Cellular and molecular determinants of sympathetic neuron development

The development of the sympathetic nervous system can be divided into three overlapping stages. First, the precursors of sympathetic neurons arise fro m undifferentiated neural crest cells that migrate ventrally, aggregate adj acent to the dorsal aorta, and ultimately differentiate into catecholaminer gic neurons. Second, cell number is refined during a period of cell death w hen neurotrophic factors determine the number of neuronal precursors and ne urons that survive. The final stage of sympathetic development is the estab lishment and maturation of synaptic connections, which for sympathetic neur ons can include alterations in neurotransmitter phenotype. Considerable pro gress has been made recently in elucidating the cellular and molecular mech anisms that direct each of these developmental decisions. We review the cur rent understanding of each of these, focusing primarily on events in the pe ripheral nervous system of rodents.