Sensory and secretory potencies and differentiations of the central nervous system.

Secretory neurons capable of elaborating neuropeptides and biogenic amines are an integral component of nervous systems. This apparatus is more extended than assumed during an earlier period of investigations. It is involved in short- and long-range communication by means of paracrine, transmitter-like, modulatory and neurohormonal types of messages. This finely adjusted activity of secretory neurons serves the control of a variety of important biological functions. Secretory pinealocytes are derivatives of pineal photoreceptors, primary sensory cells of neuronal character. In contrast to these neuron-like or paraneuronal elements, the secretory cells of the subcommissural organ are of ependymal origin.