Effects of chronic demyelination on axonal transport in experimental allergic optic neuritis

Axonal transport studies were undertaken to determine the effect of chronic demyelination on axonal function in experimental allergic optic neuritis in the guinea pig, an animal model for multiple sclerosis. Fast and slow components of axonal transport over the prelaminar, laminar, and retrolaminar portions of the optic nerve head and at the foci of demyelination in the retrobulbar optic nerve were evaluated by the autoradiographic grain-counting technique. At 6 hr there was a significant increase in grain counts over the demyelinated foci and in the regions proximal to the demyelination, including the swollen disc. At day 1 there was no significant difference in the grain counts at the site of demyelination when compared to the myelinated portion of the nerve. However, at days 3 and 7 there was a decrease in the number of grains over the demyelinated areas. These results indicate impairment of axonal function in chronic demyelination. Moreover, in this pathologic process, most of the synthesized materials appear to move in the fast transport phase, unlike in the normal optic nerve where the bulk of materials move by slow transport.