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Neural coding of lactic acid taste in Drosophila melanogaster and Aedes aegypti Ghosh, Britya


Female Aedes aegypti mosquitoes are anthropophilic. They locate human hosts by using multimodal cues like visual cues, carbon-dioxide, body heat, odor, and taste. Upon landing, female mosquitoes assess taste cues with their tarsi and proboscis to evaluate the surface before probing in to draw blood. Lactic acid is an important component of human body secretions, which plays a role in attracting mosquitoes to the human host. However, not much has been uncovered about the role of mosquito gustation in bite-initiation behavior. Does lactic acid taste on human skin elicit an appetitive response in the gravid female mosquitoes, initiating blood-feeding? While blood-feeding behavior is specific to female Aedes aegypti, both males and females engage in sugar feeding to acquire the nutrients for life processes. Is lactic acid taste an attractive gustatory cue for the sugar-feeding program? Does sexual dimorphism play a role in their gustatory response towards lactic acid? We have developed novel mosquito feeding and engorgement assays to answer these questions. We found that lactic acid is an attractive contact cue for the mosquitoes both during sugar-feeding and engorgement behavior. How acid taste is encoded, evaluated, processed, and modulates behavior are not well understood. To understand the neural coding of lactic acid taste, we used Drosophila melanogaster (flies). Flies show an appetitive response to lactic acid taste at low concentration, however as the concentration increases, they start demonstrating aversive behavior. We showed that attraction towards lactic acid taste is mediated by sweet Gustatory Receptor Neurons (GRNs), expressing Gr64f, which is a gustatory receptor similar to the G-protein-coupled receptor family. Further delving into the molecular mechanism, we found that lactic acid taste attraction in fruit flies is mediated by receptors belonging to two different families - the Gustatory Receptor (GR) family and the Ionotropic Receptor (IR) family. To our best knowledge, it is the first time the involvement of both an IR and a GR has been demonstrated in mediating taste response to a single modality.

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