Osmotic and hormonal stimulation of the third ventricular region of ducks: antidiuretic, circulatory and local neuronal responses.

By means of local microperfusion of the 3rd cerebral ventricle, antidiuretic and circulatory responses to stimulations with various hypertonic solutions and norepinephrine were analyzed in conscious ducks. The results suggest ionic rather than osmometric responsiveness of periventricular osmoreceptive elements, which is in line with single unit recordings of periventricular neurons tested in vitro for their osmoresponsiveness. These neurons were located subependymally at the site of greatest responsiveness in vivo, and corresponded to morphologically identified neurons projecting to the neuroendocrine hypothalamo-pituitary system. Antidiuresis was combined with increases in arterial pressure and heart rate in response to hypertonic stimulations with monovalent cations; divalent cations produced long-lasting antidiuresis and equivocal circulatory responses. Norepinephrine elicited antidiuresis which was accompanied by arterial hypotension and bradycardia. Osmotically and norepinephrine induced antidiuresis was combined with increases of plasma ADH concentration. Different modulatory actions of intrinsic adrenergic, angiotensinergic and vasotocinergic neurons are suggested in hypothalamic control of autonomic functions.