Galanin is a neuropeptide that is widely expressed in the mammalian brain, where it regulates many physiological processes, including feeding and nociception. Galanin has been characterized extensively in jawed vertebrates (gnathostomes), but little is known about the galanin system in the most ancient extant vertebrate class, the jawless vertebrates or agnathans. Here, we identified and cloned a cDNA encoding the sea lamprey (Petromyzon marinus) galanin precursor (PmGalP). Sequence analysis revealed that PmGalP gives rise to two neuropeptides that are similar to gnathostome galanins and galanin message-associated peptides. Using mRNA in situ hybridization, the distribution of PmGalP-expressing neurons was mapped in the brain of larval and adult sea lampreys. This revealed PmGalP-expressing neurons in the septum, preoptic region, striatum, hypothalamus, prethalamus, and displaced cells in lateral areas of the telencephalon and diencephalon. In adults, the laterally migrated PmGalP-expressing neurons are observed in an area that extends from the ventral pallium to the lateral hypothalamus and prethalamus. The striatal and laterally migrated PmGalP-expressing cells of the telencephalon were not observed in larvae. Comparison with studies on jawed vertebrates reveals that the presence of septal and hypothalamic galanin-expressing neuronal populations is highly conserved in vertebrates. However, compared to mammals, there is a more restricted pattern of expression of the galanin transcript in the brain of lampreys. This work provides important new information on the early evolution of the galanin system in vertebrates and provides a genetic and neuroanatomical basis for functional analyses of the galanin system in lampreys.

中文翻译：

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无颌甘丙肽：七鳃鳗大脑中前体的鉴定和表达定位。

甘丙肽是一种在哺乳动物大脑中广泛表达的神经肽，调节许多生理过程，包括进食和伤害感受。甘丙肽在有颌脊椎动物（颌口动物）中得到了广泛的表征，但对现存最古老的脊椎动物纲（无颌脊椎动物或无颌动物）中的甘丙肽系统知之甚少。在这里，我们鉴定并克隆了编码海七鳃鳗 (Petromyzon marinus) 甘丙肽前体 (PmGalP) 的 cDNA。序列分析表明，PmGalP 产生两种与颚口甘丙肽和甘丙肽信息相关肽相似的神经肽。利用 mRNA 原位杂交技术，绘制了表达 PmGalP 的神经元在幼虫和成年七鳃鳗大脑中的分布图。这揭示了中隔、视前区、纹状体、下丘脑、前丘脑以及端脑和间脑外侧区域的移位细胞中表达 PmGalP 的神经元。在成人中，在从腹侧大脑皮层延伸到外侧下丘脑和前丘脑的区域中观察到横向迁移的表达 PmGalP 的神经元。在幼虫中未观察到端脑纹状体和侧向迁移的表达 PmGalP 的细胞。与有颌脊椎动物的研究比较表明，隔膜和下丘脑表达甘丙肽的神经元群在脊椎动物中高度保守。然而，与哺乳动物相比，七鳃鳗大脑中甘丙肽转录物的表达模式更受限制。这项工作提供了有关脊椎动物甘丙肽系统早期进化的重要新信息，并为七鳃鳗甘丙肽系统的功能分析提供了遗传和神经解剖学基础。