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Using light to investigate taste reward circuits in Drosophila Jelen, Meghan


The refinement of foraging and feeding behavior through experience is a vital process in an animal’s life, leading to increased overall fitness and survival. Yet, little is known about how initial taste perceptions are transformed in higher order neural circuits to produce lasting changes in behavior. Using Drosophila melanogaster, we investigate the neurobiology of taste memory formation. We find that flies form appetitive and aversive short- and long-term taste memories, which are processed in the mushroom body (MB), an associative learning neuropil. Moreover, appetitive short- and long-term memory formation is regulated by distinct subpopulations of protocerebral anterior medial neurons (PAMs), and long-term memory formations requires a caloric unconditioned stimulus (the US), which we hypothesize activates of MB-MP1 neurons. Transmission of the US signal from the primary taste center in the fly brain to the extrinsic PAM neurons of MB is regulated in part by sTPNs and lTPNs, two newly discovered taste projection neurons. sTPNs respond to a variety of sweet tastants, and when silenced flies fail to form short-term memories in a simple light memory task. Contrastingly, lTPNs respond to sucrose only upon ingestion, and when silenced fail to form long-term light memories. Interestingly, sTPNs neuronal activation dynamics mirrors that of PAM DANs arborizing on the horizontal tip of the MB lobes, and lTPN signaling shows similarities to PAM-α1 neurons. Finally, we investigated the modulatory role that discrete DAN/MBON cell types play in the innate acceptance or rejection of a meal source. Upon activation, we found that most DAN/MBON pairs show a similar activation patterns to those previously shown to initiate the approach or avoidance of an odor. This implies that the valence of these discrete MB associated neurons is fixed and instructs similar output behaviors among different sensory systems.

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