Decision-making neurons for feeding behavior revealed by thermogenetic activation in Drosophila. Shinya Iguchi, Michael Gorczyca, Motojiro Yoshihara. Neurobiology, UMASS Med, Worcester, MA.

   The decision of when to eat is a complex function of both environmental variables and internal physiological state. How these external and internal determinants are integrated by the nervous system is largely unknown, and the neural substrates of the feeding decision remain poorly characterized. Work from our lab, in collaboration with B. White and K. Ito, has identified a single pair of neurons in the Drosophila brain, Fdg(feeding)-neurons, which command the entire sequence of feeding behavior (in preparation). They were identified from a screen of Gal4 lines established by the NP consortium¹ by activation of a neuron subset expressing a heat-activated cation channel, TrpA1. We used infrared laser light from a 2-photon microscope to spatially restrict heat to the cell body of either the left or right Fdg-neuron expressing TrpA1, which led to asymmetric proboscis extension in the same direction as the illuminated side and also triggered pharyngeal pump movement. Ablation of an Fdg-neuron cell body on one side by strong laser illumination made sucrose-induced proboscis extension response asymmetric, extending in the opposite direction. Furthermore, ablation of Fdg-neurons on both sides led to complete suppression of feeding behavior, indicating a pivotal role for Fdg-neurons in the feeding circuit. Here we tested various gustatory modalities that might be integrated by the feeding behavior circuit. Taking advantage of our newly devised method to record calcium signals while simultaneously observing feeding behavior², we tested the effect of satiety or bitter signals on Fdg-neuron activity correlated with feeding behavior. Fdg-neurons were activated in response to food presentation and this coincided with a proboscis extension, but only in the starved state. Fdg-neuron activation by sugar stimulus was suppressed by the bitter compound, caffeine. These results support our hypothesis that Fdg-neurons function as a decision making center, integrating multiple kinds of information. 1)Yoshihara and Ito (2000) Dros. Inf. Ser. 83:199. 2)Yoshihara (2012) JoVE, 62, e3625, DOI: 10.3791/3625.