Ultra structural evidence of axonal regeneration following intracranial transection of optic nerve.

OBJECTIVE: The present work was aimed at studying the ultra structural changes of the proximal (retinal) stump of the intracranially transected optic nerve of the rat for any possible regenerative ability.

METHODS: Specimens were collected one (1 wpo) and four weeks(4 wpo) after the transection and the cross sections of the stumps were studied by electron microscopy by dividing them into three zones, (1) the central zone, (2) the intermediate zone, and (3) the peripheral zone.

RESULTS: The present results showed evident morphological changes in these zones both in the 1 wpo and 4 wpo groups. The signs of degeneration were more marked in the central zone than in the peripheral zone and they were more prominent in the 1 wpo group than in the 4 wpo group. The most prominent sign of the degeneration was loss or lack of the healthy myelinated axons. The main evidence of the regenerative ability was the reappearance of the apparently healthy myelinated axonal profiles, with a parallel decrease of the non myelinated ones. This regenerative feature was more prominent peripherally and might be an indication that ischemia was the cause of optic nerve degeneration.

CONCLUSIONS: The present work revealed a clear morphological evidence of the regenerative capability of the intracranially transected optic nerve though it is considered as a part of the CNS.