Hypothalamic neurons secreting vasopressin and neurophysin

Abstract

These two substances are secreted by exocytosis from three pathways; supra optico hypophyseal to the posterior lobe, to the median eminence into the hypophyseal blood and from the third ventricle into the C.S.F. Antisera to neurophysins and vasopressin and their application in localisation and measurement in the blood have shown a much wider distribution of both vasopressin and oxytocin. Bioassay showed both hormones to exist in the supraoptic nucleus (SON) and in the paraventricular nucleus (PVN). Axons from the latter travel through the SON en route to the posterior pituitary so that lesions of the SON can destroy both systems. Many magnocellular sources of neurophysin and vasopressin have been found beyond the anterior hypothalamus in the preoptic area as far as the lamina terminalis, near the ventral anterior thalamus and caudally in the lateral tuberal floor. Neurophysin and vasopressin granules are concentrated in bearded segments of fibres, fill the large dilatations and are concentrated at the axon terminals in the posterior pituitary. Peptide containing axons lie in the floor of the third ventricle where secretion into the C.S.F. may well take place. Tanycytes, specialised ependymal cells, may well transport hormones from the C.S.F. to the portal blood. Using S35 cysteine the half life of neurophysin was found to be about 20 days although there seems to be a mixture of pools within granules and outside axons. Specific assays for both posterior pituitary hormones and their carriers have demonstrated release in response to smoking, oestrogens, haemorrhage and possibly other hypothalamic releasing factors.