Canonical Proprioceptors Are Largely Absent in the Intrinsic Laryngeal Muscles of the Rat Larynx

Proprioception plays a crucial role in laryngeal function for voicing and swallowing. Despite this, the physiology of laryngeal proprioception is not well-understood, and controversy remains over whether canonical proprioceptive organs, like muscle spindles, even exist in the intrinsic laryngeal muscles. This study's primary aim is to determine whether the intrinsic laryngeal muscles contain muscle spindles and Golgi tendon organs using VGLUT1, a marker for proprioceptors. This is a novel approach, as prior studies have relied on morphology and myosin composition to study this question. Larynges of 62 Sprague-Dawley rats distributed across five age groups were immunostained with VGLUT1 and other neuromarkers. Muscle spindles were identified in the lateral thyroarytenoid muscles of just three P8 rats, and no Golgi tendon organs were noted. VGLUT1-positive intramuscular receptor-like entities and flower spray-like endings were found in the intrinsic laryngeal muscles, and mucosal formations were observed clustered at the medial surfaces of the arytenoid and aryepiglottic folds. Employing VGLUT1 immunostaining, this study shows that rat intrinsic laryngeal muscles rarely contain muscle spindles and do not possess Golgi tendon organs. This suggests the possibility that the larynx exhibits a unique proprioceptive apparatus. VGLUT1-positive intramuscular and mucosal structures provide candidates for an alternative system. Further defining the role of these structures will increase our understanding of vocal fold function and ultimately lead to better treatment of vocal fold disorders.