The Neuroendocrine Division of the Nervous System: APUD Cells as Neurones or Paraneurones

Abstract

Publisher Summary This chapter provides an overview of the neuroendocrine division of the nervous system. The diffuse neuroendocrine system (DNES) is divided into central and peripheral divisions, the first of which contains the cells of the hypothalamo–pituitary axis and the pineal gland, while the second includes all those situated outside these regions. Most of the cells in the second division are located in the gastrointestinal tract and pancreas where they comprise the gastroenteropancreatic (GEP) endocrine cells. All APUD cells are potentially capable of the synthesis of both peptides and amines, but actual production of the latter in adult animals is in most cases undetectable. The central division of the DNES contains the peptide producing cells of the pineal gland, the pituitary gland, and the magno- and parvocellular groups of the hypothalamus. However, there is an obvious degree of overlap between the APUD cells, functioning in different ways, and the paraneurons—cells able to produce (1) substances identical with or related to neurotransmitters, and (2) protein/polypeptide substances which may possess hormonic actions. With the advent of multicellular organisms came the development of specialized cells in the ectoderm, or derived from the ectoderm, which synthesized and secreted biologically active amines and peptides. The mammalian DNES is therefore considered to have developed from these primitive collections of ectodermally originating neurosecretory elements and thus the DNES is rather the first, and oldest, division which has been succeeded, by a closely associated autonomic nervous system and even later by a definitive centrally situated brain.