The basis of fructose sensation: Instructions provided by the peripheral nervous system to select appropriate behavioral actions

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Gustatory stimuli are instrumental for an animal to sample its environment for energy-rich food sources to maintain survival, and to avoid unpleasant or poisonous substrates. Sugars often predict a nutritional benefit and are perceived as attractive and rewarding. Therefore, sugar-rich food sources trigger a series of behaviors including attraction, food selection, and consumption - actions that are fundamental for all animals. Insects for example - like Drosophila - are attracted to most sugars that are also preferred by humans.Sophisticated mechanisms that allow Drosophila to detect, evaluate, and consume sugars are of special importance for its larva – the feeding stage of the animal. This period of the life cycle is restricted to only about 5 days, during which the animal increases its weight up to several hundred-fold. They grow from a tiny first-instar larva of about 10 μg to a wandering third-instar larva weighing about 2 mg. The main nutrients known to be critical for this period of rapid growth are sugars besides amino acids. To efficiently detect these substances, the larva utilizes a numerical simple but efficient peripheral nervous system.Accordingly, in this project we will analyze how the peripheral nervous system perceives and processes fructose stimuli from its environment to select the appropriate action at the right time. Using the recently established connectome, available second-generation split-Gal4 tools, a newly established larval standard brain atlas (www.larvalbrain.org), and well established assays that monitor and evaluate larval behavior at high speed and resolution (FIM tracking), we will analyze three different fructose-related behaviors: fructose preference (where to feed), fructose ingestion (what to feed) and fructose reinforced olfactory learning (when to feed). We aim to provide an answer on how the numerically simple and functional accessible larval peripheral sensory system instructs food-related action selection. A task that every animal has to solve in order to survive.