Identification of the Effect of Axonal Coupling to the Glial Matrix on Axonal Kinematics By

The axonal kinematic response to different level of strain was examined in developing chick embryo spinal cords. Spinal cords were dissected from chick embryos at different days of development (E12, E14, E16, and E18), and the myelination of chick embryo spinal cord was characterized by immunohistochemical labeling of myelin basic protein (MBP), which is synthesized in the myelination process. Spinal cords at each developmental stage were dissected, exposed to different stretch ratios (1.05, 1.1, 1.15, 1.20), and fixed with paraformaldehyde at the stretched length. Spinal cords were then sectioned, stained immunohistochemically for neurofilament proteins, and imaged with epifluorescence microscopy. The tortuosities of hundreds of axons were traced by measuring the actual pathlength and the end-to-end length of randomly selected individual axons. The tortuosity distribution of axons before and after stretch was examined. During development, the length of the spinal cord increased 55% from E12E18 and white matter tracts were significantly myelinated. Axons in the unstretched spinal cord at each development stage were undulated. After stretching the spinal cord, axons straightened, with the decrease in tortuousity dependent on the development stage. The results indicated that in unstretched embryonic chick spinal cords, the average tortuosity of axons decreases naturally during development. Also, the percentage of