Graduate School of Science and Engineering, Kagoshima University, Kagoshima 890-0065, Japan.
Ushimado Marine Institute (UMI), Faculty of Environmental, Life, Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama 701-4303, Japan.
Zoolog Sci. 2024 Jun;41(3):281-289. doi: 10.2108/zs230082.
Platyhelminthes are a phylum of simple bilaterian invertebrates with prototypic body systems. Compared with non-bilaterians such as cnidarians, the bilaterians are likely to exhibit integrated free-moving behaviors, which require a concentrated nervous system "brain" rather than the distributed nervous system of radiatans. Marine flatworms have an early cephalized 'central' nervous system compared not only with non-bilaterians but also with parasitic flatworms or freshwater planarians. In this study, we used the marine flatworm as an excellent model organism in Platyhelminthes because of the early cephalized central nervous system. Here, we investigated the three-dimensional structures of the flatworm central nervous system by the use of X-ray micro-computed tomography (micro-CT) in a synchrotron radiation facility. We found that the obtained tomographic images were sufficient to discriminate some characteristic structures of the nervous system, including nerve cords around the cephalic ganglion, mushroom body-like structures, and putative optic nerves forming an optic commissure-like structure. Through the micro-CT imaging, we could obtain undistorted serial section images, permitting us to visualize precise spatial relationships of neuronal subpopulations and nerve tracts. 3-D micro-CT is very effective in the volume analysis of the nervous system at the cellular level; the methodology is straightforward and could be applied to many other non-model organisms.
扁形动物门是一类具有典型体系统的简单两侧对称的无脊椎动物。与刺胞动物等非两侧对称动物相比，两侧对称动物可能表现出整合的自由运动行为，这需要一个集中的神经系统“大脑”，而不是辐射动物的分布式神经系统。与非两侧对称动物甚至与寄生扁形动物或淡水涡虫相比，海洋扁形动物具有早期头化的“中央”神经系统。在这项研究中，我们使用海洋扁形动物作为扁形动物的优秀模式生物，因为它具有早期头化的中央神经系统。在这里，我们利用同步辐射设施中的 X 射线微计算机断层扫描（micro-CT）研究了扁形动物中央神经系统的三维结构。我们发现，获得的断层扫描图像足以区分神经系统的一些特征结构，包括围绕脑神经节的神经索、蘑菇体样结构以及可能形成视神经交叉样结构的视神经。通过 micro-CT 成像，我们可以获得未失真的连续切片图像，使我们能够可视化神经元亚群和神经束的精确空间关系。3D micro-CT 在细胞水平上对神经系统的体积分析非常有效；该方法简单直接，可应用于许多其他非模式生物。
