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Role of Octopamine in walking behavior and sucrose responsiveness
AuthorChristine Damrau, Julien Colomb and Björn Brembs
Author email bjoern©brembs.net
Author websitehttp://lab.brembs.net
DescriptionOctopamine acts as a neurohormone, a neuromodulator and a neurotransmitter, contributing to the control of the animal physiology and behavior. tßhnM14 mutant flies (defective for the enzyme synthesizing octopamine from tyramine) lack octopamine and show a 10-fold increase in their tyramine level. We report here new phenotypes for these flies in locomotion and in sucrose preference.
Using Buridan’s paradigm, where flies with clipped wings walk on a circular platform with two unreachable, opposing vertical stripes in their environment, we found a decrease in walking speed and an increase in stripe fixation in tßhnM14 mutants. These flies also show a lower response to sugar after 20 hours of starvation, a defect calling for a reassessment of previous interpretations of appetitive learning experiments. To establish sucrose preference, we used a sensitive, locomotion-independent test, based on the proboscis extension response. We also report increased longevity for tßhnM14 flies while starved to death. Thus, octopamine-less flies may show a lower response to sugar because the starvation might have less of a physiological effect. To investigate this possibility, we are comparing hemolymph sugar (trehalose and glucose) concentrations between wild type and tßhnM14 mutant flies at different starvation times.
Using a pharmacological approach of either feeding octopamine or yohimbine, a tyramine receptor blocker, we have started to test the relative importance of the tyramine increase and the lack of octopamine for the different phenotypes. In those cases where octopamine is found to be the major amine, genetic rescue experiments will identify the octopaminergic subpopulations mediating the wild type behavior.
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