Interactive responses to stimulation of the amygdaloid central nucleus and baroreceptor afferent activation in the...

Recent evidence suggests that the amygdaloid central nucleus (ACE) may contribute to the regulation of arterial baroreceptor-vagal reflex sensitivity. To obtain additional data relevant to this suggestion, interactions between stimulation of the ACE and arterial baroreceptor afferent activation were examined. New Zealand rabbits were anesthetized with alpha-chloralose and a stimulating electrode was implanted stereotaxically in the ACE. In the first series of experiments, cardiovascular responses to stimulation of the ACE were assessed during periods in which blood pressure was decreased using sodium nitroprusside or increased in the rostral arterial compartment by inflating the tip of a Swan-Ganz catheter positioned in the descending aorta. It was found that the magnitude of bradycardia to stimulation of the ACE was correlated with the level of arterial blood pressure at the onset of stimulation, such that higher blood pressures were associated with larger bradycardic responses. These data suggest that arterial baroreceptor afferent activity may be an important factor in the elicitation of bradycardia from the ACE. In the second series of experiments, the aortic nerve was isolated, and cardiovascular responses to stimulation of the aortic nerve and to low frequency (5 Hz) stimulation of the ACE were assessed both alone and in combination. Stimulation of the aortic nerve during low frequency stimulation of the ACE was found to produce bradycardia of a significantly larger magnitude than the sum of the responses produced by each stimulus presented alone. These data demonstrate that bradycardia to stimulation of baroreceptor afferent fibers is augmented significantly during low frequency stimulation of the ACE. Taken together, these results are consistent with the notion that the ACE may contribute to the sensitivity of the arterial baroreceptor-vagal reflex.