AGE-RELATED EFFECTS OF NERVE GROWTH-FACTOR ON THE MORPHOLOGY OF EMBRYONIC SENSORY NEURONS IN-VITRO

Studies of neonatal and adult mammals have shown that neuronal morphol ogy is regulated in part by the availability of target-derived neurotr ophic factor. To test whether the same is true for embryonic neurons, which are dependent on target-derived neurotrophic factors for surviva l, we grew neural crest-derived sensory neurons from the trigeminal ga nglion of avian embryos of different ages in vitro in different concen trations of nerve growth factor (NGF) and measured the number of branc h points and total length of the resulting arborizations. Although the size and complexity of arborizations increased with embryonic age up to embryonic day (E)14, neuronal morphology for embryos younger than E 14 was unaffected by the concentration of NGF in the culture medium. H owever, beginning at E14, the stage at which trigeminal neurons start to lose their absolute requirement for NGF for survival, the neurons h ad significantly more branch points and larger arborizations in higher concentrations of NGF. Thus, it appears that the extent of neurite ou tgrowth in young embryos is independent of neurotrophic factor concent ration; each neuron that receives enough neurotrophic factor to surviv e elaborates approximately the same size arbor. As trigeminal neurons mature and become less dependent on neurotrophic factor for survival, they acquire the ability to respond to neurotrophic factor with increa sed neurite growth and branching, as in neonates and adults. (C) 1993 Wiley-Liss, Inc.