The development of the noradrenergic transmitter phenotype in postganglionic sympathetic neurons.

Here we review recent data on molecular aspects of the differentiation of the noradrenergic neurotransmitter phenotype in postganglionic sympathetic neurons during avian and mammalian embryogenesis. By experimental manipulation of the chick embryo, it has been shown that neural tube and notochord are important for noradrenergic differentiation which occurs when migrating neural crest cells, the precursors of sympathetic ganglion cells, reach the dorsal aorta. Bone morphogenetic proteins expressed in the dorsal aorta before and during the time of noradrenergic differentiation are likely candidates for growth factors involved in induction of noradrenergic differentiation, in vivo. To analyze noradrenergic differentiation, enzymes of the noradrenaline bio-synthesis pathway and catecholamine stores have been used as differentiation markers. The molecules involved in neurotransmitter release which are as important for a functional noradrenergic neuron as those required for transmitter synthesis and storage are only recently being studied in this context. For a comprehensive view of the embryonic development of the noradrenergic neurotransmitter phenotype, it will be necessary to understand how the systems for synthesis, storage and release of noradrenaline are assembled during neuronal differentiation.