Brainstem topology of the vagal motoneurons projecting to the esophagus and stomach in the house musk shrew, Suncus murinus.

The central origin of vagal efferents innervating the esophagus and stomach in the house musk shrew, Suncus murinus, was studied using the retrograde tracing technique. The animals were perfused with fixative 48-72 h after HRP injection and sections were processed by HRP histochemistry. HRP application into the gastroesophagus resulted in bilateral labelling of neurons in the dorsal motor nucleus of the vagus nerve (DMX) and ambiguous nucleus (AN). Labelled neurons in the DMX were observed from all regions except from the cervical esophagus, while ones in the AN were seen from the esophagus and cardia. The more labelled neurons were observed on the right DMX from subdiaphragmatic esophagus, cardia, lesser curvature and ventral corpus, while on the left DMX from the dorsal corpus labelled neurons in the longitudinal extent of the DMX were generally located at the dorsal and dorsomedial part, and those in the middle part were scattered. Labelled neurons in the AN were located restricted in the rostral part. Our results suggest that in the Suncus murinus the rostrocaudal site-specific localization within the DMX was not found, but it was prominent in the AN. In addition, while the majority of neurons which supply the esophagus and stomach were located in the DMX, only a small number was found in the AN.