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

Abstract

LL. Water deprivation increases Fos expression in hypothalamic corticotropin-releasing factor neurons induced by right atrial distension in awake rats. Am J Physiol Regul Integr Comp Physiol 295: R1706 -R1712, 2008. First published September 10, 2008 doi:10.1152/ajpregu.00022.2008.-Atrial mechanoreceptors, sensitive to stretch, contribute in regulating heart rate and intravascular volume. The information from those receptors reaches the nucleus tractus solitarius and then the paraventricular nucleus (PVN), known to have a crucial role in the regulation of cardiovascular function. Neurons in the PVN synthesize CRF, AVP, and oxytocin (OT). Stimulation of atrial mechanoreceptors was performed in awake rats implanted with a balloon at the junction of the superior vena cava and right atrium. Plasma ACTH, AVP, and OT concentrations and Fos, CRF, AVP, and OT immunolabeling in the PVN were determined after balloon inflation in hydrated and water-deprived rats. The distension of the balloon increased the plasma ACTH concentrations, which were higher in water-deprived than in hydrated rats (P Ͻ 0.05). In addition, the distension in the water-deprived group decreased plasma AVP concentrations (P Ͻ 0.05), compared with the respective control group. The distension increased the number of Fos-and double-labeled Fos/CRF neurons in the parvocellular PVN, which was higher in the water-deprived than in the hydrated group (P Ͻ 0.01). There was no difference in the Fos expression in magnocellular PVN neurons after distension in hydrated and water-deprived groups, compared with respective controls. In conclusion, parvocellular CRF neurons showed an increase of Fos expression induced by stimulation of right atrial mechanoreceptors, suggesting that CRF participates in the cardiovascular reflex adjustments elicited by volume loading. Activation of CRF neurons in the PVN by cardiovascular reflex is affected by osmotic stimulation. cardiac reflex; paraventricular nucleus CHANGES IN BLOOD VOLUME OR arterial and venous pressure lead to activation of physiological responses to restore cardiovascular homeostasis. These responses involve regulatory adjustments that are detected by arterial baroreceptors and cardiopulmonary mechanoreceptors (19,53). Hemorrhage produces unloading of arterial baroreceptors that initiate a reflex response to increase the sympathetic vasomotor activity and vasopressin secretion (19,52). On the other side, blood volume expansion activates atrial mechanoreceptors, with an increase of heart rate, inhibition of renal sympathetic nerve activity, and a decrease of vasopressin release (5, 30). The reflex tachycardia in response to hypervolemia was first described by Bainbridge in dogs (9), and it was also described in other species, including humans (10, 12, 34, 62).The atrial mechanoreceptors are located at the venous-atrial junction of the heart, and it is continuously signaling the central venous volume to the brain. Through vagal afferent projections, the information from the atrial mechanoreceptors reaches the nuc...

Atrial stretch delays gastric emptying of liquids in awake rats

“…Central venous pressure is considered equivalent to right atrial pressure and indicates right heart preload, and it is influenced by intravascular volume, venous tone, and right ventricular function (Pittman et al, 2004). Putative impairment in cardiovascular function appears unlikely because the present basal hemodynamic values were similar to those previously reported (Benedetti et al, 2008) and remained at stable levels throughout the experiments. According to Kaufman (1984), 50 μl distension of an intra-atrial balloon does not obstruct venous return in adult rats.…”

“…Changes in venous return are well known to activate myelinated and unmyelinated afferent fibers, triggering modulatory neurohormonal inputs to several brain areas involved in blood volume balance (Coleridge et al, 1964;Antunes-Rodrigues et al, 2004;Benedetti et al, 2008). In the present work, we considered that the reflex activation of such mechanoreceptors, manifested by a tachycardia response (Kappagoda et al, 1972;Kaufman et al, 1981;Benedetti et al, 2008) during 50 and 70 μl AS, is involved in the GE delay. The role of afferent Fig.…”

Water deprivation-induced sodium appetite and differential expression of encephalic c-Fos immunoreactivity in the spontaneously hypertensive rat

“…The density of c-Fos immunoreactivity (Fos-IR), a useful marker of cell activity (1,22), has been successfully employed in mapping encephalic areas associated with selective dehydration of either the intracellular or the extracellular fluid, and water deprivation-induced double dehydration of both fluids (7,16,25,28,32,41).…”

Atrial stretch increases the gastric tonus of anesthetized rats

“…injection of a KCl-saturated solution in order to check the positions of the gastric and atrial balloon catheters by close inspection. According to Benedetti et al (2008), the distension of the intra-atrial balloon promotes an obvious and reliable inflation of the right atrium. Rats with incorrect balloon placement or rats with a balloon that did not inflate were discarded.…”