Sex differences in reproductive behavior in mammals are determined not only by the genes and by hormones produced in adulthood, but also by steroid hormones secreted by the gonads during prenatal and postnatal development. Although it is known that testicular androgens play an important role during perinatal development, androgens are metabolized into estrogens within CNS target cells. To determine whether an androgen or its estrogenic metabolite is the differentiating hormone is complicated since placental mammalian fetuses have systems which actually "protect' them from maternal estrogen. Thus, getting estrogen to the fetus and quantifying the amount of estrogen acting on the fetus developing in utero is extremely difficult but of critical importance. Dr. Fadem uses gray opossums as a model system to examine the role of estrogen. The newborns are born at a developmental stage equivalent to that of a 13-day fetal rat or 8-week human embryo. Hence, these marsupials are mammals in which much of the fetal development occurs outside the body of the mother, making the fetal environment accessible. Dr. Fadem will manipulate the hormonal milieu during early fetal life. Her work will help define the role that estrogen plays in the development of sexually dimorphic behaviors, morphology and physiology. These data will contribute to a better understanding of various human disorders that result from insufficient or excess hormone exposure during sexual differentiation.
