UC San Diego

While spinal cord injury (SCI) affects as many as 1 in every 250 people in the US, there are currently no clinically available therapies capable of improving functional recovery. SCI Patients experience debilitating paralysis, increased pain, and decreased quality of life. As such developing an effective therapeutic technique is vital. One recent therapeutic advance utilizes stem cell transplantation as a means to relay information across a spinal cord lesion. Embryonic day 14 (E14) spinal cord cells, constitutively expressing enhanced green fluorescent protein (EGFP), grafted into adult rat spinal- lesions; differentiate into neurons, grow long distances, become myelinated, and create functional neural relays. 3 months after E-14 hemisection grafts, GFP stained spinal cord cross sections caudal to the lesion, were viewed using transmission electron microscopy (TEM), in order better characterize the graft derived axons in the host spinal cord. In total 104 Graft derived axons were examined. Axon diameter ranged from 0.15 um to 1.7 um. It was found that 23% of graft-derived axons were myelinated by host Oligodendrocytes. The average diameter of myelinated axons was significantly larger than that of non -myelinated axons (p<0.05). Interestingly the G-ratio of myelinated axons was equal to that of developmentally myelinated axons, potentially overturning previous notions (0.766 [mu]m ± 0.045 [mu]m). Finally it was established that 2/3rds of graft-derived axons came into direct physical contact with host myelin, laying credence to the possibility that myelin may be a growth permissive substrate for early stage neurons