Schwann cell invasion of ventral spinal cord: the effect of irradiation on astrocyte barriers.

This study examines a radiation-induced invasion and spread of Schwann cells into ventral gray regions of the lumbar spinal cord. The prevalence of these cells within the gray matter and the time course of their appearance in the ventral spinal cord is quite different from the pattern of Schwann cell development in dorsal spinal cord reported previously. The focus is on 2 possible pathways, each involving astrocytic barriers, by which Schwann cells access the ventral gray matter. The first of these is the glia limitans covering the ventral surface of the spinal cord and the possibility that its integrity has been disrupted by the exposure to x-rays. Comparisons of the glia limitans, including its thickness, between irradiated and nonirradiated rats revealed that exposure to radiation did not result in any morphologically discernible alterations. The second barrier examined was the astrocytic covering of blood vessels. In irradiated animals the astrocyte processes that normally surround blood vessels were missing in some instances, and Schwann cells were observed at these sites. The difference between the dorsal and ventral occurrence of Schwann cells is that, whereas Schwann cells primarily follow axons, specifically dorsal root axons, to access the dorsal spinal cord, it appears that the presence of Schwann cells in the ventral portion of the spinal cord where their location is primarily in the gray matter is associated with the vasculature.