TARGET SPECIFICITY AND SIZE OF AVIAN SENSORY NEURONS SUPPORTED IN-VITRO BY NERVE GROWTH-FACTOR, BRAIN-DERIVED NEUROTROPHIC FACTOR, AND NEUROTROPHIN-3

To obtain insight into which subpopulations of sensory neurons in dors al root ganglia are supported by different neurotrophins, we retrograd ely labeled cutaneous and muscle afferents in embryonic day 9 chick em bryos and followed their survival in neuron-enriched cultures suppleme nted with either nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), or neurotrophin-3 (NT-3). We found that NGF is a wide survival factor for subpopulations of both cutaneous and muscle affere nts, whereas the survival effects of BDNF and NT-3 are restricted prim arily to muscle afferents. We also measured soma size in each neurotro phic factor. These new data show that BDNF- and NT-3-dependent cells a ppear to be a mixture of two populations of neurons: one small diamete r and the other large diameter. In contrast, based on size alone, NGF- dependent cells appear to be a single population of only small-diamete r neurons. Thus, BDNF and NT-3 may have some new, previously unreporte d effects on small-diameter afferent neurons. (C) 1994 John Wiley and Sons, Inc.