Projections from the nucleus and tractus solitarius in the cat.

After lesions in the nucleus of the tractus solitarius (NTS) in cats and kittens, the termination of degenerating fibers was localized using the Nauta and the Fink-Heimer techniques. The distribution of degenerating fibers was compared with that seen after lesions of the dorsal nucleus of the vagus (DNV) and after section of the ninth and tenth cranial nerves. The projection from the NTS is to the nucleus ambiguus (A), the other divisions of the NTS including the medial NTS and the ventrolateral NTS, and DNV, the medial reticular formation ventral to the NTS (probably the paramedian reticular nucleus), the nucleus intercalatus (INC), and the intermediate nucleus (INT). The probable functional significance of projections from the NTS to these medullary nuclei is discussed in relation to pathways of cardiovascular reflexes. Of particular note is the projection to the INT which may be part of a descending pathway to spinal cardiovascular neurons in the intermediolateral horn.