Growth responses of different subpopulations of adult sensory neurons to neurotrophic factors in vitro

Different subpopulations of adult primary sensory neurons in the dorsal roo t ganglia express receptors for different trophic factors, and are therefor e potentially responsive to distinct trophic signals. We have compared the effect of the neurotrophins nerve growth factor (NGF), brain-derived neurot rophic factor (BDNF) and NT-3, and of glial cell line-derived neurotrophic factor (GDNF) on neurite outgrowth in dissociated cultures of sensory neuro ns from the lumbar ganglia of young adult rats, and attempted to establish subset-specific effects of these trophic factors. We analysed three paramet ers of neurite growth (percentage of process-bearing neurons, length of lon gest neurite and total neurite length), which may correlate with particular types of axon growth in vivo, and may therefore respond differently to tro phic factor presence. Our results showed that percentage of process-bearing neurons and total neurite length were influenced by trophic factors, whils t the length of the longest neurite was trophic factor independent. Only NG F and GDNF were found to enhance significantly the proportion of process-be aring neurons in vitro. GDNF was more effective than NGF on small, IB4(-) n eurons, which are known to develop GDNF responsiveness early in postnatal d evelopment. NGF, and to a much lesser extent GDNF, enhanced the total lengt h of the neurites produced by neurons in culture. BDNF exerted an inhibitor y effect on growth, and both BDNF and NT-3 could partially block some of th e growth-promoting effects of NGF on specific neuronal subpopulations.