Immunohistochemical localization of basic fibroblast growth factor in mature and developing retinas of normal and RCS rats.

Basic fibroblast growth factor (bFGF) delays photoreceptor degeneration when injected intraocularly in Royal College of Surgeons (RCS) rats with inherited retinal dystrophy. In the present study, we have determined the localization of endogenous bFGF in retinas of normal and RCS rats during the normal developmental period (postnatal days 0-20) and the period of photoreceptor degeneration in RCS rats (days 20-90). bFGF was localized immunohistochemically by indirect immunoperoxidase using two different polyclonal antibodies and one monoclonal antibody against bFGF. bFGF was present in retinas as early as birth, and remained through adult age. Controls using either PBS, non-immune IgG or antibody preabsorbed with bFGF peptide were devoid of label. In normal rats between the ages of birth and postnatal day (P) 4, bFGF was found in developing ganglion cells, superficial blood vessels, some of the innermost cells in the neuroblastic layer, developing horizontal cells, and retinal pigment epithelial (RPE) cells. Between P0 and P4, the intensity of staining increased significantly in horizontal cells. From P6-P10, some cells in the inner nuclear layer remained positive, but horizontal cell staining became less intense in the central retina. The superficial vessels, ganglion cells and RPE cells also remained positive for bFGF. At P20-25, when the retina was essentially mature, bFGF was found in RPE cells, most cells of the ganglion cell layer, and many cells of the inner nuclear layer, but horizontal cells and blood vessels showed a lower concentration of bFGF than they did at younger ages. At P45 and older, blood vessels no longer showed bFGF immunoreactivity. The staining pattern in RCS rats was indistinguishable from that for normal rats at all ages examined. These results show that bFGF is present in the developing and adult rat retina in some neural cells, in addition to vessels and RPE cells. The transient elevated expression of bFGF immunoreactivity in developing horizontal cells and blood vessels suggests a possible role for this growth factor in retinal development. In addition, if RCS retinas possess any difference in bFGF localization or concentration compared to normal retinas, it must be too small to detect by immunohistochemical means, or at least with the reagents used.