In order for animals to achieve metabolic hometostasis and maintain fitness, it is
crucial for them to make appropriate feeding decisions and precisely execute feeding
behaviors. Animals make feeding decisions based on various factors including their
physiological needs and palatability of the food source. Despite of their importance,
neural and molecular mechanisms underpinning the integration of these internal and
external information have yet to be fully elucidated. In addition, octopamine, an
equivalent of mammalian norepinephrine, has been suggested to regulate feeding
behavioral responses in invertebrates. However, how octopamine modulates feeding
behavior has been unclear. Utilizing Drosophila melanogaster as a model system, I
sought to examine the neural and molecular mechanisms underlying octopaminergic
feeding modulation in this thesis.
In specific, I 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 presynaptic terminals 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, I found that
application of octopamine potentiates sensory responses to sucrose in satiated flies.
Preliminary results from the experiments investigating functional connectivity
between sensory neurons and OA-VPM4 suggest that OA-VPM4 is likely an
upstream modulator of the sensory neurons. Taken together, these findings suggest a
model by which OA-VPM4 promotes feeding behavior by modulating the activity of
sensory neurons.