Administration of arginine vasopressin to the area postrema alters
response of nts neurons to afferent inputs.
Qu, Long, Meredith Hay, and Vernon S. Bishop.
Department of Physiology, The University of Texas Health Science
Center at San Antonio, San Antonio, Texas 78284-7756
APStracts 3:0311R, 1996.
This study was designed to determine if arginine vasopressin (AVP)
facilitates the response of nucleus tractus solitarius (NTS) neurons
to baroreceptor input. In anesthetized sinoaortic denervated
vagotomized rabbits, AVP was intravenously infused (15 [mu]g/kg/min,
1 min) or microinjected into the 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/sec, 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 [mu]g/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.
Received 31 July 1995; accepted in final form 22 July 1996.
APS Manuscript Number R478-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 August 1996