( New research shows how simply varying t...)Changing length of days reverses how estrogen affects aggressiveness in mice

The study found that in the short days of winter, the class of hormones called estrogens acts to increase aggression in males of a particular type of mouse called the Oldfield Mouse (Peromyscus polionotus).

However, in the long days of summer, estrogen decreases aggression among male Oldfield mice, a species commonly found in the southeastern United States .

"We found that estrogen has totally opposite effects on behavior in these mice depending only on how much light they got each day," said Brian Trainor, co-author of the study and postdoctoral fellow in psychology and neuroscience at Ohio State University.

"It is quite a surprising finding."

The study is also important because it is one of the few that has shown how hormones other than testosterone can affect aggression in mammals.

"This goes against the common belief that testosterone is the hormone that regulates aggression," said Randy Nelson, co-author and professor of psychology and neuroscience at Ohio State. "There are now several studies showing that in some species estrogen plays a key role in aggressiveness as well."

While this research has just begun, the findings could have broad implications in humans, for issues such as aggression and the role of estrogen in promoting cancer, Trainor said.

Nelson and Trainer presented their results Oct. 18 in Atlanta at the annual meeting of the Society for Neuroscience.

A major finding of this study was that the length of exposure to daylight affected how estrogen interacted ?or didn't interact ?with genes in the brains of mice that regulated aggression.

"Typically, when scientists talk about a gene-environment interaction, they are talking about a very complicated environment," Nelson said.

"But here we have a very s
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Source:Ohio State University