Abstract
Octopamine regulates feeding behavioral responses in Drosophila melanogaster, however the molecular and circuit mechanisms have not been fully elucidated. Here, we investigated the role of a subset of octopaminergic neurons, the OA-VPM4 cluster, in sucrose acceptance behavior. Thermogenetic activation of Gal4 lines containing OA-VPM4 promoted proboscis extension to sucrose, while optogenetic inactivation reduced extension. Anatomically, the presynaptic terminals of OA-VPM4 are in close proximity to the axons of sugar-responsive gustatory sensory neurons. Moreover, RNAi knockdown of a specific class of octopamine receptor, OAMB, selectively in sugar-sensing gustatory neurons decreased the behavioral response to sucrose. By calcium imaging experiments, we found that application of octopamine potentiates sensory responses to sucrose in satiated flies. Taken together, these findings suggest a model by which OA-VPM4 promotes feeding behavior by modulating the activity of sensory neurons.
Highlights
Animals must constantly adjust their feeding behaviors to fulfill their nutritional needs
With the aid of the molecular genetic toolbox, imaging technology and behavioral studies, we found that a subset of octopaminergic neurons, the OA-VPM4 cluster, has an important role in sucrose detection
We examined the role of a cluster of ventral paired median OA neurons, OA-VPM4, because they have rich projections in the subesophageal zone (SEZ), a region that participates in taste information processing [91,92]
Summary
We examined neural and molecular mechanisms underlying octopaminergic feeding modulation in Drosophila melanogaster. Octopamine modulates sweet taste sensitivity and further regulates feeding behavior in flies. It has been unclear by which molecular mechanisms and neural circuits octopamine modulates feeding behavior responses. Activating the neurons in two distinct Gal lines containing OA-VPM4 augmented Proboscis Extension Response (PER) to an increasing concentration of sucrose. Sugar-sensing GRNs express an octopamine receptor OAMB that is necessary for increased behavioral responses to sucrose. Preliminary experiments testing if OA-VPM4 is functionally connected with sugar-sensing GRNs argue that activities of sugar-sensing GRNs are regulated by ectopic activation of OA-VPM4 These findings support a model by which octopamine released from OA-VPM4 promotes activity in the sugarsensing GRNs via OAMB to promote feeding behavior
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