CRITICAL PERIODS OF BASIC FIBROBLAST GROWTH-FACTOR AND BRAIN-DERIVED NEUROTROPHIC FACTOR IN THE DEVELOPMENT OF THE CHICKEN COCHLEOVESTIBULAR GANGLION IN-VITRO

The temporal roles of brain-derived neurotrophic factor (BDNF) and fib roblast growth factor-2 (FGF-2) in the development of sensory neurons have been studied in a cell culture preparation which models normal em bryonic inner ear development (normocytic). Previous studies showed th at FGF-2 stimulated migration and differentiation of ganglion cells fo r the first 2 days in vitro, but after 5 days led to degeneration, imp licating other factors in their later development. To see if BDNF coul d be such a factor otocysts were explanted from white leghorn embryos at the time when ganglion cell precursors normally start migrating fro m the otic epithelium. Cultures were grown in a defined medium, either with or without human recombinant FGF-2 for 2 days or with BDNF. On D ay 3, FGF-2 was replaced either with BDNF in defined medium or with de fined medium only. Measurements of neuroblast migration and neurite ou tgrowth were made by time-lapse imaging in living cultures. In culture s receiving BDNF on Day 3, cell migration and neurite outgrowth from t he explant increased for more than 3 weeks but not in cultures receivi ng only defined medium from Day 3. Cultures did not survive more than 3-4 days when receiving either BDNF in defined medium or defined mediu m alone from the first day. A neutralizing antibody to BDNF inhibited neuronal migration and neurite outgrowth, and it also blocked the effe cts of exogenous BDNF. BDNF did not enhance the effects of FGF-2 by in teracting with it. These experiments defined a temporal sequence in wh ich FGF-2 acts early in development, while BDNF affects a later stage. (C) 1997 Academic Press.