Foidart A, Balthazart J
Laboratory of Biochemistry, University of Liège, Belgium.
J Steroid Biochem Mol Biol. 1995 Jun;53(1-6):267-75. doi: 10.1016/0960-0760(95)00064-7.
In many species of vertebrates, major sex differences affect reproductive behavior and endocrinology. Most of these differences do not result from a direct genomic action but develop following early exposure to a sexually differentiated endocrine milieu. In rodents, the female reproductive phenotype mostly develops in the absence of early steroid influence and male differentiation is imposed by the early action of testosterone, acting at least in part through its central conversion into estrogens or aromatization. This pattern of differentiation does not seem to be applicable to avian species. In Japanese quail (Coturnix japonica), injection of estrogens into male embryos causes a permanent loss of the capacity to display male-type copulatory behavior when exposed to testosterone in adulthood. Based on this experimental result, it was proposed that the male reproductive phenotype is "neutral" in birds (i.e. develops in the absence of endocrine influence) and that endogenous estradiol secreted by the ovary of the female embryo is responsible for the physiological demasculinization of females. This model could be recently confirmed. Females indeed display a higher level of circulating estrogens that males during the second part of their embyronic life. In addition, treatment of female embryos with the potent aromatase inhibitor, R76713 or racemic vorozole which suppresses the endogenous secretion of estrogens maintains in females the capacity to display the full range of male copulatory behaviors. The brain mechanisms that control this sexually differentiated behavior have not been identified so far but recent data suggest that they should primarily concern a sub-population of aromatase-immunoreactive neurons located in the lateral parts of the sexually dimorphic preoptic nucleus. The zebra finch (Taeniopygia guttata) exhibits a more complex, still partly unexplained, differentiation pattern. In this species, early treatment with exogenous estrogens produces a masculinization of singing behavior in females and a demasculinization of copulatory behavior in males.(ABSTRACT TRUNCATED AT 400 WORDS)
在许多脊椎动物物种中，主要的性别差异会影响生殖行为和内分泌学。这些差异大多并非直接源于基因组作用，而是在早期暴露于性别分化的内分泌环境后形成的。在啮齿动物中，雌性生殖表型大多在没有早期类固醇影响的情况下发育，而雄性分化则是由睾酮的早期作用导致的，睾酮至少部分通过其在中枢转化为雌激素或芳香化作用来发挥作用。这种分化模式似乎不适用于鸟类。在日本鹌鹑（Coturnix japonica）中，向雄性胚胎注射雌激素会导致其成年后接触睾酮时永久丧失表现出雄性类型交配行为的能力。基于这一实验结果，有人提出鸟类的雄性生殖表型是“中性的”（即在没有内分泌影响的情况下发育），并且雌性胚胎卵巢分泌的内源性雌二醇导致了雌性的生理性去雄化。这一模型最近得到了证实。事实上，在胚胎发育后期，雌性体内循环雌激素水平确实高于雄性。此外，用强效芳香化酶抑制剂R76713或消旋伏洛唑处理雌性胚胎，抑制雌激素的内源性分泌，可使雌性保持表现出全套雄性交配行为的能力。到目前为止，尚未确定控制这种性别分化行为的脑机制，但最近的数据表明，它们主要涉及位于性二态视前核外侧部分的一群芳香化酶免疫反应性神经元。斑胸草雀（Taeniopygia guttata）表现出一种更复杂、仍部分无法解释的分化模式。在这个物种中，早期用外源性雌激素处理会使雌性的鸣叫行为雄性化，使雄性的交配行为去雄化。（摘要截选至400字）
