Lohmann R, Gahr M
Max Planck Institute for Behavioural Physiology, D-82319 Seewiesen, Germany.
J Neurobiol. 2000 Feb 5;42(2):220-31. doi: 10.1002/(sici)1097-4695(20000205)42:2<220::aid-neu6>3.0.co;2-e.
Sex differences in the vertebrate brain (brain sex) are thought to develop owing to the tissue specific action of gonadal hormones similar to the development of secondary sex characteristics of the body. Small sex differences in body anatomy could, however, retrogradely control the sexual differentiation of the central nervous system. This possibility has so far been verified only for motorneuron pools, since the connectivity of sex-specific higher brain areas to the sexual dimorphic periphery is frequently not well known. Here, we tested whether somatic sex differences feed back on higher brain areas by bilateral denervation of the syringeal musculature of zebra finches before, during, and after onset of estrogen-sensitive sexual differentiation of forebrain vocal nuclei such as RA (nucleus robustus archistriatalis). In the zebra finch, the sound-producing musculature (the syrinx), the syrinx motornucleus hypoglossus pars tracheosyringealis (nXIIts), and the RA are much larger in males compared to females. Tract tracing studies revealed that the volume and neuron size distribution of the nXIIts was sexually dimorphic in intact but not in animals denervated as juveniles. In contrast, the volume of RA and size of RA neurons of denervated animals were highly sexually dimorphic. Furthermore, estrogen masculinized the RA of denervated females. Thus, sexual differentiation of the RA but not of the nXIIts appears independent of somatic sex differences. The syrinx muscles are, however, important for the soma size of those RA neurons that project to the nXIIts.
脊椎动物大脑中的性别差异（脑性别）被认为是由于性腺激素在组织特异性作用下发展而来，类似于身体第二性征的发育。然而，身体解剖结构中微小的性别差异可能会逆向控制中枢神经系统的性别分化。到目前为止，这种可能性仅在运动神经元池得到验证，因为性别特异性的高级脑区与性别二态性外周的连接通常并不为人所知。在这里，我们测试了在诸如RA（古纹状体粗核）等前脑发声核团的雌激素敏感性性别分化开始之前、期间和之后，通过双侧去神经支配斑胸草雀的鸣管肌肉组织，身体性别差异是否会反馈到高级脑区。在斑胸草雀中，发声肌肉组织（鸣管）、鸣管运动核舌下神经气管鸣管部（nXIIts）和RA在雄性中比雌性大得多。束路追踪研究表明，nXIIts的体积和神经元大小分布在完整动物中具有性别二态性，但在幼年去神经支配的动物中则没有。相比之下，去神经支配动物的RA体积和RA神经元大小具有高度的性别二态性。此外，雌激素使去神经支配的雌性的RA雄性化。因此，RA的性别分化而非nXIIts的性别分化似乎独立于身体性别差异。然而，鸣管肌肉对于投射到nXIIts的那些RA神经元的胞体大小很重要。
