Immunocytochemical study of the hypothalamo-neurohypophysial system

Summary Antisera, with cross reactive antibodies removed by affinity chromatography, were used in the immunoperoxidase-bridge technique to study the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat. The hormones were demonstrated in different areas of the supraoptic nucleus (SON) and paraventricular nucleus (PVN), in neurosecretory fibres of the hypothalamoneurohypophysial tract, median eminence, and in nerve terminals of the neurohypophysis. Intact normal and rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain), and rats dehydrated by the administration of oral hypertonic saline were studied. In dehydrated rats the hormone concentration in the neurons, and the number of neurons containing hormone varied according to the time of dehydration stress.The observations support the hypotheses that: 1) oxytocin and oxytocinneurophysin, and vasopressin and vasopressin-neurophysin are synthesised in different neurons and are transported along different axons; 2) the SON and PVN are functionally indistinguishable in that neurons containing oxytocin or vasopressin are present in both nuclei; and 3) the two types of neurons respond to osmotic stimulation in a way that is qualitatively the same but quantitatively different.This work was supported by a grant from the Medical Research Council of New Zealand