Anatomic effect of electrical stimulation on the reinnervation of the paralyzed canine larynx

Abstract

Problem: The larynx relies on correct innervation to mediate its normal functions. The aberrantly reinnervated larynx is compromised in its vocalization and airway-protective functions. Methods: Six canines were implanted with electrical stimulation devices, and their recurrent laryngeal nerve sectioned and re-anastomosed on one side. The effects of interrupted chronic muscle stimulation of experimental animals were compared with nonstimulated control animals. Physiologic measures of electromyography of thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles demonstrated enhanced native reinnervation and reduced foreign reinnervation at 180 days in experimental animals. Fluorescent retrograde tracers true blue (TB) and fluorogold (FG) were injected into the PCA and TA, respectively. The identity and relative locations of labeled motoneurons in the nucleus ambiguus were analyzed for segregation and compared to normal animals. Results: PCA and TA muscles that appeared to become selectively reinnervated based on physiologic measurements retained the normal localization of motoneuron cell bodies in the nucleus ambiguus. Significant segregation was observed across the mediolateral axis. Animals with greater foreign reinnervation based on physiologic measurements showed more random distribution of PCA and TA motoneurons, with variable double-labeling of some neurons. Conclusion: This study provides the first direct anatomic evidence that stimulation of a denervated laryngeal muscle promotes selective reinnervation by native over foreign reinnervation. The native reinnervation appears to be from the original motoneuron projections to the PCA or TA located within the nucleus ambiguus of the brainstem. Significance: Laryngeal paralysis is a significant problem with decreased function and increased morbidity for affected individuals. This study demonstrates anatomically that stimulation of the larynx by an implantable device leads to improved reinnervation. Thus, implantable devices may be useful in the rehabilitation of patients with laryngeal paralysis. Support: Supported by NIH grant R01-DC001149.