Innervation of the carotid body of the adult rat. A serial ultrathin section analysis.

The innervation of the carotid body of adult rats was studied by means of serial ultrathin sections. A single branching nerve fiber innervates 12 chief cells through several kinds of terminals (vesicle-containing, mitochondrial sack, and calyx-type) in en-passant and bouton forms.Two types of synaptic contacts between nerve terminals and chief cells are found; type 1 in which chief cells are postsynaptic, and type 2 in which chief cells are presynaptic. Since a single nerve fiber (possibly from the glossopharyngeal nerve) forms both types of synapses with type 2 predominating, the nerve fiber is considered basically sensory or centripetal. In addition to their synaptic connections with sensory nerve fibers, chief cells located in the periphery of this organ are in synaptic relation with dendrites of a few ganglion cells adjacent to these cells. Here the chief cells are presynaptic. A few synaptic contacts between two adjacent chief cells are seen, and so are direct contacts between thief cells and preganglionic efferent nerve fibers terminating on ganglion cells.