Why some women act ‘mousy’

UC DAVIS (US) — Socially withdrawn mice could offer clues into depression and anxiety in humans, conditions that are twice as common in women as in men.

A new study finds that female California mice (Peromyscus californicus) show signs of social withdrawal after encountering stronger, more aggressive mice.

Examination of the brains of the meeker mice, show changes in an area called the nucleus accumbens, associated with motivation and reward.

The changes might help to explain why the mice became socially withdrawn, and could lead to new avenues of research on depression in humans.

“Social withdrawal is a common feature of mood disorders,” says Brian Trainor, assistant professor of psychology at University of California, Davis.

The research is published in the journal PLoS One.

Animal models are needed to understand the physiological basis of mood disorders, Trainor says. Although an animal can’t be diagnosed as “depressed,” researchers can look for changes in behavior comparable to signs of human depression.

Stressful life experiences can trigger depression in humans. To reproduce this in mice, previous studies have used a “social defeat” model. A mouse is paired for a short time with a stronger, aggressive mouse. After several such encounters in a row, the weaker mouse can become withdrawn.

But the method has a flaw, Trainor says, because it doesn’t work well for female domestic mice, which are less aggressive than males.

Understanding the differences between males and females in this area is desirable, because female humans are more vulnerable to depression than males.

For the study, Trainor used lab-bred female California mice, that in the wild, are as territorial as males and may fight with other male or female mice that enter their territory.

After just three social defeats, female mice, but not males, would become withdrawn for up to four weeks.

The research was funded by the National Institute of Mental Health.

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