Distribution of vagal preganglionic neurons in the rat brain innervating thoracic and abdominal organs revealed by retrograde DiI tracing.

To investigate the distribution and number of preganglionic neurons which regulate motility and secretion in thoracic and abdominal organs in the vagal parasympathetic nervous system, the neuronal tracer DiI was injected into the organs and the distribution of retrogradely labeled neurons was examined in the rat brainstem. The stomach received the vast majority of efferent projections from the dorsal motor nucleus of the vagus nerve (DMV). The cecum and the duodenum also received projections from the DMV, but they originated from a smaller number of preganglionic neurons. Preganglionic neurons projecting to the stomach occupied the middle part of the DMV, those projecting to the cecum occupied the lateral part of the DMV, and those projecting to the duodenum were found in the medial edge of the DMV. The ventral and dorsal sides of the stomach wall were innervated by the left and right vagus nerves, respectively. However, immediately after passing the boundary between the stomach and duodenum, the left and right vagal nerve fibers mixed in the ventral and dorsal walls of the distal gastrointestinal tract. The nucleus ambiguous is a mixture of parasympathetic preganglionic neurons and motoneurons. In this study, we revealed that the major targets of these preganglionic neurons were the lungs and other thoracic organs.