Altered structure and composition of retinal cells in dark-reared mammals

Abstract

Retinas of cats, hooded rats, and chimpanzees reared in total darkness from birth were compared with those from controls matched for age and reared in light with normal day and night variation. Microphotometric measurement of azure B binding was used to estimate ribonucleic acid (RNA) concentration in individual ganglion cells. Relative protein levels were judged visually after staining with fast green or the Millon reaction. There was a marked lowering of cytoplasmic and nucleolar RNA levels in neurons from the multipolar, bipolar, and receptor cell layers of retinas from dark-reared cats. Protein levels were also appreciably lowered in these subjects, and a significant reduction of mean nucleolar volume and in cytoplasmic cross-sectional area of ganglion cells was found. The inner plexiform layer was consistently thinner in retinas from cats reared in darkness, although there were no apparent differences in thickness of cell body layers, nor in frequencies of the several cell types within any one particular layer. Comparable but less extensive data are presented for hooded rats. Markedly depressed RNA and protein levels were also found in retinal ganglion cells of two dark-reared chimpanzees, associated with degeneration of the ganglion cell layer. The data suggest that adequate light stimulation is a major variable controlling the development of normal ribonucleoprotein levels in cells of the mammalian retina.