Three-dimensional reconstruction of bovine intradural spinal root myelin by electron microscope tomography

Electron microscope tomography was used to reconstruct three-dimensionally the configuration of heavy metal staining in bovine intradural spinal root myelin. Samples were fixed with glutaraldehyde, exposed to osmium tetroxide, embedded, thin sectioned, and finally stained with uranyl-acetate and lead citrate. Reconstructions up to 4.2 nm resolution showed a non-uniform distribution of stain in the planes of individual cytoplasmic appositions (major dense lines). In each reconstructed major dense line the stain was distributed in striated, well-defined structures. Those structures appear to be nearly parallel between neighboring major dense lines. The distribution of stain in the Schmidt-Lanterman cleft did not resemble the distribution of stain in the major dense line; however, weak striations were present. Evidence that the striated structures are not an artifact due to image calculation is discussed.