Enhanced axonal regeneration following combined demyelination plus Schwanncell transplantation therapy in the injured adult spinal cord

We have treated spinal cord injured rats with demyelination plus Schwann ce ll transplantation and assessed neurite outgrowth in a quantifiable model o f axonal regeneration. Axonal injuries of differing severity were induced i n the dorsal funiculus of adult rats using a micromanipulator-controlled Sc outen knife. Demyelinated regions were produced so as to overlap with the i njury site by the injection of galactocerebroside antibodies plus complemen t one segment cranial to the axonal injury site. Schwann cells were isolate d from the sciatic nerve, expanded in vitro, and transplanted into the inju ry site 1 day later. Animals were killed after an additional 7 days. Schwan n cells were evenly distributed throughout the region of demyelination, whi ch extended 6-7 mm cranial to the axonal injury site. The severity of axona l injury was quantified by counting degenerate axons in transverse resin se ctions, The degree of axonal regeneration was assessed by an electron micro scopic analysis of growth cone frequency and distribution relative to the s ite of axonal injury. Quantification of growth cones at a distance from the site of axonal injury indicated a strong Linear relationship (P < 0.001) b etween the number of growth cones and the number of severed axons; the rati o of growth cones to severed axons was increased by 26.5% in demyelinated p lus transplanted animals compared to demyelinated animals without a transpl ant. Furthermore, only the demyelinated plus transplanted animals contained growth cones associated with myelin in white matter immediately outside of the region of complete demyelination. Growth cones were absent in transpla nted-only animals at a distance fr the site of axonal injury. These finding s indicate that combined demyelination plus Schwann cell transplantation th erapy enhances axonal regeneration following injury and suggests that growt h cones are able to overcome myelin-associated inhibitors of neurite outgro wth in the presence of trophic support. (C) 1999 Academic Press.