Abstract：
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 Stylochoplana pusilla 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.
摘要：
Platyhelminthes是具有原型身体系统的简单双侧无脊椎动物的门。与CNIDarians等非双边主义者相比，双边主义者可能表现出综合的自由移动行为，这需要一个集中的神经系统“大脑”，而不是放射状的分布式神经系统。不仅与非双边动物，而且与寄生的扁虫或淡水涡虫相比，海洋扁虫具有早期头化的“中枢”神经系统。在这项研究中,由于早期头化的中枢神经系统，我们将海洋扁虫Stylochoplanapusilla用作Platyhelminthes的出色模型生物。这里,我们通过在同步加速器辐射设施中使用X射线显微计算机断层扫描（micro-CT）研究了扁虫中枢神经系统的三维结构。我们发现获得的断层图像足以区分神经系统的某些特征结构，包括头神经节周围的神经索，蘑菇状的身体结构，和假定的视神经形成视神经连合样结构。通过显微CT成像,我们可以获得无失真的连续切片图像，允许我们可视化神经元亚群和神经束的精确空间关系。3-Dmicro-CT在细胞水平的神经系统体积分析中非常有效；该方法很简单，可以应用于许多其他非模型生物。
