Mechanisms of Swallowing, Speech and Voice Disorders in Parkinson's Disease: Literature Review with Our First Evidence for the Periperal Nervous System Involvement.

The majority of patients with Parkinson's disease (PD) develop swallowing, speech, and voice (SSV) disorders. Importantly, swallowing difficulty or dysphagia and related aspiration are life-threatening conditions for PD patients. Although PD treatments have significant therapeutic effects on limb motor function, their effects on SSV disorders are less impressive. A large gap in our knowledge is that the mechanisms of SSV disorders in PD are poorly understood. PD was long considered to be a central nervous system disorder caused by the death of dopaminergic neurons in the basal ganglia. Aggregates of phosphorylated α-synuclein (PAS) underlie PD pathology. SSV disorders were thought to be caused by the same dopaminergic problem as those causing impaired limb movement; however, there is little evidence to support this. The pharynx, larynx, and tongue play a critical role in performing upper airway (UA) motor tasks and their dysfunction results in disordered SSV. This review aims to provide an overview on the neuromuscular organization patterns, functions of the UA structures, clinical features of SSV disorders, and gaps in knowledge regarding the pathophysiology underlying SSV disorders in PD, and evidence supporting the hypothesis that SSV disorders in PD could be associated, at least in part, with PAS damage to the peripheral nervous system controlling the UA structures. Determining the presence and distribution of PAS lesions in the pharynx, larynx, and tongue will facilitate the identification of peripheral therapeutic targets and set a foundation for the development of new therapies to treat SSV disorders in PD.

Focal Application of Neurotrophic Factors Augments Outcomes of Nerve-Muscle-Endplate Grafting Technique for Limb Muscle Reinnervation.

BACKGROUND: We have developed a novel muscle reinnervation technique called "nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ)." This study aimed to augment the outcomes of the NMEG-NMZ (NN) by focal application of exogenous neurotrophic factors (ENFs) for limb reinnervation. METHODS: Adult rats were used to conduct NN plus ENF (NN/ENF) and autologous nerve grafting (ANG, technique control). The nerve innervating the left tibialis anterior (TA) muscle was resected and the denervated TA was immediately treated with NN/ENF or ANG. For NN procedure, an NMEG pedicle was taken from the lateral gastrocnemius muscle and transferred to the NMZ of the denervated TA. For ANG, the nerve gap was bridged with sural nerve. Three months after treatment, the extent of functional and neuromuscular recovery was assessed by measuring static toe spread, maximal muscle force, wet muscle weight, regenerated axons, and innervated motor endplates (MEPs). RESULTS: NN/ENF resulted in 90% muscle force recovery of the treated TA, which is far superior to ANG (46%) and NN alone (79%) as reported elsewhere. Toe spread recovered up to 89 and 49% of the control for the NN/ENF and ANG groups, respectively. The average wet muscle weight was 87 and 52% of the control for muscles treated with NN/ENF and ANG, respectively. The mean number of the regenerated axons was 88% of the control for the muscles treated with NN/ENF, which was significantly larger than that for the ANG-repaired muscles (39%). The average percentage of the innervated MEPs in the NN/ENF-treated TA (89%) was higher compared with that in the ANG-repaired TA (48%). CONCLUSION: ENF enhances nerve regeneration and MEP reinnervation that further augment outcomes of NN. The NN technique could be an alternative option to treat denervated or paralyzed limb muscles caused by traumatic nerve injuries or lesions.

Reinnervation of Paralyzed Limb Muscle by Nerve-Muscle-Endplate Grafting Technique.

BACKGROUND: We have developed a novel reinnervation technique called nerve-muscle-endplate grafting in the native motor zone (NMEG-NMZ). However, it remains unknown whether the NMEG-NMZ is effective for limb reinnervation. OBJECTIVE: To evaluate the efficacy of the NMEG-NMZ in limb muscle reinnervation. METHODS: Forty-five adult rats were divided into 3 groups: NMEG, end-to-end anastomosis (EEA, technique control), and denervation control (DC). The left tibialis anterior muscle was denervated by resecting its nerve. For NMEG-NMZ, the denervated tibialis anterior was reinnervated by transferring a NMEG pedicle from the lateral gastrocnemius muscle. Three months after surgery, static toe spread analysis was performed for all rats and muscle force was measured for the rats treated with NMEG and EEA. Muscle weight, myofiber morphology, regenerated axons, and reinnervated motor endplates in the treated muscles were also quantified and compared with those in the DC group. RESULTS: NMEG-NMZ technique resulted in better muscle force recovery (79% of the control) compared with EEA (51% of the control, P = .048). Toe spread analysis in NMEG-NMZ reinnervated muscles showed static sciatic index = -16.8, whereas -41.4 in EEA, P < .0001). The average weight of the NMEG-NMZ reinnervated muscles (86%) was greater than those of the EEA treated (71%) and DC (26%) muscles (all P < .0001). The mean count of the regenerated axons in the muscles with NMEG-NMZ was 76% of the control, which was larger than that in the muscles with EEA (46%), P < .0001. CONCLUSION: NMEG-NMZ technique has unique advantages and is superior to EEA for muscle reinnervation and functional recovery.

Morphometric and Immunohistochemical Characteristics of the Adult Human Soft Palate Muscles.

The soft palate is the only structure that reversibly separates the respiratory and gastrointestinal systems. Most species can eat and breathe at the same time. Humans cannot do this and malfunction of the soft palate may allow food to enter the lungs and cause fatal aspiration pneumonia. Speech is the most defining characteristic of humans and the soft palate, along with the larynx and tongue, plays the key roles. In addition, palatal muscles are involved in snoring and obstructive sleep apnea. Considering the significance of the soft palate, its function is insufficiently understood. The objectives of this study were to document morphometric and immunohistochemical characteristics of adult human soft palate muscles, including fiber size, the fiber type, and myosin heavy chain (MyHC) composition for better understanding muscle functions. In this study, 15 soft palates were obtained from human autopsies. The palatal muscles were separated, cryosectioned, and stained using histological and immunohistochemical techniques. The results showed that there was a fast type II predominance in the musculus uvulae and palatopharyngeus and a slow type I predominance in the levator veli palatine. Approximately equal proportions of type I and type II fibers existed in both the palatoglossus and tensor veli palatine. Soft palate muscles also contained hybrid fibers and some specialized myofibers expressing slow-tonic and embryonic MyHC isoforms. These findings would help better understand muscle functions.

Limb Muscle Reinnervation with the Nerve-Muscle-Endplate Grafting Technique: An Anatomical Feasibility Study.

BACKGROUND: Peroneal nerve injuries results in tibialis anterior (TA) muscle paralysis. TA paralysis could cause "foot drop," a disabling condition that can make walking difficult. As current treatment methods result in poor functional recovery, novel treatment approaches need to be studied. The aim of this study was to explore anatomical feasibility of limb reinnervation with our recently developed nerve-muscle-endplate grafting (NMEG) in the native motor zone (NMZ). METHODS: As the NMEG-NMZ technique involves in nerves and motor endplates (MEPs), the nerve supply patterns and locations of the MEP bands within the gastrocnemius (GM) and TA muscles of rats were investigated using Sihler's stain and whole-mount acetylcholinesterase (AChE) staining, respectively. Five adult rats underwent TA nerve transaction. The denervated TA was reinnervated by transferring an NMEG pedicle from the ipsilateral lateral GM. At the end of a 3-month recovery period, maximal muscle force was measured to document functional recovery. RESULTS: The results showed that the TA was innervated by the deep peroneal nerve. A single MEP band was located obliquely in the middle of the TA. The GM was composed of two neuromuscular compartments, lateral (GM-l) and medial (GM-m), each of which was innervated by a separate nerve branch derived from the tibial nerve and had a vertically positioned MEP band. The locations of MEP bands in the GM and TA muscles and nerve supply patterns demonstrated that an NMEG pedicle can be harvested from the GM-l and implanted into the NMZ within the TA muscle. The NMEG-NMZ pilot study showed that this technique resulted in optimal muscle force recovery. CONCLUSION: NMEG-NMZ surgery is feasible for limb reinnervation. Specifically, the denervated TA caused by peroneal nerve injuries can be reinnervated with a NMEG from the GM-l.

Neuromuscular Specializations of the Human Hypopharyngeal Muscles.

The hypopharyngeal muscles in humans play a vital role in swallowing, speech, and respiration. Increasing evidence indicates that these muscles are specialized to perform life-sustaining upper aerodigestive functions. This review aims to provide current knowledge regarding the key structural, physiological, and biochemical features of the hypopharyngeal muscles, including innervation, contractile properties, histochemistry, biochemical properties, myosin heavy chain (MyHC) expression and regulation, and age-related alterations. These would clarify the unique neuromuscular specializations of the human hypopharyngeal muscles for a better understanding of the functions and pathological conditions of the pharynx and for the development of novel therapies to treat related upper airway disorders.

Innervation of human soft palate muscles.

Our objective was to determine the branching and distribution of the motor nerves supplying the human soft palate muscles. Six adult specimens of the soft palate in continuity with the pharynx, larynx, and tongue were processed with Sihler's stain, a technique that can render large specimens transparent while counterstaining their nerves. The cranial nerves were identified and dissection followed their branches as they divided into smaller divisions toward their terminations in individual muscles. The results showed that both the glossopharyngeal (IX) and vagus (X) nerves have three distinct branches, superior, middle, and inferior. Only the middle branches of each nerve contributed to the pharyngeal plexus to which the facial nerve also contributed. The pharyngeal plexus was divided into two parts, a superior innervating the palatal and neighboring muscles and an inferior innervating pharyngeal constrictors. The superior branches of the IX and X nerves contributed innervation to the palatoglossus, whereas their middle branches innervated the palatopharyngeus. The palatoglossus and palatopharyngeus muscles appeared to be composed of at least two neuromuscular compartments. The lesser palatine nerve not only supplied the palatal mucosa and palatine glandular tissue but also innervated the musculus uvulae, palatopharyngeus, and levator veli palatine. The latter muscle also received its innervation from the superior branch of X nerve. The findings would be useful for better understanding the neural control of the soft palate and for developing novel neuromodulation therapies to treat certain upper airway disorders such as obstructive sleep apnea.

Sensory Innervation of the Human Soft Palate.

The human soft palate plays an important role in respiration, swallowing, and speech. These motor activities depend on reflexes mediated by sensory nerve endings. To date, the details of human sensory innervation to the soft palate have not been demonstrated. In this study, eight adult human whole-mount (soft palate-tongue-pharynx-larynx-upper esophagus) specimens were obtained from autopsy. Each specimen was bisected in the midline, forming two equal and symmetrical halves. Eight hemi-specimens were processed with Sihler's stain, a whole-mount nerve staining technique. The remaining eight hemi-soft palates were used for immunohistochemical study. The soft palatal mucosa was dissected from the oral and nasal sides and prepared for neurofilament staining. Our results showed that the sensory nerve fibers formed a dense nerve plexus in the lamina propria of the soft palatal mucosa. There was a significant difference in the innervation density between both sides. Specifically, the oral side had higher density of sensory nerve fibers than the nasal side of the soft palate. The mean number and percent area of the sensory nerve fibers in the mucosa of the nasal side was 78% and 72% of those in the mucosa of the oral side, respectively (P < 0.0001). The data presented here could be helpful for further investigating the morphological and quantitative alterations in the sensory nerves in certain upper airway disorders involving the soft palate such as obstructive sleep apnea (OSA) and for designing effective therapeutic strategies to treat OSA. Anat Rec, 301:1861-1870, 2018. © 2018 Wiley Periodicals, Inc.

Immunohistochemical Detection of Motor Endplates in the Long-Term Denervated Muscle.

BACKGROUND: We have demonstrated that the native motor zone (NMZ) within a muscle is an ideal target for performing nerve-muscle-endplate band grafting (NMEG) to restore motor function of a denervated muscle. This study was designed to determine spatiotemporal alterations of the myofibers, motor endplates (MEPs), and axons in the NMZ of long-term denervated muscles for exploring if NMEG-NMZ technique would have the potential for delayed reinnervation. METHODS: Sternomastoid (SM) muscles of adult female Sprague-Dawley rats (n = 21) were experimentally denervated and denervation-induced changes in muscle weight, myofiber size, MEPs, and intramuscular nerve axons were evaluated histomorphometrically and immunohistochemically at the end of 3, 6, and 9 months after denervation. The values obtained from the ipsilateral normal side served as control. RESULTS: The denervated SM muscles exhibited a progressive reduction in muscle weight (38%, 31%, and 19% of the control) and fiber diameter (52%, 40%, and 28% of the control) for 3-, 6-, and 9-month denervation, respectively. The denervated MEPs were still detectable even 9 months after denervation. The mean number of the denervated MEPs was 79%, 65%, and 43% of the control in the 3-, 6-, and 9-month denervated SM, respectively. Degenerated axons in the denervated muscles became fragmented. CONCLUSIONS: Persistence of MEPs in the long-term denervated SM suggests that some surgeries targeting the MEPs such as NMEG-NMZ technique should be effective for delayed reinnervation. However, more work is needed to develop strategies for preservation of muscle mass and MEPs after denervation.

Nerve growth factor and basic fibroblast growth factor promote reinnervation by nerve-muscle-endplate grafting.

INTRODUCTION: This study was designed to test whether exogenous application of nerve growth factor (NGF) and basic fibroblast growth factor (FGF-2) to muscles reinnervated with nerve-muscle-endplate band grafting (NMEG) could promote specific outcomes. METHODS: The right sternomastoid muscle in adult rats was experimentally denervated and immediately reinnervated by implanting an NMEG pedicle from the ipsilateral sternohyoid muscle. A fibrin sealant containing NGF and FGF-2 was focally applied to the implantation site. Maximal tetanic force, muscle weight, regenerated axons, and motor endplates were analyzed 3 months after treatment. RESULTS: Mean tetanic force, wet muscle weight, and number of regenerated axons in the treated muscles were 91%, 92%, and 84% of the contralateral controls, respectively. The majority of endplates (86%) in the treated muscles were reinnervated by regenerated axons. DISCUSSION: Focal administration of NGF and FGF-2 promotes efficacy of the NMEG technique. Muscle Nerve 57: 449-459, 2018.

Reinnervation of denervated muscle by implantation of nerve-muscle-endplate band graft to the native motor zone of the target muscle.

INTRODUCTION: Motor endplate reinnervation is critical for restoring motor function of the denervated muscle. We developed a novel surgical technique called nerve-muscle-endplate band grafting (NMEG) for muscle reinnervation. METHODS: Experimentally denervated sternomastoid muscle in the rat was reinnervated by transferring a NMEG from the ipsilateral sternohyoid muscle to the native motor zone (NMZ) of the target muscle. A NMEG pedicle contained a block of muscle (~ 6 × 6 × 3 mm), a nerve branch with axon terminals, and a motor endplate band with numerous neuromuscular junctions. At 3 months after surgery, maximal tetanic muscle force measurement, muscle mass and myofiber morphology, motoneurons, regenerated axons, and axon-endplate connections of the muscles were analyzed. RESULTS: The mean force of the reinnervated muscles was 82% of the contralateral controls. The average weight of the treated muscles was 89% of the controls. The reinnervated muscles exhibited extensive axonal regeneration. Specifically, the mean count of the regenerated axons in the reinnervated muscles reached up to 76.8% of the controls. The majority (80%) of the denervated endplates in the target muscle regained motor innervation. CONCLUSIONS: The NMZ of the denervated muscle is an ideal site for NMEG implantation and for the development of new microsurgical and therapeutic strategies to achieve sufficient axonal regeneration, rapid endplate reinnervation, and optimal functional recovery. NMEG-NMZ technique may become a useful tool in the treatment of muscle paralysis caused by peripheral nerve injuries in certain clinical situations.

Outcomes of Muscle Reinnervation with Direct Nerve Implantation into the Native Motor Zone of the Target Muscle.

Background Our recent work has demonstrated that the native motor zone (NMZ) within a given skeletal muscle is the best site for muscle reinnervation. This study was designed to explore the outcomes of direct nerve implantation (DNI) into the NMZ of denervated sternomastoid (SM) muscle in a rat model. Methods The right SM muscle was experimentally denervated by transecting its innervating nerve. The proximal stump of the severed SM nerve was immediately implanted into a small muscle slit made in the NMZ of the muscle where denervated motor endplates were concentrated. The outcomes of DNI-NMZ reinnervation were evaluated 3 months after surgery. Specifically, the degree of functional recovery was examined with muscle force measurement. The extent of nerve regeneration and endplate reinnervation was assessed using histological and immunohistochemical methods. Results This study showed that the mean muscle force of the treated muscles was 64% of the contralateral control. Reinnervated SM muscles weighed 71% of the weight of the control muscles. Abundant regenerated axons were identified in the NMZ of the target muscle. The mean number and area of the regenerated axons in the treated muscles was computed to be 62% and 51% of the control muscles, respectively. On average, 66% of the denervated endplates in the treated muscles were reinnervated by regenerated axons. Conclusion Our results suggest that the NMZ within a muscle is an ideal site for endplate reinnervation and satisfactory functional recovery. Further studies are needed to promote the efficacy of DNI-NMZ technique for muscle reinnervation.

Alpha-Synuclein Pathology in Sensory Nerve Terminals of the Upper Aerodigestive Tract of Parkinson's Disease Patients.

Dysphagia is common in Parkinson's disease (PD) and causes significant morbidity and mortality. PD dysphagia has usually been explained as dysfunction of central motor control, much like other motor symptoms that are characteristic of the disease. However, PD dysphagia does not correlate with severity of motor symptoms nor does it respond to motor therapies. It is known that PD patients have sensory deficits in the pharynx, and that impaired sensation may contribute to dysphagia. However, the underlying cause of the pharyngeal sensory deficits in PD is not known. We hypothesized that PD dysphagia with sensory deficits may be due to degeneration of the sensory nerve terminals in the upper aerodigestive tract (UAT). We have previously shown that Lewy-type synucleinopathy (LTS) is present in the main pharyngeal sensory nerves of PD patients, but not in controls. In this study, the sensory terminals in UAT mucosa were studied to discern the presence and distribution of LTS. Whole-mount specimens (tongue-pharynx-larynx-upper esophagus) were obtained from 10 deceased human subjects with clinically diagnosed and neuropathologically confirmed PD (five with dysphagia and five without) and four age-matched healthy controls. Samples were taken from six sites and immunostained for phosphorylated α-synuclein (PAS). The results showed the presence of PAS-immunoreactive (PAS-ir) axons in all the PD subjects and in none of the controls. Notably, PD patients with dysphagia had more PAS-ir axons in the regions that are critical for initiating the swallowing reflex. These findings suggest that Lewy pathology affects mucosal sensory axons in specific regions of the UAT and may be related to PD dysphagia.

Muscle reinnervation with nerve-muscle-endplate band grafting technique: correlation between force recovery and axonal regeneration.

BACKGROUND: This study was designed to determine the correlation between functional recovery and the extent of axonal regeneration after muscle reinnervation with our recently developed nerve-muscle-endplate band grafting (NMEG) technique in a rat model. MATERIALS AND METHODS: The right experimentally paralyzed sternomastoid (SM) muscle by nerve transection was immediately reinnervated with an NMEG pedicle harvested from a neighboring sternohyoid muscle. The NMEG pedicle contained a muscle block (6 × 6 × 3 mm), a donor nerve branch with nerve terminals, and a motor endplate band. Three months after surgery, the tetanic force of the SM muscle was measured and the regenerated axons in the muscle were detected using neurofilament immunohistochemistry. RESULTS: The results showed that the maximal tetanic force (a measure of muscle functional recovery) of the NMEG-reinnervated SM muscle reached up to 66.0% of the normal control. The wet weight of the reinnervated SM muscle (a measure of muscle mass recovery) was 87.2% of the control. The area fraction of the regenerating axons visualized with neurofilament staining within the NMEG-reinnervated SM muscle (a measure of muscle reinnervation) was 42.3%. A positive correlation was revealed between the extent of muscle reinnervation and maximal muscle force. CONCLUSIONS: Our newly developed NMEG technique results in satisfactory functional outcomes and nerve regeneration. Further improvement in the functional recovery after NMEG reinnervation could be achieved by refining the surgical procedure and creating an ideal environment that favors axon-endplate connections and accelerates axonal growth and sprouting.

The human tongue slows down to speak: muscle fibers of the human tongue.

Little is known about the specializations of human tongue muscles. In this study, myofibrillar adenosine triphosphatase (mATPase) histochemical staining was used to study the percentage and distribution of slow twitch muscle fibers (slow MFs) within tongue muscles of four neurologically normal human adults and specimens from a 2-year-old human, a newborn human, an adult with idiopathic Parkinson's disease (IPD), and a macaque monkey. The average percentage of slow MFs in adult and the 2-year-old muscle specimens was 54%, the IPD was 45%, while the neonatal human (32%) and macaque monkey (28%) had markedly fewer slow MFs. In contrast, the tongue muscles of the rat and cat have been reported to have no slow MFs. There was a marked spatial gradient in the distribution of slow MFs with the highest percentages found medially and posteriorly. Normal adult tongue muscles were found to have a variety of uniquely specialized features including MF-type grouping (usually found in neuromuscular disorders), large amounts of loose connective tissue, and short branching MFs. In summary, normal adult human tongue muscles have by far the highest proportion of slow MFs of any mammalian tongue studied to date. Moreover, adult human tongue muscles have multiple unique anatomic features. As the tongue shape changes that are seen during speech articulation are unique to humans, we hypothesize that the large proportion of slow MFs and the anatomical specializations observed in the adult human tongue have evolved to perform these movements.

Parkinson disease affects peripheral sensory nerves in the pharynx.

Dysphagia is very common in patients with Parkinson disease (PD) and often leads to aspiration pneumonia, the most common cause of death in PD. Current therapies are largely ineffective for dysphagia. Because pharyngeal sensation normally triggers the swallowing reflex, we examined pharyngeal sensory nerves in PD patients for Lewy pathology.Sensory nerves supplying the pharynx were excised from autopsied pharynges obtained from patients with clinically diagnosed and neuropathologically confirmed PD (n = 10) and healthy age-matched controls (n = 4). We examined the glossopharyngeal nerve (cranial nerve IX), the pharyngeal sensory branch of the vagus nerve (PSB-X), and the internal superior laryngeal nerve (ISLN) innervating the laryngopharynx. Immunohistochemistry for phosphorylated α-synuclein was used to detect Lewy pathology. Axonal α-synuclein aggregates in the pharyngeal sensory nerves were identified in all of the PD subjects but not in the controls. The density of α-synuclein-positive lesions was greater in PD patients with dysphagia versus those without dysphagia. In addition, α-synuclein-immunoreactive nerve fibers in the ISLN were much more abundant than those in cranial nerve IX and PSB-X. These findings suggest that pharyngeal sensory nerves are directly affected by pathologic processes in PD. These abnormalities may decrease pharyngeal sensation, thereby impairing swallowing and airway protective reflexes and contributing to dysphagia and aspiration.

A three-dimensional atlas of human tongue muscles.

The human tongue is one of the most important yet least understood structures of the body. One reason for the relative lack of research on the human tongue is its complex anatomy. This is a real barrier to investigators as there are few anatomical resources in the literature that show this complex anatomy clearly. As a result, the diagnosis and treatment of tongue disorders lags behind that for other structures of the head and neck. This report intended to fill this gap by displaying the tongue's anatomy in multiple ways. The primary material used in this study was serial axial images of the male and female human tongue from the Visible Human (VH) Project of the National Library of Medicine. In addition, thick serial coronal sections of three human tongues were rendered translucent. The VH axial images were computer reconstructed into serial coronal sections and each tongue muscle was outlined. These outlines were used to construct a three-dimensional (3D) computer model of the tongue that allows each muscle to be seen in its in vivo anatomical position. The thick coronal sections supplement the 3D model by showing details of the complex interweaving of tongue muscles throughout the tongue. The graphics are perhaps the clearest guide to date to aid clinical or basic science investigators in identifying each tongue muscle in any part of the human tongue.

Alpha-synuclein pathology and axonal degeneration of the peripheral motor nerves innervating pharyngeal muscles in Parkinson disease.

Parkinson disease (PD) is a neurodegenerative disease primarily characterized by cardinal motor manifestations and CNS pathology. Current drug therapies can often stabilize these cardinal motor symptoms, and attention has shifted to the other motor and nonmotor symptoms of PD that are resistant to drug therapy. Dysphagia in PD is perhaps the most important drug-resistant symptom because it leads to aspiration and pneumonia, the leading cause of death. Here, we present direct evidence for degeneration of the pharyngeal motor nerves in PD. We examined the cervical vagal nerve (cranial nerve X), pharyngeal branch of nerve X, and pharyngeal plexus innervating the pharyngeal muscles in 14 postmortem specimens, that is, from 10 patients with PD and 4 age-matched control subjects. Synucleinopathy in the pharyngeal nerves was detected using an immunohistochemical method for phosphorylated α-synuclein. Alpha-synuclein aggregates were revealed in nerve X and the pharyngeal branch of nerve X, and immunoreactive intramuscular nerve twigs and axon terminals within the neuromuscular junctions were identified in all of the PD patients but in none of the controls. These findings indicate that the motor nervous system of the pharynx is involved in the pathologic process of PD. Notably, PD patients who have had dysphagia had a higher density of α-synuclein aggregates in the pharyngeal nerves than those without dysphagia. These findings indicate that motor involvement of the pharynx in PD is one of the factors leading to oropharyngeal dysphagia commonly seen in PD patients.