Identification of Neurons Involved in Sugar-Dependent Modulation of Water Responses in Drosophila Open Access

Abstract

During feeding, the brain must integrate many signals to produce the most appropriate behavior. Across organisms, feeding decisions can depend on internal state (e.g., hunger and thirst), sensory cues (e.g., taste and smell), and past feeding experiences. In order to understand how different signals are integrated within the brain to inform flexible behaviors, I am using Drosophila as a model organism due to access to genetic manipulations that can target individual neurons. Previous studies in the Drosophila taste system have found that brief exposure to real and artificial optogenetic sugar enhances future feeding initiation to water, a neutral stimulus in water-satiated flies, for seconds to minutes after sugar is no longer present. This process may serve to indicate local food quality when foraging for food. However, it is unclear which neuron(s) within the taste system are driving this experience-dependent modulation in feeding initiation. In this study, I focus on four neurons in the Drosophila sugar circuit, three at the second-order layer and one at the third-order layer. To characterize their roles, I used optogenetic activation to determine whether the activation of these neurons caused an increase in feeding initiation to a subsequent water stimulus. I found that activation of one second-order neuron and one third-order neuron was sufficient to enhance future water responses, while activation of the other two second-order neurons was insufficient. These results suggest that neurons in multiple layers of the sugar circuit are sufficient to enhance future water responses. Furthermore, the neurons sufficient to enhance future water responses have strong indirect and/or direct synaptic input to a premotor neuron, Roundup, establishing Roundup as a candidate neuron that receives experience-dependent modulation. These results provide knowledge of the principles of modulatory networks and give a foundation for future studies focused on how past experiences inform behavior across organisms.

Table of Contents

Introduction - 1

Figure 1. - 4

Figure 2. - 5

Figure 3. - 6

Approach and Hypothesis - 6

Preliminary Data and Goals of this Study - 7

Figure 4. - 8

Methods - 8

Genetic Crosses - 8

Fly Maintenance and Collection - 9

Proboscis Extension Response - 9

Statistical Analysis - 10

Key Resources Table - 11

Results - 11

Figure 5. - 15

Figure 6. - 16

Figure 7. - 17

Figure 8. - 18

Figure 9. - 19

Figure 10. - 20

Discussion - 20

References - 25

 

 

About this Honors Thesis

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School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Neuroscience
Keyword	Feeding behavior Optogenetics Experience-dependent change
Committee Chair / Thesis Advisor	Anita Devineni, Emory University
Committee Members	Malavika Murugan, Emory University Andrea Roeser, Emory University

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