In one study, male mice were castrated to stop production of testosterone. They were fitted with implants that controlled their testosterone levels. The males were then treated with a drug known as an aromatase inhibitor, which halts the production of estrogen. This class of drugs is commonly used to treat estrogen-dependent breast cancer.
In mice housed in short days (limited daylight as in winter), the drug halting estrogen production made the normally aggressive mice less aggressive. In mice kept in long day length conditions (as in summer), the normally docile mice were more aggressive. This showed that estrogen was indeed controlling levels of aggression in these mice.
But the researchers went further and identified the mechanisms that may underlie how the length of daylight affects the way estrogen works to either increase or decrease aggression.
"It is well known that genes interact with the environment, but scientists often don't understand how this works on the molecular level," Trainor said. "We wanted to find out more about how this interaction takes place in mice."
In one study, they looked at how day length interacted with two types of receptors in parts of the brain that affect aggression ?estrogen receptor alpha and estrogen receptor beta. These receptors are like docking stations that send signals from the estrogen molecules into the cells.
One hypothesis had been that one type of receptor was important in winter-like short days, and the other receptor in summer-like long days ?which could help begin to explain why estrogen could make mice more aggressive in winter, and less aggressive in summer.
To investigate whether this theory was true, Nelson and Trainor conducted an experiment in which they injected mice with an estrogen-like drug which attaches almost exclus
Source:Ohio State University