Does starvation-resistance in flies without octopamine explain differences in sucrose response?

Biogenic amines are involved in almost all biological processes. They modulate perception, motivation and locomotion. The fruit fly Drosophila is an ideal model system to tease apart neuronal populations mediating the aminergic effects. Using Drosophila neurogenetics, we are beginning to characterize the octopaminergic subpopulations involved in walking speed and sucrose responsiveness. Appetitive classical conditioning, using sucrose as unconditioned stimulus, is impaired in flies without octopamine. These mutant flies also show a decreased sucrose preference in a T-Maze paradigm, compared to control flies.

To exclude locomotor deficits in the mutant flies, we tested tethered flies in their proboscis extension reflex (PER). Flies without octopamine (tßh-mutants) show a lower sucrose response than control flies after having been starved for the same amount of time.

To define the starvation level of the mutant flies relative to the control flies, we performed survival tests. We found that starved flies without octopamine live longer than wild type controls, suggesting that different starvation times are required to lead to similar sucrose response. Why are flies without octopamine more resistant to starvation? To answer this question we will test hemolymph carbohydrate concentrations in wild type and mutant flies and compare the sizes and weights of both groups of flies.

Furthermore, we want to learn more about the role of octopamine in walking behavior. It is known that Drosophila larvae without octopamine crawl slower compared to the control. When adult mutant flies are tested in Buridan’s paradigm not only their walking speed is decreased, but also their fixation to vertical stripes is stronger, whereas their thigmotaxis is less pronounced compared to the genetic control.

 

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