IN-VIVO NEUROGENESIS IS INHIBITED BY NEUTRALIZING ANTIBODIES TO BASICFIBROBLAST GROWTH-FACTOR

While extracellular growth factors govern neuronal precursor mitosis i n culture, little is known about their roles in regulating neurogenesi s in vivo. Previously, we reported that subcutaneously administered ba sic fibroblast growth factor (bFGF) promoted neuroblast proliferation in P1 rat brain, in regions in which bFGF and FGF receptors are expres sed during development. To define the role of endogenous bFGF in neuro genesis, we employed a neutralizing monoclonal antibody to the factor. In culture, bFGF-induced granule precursor proliferation was progress ively inhibited by increasing concentrations of antibody. In contrast, heat-inactivated or nonneutralizing anti-bFGF antibodies were ineffec tive. The inhibition was specific for bFGF, since EGF-induced [H-3]dT incorporation was not altered. To study effects in vivo, neutralizing antibody was administered to newborn rats via the cisterna magnum. Fou r hours after injection, DNA synthesis in cerebellum and hippocampus w as decreased by 53% and 63%, respectively, suggesting that endogenous bFGF was involved in brain development. To define effects on neurogene sis specifically, granule cell precursors were isolated after antibody treatment. [H-3]dT incorporation in granule precursors was decreased by 50%, indicating that the neutralizing antibody inhibited neuroblast proliferation in vivo. In contrast, no reduction was observed using n onneutralizing or the heat-inactivated antibodies. The inhibition of p recursor proliferation following immunoneutralization of bFGF in vivo suggests that the endogenous factor normally regulates brain neurogene sis. (C) 1997 John Wiley & Sons, Inc. J Neurobiol.