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.