Longitudinal columnar organization within the dorsal motor nucleus represents separate branches of the abdominal vagus

Abstract

To identify the distribution of central preganglionics associated with each branch of the subdiaphragmatic vagus, the fluorescent tracer True Blue (TB) was administered intraperitoneally to rats with 4 out of 5 branches cauterized, and then, after 72 h, the animals were sacrificed for histological analysis. Each vagal branch contained the axons of a topographically distinct column of cells within the dorsal motor nucleus of the vagus (DMN). The columns representing the 4 branches with the largest numbers of efferents are organized as paired, bilaterally symmetrical, longitudinal distributions on either side of the medulla. Each DMN side contains a column occupying the medial two-thirds or more of the nucleus and corresponding to one of the gastric branches (left DMN, anterior gastric; right DMN, posterior gastric). Also on each side, the lateral pole of the DMN consists of a coherent cell column corresponding to one of the celiac branches (left DMN, accessory celiac; right DMN, celiac). The fifth branch, the hepatic, is represented by a limited number of somata forming a diffuse column largely coextensive with that representing the anterior gastric branch. At some levels of the DMN, the columns overlap. Labeled cells observed in the reticular formation were correlated in number, left-right ratios and response to vagotomy with those in the DMN, which suggests that they are displaced cells of the nucleus. Distributions of labeled cells in the nucleus ambiguus and the retrofacial nucleus were not tightly correlated with those of the DMN. An analysis of cell counts obtained for each of the individual branches suggests that vagal axons do not generally send collaterals through more than one branch.