Date of Award:

8-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Sara Freeman

Committee

Sara Freeman

Committee

Susannah French

Committee

Korry Hintze

Abstract

Short-chain fatty acids are biomolecules that are produced from bacterial fermentation of dietary fiber in the gut. Short-chain fatty acids are used in the gut to supply energy and reduce inflammation but are also believed to have effects on the brain. While we do not know how short-chain fatty acids affect the brain and behavior, recent research has led to the idea of using dietary changes as a treatment for mental health disorders. We aimed to visualize where short-chain fatty acids act in the brain with a particular focus on neural immune cells called microglia and the neurons that produce serotonin, a signaling molecule that modulates mood. Seven groups of mice were fed diets that varied in fat content, fiber solubility, and fiber content. We then visualized the effects of these diets on the brain using a technique called in situ hybridization, which allows us to measure and visualize the locations of mRNA for particular genes of interest. We measured mRNA for the receptors for short chain fatty acids in microglia and serotonin neurons. We found that short-chain fatty acid receptors were in high amounts on the neural immune cells and the serotonin neurons, and that they were more prevalent in the hippocampus, which is important for learning and memory. Higher amounts of dietary fiber were found to increase short-chain fatty acid receptor expression in the hippocampus while diets with more soluble fiber were important for increasing receptors in areas where serotonin is produced. Our results suggest that diet-based interventions that control the type of fiber can change the functions of the brain’s microglia and serotonin system, potentially via sensitivity to circulating levels of short chain fatty acids produced by the gut.

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