Cytologic changes of the retina and pigment epithelium during hibernation

The pigment epithelium and the retina of hibernating frogs, bats, and ground squirrels are studied electron microscopically and the findings are compared with those of the same animals obtained in normal condition. The smooth endoplasmic reticulum of the pigment epithelial cell becomes sparse and transforms into large tubular structures during the hibernation. No appreciable changes are noted in the rod outer segments of hibernating bats and frogs. However, the cone outer segments of the ground squirrel show striking disappearance during experimental hibernation. Regeneration of the cone outer segments of the squirrel retina is found to be fast when the animals are placed in a normal environment.