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Genetic dissection of octopamine action in reward-related behavior and motor control in Drosophila

The monoamine octopamine (structurally related to noradrenaline) acts as a neurohormone, a neuromodulator and a neurotransmitter in insects. Manipulations of octopamine levels lead to a plethora of behavioral effects, among them alterations in locomotion, flight or learning and memory. Drosophila with its diverse genetic toolbox is a suitable model system to dissect the function of distinct octopaminergic neuronal subpopulations coordinating modulation of diverse behavioral phenotypes. Our work focuses on two behavioral aspects: Locomotion and sugar motivation.
Starting point for the genetic dissection is a mutant of the enzyme tyramine-beta-hydroxylase (tßh) in the synthesis of octopamine from tyramine, a less investigated neurotransmitter/-modulator. This mutant has no detectable octopamine and 10-fold increased tyramine levels. Our results show that those flies have a reduced walking speed and a decreased sucrose response after starvation.
Both phenotypes can be rescued by a temperature-dependent ubiquitous expression of the tßh gene just before the test. Survival experiments and measurements of hemolymph carbohydrate concentrations indicate different starvation levels of the mutants which may explain the sugar response phenotype. Using receptor mutants we will test whether octopamine or rather tyramine are involved in the modulation of those two behaviors. We hypothesize that different subpopulations of octopaminergic neurons are involved in the two behaviors and we will investigate that question using the GAL4-UAS system.