Electron Microscopy of Nerve Fibers VII.
On the Electron Dense Radial Component in the Laminated Myelin Sheath
1963 Volume 39 Issue 3 Pages 39-53
Details
1963 Volume 39 Issue 3 Pages 39-53
The radial components of the myelin sheath in the optic nerve and spinal cord of both the frog and mouse as well as of the optic nerve in Walleri an degeneration have been studied by electron microscopy. The materials were fixed in OsO4, embedded in methacrylate, Araldite or styrene-methacrylate, and, after sectionings, stained with Pb(OH)2, KMnO4 or PbO. The results obtained are summarized as follows:
1. The radial components in transverse sections of the myelin sheath appear as a series of small thickenings which are present in the interperiod lines of myelin lamellae and stand in several rows arranged radially across the thickness ofthe myelin sheath. The width of the thickening is about 50 Å and the extent along the interperiod line is about 60 to 90 Å. In oblique or tangential sections the radial components appear as thin dense lines running in parallel array across the thickness of the sheath.
2. The spacing of the myelin lamellae increases at the site of the radial component.
3. Most of the rows of thickenings extend throughout the thickness of the myelin sheath, while some of them extend for only a part of the sheath. Sometimes 2 or more radial components are present in a thin section of a sheath, where often they are not present on the same side of the sheath. There is found no firm site for the radial component in the myelin sheath.
4. When the glial cell cytoplasm is present at the site of radial component, there are found electron-dense small particles in the cytoplasm in extension of the rows of thickenings.
5. The radial components are present in some of the myelin sheath, never present in every sheaths. They are frequently present in the optic nerve of frogs, and are pretty found in the optic nerve of mice and the spinal cord of frogs, but they are less common in the spinal cord of mice. The fine structures of the radial components are almost same in every cases.
6. The radial components are found during the deformation stage of the myelin sheath in Wallerian degeneration without marked degenerative changes.
7. The radial components are an image of the true composition and structure of some myelin sheaths, not an artifact.
