BASIC FIBROBLAST GROWTH-FACTOR, ITS HIGH-AFFINITY AND LOW-AFFINITY RECEPTORS, AND THEIR RELATIONSHIP TO FORM-DEPRIVATION MYOPIA IN THE CHICK

Form deprivation myopia in chickens is a widely accepted model to stud y visually-regulated postnatal ocular growth. Recently we showed that basic fibroblast growth factor-2 provides a ''stop'' signal for the gr owing eye. To understand further its action, we have localized basic f ibroblast growth factor-2 and its low- and high-affinity receptors in the chicken eye, and determined the localization of basic fibroblast g rowth factor receptors in the inner plexiform layer with respect to th at of neurotransmitter systems known to play a role in form-deprivatio n myopia. By immunocytochemistry and in situ hybridization, two comple mentary methods, we found that nearly all cells in the retina, and scl eral chondrocytes, contain basic fibroblast growth factor-2 protein an d messenger RNA as well as high-affinity basic fibroblast growth facto r receptor protein and messenger RNA. Immunocytochemical localization of basic fibroblast growth factor-2 binding sites (a high resolution a lternative to autoradiography), combined with N-glycanase and hepariti nase treatment or heparin competition, revealed additional binding sit es in specific synaptic layers of the inner plexiform layer and low-af finity binding sites in the choroid and optic fibre layer. Some bindin g sites in the synaptic layers were found to co-stratify with neurites of dopamine-, vasoactive intestinal polypeptide- or enkephalin-contai ning amacrine cells, suggesting that basic fibroblast growth factor-2 could modulate synaptic transmission to or from these cells. Form depr ivation did not affect the levels of basic fibroblast growth factor re ceptor-1 messenger RNA in retina/retinal pigment epithelium/choroid (N orthern blotting), but it abolished the decrease in amount of extracta ble basic fibroblast growth factor normally observed in the dark (West ern blotting). The results are discussed with respect to previous find ings on basic fibroblast growth factor-2 and basic fibroblast growth f actor receptor-1 localization in the avian and other vertebrate eyes, and their relevance to form-deprivation myopia. The widespread distrib ution of basic fibroblast growth factor-2 and its receptor makes it im possible to predict which cells might mediate the action of basic fibr oblast growth factor-2 in form-deprivation myopia. However, the altera tion in amounts of extractable retinal basic fibroblast growth factor- 2 in form-deprived, dark-adapted retinas, in which basic fibroblast gr owth factor-2 probably serves as a ''stop'' signal for ocular growth, is consistent with a role for basic fibroblast growth factor-2 in the regulation of ocular growth. (C) 1997 IBRO. Published by Elsevier Scie nce Ltd.