The connection between skeletal muscle and spinal canal membrane of Takifugu rubripes and its anatomical and physiology significance

Yang Song^1,2Wen-bin Jiang¹Yu-yu Xiong³Chun-zhuo Shi³Hua-xun Lai¹Lin-lin Chen²Bo Liu⁴Yan-yan Chi¹Ji-hang Li⁵Yi-tong Sun¹Xu-hui Zhang⁶Jing Zhang^1,7Xue Song¹Jin Gong¹Gary Hack⁸Sheng-bo Yu¹Jianfei Zhang^1*Hong-jin Sui^1*

• ¹Department of Anotomy, College of Basic Medicine, Dalian Medical University, Dalian, China
• ²Liaoning University of International Business and Economics, Dalian, China
• ³Ministry of Education, Key Laboratory of Environment Controlled Aquaculture (Dalian Ocean University), Dalian, China
• ⁴Department of Histology and Embryology, College of Basic Medicine, Dalian Medical University, Dalian, China
• ⁵Department of Radiology, Dalian University Affiliated Xinhua Hospital, Dalian, China
• ⁶Department of Human anatomy, School of Health and Life Sciences, University of Health and Rehabilitation Sciences, Qingdao, China
• ⁷JOINN Laboratories (Suzhou) Co., Ltd, Taicang, China
• ⁸Department of Advanced Oral Sciences and Therapeutics, University of Maryland School of Dentistry, Baltimore, United States

The myodural bridge (MDB) is considered one of the circulatory dynamics of cerebrospinal fluid (CSF). Initially identified in the human neck, it has since been documented across diverse vertebrates, including fish with analogous "MDB-like" structures. The teleost Takifugu rubripes, which exhibits a high degree of genetic homology with humans, serves as an excellent model for such comparative studies. Investigating its MDB-like structure can therefore provide a morphological basis for elucidating the mechanism of CSF circulation and its evolution during the vertebrate land-water transition. In this study, the morphology, development and ultrastructure of MDB-like structure of Takifugu rubripes were explored. Three fresh adult T. rubripes were selected for gross anatomy. After incubation, thirty-three T. rubripes aged 13-120 days after hatching (dah) were fixed in 10% formalin solution. The samples aged 50-120 dah were further decalcified with EDTA for histological paraffin sectioning and Masson staining. Four cases aged 106 dah were fixed with 2.5% glutaraldehyde, two of which were observed by scanning electron microscopy, and two cases were observed by transmission electron microscopy. Through light microscopy and electron microscopy, the results of the current study is that there are three types of fiber connections (MDB-like) between skeletal muscle and the spinal canal membrane in T. rubripes: (1) The fibers from the myocomma attach to the spinal canal membrane; (2) The epimysium connects to the spinal canal membrane directly or connects to the spinal canal membrane through reticular, filamentous fibers or fibers emitting from the perimysium; (3) The fibers from the end of the muscle bundle stop at the spinal canal membrane. These connections mainly exist on the sides of each vertebral interspace and may function similarly to the MDB. Developmentally, "MDB-like" structures appeared in T. rubripes hatched at 18 dah, began to transmit force at 21 dah, and may have a positive correlation in development with the muscle and spinal canal membrane. This experiment provides developmental morphological information for comparative studies on the conservation and interspecies differences of MDB in evolution and provides informational support for exploring the physiological function of MDB in humans.