Mice That Fight Rather Than Mate (IMAGE) Cold Spring Harbor Laboratory Caption Early in life, there's an important behavior-defining hormone event that determines if a mouse will express masculine sexual and territorial behaviors at puberty. This moment dictates whether or not it will act like a "typical male." Males have a testosterone surge on Day One, without which they fail to manifest masculine behaviors at puberty. Similarly, if females are given an abnormal dose of estrogen at the dawn of life, they behave in maculinized ways at puberty. Here, a female mouse (black) given early estrogen fights with a male mouse rather than mating with it, as is typical for female mice. Tollkuhn and colleagues have discovered masculinization depends on the presence of estrogen receptor-alpha specifically in inihibitory neurons in two brain regions. Credit Tollkuhn Lab, CSHL Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.