Basic fibroblast growth factor applied to the optic nerve after injury increases long-term cell survival in the frog retina

Abstract

The neuroprotective effects of basic fibroblast growth factor (bFGF) on the long-term survival of axotomized retinal ganglion cells (RGCs) were studied in the frog Rana pipiens. Cell loss was quantified in different regions of the ganglion cell layer using Nissl staining and tetramethylrhodamine dextran amine backfilling. All regions of the retina showed a significant decrease (32-66%) in RGC numbers between 4 and 16 weeks after axotomy. Some cells showed morphological and biochemical signs of apoptosis. A single application of bFGF to the optic nerve stump at the time of axotomy protected many of the cells 6 weeks after the injury, but this effect was lost by 12 weeks. A second application of bFGF, 6 weeks after the injury, rescued many RGCs at 12 weeks. In contrast, single or double injections of bFGF into the eyeball had no effect on RGC survival. Axotomized RGCs were significantly enlarged and elongated after axotomy, and these morphological changes were increased by bFGF treatment. In the normal retina and optic nerve, immunocytochemical staining showed bFGF-like immunoreactivity (-LI) in the pigment epithelial layer, in the outer segments of photoreceptors, and in occasional RGCs. Strong bFGF-LI was present in Müller cells and in optic nerve astrocytes and oligodendrocytes. FGF receptor-LI was present in photoreceptors, outer plexiform layer, retinal ganglion cell axons, and Müller cells. FGF receptor-LI was also observed in optic nerve glia.