Fibroblast growth factor-5 promotes differentiation of cultured rat septal cholinergic and raphe serotonergic neurons: comparison with the effects of neurotrophins.

Fibroblast growth factor-5 (FGF-5) is a member of the fibroblast growth factor gene family, which has a signal sequence characteristic of secretory proteins. FGF-5 mRNA has previously been shown to be present in the adult mouse brain. Here we demonstrate that recombinant FGF-5 has neurotrophic activity on cultured rat septal cholinergic and raphe serotonergic neurons. The effect of FGF-5 on serotonin uptake was stronger than that evoked with either brain-derived neurotrophic factor or neurotrophin-3. FGF-5 also increased the choline acetyltransferase activity of cultured rat septal cholinergic neurons, the effect being additive to that of nerve growth factor. In situ hybridization experiments and immunohistochemistry using a specific anti-FGF-5 antibody demonstrated that FGF-5 is expressed in rat hippocampal neurons. Like nerve growth factor mRNA, the levels of FGF-5 mRNA in the rat hippocampus increased substantially during early postnatal development. In addition, injection of the muscarinic receptor agonist pilocarpine elevated FGF-5 mRNA. The presence of the secretory FGF-5 in the rat hippocampus, a target field of septal cholinergic and raphe serotonergic neurons, suggests that FGF-5 acts as a trophic factor for these neurons also in vivo.