Female hormones may help males be manly, a new study in mice suggests.
When it comes to sex hormones, males produce mainly testosterone. But they also produce a little of the female hormone estrogen. The new study, to appear in an upcoming issue of the Proceedings of the National Academy of Sciences, shows how important that estrogen is.
Normally, male mice produce brain components that let them respond to estrogen. To see what estrogen does for male mice, scientists from the United States and Sweden genetically altered male mice to make them incapable of sensing the female hormone.
Unlike normal male mice, which would chase the females around the cage to try and mate, the genetically altered mice paid little attention to the ladies and didn't make the usual ultrasonic squeaks appropriate for mixed company.
Estrogen also seems to make male mice more aggressive. When faced with intruders, the genetically altered mice were less likely to go on the offensive.