Role of the nucleus ambiguus in the regulation of heart rate and arterial pressure

Abstract

The present study examined the effect of lesion of cell bodies in the nucleus ambiguus area on the development of neurogenic hypertension and further explored the cardiovascular responses produced by chemical and electrical stimulation of the nucleus ambiguus and the neighboring Cl region. Three days after chemical lesion of the nucleus ambiguus with kainic acid, arterial pressure and heart rate were unchanged; however, subsequent sinoaortic deafferentation produced a significantly greater increase of arterial pressure (157 ± 7 vs 132 ± 5 mm Hg) and heart rate (436 ± 10 vs 374 ± 10 beats/min) compared with those produced by sham lesion. Glutamate injected into the nucleus ambiguus increased arterial pressure and heart rate at 20 nmol/100 nl and decreased heart rate at 50 nmol/100 nl. Glutamate injected into the Cl area increased arterial pressure and heart rate at both doses. γ-Aminobutyric acid at 50 nmol/100 nl produced bradycardia and a fall in arterial pressure when injected into both the nucleus ambiguus and Cl area. The heart rate responses to γaminobutyric acid and glutamate were attenuated in sinoaortic-deafferentated rats. The nucleus ambiguus and the Cl region were mapped using electrical stimulation with microelectrodes. All points stimulated in three anteroposterior sections in the nucleus ambiguus and the Cl area produced increases in arterial pressure, whereas bradycardia was restricted to the middle of three lateral coordinates associated with the center of the nucleus ambiguus and the Cl area ventral to the nucleus ambiguus. These data indicate that 1) chemical lesion of cell bodies of the nucleus ambiguus enhances the increase of arterial pressure after sinoaortic deafferentation and 2) electrical and chemical stimulation of the nucleus ambiguus area produce both bradycardia and increased arterial pressure. The results obtained with kainic acid lesions of the nucleus ambiguus suggest that this area exerts an inhibitory influence on sympathetic vasomotor tone that, when removed, could enhance the increase of arterial pressure after sinoaortic deafferentation. We conclude that the nucleus ambiguus is involved not only in heart rate control but also in central regulation of arterial pressure through pressor systems, and perhaps separately with neuronal projections associated with the baroreceptor reflex. © Williams and Wilkins 1988. All Rights Reserved.