POTENTIAL ROLE OF MATERNAL PROGESTERONE IN THE SEXUAL-DIFFERENTIATIONOF THE BRAIN

In rats, fetal testosterone directs sexual differentiation of the brai n. However, fetuses are also exposed to maternal progesterone. Here we report that progestin receptor immunoreactivity in the medial preopti c nucleus (MPN) of fetal and neonatal rats is high in males but virtua lly absent in females. The MPN is one of the most sexually dimorphic s tructures in the rat brain and mediates several sexually differentiate d behaviors. This suggests that progesterone may play a previously ove rlooked role in the development of sex differences in the brain and be havior. Henceforth, a novel function of the mother in the sexual diffe rentiation of the CNS must be considered.