The interphotoreceptor matrix in rats with inherited retinal dystrophy.

The retinas of Royal College of Surgeons (RCS) rats with inherited retinal dystrophy and of genetic control RCS-rdy+ rats have been examined histochemically to determine whether the stainable interphotoreceptor matrix (IPM) is abnormal in dystrophic retinas. The mucosubstances that are stained with Alcian blue, Metachromatically stained with toluidine blue, or reacted with colloidal iron appear in normal retinas beginning on postnatal day 12 as an intense band of stain at the apical surface of the pigment epithelium and with less intense staining between the outer segments throughout the rest of the outer segment zone. In RCS retinas the distribution of stainable IPM differs from that in normal retinas beginning on day 12. At this time, there is a failure of the intense band of IPM staining to form completely at the apical surface of the pigment epithelium. As whorls of outer segment membranes accumulate due to the phagocytosis defect in RCS pigment epithelial cells, IPM staining almost disappears along the pigment epithelial cell surface and in the debris zone. In addition, the basal outer segment region stains much more heavily in RCS retinas than in normal retinas, a feature that presumably represents an abnormal accumulation of IPM in this region of mutant retinas. Since the abnormal distribution of stainable IPM is evident 6 to 8 days before the first pyknotic photoreceptor cell nuclei are seen, it may play a role in photoreceptor cell death in the RCS rat. Furthermore, since the difference in IPM distribution between mutant and normal retinas is first evident on the same day that disc shedding and phagocytosis begin in the normally developing retina, the abnormal IPM distribution in RCS rats may also be related to the phagocytosis defect in the mutant pigment epithelial cells.