A drosophila model for flavor perception and feeding decision
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The central nervous system (CNS) evaluates internal nutrients levels and external environmental cues to make foraging decisions: to consume enough food for energy needs, yet not too much for the body to handle. Eating disorders or obesity occur when energy balance deviates from body needs, leading to physical and psychosocial morbidity or even fatal consequences. We have developed a behavioral paradigm in Drosophila larvae that provides a quantitative readout for feeding responses. With the help of this system, we revealed that feeding behaviors in Drosophila larvae utilize sophisticated neural modulations, which implied the existence of an elementary form of cognition in this model organism. Like mammals, fly larvae make feeding decisions according to current body energy level. We have demonstrated that the motivational states are mediated through two octopamine receptors Oamb and Octβ3R downstream of two OA neuron clusters in the subesophageal ganglion. Oamb and Octβ3R exhibit counteracting effects on feeding. While Oamb neurons inhibit overfeeding in the satiated state, Octβ3R neurons promote feeding during food deprivation. The baseline feeding in satiated larvae can be disrupted by the reward system. Appetizing odor elicits motivation to feed on sweet media. Two dorsal medial neuropeptide F neurons are responsible for relaying the olfactory stimuli by responding to upstream dopamine signaling through dopamine receptor D1. The behavioral output further relies on a cluster of three NPF receptor neurons in the subesophageal ganglion region, which project to the peripheral enteric systems. Alcohol is also able to alter the feeding response by activating NPF synthesis and release. However, it only intervenes with the pathway for regulating feeding motility, leaving a separate mechanism for modulating food ingestion.