FIBER COMPOSITION OF THE SUPERIOR LARYNGEAL NERVE IN RATS AND GUINEA-PIGS

The fiber composition of the superior laryngeal nerve (SLN) which is s erved as the laryngeal afferent pathway was clarified in rats and guin ea pigs. The proportions of the number of myelinated and unmyelinated fibers in the SLN were almost the same in both rats and guinea pigs. T he unmyelinated fibers show the peak distribution of axon diameter ran ging from 0.79 to 1.00 mu m in both species, whereas the peak distribu tion of myelinated fibers ranged from 2.51 to 3.16 mu m in rats and fr om 3.98 to 5.01 mu m in guinea pigs. The mean axon diameter of unmyeli nated fibers was significantly larger in rats (mean: 1.12 mu m) than i n guinea pigs (0.96 mu m), whereas that of myelinated fibers was signi ficantly larger in guinea pigs (4.04 mu m) than in rats (3.30 mu m). S uch findings would reflect the cardiopulmonary reflexes elicited from the larynx in these animal species.