Subnuclear organization of the dorsal motor nucleus of the vagus nerve in the pigeon, Columba livia

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Abstract
The present study is the first of two papers describing the cytoarchitec-tural 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 classified according to size, morphology, location, and staining characteristics. These studies demonstrate that vagal motoneurons are localized to (1) the DMN complex, (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 constituent neurons. Comparison of these data with studies in other species indicates 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.