Ultrastructure of aortic and pulmonary baroreceptors in the domestic fowl.

Baroreceptor regions are definitely present in the arterial wall of the aorta and pulmonary arteries of the domestic fowl. In such regions, the arterial wall is modified by the interruption and absence of the elastic laminae and smooth muscle cells. The baroreceptor endings are similar ultrastructurally to the baroreceptors of the mammalian aorta and carotid sinus; therefore they are slowly adapting. Some of the amine- or peptide-containing endings, which are present in the modified regions, share the same Schwann cell with the baroreceptor endings; they probably modulate the stimulus threshold of the baroreceptor endings. Likewise, some of the cholinergic endings share the same Schwann cell with the baroreceptor endings, and may form the efferent branch of a reflex arc and thereby modify the tension of the arterial musculature which is then registered by the baroreceptor endings. There is a possibility that aminergic anc cholinergic endings interact with each other since they sometimes share the same Schwann cell. The encapsulated endings which are reported in this investigation are similar to those of the avian carotid arteries, and they, too, should be slowly adapting to pressure changes in the arterial wall.