Animals typically don't have a taste for booze. And yet researchers have bred rats who will literally work out for alcohol, bench-pressing a bar repeatedly for a refill long after sober rats have given up.
Teams at Purdue University and Indiana University have been breeding alcoholic rats for more than 30 years. Their goal: determine if there is a genetic component to addiction and find a cure. Last week they published the results of their study, which will discourage those hoping for an easy cure for addiction — but also might open the door to a genetic test that would allow people to assess their own risk of becoming addicted to substances.
The key finding is that there is no one gene that controls addiction: actually, there are 930 of them, each playing a small role. Usually genetic disorders are treated with a drug that targets a specific problematic gene. In the case of alcoholism, the only realistic drug-based solution would have to be a cocktail of pills, and even then the treatment would inhibit only a subset of genes.
Until now, the scientific community was "working on an assumption that there were a few genes affecting alcoholism," William Muir, a Purdue University geneticist, said. "This probably dashes water on the idea of treating alcoholism with a single pill."
But the bigger finding is that genes themselves play a smaller role in determining addictive behavior than previously thought. The study found that addiction is influenced by an individual's ability to regulate their genes, more than the genes themselves.
The good news is that the study could result in a complete profile of alcoholism-related genes throughout the entire human genome. This means that someday you might be able to get an evaluation of your risk index for alcoholism. However, Muir says that environmental factors play up to 70 percent of the role in creating alcoholism, with biology contributing the other 30.
Because of this, Muir worries that college students of the future might take low-risk evaluations as an excuse to binge, which could override any addiction-resistant disposition. "You can become an alcoholic without being highly genetically predisposed," he said.
It took the researchers decades to breed four groups of rats varying in their willingness to work for and recover from hard alcohol. Eventually Muir and Feng Zhou, a behaviorist and neurophysicist at Indiana University, produced a line of drunken rodent progeny that will actually forgo water for alcohol. The other three lines of study subjects are more moderate drinkers, with one group rejecting alcohol more often than not.
The process of selecting rats to breed involved putting all the parent rodents in similar environments and choosing mates based on alcohol consumption. Rats who drank at least twice as much ethanol solution as they did water were matched to produce boozy offspring. The ones who drank a maximum of half as much alcohol as water were also bred together.
The rodents were then given a bar to press several times in order to receive a reward of alcohol. The rats with the most alcoholism-associated genes pressed their bar until they got their reward, while the other rats gave up after a few tries and went to drink water instead.
Still, rats bred to have the same genetic tendency towards alcoholism may not exhibit the same addictive behavior, if they're subject to different environmental factors. Muir and Zhou also found that rats reacted in very individual ways to the same dose of alcohol. Like humans, some became sleepy while others grew aggressive after a few drinks.
Like many genetic disorders, alcoholism may be a loaded gun, but the environment has to pull the trigger. "You can't just blame your drinking on your parents," Muir said.