Rostrocaudal differences in dendritic growth and synaptogenesis in rat sympathetic chain ganglia

Vertebrate embryos show a rostral to caudal gradient of morphogenesis. I have investigated the effect of this developmental gradient on neuronal maturation and synapse formation by comparing the development of rostral and caudal sympathetic chain ganglia in the rat. In young adults the superior cervical and lumbar ganglia are almost identical in terms of neuronal morphology and quantitative aspects of innervation. In neonates, however, substantial rostrocaudal differences are apparent in dendritic complexity, number of axons innervating ganglion cells, and synaptic density. There is an associated delay in ganglion cell-target interactions in the lumbar region. My results show that rostrocaudal position is significantly correlated with the time course of dendritic growth and synaptogenesis and suggest that ganglion cell-target interactions may be important in these developmental processes. This difference in developmental rate, however, does not lead to differences in neuronal morphology or synaptic density between rostral and caudal ganglia in maturity.