Fruit flies in a recent study got a double shot of alcohol's effects, courtesy of genetics and ethanol fumes, offering new clues about alcohol tolerance.

First, the drunken flies got hyperactive. Then, they got woozy and conked out until their alcohol buzz wore off.

It was all in the name of science. Ulrike Heberlein, PhD, and colleagues were studying a newfound gene in fruit flies that appears to affect alcohol tolerance.

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Gene for Alcohol Tolerance?

Heberlein and colleagues dubbed the gene the "hangover" gene. But the gene didn't literally create hangovers. Instead, it's required for normal development of ethanol tolerance, write the researchers.

Flies with the gene built up tolerance to ethanol fumes. Tolerance allows increased amounts of alcohol to be consumed, which leads to physical dependence and addiction over time.

The gene also makes it harder for the flies to time handling stressful conditions, such as heat and a bothersome chemical, write the researchers. This means that the development of alcohol tolerance involves a pathway that handles stressors.

Flies without the gene didn't become tolerant to ethanol, the study showed.

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What About People?

The researchers only tested fruit flies, not people. But the findings might offer new clues about alcohol tolerance, writes Heberlein, an associate professor of anatomy at the University of California, San Francisco.

In people, repeated drinking can lead to alcohol tolerance. That's an "acquired resistance to the physiological and behavioral effects of the drug," write the researchers. Translation: People have to drink more to feel alcohol's effects.

Over time, alcohol tolerance "leads to physical dependence and possibly addiction," write the researchers.

Stress, genetics, and learned behavior may all be involved, write the researchers.

There is growing recognition that stress, at the level of the cell (such as damaging unstable molecules called free radicals) and throughout the body, contributes to drug- and addiction-related behaviors in mammals. Our studies show that this role may be conserved across evolution, they write.

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By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Scholz, H. Nature, August 2005; vol 436: pp 645-847. News release, Nature.