Proliferation and differentiation of progenitor cells throughout the intact adult rat spinal cord

The existence of multipotent progenitor populations in the adult forebrain has been widely studied. To extend this knowledge to the adult spinal cord we have examined the proliferation, distribution, and phenotypic fate of di viding cells in the adult rat spinal cord. Bromodeoxyuridine (BrdU) was use d to label dividing cells in 13- to 14-week-old, intact Fischer rats. Singl e daily injections of BrdU were administered over a 12 d period. Animals we re killed either 1 d or 4 weeks after the last injection of BrdU. We observ ed frequent cell division throughout the adult rodent spinal cord, particul arly in white matter tracts (5-7% of all nuclei). The majority of BrdU-labe led cells colocalized with markers of immature glial cells. At 4 weeks, 10% of dividing cells expressed mature astrocyte and oligodendroglial markers. These data predict that 0.75% of all astrocytes and 0.82% of all oligodend rocytes are derived from a dividing population over a 4 week period. To det ermine the migratory nature of dividing cells, a single BrdU injection was given to animals that were killed 1 hr after the injection. In these tissue s, the distribution and incidence of BrdU labeling matched those of the 4 w eek post injection (pi) groups, suggesting that proliferating cells divide in situ rather than migrate from the ependymal zone. These data suggest a h igher level of cellular plasticity for the intact spinal cord than has prev iously been observed and that glial progenitors exist in the outer circumfe rence of the spinal cord that can give rise to both astrocytes and oligoden drocytes.