Reflexes from the aortic baroreceptor fibers in the cervical vagus of the cat and the dog.

The baroreceptor fibers which arise from the aortic arch course centrally within the vagus nerve in the dog, and they usually follow this path in the cat. Near the origin of the superior laryngeal nerve, a separate branch of the cervical vagus (the cervical aortic nerve) arises. Previously, it was thought that this nerve contained all the important baroreceptor afferents. Aortic baroreceptor fibers that are not within the cervical aortic nerve were studied in the anesthetized cat and dog after cervical aortic and carotid sinus nerves had been sectioned. Some experiments were acute, but most were conducted 13-60 days after nerve section (to allow transected nerves to degenerate). After degeneration, baroreceptor activity was found in the peripheral aortic nerves in most animals. The sensory terminals of the surviving baroreceptor fibers were on the aortic arch on the left side and at the root of the right subclavian artery on the right side. In one of four chronic cats, four of eight chronic dogs after degeneration, and one of three animals in acute experiments a depressor response (8-70 mm Hg in chronic and 10 mm Hg in acute experiments) followed stimulation of the peripheral aortic nerve. The surviving aortic baroreceptor fibers coursed centrally in the cervical vagus.