Liposits Z, Paull W K, Wu P, Jackson I M, Lechan R M
Department of Anatomy, University of Missouri-Columbia 65212.
Histochemistry. 1987;88(1):1-10. doi: 10.1007/BF00490159.
The neuropeptide thyrotropin releasing hormone (TRH) is capable of influencing both neuronal mechanisms in the brain and the activity of the pituitary-thyroid endocrine axis. By the use of immunocytochemical techniques, first the ultrastructural features of TRH-immunoreactive (IR) perikarya and neuronal processes were studied, and then the relationship between TRH-IR neuronal elements and dopamine-beta-hydroxylase (DBH) or phenylethanolamine-N-methyltransferase (PNMT)-IR catecholaminergic axons was analyzed in the parvocellular subnuclei of the hypothalamic paraventricular nucleus (PVN). In control animals, only TRH-IR axons were detected and some of them seemed to follow the contour of immunonegative neurons. Colchicine treatment resulted in the appearance of TRH-IR material in parvocellular neurons of the PVN. At the ultrastructural level, immunolabel was associated with rough endoplasmic reticulum, free ribosomes and neurosecretory granules. Non-labelled axons formed synaptic specializations with both dendrites and perikarya of the TRH-synthesizing neurons. TRH-IR axons located in the parvocellular units of the PVN exhibited numerous intensely labelled dense-core and fewer small electron lucent vesicles. These axons were frequently observed to terminate on parvocellular neurons, forming both bouton- and en passant-type connections. The simultaneous light microscopic localization of DBH or PNMT-IR axons and TRH-synthesizing neurons demonstrated that catecholaminergic fibers established contacts with the dendrites and cell bodies of TRH-IR neurons. Ultrastructural analysis revealed the formation of asymmetric axo-somatic and axo-dendritic synaptic specializations between PNMT-immunopositive, adrenergic axons and TRH-IR neurons in the periventricular and medial parvocellular subnuclei of the PVN. These morphological data indicate that the hypophysiotrophic, thyrotropin releasing hormone synthesizing neurons of the PVN are directly influenced by the central epinephrine system and that TRH may act as a neurotransmitter or neuromodulator upon other paraventricular neurons.
神经肽促甲状腺激素释放激素（TRH）能够影响大脑中的神经元机制以及垂体 - 甲状腺内分泌轴的活性。通过免疫细胞化学技术，首先研究了TRH免疫反应性（IR）核周体和神经元突起的超微结构特征，然后在下丘脑室旁核（PVN）的小细胞亚核中分析了TRH - IR神经元成分与多巴胺β - 羟化酶（DBH）或苯乙醇胺 - N - 甲基转移酶（PNMT） - IR儿茶酚胺能轴突之间的关系。在对照动物中，仅检测到TRH - IR轴突，其中一些似乎沿着免疫阴性神经元的轮廓走行。秋水仙碱处理导致PVN小细胞神经元中出现TRH - IR物质。在超微结构水平上，免疫标记与粗面内质网、游离核糖体和神经分泌颗粒相关。未标记的轴突与TRH合成神经元的树突和核周体形成突触特化。位于PVN小细胞单位中的TRH - IR轴突表现出大量强烈标记的致密核心小泡和较少的小电子透亮小泡。经常观察到这些轴突终止于小细胞神经元上，形成纽扣型和依傍型连接。DBH或PNMT - IR轴突与TRH合成神经元的同时光镜定位表明，儿茶酚胺能纤维与TRH - IR神经元的树突和细胞体建立了联系。超微结构分析揭示了在PVN的室周和内侧小细胞亚核中，PNMT免疫阳性的肾上腺素能轴突与TRH - IR神经元之间形成了不对称的轴 - 体和轴 - 树突突触特化。这些形态学数据表明，PVN中分泌促甲状腺激素释放激素的促垂体神经元直接受中枢肾上腺素系统的影响，并且TRH可能作为神经递质或神经调节剂作用于其他室旁神经元。
