Cellular and molecular basis of detection of osmolality in insect taste system - Project Summary Ingesting food with very high osmolality can perturb internal osmotic balance and cause several physiological disorders. The fruit fly, Drosophila melanogaster, consumes food with varying osmolality and must therefore expend significant energy to maintain osmotic homeostasis. Hence it is imperative for flies to avoid consuming foods with high osmolality. However, whether high osmolality deters feeding in flies and, if so, the neurons and receptors in the fly taste system responsible for detecting high osmolality are unknown. The proposed project seeks to define the role of osmolality in modulating the feeding behavior of fruit flies. The proposed work will employ sophisticated genetic, electrophysiological, and imaging techniques in fruit flies to investigate the neural and molecular basis for the detection of high osmolality by the gustatory system. Aim 1 will define the behavioral and cellular basis for sensing the osmolality of food in the fly gustatory system. The aim is supported by my preliminary experiments that demonstrate flies have a lower preference for a sugar solution with higher osmolality compared to lower osmolality solutions at the same sucrose concentration. I will perform gustatory behavior assays to determine if the effect of high osmolality on feeding depends on the food source. I will perform further assays to investigate if high osmolality affects food consumption as well. Additionally, by silencing individual neuron types present in a taste sensilla followed by behavior experiments I will probe the role of different neuron types in feeding aversion caused by high osmolality. Aim 2 will further investigate the gustatory neurons that regulate osmolality-induced feeding behavior. My preliminary data suggest that high osmolality can inhibit sugar- induced activation of gustatory receptor neurons (GRNs) responsive to sweet taste. I will perform extracellular tip recordings, which assay action potentials in GRNs, to characterize the effects of high osmolality on the activities of GRNs. I have also outlined calcium imaging experiments to examine whether high osmolality inhibits sweet taste neurons cell-autonomously or whether activation of bitter GRNs and mechanosensory neurons also underlies the suppression of sweet GRN activity by high osmolality. Aim 3 outlines experiments to determine if chloride channels are required for the suppression of appetitive GRNs by high osmolality. This aim is supported by my preliminary findings that demonstrate that a volume- activated chloride channel is required for the inhibition of sweet GRNs by high osmolality. I have outlined tip-recording experiments to test if it is required for the inhibition of water GRNs by high osmolality as well. Additionally, I have outlined experiments to test the role of other chloride channels in the suppression of neuronal activity by high osmolality. The findings of this project would establish osmolality as an essential component influencing insect feeding decisions. Additionally, this work will provide novel insights into how aversive stimuli can deter feeding by inhibiting the activation of attractive taste pathways.
