Nerve growth factors (NGF, BDNF) enhance axonal regeneration but are not required for survival of adult sensory neurons

Largely on the basis of studies with nerve growth factor (NGF), it is now widely accepted that development of the peripheral nervous system of vertebrates is dependent in part on the interaction of immature sensory and autonomic neurons with specific survival factors that are derived from peripheral target fields. I have found, in marked contrast to an absolute requirement for NGF during development, that adult rat dorsal root ganglion sensory neurons are not dependent on NGF or other survival factors for long-term (3-4 weeks) maintenance in vitro. When dissociated and enriched, at least 70-80% of adult DRG neurons survived and extended long processes either in the absence of exogenously added NGF or upon the removal of any possible source of endogenous NGF or other neurotrophic activity (i.e., nonneuronal cells, in chemically defined culture medium, in the presence of an excess of anti-NGF antibodies, or when cultured as single neurons in microwells). Although not required for survival or expression of a range of complex morphologies, both NGF and brain-derived neurotrophic factor (BDNF) were found to stimulate the regeneration of axons from adult DRG neurons.