The Molecular Basis of Phenotypic Choices in the Sympathoadrenal Lineage

As the papers in this volume make quite clear, secretory vesicles can contain peptides, proteins, purines, and possibly other molecules in addition to classical transmitters. It is also now a commonplace observation that a single neuron can synthesize, store, and release several of these molecules. In fact, individual neurons can change the particular complement of transmitter and peptide they produce as they move through different stages of development. This phenotypic plasticity was originally observed when the environment of neurons growing in culture was altered, and more recently changes in transmitter phenotype have also been found to represent stages of normal development in vivo. Such plasticity has been observed both in vertebrates and in invertebrates. This article will briefly describe some of the molecular signals that control changes in transmitter and vesicle phenotype during development