Glial outgrowth and central-type myelination of regenerating axons in spinal nerve roots following transection and suture: light and electron microscopic study in the pig.

Glial bundles growing out of the spinal cord were observed in spinal nerve roots in the pig after their section and surgical repair. The heterotopic occurrence of glial cells, most of which were identified as astrocytes, was more frequent and more pronounced in dorsal than in ventral roots. Several of the glial bundles contained regenerated myelinated axons. These were probably myelinated by cells which showed the typical cytological criteria for oligodendrocytes and the mode of myelination was clearly of central type. It was concluded that the glial outgrowth is induced by degeneration and regeneration of axons passing the central-peripheral transition zone.