Cat carotid bodies reinnervated by normal or foreign nerves

The carotid body of the cat was reinnervated with either its native nerve, the carotid sinus nerve (CSN, re-anastomosis), or a foreign nerve, the lingual branch of the IXth cranial nerve (LN, cross-anastomosis). In both types of preparations, regenerating axons from the LN or CSN readily penetrated carotid body parenchymal tissue, as demonstrated by axoplasmic transport of radiolabeled material from the petrosal (sensory) ganglion. Electron microscopy revealed nearly normal fiber invasion into lobules of glomus (type I) and sustentacular (type II) cells following reinnervation by either the foreign or native nerve. However, while the regenerated CSN fibers formed a normal complement of specialized axon terminals in contact with type I cells, the incidence of such terminals in LN reinnervated carotid bodies was reduced by over 90% (2-19 months survival time). This low incidence of specialized LN endings was correlated with reductions in the magnitude of the chemosensory discharge elicited in these preparations by asphyxia, NaCN or acetylcholine. These data suggest that chemosensitivity depends upon intimate association between glomus cells and afferent nerve endings; and that the ability to form such contacts may reside in particular axons whose incidence is higher in the CSN than in the LN.