Axon regeneration following a lesion of the carotid nerve: electrophysiological and ultrastructural observations.

Carotid nerves of the cat were crushed and allowed to regenerate in order to study the properties of regerating fibers and the role of carotid body parenchymal cells (glomus or type I, and sustentacular or type II) in the transduction of chemosensory activity. Such activity is reinitiated 6 days after the nerves are crushed close (1-2 mm) to the carotid body. The process of recovery is delayed when a crush is made at successively greater distances (5-6 and 10-12 mm) from the carotid body. Ultrastructural studies show that the reappearance of nerve endings on the glomus-sustentacular cell complex coincides in time with the onset of chemosensory activity. The regenerated nerve endings increase in size and number and appear normal by 48 days. Some barosensory activity can be elicited 6 days after a nerve crush close to the carotid sinus, but rhythmic barosensory discharges only occur after the 21st day when myelinated axons reappear in the carotid sinus adventitia. Results suggest that recovery of chemosensory function depends on the reestablishment of apposition between regenerating carotid nerve fibers and parenchymal cells of the carotid body.