Identification, structural features, and potential functional significance of the myodural Bridge in African clawed frog, the Xenopus laevis

The myodural bridge (MDB) is an anatomical structure located in the suboccipital region, consisting of a dense fibrous connective tissue bridge connecting the suboccipital muscles to the dura mater (DM). These fibres interweave with their originating muscles and the dura, forming a functional unit known as the "myodural bridge complex" (MDBC). Previous studies, employing plastination sections, gross dissection, histological staining, and electron microscopy, have confirmed the widespread and highly conserved presence of the MDB in mammals, birds, and reptiles. To further investigate the presence of the MDB across vertebrates, this study selected the African clawed frog (Xenopus laevis), a model amphibian species, as the subject of investigation. Morphological methods, including gross dissection, paraffin section staining, and scanning electron microscopy (SEM), were used to investigate the existence and characteristics of the MDB in this species. A total of 10 sexually Mature African clawed frogs were used for the study: 3 for gross dissection, 5 for histological staining, and 2 for SEM observation. The study confirmed the presence of the MDBC in adult African clawed frogs, located in the atlanto-occipital space, where it connects the perimysium of the longissimus dorsi muscle (LGD) and the interarcualis muscle (IAR) to the dorsal atlanto-occipital membrane (DAOM) and DM. The characteristics of the MDB in adult African clawed frogs were as follows: Its fibrous components consisted predominantly of collagen fibres, with type I and type III collagen being the most abundant and elastic fibres being almost absent. The fibres between the perimysium, DAOM, and DM are interwoven. Considering the unique physiological structure and evolutionary significance of amphibians, our findings extend the known distribution of the MDB across vertebrates, enhance our understanding of adaptive changes in the MDBC among different species, and support the hypothesis that the MDBC plays a regulatory role in cerebrospinal fluid (CSF) dynamics.