Description
- Abstract:
- The sense of taste provides animals with a means of discriminating nutritive from noxious compounds in potential food sources. Neural circuits are thought to represent these compounds in terms of their taste quality, such as sweet or bitter. Sweet and bitter tastants are encoded by separate sensory cells and drive opposing behavioral responses, but the neural circuit architecture linking sensation to behavior is poorly understood, in part due to a lack of available tools for labeling and manipulating neurons at defined stages of a circuit. In this dissertation, I describe the development of trans-Tango, a genetic strategy for transsynaptic tracing that enables one to address this kind of neural circuit question. trans-Tango is implemented in the fly Drosophila melanogaster through molecular cloning and transgenesis. Its utility is then validated through tracing well-studied neural circuits of the fly’s brain, such as those in olfactory and visual systems, by means of immunohistochemistry and mosaic analysis. I then apply trans-Tango to the less well-understood gustatory system, demonstrating the existence of several second-order projection neurons connecting primary gustatory centers to higher brain regions. Using in vivo two-photon calcium imaging in Drosophila, I demonstrate that these second-order projection neurons represent sweet and bitter taste through a different strategy than first-order sensory neurons. While sweet and bitter activate different projection neuron populations, as they do for first-order neurons, water alone drives activity in bitter-responsive projection neurons. Moreover, I demonstrate that bitter-sensing neurons respond to bitter tastants not just at stimulus onset, but also at offset. These bitter offset responses are concentration-dependent and are observed in both first-order and second-order neurons of the circuit. However, while some second-order bitter neurons respond to both onset and offset, one region of the population responds specifically to offset, and another appears to respond to both sweet onset and bitter offset. These response properties are not observed in first-order neurons, and suggest a more distributed representation of taste quality in the second order of the circuit. Finally, I discuss the implications of my findings for future studies on taste in both Drosophila and mammalian models.
- Notes:
- Thesis (Ph. D.)--Brown University, 2021
Citation
Snell, Nathaniel,
"A Genetic Strategy for Transsynaptic Tracing Reveals Neural Representations of Taste in Drosophila"
(2021).
Neuroscience Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://repository.library.brown.edu/studio/item/bdr:hkhqnngr/
