The structure and development of the rat retina: an immunofluorescence microscopical study using antibodies specific for intermediate filament proteins.

Rat retina structure was studied between embryonic day 14 and adult with antibodies specific for vimentin, glial fibrillary acidic protein (GFA) and the proteins of the neurofilament triplet. Vimentin could be detected in radial processes throughout the retina at all stages studied. These processes are believed to correspond, in the developing retina, to ventriculocytes, and in the mature retina to Müller cells. They could not normally be stained with any of the other intermediate filament antibodies employed here. We did find, however, that some older albino rats possessed GFA staining in addition to vimentin in these processes. Since we never saw such staining in the retinae of mature non-albino rats, and the retinae of older albino rats often showed signs of degeneration, we concluded that such GFA expression was most likely pathological. Neurofilament protein-positive processes were first detectable at embryonic day 15 1/2 in the inner regions of the retina, and corresponded to the axons of retinal ganglion cells. Such processes were equivalently displayed with antibodies to 68 K and 145 K protein, but were negative with 200 K protein. Some 68 K and 145 K positive fibers could also be decorated with vimentin antibody at this stage, though at later stages this was not the case. At later development stages more 68 K and 145 K neurofilament positive processes appeared, and after the first post-natal week progressively more of such processes became in addition 200 K positive, so that almost all neurofilament positive fibers in the adult stained for all three proteins. Such fibers, in the mature retina corresponded to 68 K and 145 K positive optic nerve fibers, and the processes of neurones in the inner plexiform layer. All fibers in the mature optic nerve fiber layer, but not all of those in the inner plexiform layer were stainable with 200 K antibodies. At 4 days post-natal we were able to detect 68 K and 145 K protein positive profiles in the outer regions of the developing retina, the prospective outer plexiform layer. Such profiles were always in addition vimentin positive, but negative for 200 K protein. During further development such profiles became ordered into a well defined layer and from about post-natal day 13 all of them began to acquire 200 K protein. They could be identified as the processes of horizontal cells. They continued to express vimentin in addition to the three triplet proteins in the adult, a so far unprecedented situation. We were able to detect neurofilament staining in the mature retina only in the above described regions, the inner and outer nuclear layer and the photoreceptor processes being completely free of staining. GFA was first detected in short processes adjacent to the inner limiting membrane which penetrated the optic nerve fiber layer. Such profiles were first detectable in the eye of the newborn animal, and were invariably identically stainable with vimentin at this age. These profiles could be stained with both vimentin and GFA at all later stages examined, although GFA staining became very much stronger than vimentin staining in some profiles in the adult. The results presented here are discussed in terms of development of the different retinal cell types.