Ultrastructural degradation of the carotid body in the aged rat: is there a role for atherosclerosis in the main carotid arteries?

In this study we examined the potential role of atherosclerosis in the main arteries supplying blood to the carotid body in the organ's morphological degradation with age. We addressed this issue by comparing the ultrastructural picture of carotid bodies and of fragments of the carotid artery bifurcation in two age-extreme groups of rats: young - 3 months old and senescent - 24 months old. Tissues were excised under surgical anesthesia, fixed in aldehydes, and processed for transmission electron microscopy. We found that the old carotid body parenchyma exhibited profound degenerative changes. Chemoreceptor cells were at various stages of atrophy, ranging from swollen mitochondria and fewer secretory vesicles to dark dehydrated cells. In contrast, the senescent carotid artery bifurcation was little different from that in young rats. Particularly, endothelial cells were in perfect condition. There were some changes in deeper arterial wall layers such as breaks in the continuity of elastic bands or a subtly different phenotype of smooth muscle cells. No foam cells or calcium build-ups were found in the arterial walls. Such changes correspond to the process of arterial wall stiffening in old age rather than to the outright atherosclerosis. Lack of atherosclerosis in the common carotid arteries, which could hamper blood flow, argues against its playing a role in the morphological age-changes in the carotid bodies.