Organization of the ambiguus nucleus in the frog (Rana esculenta)

Abstract

The common root of the glossopharyngeal, vagal, and accessory nerves and the individual branches of the vagus complex were labeled with cobalt, and the organization of the ambiguus nucleus was studied. The cell column labeled through the common root extended from the upper part of the medulla to the rostral spinal cord over a distance of about 3,500 microns. The labeling of individual branches revealed four subdivisions. 1) The pharyngomotor subdivision occupied the rostral 800 microns of the cell column. It gave origin to the innervation of the pharyngeal muscles. 2) The visceromotor subdivision, consisting of small and medium-sized cells labeled by way of the visceral branches of the vagus, was found in the rostrocaudal extent of the medulla. 3) the laryngomotor subdivision extended in the obex region over a distance of more than 1,000 microns. It supplied the sphincter muscles of the larynx. The dilator laryngeal muscle was represented in the rostral part of the visceromotor subdivision. 4) The accessory nerve subdivision was located in the lower medulla and the rostral spinal cord. From the results, the following conclusions are drawn. 1) The basic organization of the frog ambiguus nucleus is comparable to that of the rat, differences in nuclear organization reflecting differences in peripheral structures. 2) The cytoarchitectonic structure of the four subdivisions innervating different peripheral targets characteristically differ from each other. 3) On the basis of its characteristic neuronal morphology, the accessory nerve nucleus is regarded as an independent structure.