Science inspired by nature – down the road with fruit flies – from the appeal of fruit to research on the development of addiction
Text written by senior lecture Ana Filošević Vujnović, PhD.
Fruit flies are dipteran insects that are widespread in all parts of the Republic of Croatia, as well as in most of Europe and the world. These insects are traditionally found most often near fruit, and wine cellars, attracted by fragrant aromas and the product of alcoholic fermentation, ethanol. But you probably didn’t know that these tiny animals, approximately 3-5 millimeters in length, have been used for more than a century in various scientific researches, especially in the research of the nervous system.
What is the reason that flies are so interesting to scientists? Primarily, flies have a short development cycle that lasts about 14 days and allows testing a very large number of individuals in a short time, while their average life span is about one and a half months, and the maximum is three months. As shown in the picture (bottom left), one cultivation bottle can contain hundreds of flies, which do not take up a lot of space, are cheap and easy to breed, and most importantly, are not subject to strict ethical regulations as is the case with mice or rats. Adults have 6 legs, two wings, two red complexes eyes and a proboscis, similar to an elephant, with which they lick food from the substrate. If you have asked yourself, do flies see, hear, smell and taste, the answer is yes. As shown in the picture (top left), the difference between males and females is primarily in their size, males are smaller than female. The fly that is in the foreground on the pen and is briskly cleaning itself with the first pair of legs (top left) certainly caught your eye. You noticed that it has white eyes and curled wings, while the flies in the adjacent picture have red eyes and straight wings. The mentioned features are used every day to monitor genetic manipulations, while in the past they served as a tool for proving hereditary traits for which genes are responsible.
How and why flies in addiction research? Primarily, the forced administration of various narcotic drugs through food, via injection or aerosol was tested, which would expose the flies to a certain dose of the tested substance. This is followed by the monitoring of activity, where as a result activity increases, while their sleep decreases. Yes, you read that right, flies like us sleep at night and are active during the day. Activity and sleep are tested in the system shown in the picture (bottom left). One fly is placed in one plastic tube that has food with a narcotic drug at one end, and a piece of sponge at the other. A beam of light passes through the middle of the displayed device, which, when it is interrupted for the purpose of crossing the fly, sends information to the computer about the number of crossings of the middle of the tube in a unit of time, which is usually one minute. By using this and similar approaches, it was shown that flies can develop tolerance, which means that they need an increasing dose to achieve the same intoxication effect measured as activity, and different genes were tested on them, which were shown to be associated with an increase in activity after taking an narcotic drugs.
When given a free choice, do you think a fly will choose food with or without a drug like cocaine? The answer is yes, flies willingly consume a solution with narcotic drugs and prefer it over a solution without narcotic drugs. Research is currently being done on different classes of narcotic drugs to study the influence of different genes, nerve cells or brain regions on this type of behavior, and of course the influence of environmental factors. One interesting fact is that flies that previously spent some time in isolation reduce their preferential consumption of narcotic drugs compared to those that stayed in a group, while the first studies of addiction using this paradigm were on ethanol, which was later shown to be applicable to other classes of narcotic drugs.
The images are the property of the Laboratory for Behavioral Genetics, Faculty of Biotechnology and Drug Development, University of Rijeka.