BACKGROUND: Little is known of the central efferent neurons innervating the smooth muscle esophagus. The aim of this study was to define the location of the efferent neural pathways of the brain stem swallowing mechanism in the cat, particularly those supplying the esophageal body smooth muscle. METHODS: Fluorescent, retrogradely transported tracers were injected into the cervical striated muscle and thoracic smooth muscle segments of the esophagus and also the lower esophageal sphincter. RESULTS: Striated muscle efferents were found in the rostral nucleus ambiguus, but approximately 8% were located in the dorsal motor vagal nucleus. Smooth muscle efferents were present in the dorsal motor vagal nucleus in two groups, one rostral and one caudal to the obex. An additional group was found in nucleus retroambiguus. Approximately 8% of the total smooth muscle efferents were present in rostral nucleus ambiguus and were lateral to the striated muscle efferents. The lower esophageal sphincter efferents had a similar distribution to the smooth muscle efferents, but the rostral concentration of cells in the dorsal motor vagal nucleus was shifted caudally. CONCLUSIONS: Esophageal body smooth muscle motoneurons are arranged with a similar distribution to those innervating the lower esophageal sphincter but with some topographic variation.
BACKGROUND: Little is known of the central efferent neurons innervating the smooth muscle esophagus. The aim of this study was to define the location of the efferent neural pathways of the brain stem swallowing mechanism in the cat, particularly those supplying the esophageal body smooth muscle. METHODS: Fluorescent, retrogradely transported tracers were injected into the cervical striated muscle and thoracic smooth muscle segments of the esophagus and also the lower esophageal sphincter. RESULTS: Striated muscle efferents were found in the rostral nucleus ambiguus, but approximately 8% were located in the dorsal motor vagal nucleus. Smooth muscle efferents were present in the dorsal motor vagal nucleus in two groups, one rostral and one caudal to the obex. An additional group was found in nucleus retroambiguus. Approximately 8% of the total smooth muscle efferents were present in rostral nucleus ambiguus and were lateral to the striated muscle efferents. The lower esophageal sphincter efferents had a similar distribution to the smooth muscle efferents, but the rostral concentration of cells in the dorsal motor vagal nucleus was shifted caudally. CONCLUSIONS: Esophageal body smooth muscle motoneurons are arranged with a similar distribution to those innervating the lower esophageal sphincter but with some topographic variation.