An HRP study of location of the rabbit palatopharyngeal motoneurons and peripheral course of their axons.

The location of the rabbit palatopharyngeal motoneurons and the peripheral course of their axons were investigated with intramuscular injection of HRP either in the normal animal or in conjunction with intracranial severing of the vagal rootlets. Labeled palatopharyngeal motoneurons were ipsilaterally located within a subdivision of the nucleus ambiguus which is formed by a compact arrangement of the smallest neurons of the nucleus and situated in the rostral of the nucleus. We named that subdivision the compact cell group (CoG). The labeled motoneurons occupied the caudal half of the CoG at a level from about 500 to 1,900 microns rostral to the obex. Labeling was completely abolished by severing the vagal rootlets, indicating that the axons of the palatopharyngeal motoneurons traversed the vagal rootlets.