Light- and electron-microscopic localization of basic fibroblast growth factor in adult rat retina

An antiserum against basic fibroblast growth factor (bFGF) was characterized by immunoblot and used to localize bFGF-immunoreactivity in the adult rat retina. Crude homogenate of the retina, when examined with immunoblotting, exhibited a main band with the same molecular weight (18kDa) as bFGF. Light microscopic immunohistochemistry demonstrated intense bFGF staining in the photoreceptor outer segments and the outer plexiform layer, and weak immunostaining in some cells of the outer nuclear layer, inner nuclear layer and ganglion cell layer. The most intense bFGF-immunoreactivity was noted in glial (Müller) cells with vertically oriented thin processes. There were also immunoreactive pigment epithelial cells and mesenchymal cells in the choroid. Under electron microscopy, the outer plexiform layer was found to contain immunoreactive products exclusively in the axon terminals of photoreceptor cells which formed synapses with bipolar cell processes. The more widespread and uneven localization of bFGF-immunoreactivity in the mature rat retina than previously demonstrated suggests that endogenous bFGF is involved in complex physiological events other than retinal regeneration and histogenesis.