During the past two decades the progress in neuroendocrine research, stimulated by the increasing general interest in neurosciences, has been very impressive. Most of these efforts have concentrated on peuroendocrine nerve cells and their systems. Even if some aspects have remained open to discussion, the principal functional role of the neuroendocrine units capable of elaboration of biological active peptides (peptidergic neurons) is quite well understood. The same holds true for the central aminergic neurons and for such photoreceptor-derived paraneuronal elements as the pinealocytes. The...