Age-related myelin dynamics revealed by increased oligodendrogenesis and short internodes.

Aging is associated with many functional and morphological central nervous system changes. It is important to distinguish between changes created by normal aging and those caused by disease. In the present study we characterized myelin changes within the murine rubrospinal tract and found that internode lengths significantly decrease as a function of age which suggests active remyelination. We also analyzed the proliferation, distribution and phenotypic fate of dividing cells with Bromodeoxyuridine (5-bromo-2-deoxyuridine, BrdU). The data reveal a decrease in glial cell proliferation from 1 to 6, 14 and 21 months of age in gray matter 4 weeks post-BrdU injections. However, we found an increase in gliogenesis at 21st month in white matter of the spinal cord. Half of newly generated cells expressed NG2. Most cells were positive for the early oligodendrocyte marker Olig2 and a few also expressed CC1. Very few cells ever became positive for the astrocytic markers S100beta or GFAP. These data demonstrate ongoing oligodendrogenesis and myelinogenesis as a function of age in the spinal cord.