School of Biological Sciences, National Institute of Science Education and Research (NISER)-Bhubaneswar, Jatni, India.
Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, India.
J Comp Neurol. 2019 Apr 15;527(6):1070-1101. doi: 10.1002/cne.24570. Epub 2018 Dec 28.
Thyrotropin-releasing hormone (TRH) regulates the hypothalamic-pituitary-thyroid axis in mammals and also regulates prolactin secretion, directly or indirectly via tuberoinfundibular dopamine neurons. Although TRH is abundantly expressed in teleost brain and believed to mediate neuronal communication, empirical evidence is lacking. We analyzed pro-TRH-mRNA expression, mapped TRH-immunoreactive elements in the brain and pituitary, and explored its role in regulation of hypophysiotropic dopamine (DA) neurons in the catfish, Clarias batrachus. Partial pro-TRH transcript from C. batrachus transcriptome showed six TRH progenitors repeats. Quantitative real-time polymerase chain reaction (qRT-PCR) identified pro-TRH transcript in a number of different brain regions and immunofluorescence showed TRH-immunoreactive cells/fibers in the olfactory bulb, telencephalon, preoptic area (POA), hypothalamus, midbrain, hindbrain, and spinal cord. In the pituitary, TRH-immunoreactive fibers were seen in the neurohypophysis, proximal pars distalis, and pars intermedia but not rostral pars distalis. In POA, distinct TRH-immunoreactive cells/fibers were seen in nucleus preopticus periventricularis anterior (NPPa) that demonstrated a significant increase in TRH-immunoreactivity when collected during preparatory and prespawning phases, reaching a peak in the spawning phase. Although tyrosine hydroxylase (TH)-immunoreactive neurons in NPPa are hypophysiotropic, none of the TRH-immunoreactive neurons in NPPa accumulated neuronal tracer DiI following implants into the pituitary. However, 87 ± 1.6% NPPa TH-immunoreactive neurons were surrounded by TRH-immunoreactive axons that were seen in close proximity to the somata. Superfused POA slices treated with TRH (0.5-2 μM) significantly reduced TH concentration in tissue homogenates and the percent TH-immunoreactive area in the NPPa. We suggest that TRH in the brain of C. batrachus regulates a range of physiological functions but in particular, serves as a potential regulator of hypophysiotropic DA neurons and reproduction.
促甲状腺素释放激素 (TRH) 调节哺乳动物的下丘脑-垂体-甲状腺轴，也通过结节漏斗多巴胺神经元直接或间接调节催乳素的分泌。尽管 TRH 在硬骨鱼脑中大量表达，并被认为介导神经元通讯，但缺乏经验证据。我们分析了前 TRH-mRNA 的表达，绘制了脑垂体中的 TRH 免疫反应元素，并探索了它在鲶鱼 Clarias batrachus 中调节促垂体多巴胺 (DA) 神经元的作用。从鲶鱼转录组中获得的部分前 TRH 转录本显示了六个 TRH 前体重复。定量实时聚合酶链反应 (qRT-PCR) 在许多不同的脑区识别出前 TRH 转录本，免疫荧光显示嗅球、端脑、视前区 (POA)、下丘脑、中脑、后脑和脊髓中有 TRH 免疫反应细胞/纤维。在垂体中，神经垂体、前远侧部和中间部可见 TRH 免疫反应纤维，但远侧部未见。在 POA 中，在室周前核 (NPPa) 中观察到明显的 TRH 免疫反应细胞/纤维，在准备和产卵前阶段收集时，TRH 免疫反应性显著增加，在产卵阶段达到峰值。尽管 NPPa 中的酪氨酸羟化酶 (TH) 免疫反应性神经元是促垂体的，但没有一个 NPPa 中的 TRH 免疫反应性神经元在植入垂体后积累神经元示踪剂 DiI。然而，NPPa 中的 87±1.6%的 TH 免疫反应性神经元被 TRH 免疫反应性轴突包围，这些轴突与神经元体非常接近。用 TRH (0.5-2 μM) 孵育 POA 切片可显著降低组织匀浆中的 TH 浓度和 NPPa 中 TH 免疫反应性面积的百分比。我们认为，鲶鱼脑中的 TRH 调节一系列生理功能，但特别是作为促垂体 DA 神经元和生殖的潜在调节剂。
