In vitro neurophysiology of identified rat hypothalamic 'neuroendocrine' neurons.

Stable synaptic and antidromic electrophysiological recordings were obtained for 10-15 h from identified neurohypophyseal and tuberoinfundibular neurons using an acute explant of rat hypothalamus maintained in vitro through perfusion of the carotid artery with oxygenated artificial media. Synaptic potentials from preoptic and median eminence stimulation were blocked during perfusion with 12 m M Mg++-containing solutions. Antidromic and spontaneous action potentials recorded in neurohypophyseal neurons were followed by a transient after-hyperpolarization of 3-10 mV, due primarily to a brief increase in potassium conductance. Evidence favoring the existence of a synaptic recurrent inhibitory pathway was present in records obtained from tuberoinfundibular neurons, but not from neurohypophyseal cells.

Vasopressin and neurophysin: high concentrations in monkey hypophyseal portal blood.

Vasopressin and its binding protein, neurophysin, were measured by radioimmunoassay in the hypophyseal portal blood of monkeys after cannulation of individual long portal veins. Mean vasopressin concentrations (13,800 picograms per milliliter) in portal blood were more than 300 times as high as those in the systemic circulation (42 picograms per milliliter). Neurophysin concentration was approximately 25 times as high in portal as in systemic blood. By immunoperoxidase techniques, high concentrations of neurophysin were demonstrated around portal capillaries of the median eminence. These studies indicate direct secretion of vasopressin and neurophysin into the portal circulation; the quantities secreted during stress may be sufficient to exert significant effects on secretion of anterior pituitary hormone.

The hypothalamic neurosecretory pathways for the release of oxytocin and vasopressin in the cat.

1. The neurones of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) were stimulated electrically in lactating cats under chloralose anaesthesia. Milk-ejection responses were used to monitor the release of oxytocin and vasopressin and both hormones were assayed in samples of blood collected during stimulation. The position of the tip of the stimulating electrode was confirmed from brain sections stained selectively for cystine-rich neurosecretory material.2. A previous finding that stimulation of the SON in the cat releases vasopressin without oxytocin was confirmed.3. Stimulation of the PVN caused both hormones to be released. The ratio of their concentrations in blood was variable; this suggests release from separate neurones.4. Both hormones were also released on stimulation of the median eminence but not of the zone lying vertically between this structure and the PVN. No neurosecretory material was detected in this zone. These findings argue against the existence of a direct or medial paraventriculo-hypophysial pathway running downwards along the wall of the third ventricle.5. Study of sections from unstimulated brains confirmed that the tractus paraventricularis cinereus of Greving which runs ventro-laterally from the PVN towards the SON, represents the principal efferent pathway for neurosecretory fibres from the PVN.6. The results are discussed in relation to the problem of the independent release of oxytocin and vasopressin in response to physiological stimulation of the neurohypophysis.