Early development of postganglionic sympathetic trunk neurons in the chick embryo

The main object of this investigation was to determine at which embryonic age the axonal endings of the first outgrowing sympathetic trunk neurons reach the shank musculature of the chick embryo. Horseradish peroxidase was injected in the shank musculature at different embryonic ages. Labelling of the sympathetic trunk perikarya was considered as evidence for the presence of sympathetic axonal endings in the injected area of the shank musculature. The earliest labellings were found at 8 days of incubation in the sympathetic ganglia attributed to the ischiadic plexus. The comparison of the subsequent developmental stages of sympathetic trunk neurons with the developmental stages of motoneurons, primary spinal sensory neurons and postganglionic ciliary neurons showed that the sympathetic trunk neurons are the last to establish contacts with their targets in the periphery.