Department of Invertebrate Zoology, Faculty of Biology, Lomonosov Moscow State University, Moscow, Russia.
Front Neural Circuits. 2023 Sep 7;17:1235915. doi: 10.3389/fncir.2023.1235915. eCollection 2023.
As the sister group to all Bilateria, representatives of the phylum Cnidaria (sea anemones, corals, jellyfishes, and hydroids) possess a recognizable and well-developed nervous system and have attracted considerable attention over the years from neurobiologists and evo-devo researchers. Despite a long history of nervous system investigation in Cnidaria, most studies have been performed on unitary organisms. However, the majority of cnidarians are colonial (modular) organisms with unique and specific features of development and function. Nevertheless, data on the nervous system in colonial cnidarians are scarce. Within hydrozoans (Hydrozoa and Cnidaria), a structurally "simple" nervous system has been described for and zooids of several colonial species. A more complex organization of the nervous system, closely related to the animals' motile mode of life, has been shown for the medusa stage and a few siphonophores. Direct evidence of a colonial nervous system interconnecting zooids of a hydrozoan colony has been obtained only for two species, while it has been stated that in other studied species, the coenosarc lacks nerves.
In the present study, the presence of a nervous system in the coenosarc of three species of colonial hydroids - the athecate , and thecate and - was studied based on immunocytochemical and ultrastructural investigations.
Confocal scanning laser microscopy revealed a loose system composed of delicate, mostly bipolar, neurons visualized using a combination of anti-tyrosinated and anti-acetylated a-tubulin antibodies, as well as anti-RF-amide antibodies. Only ganglion nerve cells were observed. The neurites were found in the growing stolon tips close to the tip apex. Ultrastructural data confirmed the presence of neurons in the coenosarc epidermis of all the studied species. In the coenosarc, the neurons and their processes were found to settle on the mesoglea, and the muscle processes were found to overlay the nerve cells. Some of the neurites were found to run within the mesoglea.
Based on the findings, the possible role of the colonial nervous system in sessile hydroids is discussed.
作为所有两侧对称动物的姊妹群，刺胞动物门（海葵、珊瑚、水母和水螅）的代表具有可识别且发达的神经系统，多年来一直受到神经生物学家和演化发育生物学家的关注。尽管刺胞动物的神经系统已经有很长的研究历史，但大多数研究都是在单一生物体上进行的。然而，大多数刺胞动物是具有独特和特定发育和功能特征的群体（模块化）生物。尽管如此，关于群体刺胞动物神经系统的数据仍然很少。在水螅动物门（水螅纲和刺胞动物门）中，已经为几个群体物种的 和水螅型描述了结构上“简单”的神经系统。与动物的运动生活方式密切相关的更复杂的神经系统组织已被证明存在于水母阶段和少数水螅水母中。只有两种水螅动物的群体中发现了相互连接水螅型的群体神经系统的直接证据，而在其他研究的物种中，群体组织缺乏神经。
在本研究中，基于免疫细胞化学和超微结构研究，研究了三种群体水螅 - 无腔水螅 、有腔水螅 和 - 的群体组织中神经系统的存在。
共聚焦扫描激光显微镜显示，由使用抗酪氨酸化和抗乙酰化 α-微管蛋白抗体以及抗 RF-酰胺抗体组合可视化的精细、大多为双极神经元组成的松散系统。只观察到神经节神经元。神经突被发现存在于靠近尖端的生长茎尖中。超微结构数据证实了所有研究物种群体组织表皮中神经元的存在。在群体组织中，发现神经元及其突起位于中胶层上，肌肉突起覆盖在神经细胞上。一些神经突被发现存在于中胶层内。
基于这些发现，讨论了群体神经系统在固着水螅中的可能作用。
