| Abstract: | The medullary distribution of afferent fibers and cells of origin of the cervical vagal trunk and of the vagal innervation of the stomach have been studied using the anterograde and retrograde transport of horseradish peroxidase (HRP). Injections of HRP were made into the cervical vagus nerve, the stomach wall, the proximal small intestine, or the peritoneal cavity. Two to four days following the injections, the rats were perfused and the medullae oblongatae and nodose ganglia were processed using the tetramethyl benzidine method. Cervical vagus nerve injections of HRP resulted in heavy anterograde labeling in the ipsilateral nucleus of the tractus solitarius (NTS) and the commissural nucleus. Lighter labeling was seen in these regions on the contralateral side, but did not extend as far rostrally in the NTS. Labeling was also seen in the area postrema. Retrogade labeling of somata was present in the ipsilateral side in the nodose ganglion, throughout the whole extent of the dorsal motor nucleus of the vagus, much of the nucleus ambiguus and in rostral levels of the cervical spinal cord. After stomach injections, labeling indicative of afferent fibers was observed bilaterally in the dorsomedial and medial portions of the NTS and in the commissural nucleus. Labeled efferent fibres arose from neurons in the dorsal motor nucleus of the vagus, nucleus ambiguus and the cervical spinal cord. Retrogradely labeled somata were found bilaterally, throughout the rostrocaudal length of the dorsal motor nucleus in all cases with stomach injections. In some, but not all cases, labeled somata were seen bilaterally in compact areas within the nucleus ambiguus, particularly rostrally. Control injections of HRP into the intestinal wall and peritoneal cavity indicated that the stomach was the primary source of afferent and efferent labeling in the medulla following subdiaphragmatic injections. |
