Central neural regulation of carotid baroreceptor reflexes in the cat

Reflex changes of the mean aortic blood pressure (BP) to carotid sinus stretch or carotid occlusion in anesthetized vagotomized cats were observed following ablation or electrical stimulation of brain. Decerebration produced augmentation of the depressor response to sinus stretch, reduction of the pressor response to carotid occlusion, and fall of BP. Subsequent cerebellectomy produced an increase of depressor and pressor responses. Midpontine section produced disappearance of the pressor response to carotid occlusion and appearance of a "paradoxical" pressor response to sinus stretch. Stimulation within hypothalamus and reticular formation produced augmentation and a barbiturate-sensitive poststimulus depression of pressor response without changes in BP. It is concluded that baroreceptor reflex responsiveness is under tonic and phasic control of brain structures above medulla and that pressor and depressor limbs of the reflex are not reciprocal and modified independently of each other and of the BP. This suggests functional separation of brainstem neurons involved in reflex and tonic BP control and that some cerebral regulation of BP is indirectly mediated through vascular reflexes.