a genetic method to inducibly suppress adult neurogenesis and investigated its effect on behavior and bulbar activity. Mice without young adult-born neurons (ABNs) showed normal ability in discriminating very different odorants but were impaired in fine discrimination. Furthermore, two-photon calcium imaging of mitral cells (MCs) revealed that the ensemble odor representations of similar odorants were more ambiguous in the ablation animals. This increased ambiguity was primarily due to a decrease in MC suppressive responses. Intriguingly, these deficits in MC encoding were only observed during task engagement but not passive exposure. Our results indicate that young olfactory ABNs are essential for the enhancement of MC pattern separation in a task engagement-dependent manner, potentially functioning as a gateway for top-down modulation.

Highlights

There was no difference in the density of Glial Fibrillary Acidic Protein (GFAP)-positive astrocytes in VGCC-treated Gfap-tk+ and Gfap-tk- mice in the olfactory bulb (p=0.9911, Wilcoxon rank sum test; Figure 1E) nor in the hippocampus dentate gyrus (p=0.1359, Wilcoxon rank sum test), consistent with a previous report (Snyder et al, 2011)
These results indicate that dentate gyrus (DG) postnatally-born neurons that include adult-born neurons (ABNs) are not essential for fine olfactory discrimination and the behavioral impairment in Gfap-tk+ ablation group was primarily caused by the absence of ABNs in the olfactory bulb
We ablated young ABNs in adult mice and investigated the consequences on their behavior and mitral cells (MCs) activity to probe the functional significance of adult neurogenesis

Summary

Introduction

Local inhibitory neurons in the olfactory bulb, including ABNs, likely control olfactory perception by providing inhibition onto MCs. Neuroscience eLife digest Most brain cells or neurons form early in life. Adult neurogenesis produces many new cells in the olfactory bulb, a part of the brain that processes smells. This is likely because the sense of smell is important for the survival of these animals. To assess the role of ABNs in the olfactory bulb, we adopted a genetic method to inducibly suppress adult neurogenesis We reasoned that this chronic ablation allows us to probe for the functions of ABNs which cannot be compensated for by other inhibitory neurons. This difference in suppressive responses was only observed when animals were actively engaged in the task

Results

Discussion

Materials and methods

Funding Funder