Reaction by the rat hypothalamus-hypophyseal system to stress from immobilization

Cytophysical changes in the ultrastructure of the neurosecretory hypothalamus under conditions of total short term immobility and partial long term immobility are investigated. Electron microscope morphological studies revealed a stimulatory response of the hypothalamus hypophyseal system of the rat brain to stress produced by immobilization. Total immobilization for two days resulted in changes in the neurons of the supraoptical and paraventricular nuclei and in the fibers of the neurohypophysis indicating an increased production of neurosecretory granules, their rapid flow and enhanced secretion to the blood. Partial immobilization of the animals for 3 weeks produced changes of a somewhat different character and of weaker intensity, which may be considered as a manifestation of the adaptation of the system and of the whole organism to the changed condition.