Electromyographic and histologic evolution of the recurrent laryngeal nerve from transection and anastomosis to mature reinnervation

The Laryngoscope (Impact Factor: 1.98). 01/2011; 121(2):325 - 331. DOI: 10.1002/lary.21290

ABSTRACT Objectives:To describe the natural evolution of recurrent laryngeal nerve (RLN) reinnervation in an animal model.Study Design:Twenty Sprague Dawley rats underwent unilateral RLN transection and anastomosis. Animals were sacrificed at 4, 8, 12, 16, and 20 weeks. Prior to sacrifice, each rat underwent electromyography (EMG) and visual grading of vocal fold motion. Bilateral RLNs were harvested and evaluated histologically.Results:EMG revealed synkinetic reinnervation at all time periods except at 4 weeks. EMG evolution plateaued at 16 weeks. Vocal fold motion was slight in three rats at 4 weeks but was otherwise absent except for one rat at 12 weeks. Histologic changes of the axons and their myelin sheaths were consistent at each time period. At 16 weeks, histologic changes plateaued.Conclusions:Consistent EMG, histologic, and vocal fold motion changes occur at specific time periods during RLN reinnervation after transection and anastomosis in a rat model. Reinnervation is mature at 16 weeks. Findings corroborate theories of preferential and synkinetic reinnervation after RLN transection. Use of a rat model to investigate the effect of interventions on RLN reinnervation requires a minimum of 16 weeks between transection and investigation to allow for maturation of reinnervation. Laryngoscope, 2011

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    ABSTRACT: OBJECTIVE/HYPOTHESIS: Optimal management of vocal fold paralysis would entail recurrent laryngeal nerve (RLN) reinnervation resulting in normal vocal fold motion. Unfortunately, RLN reinnervation currently results in a non-functional vocal fold due to synkinetic reinervation. Therapeutic interventions which guide regenerating axons back to the appropriate muscle would prevent synkinesis and restore vocal fold and glottal function. The initial step towards developing these therapies is the elucidation of the embryologic innervation of the larynx. This study aims to identify the age of occurrence, timing and pattern of embryologic innervation of the rat larynx, hypothesizing that differences in these parameters exist between distinct laryngeal muscles. STUDY DESIGN: Descriptive Anatomic Study METHODS: The larynx of rats aged E15, 16, 17, 19 and 21 were harvested and then sectioned. Two rats were used for each age. Sections were co-labeled with Neuronal Class III Beta-Tubulin Polyclonal Antibody to identify the presence of axons and Alexa 488 conjugate Alpha- Bungarotoxin to identify the presence of motor endplates. The age at which axons and motor endplates were first present was noted. The position and pattern of the axons and motor endplates was recorded in relation to each other as well as the musculoskeletal anatomy of the larynx. The time at which axons appeared to innervate the medial thyroarytenoid muscle (MTA), lateral thyroarytenoid muscle (LTA) and the posterior cricoarytenoid muscle (PCA) was documented. RESULTS: Findings in the rat suggest the RLN reaches the larynx and begins branching by E15. Axons branch dorsally first and reach the PCA before the other muscles. Branching towards the MTA occurs only after axons have reached the LTA. By E19 RLN axons have been guided to and selected their respective muscles with formation of neuromuscular junctions (NMJ) in the PCA, LTA and MTA, though the formation of NMJ in the MTA was comparatively delayed. CONCLUSION: This study describes the embryologic innervation of the rat larynx and suggests that there are distinct differences in the age of occurrence, timing and pattern of innervation of PCA, LTA and MTA of the rat. These findings lay the foundation for studies investigating the role of guidance cues in RLN axon guidance and the utility of these cues in the treatment of RLN injury via the stimulation of functional, non-synkinetic reinnervation.
    The Laryngoscope 05/2013; · 1.98 Impact Factor
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    ABSTRACT: To evaluate and describe the cartilaginous and muscular development of the rat larynx. Histologic evaluation. The larynges of Sprague Dawley rats of embryonic day (E) 13, 15, 17, 19, 21, postnatal day 0, 14, and adult of 250 gm were collected. Four larynges of each age were harvested, cut into 15-μm serial sections, stained with hematoxylin and eosin, and evaluated under light microscopy. Representative digital images were recorded and evaluated at the preglottic (supraglottic in humans), glottic, and postglottic (subglottic in humans) levels. Brachial arches were observed at E13. At E17, immature structures of the larynx, including skeletal muscle, cartilage, and the lumen were identifiable. Chondrification and muscle formation were clearly seen by E19. The muscular and cartilagenous components of the larynx were well established by E21. During the span between birth and adult maturation, the size of the larynx increased from a height of 1.10 mm to 2.90 mm, and from a width of 1.80 mm to 5.40 mm, and from a length of 1.38 mm to 4.77 mm in the stained section. Although developed at E21, the laryngeal structures continued to grow by approximately 30%. Rat laryngeal development parallels that in mice and humans. In the rat, at E17 immature structures of the larynx are identifiable, they are well developed at birth and grow by approximately 30% into adulthood. Understanding the chronology and morphology of the embryogenesis of the rat laryngeal musculature is essential and will allow for further evaluation of the embryologic innervation of these muscles. N/A. Laryngoscope, 2013.
    The Laryngoscope 08/2013; · 1.98 Impact Factor
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    ABSTRACT: Changes in motoneurons innervating laryngeal muscles after section and regeneration of the recurrent laryngeal nerve (RLN) are far from being understood. Here, we report the somatotopic changes within the nucleus ambiguus (Amb) after the nerve injury and relates it to the resulting laryngeal fold impairment. The left RLN of each animal was transected and the stumps were glued together using surgical fibrin glue. After several survival periods (1, 2, 4, 8, 12, 16 weeks; at least six rats at each time point) the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were injected with fluorescent-conjugated cholera toxin and the motility of the vocal folds evaluated. After section and subsequent repair of the RLN, no movement of the vocal folds could be detected at any of the survival times studied and the somatotopy and the number of labeled motoneurons changed. From 4 wpi award, the somatotopy was significantly disorganized, with the PCA motoneurons being located rostrally relative to their normal location. A rostrocaudal overlap between the two pools of motoneurons supplying the PCA and TA muscles was observed from 2 wpi onwards. Hardly any labeled neurons were found in the contralateral Amb in any of the experimental groups. An injury of the RLN leads to a reinnervation of the denervated motor endplates of PCA and TA. However, misdirected axons sprout and regrowth from the proximal stump to the larynx. As a result, misplaced innervation of muscles results in a lack of functional recovery of the laryngeal folds movement following a RLN injury. Anat Rec, 2014. © 2014 Wiley Periodicals, Inc.
    The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 01/2014; · 1.34 Impact Factor