Distribution of motoneurons in the brain stem of monkeys, innervating the larynx.

Following HRP (Horseradish Peroxidase) injections to cricothyroid muscle, recurrent laryngeal nerve and the vagal nerve at the level of nodose ganglion, labeled motoneurons were found to show a characteristic distribution in the brain stem of the monkey. Cricothyroid motoneurons extended from a level caudal to the facial nucleus to a level caudal to the middle part of the inferior olivary nucleus (IO) and were scattered around the outer area of nucleus ambiguus (Amb). Motoneurons supplying the recurrent laryngeal nerve were found between a level rostral to the middle of IO and its caudal end. Distribution was compact in the lateral part, but was scattered in the dorsomedial part of Amb. On injection of HRP into the nodose ganglion of the vagal nerve, labeled motoneurons were seen in two cell columns: In the Amb and in the dorsal motor nucleus of the vagus. The former extended from the rostral level of IO to the caudal end of IO, also showing connections with the retroambigual nucleus.