Intrinsic Tongue Muscles Research Articles

Basic characteristics of tongue pressure and electromyography generated by articulation of a syllable using the posterior part of the tongue

The basic function of the tongue in pronouncing diadochokinesis and other syllables is not fully understood. This study investigates the influence of sound pressure levels and syllables on tongue pressure and muscle activity in 19 healthy adults (mean age: 28.2 years; range: 22–33 years). Tongue pressure and activity of the posterior tongue were measured using electromyography (EMG) when the velar stops /ka/, /ko/, /ga/, and /go/ were pronounced at 70, 60, 50, and 40 dB. Spearman's rank correlation revealed a significant, yet weak, positive association between tongue pressure and EMG activity (ρ = 0.14, p < 0.05). Mixed-effects model analysis showed that tongue pressure and EMG activity significantly increased at 70 dB compared to other sound pressure levels. While syllables did not significantly affect tongue pressure, the syllable /ko/ significantly increased EMG activity (coefficient = 0.048, p = 0.013). Although no significant differences in tongue pressure were observed for the velar stops /ka/, /ko/, /ga/, and /go/, it is suggested that articulation is achieved by altering the activity of both extrinsic and intrinsic tongue muscles. These findings highlight the importance of considering both tongue pressure and muscle activity when examining the physiological factors contributing to sound pressure levels during speech.

The feasibility of visualizing and quantifying muscle changes in postoperative oral cancer patients using Quantitative Muscle Ultrasound (QMUS)

PurposeQuantitative muscle ultrasound (QMUS) is a patient friendly tool for examining orofacial muscles. Resection of tissue can have an effect on the architecture and function of these muscles. The aim of this study is to investigate the feasibility of visualizing and quantifying muscle changes in postoperative oral cancer patients and to relate the findings to tumor and patient characteristics.MethodsAdult patients with a resected first primary pT1 or T2 oral squamous cell carcinoma, at least one year post operatively, where included. Ultrasound data were collected of the geniohyoid muscle, digastric muscles, masseter muscle, transverse muscle and genioglossus muscle. Ultrasound images were labeled as clearly visible, questionable or unclear. Of the clear muscles, echogenicity and muscle thickness were measured.Results37 patients were included. The masseter muscle was clearly visible in all ultrasound images, both intrinsic tongue muscles had the lowest visibility (45.9%). There was a significant correlation between visibility and tumor localization for the genioglossus (p = 0.029). Age correlated with the visibility of the genioglossus muscle, BMI with the genioglossus and transverse muscles. Echogenicity and muscle thickness of the clearly identified muscles did not differ from normative values.ConclusionQMUS of orofacial muscles is feasible in postoperative oral cancer patients with relatively small tumor sizes. Tongue resections negatively affected the visibility of the two intrinsic tongue muscles. These preliminary results for particular muscles indicate that the use of ultrasound might be promising in oral cancer patients to help determine targeted goals in post-operative rehabilitation.

Timeline of hypoglossal motor neuron death and intrinsic tongue muscle denervation in high-copy number SOD1G93A mice.

In amyotrophic lateral sclerosis (ALS) postmortem tissue and the SOD1 mouse model at mid-disease, death of hypoglossal motor neurons (XII MNs) is evident. These XII MNs innervate the intrinsic and extrinsic tongue muscles, and despite their importance in many oral and lingual motor behaviours that are affected by ALS (e.g., swallowing, speech, and respiratory functions), little is known about the timing and extent of tongue muscle denervation. Here in the well-characterised SOD1G93A (high-copy) mouse model, we evaluated XII MN numbers and intrinsic tongue muscle innervation using standard histopathological approaches, which included stereological evaluation of Nissl-stained brainstem, and the presynaptic and postsynaptic evaluation of neuromuscular junctions (NMJs), using synapsin, neurofilament, and α-bungarotoxin immunolabelling, at presymptomatic, onset, mid-disease, and endstage timepoints. We found that reduction in XII MN size at onset preceded reduced XII MN survival, while the denervation of tongue muscle did not appear until the endstage. Our study suggests that denervation-induced weakness may not be the most pertinent feature of orolingual deficits in ALS. Efforts to preserve oral and respiratory functions of XII MNs are incredibly important if we are to influence patient outcomes.

The development of thoracic and abdominal muscle depends on SDF1 and CXCR4

In vertebrates, the lateral body wall muscle formation is thought to be initiated by direct outgrowth of the dermomyotomes resulting in the elongation of the hypaxial myotomes. This contrasts with the formation of the muscles of the girdle, limbs and intrinsic tongue muscles, which originate from long-range migrating progenitors. Previous work shows that the migration of these progenitors requires CXCR4 which is specifically expressed in the migrating cells, but not in the dermomyotome. Here, we show that cells in the ventrolateral-lip (VLL) of the dermomyotome at the flank level express CXCR4 in a pattern consistent with that of Pax3 and MyoR. In ovo gain-of-function experiments using electroporation of SDF-1 constructs into the VLL resulted in increased expression of c-Met, Pax3 and MyoD. In contrast, a loss-of-function approach by implantation of CXCR4-inhibitor beads into the VLL of the flank region caused a reduction in the expression of these markers. These data show that CXCR4 is expressed in the VLL, and by experimentally manipulating the CXCR4/SDF-1 signaling, we demonstrate the importance of this axis in body wall muscle development.

Use of suction electrodes for measurement of intrinsic tongue muscular endurance during lingual pressure generation.

Lingual pressure (LP) generation is cooperatively controlled not only by the intrinsic tongue (I-ton) muscles but also by hyoid muscle activation. However, the measurement of endurance and fatigue properties of I-ton muscles is difficult due to the instability of electrodes. The purpose of this study was to apply suction electrodes to measure electromyograms (EMGs) of I-ton muscle and to evaluate integrated EMG amplitude (iEMG) and mean power frequency (MPF) of EMG in the I-ton and hyoid muscles performing continuous LP. Twenty healthy adult volunteers (10 males, 10 females, mean age 28.8 years) were instructed to perform 10-s LP generation tasks at 25%, 50%, 75% and 100% of maximum LP in randomised order with visual feedback. During each task, EMGs of the I-ton, suprahyoid (S-hyo), infrahyoid (I-hyo) and masseter (Mass) muscles were simultaneously recorded. The iEMG and MPF of EMG burst during 10-s LP tasks were compared. The recording period was divided into three substages to analyse temporal changes with the Friedman test. During the 10-s task, the iEMG significantly increased as the LP strength increased (p < .001). There was no time-dependent change in the I-ton iEMG; however, the MPF of the I-ton EMG burst decreased in all tasks (p < .05). The S-hyo and I-hyo iEMGs gradually increased, especially with strong LP (p < .01). While I-ton muscles may easily fatigue during 10-s LP generation, S-hyo and I-hyo muscles may help compensate for the weakened I-ton muscle activity by increasing their activity to maintain LP.

Sarcopenia of the longitudinal tongue muscles in rats

The tongue is a muscular hydrostat, with lingual movements occurring during breathing, chewing, swallowing, vocalization, vomiting, coughing and grooming/sexual activities. In the elderly, reduced lingual dysfunction and weakness contribute to increased risks of obstructive sleep apnea and aspiration pneumonia. In Fischer 344 (F344) rats, a validated model of aging, hypoglossal motor neuron death is apparent, although there is no information regarding tongue strength. The intrinsic tongue muscles, the superior and inferior longitudinal, transversalis and verticalis exist in an interdigitated state. Recently, we established a method to measure the specific force of individual intrinsic tongue muscle, accounting for the tissue bulk that is not in the direction of uniaxial force. In the longitudinal muscles of 6- (n = 10), 18- (n = 9) and 24-month-old (n = 12) female and male F344 rats, we assessed specific force, fatigability, fiber type dependent cross-sectional area (CSA) and overall CSA. Muscle force and fatigue was assessed ex vivo using platinum plate simulation electrodes. Tongue muscles were frozen in melting isopentane, and transverse sections cut at 10 µm. Muscle fiber type was classified based on immunoreactivity to myosin heavy chain (MyHC) isoform antibodies. In H&E stained muscle, CSA and uniaxial muscle contributions to total tongue bulk was assessed. We observed a robust ∼30% loss of longitudinal specific force, with reductions in overall longitudinal muscle fiber CSA and specific atrophy of type IIx/IIb fibers. It will be important to investigate the mechanistic underpinnings of hypoglossal motor neuron death and tongue muscle weakness to eventually provide therapies for age-associated lingual dysfunctions.

The transcription factors Foxf1 and Foxf2 integrate the SHH, HGF and TGFβ signaling pathways to drive tongue organogenesis.

The tongue is a highly specialized muscular organ with diverse cellular origins, which provides an excellent model for understanding mechanisms controlling tissue-tissue interactions during organogenesis. Previous studies showed that SHH signaling is required for tongue morphogenesis and tongue muscle organization, but little is known about the underlying mechanisms. Here we demonstrate that the Foxf1/Foxf2 transcription factors act in the cranial neural crest cell (CNCC)-derived mandibular mesenchyme to control myoblast migration into the tongue primordium during tongue initiation, and thereafter continue to regulate intrinsic tongue muscle assembly and lingual tendon formation. We performed chromatin immunoprecipitation sequencing analysis and identified Hgf, Tgfb2 and Tgfb3 among the target genes of Foxf2 in the embryonic tongue. Through genetic analyses of mice with CNCC-specific inactivation of Smo or both Foxf1 and Foxf2, we show that Foxf1 and Foxf2 mediate hedgehog signaling-mediated regulation of myoblast migration during tongue initiation and intrinsic tongue muscle formation by regulating the activation of the HGF and TGFβ signaling pathways. These data uncover the molecular network integrating the SHH, HGF and TGFβ signaling pathways in regulating tongue organogenesis.

Post traumatic near total amputation of apex of tongue: a rare case report

Post traumatic near total amputation of apex of tongue is a rare scenario but when happens it causes life threatening situation due to active intraoral bleeding and risk of aspiration especially in children. Tongue is a unique organ which has very rich blood supply and resides in intraoral cavity. Due to its rich blood supply profuse bleeding is commonly seen after the tongue injury. It helps in swallowing, speech, taste, mastication and airway protection. It facilitates perception of gustatory stimuli. Here author presents a case of 13 months old female child, who presented to emergency department with history of fell down from the bed and sustained tongue injury with profuse bleeding. On examination patient had near total amputation of apex of tongue. Gentle debridement followed by meticulous complex repair of intrinsic muscles of tongue was done. On post-operative day two patient was discharged uneventfully.

Histopathological alterations of the intrinsic tongue muscles following zoledronic acid treatment in a rat model.

Bisphosphonates (BPs) are widely used as anti-bone-resorptive agents. Despite the great benefits of BPs, they may cause local and systemic adverse side effects. The aim of this study was to evaluate the histopathological effect zoledronic acid (ZA), which belongs to BPs, has on the intrinsic tongue muscles in a rat model. A total of 30 adult male albino rats were divided into 3 groups (10 rats each): group I served as a control; group II was given an intraperitoneal (i.p.) injection of 0.2 mg/kg of ZA once per week for 3 weeks; and group III received the same dosage of ZA, but for 8 weeks. After the animals were euthanized, the tongue tissue was dissected and examined histologically, histochemically and immunohistochemically. Histologically, a normal architecture of the muscle fascicles was observed in the control group. Group II showed degenerated muscle fibers with an indistinct sarcolemma. In group III, the muscle fibers were degenerated with severe sarcoplasmic dissolution. The histochemical examination using Masson's trichrome (MT) demonstrated a significant increase in collagen fibers in groups II and III as compared to the control group. The immunohistochemical results revealed a statistically significantly higher expression of nuclear factor kappa B (NF‑κB) in the ZA-treated groups (II and III) as compared to the control group, with the highest mean value recorded in group III. Zoledronic acid induced histopathological changes to the intrinsic tongue muscles, and this effect was exaggerated with a longer duration of administration.

XROMM and diceCT reveal a hydraulic mechanism of tongue base retraction in swallowing

During primate swallowing, tongue base retraction (TBR) drives the food bolus across the oropharynx towards the esophagus and flips the epiglottis over the laryngeal inlet, protecting against penetration and aspiration of food into the airway. Despite the importance of TBR for swallowing performance, the mechanics of TBR are poorly understood. Using biplanar videoradiography (XROMM) of four macaque monkeys, we tested the extrinsic muscle shortening hypothesis, which posits that shortening of the hyoglossus and styloglossus muscles pulls the tongue base posteriorly, and the muscular hydrostat or intrinsic tongue muscle hypothesis, which suggests that, because the tongue is composed of incompressible fluid, intrinsic muscle shortening increases tongue length and displaces the tongue base posteriorly. Our data falsify these hypotheses. Instead we suggest a novel hydraulic mechanism of TBR: shortening and rotation of suprahyoid muscles compresses the tongue between the hard palate, hyoid and mouth floor, squeezing the midline tongue base and food bolus back into the oropharynx. Our hydraulic mechanism is consistent with available data on human tongue swallowing kinematics. Rehabilitation for poor tongue base retraction might benefit from including suprahyoid muscle exercises during treatment.

What Happens to Swallowing Muscles after Stroke?: A Prospective Randomized Controlled Electrophysiological Study.

Stroke is the most frequent reason of neurological dysphagia Electrophysiological studies can be used to evaluate oral, pharyngeal and initial phase of esophageal phase. This study aims to noninvasively evaluate mastication, mimic, and tongue muscles of stroke patients, which play an important role in the oral phase of swallowing process and compare them with healthy individuals. This study was conducted at the Physical Medicine and Rehabilitation Clinic of our hospital between January 2014 and December 2016. Fifty-one patients who were admitted to our clinic with stroke and 51 healthy individuals were evaluated for the study. Demographic features of individuals were recorded. The swallowing intervals and motor action potentials (MAPs) of trigeminal, facial and hypoglossal nerves were measured. After four weeks of treatment schedule, patients were re-evaluated. The Wilcoxon Signed Rank test, the Mann-Whitney U test and Fisher exact test were used in this study. The all swallowing intervals were found prolonged compared to the healthy controls (P < 0.05). The MAPs of the masseter, orbicularis oculi, and intrinsic tongue muscles were significantly lower in patient group (P < 0.05). After treatment, we found significant improvement for all parameters in patient group, but the swallowing intervals were still significantly prolonged, and MAPs of these muscles were still lower (P < 0.05). Although swallowing is examined as different phases, the process is complicated and should be evaluated totally. In post-stroke dysphagia, oral phase of swallowing process is as important as phayngeal phase and perioral, mastication, and tongue muscles are influenced even in an early period as a month.

Functional Swallowing Units (FSUs) as organs-at-risk for radiotherapy. PART 1: Physiology and anatomy

Background and purposeWhen optimising radiotherapy treatments today, the pharyngeal constrictor muscles and the larynx are usually regarded as the swallowing organs at risk (SWOARs). The purpose of this study was to identify and describe additional, previously undefined groups of muscles (functional units) involved in crucial components of swallowing (hyolaryngeal elevation (HLE), tongue base retraction (TBR) and tongue motion), and to emphasise their relevance in radiation-induced dysphagia. Material and methodsBased on available literature on human anatomy and swallowing physiology, the functional units of muscles involved in HLE, TBR and tongue motion have been identified and described. Results and conclusionFunctional swallowing units (FSUs) were defined as groups of swallowing muscles sharing their function, that are in close proximity to each other. Seven FSUs involved in HLE, TBR and tongue motion were identified: floor of mouth, thyrohyoid muscles, posterior digastric/stylohyoid muscles complex, longitudinal pharyngeal muscles, hyoglossus/styloglossus muscles complex, genioglossus muscles, intrinsic tongue muscles. The swallowing physiology and anatomy of the FSUs described in this paper will lead to a greater understanding of radiation-induced dysphagia mechanisms and, consequently, to an improvement in the development of swallowing sparing strategies. This article (PART 1) serves as the theoretical foundation for a subsequent article (PART 2), which provides detailed delineation guidelines for FSUs.

Radiation Therapy Dose-Volume Correlates Predict Videofluoroscopy-Detected Dysphagia Per DIGEST after IMRT for Oropharyngeal Carcinoma: Results of a Prospective Registry

Our primary aim was to prospectively validate retrospectively studied dosimetric parameters predictive of radiation-associated dysphagia (RAD) after intensity modulated radiation therapy (IMRT) for oropharyngeal cancer (OPC). The secondary aim was to validate grade ≥2 dichotomization of a published videofluoroscopic dysphagia grade (Dynamic Imaging Grade for Swallowing Toxicity, DIGEST) as a radiation dose-sensitive cutoff for RAD. Ninety-seven patients with stage I-IV OPC underwent videofluoroscopy pre- and 3-6 months after IMRT per an IRB-approved prospective registry protocol. Dysphagia severity was graded per DIGEST criteria (dichotomized grade≥2 as moderate/severe RAD). Multivariate regression analysis identified clinical and dosimetric predictors of RAD. Dose-volume histogram (DVH) of superior/ middle/inferior pharyngeal constrictors (S/M/IPC), intrinsic tongue muscle (ITM), geniohyoid muscle (GHM), genioglossus muscle (GGM), mylohyoid muscle (MHM), anterior digastric muscle (ADM), and glottic, supraglottic areas were calculated. Recursive partitioning analysis (RPA) and Bayesian Information Criteria (BIC) were used to identify dose-volume effects associated with moderate/severe RAD. The median age was 61 (range: 35–86) years and 47% were current/former smokers. The majority of tumors (47%) originated from the base of the tongue; 27% and 48% of the patients presented with advanced T (i.e., T3-4) and N2 disease, respectively. HPV/p16 status was positive in 95% of tumors. Concurrent chemotherapy (CRT) was delivered in 23%. Median RT dose was 69.96 (range: 50-70) Gy. At 3-6 months after IMRT, 70% had MBS-evident RAD (DIGEST grade ≥1) and 31% had moderate/severe dysphagia (i.e. DIGEST grade ≥2). Intensified treatment modalities (induction+CRT), advanced T stage, in addition to higher RT mean dose of GHM and GGM (p=0.004 and 0.0089, respectively) were significantly associated with moderate/severe RAD in multivariate analysis. RPA identified GHM V61 ≥ 18.57% (LogWorth 7.3, p<0.0001), SPC V55 ≥ 97.46% (LogWorth 3.8, p=0.0001) and supraglottic V23 ≥92.54% (LogWorth 2.8, p=0.001) as dose-volume thresholds for moderate/severe RAD (AUC 0.9 and 0.7 across training and validation sets, respectively). V61 ≥ 18.57% of GHM had the optimal model performance for prediction of DIGEST grade ≥2 in the subsequent multivariate analysis. The findings from this prospective longitudinal study validate prior observations that dose to submental musculature predicts increased burden of dysphagia after oropharyngeal IMRT. Findings also support dichotomization of DIGEST grade ≥2 as a dose-dependent split for use in endpoint reporting or predictive dose-response analysis of videofluoroscopy results.

Patient-Reported Outcome Measures of Long-Term Swallowing Function after Oropharyngeal Radiation Therapy: A Cross-Sectional Methods Comparison

Definitive radiation therapy (RT) plays an important role in the curative treatment of many patients with oropharyngeal cancer (OPC), but carries a risk of long-term toxicity including the development of severe dysphagia. Here we characterize the relationship of patient-reported outcomes (PRO) of swallowing to quality of life (QOL) and radiation dose in long-term OPC survivors following definitive RT. Patients with non-metastatic OPC treated with definitive RT at a single institution between January 2000 and April 2014 were examined. All patients completed the MD Anderson Symptom Inventory—Head and Neck (MDASI-HN), the MD Anderson Dysphagia Inventory (MDADI), and the EuroQol five dimension questionnaire (EQ-5D VAS) 12 months or more following end of RT in a cross-sectional survivorship survey. A single dysphagia question from MDASI-HN (designated MDASI-HN-S) was used. An MDASI-HN-S score ≥6 and composite MDADI score <60 were considered representative of moderate-severe swallowing dysfunction. The Bayesian information criteria (BIC) were used to test the predictive power of MDASI-HN-S and composite MDADI with QOL as measured by EQ-5D VAS. The modified Breiman recursive partitioning analysis (RPA) was used to identify an MDASI-HN-S cut off score for poor QOL. To assess validity of PRO cutpoints, the mean dose to candidate regions of interest (ROI) were compared in patients with and without moderate/severe dysphagia symptoms. A total of 714 patients met criteria for inclusion, with 91.9% treated with intensity modulated radiotherapy (IMRT) and a mean time from treatment of 6.7 years. Moderate/severe dysphagia was reported by 17% and 16% of respondents by MDASI-HN-S and composite MDADI, respectively. QOL as measured by EQ-5D VAS was lower in those with moderate/severe dysphagia per both MDASI-HN-S (63.4 vs 83.5, p<0.001) and composite MDADI scores (64.5 vs 83.2, p< 0.001). Although both inventories were predictive of QOL, the model including MDASI-HN-S was slightly more parsimonious for discrimination of EQ-5D VAS scores compared to composite MDADI (BIC of 6062 vs 6076). Recursive partitioning analysis showed that an MDASI-HN-S cutoff score of ≥6 correlated best with EQ-5D VAS decline (LogWorth 2.7, p<0.001). Among 320 patients with available DICOM-RT plans, a higher mean dose to the contralateral anterior digastric muscle, intrinsic tongue muscles, and larynx was associated with moderate-severe dysphagia by both MDASI-HN-S and composite MDADI (all p <0.05). In long-term survivors of OPC following definitive RT, the single item dysphagia MDASI-HN-S question performed as well as the 20-item MDADI for discrimination of patient-reported dysphagia and QOL. Dose-response relationships to candidate ROIs were similar for the two questionnaires.

(OA32) Chronic Radiation-Associated Dysphagia in Oropharyngeal Cancer Survivors: Towards Age-Adjusted Dose Constraints for Deglutitive Muscles

Chronic radiation-associated dysphagia (RAD) is a dreaded complication following head and neck radiotherapy. Different factors likely contribute to the development of late RAD. We hypothesize that age may be a significant factor predisposing patients to develop long term swallow dysfunction. We sought to model chronic RAD in patients treated with IMRT for oropharyngeal cancer as a function of age at time of treatment and dose to non-target swallowing muscle regions of interest (ROIs). We examined a group of 300 patients with T1-T4N0-3M0 oropharyngeal cancer patients who received definitive IMRT and concurrent chemotherapy at the University of Texas MD Anderson Cancer Center between 2002 - 2013. Chronic RAD was defined as any of the following ≥ 12 months post-IMRT: videoflouroscopy/endoscopy detected aspiration or stricture, gastrostomy tube, and/or aspiration pneumonia. DICOM-RT plan data were autosegmented using a validated region-of-interest (ROI) library and included inferior, middle and superior constrictors (IPC, MPC, and SPC), anterior and posterior digastrics (ADM, PDM), mylo/geniohyoid complex (MGM), intrinsic tongue muscles (ITM), and gengioglossus (GGM). Age was binned by decade of life, <50, 50-59, 60-69, and >=70 years of age. The probability of chronic RAD as a function of mean dose (to the above ROIs), stratified by age, was estimated by using logistic probability models and subsequent unsupervised nonlinear curve. Of 300 patients, 34 patients developed chronic RAD (11%). Age as a continuous and discrete variable was a significant correlate of chronic RAD, both independently and in concert with continuous dose for all muscle groups examined. Substantively distinct muscle-specific dose-response profiles were observed as a function of age (e.g. a patient in their 50s who received 60 Gy to the SPC had an observed 5% chronic-RAD rate, while a 70-year-old cohort (at the same dose level) exhibited a 20% rate.) Serial muscle-specific dose-response analysis demonstrated the effect to be stable across all observed muscle ROIs, with a FDR-corrected p<0.05 for all dose/muscle/age models, suggesting that an inclusion of dose as a covariate improves modeling of chronic RAD. Age at time of treatment appears to moderate dose-response probability of chronic RAD after chemo-IMRT for OPSCC. Our data demonstrate aging muscles show lower dose thresholds toward the development of potentially meaningful clinically apparent late RAD. Further investigation into age-specific dose constraints and age-adjusted dysphagia prophylaxis models appears warranted; however, our data suggest that uniform monolithic dose constraints may fail to accurately prognosticate or preclude clinical toxicity in aged populations.

Differential impact of tongue exercise on intrinsic lingual muscles.

Aging is associated with muscle fiber hypotrophy and decreased percentages of rapidly contracting myosin heavy chain (MyHC) type IIb muscle fibers. Tongue exercise programs used to treat dysphagia target age-related decline in tongue muscle function, but the impact of exercise on the intrinsic tongue muscles is unknown. We hypothesized that exercise would induce muscle fiber hypertrophy and increase the percentage of MyHC IIa fibers in the intrinsic tongue. Animal model. Eight old and eight young-adult rats underwent 8 weeks of tongue exercise training, and 8 animals of each age group served as controls. Longitudinal, transverse, and verticalis muscle samples from the anterior, middle, and posterior regions of the tongue were sectioned and stained to determine muscle fiber diameter and MyHC composition. MyHC fiber type distribution was altered by exercise, and the effects differed by muscle and region of the tongue. In the exercise groups, as compared to the control groups, the anterior transverse and middle superior longitudinal muscles had significantly reduced percentages of MyHC IIx positive fibers and higher percentages of rapidly contracting fatigable MyHC IIb positive muscle fibers, whereas the middle transverse and posterior longitudinal muscles had increased percentages of the less rapidly contracting and more fatigue-resistant MyHC IIa fibers. The impact of exercise did not differ with age, as there was no significant interaction between age and exercise. Tongue exercise had no significant effect on muscle fiber diameter. The impact of exercise varied among the tongue muscles, which may indicate different functional contributions to the tongue exercise task. NA Laryngoscope, 128:2245-2251, 2018.

DPP9 enzyme activity controls survival of mouse migratory tongue muscle progenitors and its absence leads to neonatal lethality due to suckling defect

Dipeptidyl peptidase 9 (DPP9) is an intracellular N-terminal post-proline-cleaving enzyme whose physiological function remains largely unknown. We investigated the role of DPP9 enzyme in vivo by characterizing knock-in mice expressing a catalytically inactive mutant form of DPP9 (S729A; DPP9ki/ki mice). We show that DPP9ki/ki mice die within 12–18h after birth. The neonatal lethality can be rescued by manual feeding, indicating that a suckling defect is the primary cause of neonatal lethality. The suckling defect results from microglossia, and is characterized by abnormal formation of intrinsic muscles at the distal tongue. In DPP9ki/ki mice, the number of occipital somite-derived migratory muscle progenitors, forming distal tongue intrinsic muscles, is reduced due to increased apoptosis. In contrast, intrinsic muscles of the proximal tongue and extrinsic tongue muscles, which derive from head mesoderm, develop normally in DPP9ki/ki mice. Thus, lack of DPP9 activity in mice leads to impaired tongue development, suckling defect and subsequent neonatal lethality due to impaired survival of a specific subset of migratory tongue muscle progenitors.

Analysis of the Primate “Squeeze‐back” Swallowing Mechanism using X‐ray Reconstruction of Moving Morphology and Fluoromicrometry

The primate hyolingual apparatus is a complex composite of a muscular hydrostat and a floating bone that is essential for feeding. In particular, the characteristic elevation (i.e., the “squeeze‐back” mechanism) and retraction of the tongue base during swallowing may be important in flipping the epiglottis to protect the laryngeal inlet. However, the link between hyolingual muscle behavior and hyolingual kinematics is poorly supported by in vivo data. Tongue base elevation and retraction could be due to one or a combination of three mechanisms thanks to its redundant morphology: intrinsic tongue muscles inducing hydrostatic deformation, extrinsic muscles moving the whole tongue, or hyoid elevation and protraction deforming the tongue. We evaluated these possibilities using a macaque model system. We implanted two rhesus macaques (one male, one female) with tantalum beads and filmed them during feeding using biplanar videofluoroscopy for X‐ray Reconstruction of Moving Morphology and fluoromicrometry workflows to measure hyoid kinematics, tongue deformation, and muscle length change with high spatiotemporal resolution. The results of general linear models demonstrate significant effects of hyoid movement and hydrostatic deformation on tongue base elevation, while all three mechanisms predict tongue base retraction (p &lt; 0.001). Future directions include incorporating electromyography to understand how hyolingual muscle activity, especially active shortening, generates to tongue movement. These findings not only give insight into the biomechanics of the hyolingual apparatus, but they are also relevant for dysphagia rehabilitation as they suggest that more muscles are involved in tongue base retraction‐‐and perhaps epiglottic flipping‐‐than previously thought.Support or Funding InformationThis research was supported by the NIH (R01 DE023816‐03 and T32 HD007009‐41) and the NSF (MRI 1338066).

Alterations of intrinsic tongue muscle properties with aging.

Age-related decline in the intrinsic lingual musculature could contribute to swallowing disorders, yet the effects of age on these muscles is unknown. We hypothesized there is reduced muscle fiber size and shifts to slower myosin heavy chain (MyHC) fiber types with age. Intrinsic lingual muscles were sampled from 8 young adult (9 months) and 8 old (32 months) Fischer 344/Brown Norway rats. Fiber size and MyHC were determined by fluorescent immunohistochemistry. Age was associated with a reduced number of rapidly contracting muscle fibers, and more slowly contracting fibers. Decreased fiber size was found only in the transverse and verticalis muscles. Shifts in muscle composition from faster to slower MyHC fiber types may contribute to age-related changes in swallowing duration. Decreasing muscle fiber size in the protrusive transverse and verticalis muscles may contribute to reductions in maximum isometric tongue pressure found with age. Differences among regions and muscles may be associated with different functional demands. Muscle Nerve 56: E119-E125, 2017.

Isolated Tongue Paralysis as Presentation of Seropositive Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by a characteristic clinical presentation or positivity for the anti-aquaporin-4 antibody. Lesions involving the dorsal medulla are typical of NMOSD, but isolated tongue paralysis has not been reported previously. We report a rare case of NMOSD presenting with isolated tongue paralysis and swelling due to intrinsic tongue muscle paralysis, which was caused by bilateral involvement of the hypoglossal nuclei in the lower dorsal medulla oblongata. Key Words: Neuromyelitis optica spectrum disorder, Medulla oblongata, Aquaporin-4