Functional Dynamics of the Central System of Regulation of Na+/Osmotic Homeostasis

In this paper, we analyze the phenomenon of functional dynamics (FD), i.e., modifications developing in neuronal networks of adult animals and resulting from the influence of long-lasting functional loadings on the systems, which are controlled with the involvement of these networks. Special attention is paid to the FD of the hypothalamic structures involved in the regulation of Na+/osmotic homeostasis. The paper is a "hybrid" of a review of existing data on the state of the problem and a brief description of the results obtained by the authors. Data on the structural manifestations of the FD (first of all, on changes in the glia-neuron relations) observed in the hypothalamic nuclei and structures connected with the hypothalamus after water-salt loadings, lactation, etc. are presented. The respective similar, in general, modifications related to changes in the physiological conditions that develop in the hippocampus and neocortex are also described. The relation of the structures of the preoptic/anterior hypothalamus (PO/AHTh) to the system of central control of osmotic homeostasis is discussed. A pharmacological experimental model providing creation of long-lasting shifts in the water/electrolyte balance, which was proposed by the authors, is described, and limits of its adequacy are discussed. The pattern of responses of the neurons, which form a neuronal network of the PO/AHTh, to hypo- and hyperosmotic discrete stimulations and modifications of these responses against the background of experimental hypo- or hypernatremia are analyzed. The authors propose an original scheme of a minimum mesh of the neuronal network under study allowed them to interpret the observed phenomena. Possible mechanisms of induction of the FD of the analyzed system considering the known mechanisms of modification of the efficiency of synaptic transmission are discussed.