Semester

Fall

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Andrew Dacks

Committee Member

Kevin Daly

Committee Member

Gary Marsat

Abstract

Neuromodulatory circuits are a necessary component of neural flexibility as they are able to act differentially depending on the receptors expressed by their downstream targets. Identifying the synaptic partners of modulatory neurons and determining the neurotransmitter and receptor content of these partners is necessary to identify the rules governing neuromodulatory circuits. In this study, I characterized the circuit of the contralaterally projecting, serotonin-immunoreactive deutocerebral neurons (CSDns), the sole synaptic source of the neuromodulator serotonin in the olfactory circuit of Drosophila melanogaster, by identifying the strongest synaptic partners of the CSDns, and the expression of genes encoding neurotransmitters and receptors of these partners. I found that 1) this circuit forms a loop, as the strongest downstream partner of the CSDns itself synapses on the strongest upstream partner of the CSDns, 2) the loop is composed entirely of inhibitory connectivity, and 3) one node of this loop is of a neuron class is a feedback neuron, while the other is a local interneuron. Thus, serotonin acts locally in the sensory circuit, while being regulated from a higher level processing area. This result in the simple invertebrate olfactory circuit is regulated in a manner similar to the corticobulbar loop found in the mammalian olfactory circuit, suggesting that these features may be conserved across neural complexity. In all, this highlights the complexity of serotonergic circuitry at the cellular and molecular level, and provides a reference to which other modulatory circuits can be compared.

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