Laryngeal Synkinesis following Reinnervation in the Rat: Neuroanatomic and Physiologic Study Using Retrograde Fluorescent Tracers and Electromyography

Abstract

The functional organization of laryngeal motoneurons in the nucleus ambiguous (NA) was evaluated in adult male rats before and after recurrent laryngeal nerve section and reinnervation. Using retrograde double labeling techniques with fluorescent probes, we obtained the number and position of labeled neurons by using the Bioquant 3-D imaging system. Reinnervation was documented by electromyography. In nine control animals vector analysis revealed significant (p less than .05) separation of the posterior cricoarytenoid (PCA) muscle motoneurons and the thyroarytenoid and lateral cricoarytenoid (TA/LCA) muscle motoneurons. The PCA motoneurons were positioned ventromedially in the NA, and TA/LCA motoneurons were found dorsolaterally in the NA. Rostral-caudal separation was not significant. Electromyography revealed phasic electrical activity synchronous with respiration in the PCA, and activity synchronous with deglutition in the TA/LCA. In four animals surviving 15 weeks following recurrent laryngeal nerve section and primary neurorrhaphy, functional organization within the NA was lost and phasic motor unit activity synchronous with respiration was seen in the TA/LCA muscle as well as the PCA. Vector analysis revealed the reinnervating motoneurons for both the PCA and TA/LCA to be positioned dorsolaterally, similar to the control group TA/LCA motoneurons. These findings demonstrate a shift in the topographic organization of laryngeal motoneurons within the NA following reinnervation, with random organization occurring at the neurorrhaphy site.

Adenoviral GDNF gene transfer enhances neurofunctional recovery after recurrent laryngeal nerve injury

“…The failure of reinnervation procedures is the result of multiple factors, including decreased motor fiber density, existing laryngeal muscle atrophy, central motoneuron loss in the nucleus ambiguus, and inappropriate or misdirected innervation by antagonistic motoneurons. 7,8 The discovery of neurotrophic factors that support neuronal survival during development and neuronal function throughout adulthood has generated broad interest in the use of these factors in facilitating recovery after peripheral nerve injury. A multitude of neurotrophic factors have been shown to prevent motoneuron loss, enhance nerve sprouting, preserve motor endplate morphology, and promote reinnervation.…”

The clinical value of laryngeal electromyography in laryngeal immobility

“…Rhee et al 40 studied laryngeal reinnervation in rats and found that it followed a random pattern. Flint et al, 41 studying key aspects of laryngeal reinnervation, also found random motoneuron organization after reinnervation. These findings suggest that adductor muscles may be innervated by abductor fibers and vice versa, resulting in reinnervation without functional recovery (laryngeal synkinesis).…”

Short-term laryngeal electromyography and histopathological findings after primary reconstruction of the inferior laryngeal nerve in rabbits: prospective study

“…An equivalent incidence of synkinetic reinnervation is believed to occur in humans. [11][12][13][14] Based on the above research assumption, we found a synkinesis incidence of 60 per cent. Although comparable to previous reports, this incidence is lower than expected.…”