Optic disc and optic nerve of the blind cape mole-rat (Georychus capensis): a proposed model for naturally occurring reactive gliosis.

Recent studies of the visual system of animal species that live in a subterranean environment show not only regressive but also progressive morphological features. In this regard the aim of the present investigation is to describe the structural organisation of the eye and optic nerve of the adult Cape mole-rat, with special emphasis on both glial cell population and myelination. The main results are: (a) astrocytes show identical features to those occurring in reactive gliosis; (b) optic fibers vary greatly in diameter; (c) very small axons are myelinated and are often surrounded by a thicker sheath than larger optic fibers; (d) a large onion bulb-like structure composed of optic fibers, glia, and ganglion cells is found within the choriocapillary layer. These results suggest that the Cape mole-rat and probably other subterranean rodents may serve as a model to study spontaneous gliosis as well as mechanisms involved in myelination and degenerative processes.