The early evolution of neurofilamentous accumulations due to 2,5-hexanediol in the optic pathways of the rat.

Rats were given 2,5-hexanediol in their water for more than 5 weeks. The changes in the optic pathways were studied both qualitatively and quantitatively. Increase in 10-nm filaments within axons was noticeable from 10 days onwards in the superior colliculus and in the brachium of the superior colliculus. From then onwards there was a steady increase in the number of affected axons, and their gross enlargement occurred. The proportion of affected fibres in the brachia was in fact few, but all fibres were of retinotectal origin. Less than half of those in the superior colliculus that were swollen were of retinal origin. Measurement of axon diameter versus myelin sheath thickness showed gross relative thinning of the latter. Axon degeneration did not occur but there was increasing ultrastructural evidence of impairment of transport of organelles both centrifugally and centripetally as the filamentous masses accumulated.