The effects of 2,5-hexanedione on the retina of albino rats.

Male Sprague-Dawley rats received 1% 2,5-hexanedione in their drinking water for a period of 5 weeks. The rats were by this time paralyzed in the hind limbs. Half of the rats were then sacrificed while the remaining rats were allowed to recover for 13 weeks. A control group of rats were housed and fed under identical conditions and were studied in parallel. The axonal changes in the optic pathways and the abnormalities of the retina were examined histologically in all groups including immuno-peroxidase staining with antibodies for neurofilament proteins. The retinas of the rats sacrificed immediately following treatment showed a reduction of the outer nuclear layer and the outer and inner segments of the rods and cones as compared with the controls (p less than or equal to 0.01). The rats permitted recovery for 13 weeks and then sacrificed had lost almost completely their rods and cones (p less than or equal to 0.001). Some of the rats had a small residue of the rods and cones at the Ora Serrata. No decrease in the thickness of any other retinal layer was seen. Swellings of the axons in the optic pathways and of the axons innervating the iris were discerned in the treated rats. There was no evidence of an inflammatory response in the retina to the cell loss at any time. Whether this lethal damage to the rods and cones is caused by the 2,5-hexanedione alone or in combination with light energy remains to be elucidated.