The impact of basic fibroblast growth factor on photoreceptor function andmorphology

PURPOSE. To assess the impact of basic fibroblast growth factor (bFGF) on p hotoreceptor function and morphology. METHODS. Impact was assessed in two models. In one, the endogenous expressi on of bFGF in photoreceptors was raised by sectioning one optic nerve of ra ts 3 to 4 weeks before study. In the other, bFGF was injected into the vitr eous chamber in rats and cats. Retinal function was assessed from the elect roretinogram (ERG), and retinal morphology was studied using DNA dyes, immu ne, labeling, and in situ hybridization. RESULTS. In both models of bFGF upregulation, the ERG b-wave was suppressed over a wide stimulus range and in light- and dark-adapted conditions, nle a-wave was not suppressed by either procedure and at the brightest intensit ies was enhanced by both procedures. In nerve-sectioned eyes, outer retina appeared normal histologically, but levels of bFGF protein in the inner:rnd outer nuclear layers were raised, whereas bFGF mRNA levels remained unchan ged. In both models, levels of synaptophysin in the outer plexiform layer a nd of cytochrome oxidase in inner segments were raised in association with increases in bFGF protein levels. CONCLUSIONS. bFGF increased the ability of photoreceptors to respond to lig ht but attenuated the transmission of this response to inner retinal cells, presumably by blocking the photoreceptor-bipolar synapse. If the expressio n of bFGF protein is upregulated in human photoreceptor dystrophies, it may contribute a reversible component to the loss of vision. The relationship, between these actions of bFGF and its ability to protect photoreceptors fr om stress remains to be established.