AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 5 955-R962, Copyright © 1990 by American Physiological Society
Mechanisms of pressor response produced by stimulation of nucleus ambiguus
B. H. Machado and M. J. Brody
Department of Pharmacology, University of Iowa, College of Medicine, Iowa City 52242.
We showed previously that activation of nucleus ambiguus (NA) induced
bradycardia and increased arterial pressure. In this study, we compared
responses produced by electrical and chemical (glutamate) stimulation of NA
and adjacent rostral ventrolateral medulla (RVLM). Equivalent pressor
responses were elicited from both areas. However: 1) The response from RVLM
was elicited at a lower frequency. 2) Regional vascular resistance changes
were different, i.e., electrical stimulation of NA increased vascular
resistance in hindquarters much more than the renal and mesenteric beds. In
contrast, electrical and chemical stimulation of RVLM produced a more
prominent effect on the renal vascular bed. 3) Bradycardia was elicited
from NA at lower current intensity. 4) Glutamate produced bradycardia only
when injected into NA. Studies in rats with sinoaortic deafferentation
showed that bradycardic response to activation of NA was only partly reflex
in origin. We conclude that 1) NA and RVLM control sympathetic outflow to
regional vascular beds differentially and 2) the NA region involves
parasympathetic control of heart rate and sympathetic control of arterial
pressure.
