Innervation of the rat aortic (subclavian) body: An ultrastructural study following axonal degeneration

Abstract

The rat aortic (subclavian) body was studied to determine the type (afferent or efferent), source, and characteristics of the nerves which innervate these arterial chemoreceptors. To determine whether the nerve endings adjacent to the glomus cells were afferent (sensory) or efferent, axonal degeneration experiments were performed in which the vagus nerve was sectiones either above or below the nodose ganglion. The results of these studies confirm that almost all of the nerves are afferent axons whose nerve cell bodies are located in the nodose ganglion. Additionally, following injections of 6-OHDA, no axonal endings could be identified which were sympathetic postganglionic in origin. The few nerve endings which did not degenerate (∼5%) may be preganglionic sympathetic fibers from the inferior cervical ganglion. Synaptic connections between nerve endings and glomus cells include afferent nerve endings which are postsynaptic to glomus cells, a few presynaptic to glomus cells are rarely, some which form reciprocal synapses. All of the axonal endings are characterized by small clear-core synaptic vesicles (diameter = 45.4 nm) and a few larger dense-core vesicles (diameter = 74.2 nm). Glomus cells of the rat aortic body are characterized by an abundance of dense-core vesicles which average 109.6 nm in diameter. Glomus cells appeared to be of only one variety and were observed in synaptic contacty with one another. The results of this study demonstrate that there are differences between the aortic and carotid bodies, especially with respect to the sophistication of their synaptic connections. These morphological differences may be related to several of the known physiological differences between these chemoreceptors.