The neuroendocrine system: organization and homeostatic role

The neuroendocrine system (NES) of Vertebrates can be defined as a set of cells organized in single organs and diffuse elements, sharing co-production of amine hormone/transmitters, peptide hormone/transmitters and specific markers of neural determination. In this perspective, the hypothalamic-pituitary-target organ axis (H-P axis), the autonomic nervous system (ANS) and the diffuse neuroendocrine or APUD system contribute to the NES. However, in Mammals and man virtually any compartment of the body harbors elements, often with different embryologic origin, having at least some of the NES features. Thus, all anatomical structures may be part of a wide functional circuitry, based on "internal secretions", that supersedes the current view of the NES. Historically, metaphysical antecedents of this concept can be found in the biomedical tradition dealing with the idea of the so called "vital energy". Currently, the "internal secretions" circuitry can be envisaged as an informational supersystem encompassing the H-P axis, ANS, APUD, immune and any other body system performing autocrine, paracrine and/or endocrine regulations, that superintends the homeostatic balance. Evolutionary evidence shows that diffuse autocrine/paracrine/endocrine, peptidergic secretions would be the oldest and hierachically simplest signals, with respect to the later and hierarchically more complex ANS and H-P axis outputs, to regulate body homeostasis. Therefore, the new acronym "Triune Information Network" (TIN) is proposed for the informational supersystem of internal secretions acting in Mammals and man via progressively higher levels of control (diffuse autocrine/paracrine/endocrine secretions, ANS and H-P axis) on a common energetic substrate: the internal body milieu.