THE EFFECT OF A CHRONIC BREAKDOWN OF THE BLOOD OPTIC-NERVE BARRIER ONTHE SEVERED OPTIC-NERVE IN ADULT-RAT

The changes brought about in the severed optic nerve of an adult rat w hen the blood-optic nerve barrier was chronically broken down by the l ocal application of a solution of mannitol is described. Axonal labell ing indicated that axons did not regenerate across the lesion site, re futing the suggestion that breakdown of the blood-optic nerve barrier can stimulate axonal regeneration. However, we observed that blood ves sels were dilated and, between the eye and lesion site, provided a sub strate for regenerating axonal sprouts. We suggest that blood-borne ag ents may directly or indirectly influence the navigation of the growth cones of regrowing axons.