Each year in the U.S. there are an estimated 10,000 new spinal cord injury (SCI) cases, and there are an estimated 200,000 patients living with chronic SCI. SCI destroys neuronal connectivity by severing descending motor and ascending sensory pathways. Such damage results in permanent paralysis and loss of sensation below the level of injury. Cavitation or formation of a gap inevitably occurs due to secondary injury events. A bridging strategy using Schwann cell (SC)-seeded guidance channels can effectively promote regeneration of injured axons across the lesion gap. Additional treatments aiming at overcoming formidable barriers at the distal graft-host interface can further axonal growth. The goal of this investigation is to 1) improve axonal ingrowth into the bridge environment by adding glial cell line-derived trophic factor (GDNF) into SC-grafts, 2) promote significant axonal outgrowth and synaptic reconnection in the distal spinal cord and 3) define mechanisms by which GDNF promotes regeneration of injured axons. To accomplish this, a rat model of spinal cord hemisection and SC-seeded minichannel implantation will be used to establish that GDNF promotes substantial axonal regeneration across the SC-seeded bridge, re-entry into the distal host spinal cord, and reconnection with target neurons. The mechanisms underlying the action of GDNF will also be addressed. Experimental methods and techniques to be used include cell culture, animal microsurgery, immunohistochemistry, light and electron microscopy, confocal microscopy, anterograde and retrograde tracing, immunoelectron microscopy, and Western blotting.
