Department of Neuroscience, Karolinska Institutet, 17177 Stockholm, Sweden.
J Comp Neurol. 2010 Sep 1;518(17):3464-94. doi: 10.1002/cne.22407.
Serotonin neurons play a major role in many normal and pathological brain functions. In the rat these neurons have a varying number of cotransmitters, including neuropeptides. Here we studied, with histochemical techniques, the relation between serotonin, some other small-molecule transmitters, and a number of neuropeptides in the dorsal raphe nucleus (DRN) and the adjacent ventral periaqueductal gray (vPAG) of mouse, an important question being to establish possible differences from rat. Even if similarly distributed, the serotonin neurons in mouse lacked the extensive coexpression of nitric oxide synthase and galanin seen in rat. Although partly overlapping in the vPAG, no evidence was obtained for the coexistence of serotonin with dopamine, substance P, cholecystokinin, enkephalin, somatostatin, neurotensin, dynorphin, thyrotropin-releasing hormone, or corticotropin-releasing hormone. However, some serotonin neurons expressed the gamma-aminobutyric acid (GABA)-synthesizing enzyme glutamic acid decarboxylase (GAD). Work in other laboratories suggests that, as in rat, serotonin neurons in the mouse midline DRN express the vesicular glutamate transporter 3, presumably releasing glutamate. Our study also shows that many of the neuropeptides studied (substance P, galanin, neurotensin, dynorphin, and corticotropin-releasing factor) are present in nerve terminal networks of varying densities close to the serotonin neurons, and therefore may directly or indirectly influence these cells. The apparently low numbers of coexisting messengers in mouse serotonin neurons, compared to rat, indicate considerable species differences with regard to the chemical neuronatomy of the DRN. Thus, extrapolation of DRN physiology, and possibly pathology, from rat to mouse, and even human, should be made with caution.
血清素神经元在许多正常和病理脑功能中起主要作用。在大鼠中，这些神经元有多种共递质，包括神经肽。在这里，我们使用组织化学技术研究了小鼠中背缝核（DRN）和相邻腹侧导水管周围灰质（vPAG）中的血清素、一些其他小分子递质和一些神经肽之间的关系，一个重要的问题是确定与大鼠的可能差异。即使分布相似，小鼠中的血清素神经元缺乏大鼠中广泛存在的一氧化氮合酶和甘丙肽共表达。虽然在 vPAG 中部分重叠，但没有证据表明血清素与多巴胺、P 物质、胆囊收缩素、脑啡肽、生长抑素、神经降压素、促甲状腺素释放激素或促肾上腺皮质激素释放激素共存。然而，一些血清素神经元表达γ-氨基丁酸（GABA）合成酶谷氨酸脱羧酶（GAD）。其他实验室的工作表明，与大鼠一样，小鼠中线 DRN 中的血清素神经元表达囊泡谷氨酸转运体 3，可能释放谷氨酸。我们的研究还表明，研究中许多神经肽（P 物质、甘丙肽、神经降压素、促肾上腺皮质激素释放因子）存在于靠近血清素神经元的神经末梢网络中，密度不同，因此可能直接或间接影响这些细胞。与大鼠相比，小鼠血清素神经元中共存的信使数量明显较少，这表明 DRN 的化学神经元解剖在物种间存在很大差异。因此，从大鼠到小鼠，甚至人类，对 DRN 生理学，甚至病理学的推断都应该谨慎进行。
