Development of myodural bridge located within the atlanto-occipital interspace of rats

The myodural bridge (MDB) is a dense connective tissue structure that connects the subocciptal musculature to the spinal dura mater. The purpose of this study was to clarify morphological evolution characteristics and compositional changes in the fibrous structures of MDB during its growth and development in the atlanto-occipital interspace. For this, histological sections from Sprague-Dawley (SD) rats (age, E17 to adulthood) were stained with Masson's Trichrome and Picrosirius Red. The results demonstrated that at age E18, the posterior arch of the atlas was completely closed and MDB fibers had already begun to form. In rat embryos (E18-E21), only few fibers and muscles were present in the suboccipital region, and these were lightly stained. In postnatal rats, an obvious increase in the amount of fibers and muscle tissues was noted. At age P1, MDB fibers originated from the rectus capitis posterior minor muscle and merged into the atlanto-occipital membrane, which was closely attached to the spinal dura mater. As rats matured, MDB fibers gradually became denser and more organized. This study also showed that in postnatal rats, MDB was mainly composed of type I collagen fibers. By observing the development of MDB in SD rats, the function of MDB can be further understood. This study provides a morphological basis for future functional studies involving the MDB.