Glial cells in degenerating and regenerating optic nerve of the adult rat

The glial cell reaction both in degenerating and regenerating adult rat opt ic nerve was studied by immunohistochemistry and electron microscopy. Degen eration in the optic nerve was achieved by complete transection, and the re tinal stump was then analyzed. The regeneration was observed by autotranspl antation of a sciatic nerve segment to the transected retinal stump. In bot h cases, optic nerve axons were labeled anterogradely with rhodamine, follo wed by immunohistochemical staining. Glial fibrillary acidic protein-positi ve astrocytes covered the transected end of degenerating optic nerve, where as in the regenerating optic nerve they enwrapped axonal bundles emerging f rom the optic nerve stump and migrated together into the transitional zone intervening between the retinal stump and graft. In electron microscopy, di rect attachment of astrocyte and Schwann cell was found within the transiti onal zone, whereby these cells were holding axone between them. Decrease of 04 immunoreactivity, which labels oligodendrocytes, was apparent in the tr ansected end of retinal stump during the regeneration. The ED1-positivity, which labels microglia/macrophages, was found in cells accumulated in the t ransitional zone of degenerating optic nerve, whereas during regeneration, ED1-immunoreactive cells were also distributed in the retinal stump. These results suggest that astrocytes, usually considered to interfere with optic nerve regeneration, change their characteristics in the presence of periph eral nerve graft and guide the regenerating axons in cooperation with Schwa nn cells. The response of oligodendrocytes and microglia/macrophages may al so be modulated by peripheral nerve. (C) 1999 Elsevier Science Inc.