[The significance of feedback in accomplishing the rat hypothalamic nonapeptidergic center reaction to short-term immobilization stress]

Abstract

Stress response of oxytocin- and vasopressinergic cells in the supraoptic and paraventricular centers of the hypothalamus was studied morphometrically in rats with intact hypophysis and 7 days after hypophysectomy. Severe immobilization (for 20 min.) was applied as an unspecific short-term stress. In nonoperated rats the immobilization resulted in diminution of functional activity of vasopressinergic cells in the paraventricular nucleus exclusively: nucleolar volume of these cells reduced to 80% (P < 0.05). The same pattern of reaction of nonapeptidergic cells was revealed in the hypophysectomized rats under stress immobilization. The stress blood concentration of vasopressin, ACTH, 11-HOCS clearly increased in nonoperated rats but not in the hypophysectomized rats. TSH plasma concentration and the thyroid gland activity did not alter under stress in both groups of rats. Thus, the data evidence for the response of nonapeptidergic hypothalamic centers is not influenced by fluctuations of the hormone level in blood under short-term stress.