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Mammals

The Oregonian, July 11, 2010

A real party animal helps scientists study alcohol abuse
By Joe Rojas-Burke

Prairie voles, by their nature, stick with one mate for life and devotedly care for babies together. But given alcohol to drink, many become staggering drunkards prone to stepping out on their partners.

Sound familiar? The overlap with human tendencies makes the mouse-like rodent an ideal model to study the social aspects of excessive drinking, say researchers at Oregon Health & Science University and the Portland Veterans Affairs Medical Center.

"They not only drink alcohol, they prefer it over water," says Allison Anacker, a neuroscience graduate student at OHSU. Taste tests show they prefer drinks with 6 percent alcohol – about the same as beer, notes Andrey Ryabinin, a professor of behavioral neuroscience at OHSU.

Lack of good animal models is a long-standing problem for researchers seeking new and more effective treatments for alcoholism. Mice and rats -- the traditional lab rodents -- won't drink alcohol if they can avoid it, forcing researchers to rely on inbred strains selected for their unnatural lust for the hard stuff. Rats and mice aren't big on social bonding, so studying them can't shed much light on how relationships affect boozing, says Ryabinin.

Among prairie voles, social bonds play as big a role on drinking behavior as they do in any college fraternity, experiments by Ryabinin, Anacker and colleagues suggest.

In a study appearing in the journal Addiction Biology, sharing a cage with a sibling prompted voles to imbibe more liquor. Each animal had access to two drinking bottles: one with plain water and another spiked with alcohol. A screen kept the paired animals from reaching each other's bottles, making it easy for researchers to measure how much they drank.

The isolated voles drank nearly equal amounts of plain water and alcohol-spiked water. The siblings housed together partied down. On average, four-fifths of their fluid intake came from the alcohol-spiked source. But that isn't all. The pairs living together also matched each other drink for drink.

Some voles drank so much they staggered and fell and had trouble getting back on their feet. Others drank more moderately. But each vole always drank nearly the same amount as its cage-mate.

"They get a buzz and somehow they are getting the other vole to match their level of intoxication. At least that's the idea we have," Ryabinin says. The researchers don't yet know how the voles coordinate their drinking. Only alcohol prompts the behavior. In a parallel experiment using water spiked with saccharine, a non-caloric sweetener loved by voles, the paired animals drank more of the sweet drink but didn't match each other's intake.

While human behavior is too complicated for any one animal model to fully represent, voles should prove useful for probing social dimensions of drinking, says Kenneth J. Sher, a University of Missouri professor who studies the psychology of alcohol addiction.

"In humans with rare exception drinking is a social activity," Sher says. Traditional animal models of alcohol consumption, he says, use isolated rats or mice drinking in an asocial context. Prairie voles give researchers the means to perform social drinking experiments not feasible with human volunteers – such as plying heavy drinkers with alcohol and dictating their contacts with others for long stretches of time -- without having to use monkeys or chimpanzees that are more expensive and difficult to work with.

Among Ryabinin's ideas: testing whether the influence of companions can reduce the effectiveness of drugs such as naltrexone, prescribed to stop alcoholics from drinking.

The animals could help scientists better understand the brain changes that make people vulnerable to alcohol addiction. Prairie voles have been intensively studied for years by brain researchers seeking an explanation for their striking monogamy, a habit practiced by less than 5 percent of mammal species. Scientists have identified distinct signaling pathways and brain cell receptors active in reinforcing the animals' lasting bonds with partners.

Those signaling pathways appear to play a role in addictive behavior, as well, according to neuroscientist Zuoxin Wang at Florida State University. Wang and colleagues have recently begun using prairie voles to study whether brain signaling pathways reinforce amphetamine-seeking in the same way they reinforces social bonding. Dopamine signaling, part of the brain's reward system, may be more active in the brains of animals when they are connected with a sibling or a mate, Ryabinin and colleagues speculate, leading them to experience greater feelings of reward from alcohol, thus prompting them to drink more when housed in pairs.

Preliminary findings at OHSU also suggest that high alcohol consumption can interfere with the voles' naturally close bonds. Even in the rodent world, boozing too much is an invitation for domestic strife.

© 2010 Oregon Live LLC.

Photo © Paul S. Hamilton