Right Atrial Stretch Induces Renal Nerve Inhibition and c‐fos Expression in Parvocellular Neurones of the Paraventricular Nucleus in Rats

Abstract

The paraventricular nucleus of the hypothalamus plays a pivotol role in the regulation of plasma volume. Part of the response to an increase in volume load is an inhibition of renal sympathetic nerve activity. The present experiments were designed to determine which subnuclei of the paraventricular nucleus are involved in this sympatho-inhibitory response. Experiments were performed on anaesthetised rats. Activated neurones were recognised by the expression of the early gene c-fos, identified by immunohistochemical labelling of its protein product Fos. Plasma volume loading with 4 % Ficoll 70, using an infusion-withdrawal procedure (2 ml over 1 min) repeated 15 times over 1 h revealed a total of 775 ± 101 (n = 6) Fos-positive neurones scattered throughout both the magnocellular and parvocellular subnuclei. In comparison, sustained hypertension resulted in 452 ± 56 (n = 3) Fos-positive neurones similarly distributed, whereas a normotensive control group (n = 3) displayed 115 ± 18 Fos-positive neurones. Because of this lack of a specific effect we used a more selective stimulation of right atrial receptors via a balloon placed at the junction of the superior vena cava and the right atrium so it did not impede venous return. Inflation of the balloon inhibited renal sympathetic nerve activity (36 ± 5 %, n = 7) and repetitive inflation over 1 h resulted in c-fos activation of a small number of neurones (54 ± 14) located only in the parvocellular subnuclei. Whether these are inhibitory interneurones acting within the paraventricular nucleus, or spinally projecting neurones which inhibit or excite renal sympathetic activity by an action in the spinal cord remains to be determined. Experimental Physiology (2002) 87.1, 25-32.

Water deprivation increases Fos expression in hypothalamic corticotropin-releasing factor neurons induced by right atrial distension in awake rats

“…Selective activation of atrial mechanoreceptors has been described in response to right atrial distension by inflation of a small balloon placed at the superior vena cava-right atrium junction, without obstruction of blood flow to the heart (37). Using this method, others have described an activation of parvocellular neurons (21,47) and an inhibition of magnocellular neurons in the PVN (29).…”

Synchrony analysis between blood pressure and sympathetic nerve signal inhibited by atrial receptor stimulation in Wistar rats

“…1994;Coote, 1995) by responding to signals from volume receptors situated at the vein-atrium junctions (Deng & Kaufman, 1998;Deering & Coote, 2000;Pyner et al 2002).…”

“…A key role in plasma volume homeostasis is exerted by low pressure volume receptors located at the veinatrium junctions (Linden, 1987). These receptors induce a reflex inhibition of RSNA, which is mediated via the PVN (Coote, 1995;Badoer, 1996;Pyner et al 2002). There are circumstances such as heart failure where, despite the increased activity of atrial receptors due to venous volume expansion, there is an increase rather than a decrease in RSNA, implying that inhibitory feedback from these receptors has been overcome by facilitatory inputs to the central neurones.…”

“…Therefore, in the present study we introduced crosssample entropy to estimate asynchrony of the relationship between BP and RSNA during stimulation of right atrial receptors by balloon inflation under two conditions. The first was balloon-on stimulation alone, which decreases RSNA but does not change BP (Pyner et al 2002) and the second was when this same stimulus was applied during stimulation of a region of the PVN, which increased RSNA and BP.…”

“…The cannula was held in position by ligating it to the right clavicle. The balloon was connected to a syringe (5 ml) and inflated for > 30 s to approximately 0.5 cm in diameter to stretch the vein-atrium junction during the experiments (Kaufman, 1984;Pyner et al 2002). Histological verification of injection sites At the end of each experiment, the brain was removed and fured in formalin.…”