Development of the Autonomic Nervous System

Development of the autonomic nervous system (ANS) proceeds in a stereotyped manner from the migration of the neural crest cells from particular rostrocaudal levels of the spinal cord to the growth of axons to their peripheral targets. Migration of the neural crest cells proceeds in two main streams: dorsolateral to the somites and ventromedially through the rostral portion of the somites. It is the latter stream that produces the neurons and nonneuronal cells of the ANS, while the former stream produces pigment cells or melanocytes. This specificity arises through the response of the cells to growth factors released into the environment through which the neural crest cells migrate or the axons grow. The final differentiation and survival of the autonomic neurons rely on the acquisition of additional growth factors from their presumptive targets. The release of these factors may be reciprocal in response to the release of transmitters from the growing axons. Complex responses to multiple factors may assist in the development of specifically coupled neurons and effectors.