Immunocytochemical localization of interphotoreceptor retinoid-binding protein in developing normal and RCS rat retinas.

Interphotoreceptor retinoid-binding protein (IRBP) was localized immunocytochemically in developing normal and RCS rat retinas. IRBP was present in normal and RCS neural retinas on the day after birth (postnatal day 2, P2) to P8 in the space between the neuroblastic layer and the retinal pigment epithelium (RPE). The presence of IRBP prior to the development of outer segments (OS) suggests that OS formation is not linked temporally with IRBP secretion. On P10, staining was confined to the interphotoreceptor space with an intense band of label adjacent to the RPE. This staining pattern persisted in normal rats throughout development and until P18 in RCS rats. On P18, anti-IRBP staining in the RCS was spread evenly throughout the OS layer with no intense band of label adjacent to the RPE and after P18, there was decreased staining with anti-IRBP. On P45 and later, no staining of the RCS retina was found with anti-IRBP. Immunoblots of normal and RCS retinas corroborated the results from immunocytochemical staining. These findings suggest that IRBP may be synthesized in the photoreceptors, but is not abnormal in amount or distribution prior to onset of retinal degeneration in the RCS rat.