Hurley D L, Wee B E, Phelps C J
Department of Cell and Molecular Biology, Tulane University, New Orleans, La., USA.
Neuroendocrinology. 1998 Sep;68(3):201-9. doi: 10.1159/000054367.
Several genetic mutations in mice and rats that produce lifelong growth hormone (GH) deficiency result in overexpression of GH-releasing hormone (GHRH) mRNA in hypothalamic arcuate nucleus neurons. In order to examine the development of this condition, GHRH mRNA expression was quantified in Ames dwarf (df/df) and normal (DF/?) mice at 1 (day of birth), 3, 7, 14, 21 and 60 postnatal days (d) following in situ hybridization. Total mRNA was assessed using computer-assisted densitometry after X-ray film autoradiography, and mRNA expression per neuron was quantified by counts of grains per cell after emulsion autoradiography. Total GHRH mRNA was the same in dwarf and normal mice at 1, 3 and 7d. GHRH mRNA in dwarfs increased at 14d to 240% of that in DF/? (p < 0.005); the percentage overexpression in dwarf mice remained >/=200% through 60d, although total GHRH mRNA increased in both dwarfs and normals during this period. GHRH mRNA per neuron was the same in normal and dwarf mice at 1d, then increased in dwarfs to 190% of that in normals at 3d (p < 0.05), and rose to 300% of normal levels by 7d and beyond (p < 0. 005). There was no sexual dimorphism in expression by either measure in normal or dwarf mice. These results indicate that an increase in GHRH mRNA in Ames dwarf mice is first detectable at 3d, a period of approximately 7d after the failure to initiate GH production, which occurs normally at embryonic day 17.5. The onset of GHRH overexpression occurs earlier than the decline of either hypophysiotropic somatostatin or dopamine in Ames dwarf mice. This difference may be due to the stimulatory action of GHRH, as opposed to the inhibitory effects of factors examined previously.
在小鼠和大鼠中，几种导致终身生长激素（GH）缺乏的基因突变会导致下丘脑弓状核神经元中生长激素释放激素（GHRH）mRNA的过度表达。为了研究这种情况的发展过程，在出生后1天（出生日）、3天、7天、14天、21天和60天，通过原位杂交对艾姆斯侏儒（df/df）小鼠和正常（DF/?）小鼠的GHRH mRNA表达进行了定量分析。在X射线胶片放射自显影后，使用计算机辅助密度测定法评估总mRNA，并在乳胶放射自显影后通过每个细胞的颗粒计数来定量每个神经元的mRNA表达。在1天、3天和7天时，侏儒小鼠和正常小鼠的总GHRH mRNA相同。侏儒小鼠的GHRH mRNA在14天时增加到DF/?小鼠的240%（p < 0.005）；尽管在此期间侏儒小鼠和正常小鼠的总GHRH mRNA都有所增加，但侏儒小鼠的过表达百分比在60天时仍保持≥200%。在1天时，正常小鼠和侏儒小鼠每个神经元的GHRH mRNA相同，然后在侏儒小鼠中，3天时增加到正常小鼠的190%（p < 0.05），到7天时及以后上升到正常水平的300%（p < 0.005）。无论是正常小鼠还是侏儒小鼠，通过这两种测量方法，其表达均无性别差异。这些结果表明，在艾姆斯侏儒小鼠中，GHRH mRNA的增加最早在3天时可检测到，这是在正常情况下胚胎第17.5天开始产生GH失败后约7天的时期。GHRH过度表达的开始时间早于艾姆斯侏儒小鼠中促垂体生长抑素或多巴胺的下降时间。这种差异可能是由于GHRH的刺激作用，与之前研究的因子的抑制作用相反。
