The effect of sleep deprivation on the reaction time of Drosophila melanogaster flies

By Rebecca Mckelvey 2016

By Filitsa Theodoridou

 

As part of my research placement at Imperial College London, I was given the fantastic opportunity by my supervisor, Dr Alice French, to take on my own mini-project. The idea was to test whether the speed of probosis extension reflex (PER) differs between slept and sleep deprived Drosophila melanogaster flies. This was greatly exciting, as Drosophila has not yet been established as a model for sleep deprivation, which meant that I was privileged to fully engage with the scientific method from its preliminary stages.

The null hypothesis was that sleep deprivation worsens reaction times in flies, as it seems to do in humans, so sleep deprived flies should take longer to extend their probosis in response to a food stimulus. To test this, we isolated male wild type flies, and sleep and food deprived them overnight using ethoscopes- ingenious devices, which allow the level of sleep and movement of flies to be controlled, tracked and observed using electronic sensors- and stimulated the taste receptors on their hair legs with different concentrations of sucrose solutions. However, the limitation identified on this assay was that there could be both variability of sleep and hunger among the different flies, which could be affected by more than one factor.

Therefore, I suggested taking our experiments to a different tangent, using vinegar as the stimulus, in order to eliminate the issue of controlling hunger. Flies have positive chemotaxis to vinegar, so the time the flies from each group would take to walk towards a vinegar odour source was to be recorded. The initial apparatus set up used to investigate this is displayed in figure 1; the odour was delivered via the tubes and a “finishing line” was set 8 cm away from the yellow line starting point. To our great disappointment, however, hours of meticulous tube cutting and assembling seemed to have gone to waste when our flies found a cosy place to rest inside the towers and mutinied against participating in the experiment.

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Figure 1

 

The result? I progressed to the set up seen in fig. 2a. This used the same principle, with the main difference being that the vinegar was not being vaporised, but pipetted in the tubes as a drop instead. What we obtained from this set up was- unsurprisingly- yet another limitation. Despite being extremely proud of the idea, the actual running of the experiment proved to be disastrous, as the set up was too fragile to pull the wires (and ultimately release the flies) at the same time, even when they were all tied to a medal rod. I am certain the result was a bit more triumphant for the flies as they almost all managed to flee the scene.

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Figure 2a (top) and figure 2b (bottom)

 

In the end, the wonders of 3-D printing seemed to save us. Using Cura software, and aided by my supervisor, I designed a trap-door system (fig. 2b), which allowed the flies to be very neatly released simultaneously, without giving them the option of hiding away. I was hugely fascinated by how easily and quickly 3-D printing allowed us to obtain everything we needed for the experiment, which made me realise how valuable it can be for so many types of research. And most of all, 3-D printing the equipment allowed us to obtain some much anticipated data, for which I could not have been more grateful!
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To conclude, I absolutely loved the pressure and excitement of getting each experiment to work and learned that, as a scientist, it is important to view every mistake as a learning curve that will open doors to new ideas and inventions. The heartbeat and anticipation every time we put a new set up to test was far greater than the slightly underwhelming feeling of hours having gone to waste if it did not. One thing is certain: life as a scientist is an emotional roller-coaster. But then again, who doesn’t love roller-coasters?