It has been generally acknowledged that environment could alter the morphology and functional differentiation of vertebrate brain. However, as the largest group of all vertebrates, studies about the structures and functions of various brain subregions in teleost are still scarce. In this study, using grass carp as a model, histology method and RNA-sequencing were recruited to examine the microstructure and transcript levels among different brain subregions and pituitary. Histological results showed that the grass carp brain was composed of six parts, including olfactory bulb, telencephalon, hypothalamus, optic tectum, cerebellum, and medulla oblongata. In addition, compared to elasmobranchs and non-teleost bony ray-finned fishes, grass carp lost the hypothalamo-hypophyseal portal system, instead the hypophysiotropic neurons were directly terminated in the pituitary cells. At the transcriptomic level, our results suggested that the olfactory bulb might be related to reproduction and immune function. The telencephalon was deemed to be involved in the regulation of appetite and reproduction. The optic tectum might play important roles in the vision system and feeding. The hypothalamus could regulate feeding, and reproduction process. The medulla oblongata was related with the auditory system. The pituitary seemed to play pivotal roles in energy metabolism, organ development and reproduction. Finally, the correlation analysis suggested that the hypothalamus and the telencephalon were highly related, and close anatomical connection and overlapping functions suggested that the telencephalon and hypothalamus might be the regulation center of feeding and reproduction among teleost brain. This study provided a global view of the microstructures and specific functions of various brain subregions and pituitary in teleost. These results will be very helpful for further study in the neuroendocrinology regulation of growth and reproduction in teleost brain-pituitary axis.

中文翻译：

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草鱼（Ctenopharyngodon idellus）的各个脑子区域和垂体的结构和功能分析。

人们普遍认为，环境可以改变脊椎动物大脑的形态和功能分化。然而，作为所有脊椎动物中最大的群体，关于硬骨鱼的各个脑子区域的结构和功能的研究仍然很少。在这项研究中，以草鱼为模型，采用组织学方法和RNA测序技术来检查不同脑子区域和垂体之间的显微结构和转录水平。组织学结果表明，草鱼脑由嗅球，端脑，下丘脑，视轴，小脑和延髓六个部分组成。此外，与弹性支和非远鳍骨射线鱼相比，草鱼失去了下丘脑-垂体门系统，相反，促垂体神经元直接终止于垂体细胞。在转录组水平上，我们的结果表明嗅球可能与生殖和免疫功能有关。端脑被认为参与了食欲和生殖的调节。视神经台可能在视觉系统和进食中起重要作用。下丘脑可以调节摄食和繁殖过程。延髓与听觉系统有关。垂体似乎在能量代谢，器官发育和繁殖中起关键作用。最后，相关性分析表明下丘脑和端脑高度相关，紧密的解剖联系和重叠的功能表明，端脑和下丘脑可能是硬骨质大脑进食和繁殖的调节中心。这项研究为硬骨鱼的各个脑子区域和垂体的微观结构和特定功能提供了一个整体视图。这些结果对于进一步研究硬骨质脑-垂体轴的生长和繁殖的神经内分泌调节将非常有帮助。