Afferent pathways of aortic baroreceptor fibers in guinea pigs

In guinea pigs, afferent fibers from aortic baroreceptors emerge from the aortic arch, and travel centrally as separate aortic depressor nerves (distinct from the vagus, the cervical sympathetic trunks and the recurrent laryngeal nerves) that merge into the superior laryngeal nerves. In guinea pigs anesthetized with urethane, orthodromic electrical stimulation of afferents in the aortic depressor and superior laryngeal nerves resulted in reflex hypotension. Bipolar electrical recording of afferent activity from the aortic depressor nerves revealed bursts of activity that were synchronous with cardiac systole. Activity of the nerves increased when arterial blood pressure was raised by phenylephrine, and it decreased when the pressure was lowered by sodium nitroprusside. Pulse-synchronous activity was recorded from the superior laryngeal nerve； severing the ipsilateral aotic depressor nerve eliminated this activity.