Developing sympathetic neurons express a neuronal trait before a catecholaminergic synthetic enzyme in vivo

How multiple mature phenotypic traits are regulated in developing neurons remains a central problem in developmental neurobiology. Mature sympathetic neurons express general neuronal epitopes, including neuron specific tubulin (NST) as well as markers involved in neurotransmitter synthesis including tyrosine hydroxylase (TH). To investigate the relationship between neuronal differentiation and neurotransmitter development, the order of appearance of NST and TH was determined in both chick and rat embryonic sympathetic ganglia by double-label immunohistochemistry. In differentiated ganglia, these two markers were expressed in virtually all sympathetic neurons examined. By contrast, at early stages of embryonic development in both chick and rat, sympathetic ganglia contained many NST immunoreactive (IR) cells, but few precursors were TH-IR. With further development, more NST-IR cells were also TH-IR, and these two markers gradually became coexpressed with subsequent development. These data provide evidence that general neuronal and neurotransmitter differentiation events are separable and independently regulated during cellular diversification in the adrenergic lineage.