Stuesse S L, Stuesse D C, Cruce W L
Neurobiology Department, Northeastern Ohio Universities College of Medicine, Rootstown 44272, USA.
J Comp Neurol. 1995 Jul 31;358(3):414-27. doi: 10.1002/cne.903580308.
The vertebrate reticular formation, containing over 30 nuclei in mammals, is a core brainstem area with a long evolutionary history. However, not all reticular nuclei are equally old. Nuclei that are widespread among the vertebrate classes are probably ones that evolved early. We describe raphe nuclei in the reticular formation of three cartilaginous fishes that diverged from a common ancestor over 350 million years ago. These fishes are Hydrolagus colliei, a holocephalan, Squalus acanthias, a small-brained shark, and Heterodontus francisci, a large-brained shark. Nuclear identification was based on immunohistochemical localization of serotonin and leu-enkephalin, on brainstem location, and on cytoarchitectonics. Raphe nuclei are clustered in inferior and superior cell groups, but within these groups individual nuclei can be identified: raphe pallidus, raphe obscurus, and raphe magnus in the inferior group and raphe pontis, raphe dorsalis, raphe centralis superior, and raphe linearis in the superior group. Hydrolagus lacked a dorsal raphe nucleus, but the nucleus was present in the sharks. The majority of immunoreactive cells are found in the superior group, especially in raphe centralis superior, but immunoreactive cells are present from spinal cord to caudal mesencephalon. The distribution and cytoarchitectonics of serotoninergic and enkephalinergic cells are similar to each other, but raphe nuclei contain fewer enkephalinergic than serotoninergic cells. The cytoarchitectonics of immunoreactive raphe cells in cartilaginous fishes are remarkably similar to those described for raphe nuclei in mammals; however, the lack of a raphe dorsalis in Hydrolagus indicates that either it evolved later than the other raphe nuclei or it was lost in holocephalan fishes.
脊椎动物的网状结构在哺乳动物中包含30多个核团，是脑干的核心区域，具有悠久的进化历史。然而，并非所有的网状核团都同样古老。在脊椎动物类群中广泛分布的核团可能是早期进化而来的。我们描述了三种软骨鱼类网状结构中的中缝核，它们在3.5亿多年前从一个共同祖先分化而来。这些鱼类分别是银鲛科的太平洋长吻银鲛、脑容量较小的鲨鱼白斑角鲨，以及脑容量较大的鲨鱼条纹异齿鲛。核团的鉴定基于5-羟色胺和亮氨酸脑啡肽的免疫组织化学定位、脑干位置以及细胞构筑学。中缝核聚集在下细胞群和上细胞群中，但在这些群内可以识别出单个核团：下细胞群中有中缝苍白核、中缝隐核和中缝大核，上细胞群中有中缝脑桥核、中缝背核、中缝中央上核和中缝线性核。太平洋长吻银鲛没有背侧中缝核，但该核团在鲨鱼中存在。大多数免疫反应细胞见于上细胞群，尤其是中缝中央上核，但从脊髓到中脑尾部都有免疫反应细胞。5-羟色胺能和脑啡肽能细胞的分布和细胞构筑学彼此相似，但中缝核中的脑啡肽能细胞比5-羟色胺能细胞少。软骨鱼类中免疫反应性中缝细胞的细胞构筑学与哺乳动物中缝核的描述非常相似；然而，太平洋长吻银鲛缺乏背侧中缝核表明，要么它比其他中缝核进化得晚，要么它在全头类鱼类中丢失了。
