There are more than a thousand kinds of rodents scampering about our planet, but prairie voles are special.
Unlike most, these creatures form monogamous pair bonds, and they also like to drink alcohol, features that make the North American grassland dwellers an interesting comparison to humans. (Related: "Two Prairie Voles Walk Into a Bar... Then Scientists Study Alcohol's Effects on Couples Bonding.")
According to a study published November 17 in the journal Frontiers in Psychiatry, in fact, prairie vole couples have similar problems as humans when one mate hits the bottle a little too hard.
Among humans, researchers have found that heavy drinking can be rough on relationships, sometimes leading to divorce. One study found that excessive alcohol or drug use was the third most commonly reported cause for divorce in the United States.
Relationships are most likely to break down when one partner drinks heavily and the other does not, although the relationship usually stays on track if both are heavy drinkers. It isn't clear, however, whether problematic drinking is the cause or the effect of the relationship woes.
That's where the voles come in. To see whether alcohol consumption causes break-ups, Oregon Health and Science University graduate student Andre T. Walcott rounded up more than a hundred voles and allowed them to settle into pairs. Then Walcott supplied them with liquor.
In one third of the couples, the male was offered a 10 percent alcohol solution and a bottle of water, while the female was offered water. In the next group, both the males and the females were allowed to imbibe. A third group consisted of pairs offered only water, to serve as controls.
The voles did not ignore the booze made available to them. "These animals drink a lot of alcohol,” says neuroscientist Andrey E. Ryabinin, who oversaw the study. “In a day, they can drink [an amount] comparable to 15 bottles of wine." (Read how sex can change male prairie vole brains.)
After they'd had their drink, Walcott and Ryabinin offered the males a chance to cuddle up with their partners or to spend time with a second, unfamiliar female.
The team found that males who drank alone spent less time with their original partners than the other males spent with their original partners. When partners drank together, or both abstained, they were more likely to hang out with each other. (See National Geographic's pictures of animals in love.)
The researchers also discovered that the males in discordant pairs—in which one drank and the other did not—showed different activity levels in a part of the brain called the periaqueductal gray, compared with males that had the same drinks as their mates.
"That's interesting because it's an area that has a lot of oxytocin receptors," says Karen Bales, a neurobiologist at the University of California, Davis, who was not involved in the research.
Oxytocin is the "love hormone," known to be involved in facilitating the bond between partners, both in rodents and humans. Exactly what this finding means, and whether it has implications for people as well, is a question for future research, says Ryabinin. (Also see "Owl Monkeys Shed Light on Evolution of Love.")
But it does suggest there may be a biological basis for the negative effects of solo drinking on relationships, beyond the impacts of alcohol exposure itself.
As for Walcott and Ryabinin, they are now hard at work on a follow-up study. This time, they will be looking at how drinking by female voles influences couple behavior, watching to see if the effects are the same.