The common peptides and the cytochemistry of their cells of origin

Thirtyfive biologically active peptides are products of the 40 cells of the APUD series, which constitute the Diffuse Neuroendocrine System (DNES). Twentyone of these peptides are found not only in the cells and processes of the DNES but also in the cells and the processes of the nervous system. Hence the appellation common. To the seven original common cytochemical features of the APUD cells it is possible to add the positive results of 3 subsidiary staining techniques (Lead haematoxylin, Argyrophilia, Formaldehyde-Fluorescamine), a singly cytochemical method (Formaldehyde-ozone), and an immunocytochemical molecular marker method (neuron-specific enolase; NSE). Application of this last method demonstrates NSE in the APUD cells and confirms their origin from "neuroendocrine-programmed epiblast."