Fliers E, Wiersinga W M, Swaab D F
Department of Endocrinology and Metabolism, Academic Medical Center of the University of Amsterdam, The Netherlands.
Thyroid. 1998 Oct;8(10):921-8. doi: 10.1089/thy.1998.8.921.
Although the tripeptide thyrotropin-releasing hormone (TRH) was the first hypothalamic hormone to be isolated and characterized, only very few data were available on the central component of the hypothalamus-pituitary-thyroid (HPT) axis in the human brain until recently. We used immunocytochemistry to describe, for the first time, the distribution of TRH-containing cells and fibers in the human hypothalamus. Brain material was obtained with a short postmortem delay followed by fixation in paraformaldehyde, glutaraldehyde, and picric acid. Many TRH-containing cells were present in the paraventricular nucleus (PVN), especially in its dorsocaudal part. Some TRH cells were found in the suprachiasmatic nucleus (SCN), which is the circadian clock of the brain, and in the sexually dimorphic nucleus (SDN), which is in agreement with earlier observations in the rat hypothalamus. Dense TRH-containing fiber networks were present not only in the median eminence but also in a number of other hypothalamic areas, suggesting a physiological function of TRH as a neuromodulator or neurotransmitter in the human brain, in addition to its neuroendocrine role in pituitary secretion of thyroid-stimulating hormone (TSH). As a next step, we developed a technique for TRH mRNA in situ hybridization using a [35S] CTP-labeled TRH cRNA antisense probe in formalin-fixed paraffin-embedded sections. Numerous heavily labeled TRH mRNA-containing neurons were detected in the caudal part of the PVN, while some cells were present in the SCN and in the perifornical area. These results demonstrated the value of in situ hybridization for elucidating the chemoarchitecture of the human hypothalamus in routinely fixed autopsy tissue and enabled us to perform quantitative studies. As part of the neuroendocrine response to disease, serum concentrations of thyroid hormone decrease without giving rise to elevated concentrations of TSH, suggesting altered feedback control at the level of the hypothalamus and/or pituitary. In order to establish whether decreased activity of TRH cells in the PVN contributes to the persistence of low TSH levels in nonthyroidal illness (NTI), hypothalamic TRH gene expression was investigated in patients whose plasma concentrations of thyroid hormones had been measured just before death. Quantitative in situ hybridization showed a positive correlation of total TRH mRNA in the PVN and serum concentrations of TSH and triiodothyronine (T3) less than 24 hours before death, supporting our hypothesis. Current experiments aim at elucidating the mechanism by which hypothalamic thyroid hormone feedback control in TRH cells of patients with NTI is changed.
尽管三肽促甲状腺激素释放激素（TRH）是首个被分离和鉴定的下丘脑激素，但直到最近，关于人类大脑下丘脑-垂体-甲状腺（HPT）轴中枢部分的可用数据仍非常少。我们首次使用免疫细胞化学方法描述了含TRH的细胞和纤维在人类下丘脑中的分布。脑材料在死后短时间内获取，随后用多聚甲醛、戊二醛和苦味酸固定。室旁核（PVN）中存在许多含TRH的细胞，尤其是在其背尾部分。在视交叉上核（SCN）（即大脑的生物钟）和性二态核（SDN）中发现了一些TRH细胞，这与先前在大鼠下丘脑中的观察结果一致。不仅在正中隆起，而且在许多其他下丘脑区域都存在密集的含TRH纤维网络，这表明TRH除了在垂体分泌促甲状腺激素（TSH）中发挥神经内分泌作用外，在人类大脑中还作为神经调节剂或神经递质发挥生理功能。下一步，我们开发了一种在福尔马林固定石蜡包埋切片中使用[35S] CTP标记的TRH cRNA反义探针进行TRH mRNA原位杂交的技术。在PVN的尾部检测到大量标记强烈的含TRH mRNA的神经元，而在SCN和穹窿周区域也有一些细胞。这些结果证明了原位杂交在阐明常规固定尸检组织中人类下丘脑化学结构方面的价值，并使我们能够进行定量研究。作为对疾病的神经内分泌反应的一部分，甲状腺激素的血清浓度降低，而促甲状腺激素浓度并未升高，这表明下丘脑和/或垂体水平的反馈控制发生了改变。为了确定PVN中TRH细胞活性降低是否导致非甲状腺疾病（NTI）中促甲状腺激素水平持续偏低，我们对在死亡前刚测量过血浆甲状腺激素浓度的患者的下丘脑TRH基因表达进行了研究。定量原位杂交显示，死亡前不到24小时，PVN中总TRH mRNA与促甲状腺激素和三碘甲状腺原氨酸（T3）的血清浓度呈正相关，支持了我们的假设。目前的实验旨在阐明NTI患者TRH细胞中下丘脑甲状腺激素反馈控制发生改变的机制。
