Acidic fibroblast growth factor enhances regeneration of processes by postnatal mammalian retinal ganglion cells in culture
Calcitonin Gene-Related Peptide
Postnatal rat retinal ganglion cells (RGCs) were identified with specific fluorescent labels and placed in culture. Under these conditions, the outgrowth of processes by RGCs was found to be promoted to a far greater degree by acidic fibroblast growth factor (aFGF) than by basic fibroblast growth factor (bFGF). The effect of aFGF and bFGF on process extension by solitary RGCs was quantified after 24 hr in culture, a time when neither a FGF nor bFGF enhanced RGC survival. The action of aFGF on process outgrowth was markedly potentiated by the addition of heparin (10 micrograms/ml) to the medium, but heparin alone had no effect. In the presence of heparin, half-maximal process outgrowth occurred at an aFGF concentration of less than 20 pg/ml (1 pM). Since all of the centrally projecting processes have already been formed in the living animal prior to use (at 7-12 days of age), at least a portion of the process outgrowth in culture appears to represent a regenerative phenomenon. Statistical analysis of the increase in process growth revealed that aFGF with heparin contributed to both neurite initiation and elongation. The mean number of glial cells, identified with polyclonal antiserum against glial fibrillary acidic protein, was slightly increased in cultures receiving aFGF plus heparin, but this effect was variable, and these glial cells were not in contact with the solitary RGCs that were scored for regeneration of processes. Thus, glial cells probably did not exert a direct physical influence on the degree of process outgrowth observed in the solitary RGCs, although a humoral effect cannot be totally excluded. These results suggest that aFGF has a potent influence on the outgrowth of processes by a neuron in the mammalian central nervous system. The potentiation of this effect by heparin leads us to speculate that the interaction of aFGF with a heparin-like molecule located in the extracellular matrix (such as heparan sulfate proteoglycan) may produce physiological effects in vivo. Furthermore, the lack of a substantial effect of bFGF in this system under these conditions shows that a specific population of mammalian central neurons may be differentially influenced by these two closely related peptide growth factors.