Independent insulin signaling modulators govern hot avoidance under different feeding states

Thermosensation is critical for the survival of animals. However, mechanisms through which nutritional status modulates thermosensation remain unclear. Herein, we showed that hungry Drosophila exhibit a strong hot avoidance behavior (HAB) compared to food-sated flies. We identified that hot stimulus increases the activity of alpha 'beta ' mushroom body neurons (MBns), with weak activity in the sated state and strong activity in the hungry state. Furthermore, we showed that alpha 'beta ' MBn receives the same level of hot input from the mALT projection neurons via cholinergic transmission in sated and hungry states. Differences in alpha 'beta ' MBn activity between food-sated and hungry flies following heat stimuli are regulated by distinct Drosophila insulin-like peptides (Dilps). Dilp2 is secreted by insulin-producing cells (IPCs) and regulates HAB during satiety, whereas Dilp6 is secreted by the fat body and regulates HAB during the hungry state. We observed that Dilp2 induces PI3K/AKT signaling, whereas Dilp6 induces Ras/ERK signaling in alpha 'beta ' MBn to regulate HAB in different feeding conditions. Finally, we showed that the 2 alpha 'beta '-related MB output neurons (MBONs), MBON-alpha ' 3 and MBON-beta ' 1, are necessary for the output of integrated hot avoidance information from alpha 'beta ' MBn. Our results demonstrate the presence of dual insulin modulation pathways in alpha 'beta ' MBn, which are important for suitable behavioral responses in Drosophila during thermoregulation under different feeding states. Thermosensation is critical for the survival of animals, but the mechanisms by which nutritional status modulates thermosensation remain unclear. Behavioral and live brain imaging studies reveal why food-sated fruit flies prefer to stay at relatively higher temperatures compared to hungry flies.

Automated summary

Thermosensation is critical for animal survival. This study reveals that nutritional status affects thermosensation in fruit flies, with hungry flies exhibiting stronger hot avoidance behavior. The activity of specific neurons in the brain is increased in hungry flies and these neurons receive the same level of hot input in both food-sated and hungry states. Insulin-like peptides regulate the activity of these neurons depending on feeding conditions. Surprisingly, different signaling pathways are involved in the regulation of hot avoidance behavior based on the type of insulin-like peptide. Finally, two specific neurons are found to be necessary for the output of integrated information related to hot avoidance behavior. These findings provide insights into the mechanisms of thermosensation modulation and its importance for animal survival.