Drunken Flies and Alcohol Addiction
Leyli Beheshti, Kinza Qureshi, and Lili Razavi
Abstract
Alcoholism is a serious problem around the world. Alcoholism can lead to many neuron
damages if consumed in large amount. Due to the resemblance between mammals and
Drosophila melanogaster (fruit flies), fruit flies were used as a model to study the alcohol effects
and also alcohol related behaviors in humans. It was hypothesized that there is an increase in
alcohol tolerance throughout generations after fruit flies being exposed to ethanol. Ten samples
of fruit flies were used for the parent generation and 45 fruit flies were used for the first
generation; they were introduced into the inebriometer to measure the sensitivity of Drosophila
to alcohol vapor. The time for the flies to fall down to the bottom of the column was noted for
each generation. The mean time for the parent fruit flies were 28.69±3.080 minutes (±SEM,
n=10) and for the first generation were 10.60±0.0341 minutes (±SEM, n=45). A one-tailed
unpaired t-test (p-value=6.33x10-6) revealed a significant difference in the average time between
the two generations. Our hypothesis says that there is an increase in alcohol tolerance throughout
generations after fruit flies being exposed, but the result shows that there is a lower tolerance
toward alcohol for the first generation. Possible explanation might be that the fruit flies were
exposed to the alcohol too frequently leading to them still being intoxicated when the next
dosage came.
Introduction
Alcohol is considered one of the most consumed drugs in the world. People use alcohol
to cope with the stress and struggles they experience throughout their lives and a non-controlled,
continuous usage can ultimately lead to alcoholism. The social, economic, and personal abuse
and addiction to alcohol is immeasurable. Alcohol actives certain areas of the brain that leads to
an increase release of dopamine. Dopamine elevation provides a sense of pleasure and a positive
reinforcement (Diamond and Gordan, 1997). There is not a perfect model organism that can
depict exactly what can occur in humans when exposed to ethanol; however, they can model
particular aspect of addiction. By researching about the effects of alcohol on fruit flies, scientists
are able to find ways to control alcoholism in humans by getting a better understanding of how
the brain reacts to ethanol and how to reverse its effects. Such an understanding will inevitably
lead to better treatments for alcohol addiction (Rothenfluh, 2002).
The fruit fly, Drosophila melanogaster, has been a leading model for aging research since
early in the twentieth century. The benefits of using D. melanogaster for research include its
short life span (1 to 2 months), inexpensive and easy to culture. Fruit flies have an advance
nervous system (approximately 300,000 neurons) and are capable of various complex emotions
(Hall, 1994; DeZazzo and Tully,1995; Hall, 1998; Sokolowski, 2001). Furthermore, they are
easy to rear and have a generation time of only approximately 2 weeks, allowing scientists to
explore certain traits and behaviors over a large number of generations in a very short period.
Drosophila genome has revealed similarities between flies and mammals and can be a good
animal model to study alcohol effects and behaviors (Adams et al. 2000). The natural habitat of
fruit flies is fermenting plants, which usually have about 3% of alcohol. Fruit flies can
metabolize alcohol for use of energy (Geer et al. 1993).
When exposed to low dosages, fruit flies show signs of being energized and when exposed to
higher dosages, the flies lose their balance and sedation (Moore, et al. 1998). By researching
about the effects of alcohol on fruit flies, scientists are able to find ways to control alcoholism in
humans by getting a better understanding of how the brain reacts to ethanol and how to reverse
its effects. For our experiment we are going to see if there is an increase in tolerance in the first
generation compared to the parent generation.
Methods and Materials
The experiment took place over a 4 week period (from October 26, 2015 to November
18, 2015) in SM 244 at Saddleback College. Equipment was purchased from PetSmart in Laguna
Niguel, CA and fruit flies were provided by the Biology department of Saddleback College. Two
of the three soda bottles had the bottom portion cut off and the three bottles were stacked on top
of each other to make a column. The bottle was taped together and three holes were cut into the
column: two at the top bottle that were across from each other and one at the bottom one. A tube
was placed from the Erlenmeyer flask to one of the holes at the top of the column. A tube with
anhydrous calcium sulfate placed in-between was used in order to avoid condensation of the air
mixture. Another tube was placed from the bottom of the column to the Stable systems flow
meter that sucked out about 720 mL/min. The air pump was connected to the Erlenmeyer flask
with tubing. The was cut and connected to each end of a small plastic tube that was placed into
the rubber stopper which connected to each end of a small plastic tube that was placed into the
ethanol. A picture of the set is seen below.
150 mL of ethanol was placed into the Erlenmeyer flask with the air stone and was heated
while air was pumped through to create the ethanol - air mixture. An air flow pump was used to
take 720 mL of air out in order to keep a constant amount of the ethanol - air mixture in the
column. After waiting for 10 minutes, a syringe, with the bottom portion cut off, was inserted
into the foam stopper and then placed into the tube that contained the fruit flies. Two fruit flies
were placed into the syringe and then placed into the column and the timer started. The time was
noted when a fly had fallen to the bottom of the column. After all the flies had fallen, the times
were noted; the flies were placed into a new tube and were left to reproduce the next generation.
After the new generation had grown into adults, they went through the same process and left to
reproduce the next generation.
Figure 1. The picture above shows the set up of the project.
Results
The average time for the flies for each group to pass out is seen in Figure 1, which shows
that the parent generation took much longer than the first generation to pass out. A one-tailed
unpaired t-test was taken on the times from each group and was found that there is significant
difference between the groups (p-value =6.33x10-6). The mean for the parent generation was
28.69 minutes with a standard error 3.080 minutes and 10.60 minutes with a standard error of
0.341 minutes for the second generation. The results reveal that the parent generation was more
tolerant to the alcohol since they were able to survive in the ethanol air mixture for a longer
period of time. The second generation passed out at a significantly lower time and has a smaller
standard error compared to the parent generation. The results go against our hypothesis that the
first generation will have a higher tolerance towards the mixture compared to the parent
generation.
Average Time Until Passing Out (min)
35
30
25
20
15
10
5
0
Parent Generation
First Generation
Figure 2. This graph shows the average time it took the fruit flies to pass out when exposed to
ethanol. The parent generation took far longer than the first generation. Error bars are mean +
SEM (p-value =6.33x10-6).
Discussion
The purpose of this experiment was to see if there is an increase in alcohol tolerance from
one generation to the next. Fruit flies were used as a model for humans since they have
similarities in their genome and contain a variety of emotions (Hall, 1994; DeZazzo and
Tully,1995; Hall, 1998; Adams et al. 2000; Sokolowski, 2001). Once exposed to ethanol, fruit
flies have an increase in their sensitivity and tolerance towards alcohol which can affect their
neurons (Scholz et al., 2000). The data collected revealed that the parent generation had a higher
tolerance towards the ethanol-air mixture compared to the first generation. In this study, the data
did not support our hypothesis, that there is an increase in alcohol tolerance throughout exposed
generations. Although, this study revealed significant difference in the mean time between two
generations. Our data collection opposed other studies on exposing fruit flies to the alcohol, and
possible explanations might be that the fruit flies were exposed to the alcohol too frequently
leading them being intoxicated when the next dosage came. Further study should be done to
investigate the alcohol tolerance of exposed fruit flies through multiple generations by
considering the fact of the exposed fruit flies are not intoxicated when their next dosage comes.
It can be seen that the fly still contains some alcohol in their system is they are “hyperactive and
disoriented” (Moore, et al. 1998). By considering this fact, the future generations can become
more tolerant to alcohol than the previous generations.
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