Cytoarchitectonic organization of laryngeal motoneurons within the nucleus ambiguus of the cat.

The central distribution of laryngeal motoneurons was studied in the cat by retrograde axonal transport of horseradish peroxidase. The enzyme was injected selectively into the cricothyroid (CT), lateral cricoarytenoid and thyroarytenoid (LCA-TA), and posterior cricoarytenoid (PCA) muscles of the larynx with or without the previous sectioning of the left laryngeal recurrent nerve (LR) or the left superior laryngeal nerve (SL). The CT motoneurons appeared as a compact group of medium-size cells located in the rostral one-third of the nucleus ambiguus (nA). The LCA-TA motoneurons were found in the caudal two-thirds of the nA, constituting a loose group of large motoneurons. The PCA motoneurons were located throughout the whole extend of the nA, the cells being large in the caudal pole and smaller in the rostral one-third of nA. Laryngeal muscle innervation was exclusively of ipsilateral origin. Axonal projections in the brain stem were different depending on the nerve (LR or SL) by which the efferent fibers were sent.