Activity and state-dependent modulation of salt taste behavior via pharyngeal neurons in Drosophila melanogaster

Sodium present in NaCl is a fundamental nutrient required for many physiological processes. In animals, including Drosophila, low-salt concentrations induce attraction and high-salt concentrations evoke aversive behavior. Although the cellular basis of low and high salt taste detection has been described, the mechanisms regulating high salt consumption and salt taste modulation in animals remain elusive. Thus, we investigated the neural mechanisms behind high NaCl consumption in adult Drosophila, focusing on how flies adjust their acceptance of high salt based on their diet. Our findings show that long-term exposure to high salt increases the taste sensitivity of pharyngeal LSO neurons, which, in turn, enhances high salt intake. Exposing flies to a high NaCl diet for three days shows a decline in high salt aversion under starvation. Our results suggest that this modulation requires active LSO neurons and a starvation state or dopamine as genetic suppression of LSO pharyngeal neuronal activity in high NaCl-fed flies inhibit excessive salt intake. We also found that several independent taste receptor neurons and pathways are involved in such a modulation. Silencing any one of multiple LSO neuronal types inhibits excessive salt intake. Our study suggests that flies can adapt to the amount of salt ingested over several days, indicating the presence of a critical mechanism that resets the salt appetite and related neural circuits.