Partial Recovery of Proprioception in Rats with Dorsal Root Injury after Human Olfactory Bulb Cell Transplantation

Transplanted human olfactory ensheathing cells (hOECs) were mixed with collagen into a unilateral transection of four dorsal roots (C6-T1) in a rat model. By mixing with collagen, the limited numbers of hOEC were maximized from an olfactory bulb biopsy and optimize cavity filling. Cyclosporine was administered daily to prevent immune rejection. Forelimb proprioception was assessed weekly in a vertical climb task. Half of the rats receiving hOEC transplants showed some functional improvement ("responders") over six weeks of the study while the other half did not ("nonresponders") and performed similarly to "injured only" rats. Transplanted cells were seen at both one week and six weeks after the surgical procedure; many were concentrated within the lesion cavity, but others were found with elongated processes in the overlying connective tissue. There were some fibers in the injury area associated with transplanted cells that were immunostained for neurofilament and TUJ1. Responder and nonresponder rats were compared with regard to microglial activation within the deep dorsal horn of cervical levels C7, C8 and also axon loss within the cuneate fasciculus at cervical level C3. Little difference was seen in microglial activation or axonal loss that could account for the improved proprioception in the responders group. This preliminary study is the first to transplant human olfactory bulb cells into a rat model of dorsal root injury; by refining each component part of the procedure, the repair potential of OECs can be maximized in a clinical setting.