Thyroid Hormone Controls the Function of Hypothalamic GRF and SRIF Neurons

1.成年雄性大鼠下丘脑GRF和SRIF神经元的神经网络以及SRIF在生长激素（GH）分泌中的作用。(1)弓状核（Arc）中的GRF神经元通过纹状体终末与血管外侧杏仁核（BLA）相连，而室周核（Pe）中的SRIF神经元与脑干中的去甲肾上腺素能神经元相连。(2)Pe毁损后正中隆起SRIF含量明显减少，GH细胞对GRF刺激的敏感性降低。(3)SRIF预处理促进了2倍的GH从分散的细胞中释放，也促进了GRF刺激引起的细胞内游离Ca^2+离子的增加.甲状腺激素对Fos样蛋白、甲状腺激素和SRIF受体的影响。(1)在成年雄性大鼠脑内发现了大量Fos样免疫反应（IR），IR分布于室旁核（mPVN & pPVN）的大细胞区和小细胞区、下丘脑前部、下丘脑外侧、 关于我们 和梨状皮质。甲状腺切除术后6天，室旁核中Fos样IR细胞的数量增加了2倍。(2)甲状腺激素受体家族erbA α 2 mRNA在大鼠脑内分布广泛，主要集中在下丘脑室旁核、下丘脑腹内侧核、Arc、海马、内侧杏仁核、大脑皮质和梨状皮质。Tx后，在这些区域的受体基因表达没有显着变化，除了在PVN，这表明PVN-TRH神经活性和循环甲状腺激素浓度之间的负反馈相关性。(3)Tx对GRF基因表达的影响仍在研究中。但最近唐斯等（1990）报道，Tx或垂体切除刺激GRF基因表达，而甲状腺激素或GH替代抑制该增加，提出GH和GRF基因表达之间存在负反馈机制。(4)SRIF受体广泛分布于大鼠大脑皮质、内杯状核、海马、缰核和BLA等区域。Pe损伤后，PVN和上述区域SRIF受体数量明显增加。然而，Tx没有引起受体数量的变化，除了增加BLA和甲状腺素替代不能恢复的变化。少

1. Neuronal networks of hypothalamic GRF and SRIF neurons in adult male rats and the role of SRIF in relation to growth hormone (GH) secretion.(1) GRF neurons in the arcuate nucleus (Arc) were connected to the vasolateral amygdala (BLA) via the stria terminals, while SRIF neurons in the periventricular nucleus (Pe), have connections to noradrenergic neurons in the brain stem. (2) Pe lesion markedly reduced SRIF content in the median eminence and blunted the sensitivity of pituitary GH cells to GRF stimulation. (3) SRIF pretreatment facilitated 2-fold GH release from the dispersed cells and also the increase in intracellular free Ca^<2+> ions by GRF stimulation.2. Effects of thyroid hormone on fos-like protein, thyroid hormone and SRIF receptors.(1) A number of fos-like immunoreactivity (IR) was examined in adult male rat brains and the IRs were found in the magnocellular and parvocellular regions of the paraventricular nucleus (mPVN & pPVN), anterior hypothalamus, lateral hypothalamus, … More and pyriform cortex. Six days after thyroidectomy (Tx), the number of fos-like IR cells increased 2-fold in PVN. (2) The mRNA of erbA alfa2, one of thyroid hormone recepror family was widely distributed in rat brains, particularly a dense localization was observed in the PVN, hypothalamic ventromedial nucleus, Arc, the hippocampus, medical amygdala, cerebral cortex, and pyriform cortex. After Tx, there was no significant change in the receptor gene expression in these regions, except in PVN, suggesting a negative feedback interrelation between PVN-TRH neural activity and circulating thyroid hormone concentration. (3) Changes in gene expression of GRF by Tx is still under investigation. But recently Downs et al. (1990) reported that Tx or hypophysectomy stimulates GRF gene expression, while thyroid hormone or GH replacement suppresses the increase, proposing that there is a negative feedback mechanism between GH and GRF gene expression. (4) SRIF receptors in rat brains were widely distributed in the regions such as the cerebral cortex, endopyriform nucleus, hippocampus, habenular nucleus and BLA. The number of SRIF receptor in these regions and PVN significantly increased after Pe lesion. However, Tx caused no change in the receptor number except an increase in BLA and thyroxine replacement could not restore the change. Less