Date of Award

2025

Document Type

Thesis

Degree Name

MS in Neuroscience

Department

Biological Sciences

First Advisor

Robert Kozol

Second Advisor

Javier F. Juarez

Third Advisor

Dianella G Howarth

Abstract

Serotonin is a neurotransmitter system that is essential for driving behavior related to movement, attention and foraging. In humans, an increase or decrease in healthy levels of serotonin result in neuropsychological issues, including anxiety and depression. Despite these health concerns, our understanding of serotonin regulation and homeostasis is still poorly understood and needs more research from a variety of model and non-model animal systems. This study was designed to study serotonin homeostasis in the blind Mexican cavefish, a non- model system for understanding complex biological traits. The blind Mexican cavefish provides a multi-population species that includes river dwelling fish with eyes, that are considered ancestral, and cave derived populations that lack eyes and pigment. Previous research found that cavefish exhibit increased levels of serotonin that is hypothesized to drive decreased sleep and increased activity in cavefish. We wanted to test the hypothesis that increased levels of serotonin are sequestered or degraded in the brain via genetic compensation. To test this hypothesis, we compared mRNA gene expression of the serotonin promoting enzymes tryptophan hydroxylase 1 and 2 (tph1 and tph2) between surface and cave larvae. However, we did not find significant differences in gene expression between the two populations. To further explore serotonin regulation, we quantified the number of cells in the locus coeruleus expressing the serotonin transporter solute carrier family 6 member 4 (slc6a4a). We did find a significant increase in neurons expressing slc6a4a in the dorsal raphe of cavefish. This research provides insight into the regulation of serotonin in a non-model species, the blind Mexican cavefish. Future work will functionally test whether free serotonin is sequestered more rapidly before being implemented in circuits.

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