Rissman E F, Li X
Department of Biology, University of Virginia, Charlottesville, Virginia, 22903, USA.
Gen Comp Endocrinol. 1998 Dec;112(3):346-55. doi: 10.1006/gcen.1998.7135.
Many vertebrates have more than one molecular form of gonadotropin-releasing hormone (GnRH) present in brain. In all cases documented to date, GnRH neurons located in the forebrain are critical players in the brain-pituitary-gonadal feedback axis although the details of how steroids regulate GnRH remain elusive. The function of the second form, usually produced in cells in the midbrain, is not known. It has been hypothesized that this GnRH acts as a neurotransmitter. In the musk shrew (Suncus murinus), as in other mammals, the forebrain cells produce mammalian GnRH (mGnRH) and chicken-II GnRH (cGnRH-II) is present in midbrain neurons. Immunocytochemical analyses were performed to examine sex differences and determine whether the presence or absence of the gonads had any affect on cell number and/or fiber area in the major terminal fields of both forms of GnRH. We detected a significant sex difference in the numbers of immunoreactive (ir) neurons containing mGnRH and cGnRH-II. In both GnRH systems, males have significantly more GnRH-ir cells than females. Furthermore, ovariectomy significantly increased the number of mGnRH-ir and cGnRH-II-ir cell bodies in female brains. In females, changes in the size of the immunoreactive fiber area of the medial habenula were identical to those noted for cGnRH-II cells. In males, the major terminal field for the mGnRH fibers was significantly larger in gonad-intact than in castrated males. In sum, ovarian hormones regulate cGnRH-II production and release, as well as some aspects of mGnRH production in neurons. In males, mGnRH fiber area is sensitive to changes in testicular hormones. These data suggest that the phylogenetically conserved cGnRH-II form is regulated by ovarian hormones and, thus, may be involved in the brain-pituitary-gonadal feedback axis.
许多脊椎动物的大脑中存在不止一种分子形式的促性腺激素释放激素（GnRH）。在迄今为止记录的所有案例中，位于前脑的GnRH神经元是脑-垂体-性腺反馈轴中的关键角色，尽管类固醇调节GnRH的具体细节仍不清楚。第二种形式的GnRH通常由中脑细胞产生，其功能尚不清楚。有人推测这种GnRH起着神经递质的作用。与其他哺乳动物一样，在麝鼩（Suncus murinus）中，前脑细胞产生哺乳动物GnRH（mGnRH），中脑神经元中存在鸡II型GnRH（cGnRH-II）。进行了免疫细胞化学分析，以检查性别差异，并确定性腺的有无是否对两种形式的GnRH主要终末区域的细胞数量和/或纤维面积有任何影响。我们检测到含有mGnRH和cGnRH-II的免疫反应性（ir）神经元数量存在显著的性别差异。在这两种GnRH系统中，雄性的GnRH-ir细胞明显多于雌性。此外，卵巢切除术显著增加了雌性大脑中mGnRH-ir和cGnRH-II-ir细胞体的数量。在雌性中，内侧缰核免疫反应性纤维面积的变化与cGnRH-II细胞的变化相同。在雄性中，性腺完整的雄性mGnRH纤维的主要终末区域明显大于去势雄性。总之，卵巢激素调节cGnRH-II的产生和释放，以及神经元中mGnRH产生的某些方面。在雄性中，mGnRH纤维面积对睾丸激素的变化敏感。这些数据表明，系统发育上保守的cGnRH-II形式受卵巢激素调节，因此可能参与脑-垂体-性腺反馈轴。
