Effect of nucleus ambiguus lesion on the development of neurogenic hypertension

These studies evaluated the role of the nucleus ambiguus in regulating heart rate and cardiovascular activity. Three days after lesion of the nucleus ambiguus, arterial pressure and heart rate were unchanged; however, subsequent sinoaortic deafferentation produced a significantly greater increase of pressure (156 +/- 4 vs 124 +/- 6 mm Hg) compared to sham lesion. In both groups the heart rate was increased after deafferentation and the intrinsic heart rate (rate seen after autonomic blockade with atropine and propranolol) was significantly reduced. When the sequence was reversed (deafferentation before lesion), pressure (126 +/- 6 vs 126 +/- 7 mm Hg) and heart rate (334 +/- 17 and 340 +/- 16 beats/min) were not altered; however, intrinsic rate fell more. When the nucleus ambiguus was stimulated electrically, two responses emerged: increased pressure without rate changes and increased pressure with bradycardia. These data indicate that 1) lesion of the nucleus ambiguus facilitates hypertension produced by sinoaortic deafferentation unless lesioning follows deafferentation; and 2) stimulation of the nucleus ambiguus produces a pressor effect that is independent of the bradycardic response. We conclude that the nucleus ambiguus may be related to autonomic control of both heart rate and arterial pressure.