Raphespinal and reticulospinal neurons project to the dorsal vagal complex in the rat.

Stimulation of the caudal raphe nuclei alters visceral functions. The caudal raphe nuclei project to the nucleus of the solitary tract, which receives the central terminations of vagal afferents and plays an important role in the central integration of autonomic activities. The caudal raphe nuclei also project to the somatic and preganglionic autonomic motoneurons of the spinal cord. Diamidino yellow was injected into the nucleus of the solitary tract, and fast blue was injected into either the cervical, thoracic, or lumbar spinal cord. Large numbers of double-labeled neurons were present within the caudal raphe nuclei and the adjacent reticular formation of the medial tegmental field. This observation documents that individual raphespinal and reticulospinal neurons project an axon collateral to the nucleus of the solitary tract. These data demonstrate the anatomic substrate for global modulation of the autonomic motoneuron pool by the caudal raphe nuclei.