Love and neurobiology

Studying the mating habits of rodents may shed light on intimate human relationships

Ideas: Nature

August 15, 1999|By Robert Cooke | Robert Cooke,SUN STAFF

By studying the behavior and the brains of obscure mouselike rodents called voles, scientists are beginning to see why falling in love and staying in love are two different things.

Neuroscientist Tom Insel and his team at Emory University's Yerkes Primate Center in Atlanta are carefully following the animals' mating habits and finding that genetic differences separate the homebodies from the playboys.

They are comparing two species of Midwestern voles, trying to explain why prairie voles mate for life, while their mountain cousins are promiscuous. Their subject is, in essence, "the neurobiology of love," Insel said.

How this may relate to the human condition is not known. But humans, like prairie voles, have a strong tendency to monogamy, form enduring and selective pair bonds, and get papa involved in child rearing. Both of the neural signaling molecules that Insel is studying in voles -- oxytocin and vasopressin -- are also known to be active in humans.

Voles were chosen for study because of the stark differences in mating behavior displayed by the two similar species. In fact, the prairie voles and mountain voles are about 99 percent identical in their genes.

Insel and his co-workers think the differences in mating behavior are linked to varying patterns of receptor molecules in the brain.

The locations of receptors are determined, at least in part, by the genes an animal inherits and whether certain genes are active in various tissues.

In female prairie voles, for example, the receptors for oxytocin are found in the brain regions associated with "reward." In contrast, in female mountain voles the same receptors are not involved in the reward system. So there appears to be little reward reinforcement, and mountain females don't attach to one male more than another.

Receptors on brain cells act like doorbells, and agents such as oxytocin and vasopressin are the messengers that come by to ring them. Once the bells are activated, the cells themselves are stimulated to perform certain tasks, such as making new proteins or hormones.

"Remarkably," Insel said, in prairie voles the two hormone-like agents "appear to be important for the formation of social attachments, the initiation of parental care, and possibly some aspects of the infant's attachment behavior."

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