Mechanisms of pressor response produced by stimulation of nucleus ambiguus.
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.
Machado
B H
BH
Department of Pharmacology, University of Iowa, College of Medicine, Iowa City 52242.
Brody
M J
MJ
D000818:Animals; D001794:Blood Pressure / Q000502:physiology*; D004558:Electric Stimulation; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D007821:Laryngeal Muscles / Q000294:innervation*; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D010609:Pharyngeal Muscles / Q000294:innervation*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014655:Vascular Resistance
D005971:Glutamates; D010656:Phenylephrine; D018698:Glutamic Acid