on Tuesday, March 13th, 2012 8:22 | by Christine Damrau
Octopamine is a biogenic amine involved in insect physiology and behavioral control. In Drosophila, it was suggested to be necessary for appetitive olfactory learning (Schwaerzel et al., 2003). The available fly mutant tßh cannot convert tyramine into octopamine. We have found that the preference of these mutant flies for sugar (tested in a T-maze) as well as the responsiveness to a serial dilution of sugar (tested in a proboscis extension assay) is decreased compared to their genetic control “w+” (unpublished). We wondered whether the flies have different physiological state and hence different motivation, or if octopamine is involved in the neuronal coding of motivation per se. We therefore want to examine the physiological state of these flies.
In a first approach, we starved flies to death in bottles containing only a cotton pad moisturized with water. Dead flies were counted periodically and kept in the bottles. The survival curve shows that the tßh mutant flies die later (Fig.1a): The time point for 50 % of the flies to die is significantly higher in tßh mutant flies than the one of the control w+. Gender had no effect (ANOVA, gender: p=0.13, genotype: p<0.04). Data from male and female were thus pooled in the figures. These results show that starvation affects differently control and mutant flies. Obviously tßh mutants are more resistant to starvation.
The different physiological state could be due to different activity levels and consequently less energy requirements in tßh flies. To test for this hypothesis, we will use a second approach and measure trehalose content in the hemolymph of the flies. It has been shown that trehalose level decreases with starvation (Meunier et al., 2007). Furthermore there is a correlation found between trehalose level and survival (Isabel et al., 2004). A different metabolic rate in tßh mutants may explain a different trehalose content and the higher survival rate after the same starvation time.
In the future, we hope to be able to titrate the physiological state of the fly using the measure of the trehalose content in their hemolymph, in order to test the sugar responsiveness of mutant and control flies with adapted physiological state. This will allow us to separate the role of octopamine on the fly physiology and its role on the fly motivation.
Category: Biogenic Amines