Energy & balance: the role of hindbrain catecholaminergic afferent projections to the hypothalamus

UnrestrictedThe word homeostasis is derived from the Greek hómos “similar” and histemi “standing still”. It is used to describe a general concept of environmental stability that is maintained within living organisms. An example is body temperature in humans, which can be consistently observed around 37ºC (98.6ºF). The term and concept are attributed to American physiologist, Walter Bradford Cannon, around the turn of the twentieth century. At that time, the concept of homeostasis built upon French physiologist, Claude Bernard’s, use of milieu de l’intérieur (the environment within) during the mid-nineteenth century to describe the stability and protection of internal organs and tissues by the blood.; ".... the blood constitutes an actual organic environment, an intermediary between the external environment and the (internal) living molecules, which cannot safely be brought into contact with their external environment ..." –An Introduction to the Study of Experimental Medicine. preface by L Henderson, 1926.; This concept was later expanded to incorporate the general stability of a living organism’s internal environment.; “The fixity of the milieu supposes a perfection of the organism such that the external variations are at each instant compensated for and equilibrated.... All of the vital mechanisms, however varied they may be, have always one goal, to maintain the uniformity of the conditions of life in the internal environment .... The stability of the internal environment is the condition for the free and independent life.” –Lectures on the Phenomena of Life Common to Animals and Plants, 1974. English translation of the original by HH Hoff, R Guillemin and L Guillemin. American Lecture Series, Charles C Thomas, Springfield, USA; These ideas are part of a long transition from the ancient notions of humors and life forces to a systematic approach of investigation into the “self-regulation” of the body.; The concept of self-regulation, is fundamental to the field of cybernetics, which emerged in the twentieth century and is focused on the study of regulatory systems. The term cybernetics dates back to Plato (in the context of government and governance of people) and the Greek derivation of the word, kybernetes, is the same root of which the word government is derived. William Ross Ashby (aka Ross Ashby) an English psychiatrist that greatly influenced cybernetics, was the author of Design for a Brain (1952) in which several definitions and concepts are outlined including stability, feedback and adaptation. These three terms provide the conceptual foundations of which the present work is derived.; Here, we examine regulatory mechanisms towards homeostasis represented within the components of the Hypothalamic-Pituitary-Adrenal (HPA) Axis. A main focus is the afferent neuronal circuitry that influences the hypothalamus, and the consequent regulation of pituitary and adrenal hormones that are essential in the maintenance of energy balance and metabolic homeostasis in living organisms