Date of Award

8-2021

Document Type

Thesis

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Dr. Michael Chao

Abstract

The neurotransmitter dopamine regulates chemosensory avoidance behavior in the model organism Caenorhabditis elegans. Avoidance behaviors are mediated by the polymodal ASH nociceptive sensory neurons, and behavioral avoidance of stimuli detected by ASH is less robust when dopamine signaling is impaired. We are investigating the neural response of the ASH neurons to various stimuli; our investigation includes the behavioral and physiological responses from the ASH neurons as dopamine signaling is manipulated to better understand the effects of dopamine on these sensory neurons. We hypothesize that dopamine plays a regulatory role on the ASH neurons, lessening the response of the ASH neuron to noxious environmental stimuli while the animal is in the presence of adequate food resources. Behavioral assays revealed that cat-2 mutants, which are dopamine deficient, had decreased behavioral response to the bitter tastant quinine compared to wildtype animals. In addition, normal response to quinine was restored to cat-2 mutant animals in the presence of exogenous dopamine. Using a custom microfluidics device and the transgenically-expressed Ca2+ sensor GFP variant G-CaMP, we found that intracellular [Ca2+] changes in ASH neurons mirrors the behavioral responses in wildtype and cat-2 mutants, and that exogenous dopamine restores grossly normal response to cat-2 mutants. The dop-1 and dop-4 dopamine receptor mutants had similar behavioral responses to quinine as the cat-2 mutant while being resistant to exogenous dopamine. However, both the dop-1 and dop-4 receptor mutants showed increased Ca2+ influx in ASH neurons when compared to wildtype animals. Collectively our data suggests that dopamine plays a regulatory role on the ASH neurons.

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