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AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 2 519-R525, Copyright © 1997 by American Physiological Society
ARTICLES |
L. Qu, M. Hay and V. S. Bishop
Department of Physiology, The University of Texas Health Science Center at San Antonio, 78284-7756, USA.
This study was designed to determine if arginine vasopressin (AVP) facilitates the response of nucleus of the solitary tract (NTS) neurons to baroreceptor input. In anesthetized sinoaortic-denervated vagotomized rabbits, AVP was intravenously infused (15 microg x kg(-1) x min(-1), 1 min) or microinjected into the area postrema (AP; 1 ng/nl, 10 nl). Extracellular recordings of evoked NTS neuronal responses to electrical stimulation of the aortic depressor nerve (ADN) or vagus nerve (1 Hz, 2-20 V, 0.05-0.6 ms) were evaluated before and after AVP administration. In neurons receiving input from the ADN (n = 19), 58% of them increased their responses after AVP (40.3 +/- 5.0 to 71.5 +/- 4,8%, P < 0.001). Similarly, in neurons activated by vagal stimulation (n = 22), 55% of them were facilitated during AVP administration (59.7 +/- 12.8 to 90.8 +/- 10.7%, P < 0.01). This action of AVP was independent of the mode of AVP administration, since either microinjection or venous infusion was effective in augmenting responses of NTS neurons to aortic/vagal stimulation. In an additional 37 spontaneous NTS neurons, AVP showed no effect on the mean baseline firing rate (8.9 +/- 1.3 vs. 9.6 +/- 1.3 spikes/s, P > 0.05), but increased neuronal activity in 54% of neurons (6.9 +/- 1.3 vs. 13.1 +/- 1.7 spikes/s, P < 0.01). In two rabbits pretreated with vasopressin antagonist (15 microg/kg iv), AVP failed to produce facilitatory effects (n = 8). The results of this study provide evidence in support of the hypothesis that circulating peptides modulate the arterial baroreflex via activation of neurons in the AP.
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