The structural integrity of glial scar tissue associated with a chronic spinal cord lesion can be altered by transplanted fetal spinal cord tissue

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Abstract
The potential for fetal spinal cord (FSC) tissue transplants to modify an established glial scar or to restrict the reformation of a scar following surgical manipulation of a chronic lesion site was studied in the injured rat spinal cord. Six to eight weeks after preparation of a hemisection lesion cavity, glial scar tissue was left intact in one group, whereas in a second group it was excised prior to transplantation of a suspension of FSC tissue. From the first group, examination of serial sections through the graft‐host interface that had been immunoreacted for glial fibrillary acidic protein (GFAP) demonstrated that in many cases the glial scar no longer was a continuous wall separating the two tissues. Quantitation of the area occupied by these discrete gaps in the scar provided an Index of Fusion, indicating the extent of direct contact between the transplant and host spinal cord. In some animals this constituted as much as 60% of the interface, while in others there were no breaks in the scar (0% fusion). Reinjury of the spinal cord lead to a rapid astrocytic response culminating in the re‐establishment of a dense matrix of glial cells and processes covered by a basal lamina. This reformed scar effectively isolated the spinal cord from the external environment of the cavity. When FSC tissue was transplanted after first removing scar tissue the continuity of reformed glial scarring at the graft‐host interface was altered. Distinct gaps in the scar appeared randomly along the interface. The mean Index of Fusion for animals receiving a moderate reinjury (removal of scar tissue only) was not as high as for those animals in which a more severe reinjury (expansion of the cavity by 0.5 mm) was performed before transplantation. The extent of graft‐host fusion was not significantly improved when scar tissue was removed prior to transplantation. These findings support the hypothesis that the presence of FSC tissue will have an effect on the persistence of glial scar tissue in a chronic lesion site as well as limit the extent to which a new scar is formed in response to a second injury to the spinal cord.