Cells of origin of motor axons in the subdiaphragmatic vagus of the rat

The central cell groups that give rise to the motor axons that travel in the subdiaphragmatic vagus were re-examined in the rat by transecting the dorsal or ventral vagus near the stomach and incubating the nerve stump in crystalline horseradish peroxidase (HRP). An exceedingly large percentage of cells was labeled throughout the dorsal motor nucleus of the vagus (mX), with labeled cells extending even beyond the rostro-caudal limits of the nucleus usually assigned on the basis of cytoarchitecture alone. Different patterns of cell-labeling could be correlated with one or the other of the two vagal branches. Incubation of the ventral branch labeled cells only in the left mX, while incubation of the dorsal branch labeled cells on both sides, although more extensively on the right. HRP-positive somata were also observed bilaterally in the nucleus ambiguus (NA) after incubation of either branch of the subdiaphragmatic vagus; this finding is in contrast to previous accounts in which motor fibers from NA were considered to project only to cervical and thoracic structures. These results suggest that mX and NA are responsible for a substantial component of abdominal innervation in the rat.