Central connections of the sensory and motor nuclei of the vagus nerve.

Recent morphological and immunohistochemical studies bearing on the central pathways involved in processing vagal afferent information and in modulating the activity of vagal preganglionic neurons are summarized. The nucleus of the solitary tract (NTS), the principal recipient of first order vagal afferent inputs, projects to preganglionic cell groups of both divisions of the autonomic nervous system, to motor nuclei of cranial nerves that supply the face and tongue, to a series of 'relay' nuclei in the brainstem, and to a number of cell groups in the hypothalamus and the limbic region of the telencephalon that integrate autonomic, neuroendocrine and regulatory behavioral responses. With the exception of the cranial nerve motor nuclei, each cell group in receipt of direct inputs from the NTS projects back to this region and/or to the vagal motor nuclei, and is thereby in a position to influence vagal motor outflow. This central vagal system is further characterized by the presence of neurons that contain an impressive diversity of neuropeptides and monoamines. Examples are cited to illustrate how biochemically specified projections within this system are organized, and how they provide potential substrates for encoding information transfer between its components.