Apud Cells and Paraneurons: Embryonic Origin

Abstract

This chapter reviews the main aspects of the concept of amine precursor uptake and decarboxylation (APUD) that was aimed at grouping diverse cell types whose main common feature was the ability to synthesize the so-called biogenic or monoamines. In the period of the development of the APUD concept, it was noticed that the ability to take up amine precursors such as dopa and 5-HTP and decarboxylate them with the formation of monoamines such as catecholamines and serotonin was common to a number of cell types. Criteria for the membership of the APUD series have changed in the present. This concept was extended to the paraneuron concept to emphasize the close relationship between conventional neurons and neuron-like cells, paraneurons, some of which are APUD cells located in the amphibian cutaneous glands, the placenta, the thymus, and the APUD neurons of the hypothalamus and sympathetic ganglia. Cells such as the monoamine-storing cells in the avian aortic wall are regarded as paraneurons. The study of such similarities between APUD and paraneurons cells has helped in the recognition of the fact that neurons and polypeptide-secreting endocrine cells are not completely disparate entities.