Oxygen transport in intraspinal fetal grafts: graft-host relations.

In the present experiments, we determined tissue oxygen tension (PtO2) levels within the injured spinal cords of adult rats following transplantation of fetal spinal cord tissue. Partial resection cavities were made at L1-L2 levels after which whole pieces of 14-day donor tissue were placed into the cavities. Analysis of recordings obtained from graft tissues at 1 and 2 months after transplantation revealed low PtO2 values in many cases. Even the more extensively developed transplants at 3 months continued to show mean PtO2 levels lower than those taken from normal, mature spinal cord tissue. Measurements from host tissue, adjacent to a lesion in which no graft was introduced, showed normal or elevated PtO2 levels. In contrast, where extensive host and graft integration had occurred, the PtO2 levels of adjacent host resembled those obtained within the transplants. On the other hand, in cases of poor host-graft integration, characterized by either cellular or fibrotic graft-host interfaces or large cysts, the PtO2 tensions exceeded normal levels. Therefore, the present results show that when fetal grafts are placed acutely into an aspiration cavity within the adult spinal cord, the transplants quickly establish an oxygen microenvironment resembling that found during normal fetal development. Oxygen transport is therefore a regulated variable in the graft neuropil as it is in the normally developing spinal cord. Furthermore, in the presence of closely approximated fetal transplants, adjacent host tissue assumes tissue oxygen levels that mimic those in the graft. This "inductive" effect gradually diminishes as development proceeds and may be the hallmark of successful graft-host integration.