Peripheral nerve regeneration through grafts of living and freeze-dried CNS tissue

The ability of peripheral nerve fibres to regenerate through the central nervous system (CNS) extracellular matrix in the presence of CNS myelin debris was examined using living and freeze-dried optic nerve grafts. The grafts were placed end-to-end with the proximal stumps of severed common peroneal nerves of inbred mice. Within a 4 week period, regenerating peripheral nervous system fibres were found in only two of 14 living grafts. However axons always grew into freeze-dried grafts within one week, despite the presence of CNS myelin debris. The regenerating axons in freeze-dried grafts were accompanied by Schwann cells and were initially found associated with the inner aspect of the glial basal lamina. Although the extracellular matrix of the freeze-dried CNS tissue was subsequently reorganized by invading cells, it seems likely that neither the nature of the CNS extracellular matrix nor the presence of CNS myelin debris had a major inhibitory influence on peripheral nerve regeneration. It is suggested that the presence of living astrocytes covered by a basal lamina at the proximal end of the living optic nerve grafts may inhibit their penetration by regenerating axons.