Postmortem changes in ultrastructures of the mouse intervertebral disc.

To elucidate the effects of nutrition and oxygen deficiencies on the intervertebral disc, cell components of mouse intervertebral discs and their postmortem changes were observed by electron microscopy. The annulus fibrosus could be divided into an inner and outer region. The main cell components of the annulus fibrosus were fibroblast-like cells in the outer region and chondrocytes in the inner region. The nucleus pulposus consisted of massively packed notochordal cells. The cartilage plates could also be divided into two zones: articular cartilage and growth cartilage containing chondrocytes. Postmortem degenerative changes proceeded from the peripheral to the central parts of the intervertebral disc, ie, showing degeneration of first the fibroblast-like cells, next the chondrocytes, and finally, the notochordal cells. The findings suggest that cells situated at the periphery predominantly depend on aerobic metabolism, whereas the cells situated more centrally depend on anaerobic metabolism. Furthermore, postmortem changes of the nucleus pulposus were similar to age-related changes. The age-related changes or degeneration in the intervertebral disc appear to be related to deficiencies of nutrition or oxygen caused by changes in structures of the disc and the surrounding tissues.