Effect of environmental enrichment on airflow based learning

Abstract

A non-canonical yet imperative function of the rodent olfactory system is to process airflow related information. Studies from our laboratory, involving surgical and optogenetic modification of the Olfactory Bulb (OB) circuitry has determined its role in airflow detection and discrimination. This was further confirmed in transgenic mice in which a subunit of glutamatergic AMPA receptors (GluA2) was knocked down heterozygously from GAD2 expressing interneurons (GAD2GluA2Δht mice). These mice were unable to accurately discriminate between two airflows. While it is known that Environmental Enrichment (EE) can lead to better learning and memory, we aimed to test its efficacy in observed sensory deficit in GAD2GluA2Δht mice. Our EE paradigm also included olfactory and somatosensory enrichment. To test the effect of EE, we carried out Go/No-Go odor and flow discrimination training while animals were living in the enriched environment. EE resulted in the rescue of learning deficits observed in airflow information processing abilities of GAD2GluA2Δht mice. In addition, EE led to faster learning pace in a flow coupled with odor discrimination task. As a first step in probing the neural mechanisms underlying the rescue of learning deficits in enriched GAD2GluA2Δht mice, we investigated changes in neural activity marker c-Fos and adult neurogenesis (using BrdU) in OB. Immunohistochemistry and imaging using confocal microscopy was performed in order to quantify c-Fos activation and BrdU positive cells in OB. As compared to the non-enriched group, there was increased OB interneuronal activation observed in enriched group. However, there was no EE dependent increase in OB adult neurogenesis. Our findings call for further experiments dissecting physiological changes in OB circuitry of EE and non-EE mice, which will help us establishing the causality of observed behavior.