Reaction of the paraventricular nucleus of the hypothalamus and the dorsal nucleus of the vagus of rats to change in the gravitational environment.

Abstract

An investigation of the functional state of brain structures participating in the organization and realization of vegetative reactions in mammals in the presence of a change in the gravitational milieu seems necessary both for the understanding of the mechanisms of the regulation of the homeostatic functions of the organism and for the development of means of support of the organism's homeostasis under conditions of prolonged change in the gravitational environment it inhabits. The hypothalamus, as is known, has a substantial role in the regulation of the vegetative reactions effected through the autonomic nervous system. The realization of the vegetative reactions is determined to a substantial degree by the dorsal nucleus of the vagus, which fulfills the role of postsynaptie efferent output of the medullary center of the vagus. A decrease in the concentration of insulin in blood plasma, found in man during space flight [9], as well as hypofunction of pancreatic/3cells, detected in a morphological investigation in rats in weightlessness [2], make it possible to hypothesize the occurrence in weightlessness of a shift to a different (as compared with conditions of terrestrial gravity) level of the functioning of mechanisms regulating the insulin-synthesizing and insulin-secreting functions of the pancreatic islet apparatus. According to the conception of I. G. Akmayev [1], a descending hypothalamic neural pathway, beginning in the paraventricular nucleus (PVN) of the hypothalamns and terminating in the medulla oblongata in the dorsal nucleus of the vagus (DNV), the cholinergie preganglionie neurons of which exert a stimulating influence on the secretion of insulin by pancreatic/3--cells [I 1, 14, 15], and which are activated in alloxan diabetes [6], is one of the pathways of the regulation of the function of the pancreatic/3--cells. Information regarding the state of the structure and function of neurons in the PVN of the hypothalamns and the DNV of the medulla oblongata in mammals under altered gravitational conditions is lacking in the literature. All of the above determined our interest in the reaction of the DNV and the PVN of the hypothalamus to changes in the gravitational milieu.