Generating diversity: Mechanisms regulating the differentiation of autonomic neuron phenotypes

Sympathetic and parasympathetic postganglionic neurons innervate a wide range of target tissues. The subpopulation of neurons innervating each target tissue can express unique combinations of neurotransmitters, neuropeptides, ion channels and receptors, which together comprise the chemical phenotype of the neurons. The target-specific chemical phenotype shown by autonomic postganglionic neurons arises during development. In this review, we examine the different mechanisms that generate such a diversity of neuronal phenotypes from the pool of apparently homogenous neural crest progenitor cells that form the sympathetic ganglia. There is evidence that the final chemical phenotype of autonomic postganglionic neurons is generated by both signals at the level of the cell body that trigger cell-autonomous programs, as well as signals from the target tissues they innervate.