The neurosecretory neuron in neuroendocrine regulatory mechanisms.

Abstract

Synopsis. The widespread occurrence of neurosecretory neurons in the animal kingdom suggests a functional significance that is basic and special. The explanation of the need for this unusual cell type lies in the fact that it forms a link between the nervous and the systems whose functional interdependence forms the basis for the effectiveness of regulatory mechanisms in the animal world. These two integrative systems function in different ways. The neurosecretory cell, with its dual characteristics, and this cell alone, seems capable of receiving messages in neural language, and of transmitting this information in modified endocrine language to glandular cells. The neurosecretory neuron occupies a central position in neuroendocrine interactions, not only because it is geared for communication with the apparatus, but because it serves as a singular channel (final common path, E. Scharrer, 1965) through which a multitude of afferent stimuli, after being processed, are channeled to a variety of way stations and thus exert control over their effector organs. One of the most fertile concepts in the progress of research has been that of the functional interdependence of organs concerned with regulatory mech? anisms. Under physiological conditions, in? dividual glands of internal secretion do not function autonomously, but rather as links in an ever-changing sequence of events. In their entirety, these glands constitute the apparatus, one of the two in? tegrative organ systems of higher organisms. Environmental stimuli affecting the en? docrine system reach it by way of the nerv? ous apparatus, the other of the two sys? tems of communication. Its makeup of innumerable links (neuron chains) is too well known to require discussion. What has not been fully appreciated, however, until very recently is the high degree of mutual interdependence that exists between the nervous and the systems. And yet, the situation could not be otherwise, because heterogeneous directives aimed at a given effector organ simultaneously, in order to be effective at all, must not contradict each other. The manner in which the two integrative systems communicate with each other in coordinating the body's autonomic adjustments, and the outcome of this combined activity, constitute Neuroendocrinology. This young, but rapidly expanding dis? cipline encompasses many facets of mutual interacfion (see Scharrer and Scharrer,