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The Impact of Antibiotics on the Intestinal Microbiome and the Gut‐Brain Axis in Zebrafish

Anxiety disorders affect over 40 million adults in the United States. Current research indicates a correlation between antibiotic exposure and the onset of anxiety. Recent findings illustrate the microbiome's role in this relationship through the bidirectional communication pathway between the gut and the brain, known as the gut‐brain axis. This study utilizes zebrafish as a model organism to examine the impact of antibiotics on the composition of the microbiome, and subsequently stress‐related behaviors. It is hypothesized that antibiotic treatment will lead to sustained changes in the microbiome and an increase in anxiety‐like behavior. Adult zebrafish were treated with antibiotics for one week then put through a net‐stress and death‐induced odors, after which, swimming behaviors were tracked. Intestinal tissue was collected and bacterial DNA was isolated to quantify total intestinal bacterial using qPCR. In order to assess stress hormone production, intestinal RNA was isolated and corticotropin‐releasing hormone binding protein (CRHbp) was quantified via RT‐PCR. Results confirmed antibiotic treatment induced a 20% decrease in universal gut bacteria in the treated fish (n = 12 p < 0.05) versus control fish. Antibiotic treatment also correlated with decrease in exploratory behavior, illustrated by a significant decrease in top tank entries (n = 12, p < 0.01) indicating treated fish were stressed. Moreover there was a corresponding 2‐fold increase in CRHbp RNA (n= 5, p < 0.05) signifying an increase in cortisol production. Interestingly, following reestablishment of the gut microbiome, fish demonstrated exploratory behavior as seen by an increase in top tank entries (p < 0.01), demonstrating a reduction in stress correlated with reestablishment of intestinal bacteria. There were no significant differences in CRHbp expression in reestablished fish. Collectively, these results signify a decrease in the diversity of the gut microbiome may elicit anxiety in zebrafish. This data warrants further investigation into the mechanism of the gut‐brain axis and how antibiotics influence microbial‐induced changes in behavior.