AJP - Heart and Circulatory Physiology, Vol 248, Issue 6 937-H944, Copyright © 1985 by American Physiological Society
Anterior hypothalamic lesions impair reflex bradycardia selectively in rats
E. Miyajima and R. D. Bunag
To determine whether removal of the anterior hypothalamus would alter
baroreflex activity, reflex inhibition of heart rate and renal nerve
activity during pressor responses to intravenous phenylephrine was examined
in rats with bilateral anterior hypothalamic lesions. Although there were
no differences in basal blood pressure and heart rate 10 days after
surgery, reflex bradycardia was significantly reduced in awake lesioned
rats compared with sham-operated controls. The differences in reflex
bradycardia were abolished by cholinergic blockade with atropine but
unaltered by beta-adrenergic blockade with propranolol. Because attenuation
of chronotropic reflexes by anterior hypothalamic lesions resembled that
produced by cholinergic blockade, vagal inhibition must be at least partly
responsible. Reflex bradycardia was still attenuated even in lesioned rats
anesthetized with alpha-chloralose, but renal nerve activity was as
inhibited as in sham-operated rats. These results suggest that the anterior
hypothalamus participates in baroreflex regulation of heart rate by
altering parasympathetic tone but without affecting cardiac or renal
sympathetic nerve activity.
