Wednesday, 28 March 2012

SEX DEPRIVED FRUIT FLIES & ALCOHOL

By Robin-Lee Troskie

It would be extremely naive and ignorant to regard Homo sapiens as a ‘higher species’ especially when our often troubled and senseless behaviour says otherwise. Our over zealousness can be demonstrated by modelling one of societies greatest and most complex crisis’s – drug abuse – and testing it in an experiment using
Fruit flies (Miller 2003).


The experiment, undergone by neurologist Ulrike Heberlein at the University of California, and researchers from Howard Hughes Medical Institute Research Centre showed the similarities of alcoholism between humans and fruit flies (Drosophila melanogaster) (Ledford 2012) with regard to sexual rejection and the over sexed nature brought about when an excess of alcohol was consumed.
It should be noted that two thirds of fruit fly genes are identical to that of humans and are the basis of many experiments because they are “cheap, prolific, simple to breed, and perhaps most significant, their genes are easy to examine and manipulate” (Miller 2003). This ease of manipulation made them the perfect experimental organism for Heberlein’s research.
Neurologist Galit Shohat-Ophir from Howard Hughes Medical Institute Research Centre carried out an experiment which “subjected male flies to four days of repeated rejection by pairing them with females who had already mated” (Yong 2012). She discovered that male fruit flies were more likely to consume food injected with alcohol when sexually rejected by females.

They revealed a neurotransmitter called neuropeptide F, or NPF, which is responsible for this behaviour in the flies. Males exhibited low levels of neuropeptide F when refused sex by females, ultimately “driving them to seek rewards in alcohol” (Yong 2012).  It was also observed that when flies were artificially given neuropeptide F, boosting their levels, no interest in alcohol was showed even if the fly was denied sex.  Also flies that were rejected but then shortly allowed to mate afterwards showed no appeal in the alcohol infused food (Yong 2012).

In the experiment, the higher exposure to ethanol the more similarities flies demonstrated to humans. “
As the concentration of ethanol in the body rises, flies begin to become uncoordinated and oblivious to their surroundings: they get tipsy. “They bump into each other. They bump into the walls,” says Heberlein” (Ledford 2012). Amazingly, the alcohol concentration in flies that induced these drunken actions was almost identical to the amount seen in humans. Shohat-Ophir noted that the more alcohol the male flies were exposed to the less discriminating they became of their mates gender. Soon male flies were chasing other male flies while serenading each other “with a traditional fruitfly courtship song played on vibrating wings” (Lee, Kim, Dunning, Han 2008).
The experiment showed that neuropeptide F is directly linked with the brains neural pathways of the reward system, which brings pleasure from consuming food and having sex. These pathways however, when subject to a negative experience like sexual rejection, can be taken over by alcohol, biasing them towards the addictive substance and causing “an outcome that may lead to alcohol dependence” (Thiele, Marsh, Ste Marie, Bernstein, Palmiter 1998).   
This ‘cycle of alcoholism’ in flies can also be seen in humans; however, the neurotransmitter responsible for the rewards system in animals is called neuropeptide Y or NPY. “NPY could be the connection between negative experiences
and humans seeking rewards in drug dependence. If so, Heberlein says, it might be possible to break this link by boosting levels of the neurotransmitter — like feeding NPF to flies to stop them turning to alcohol” (Yong 2012). Heberlein also describes that low levels of neuropeptide Y are strongly related with not only excessive alcohol consumption but also with suicides, post-traumatic stress disorders, anxiety and obesity (Rasmusson 2000).
These experiments are still continuing as scientists search for a definite link between alcoholism and negative experiences in the rewards system. With the combination of modern technology and advances in genetics, scientists can continue to experiment on flies to understand the genetic makeup of humans that causes drug addictions and discover ways to prevent it. Genetics opens up a whole new world of discoveries and each time brings us one step closer to understanding the mysteries of evolution and the way the world and everything on it functions in complete equilibrium.
References
1. Miller, J., 2003, Ulrike Heberlein: High Flies Have Heberlein Hopeful, viewed 17 March 2012 < http://pub.ucsf.edu/magazine/200305/heberlein.html >
2. Yong, E., Nature Publishing Group, 2012, Rejected flies turn to booze, viewed 17 March 2012, < http://www.nature.com/news/rejected-flies-turn-to-booze-1.10227 >
3. Ledford, H., Nature Publishing Group, 2012, Drunken flies get hypersexual, viewed 16 March 2012, < http://www.nature.com/news/2008/080103/full/news.2007.402.html >
4. Lee, H. G., Kim, Y. C., Dunning, J. S. & Han, K. A. PLoS ONE 3, e1391 (2008)
5.  Thiele, T. E., Marsh, D. J., Ste Marie, L., Bernstein, I. L. & Palmiter, R. D. Nature 396, 366369 (1998)
6. Rasmusson, A. M., et al. Biol. Psychiatry 47, 526539 (2000)

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