Date of Award

Fall 2015

Project Type

Thesis

Program or Major

Zoology

Degree Name

Master of Science

First Advisor

Winsor H Watson

Second Advisor

Leslie J Curren

Third Advisor

James M Newcomb

Abstract

In recent years, scientists have begun to study satiation as a means of understanding changes in motivational state. Satiated animals not only show a reduction in feeding behaviors, but also in locomotion, and even show changes in their responses to various stimuli. Therefore, satiation is a qualitative change in the behavioral state of an animal. Although the behavioral characteristics of satiation are well understood, as are the changes in hormone release following a meal, the neural correlates of satiation are less understood. In particular, few studies have attempted to determine how satiating signals reconfigure feeding neural networks. To begin to address this topic, I studied satiation in the nudibranch Melibe leonina, an organism that is ideally suited for studies on the neural correlates of feeding behavior. In the first chapter of my thesis I documented the time course of satiation in Melibe, and demonstrated that stomach distention from food reduces the motivation to feed in this species. Additionally, I obtained data that suggest that a small amount of stomach distention may enhance feeding, an idea that has not been previously discussed in the literature. In the second chapter I determined that the posterior nerves, which run from the buccal ganglia to the tree ganglia (a pair of ganglia that lie on the surface of the middle of the stomach), respond to stomach distention, and that posterior nerve activity reduces the motivation to feed in Melibe. I demonstrated that stomach distention changes the signaling between the brain and buccal ganglion and terminates ficitive swallowing rhythms from the anterior nerve of the buccal ganglion. Additionally, I obtained preliminary evidence to suggest that the molluscan peptide SCPB enhances feeding in Melibe, although it does not appear to initiate feeding. Lastly, I demonstrated that exposure to food at night inhibits nighttime bouts of locomotion in Melibe, but consumption of a meal prior to nightfall does not appear to alter locomotion. Based on these locomotion studies, I propose a model to explain how stomach distention and circadian clocks interact to regulate behavioral state at night. These results establish an important background necessary for studies of satiation in Melibe, enabling future studies on the feeding network reconfigurations caused by stomach distention.

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