Animal models help scientists to understand human behavior and
develop new drugs to treat pathologies. This week’s DRAM reviews a study that
examines an animal model of drinking behavior. Devineni and Hebertein (2009) sought to determine
if the drinking behavior of drosophila flies resembles human drinking behavior
and if genetic mutations modify this behavior.
Method
- Investigators gave flies the opportunity to
choose between ethanol-containing and nonethanol-containing food. Researchers
calculated a preference index (PI) as (ethanol consumption – nonethanol
consumption) / total consumption. The index ranged from -1 to 1, with positive
numbers indicating preference for ethanol.
- Researchers measured the following:
- the
basic preference of flies
- the
pattern of preference change across time and ethanol concentration shifts
- the
preference change after periods of starvation or ethanol deprivation
- ethanol preference of different mutations.
- the
basic preference of flies
- At
baseline, the flies consistently showed a statistically significant
preference for the ethanol-containing food, even when the caloric ratio
between ethanol and nonethanol food was balanced.
- The
preference for ethanol-containing food increased for the first few days but
leveled off after 4 – 5 days.
- The level
of preference increased with larger ethanol dose concentration.
- Starved
flies were willing to consume ethanol at levels sufficient to produce
behavioral intoxication.
- After
being deprived of ethanol for several days, flies quickly resumed ethanol
consumption when given an opportunity.
- Previous
testing of 27 different types of mutations by the researchers had found one
mutant -- krasavietz – or
handsome in Russian – that exhibited a significantly lower preference for
alcohol compared to the non-mutated controls. The “handsome” flies were
studied in this experiment (see Figure 1).During the first two days the
“handsome” flies showed no preference for alcohol, a behavior that was
significantly different from controls who took to alcohol immediately.
Figure 1. Five day ethanol preference for control group and mutant fly krasavietz (handsome). N = 25.
- No
animal model provides a perfect analog to human alcohol consumption or
alcoholism. For example, social and cultural factors influence human
alcoholism, and these influences are difficult to create within animal
studies.
Conclusions
This study indicates that drosophila’s drinking behavior
resembles human drinking patterns in many facets. Similar to humans,
drosophila’s initial preference to ethanol containing food is low and apt to vary,however gradually it increases and becomes consistent. Drosophila gradually are attracted
to ethanol despite its aversive taste and intoxicating effect. One
characteristic of human alcohol dependence is relapse – a return to previous
levels of alcohol consumption after a period of abstinence (Hunt,
Barnett, & Branch, 1971). Flies also exhibit
a relapse-like behavior after ethanol deprivation. Devineni and Hebertein
(2009) showed that a mutation, specific to a single gene, is related to low
preference for ethanol. Identifying this and potentially other mutations help
scientists to understand the potential molecular mechanisms
underlying alcohol preference. No animal model can explain all facets of
alcohol dependence among humans. However, a better scientific understanding of ethanol
preference in both animals and humans may lead to the discovery of features
common to a general reward pathway involved with addiction.
Devineni, A. V., & Hebertein, U. (2009). Preferential Ethanol
Consumption in Drosophila Models Features of Addiction. Current Biology, 19, 2126-2132.
Hunt, W. A., Barnett, L. W., & Branch, L.
G. (1971). Relapse rates in addictions programs. . Journal of Clinical Psychology 27, 455 - 456.
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