Response of axons and glia at the site of anastomosis between the optic nerve and cellular or acellular sciatic nerve grafts.

Axonal and glial reactions at the site of optic nerve section and at the junctional zone between optic nerve and normal or acellular peripheral nerve grafts have been studied. Following optic nerve section, no axons grew into the distal optic nerve stump. Similarly, no axons invaded the acellular peripheral nerve grafts, although in both instances fibres did regenerate into the junctional zone and a few remained there at least until 30 days post lesion (dpl, the duration of the experiments). Axons regenerated into normal peripheral nerve grafts by 3-5 dpl and by 10 dpl large numbers had penetrated deeply into the grafts. The glial response to injury appeared similar in both groups of grafted animals. Astrocytes and oligodendrocytes grew out into the junctional zone over the 5-7 day period and invaded the margins of the cellular grafts by 10 dpl. They did not penetrate the acellular nerves or distal optic nerve stumps. We were unable to determine whether Schwann cells invaded the junctional zone from the normal peripheral nerve grafts. Schwann cells are both GFAP+ and Vim+, especially when reacting after injury, and Lam- when not associated with axons: it is therefore possible that Schwann cells from the cellular grafts contributed to the population of GFAP+, Vim+ cells in the junctional zone of the cellular grafts. Anti-laminin immunoreactivity persisted in the basal lamina tubes of both the normal and acellular peripheral nerve grafts. Thus, the failure of axon regeneration into acellular peripheral nerve grafts can be correlated with the absence of Schwann cells and does not appear to be related to the presence of laminin.