Hypothalamic control of baroreceptor reflexes.

GEBBER, GERARD L,, AND DAVID 's/v. SNYDER. Hypothalamic confrol of the barorecepfor reflexes. Am. J. Physiol. 2 18 ( 1) : 12+ 13 I . 1969.-The elect of hypothalamic stimulation was studied on the cardiac and vascular efferent components of the baroreceptor reflexes. Bradycardia evoked by carotid sinus nerve stimulation or norepinephrine was blocked by hypothalamic stimulation in spinal cats. These data demonstrate the existence of a suprabulbar system which functions to inhibit vagal bradycardia induced by baroreceptor activation. In contrast, baroreceptor modulation of central sympathetic outflow was functionally important during hypothalamic stimulation. The depressor response produced by carotid sinus stretch was not reduced by hypothalamic stimulation in vagotomized cats. The pressor response evoked by hypothalamic stimulation was markedly enhanced during carotid occlusion or following section of the carotid sinus nerves, Also, peripheral sympathetic nerve discharges elicited by hypothalamic stimulation were reduced when arterial pressure was raised. It is concluded that tachycardia associated with the pressor response evoked by hypothalamic stimulation was the result not only of increased cardiac sympathetic nerve activity, but also of inhibition of baroreceptor-induced vagal activation.