THE JOURNAL OF COMPARATIVE NEUROLOGY 217:31-46 (1983) Subnuclear Organization of the Dorsal Motor Nucleus of the Vagus Nerve in the Pigeon, zyxw CoZumba zyx Zivia DAVID MILES KATZ AND HARVEY J. KARTEN Department of Neurobiology and Behavior (D.M.K. and H.J.K.), Department of Psychiatry and Behavioral Science (H.J.K.), State University of New York at Stony Brook, Stony Brook, New York 11794 ABSTRACT The present study is the first of two papers describing the cytoarchitec- turd and functional organization of the dorsal motor nucleus of the vagus nerve (DMN complex)in the pigeon. This paper describes the distribution of vagal motoneurons within the pigeon brainstem, and the cytoarchitectural organization of the DMN complex. Our description is based on studies of Nissl-stained tissue from normal animals and on experimental studies using retrograde tracing techniques. Cells within the DMN complex were classi- fied according to size, morphology, location, and staining characteristics. These studies demonstrate that vagal motoneurons are localized to (1) the DMN complex, zyxwvut (2) the region of the nucleus ambiguus, and (3) the region of the reticular formation extending between the dorsal motor nucleus and the nucleus ambiguus. Our cytoarchitectural studies indicate that the DMN complex is composed of at least 11 cytoarchitecturally distinct subnuclei. These subnuclei are evident in normal tissue and are especially prominent in cases where HRP backfilling produces a Golgi-like staining of the motoneu- rons. The subnuclei can be distinguished by their positions within the DMN complex and by the size, shape, and staining chracteristics of their constitu- ent neurons. Comparison of these data with studies in other species indi- cates similar patterns of cytoarchitectural organization in the DMN com- plex of some mammals. The diversity of nuclear subgroups within the DMN complex may be related to the heterogeneity of target organs innervated by these cells. Key words: vagal motoneurons, anatomical segregation, neuronal cytoarchitecture, visceral representation, autonomic regulation The dorsal motor nucleus of the vagus nerve contains the cells of origin of vagal motor fibers that innervate car- diovascular, respiratory, and gastrointestinal organs. Our laboratory is interested in identifying the subpopulations of vagal motoneurons that innervate individual peripheral organs as a step toward understanding the anatomical or- ganization of organ-specific autonomic pathways. The present report is the first of two papers describing the cy- toarchitectural and functional organization of the dorsal motor nucleus of the pigeon. The first paper describes the location, extent, and cytoarchitectural organization of the nucleus in normal tissue, using retrograde tracing tech- niques. The second paper describes the topographic repre- zyxwv 0 1983 ALAN R. LISS, INC. sentation of individual vagal targets within the dorsal motor nucleus. During the last 100 years, numerous investigators have studied visceral representation within the dorsal motor nu- Accepted December 22, 1982. Dr. Katz’s present address is Division of Developmental Neu- rology, Cornell University Medical College, 515 E. 71st., S-700, New York, NY 10021. Address reprint requests to Dr. Harvey J. Karten, Department of Neurobiology and Behavior, S.U.N.Y., Stony Brook, NY 11794.