In 1981, I published a paper in the first issue of the Journal of Neuroscience with my postdoctoral mentor, Dr. Richard Bunge. At that time, the long-standing belief that each neuron expressed only one neurotransmitter, known as Dale’s Principle (Dale, 1935), was being hotly debated following a report by French embryologist Nicole Le Douarin showing that neural crest cells destined for one transmitter phenotype could express characteristics of another if transplanted to alternate sites in the developing embryo (LeDouarin, 1980). In the Bunge lab, we were able to more directly test the question of phenotypic plasticity in the controlled environment of the tissue culture dish. Thus, in our paper, we grew autonomic catecholaminergic neurons in culture under conditions which promoted the acquisition of cholinergic traits and showed that cells did not abandon their inherited phenotype in order to adopt a new one but instead were capable of dual transmitter expression. In this Progressions article, I detail the ...