Spinal afferents for peripheral osmoreceptors in the rat.

Superfusion of the hepatic portal vein with hypertonic saline solutions increases the electrical activity of the hypothalamo-neurohypophysial tract. Bilateral cervical vagotomy had no effect on this response in all rats studied. Section of the hepatic branch of the vagus abolished the hypothalamic response in only two animals, but injection of xylocaine into the spinal cord at thoracic levels abolished the response in all remaining animals. The results suggest that peripheral osmoreceptors of the portal vein activate the hypothalamo-neurohypophysial system through a spinal afferent pathway.