Guard the bourbon fruitcake: Fruit flies like a little booze in their food. And once they get a nip, they’re hooked, say scientists studying Drosophila melanogaster, the darling of genetic scientists around the world. The flies show evidence of alcohol addiction, including drinking despite dangerous consequences, a study appearing online December 10 in Current Biology reports.
Studying a model of alcoholism in a simple organism like the fruit fly may lead to a better understanding of the disease in humans. The new research is “a big step forward,” says Zachary Rodd, a behavioral pharmacologist who studies rodent models of alcoholism at Indiana University School of Medicine in Indianapolis. “It’s always good to have many models. Each model has its benefits and its limitations. Drosophila has a lot of positives behind it.”
Earlier studies found that alcohol has profound physiological effects on fruit flies, but the new study is one of the first to offer flies the choice to drink. Anita Devineni and Ulrike Heberlein, both of the University of California, San Francisco, devised a fly-sized drinking device reminiscent of the water bottles in hamster cages. Flies held inside vials could sip from thin tubes holding either liquid food spiked with 15 percent ethanol or plain liquid food. The researchers measured the descent of the liquids inside each tube to get a readout of which food the flies preferred.
Flies slurped down the booze-laden food much faster than the straight food, the researchers found. This alcohol preference became stronger over five days as the animals adjusted to the drinking. When Devineni and Heberlein varied the amount of alcohol in the food, they found that flies that had been drinking for only one to two days didn’t seem to like the strong stuff, but regular drinkers that had been consuming alcohol for four to five days did. These flies drank food that contained up to 25 percent alcohol.
As the flies drank alcohol, Devineni observed drunken behavior such as hyperactivity and loss of coordination. The researchers were unable to get exact measurements of alcohol levels in individual flies because they’re so small. “I think they are intoxicated, but it’s unclear to what degree,” Devineni says.
Fruit flies accustomed to alcohol continued to drink despite potential harm, the team found. When the researchers laced the booze-food mix with small amounts of the toxic chemical quinine, those flies continued to drink, even though fruit flies normally avoid the chemical. “I was actually pretty surprised when they continued to drink it,” Devineni says.
In another test, flies were allowed to drink freely for five days, then were deprived of alcohol for either one or three days. After the dry period, the flies immediately returned to peak levels of drinking, a hallmark of relapse.
This fruit fly model of alcoholism may provide researchers with new experimental options, such as the ability to easily track down genes that are involved with the disease. Some of these genes may be the same as those in humans. “It’s known that there’s a strong genetic component to alcoholism,” Devineni says. “Flies are one of the best model systems for genetics,” she adds.
This fruit fly has been exposed to ethanol vapor, which renders it uncoordinated.
Credit: Fred Wolf