Development of Sexual Behavior: A Marsupial Model

哺乳动物生殖行为的性别差异不仅由基因和成年期产生的激素决定，还与性腺在产前和产后发育过程中分泌的类固醇激素有关。虽然已知睾丸雄激素在围产期发育中起重要作用，但雄激素在中枢神经系统靶细胞内代谢为雌激素。确定雄激素或其雌激素代谢物是分化激素是很复杂的，因为哺乳动物胎盘胎儿的系统实际上“保护”它们不受母体雌激素的影响。因此，让雌激素进入胎儿体内并量化雌激素在子宫内作用于胎儿发育的量是极其困难的，但却至关重要。法登博士以灰负鼠为模型系统来研究雌激素的作用。新生儿出生时的发育阶段相当于13天的胎鼠或8周的人类胚胎。因此，这些有袋动物是大部分胎儿发育发生在母亲体外的哺乳动物，使胎儿环境易于进入。费登医生会在胎儿早期控制激素环境。她的工作将有助于确定雌激素在两性二态行为、形态学和生理学的发展中所起的作用。这些数据将有助于更好地理解在性别分化过程中由于激素暴露不足或过量而导致的各种人类疾病。

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.