Gilmore Desmond Philip
Laboratory of Human Anatomy, Institute of Biomedical and Life Sciences, University of Glasgow, Scotland.
Int Rev Cytol. 2002;214:193-224. doi: 10.1016/s0074-7696(02)14006-x.
It is now evident that gonadal steroids, acting within a limited critical period during fetal or neonatal life, bring about sexual differentiation of both the reproductive tract and the central nervous system (CNS) in eutherians. This results in structural dimorphism in several regions of the brain and spinal cord and the programming of future patterns of adult reproductive behavior. At birth the CNS of marsupials is very underdeveloped and debate continues as to the importance of hormones in its sexual differentiation. Nevertheless, some sexually dimorphic regions have been identified, including the lateral septal nucleus in the hypothalamus and the spinal nucleus of the bulbocavernosus and dorsolateral nucleus in the spinal cord, but interestingly not the cremasteric nucleus, which is dimorphic in eutherians. To date, no apparent sex differences in estrogen and androgen receptor-immunoreactive structures have been detected in the marsupial brain; however, higher levels of aromatase activity during early development in male opossums have been reported. Sex differences have been identified in the localization of cholecystokinin-immunoreactive structures in the marsupial brain indicating that the expression of this neuropeptide is differentially regulated in each sex. A sex difference also exists in the density of arginine vasopressin-immunoreactive fibers. Arguments continue as to whether sexually dimorphic behavior in marsupials, as in eutherians, is largely predetermined by hormones acting on the CNS early in development or if it is entirely dependent on the adult steroid hormonal environment.
现在很明显，性腺类固醇在胎儿期或新生儿期的有限关键期内发挥作用，导致真兽类动物的生殖道和中枢神经系统（CNS）发生性分化。这导致大脑和脊髓的几个区域出现结构二态性，并为成年生殖行为的未来模式进行编程。有袋类动物出生时，其中枢神经系统非常不发达，关于激素在其性分化中的重要性的争论仍在继续。尽管如此，已经确定了一些性二态区域，包括下丘脑的外侧隔核、球海绵体肌的脊髓核以及脊髓的背外侧核，但有趣的是，提睾肌核没有被确定为性二态，而在真兽类动物中它是性二态的。迄今为止，在有袋类动物的大脑中尚未检测到雌激素和雄激素受体免疫反应结构的明显性别差异；然而，有报道称雄性负鼠在早期发育过程中芳香化酶活性较高。已经确定有袋类动物大脑中胆囊收缩素免疫反应结构的定位存在性别差异，这表明这种神经肽的表达在每种性别中受到不同的调节。精氨酸加压素免疫反应纤维的密度也存在性别差异。关于有袋类动物的性二态行为，如同在真兽类动物中一样，在很大程度上是由发育早期作用于中枢神经系统的激素预先决定的，还是完全依赖于成年期的类固醇激素环境，争论仍在继续。
