Francis R C, Jacobson B, Wingfield J C, Fernald R D
Neuroscience Program, Stanford University, California 94305.
J Neurobiol. 1992 Oct;23(8):1084-93. doi: 10.1002/neu.480230812.
In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.
在非洲丽鱼科鱼类伯氏朴丽鱼中，雄性分为有领地意识和无领地意识两种类型。有领地意识的雄性会抑制无领地意识雄性的生殖功能，并且它们的性腺更大，视前区（POA）中含促性腺激素释放激素（GnRH）的神经元也更大。我们描述了一项实验，旨在通过确定性腺性类固醇对GnRH神经元的反馈作用，来确立这些雄性中大型GnRH神经元与大型睾丸之间的因果关系。对有领地意识的雄性进行去势手术或假手术，4周后将它们处死。测量循环类固醇水平，并用抗鲑鱼GnRH抗体对脑矢状切片进行染色，从而使含GnRH的神经元可视化。用计算机辅助成像系统测量抗体染色神经元的胞体面积。完全去势的雄性循环性类固醇[11 - 酮睾酮（11KT）和睾酮（T）]以及17β - 雌二醇（E2）的水平显著降低。与完整的有领地意识雄性相比，去势雄性的POA GnRH神经元平均胞体大小显著增加。因此，在成熟动物中，性腺类固醇对含GnRH神经元的生长起到抑制作用，性腺产物并非有领地意识雄性特有的大型GnRH神经元形成的原因。
