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A population of precursor cells is known to exist in the subependyma of the lateral ventricles in adult rodents. However, the source of the precursor cells in the adult mammalian spinal cord has not been identified in vivo, although the adult spinal cord was recently reported to contain neural stem cells in vitro. In this study we found active cell proliferation and nestin expression in the adult ependyma of the central canal after spinal cord injury. The normal ependyma showed limited proliferative activity indicated by a low Ki-67 labeling index (1.5% at T1 level) and no immunoreactivity to nestin, a marker for neural precursor cells. In contrast, the spinal cord injured by clip compression demonstrated a dramatic increase in ependymal proliferation indicated by a high Ki-67 labeling index (maximum of 26% at 3 days d after injury) and concomitant strong nestin expression in the ependyma. These responses were downregulated by 7 d after injury. The increased cell proliferation in the ependyma was observed only at sites immediately adjacent to the lesion. After injury, nestin positive, GFAP negative cell populations were found in areas surrounding the ependymal layer, which suggests migration of the ependymal cells. These results indicate the precursor cell qualities of the adult ependyma after injury. Thus, we propose the ependyma of the central canal, which is normally latent but activates locally and temporally in response to spinal cord injury, as the in vivo source for precursor cells in the adult mammalian spinal cord.
Namiki et al. (Sat,) studied this question.