Author ORCID Identifier

https://orcid.org/0009-0007-0782-2559

Semester

Summer

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Kevin Daly

Committee Co-Chair

Eric Horstick

Committee Member

Gary Marsat

Abstract

Descending neurons (DNs) play a critical role in sensorimotor integration by relaying motor information to the ventral nerve cord (VNC). Within the VNC, local interneurons, other DNs, and ascending neurons (ANs) make circuits with sensory and motor neurons to modify flies’ behavior. One important AN pair in Drosophila Melanogaster is mesothoracic ascending histaminergic neurons (MsAHNs), which are known to convey predictive wing motor signals to the brain. DNg32 is the primary upstream synaptic partner of MsAHNs, integrating DNg32 input with other inputs to generate predictive motor signals. The goals of this study were to 1) map the synaptic connectivity of DNg32, 2) determine its neurotransmitter identity, and 3) assess its functional role in flight behavior. Using electron microscopy volume reconstruction of the brain and VNC, we reconstructed DNg32’s main pre- and postsynaptic partners. We found that DNg32 receives bilateral input from auditory-related commissural neurons in the brain, suggesting they may contribute to bilateral fusion of mechanosensory information. DNg32 also projects contralaterally and unilaterally to the wing and haltere tectulum within the VNC, positioning it to provide flight steering signals to flight control circuits. Using molecular genetic markers with immunohistochemistry, we confirmed that DNg32 is cholinergic. To examine DNg32’s role in behavioral performance. The FlyTrap assay quantifies odor-guided flight performance by measuring flies’ capture in an attractive odor trap in 10-minute intervals over 60 minutes. We genetically manipulated DNg32 function using targeted ablation (UAS-rpr) or synaptic silencing (UAS-BoNT-C). Here, we found that ablation or silencing of DNg32 results in a significant increase in the trapping rate, suggesting an increased rate of flights of equal success and/or increased odor-guided performance. To resolve these possibilities, we used the FlyFall assay, which captures high-speed (600 fps) videos of voluntary takeoffs. We again disrupted DNg32 activity and quantified the number of flights per recording and flight quality. Both DNg32 ablation and silencing led to increased takeoff frequency; however, they also resulted in flight instability as indicated by increased rate of crashing. As a final experiment, we used an optogenetic tool (UAS-CsChrimson) to photoactivate DNg32 in the FlyFall assay. We find that DNg32 activation significantly suppressed the rate of takeoffs, but flight quality was not significantly affected. Together, these results suggest that DNg32 plays a role in flight behavior and may provide steering information for flies to modify their flight path.


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