Genetic dissection of octopamine action in Drosophila motivation, reward and motor control
Final Report Abstract
All animals constantly negotiate external with internal demands before and during action selection. Energy homeostasis is a major internal factor biasing action selection. For instance, in addition to physiologically regulating carbohydrate mobilization, starvation-induced sugar shortage biases action selection towards food-seeking and food consumption behaviors. Biogenic amines are often involved when such widespread behavioral biases need to be orchestrated. In mammals, norepinephrine (noradrenalin) is involved in the counterregulatory response to starvation-induced drops in glucose levels. The invertebrate homologue of noradrenalin, octopamine (OA) and its precursor tyramine (TA) are neuromodulators operating in many different neuronal and physiological processes. We investigated the role of those two modulators in Drosophila sugar responsiveness. Tyrosine-ß-hydroxylase (tßh) mutants are unable to convert TA into OA. Starved mutants show a reduced sugar response and their hemolymph sugar concentration is elevated compared to control flies. When starved to death, they survive longer. Temporally controlled rescue experiments revealed an action of the OA/TA-system during the sugar response, while spatially controlled rescue experiments suggest actions also outside of the nervous system. Additionally, the analysis of four OA- and four TA-receptor mutants suggests an involvement of both receptor types in the animals' physiological and neuronal counterregulatory response to starvation. Biogenic amines are also involved in spatial and temporal parameters of locomotion. However, the neurogenetic study of these processes is complicated by differential dominance effects of the tßh gene locus. In walking speed there appears to be an over-dominant relationship where one gene copy leads to faster walking flies than both null mutants and wild type flies. In contrast, fixation behavior seems to require both copies of the tßh gene for complete functionality. Our experiments suggest that these effects are connected to the level of both tyramine and octopamine and that these levels are differentially involved in the different behavioral tasks.
Publications
- (2011): Does starvation-resistance in flies without octopamine explain differences in sucrose preference and learning? Soc. Neurosci. Abstr., 615.11
Damrau C, Colomb J, Brembs B
(See online at https://doi.org/10.5283/epub.28530) - (2012): Role of Octopamine in walking behavior and sucrose responsiveness. European Drosophila Neurobiology Conference (Neurofly), Padua, Italy
Damrau C, Colomb J, Brembs B
(See online at https://doi.org/10.5283/epub.28695) - (2012): What role does octopamine play in behavioral control in Drosophila? Soc. Neurosci. Abstr., 398.04
Damrau C, Colomb J, Brembs B
(See online at https://doi.org/10.5283/epub.28533) - (2013): Genetic dissection of octopamine action in rewardrelated behavior and motor control in Drosophila Soc. Neurosci. Abstr., 169.20
Damrau C, Brembs B, Colomb J
- 2016. A decision underlies phototaxis in an insect. Open Biol. 6: 160229
Gorostiza EA, Colomb J, Brembs B
(See online at https://doi.org/10.1098/rsob.160229)
