Effects of Chemoreceptor and Baroreceptor Stimulation on the Discharge of Hypothalamic Supraoptic Neurones in Rats

Abstract

Experiments have been performed to examine the effects of activating the carotid body chemoreceptors and the arterial baroreceptors on the discharge of neurones within the hypothalamic supraoptic nucleus of the rat. Chemoreceptors were activated by intracarotid injection of 0.9% NaCl solution equilibrated with 100% CO2. The baroreceptors of the carotid sinus and aortic arch were activated by raising the blood pressure with an intravenous injection of phenylephrine. Chemoreceptor stimulation activated and baroreceptor stimulation inhibited the discharge of all the phasically discharging neurones tested. Neither stimulus had any consistent effect on non-phasically discharging neurones, although slight inhibition occasionally occurred. Anaesthesia of the carotid bifurcation abolished the effects of cardiovascular stimulation on the supraoptic neurones. Responses resumed when the anaesthesia wore off. However, the anaesthesia also seemed to alter the phasic pattern of discharge. The results are discussed with reference to the influence of the cardiovascular receptors upon the neurones in the supraoptic nucleus, and with reference to possible roles for the cardiovascular reflexes in control of vasopressin secretion.

Neurones in the supraoptic nucleus of the rat are regulated by a projection from the suprachiasmatic nucleus

“…Such a difference was unexpected since the circadian profiles of plasma and pituitary levels of oxytocin and vasopressin are indistinguishable (Windle et al 1992). There are, however, other sensory inputs, including those involved with milk ejection (Lincoln & Wakerley, 1974), gastric distension (Renaud, Tang, McCann, Stricker & Verbalis, 1987) and baroreception (Harris, 1979), which are known to affect oxytocin and vasopressin cells differentially. Since a high proportion of supraoptic neurones receive afferents from the SCN, the projections we describe probably play an important role in the control of magnocellular activity but the situation is clearly complex.…”

A gamma‐aminobutyric‐acid‐mediated baroreceptor input to supraoptic vasopressin neurones in the rat.

“…This would be ideally suited from central transmission of information arising in peripheral chemoreceptors (cf. Harris, 1979) or hepatic portal osmoreceptors (Baertschi & Vallet, 1981). While the locus coeruleus does appear to participate in central pathways transmitting data on peripheral baroreceptor activity, the precise mechanisms and central pathways whereby these inputs ascend to the proposed GABAergic neurones in the rostral hypothalamus require more detailed evaluation.…”

“…Units demonstrating phasic or continuous activity that was transiently suppressed by this manoeuvre were classified as VP secreting; those whose continuous firing was unresponsive to baroreceptor activation were classified as OXY secreting (cf. Harris, 1979). Most cells were located in the posterior and ventral portions of the s.o.n., where a majority of the neurosecretory neurones are VP immunoreactive (cf.…”

Electrical activation and c‐fos mRNA expression in rat neurosecretory neurones after systemic administration of cholecystokinin.

“…Scale bar (bottom left): A, B, 2-1 mm; C, D, 400 ,um; E, 160 gum; F, 100,um; (Renaud et al 1987) and lack of response to i.v. injection of phenylephrine (Harris, 1979), stimuli which selectively excite oxytocin neurones and inhibit vasopressin neurones respectively.…”