Purpose: To determine the temporal and spatial pattern of rod opsin appearance in Macaca monkey retina.
Methods: Frozen sections from fetal day (Fd) 55 to adulthood (birth = Fd168) containing the entire horizontal meridian were stained using Rho4D2 monoclonal antiserum visualized with immunofluorescent labeling. At Fd66, Fd79, and Fd89, retinal samples taken at known eccentricities were studied from the opposite eye using standard electron microscope methods.
Results: Rod opsin was detected at Fd66 in or near the fovea, and a second focus appeared at Fd75 to Fd77 near the optic disc in the nasal rod ring. The earliest opsin appeared in the apical stubs, which resembled the apical connecting cilium in the electron microscope. Staining of the entire cell body membrane, including the synaptic spherule, was present 4 to 7 days later. Opsin expression had a nasal bias with rods at the nasal ora labeled at Fd140, whereas temporal ora was not labeled until Fd155. Cell body labeling disappeared by Fd132 across central retina but persisted into the first postnatal year in far peripheral retina. Outer segment (OS) length measurements showed that rods in the rod ring had the longest OS between Fd115 and postnatal week 9. Rod OS at all retinal eccentricites continued to elongate between 11 months of age and adulthood.
Conclusions: Rod opsin expression follows a foveal-to-peripheral gradient beginning at Fd66 and ending near birth. Rod opsin is detected first in the connecting cilium and slightly later in the entire cell membrane, and then cell membrane labeling disappears as the heavily labeled OS elongates. Although the first OS appear on rods near the fovea, these OS still are short at birth and do not reach adult length until after 2 years of age. The longest OS at birth are found on rods at the rod ring, suggesting that this region could have higher scotopic sensitivity than central retina at birth.