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Stress, microbiome, and the physiology of learning: unraveling complex interactions in the development of a learned behavior

Abstract

Acute and chronic stress during childhood can have profoundly detrimental effects on physical and mental health. Early-life stress can lead to modifications to the structure of DNA, which changes the way genes are expressed, potentially leading to negative effects on health and well-being. There are hints in human studies that stress and trauma in children are associated with language impairments and achievement gaps in school. However, a major question remains unresolved: how does developmental stress affect the learning process, and what changes in the brain underlie these effects? Further, emerging evidence suggests that bacteria in the gut have major effects on multiple axes of health, including mental and behavioral health. Antibiotics are routinely used in medicine, especially during childhood, but often have the side effect of disrupting the "good" bacteria in the gut. This project aims to understand 1) whether stress causes lasting changes to learning-related gene expression in the brain and 2) whether disruptions to gut bacterial communities can induce stress and impair learning. Understanding how to prevent and mediate these effects of early-life stress is critical to fostering lifelong educational achievement. Songbirds and humans share the unique ability to learn vocalizations, as well as certain genes and neural structures associated with vocal learning and brain development. In addition, song is a robust, quantifiable measure of learning, and songbirds exhibit impaired song-learning ability after early-life stress. This project will examine the effects of developmental stress on learning, the brain, and the microbiome, using the zebra finch as a songbird model system. Zebra finch nestlings will be differentially treated either with orally administered corticosterone, to mimic the hormonal and physiological effects of chronic stress, or with a vector control. The investigator will also administer antibiotics to a subset of birds to test whether perturbations to the microbiome can induce a stress response that affects learning. After the treatment phase, juvenile zebra finches will be placed with an adult male zebra finch tutor. The investigator will continuously record all sounds produced by the juvenile for the 60-day duration of the song-learning period to quantify and compare the rate and accuracy of song learning across treatments. The investigator will then collect neural tissue from regions of the brain known to be involved in song learning, as well as regions unrelated to song development, to assess gene expression across brain nuclei and treatments with RNAseq. Fecal samples will be collected at regular time points for 16S sequencing to analyze microbial composition. Taken together, these experiments on the effects of early-life stress in songbirds will shed light on the underlying connections between stress, the microbiome, and learning.

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Project Period

2019-2022