Age-related changes in the nucleus pulposus of intervertebral disc in mice. An electronmicroscopic study.

The nucleus pulposus of the intervertebral discs in mice from newborn to four months of age was examined by electron microscopy. The nucleus pulposus was packed with the cells which were distended with large vacuoles and aggregations of glycogen particles. These cells contained many filaments and poorly developed organelles. Numerous pinocytotic vesicles were present along the cell surface. Neighboring cells were connected with desmosomes. Thus, the cells composing the nucleus pulposus were similar to notochordal cells. The intercellular space contained granular substances as seen in the matrix of the cartilage. In the peripheral region of the nucleus pulposus, the cells relatively rich in organelles were occasionally observed. At two months or more of age, vacuoles of the cells of the nucleus pulposus became larger and more numerous, and the scanty cytoplasm contained fewer organelles but well-developed filaments. However, many pinocytotic vesicles could be still observed along the cell surface. Degenerated cells appeared.