Dudas Bertalan, Merchenthaler Istvan
Neuroendocrine Organization Laboratory (NEO), Lake Erie College of Osteopathic Medicine (LECOM), Erie, PA, 16509, USA.
Department of Epidemiology and Public Health and Anatomy and Neurobiology, University of Maryland Baltimore, 10 South Pine Street MSTF 977, Baltimore, MD, 21201, USA.
Brain Struct Funct. 2020 Sep;225(7):2193-2201. doi: 10.1007/s00429-020-02120-8. Epub 2020 Jul 31.
Thyrotropin-releasing hormone (TRH) has a critical role in the central regulation of thyroid-stimulating hormone (TSH) from the anterior pituitary, and subsequently, thyroid hormone secretion from the thyroid gland. In addition to its role in the regulation of HPT axis, TRH is a potent regulator of prolactin (PRL) secretion by stimulating PRL secretion either directly from lactotrophs or indirectly via its action on the tuberoinfundibular dopamine (TIDA) neurons. In rodents, the TRH neurons which regulate TSH and thyroid hormone secretion, called hypophysiotropic TRH neurons, are in the medial subdivision of the parvicellular paraventricular nucleus (PVN). In humans, the PVN also contains a large population of TRH neurons, especially in its medial part, but the location of hypophysiotropic TRH neurons is not yet known. In addition to regulating TSH and PRL secretion, TRH also functions as a neurotransmitter/neuromodulator. In rodents and teleosts, TRH axons densely innervate TIDA neurons to inhibit tyrosine hydroxylase (TH) biosynthesis, neuronal firing, and dopamine turnover which may contribute to increasing PRL secretion. No such connections have been reported in humans, although dopaminergic neurons express TRH receptors and TRH also regulates PRL secretion. The objectives of this study were to map TRH-IR and TH-IR structures in the human hypothalamus with single-label light microscopic immunocytochemistry and study their interaction with double-label light microscopic immunocytochemistry. We show that TRH-IR nerve terminals densely surround TH-IR neurons (perikarya and dendrites) in the infundibulum of the human hypothalamus. The micrographs illustrating these juxtapositions were taken by Olympus BX45 microscope equipped with a digital camera and with 100X oil immersion objective. Composite images were created from the consecutive micrographs if the neurons were larger than the frame of the camera, using Adobe Photoshop software. As no gaps between TRH-IR and TH-IR elements were seen, these contacts may be functional synapses by which TRH regulates the activity of dopaminergic neurons and subsequently TSH and PRL secretion.
促甲状腺激素释放激素（TRH）在垂体前叶促甲状腺激素（TSH）的中枢调节以及随后甲状腺激素从甲状腺的分泌过程中发挥着关键作用。除了在调节下丘脑 - 垂体 - 甲状腺（HPT）轴方面的作用外，TRH还是催乳素（PRL）分泌的有效调节因子，它可通过直接刺激催乳素细胞分泌PRL或通过其对结节漏斗多巴胺（TIDA）神经元的作用间接刺激PRL分泌。在啮齿动物中，调节TSH和甲状腺激素分泌的TRH神经元，即促垂体TRH神经元，位于小细胞室旁核（PVN）的内侧亚区。在人类中，PVN也含有大量的TRH神经元，尤其是在其内侧部分，但促垂体TRH神经元的位置尚不清楚。除了调节TSH和PRL分泌外，TRH还作为神经递质/神经调节剂发挥作用。在啮齿动物和硬骨鱼中，TRH轴突密集地支配TIDA神经元，以抑制酪氨酸羟化酶（TH）的生物合成、神经元放电和多巴胺周转，这可能有助于增加PRL分泌。虽然多巴胺能神经元表达TRH受体且TRH也调节PRL分泌，但在人类中尚未报道有此类连接。本研究的目的是通过单标记光镜免疫细胞化学方法绘制人类下丘脑TRH免疫反应（TRH-IR）和TH免疫反应（TH-IR）结构，并通过双标记光镜免疫细胞化学方法研究它们之间的相互作用。我们发现，在人类下丘脑漏斗部，TRH-IR神经末梢密集地围绕着TH-IR神经元（胞体和树突）。展示这些并列情况的显微照片是由配备数码相机和100倍油浸物镜的奥林巴斯BX45显微镜拍摄的。如果神经元大于相机框架，则使用Adobe Photoshop软件从连续的显微照片中创建合成图像。由于未观察到TRH-IR和TH-IR元素之间存在间隙，这些接触可能是功能性突触，通过它们TRH调节多巴胺能神经元的活性，进而调节TSH和PRL分泌。
