Penetration of protein tracers into the epiretinal portion of the optic nerve in the rabbit nerve.

Horseradish peroxidase and fluorescein-labelled globulin were injected into the vitreous of adult and 11- to 13-day-old New Zealand albino rabbits. Both tracers diffused rapidly into the myelinated nerve fibre layer (the "medullary rays"), which extends over a long distance within the retina in these animals. The tracers penetrated also for some distance into the optic nerve beyond the lamina cribosa, where they were incorporated into a large number of cells in the nerve. This finding of a rapid diffusion of macromolecules into the medullary rays after intravitreal injection makes this experimental model suitable for the study of factors interfering with myelin or myelination.