BASIC FIBROBLAST GROWTH-FACTOR (FGF-2) AFFECTS DEVELOPMENT OF ACOUSTICO-VESTIBULAR NEURONS IN THE CHICK-EMBRYO BRAIN IN-VITRO

The effects of basic fibroblast growth factor (FGF-2) on presumptive a uditory and vestibular neurons from the medulla were studied in primar y cell cultures. The part of the rhombic lip that forms nucleus magnoc ellularis (homologue of the mammalian anteroventral cochlear nucleus) was explanted from white leghorn chicken embryos at Hamburger-Hamilton stage 28 (E5.5), the time when precursors of the magnocellularis bush y cells migrate and begin to differentiate in situ. In vitro the neuro blasts migrated onto 2-D substrates of purified collagen, differentiat ed, and expressed neuronal markers. One-half of the cultures were supp lemented with human recombinant FGF-2 (10 ng/ml daily) for 5-7 days; t he others, with fetal bovine serum. FGF-2 more than doubled the length of neurite outgrowth during the first 3 day treatment compared to ser um, but the number of migrating neuroblasts was unaffected. Although n eurites attained greater lengths in FGF-2, they usually degenerated af ter 4-5 days; in serum their growth continued for several weeks. Diffe rentiation of neuronal structure, including axons and dendrites, began within 1-2 days in bFGF but required at least 5-7 days in serum. Hist ochemical observations in vitro and in situ with antibodies to FGF rec eptor demonstrated immunopositive patches on acoustico-vestibular neur oblasts at stage 28, when they are migrating and first forming their a xons. The findings suggest that FGF-2 stimulates neurite outgrowth in the cochlear and vestibular nuclei. FGF-2 may accelerate cell death by overstimulating neuroblasts, but other factors are needed to sustain their further development.