On the anatomical organization of the vagal nuclei

The neurons of origin of the right vagus and its components in both the monkey (Macaca fascicularis) and albino rats were localized by the retrograde transport of horseradish peroxidase (HRP) applied to the stomach wall, the vagal trunk and its recurrent laryngeal branch. An attempt was also made to localize the neurons forming the superior laryngeal nerve and those supplying the thoracic organs by a combination of operative procedures. The results showed that the stomach was innervated by neurons distributed throughout the entire rostrocaudal extent of the dorsal motor nucleus (DMN) on both sides of the brain stem. Neurons scattered throughout the entire extent of the DMN and nucleus ambiguus (NA) supplied the thoracic viscera. There did not appear to be any topographic arrangement in the DMN neurons supplying the abdominal and thoracic viscera as reported by other workers, and there was no clear evidence of crossing of vagal fibers in the monkey brain stem, though such crossing was seen in the rat brain stem. Both the superior and inferior ganglia of the vagus nerve were labeled following application of HRP to the vagal trunk. Neurons in the caudal part of the NA gave rise to fibers in the ipsilateral recurrent laryngeal nerve, at least on the right side. The neurons giving rise to the superior laryngeal nerve could not be delineated in this study. In all the experimental procedures described, the hypoglossal nucleus was labeled only after applying HRP to the hypoglossal nerve.