Modulation of the baroreceptor reflex by stimulation of the hypothalamic defense and vigilance areas.

Electrical stimulation of the hypothalamic defense area (HDA) elicits a pressor/tachycardia response that is believed to prepare an animal for fight or flight. In contrast, electrical stimulation of the hypothalamic vigilance area (HVA) evokes a pressor/bradycardia response that is associated with the inhibition of movement. The differences in the behavioral components of these two affective response patterns suggest differential modulation of the baroreceptor reflex. The present study tested this idea by assessing the effects of electrical stimulation of the HDA and the HVA upon the bradycardia/depressor response elicited by stimulation of the aortic nerve (AN) in rabbits. Concurrent HDA and AN stimulation was observed to attenuate the AN-elicited bradycardia but enhanced the depressor response elicited by AN stimulation. In contrast, concurrent stimulation of the HVA and AN enhanced the bradycardia elicited by AN stimulation but reduced the magnitude of the AN-elicited depressor response. These results provide evidence for differential modulation of the baroreceptor reflex during the defense and vigilance reactions.