Schwann Cells as Facilitators of Axonal Regeneration in CNS Fiber Tracts

Abstract

Studies of human spinal cord injury by Richard Bunge and colleagues in The Miami Project to Cure Paralysis emphasize that, in most cases, gray matter loss is localized to one or only a few segments. Despite the limited loss of spinal cord neurons in those cases in which damage is localized linearly, extensive injury across the diameter of the cord abolishes much of the signalling required for motor functioning below the level of injury. In 35% of the 46 injured human cords studied to date, injury extends across the entire width of the cord (Bunge et al., 1993, 1996). Thus, the most debilitating aspect of these injuries derives from interruption of nerve fibers in the long ascending and descending tracts in the white matter, rather than from damage to the neuronal population. We, therefore, have attempted to create bridges for nerve fiber regrowth across areas of spinal cord injury to re-establish the requisite signalling. It is now well known that after injury the central neuron is able to regenerate its axon if the local environment is suitable. Requirements include an appropriate substratum for growth, sufficient quantities of specific neurotrophic factors, and the absence of neurite growth inhibitors such as myelin- and astrocyte-related proteins.