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What role does octopamine play in behavioral control in Drosophila
AuthorChristine Damrau and Björn Brembs
Author email bjoern©brembs.net
Author websitehttp://lab.brembs.net
DescriptionThe mono amine octopamine (structurally related to noradrenaline) acts as a neurohormone, a neuromodulator and a neurotransmitter. Due to this diversity of physiological functions, manipulations of octopamine levels lead to a plethora of behavioral effects, among them alterations in sucrose preference, 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, in order to elucidate their role in the diverse behavioral phenotypes.
Starting point for this dissection is a mutant of the rate-limiting enzyme in the synthesis of octopamine from tyramine, the tyramine-beta-hydroxylase (tßh). Antibody stainings of this mutant show that there is no octopamine and a 10-fold increased tyramine level in such flies. We focus on two behavioral aspects. We study walking behavior in Buridan’s paradigm where flies with clipped wings walk in a circular environment with two stripes situated at 180°, i.e., opposite of each other. Furthermore, we investigate proboscis extension as a locomotion-independent test for sucrose preference after starvation. We hypothesize that different subpopulations of octopaminergic neurons are involved in the two different behaviors.
In Buridan’s paradigm, tßh mutant flies show a decreased walking speed but increased fixation of the stripes. Rescue experiments suggest that walking speed is tyramine-dependent, while the fixation behavior is under octopaminergic control. Octopamine-less flies are also impaired in olfactory learning. This deficit may be due to an impairment in the naïve response to sugar, as we found an increased response threshold for tßh mutants to extend their proboscis to increasing concentrations of sucrose after 20h of starvation. We will present results from rescue experiments testing whether octopamine or tyramine are involved in this effect. To investigate the starvation level of the mutant flies relative to the control flies, we performed mortality tests. We found that starved flies without octopamine live longer than wild type controls, suggesting that increased starvation times may be required to lead to similar sucrose preference (and hence maybe learning) in flies without octopamine. We will present hemolymph carbohydrate concentrations in wild type and mutant flies as well as the sizes and weights of both groups of flies during starvation in order to find out if the increased resistance to starvation in tßh mutants is due to metabolic effects.
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