Viscerotopic representation of the upper alimentary tract in the medulla oblongata in the rat: The nucleus ambiguus

TLDR

The nucleus ambiguus innervates thoracic and abdominal viscera as well as upper alimentary tract musculature, but the literature disagrees on how its regions map to specific organs. This study aimed to systematically map the viscerotopic organization of the nucleus ambiguus. In 102 rats, tracers were injected into cranial nerves IX, X, XI, their major branches, and target organs to trace neuronal projections. The results revealed two longitudinal divisions: a dorsal special visceral efferent division with three rostrocaudally aligned subdivisions (esophagomotor, pharyngolaryngomotor, laryngomotor) each showing distinct dendroarchitecture, and a ventral general visceral efferent division spanning the medulla and containing preganglionic neurons for cardiac and supradiaphragmatic structures.

Abstract

Abstract The nucleus ambiguus has been reported to innervate various thoracic and abdominal viscera in addition to the musculature of the upper alimentary tract. However, the literature is contradictory as to how different regions of the nucleus ambiguus innervate specific organs. Therefore, a systematic investigation of the viscerotopic organization of the nucleus ambiguus was undertaken. In 102 rats, 0.5–10.0 μl of HRP, WGA‐HRP, cholera toxin‐HRP or fluorescent tracers were injected into the IXth, Xth, and XIth cranial nerves and the major branches of the Xth as well as organs supplied by them. The results demonstrate that the nucleus ambiguus in the rat is made up of two major longitudinal divisions: a dorsal division comprised of three rostrocaudally aligned subdivisions representing the special visceral efferent component, and a ventral division comprised of at least two subdivisions representing the general visceral efferent component. The dorsal division corresponds to the nucleus ambiguus in the narrow sense and comprises a rostral esophagomotor compact formation, an intermediate pharyngolaryngomotor semicompact formation, and a caudal laryngomotor loose formation. Each of these formations displays a characteristic dendroarchitecture. The stylopharyngeal and cricothyroid motoneurons are displaced rostrad from the main pharyngeal and laryngeal motoneuronal pools. Thyropharyngeal (lower constrictor) motoneurons occupy the rostral half of the semi‐compact formation and hyopharyngeal (middle constrictor) motoneurons its entire length. The ventral division of the nucleus ambiguus corresponds to the external formation , extends along the entire length of the medulla oblongata, and contains preganglionic neurons innervating the heart and supradiaphragmatic structures innervated by the glossopharyngeal and the superior laryngeal nerves.