'Printed in Great Britain INFLUENCES OF THE GLIAL ENVIRONMENT ON THE ELONGATION OF AXONS AFTER INJURY: TRANSPLANTATION STUDIES IN ADULT RODENTS

Tissue transplantation methods, previously used to study neural develop-ment, myelination and inherited disorders of myelin can be applied also to the investigation of repair and regeneration in the mammalian CNS. The elon-gation of axons from injured peripheral nerve or CNS has been studied in adult mice and rats by observing the growth of axons into PNS or CNS tissue grafts. Following spinal cord injury and also after transplantation of optic nerves into the PNS there is axonal sprouting but these neuronal processes fail to elongate more than a few mm into the surrounding glia. On the other hand if segments of a peripheral nerve are grafted into the transected spinal cord, axons arising from spinal neurons and dorsal root ganglia become associated with the transplanted Schwann cells and elongate along the graft, approxi-mately 1 cm. Recently the elongation of axons from spinal and medullary neurones was studied using a new experimental model which employed PNS grafts as ' bridges ' to connect the spinal cord and the brain stem. In a serie