Fibroblast growth factor and its implications for developing and regenerating neurons.

FGF is a multifunctional heparin-binding protein which was characterized by its mitogenic and angiogenic action outside the nervous system. Recent data confirm this multifunctionality also with regard to the nervous system. The distribution of FGF and its receptors seems not to be in agreement with the idea of a single function for one population but argues for a more complex action, which might be dependent on the development stage and cell type. FGF and its receptors are widely distributed in the nervous system. In brainstem and spinal cord motoneurons and in sensory ganglia the FGF-2 staining pattern is developmentally regulated suggesting a functional change during embryonic and postnatal development. In addition, after nerve lesion the FGF-2 expression is altered in sensory and motoneurons. Administration of FGF-2 reveals trophic effects on survival and transmitter metabolism in vivo and in vitro. According to a more general neurotrophic factor concept, a physiological role of FGF for distinct neuron populations during development is likely. In the motor system, for example, FGF could act synergistically with certain neurotrophins, CNTF, or other non-identified co-factors. In the sensory system, a possible non-neurotrophic role for at least postnatal and adult sensory neurons has to be further addressed in the future. In order to further define and characterize the actions of the FGFs a mapping of the different family members and their respective receptor molecules during development and in the adult has to be done.