Altered pattern of vasopressin distribution in the hypothalamus of rats subjected to immobilization stress. An immunohistochemical study.

Generally, the CRF-like activity of vasopressin is studied in experiments involving adrenalectomy and corticosteroid replacement. In order to avoid this complex type of stress, male and female (diestrus, estrus) rats were exposed to 5 min to immobilization stress and sacrificed 5, 15, and 30 min thereafter. After a survival period of 5 min the vasopressin-synthesizing part of the paraventricular nucleus exhibited an increased activity. Vasopressin-reactive axons in the pericapillary layer of the median eminence and among the solid cell clusters of the pars tuberalis became more conspicuous and increased in number. In this group of experimentally treated animals the prechiasmatic division of the supraoptic nucleus did not show any changes in immunoreactivity. The same holds true for the neurohypophyses in all experimental groups. In animals with increased survival times the supraoptic nucleus exhibited a slightly increased activity, whereas the staining intensity of the paraventricular nucleus decreases gradually. From these results it can be concluded that the paraventricular nucleus is involved in the first phase of the stress response. The problem of vasopressin or a very similar peptide synthesized in this nucleus and exerting a CRF-releasing function is discussed.