Processing Gustatory Information in the Fly Brain

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Sugars are essential nutrients that allow animals to derive energy from the environment to survive, as individuals and as species. Gustatory receptors on sensory neurons directly detect sugars in potential food sources, allowing animals to assess nutrient value. Sugar detection by the gustatory system drives innate feeding behaviors, arguing that the inherent value of sugars is embedded in innate circuits set up in development and refined over evolution. In addition, sugars are critical to animal survival and serve as rewarding stimuli that impart positive valence to other cues for learned associations. The long-term objective of this proposal is to gain insight into the taste pathways that detect sugars, to determine how these essential compounds promote feeding and act as reward signals. Aim 1 will examine taste processing pathways from sensory detection to feeding initiation, using behavioral, functional, and anatomical studies of several neurons in the circuit. These studies will provide insight into how taste detection and internal state are integrated in neural circuits to arrive at feeding decisions and to carry them out. Aim 2 will examine how sugar taste detection serves as a reward to impart positive valence onto other associated cues. These studies will test the hypothesis that there are two pathways that convey different aspects of reward, one taste-specific pathway and one pathway that relays a broader environmental context. These studies will determine how sugar sensory activation is transformed into the rewarding qualities of sweet taste in the memory system. The proposed molecular genetic, cellular and functional approaches will provide a comprehensive analysis of taste processing that is difficult to achieve in other systems. These studies will provide insight into how gustatory information is processed in the brain and an essential foundation for understanding insect feeding, relevant to limiting the spread of insect-borne disease.