Projections of the internal branch of the superior laryngeal nerve of the cat.

The internal branch of the superior laryngeal nerve (iSLN) conveys sensory afferent information from receptors located in the laryngeal mucosa. The objectives of this study were: to determine the specific anatomical location of iSLN cell bodies within the nodose ganglion; to ascertain whether the jugular ganglion might also contain iSLN afferent bodies; to determine whether the iSLN contains sympathetic efferents originating in the cervical sympathetic ganglion; to determine whether the cell bodies of these efferents, if present, are localized within a specific region of this ganglion and to trace the transganglionic projection of iSLN afferents into the brain stem. Horseradish peroxidase was applied to the iSLN in ten adult cats. Following a survival period of 72 hours, the animals were sacrificed and the tissue was processed according to the tetramethylbenzidine method. Reaction product was localized in the rostral end of the nodose ganglion extending into the exiting vagus nerve, in the caudal end of the jugular ganglion and in the posterior portion of the cervical sympathetic ganglion. Transganglionic projections to the nucleus tractus solitarius were localized primarily in the dorsolateral subnucleus with substantial amounts of reaction product also in the intermediate and interstitial subnuclei. Except for a small bilateral projection observed in the commissural subnucleus, no other projections were seen to any other brain stem structures.