Age-related changes in rat intrinsic laryngeal muscles: analysis of muscle fibers, muscle fiber proteins, and subneural apparatuses

The role of ultrasonic vocalizations in rat laryngological investigations

Rat ultrasonic vocalizations (USVs) have traditionally been used in psychosocial and psychobiological studies to understand emotion, social behavior, cognition, and associative learning. However, recent studies have expanded the goal of USVs to include the study of the laryngeal system and the effects of disease processes on vocal sensorimotor control. Without the foundational understanding of the goals of this area of laryngological research, fundamental differences in study objectives between psychobehavioral and laryngological studies can easily be missed, leading to misconceptions and misinterpretations of the role USVs play in laryngology-focused studies. Standardization of terminology and methods are also needed to improve communication, enhance study replicability, and prevent ambiguity that can lead to misinterpretations of study objectives and findings in this line of research. The primary objective is to describe the role of USVs in studies of laryngeal anatomy and physiology, with a focus on their connections to the neuromuscular and neurological aspects of the laryngeal system, particularly in relation to vocal sensorimotor control and voice disorders. It is intended for novice investigators interested in laryngology-specific USV research. Researchers experienced in USV studies within the context of the larynx and vocal sensorimotor control first outline the development and refinement of various USV elicitation methods. They provide insights into how these approaches have been tested across different studies and laboratories. Finally, they advocate for standardizing terminology and methodologies to enhance study replicability, reduce ambiguity, and foster collaboration across research groups.

Normative aging results in degradation of gene networks in a zebra finch basal ganglia nucleus dedicated to vocal behavior

Aging increases brain susceptibility to neurodegenerative diseases, but the mechanisms are not clear. Vocal behavior provides an accessible, reliable, and sensitive biomarker to address this because voice changes in middle age can be early indicators of neurodegenerative diseases. The adult male zebra finch is an excellent model organism for these studies due to well-characterized vocal brain circuitry and strong homology to human brain centers. We performed RNA sequencing of song-dedicated basal ganglia nucleus Area X followed by weighted gene co-expression network analyses to examine changes in gene patterns across younger adult, middle, and older ages. Song-correlated gene networks degrade with age, with modules losing their coherence and migrating to different sets of genes, and changes in connection strength particularly for hub genes including those associated with human speech, Parkinson's, and Alzheimer's diseases. Gene pathway enrichment analyses reveal a lack of ongoing metabolic and biogenic processes in older finches. Our findings provide a robust platform for targeting network hubs in the treatment of neurologically driven human vocal disorders.

Assessment of Formalin-Fixed Bovine Larynx Asymmetry Using Geometric Morphometry

The vibrations of the larynx produce the voice. Little is known about morphology and the size of cattle larynx. The aim of the study was to quantify the shape asymmetry of the larynx in calves obtained postmortem using a geometric morphometric approach. A sample of 14 larynges from calves (in an age range 335-625 days) belonging to "Bruna dels Pirineus" breed and its F1 crosses was obtained in an abattoir during the first semester of 2021. Laringes were dissected and preserved in the laboratory until their photograph was taken Landmark sets were superimposed on images of fixed transverse sections of larynges. Using geometric morphometric techniques, we analyzed the presence of asymmetries. Asymmetry between sexes was assessed by means of a Canonical Variate Analysis on regression residuals of asymmetric components using the Mahalanobis distance, which assumes a lack of isotropy. Significant differences in the morphometric profile were found between the right and left larynx and between the sexes (p < 0.05). Results demonstrate differences between right and left larynx sides as directional asymmetry, at least in fixed structures. Our findings provide a foundation for quantifying the possible contribution of larynx asymmetry among cattle. This study can be considered the first to detect larynx asymmetries in cattle. Studies with a larger sample size are needed to validate the information in large populations. One limitation is that the present study does not have samples from adult animals, so it would be interesting to know if the results are similar among them.

Effect of Aging on the Vocal Muscle

INTRODUCTION

Sarcopenia is a common and natural condition in the elderly, and leads to loss of muscle mass and function. In the presbylarynx there is atrophy of the vocal folds, however the degree of vocal muscle atrophy is poorly studied and the results are contradictory.

AIMS

The aim of this study was to evaluate the effect of aging on the vocal muscle (thyroarytenoid muscle).

METHODS

Thirteen larynxes removed during necropsy from 13 cadavers were included into two age groups: Control group - G1 (n5), between 25 and 40 years; Elderly Group - GI (n-8), aged 70 years or older. The vocal folds were dissected and prepared for scanning electron microscopy, ensuring a cross-section in the musculature area to allow measurements of muscle fiber parameters. Images were analyzed and photographed at different magnifications. Through the ImageJ software, ten distinct fields of each part were selected. Parameters studied: area, perimeters and diagonals of the thyroarytenoid muscle bundles of both groups.

RESULTS

The cross-sectional areas, perimeters and diagonals of the muscle fibers of the thyroarytenoid muscle of the elderly group were significantly smaller than those of the control group.

CONCLUSION

We demonstrated that the vocal muscle is affected in the presbylarynx, with a reduction of its muscle fibers, corresponding to muscle atrophy. However, these findings may not be directly related to vocal symptoms because the patient may develop muscle compensatory mechanisms capable of reducing glottic insufficiency.

An optimized method for high-quality RNA extraction from distinctive intrinsic laryngeal muscles in the rat model

Challenges related to high-quality RNA extraction from post-mortem tissue have limited RNA-sequencing (RNA-seq) application in certain skeletal muscle groups, including the intrinsic laryngeal muscles (ILMs). The present study identified critical factors contributing to substandard RNA extraction from the ILMs and established a suitable method that permitted high-throughput analysis. Here, standard techniques for tissue processing were adapted, and an effective means to control confounding effects during specimen preparation was determined. The experimental procedure consistently provided sufficient intact total RNA (N = 68) and RIN ranging between 7.0 and 8.6, which was unprecedented using standard RNA purification protocols. This study confirmed the reproducibility of the workflow through repeated trials at different postnatal time points and across the distinctive ILMs. High-throughput diagnostics from 90 RNA samples indicated no sequencing alignment scores below 70%, validating the extraction strategy. Significant differences between the standard and experimental conditions suggest circumvented challenges and broad applicability to other skeletal muscles. This investigation remains ongoing given the prospect of therapeutic insights to voice, swallowing, and airway disorders. The present methodology supports pioneering global transcriptome investigations in the larynx previously unfounded in literature.

Distribution of lip-seal strength and its relation to oral motor functions

Objectives

Lip‐seal strength, which represents the muscle strength of the lips, appears to chiefly contribute to mastication and pronunciation. However, the functional characteristics of lip‐seal strength in adults are still undefined. The present study aimed to understand not only the distribution of lip‐seal strength in adult men and women but also the effect of age on this strength and identify oral motor functions correlated with lip‐seal strength.

Materials and methods

The subjects included 339 participants (men: 170, age 39.2 ± 18.2 years; women: 169, age 43.1 ± 19.7 years). Oral motor function was evaluated for lip‐seal strength, oral diadochokinesis (ODK), tongue pressure, occlusal force, and masticatory performance. Statistical analyses included the Shapiro–Wilk, Mann–Whitney U, and Jonckheere–Terpstra tests, in addition to the Spearman's correlation analysis and curvilinear regression analysis.

Results

Lip‐seal strength did not have a normal distribution (p < 0.001). The mean ± standard deviation and median (first quartile, third quartile) of lip‐seal strength were 11.2 ± 3.4 and 10.9 (8.7, 13.2)N for the whole sample, 12.3 ± 3.4 and 11.9 (9.4, 14.4)N for men, and 10.2 ± 3.0 and 9.9 (8.0, 12.0)N for women. A significant difference was observed in lip‐seal strength between men and women (p < 0.001). Oral motor functions showed a marked correlation with lip‐seal strength, including tongue pressure, occlusal force, and masticatory performance and ODK (/pa/ and /ta/), tongue pressure, and masticatory ability in men and women, respectively. In women, lip‐seal strength declined with increase in age.

Conclusions

Lip‐seal strength was non‐normally distributed in both men and women, and lip‐seal strength was affected by age only in women. Lip‐seal strength and multiple oral motor functions were significantly correlated. Because the indicators of perioral muscle strength and performance were correlated with lip‐seal strength, lip‐seal strength may also partially reflect the condition of the perioral muscles.

Physics of phonation offset: Towards understanding relative fundamental frequency observations

Relative fundamental frequency (RFF) is a promising assessment technique for vocal pathologies. Herein, we explore the underlying laryngeal factors dictating RFF behaviours during phonation offset. To gain physical insights, we analyze a simple impact oscillator model and follow that with a numerical study using the well-established body-cover model of the vocal folds (VFs). Study of the impact oscillator suggests that the observed decrease in fundamental frequency during offset is due, at least in part, to the increase in the neutral gap between the VFs during abduction and the concomitant decrease in collision forces. Moreover, the impact oscillator elucidates a correlation between sharper drops in RFF and increased stiffness of the VFs, supporting experimental RFF studies. The body-cover model study further emphasizes the correlation between the drops in RFF and collision forces. The numerical analysis also illustrates the sensitivity of RFF to abduction initiation time relative to the phase of the phonation cycle, and the abduction period length. In addition, the numerical simulations display the potential role of the cricothyroid muscle to mitigate the RFF reduction. Last, simplified models of phonotraumatic vocal hyperfunction are explored, demonstrating that the observed sharper drops in RFF are associated with increased pre-offset collision forces.

Biological and Acoustic Sex Differences in Rat Ultrasonic Vocalization

The rat model is a useful tool for understanding peripheral and central mechanisms of laryngeal biology. Rats produce ultrasonic vocalizations (USVs) that have communicative intent and are altered by experimental conditions such as social environment, stress, diet, drugs, age, and neurological diseases, validating the rat model's utility for studying communication and related deficits. Sex differences are apparent in both the rat larynx and USV acoustics and are differentially affected by experimental conditions. Therefore, the purpose of this review paper is to highlight the known sex differences in rat USV production, acoustics, and laryngeal biology detailed in the literature across the lifespan.

Determining the Underlying Relationship Between Swallowing and Maximum Vocal Pitch Elevation: A Preliminary Study of Their Hyoid Biomechanics in Healthy Adults

Purpose Deficiencies in swallowing (aspiration) and in maximum vocal pitch elevation have been shown to correlate in dysphagia. However, the underlying mechanisms that may explain this relationship are not known. In this study, we compare hyoid kinematics between swallowing and maximum vocal pitch elevation in healthy adults. Method Ten young (M = 21 ± 1.33 years) and eight older (M = 72.85 ± 5.59 years) healthy adults completed trials of maximum vocal pitch elevation (vowels /a/ and /i/) and swallowing (thin liquid and pudding) under videofluoroscopy. Superior and anterior hyoid excursions were obtained using kinematic analysis. Two-way analyses of variance and Spearman rho correlations were used to examine differences and relationships between swallowing and maximum pitch elevation biomechanics. Results Superior hyoid excursion was significantly greater for liquid swallows compared to pitch elevation tasks (/a/ and /i/; p = .002; Cohen's d = 1.28; p = .0179, Cohen's d = 1.03, respectively) and for pudding swallows compared to pitch tasks (p = .000, Cohen's d = 1.64; p = .001, Cohen's d = 1.38, respectively). Anterior hyoid excursion was not significantly different between the two functions, but was overall reduced in the older group (p = .0231, Cohen's d = .90). Furthermore, there was a moderate positive correlation between the degree of superior excursion during liquid swallows and maximum pitch elevation for both vowels (r s = .601, p = .001; r s = .524, p = .003) in young adults, and between the degree of anterior excursion during liquid swallows and pitch elevation for both vowels (r s = .688, p = .001; r s = .530, p = .008) in older adults. Conclusions Swallowing and maximum pitch elevation require similar anterior, but not superior, hyoid excursion in healthy adults. Differential correlations between the two tasks for each age group may be associated with age-related muscle changes. We provide evidence of partially shared biomechanics between swallowing and maximum pitch elevation.

Injectable basic fibroblast growth factor-loaded alginate/hyaluronic acid hydrogel for rejuvenation of geriatric larynx

Increase in the geriatric population has led to an increase in the number of elderly patients with laryngeal atrophy and dysfunction. Symptoms of voice change, dysphagia, and aspiration pneumonia negatively influence patient's health status, quality of life, and life span. Injection laryngoplasty used to treat laryngeal dysfunctions does not recover intrinsic functions of the larynx. Thus, we fabricated an injectable basic fibroblast growth factor (bFGF)-loaded alginate (ALG)/hyaluronic acid (HA) hydrogel for inducing rejuvenation of geriatric laryngeal muscles. Optimal in situ-forming bFGF-loaded ALG/HA hydrogel for injection laryngoplasty was prepared and the release profile of bFGF was analyzed. For in vivo analysis, the bFGF-loaded ALG/HA hydrogel was injected into the laryngeal muscles of 18-month-old Sprague-Dawley rats. The rejuvenation efficacy of bFGF-loaded ALG/HA hydrogel in geriatric laryngeal muscle tissues 4- and 12-weeks post-injection was evaluated by quantitative polymerase chain reaction (qPCR), histology, immune-fluorescence staining and functionality analysis. The bFGF-loaded ALG/HA hydrogel induced an increase in the expression of myogenic regulatory factor-related genes, hypertrophy of muscle fiber, proliferation of muscle satellite cells, and angiogenesis and decreased interstitial fibrosis. Administration of the bFGF-loaded ALG/HA hydrogel caused successful glottal gap closure. Thus, the bFGF-loaded ALG/HA hydrogel could be a promising candidate for laryngoplasty aimed at rejuvenating geriatric larynx. STATEMENT OF SIGNIFICANCE: In this manuscript, optimal in situ-forming bFGF-loaded ALG/HA hydrogel for injection laryngoplasty was prepared and the release profile of bFGF was analyzed. Herein, we introduced the materials and methods of injection laryngoplasty for geriatric rat experiment. In addition, we studied effects of bFGF-loaded ALG/HA hydrogel on the therapeutic rejuvenation of geriatric rat larynx. The bFGF-loaded ALG/HA hydrogel induced an increase in the expression of myogenic regulatory factor-related genes, hypertrophy of muscle fiber, proliferation of muscle satellite cells, and angiogenesis and decreased interstitial fibrosis. Furthermore, our functional analysis through the high-speed camera setup demonstrated that the administration of the bFGF-loaded ALG/HA hydrogel induced successful glottal gap closure. Thus, the bFGF-loaded ALG/HA hydrogel could be a promising candidate for injection laryngoplasty with therapeutic effects.

A Tutorial of the Effects of Sex Hormones on Laryngeal Senescence and Neuromuscular Response to Exercise

Purpose The purpose of this tutorial is to summarize how sex hormones affect both laryngeal senescence and neuromuscular response to exercise, highlighting the importance of considering sex differences in developing treatment for the senescent voice. Conclusion Men and women's voices are sexually dimorphic throughout the life span, including during the laryngeal adaptations observed during senescence. Therefore, presbyphonia (age-related dysphonia) likely clinically manifests differently for men and women due to differences in how the male and the female larynx change in response to aging. Because sexual dimorphism is evident in both laryngeal aging and response to exercise, voice therapy programs aimed at treating the typical and disordered aged voice should consider sex differences in their design.

Volumetric analysis of vocal fold atrophy via magnetic resonance imaging

Objective

To quantitatively test the hypothesis that older patients have increased thyroarytenoid muscle atrophy by comparing thyroarytenoid muscle volumes across different age groups.

Methods

A retrospective chart review was conducted. The study included 111 patients with no history of laryngeal pathology. Two investigators reviewed magnetic resonance imaging studies of these patients and manually traced the thyroarytenoid muscles on multiple slices bilaterally. Thyroarytenoid muscle volumes were then computed using imaging analysis software. Patients were stratified into three age groups (18–50 years, 51–64 years, and 65 years or older) for comparison.

Results

Intra- and inter-rater reliabilities were excellent for all measurements (intraclass correlation co-efficient > 0.90). There was no statistically significant difference in the mean volumes of left and right thyroarytenoid muscles in all age and gender groups.

Conclusion

Given the lack of statistically significant difference in thyroarytenoid muscle volume between age groups on magnetic resonance imaging, the prevailing assumption that age-related thyroarytenoid muscle atrophy contributes to presbyphonia should be re-examined.

Subcutaneous Neurotrophin 4 Infusion Using Osmotic Pumps or Direct Muscular Injection Enhances Aging Rat Laryngeal Muscles

Laryngeal dysfunction in the elderly is a major cause of disability, from voice disorders to dysphagia and loss of airway protective reflexes. Few, if any, therapies exist that target age-related laryngeal muscle dysfunction. Neurotrophins are involved in muscle innervation and differentiation of neuromuscular junctions (NMJs). It is thought that neurotrophins enhance neuromuscular transmission by increasing neurotransmitter release. The neuromuscular junctions (NMJs) become smaller and less abundant in aging rat laryngeal muscles, with evidence of functional denervation. We explored the effects of NTF4 for future clinical use as a therapeutic to improve function in aging human laryngeal muscles. Here, we provide the detailed protocol for systemic application and direct injection of NTF4 to investigate the ability of aging rat laryngeal muscle to remodel in response to NTF4 application. In this method, rats either received NTF4 either systemically via osmotic pump or by direct injection through the vocal folds. Laryngeal muscles were then dissected and used for histological examination of morphology and age-related denervation.

Sexual dimorphism in laryngeal muscle fibers and ultrasonic vocalizations in the adult rat

OBJECTIVE

The human voice is sexually dimorphic in obvious ways, such as differences in fundamental frequency and gross laryngeal anatomy, but also in less apparent ways, such as in the prevalence and types of voice disorders and the manifestation of voice changes in advanced age. Differences between males and females are rarely explored, however, in mechanistic animal studies. The goal of this study was to explore sexual dimorphism in laryngeal function and structure in adult rats by examining ultrasonic vocalization acoustics and muscle fiber size and type in the thyroarytenoid muscle.

STUDY DESIGN

Animal group comparison.

METHODS

Spontaneous ultrasonic vocalizations from 10 male adult rats and 10 female adult rats were recorded, classified, and acoustically analyzed. Cross-sections of the thyroarytenoid muscle were stained and imaged for analysis of muscle fiber size and type. Acoustic and muscle parameters were statistically compared between sexes.

RESULTS

Male rats had a lower mean frequency of short ultrasonic vocalizations. Male rats also had a larger mean fiber size in the external division of the thyroarytenoid and larger overall muscle area in both the vocalis and external divisions of the thyroarytenoid. However, muscle fiber type compositions were similar between sexes in both the vocalis and external division of the thyroarytenoid muscles.

CONCLUSION

Functional and structural laryngeal differences exist between adult male and female rats; therefore, the rat model can be used to further study sexual dimorphism of the voice.

LEVEL OF EVIDENCE

NA. Laryngoscope, 127:E270-E276, 2017.

Alterations of intrinsic tongue muscle properties with aging

INTRODUCTION

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.

METHODS

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.

RESULTS

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.

DISCUSSION

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.

Muscle fiber types composition and type identified endplate morphology of forepaw intrinsic muscles in the rat

The failure to accept reinnervation is considered to be one of the reasons for the poor motor functional recovery of intrinsic hand muscles (IHMs) after nerve injury. Rat could be a suitable model to be used in simulating motor function recovery of the IHMs after nerve injury as to the similarities in function and anatomy of the muscles between human and rat. However, few studies have reported the muscle fiber types composition and endplate morphologic characteristics of intrinsic forepaw muscles (IFMs) in the rat. In this study, the myosin heavy chain isoforms and acetylcholine receptors were stained by immunofluorescence to show the muscle fiber types composition and endplates on type-identified fibers of the lumbrical muscles (LMs), interosseus muscles (IMs), abductor digiti minimi (AM) and flexor pollicis brevis (FM) in rat forepaw. The majority of IFMs fibers were labeled positively for fast-switch fiber. However, the IMs were composed of only slow-switch fiber. With the exception of the IMs, the other IFMs had a part of hybrid fibers. Two-dimensional morphological characteristics of endplates on I and IIa muscle fiber had no significant differences among the IFMs. The LMs is the most suitable IFMs of rat to stimulate reinnervation of the IHMs after nerve injury. Gaining greater insight into the muscle fiber types composition and endplate morphology in the IFMs of rat may help understand the pathological and functional changes of IFMs in rat model stimulating reinnervation of IHMs after peripheral nerve injury.

Enhancement of aging rat laryngeal muscles with endogenous growth factor treatment

Clinical evidence suggests that laryngeal muscle dysfunction is associated with human aging. Studies in animal models have reported morphological changes consistent with denervation in laryngeal muscles with age. Life-long laryngeal muscle activity relies on cytoskeletal integrity and nerve-muscle communication at the neuromuscular junction (NMJ). It is thought that neurotrophins enhance neuromuscular transmission by increasing neurotransmitter release. We hypothesized that treatment with neurotrophin 4 (NTF4) would modify the morphology and functional innervation of aging rat laryngeal muscles. Fifty-six Fischer 344xBrown Norway rats (6- and 30-mo age groups) were used to evaluate to determine if NTF4, given systemically (n = 32) or directly (n = 24), would improve the morphology and functional innervation of aging rat thyroarytenoid muscles. Results demonstrate the ability of rat laryngeal muscles to remodel in response to neurotrophin application. Changes were demonstrated in fiber size, glycolytic capacity, mitochondrial, tyrosine kinase receptors (Trk), NMJ content, and denervation in aging rat thyroarytenoid muscles. This study suggests that growth factors may have therapeutic potential to ameliorate aging-related laryngeal muscle dysfunction.

The effects of treadmill running on aging laryngeal muscle structure

OBJECTIVES/HYPOTHESIS

Age-related changes in laryngeal muscle structure and function may contribute to deficits in voice and swallowing observed in elderly people. We hypothesized that treadmill running, an exercise that increases respiratory drive to upper airway muscles, would induce changes in thyroarytenoid muscle myosin heavy chain (MHC) isoforms that are consistent with a fast-to-slow transformation in muscle fiber type.

STUDY DESIGN

Randomized parallel group controlled trial.

METHODS

Fifteen young adult and 14 old Fischer 344/Brown Norway rats received either treadmill running or no exercise (5 days/week/8 weeks). Myosin heavy chain isoform composition in the thyroarytenoid muscle was examined at the end of 8 weeks.

RESULTS

Significant age and treatment effects were found. The young adult group had the greatest proportion of superfast-contracting MHCIIL isoform. The treadmill running group had the lowest proportion of MHCIIL and the greatest proportion of MHCIIx isoforms.

CONCLUSION

Thyroarytenoid muscle structure was affected both by age and treadmill running in a fast-to-slow transition that is characteristic of exercise manipulations in other skeletal muscles.

LEVEL OF EVIDENCE

NA. Laryngoscope, 126:672-677, 2016.