Rossmanith W G, Marks D L, Clifton D K, Steiner R A
Department of Obstetrics and Gynecology, University of Washington, Seattle 98195.
Endocrinology. 1994 Oct;135(4):1401-8. doi: 10.1210/endo.135.4.7523097.
The onset of puberty reflects the developmental activation of GnRH neurons whose secretory activity awakens the reproductive axis; however, the cellular mechanisms involved in this activational process remain poorly understood. GnRH neurons coexpress the neuropeptide galanin, and we have previously shown that galanin's level of coexpression is linked to the activity state of GnRH neurons. We theorized that altered expression of galanin by GnRH neurons may be an important mechanism related to activation of GnRH neurons at puberty. We examined two hypotheses related to this idea. First, we tested the hypothesis that expression of galanin messenger RNA (mRNA) in GnRH neurons is induced across the transition from prepubertal to adult life in the rat. To accomplish this, we used double label in situ hybridization and image analysis to compare cellular levels of galanin mRNA in GnRH neurons between groups of prepubertal and adult male and female rats. Levels of galanin mRNA within GnRH neurons increased significantly across puberty in both sexes. In females, galanin mRNA signal in GnRH neurons increased approximately 8-fold, whereas in males, cellular galanin mRNA signal levels increased about 2-fold. The number of identifiable GnRH neurons was not significantly different among the experimental groups. Next, we examined the hypothesis that pubertal induction of galanin mRNA in GnRH neurons reflects the activational effects of gonadal hormones associated with the onset of puberty. To test this, we killed groups of prepubertal male and female rats together with adult male and female animals that had been either castrated or sham castrated at a prepubertal age. In animals that had been prepubertally castrated, no developmental increase in galanin mRNA in GnRH neurons was observed, whereas in sham-castrated animals, levels of galanin mRNA in GnRH neurons were again shown to be higher in adult compared to prepubertal animals of both sexes, as had been demonstrated in the first experiment. We conclude that galanin message expression in GnRH neurons is induced during the transition from the juvenile to the adult state through a gonad-dependent process. This developmental increase in galanin gene expression is one mechanism by which the capacity for the synthesis and secretion of galanin by GnRH neurons may be enhanced, which, in turn, could facilitate the functional activity of GnRH neurons and amplify their trophic effect on the pituitary.
青春期的开始反映了促性腺激素释放激素（GnRH）神经元的发育激活，其分泌活动唤醒了生殖轴；然而，这一激活过程所涉及的细胞机制仍知之甚少。GnRH神经元共表达神经肽甘丙肽，我们之前已经表明，甘丙肽的共表达水平与GnRH神经元的活动状态有关。我们推测，GnRH神经元中甘丙肽表达的改变可能是与青春期GnRH神经元激活相关的一个重要机制。我们研究了与这一观点相关的两个假设。首先，我们测试了这样一个假设，即从青春期前到成年期的转变过程中，大鼠GnRH神经元中甘丙肽信使核糖核酸（mRNA）的表达会被诱导。为了实现这一点，我们使用双标记原位杂交和图像分析来比较青春期前和成年雄性及雌性大鼠组中GnRH神经元中甘丙肽mRNA的细胞水平。在两性中，GnRH神经元内甘丙肽mRNA的水平在青春期期间均显著增加。在雌性中，GnRH神经元中的甘丙肽mRNA信号增加了约8倍，而在雄性中，细胞内甘丙肽mRNA信号水平增加了约2倍。各实验组中可识别的GnRH神经元数量没有显著差异。接下来，我们研究了这样一个假设，即GnRH神经元中甘丙肽mRNA的青春期诱导反映了与青春期开始相关的性腺激素的激活作用。为了验证这一点，我们处死了青春期前的雄性和雌性大鼠组，以及在青春期前已被阉割或假阉割的成年雄性和雌性动物。在青春期前被阉割的动物中，未观察到GnRH神经元中甘丙肽mRNA的发育性增加，而在假阉割的动物中，与两性的青春期前动物相比，成年动物GnRH神经元中甘丙肽mRNA的水平再次显示更高，这与第一个实验的结果一致。我们得出结论，GnRH神经元中甘丙肽信息的表达是通过一个性腺依赖的过程在从幼年到成年的转变过程中被诱导的。甘丙肽基因表达的这种发育性增加是一种机制，通过该机制GnRH神经元合成和分泌甘丙肽的能力可能会增强，这反过来又可以促进GnRH神经元的功能活动，并放大它们对垂体的营养作用。
