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Department of Physiology and Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri 65211
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-
-hydroxylase immunofluorescence in hindbrain regions that contain noradrenergic neurons. Baroreceptors were stimulated by increasing blood pressure >40 mmHg with phenylephrine (10 µg · kg
1
· min1 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--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.
Fos; supraoptic nucleus; sinoaortic deafferentation
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