Localization of laryngeal motoneurons in the medulla oblongata of guinea pigs.

The distribution of motoneurons in the brain stem innervating the laryngeal muscles cricothyroid, posterior cricoarytenoid, and thyroarytenoid-lateral cricoarytenoid in the adult guinea pig was investigated. Horseradish peroxidase was injected into individual muscles or applied to the cut end of the superior laryngeal nerve and the recurrent laryngeal nerve. The laryngeal motoneuron pool of guinea pig is divided into two separate areas: the rostral retrofacial nucleus and the caudal nucleus ambiguus. Superior laryngeal and cricothyroid motoneurons were present only in the retrofacial nucleus, while recurrent laryngeal motoneurons were present in both the nucleus ambiguus and the retrofacial nucleus. Posterior cricoarytenoid motoneurons were located in the rostral and ventrolateral part of the recurrent laryngeal motoneuron pool in the nucleus ambiguus. The thyroarytenoid-lateral cricoarytenoid motoneurons partially overlapped the posterior cricoarytenoid pool and extended more dorsomedially and caudally in the nucleus. Our findings on the distribution of perikarya in the laryngeal motoneuron of the guinea pig are essentially the same as those of other mammals.