Vagal efferent projections: Viscerotopy, neurochemistry and effects of vagotomy

In summary, the DMV and AMB have welldefined viscerotopic organizations that are distinguishable in terms of both afferent inputs and neurochemical architecture. The complex afferent and efferent connections at the level of the brainstem (Hopkins and Ellenberger, 1994) and multitude of direct and indirect inputs from higher levels of the neuraxis (Oppenheimer and Hopkins, 1994) emphasize the importance of a clear understanding of the organization of the final common brainstem pathways of the 'emotional motor system' that mediate autonomic responses to emotion and emotional stress. Neurochemical changes following vagal lesions are selective for specific viscera and are not uniform among functional subdivisions in the two nuclei. The visceratopic organization of vagal motoneurons thus may also be reflected in differences in trophic support and pathophysiology. Neurons which belong to one class, i.e. general visceral efferent or special visceral efferent, are different neurochemically and respond differentially to axotomy. The significance of these differences is unknown but must reflect biochemical trophic mechanisms relation to survival or death of neurons.