HIGH SPECIFICITY OF NEUROTROPHINS IN THE EMBRYONIC CHICKEN TRIGEMINALSYSTEM

Studies of cell lines and some cultured neurons have demonstrated pote ntial cross-talk between neurotrophins and their receptors; high conce ntrations of neurotrophins can exhibit either agonist or antagonistic actions on heterologous neurotrophin receptors. We have studied neurot rophin discrimination among the sensory neurons of the embryonic chick en trigeminal system. We show that nerve growth factor (NGF) at a conc entration that is six orders of magnitude greater than that required t o promote the survival of NGF-dependent dorsomedial trigeminal ganglio n (DMTG) neurons has no effect on the survival of brain-derived neurot rophic factor (BDNF)-dependent trigeminal mesencephalic nucleus (TMN) neurons and does not affect the dose-response relationship of these ne urons to BDNF. A similar high level of neurotrophin-3 neither promotes the survival of BDNF-dependent ventrolateral trigeminal ganglion neur ons nor affects the dose response of these neurons to BDNF. High level s of BDNF have a negligible effect on the survival of mid-embryonic DM TG neurons. These results show that some neurons are able to discrimin ate completely between neurotrophins at very high concentrations, indi cating that neurotrophin responses can be far more highly specific tha n previously appreciated.