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Study says gene encourages monogamy

It didn't take couples counseling to turn polygamous male meadow voles into faithful partners. All researchers needed was a gene, according to a study published today.

Scientists took a gene from a close, but monogamous, relative, the prairie vole, and inserted it into the brains of 11 meadow voles. The furry mammals quit their philandering habits, huddled longer with their partners, and became better dads.

''This is really remarkable: A single gene expressed in a functioning circuit can have a profound effect on a behavior as complex as pair bonding," said coauthor Larry Young, a researcher in the department of psychiatry and behavioral sciences at Emory University in Atlanta.

Monogamy can apparently be flicked on by a gene in a mammal that has never written a sonnet. ''The relevance of this study is that when you compare species, there does seem to be a genetic and evolutionary basis for this behavior," said Steven Pinker, a cognitive scientist at Harvard University, who argues against those who consider romance a human invention.

The study, published in the journal Nature, was ''in essence recreating a singular evolutionary event in the laboratory," the authors wrote.

It has long been known that meadow voles are polygamous, while prairie voles are monogamous. ''They mate, they form bonds, they have a social structure much like humans," Young said, referring to prairie voles.

He and his colleagues decided to look for a genetic reason for the difference between the two voles.

In previous studies, they found that monogamous prairie voles have a receptor in the reward center of the brain for a hormone called vasopressin,which is responsible for feelings of pleasure in voles and in humans. The meadow voles lack the vasopressin receptors in that area of the brain, called the ventral pallidum.

So the scientists inserted the gene for vasopressin receptors into that region of the brain and then left the male meadow voles with a single female vole for 24 hours. The researchers later put the male voles into cages between the first female and another female.

The males with the vasopressin receptor gene consistently chose to huddle with the familiar female rather than seek out a new female. Members of the control group, which received a dummy gene or had the vasopressin gene inserted in another area of the brain, mixed with both females indiscriminately or spent time alone.

According to Young, vasopressin most probably ''makes you pay attention to who you are with."

In a second experiment, the researchers found that when they blocked the brain pathways that control pleasure, the newly monogamous voles reverted to noncommittal behavior.

The researchers concluded that monogamy might be a result of simple conditioning, an association between memory of an individual and pleasure.

The research into the role of vasopressin could lead to possible treatments of disease. ''In humans, there are diseases where there are severe disruptions in social behavior," Young said. ''Autism is the key example."

Carolyn Johnson can be reached at cjohnson@globe.com.

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