The Functional Morphology of the Hypothalamo-Hypophyseal Neurosecretory System (HHNS) After Direct and Reflex Stimulation of the Hypothalamus in Cats
The functional morphology of the HHNS was investigated in physiologically acute experiments on cats under chloralose anesthesia. Stimulation (with vasoconstrictory effect) of the sympathetic trunk, vagus nerve, and supraoptic nuclei (NSO) was used. Stimulation of the preoptic zone, which caused vasodilatation, was performed as a control experiment. Other control animals were under adequate experimental conditions but were not stimulated. The microscopic preparations were stained by paraldehyde fuchsin, and light microscopy was performed. In control animals after preoptic stimulation, moderate signs of HHNS activity were observed in the NSO and paraventricular nuclei (NPV). The anesthesia and operation caused the release of neurosecretory material (NSM) from the posterior lobe. After stimulation of the NSO and the sympathetic trunk, the quantity of NSM in the posterior lobe was greater than that found after vagal stimulation. The stressor type of activation was observed after vagal stimulation. No changes were observed in the NPV after sympathetic and unilateral NSO stimulation. In these experiments, only the NSO was activated, the size of nucleoli of neurosecretory cells being increased. There were more light cells with intensive NSM synthesis and release in experimental animals than in controls. The infundibular part of the neurohypophysis contained the greatest amount of NSM. After unilateral NSO stimulation the activation of NSO was observed mostly on the side of stimulation. The reaction of the bilateral accessory neurosecretory cells was similar to that of the NSO, but less pronounced. In all cases where peripheral vasoconstriction was observed, the activation of NSO was evident. Since NSO is the main site of vasopressin synthesis, our data suggest vasopressin participation in vasoconstrictor mechanisms.