A re-assessment of long distance growth and connectivity of neural stem cells after severe spinal cord injury

• We confirm robust engraftment of neural stem cells at spinal cord injury sites.
• Two different grafting methods were used in the original study.
• Only one of two grafting methods led to filling of the lesion cavity.
• There was robust outgrowth of axons from grafts; ingrowth of host axons was limited.
• Neural stem cell grafts did not significantly enhance recovery of locomotor function.

As part of the NIH “Facilities of Research Excellence—Spinal Cord Injury” project to support independent replication, we repeated key parts of a study reporting robust engraftment of neural stem cells (NSCs) treated with growth factors after complete spinal cord transection in rats. Rats (n = 20) received complete transections at thoracic level 3 (T3) and 2 weeks later received NSC transplants in a fibrin matrix with a growth factor cocktail using 2 different transplantation methods (with and without removal of scar tissue). Control rats (n = 9) received transections only. Hindlimb locomotor function was assessed with the BBB scale. Nine weeks post injury, reticulospinal tract axons were traced in 6 rats by injecting BDA into the reticular formation. Transplants grew to fill the lesion cavity in most rats although grafts made with scar tissue removal had large central cavities. Grafts blended extensively with host tissue obliterating the astroglial boundary at the cut ends, but in most cases there was a well-defined partition within the graft that separated rostral and caudal parts of the graft. In some cases, the partition contained non-neuronal scar tissue. There was extensive outgrowth of GFP labeled axons from the graft, but there was minimal ingrowth of host axons into the graft revealed by tract tracing and immunocytochemistry for 5HT. There were no statistically significant differences between transplant and control groups in the degree of locomotor recovery. Our results confirm the previous report that NSC transplants can fill lesion cavities and robustly extend axons, but reveal that most grafts do not create a continuous bridge of neural tissue between rostral and caudal segments.