Starvation and activity dependent modulation of salt taste behavior in Drosophila

Background Sodium present in NaCl is a fundamental nutrient required for many physiological processes but high salt consumption in western world is contributing health risk to all age individuals. Although high salt detection pathways have been studied in great detail, the mechanisms that regulate high salt consumption in animals are largely unknown. To understand how pre-exposure to high NaCl diet modulates subsequent feeding behavior, we looked into the neural mechanisms of high NaCl consumption in adult Drosophila. Method We used Neuro-Genetics, imaging and behavioral assays to determine how flies respond to high NaCl exposure. Result We studied the neural mechanism by which flies modify their acceptance of high salt as a function of diet, where a long-term high-salt exposure increases taste sensitivities of pharyngeal LSO (Labral sense organ) neurons and enhances high salt intake. We discovered that exposing flies to high NaCl diet (200mM NaCl in fly food) for three days modify their feeding responses to high levels of salt. High NaCl fed flies show decline in high salt aversion under starvation. Genetic suppression of LSO pharyngeal neurons in high NaCl fed flies inhibits excessive salt intake. We found that this modulation requires functional LSO neurons and starvation state, and that multiple independent taste receptor neurons and pathways are involved in this process. Silencing any one of multiple LSO neuronal types inhibits excessive salt intake. Conclusion Our data support the idea that high dietary salt modulates and reshapes salt and other taste curves to promote over consumption of food in flies. Our study suggest flies can adapt to the amount of salt ingested over several days, indicating the presence of a critical mechanism to reset the salt appetite and related neural circuits. Identification of new molecular sensors for salt and related neural controls such as hormones, neuropeptides, and neurotransmitters may yield insights into the coordination of processes in the nervous system.