Role of the locus ceruleus in baroreceptor regulation of supraoptic vasopressin neurons in the rat.
Grindstaff, Ryan J., Regina R. Grindstaff, Margaret J. Sullivan, and J. Thomas Cunningham.
Department of Physiology and Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri 65211
APStracts 7:0138R, 2000.
The goal of this study was to identify the source of baroreceptor-related noradrenergic innervation of the diagonal band of Broca (DBB). Male Sprague-Dawley rats underwent sinoaortic denervation (SAD, n = 13) or sham SAD surgery (n = 13). We examined Fos expression produced by baroreceptor activation and dopamine-ß-hydroxylase immunofluorescence in hindbrain regions that contain noradrenergic neurons. Baroreceptors were stimulated by increasing blood pressure >40 mmHg with phenylephrine (10 µg•kg"minus"1•min"minus"1 iv) in sham SAD and SAD rats. Controls were infused with 0.9% saline. Only the locus ceruleus (LC) demonstrated a baroreceptor-dependent increase in Fos immunoreactivity in dopamine-ß-hydroxylase-positive neurons. In a second experiment, normal rats received rhodamine-labeled microsphere injections in the DBB (n = 12) before phenylephrine or vehicle infusion. In these experiments, only the LC consistently contained Fos-positive cells after phenylephrine infusion that were retrogradely labeled from the DBB. Finally, we lesioned the LC with ibotenic acid and obtained extracellular recordings from identified vasopressin neurons in the supraoptic nucleus. LC lesions significantly reduced the number of vasopressin neurons that were inhibited by acute baroreceptor stimulation. Together, these results suggest that noradrenergic neurons in the LC participate in the baroreflex activation of the DBB and may thus be important in the baroreflex inhibition of vasopressin-releasing neurons in the supraoptic nucleus.
Received 27 May 1999; accepted in final form 9 February 2000
APS Manuscript Number R312-9.
Article publication pending Am J Physiol Regulatory Integrative Comp Physiol
ISSN 1080-4757 Copyright 2000 The American Physiological Society.
Published in APStracts on 12 May 2000