Hypothalamo-Pituitary Neurosecretory System of Rats After a 22-Day Space Flight
The purpose of this investigation was to do a morphologic study of the hypothalamus-pituitary system of rats flown for 22 days on board the biosatellite “Cosmos-605.” The animals were sacrificed 2 and 27 days postflight. The functional state of the hypothalamus-pituitary system was assessed by histologic, histochemical, and morphometric methods. On the 2nd postflight day, morphologic signs of an increase in the functional activity of neurons of the supraoptic nuclei of the hypothalamus were found. These comprise (1) increase in the nuclear volume and neuronal size, (2) decrease in the intensity of neuronal staining of chromatophilic substance, (3) uniform distribution of neurosecretory granules in the neuronal bodies, and (4) reduction of their content in axons at the level of the supraoptic nuclei and in terminals of the posterior pituitary. The lack of such changes in control rats not subjected to space flight suggests that they were induced by that flight, or were postflight responses of the hypothalamus-pituitary system. Two days seems to be a sufficient period of time for morphologic reactions to develop in response to the gravity change. The changes found in the hypothalamuspituitary neurosecretory system of rats 2 days postflight are indicative of an increased production of ADH-vasopressin and are in agreement with the evidence on increased antidiuretic activity in the blood of cosmonauts during the 1st postflight day.