Cellular changes during repair of a cryogenic spinal cord injury in the rat: an electron microscopic study

Cryogenic injury of adult, rat spinal cord was produced under controlled non-invasive conditions to study repair and regeneration in adult, mammalian central nervous tissue in which tissue continuity and integrity are relatively preserved. Under these experimental conditions axons and myelin are destroyed, a matrix of glial cells is preserved, and regrowth of axons is apparent. Electron microscopic studies at 7, 15, 30 and 60 days post-injury demonstrate axonal structures indicative of regrowth, astrocytic structures which appear to provide support to both matrix and axons and myelination of axons by both oligodendrocytes and Schwann cells. These cellular events restore much of the normal structure within the injured area up to its junction with the Wallerian zone. In this junctional zone morphologic evidence may indicate continuing cellular activity, even at 60 days, in axons, astrocytes and myelinating cells. These studies suggest that under ideal conditions damaged axons may be capable of regeneration within the adult mammalian central nervous system and that this model provides an opportunity to define some of the mechanisms.