Pathological changes in the optic chiasm of the cat following local injection of diphtheria toxin.

The optic chiasm in 14 cats was injected stereotactically with small amounts of diphtheria toxin and the morphological changes were examined by light and electron microscopy. Phagocytosis was already well-marked at 3 hr after injection and massive at 1 week. Intercellular oedema was extensive in the first week and, though diminished, was still present after 1 month. The oedema was most marked in the subendothelial regions in the early stages but was found among the nerve fibres and glial processes in those animals which survived for longer periods. Demyelination and Wallerian-type degeneration were established at 3 hr after injection and both processes continued up to 2 months and beyond. Scarring and an absolute loss of nerve fibres were present in the longer-surviving animals. Unequivocal evidence of remyelination was not obtained.