Maternal Hormone Progesterone May Be a Major Player in Sculpting Male Brains, UMass Amherst Researchers Suggest

AMHERST, Mass. - A recent study conducted by researchers at the University of Massachusetts suggests that a major player in building male brains may come from a surprising source - mothers. The study, conducted by graduate student Princy Quadros and assistant psychology professor Christine Wagner, was presented earlier this week at the meeting of the Society for Neuroscience in Miami, Fla.

Scientists have known for nearly two decades that there are structural and neurobiological differences between the brains of males and females. The UMass study indicates that during pregnancy, the maternal hormone progesterone may play an important role in creating those differences. It was previously believed that fetal steroids were solely responsible for bringing about gender differences in the brain.

Although the study was conducted on rats, researchers believe that the findings may be analogous for humans. "It''s been known for many years that there are many gender differences in the human brain," said Wagner. "The sex differences in the brains of rats seem to parallel those found in humans. Therefore, this finding may offer us a window into the fetal development of human brains."

Progesterone is the most abundant hormone in the mother''s body during pregnancy, Wagner said. It essentially maintains the pregnancy. "Our research demonstrated that progesterone from the mother''s blood can enter the blood and brain of the fetus," said Wagner. Once it has entered the brain, the hormone fits into certain receptors, like two puzzle pieces that fit together. This linking together of progesterone and receptor actually modifies the function of the brain cells, according to Wagner. Furthermore, fetal males appear to have a heightened sensitivity to this female hormone, because they have many more receptors that respond to progesterone than do female fetuses.

The process is an intricate one: Testosterone, produced by testes in the fetal male, enters a specific part of the brain called the medial preoptic nucleus (MPN). There, the testosterone is converted to another hormone, estradiol. Estradiol, like a key opening a lock, activates the production of progesterone receptors during the brain''s development by switching on a certain gene. Because females produce levels of testosterone that are insignificant, their brains produce far fewer progesterone receptors.