Hypothalamic integration of body fluid regulation.

Abstract

The progression of animal life from the paleozoic ocean to rivers and diverse econiches on the planet's surface, as well as the subsequent reinvasion of the ocean, involved many different stresses on ionic pattern, osmotic pressure, and volume of the extracellular fluid bathing body cells. The relatively constant ionic pattern of vertebrates reflects a genetic "set" of many regulatory mechanismsparticularly renal regulation. Renal regulation of ionic pattern when loss of fluid from the body is disproportionate relative to the extracellular fluid composition (e.g., gastric juice with vomiting and pancreatic secretion with diarrhea) makes manifest that a mechanism to produce a biologically relatively inactive extracellular anion HCO3 exists, whereas no comparable mechanism to produce a biologically inactive cation has evolved. Life in the ocean, which has three times the sodium concentration of extracellular fluid, involves quite different osmoregulatory stress to that in freshwater. Terrestrial life involves risk of desiccation and, in large areas of the planet, salt deficiency. Mechanisms integrated in the hypothalamus (the evolutionary ancient midbrain) control water retention and facilitate excretion of sodium, and also control the secretion of renin by the kidney. Over and above the multifactorial processes of excretion, hypothalamic sensors reacting to sodium concentration, as well as circumventricular organs sensors reacting to osmotic pressure and angiotensin II, subserve genesis of sodium hunger and thirst. These behaviors spectacularly augment the adaptive capacities of animals. Instinct (genotypic memory) and learning (phenotypic memory) are melded to give specific behavior apt to the metabolic status of the animal. The sensations, compelling emotions, and intentions generated by these vegetative systems focus the issue of the phylogenetic emergence of consciousness and whether primal awareness initially came from the interoreceptors and vegetative systems rather than the distance receptors.In the higher mammals, the functions centered in the hypothalamus play a paramount role in integrating the many physiological systems controlling the milieu interieur. These hypothalamic processes range from genetically determined patterns of ingestive behavior that correct body deficits and, in turn, involve associated cognitive and memory functions of the cortex, to the other extreme of the control of excretory processes, in a mode apt to the metabolic status of the animal.Some evolutionary aspects of body fluid control will be described first as a general biological context of the mechanisms in mammals.Mountain building, like the Grand Canyon uplift in the Cambrian and subsidence in the Ordivician periods, provided conditions of rivers flowing into the ocean, and, probably during this time, protovertebrates with spindle body and segmentally arranged muscles adapted to rhythmic contractions evolved (reviewed in refs. 1 and 2). Later, irradiation of vertebrates from estuaries, rivers, and swamps involved pro...

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A comparative analysis of transcribed genes in the mouse hypothalamus and neocortex reveals chromosomal clustering

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