Why do axons fail to regenerate in the spinal cord?
The axons have a poor regenerative response In order to produce regeneration in the spinal cord various problems have to be overcome. The first problem is that axons in the CNS simply do not try very hard to regenerate. There is an enormous difference between the vigour of regeneration between axons in the PNS and CNS, and between embryonic and regenerative growth. When a peripheral nerve is crushed anywhere along its length the axons rapidly make new growth cones, and the neurones quickly upregulate expression of genes, such as those for GAP-43 whose products are associated with and take part in the regenerative process.7,8 The result is rapid regeneration of the axons back to appropriate targets where they restore functional connections. Axons cut in the CNS do not respond in the same way. Where the CNS is lesioned only neurones whose axons have been cut within a few cell diameters of the cell body upregulate regeneration-associated genes, and similarly if a permissive environment su
