Contractile dysfunction and altered metabolic profile of the aging rat thyroarytenoid muscle

Male and female syringeal muscles exhibit superfast shortening velocities in zebra finches

Vocalisations play a key role in the communication behaviour of many vertebrates. Vocal production requires extremely precise motor control, which is executed by superfast vocal muscles that can operate at cycle frequencies over 100 Hz and up to 250 Hz. The mechanical performance of these muscles has been quantified with isometric performance and the workloop technique, but owing to methodological limitations we lack a key muscle property characterising muscle performance, the force-velocity relationship. Here, we quantified the force-velocity relationship in zebra finch superfast syringeal muscles using the isovelocity technique and tested whether the maximal shortening velocity is different between males and females. We show that syringeal muscles exhibit high maximal shortening velocities of 25L0 s-1 at 30°C. Using Q10-based extrapolation, we estimate they can reach 37-42L0 s-1 on average at body temperature, exceeding other vocal and non-avian skeletal muscles. The increased speed does not adequately compensate for reduced force, which results in low power output. This further highlights the importance of high-frequency operation in these muscles. Furthermore, we show that isometric properties positively correlate with maximal shortening velocities. Although male and female muscles differ in isometric force development rates, maximal shortening velocity is not sex dependent. We also show that cyclical methods to measure force-length properties used in laryngeal studies give the same result as conventional stepwise methodologies, suggesting either approach is appropriate. We argue that vocal behaviour may be affected by the high thermal dependence of superfast vocal muscle performance.

Utilizing novel recurrent laryngeal motor nerve conduction studies to characterize the aging larynx: A pilot study

Objectives

Age-related changes to the larynx are associated with dysphonia and contribute to reduced quality of life. This study utilizes recurrent laryngeal motor nerve conduction studies (rlMNCS) to determine if neurophysiologic changes occur in the aging larynx using an aging rat model.

Study Design

Animal study.

Methods

In vivo rlMNCS were performed in 10 young hemi-larynges (3-4 months) and 10 aged hemi-larynges (18-19 months) rats (Fischer 344 × Brown Norway F344BN). Recording electrodes were placed into the thyroarytenoid (TA) muscle through direct laryngoscopy. Recurrent laryngeal nerves (RLNs) were directly stimulated with bipolar electrodes. Compound motor action potentials (CMAPs) were obtained. RLN cross-sections were stained with toluidine blue. Axon count, myelination, and g-ratio were quantified utilizing AxonDeepSeg analysis software.

Results

rlMNCS were successfully obtained in all animals. Mean CMAP amplitude and negative durations in young rats were 3.58 ± 2.20 mV and 0.93 ± 0.14 mS (mean dif: 0.17; 95% CI: -2.21 to 2.54), respectively, and 3.74 ± 2.81 mV and 0.98 ± 0.11 mS (mean dif: 0.050; 95% CI: -0.07 to 0.17). No significant differences in onset latency or negative area were observed. Mean axon count in young rats (176 ± 35) was comparable to that in old rats (173 ± 31). Myelin thickness and g-ratio did not differ between groups.

Conclusions

There were no statistically significant differences in RLN conduction or axon histology between young and aged rats in this pilot study. This work provides a basis for future, adequately powered studies, and may lead to a tractable animal model to study the aging larynx.

Level of Evidence

5.

Bioengineered 3D Skeletal Muscle Model Reveals Complement 4b as a Cell-Autonomous Mechanism of Impaired Regeneration with Aging

A mechanistic understanding of cell-autonomous skeletal muscle changes after injury can lead to novel interventions to improve functional recovery in an aged population. However, major knowledge gaps persist owing to limitations of traditional biological aging models. 2D cell culture represents an artificial environment, while aging mammalian models are contaminated by influences from non-muscle cells and other organs. Here, a 3D muscle aging system is created to overcome the limitations of these traditional platforms. It is shown that old muscle constructs (OMC) manifest a sarcopenic phenotype, as evidenced by hypotrophic myotubes, reduced contractile function, and decreased regenerative capacity compared to young muscle constructs. OMC also phenocopy the regenerative responses of aged muscle to two interventions, pharmacological and biological. Interrogation of muscle cell-specific mechanisms that contribute to impaired regeneration over time further reveals that an aging-induced increase of complement component 4b (C4b) delays muscle progenitor cell amplification and impairs functional recovery. However, administration of complement factor I, a C4b inactivator, improves muscle regeneration in vitro and in vivo, indicating that C4b inhibition may be a novel approach to enhance aged muscle repair. Collectively, the model herein exhibits capabilities to study cell-autonomous changes in skeletal muscle during aging, regeneration, and intervention.

Subjective voice change was associated with appendicular skeletal muscle mass in elderly men, but not in women: A cross-sectional study

OBJECTIVES

To investigate the relationship between subjective voice changes and appendicular skeletal muscle in the elderly in Korea.

DESIGN

Retrospective cross-sectional study.

SETTING

Population-based survey data were collected by the Korean National Health and Nutrition Examination Survey between January 2009 and December 2011.

PARTICIPANTS

A total of 2611 participants (1081 men and 1530 women) aged 65 to 80 years were enrolled in the Korean National Health and Nutrition Examination Survey from 2009 to 2011. A 70-degree laryngeal endoscopy was performed to check for abnormalities in the larynx, while dual-energy x-ray absorptiometry was utilised to measure appendicular skeletal muscle mass. The correlation between subjective voice change and appendicular skeletal muscle index (ASMI) was analysed using a linear-by-linear association test and logistic regression analysis.

RESULTS

When comparing ASMI according to the presence or absence of subjective voice change, elderly men showed significantly lower ASMI values when subjective voice change was present (p = .021). However, in women, the ASMI was not significantly lower in the presence of subjective voice changes (p = .365). We confirmed that subjective voice change was significantly lower in the highest quintile of ASMI compared to lowest quintile of ASMI in the men using logistic regression analysis (B 0.281, 95% confident interval 0.082-0.964, p < .044).

CONCLUSIONS

This study has shown that in Korean men aged >65 years, subjective voice abnormality significantly increased as skeletal muscle mass decreased. Further longitudinal studies are needed to determine whether a correlation exists between objective voice test results and ASMI.

Identification of novel pleiotropic gene for bone mineral density and lean mass using the cFDR method

Bone mineral density (BMD) and whole-body lean mass (WBLM) are two important phenotypes of osteoporosis and sarcopenia. Previous studies have shown that BMD and lean mass were phenotypically and genetically correlated. To identify the novel common genetic factors shared between BMD and WBLM, we performed the conditional false discovery rate (cFDR) analysis using summary data of the genome-wide association study of femoral neck BMD (n = 53,236) and WBLM (n = 38,292) from the Genetic Factors for Osteoporosis Consortium (GEFOS). We identified eight pleiotropic Single Nucleotide Polymorphism (SNPs) (PLCL1 rs11684176 and rs2880389, JAZF1 rs198, ADAMTSL3 rs10906982, RFTN2/MARS2 rs7340470, SH3GL3 rs1896797, ST7L rs10776755, ANKRD44/SF3B1 rs11888760) significantly associated with femoral neck BMD and WBLM (ccFDR < 0.05). Bayesian fine-mapping analysis showed that rs11888760, rs198, and rs1896797 were the possible functional variants in the ANKRD44/SF3B1, JAZF1i, and SH3GL3 loci, respectively. Functional annotation suggested that rs11888760 was likely to comprise a DNA regulatory element and linked to the expression of RFTN2 and PLCL1. PLCL1 showed differential expression in laryngeal posterior cricoarytenoid muscle between rats of 6 months and 30 months of age. Our findings, together with PLCL1's potential functional relevance to bone and skeletal muscle function, suggested that rs11888760 was the possible pleiotropic functional variants appearing to coregulate both bone and muscle metabolism through regulating the expression of PLCL1. The findings enhanced our knowledge of genetic associations between BMD and lean mass and provide a rationale for subsequent functional studies of the implicated genes in the pathophysiology of diseases, such as osteoporosis and sarcopenia.

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.

Machine-Learning Analysis of Voice Samples Recorded through Smartphones: The Combined Effect of Ageing and Gender

Background: Experimental studies using qualitative or quantitative analysis have demonstrated that the human voice progressively worsens with ageing. These studies, however, have mostly focused on specific voice features without examining their dynamic interaction. To examine the complexity of age-related changes in voice, more advanced techniques based on machine learning have been recently applied to voice recordings but only in a laboratory setting. We here recorded voice samples in a large sample of healthy subjects. To improve the ecological value of our analysis, we collected voice samples directly at home using smartphones. Methods: 138 younger adults (65 males and 73 females, age range: 15–30) and 123 older adults (47 males and 76 females, age range: 40–85) produced a sustained emission of a vowel and a sentence. The recorded voice samples underwent a machine learning analysis through a support vector machine algorithm. Results: The machine learning analysis of voice samples from both speech tasks discriminated between younger and older adults, and between males and females, with high statistical accuracy. Conclusions: By recording voice samples through smartphones in an ecological setting, we demonstrated the combined effect of age and gender on voice. Our machine learning analysis demonstrates the effect of ageing on voice.

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.

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.

Muscle Bioenergetic Considerations for Intrinsic Laryngeal Skeletal Muscle Physiology

PURPOSE

Intrinsic laryngeal skeletal muscle bioenergetics, the means by which muscles produce fuel for muscle metabolism, is an understudied aspect of laryngeal physiology with direct implications for voice habilitation and rehabilitation. The purpose of this review is to describe bioenergetic pathways identified in limb skeletal muscle and introduce bioenergetic physiology as a necessary parameter for theoretical models of laryngeal skeletal muscle function.

METHOD

A comprehensive review of the human intrinsic laryngeal skeletal muscle physiology literature was conducted. Findings regarding intrinsic laryngeal muscle fiber complement and muscle metabolism in human models are summarized and exercise physiology methodology is applied to identify probable bioenergetic pathways used for voice function.

RESULTS

Intrinsic laryngeal skeletal muscle fibers described in human models support the fast, high-intensity physiological requirements of these muscles for biological functions of airway protection. Inclusion of muscle bioenergetic constructs in theoretical modeling of voice training, detraining, fatigue, and voice loading have been limited.

CONCLUSIONS

Muscle bioenergetics, a key component for muscle training, detraining, and fatigue models in exercise science, is a little-considered aspect of intrinsic laryngeal skeletal muscle physiology. Partnered with knowledge of occupation-specific voice requirements, application of bioenergetics may inform novel considerations for voice habilitation and rehabilitation.

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.

Perioperative Voice Recovery: An Exercise Physiology Perspective

Voice professionals have differing views on the amount of voice rest prescribed before and after laryngeal surgery. Current recommendations are largely based on a long-standing belief that voice rest is good for the vocal mechanism, particularly when pathology is present or following surgical interruption of the vocal fold tissue. There is little evidence to support the benefit of extensive voice rest prior to laryngeal surgery, as is often recommended in the performing arts. In fact, preoperative voice therapy has shown benefit for postoperative voice outcome. From a wound-healing perspective, voice conservation immediately following vocal fold surgery contributes to the best vocal function outcome. There is no supportive evidence for postoperative voice rest that extends for weeks into months, as some performing artists have reported following surgery. From the perspective of skeletal muscle cell physiology and what is currently known about skeletal muscle adaptations that occur with training and detraining, a guideline for optimal voice recovery and return to performance may be clearer. The well-intentioned, long-held belief that extensive voice conservation is good for the voice may actually trigger a skeletal muscle detraining cascade that could lengthen return to optimal voice function, particularly in the vocal performing arts.

Effects of aging on thyroarytenoid muscle regeneration

OBJECTIVES/HYPOTHESIS

Regenerative properties of age-associated changes in the intrinsic laryngeal muscles following injury are unclear. The purpose of this study was to investigate the regenerative properties of the thyroarytenoid (TA) muscle in an aging rat model. The hypothesis was that following myotoxic injury, old animals would exhibit a decrease in mitotic activities of muscle satellite cells when compared with younger rats, suggesting reduced regenerative potential in the aging rat TA muscle.

STUDY DESIGN

Animal group comparison.

METHODS

Regeneration responses following injury to the TA muscle were examined in 18 young adult, middle-aged, and old Fischer 344/Brown Norway rats. TA muscle fiber cross-sectional area (CSA), satellite cell mitosis (number/fiber), and regeneration index (CSA injured side/CSA noninjured side) were measured and compared across age groups.

RESULTS

Young adult animals had a significantly higher regeneration index than the middle-aged and old groups. Within the lateral region of the TA muscle (LTA), the regeneration index was significantly higher in the young adult animals than in the middle-aged and old animals. The regeneration index of the medial TA was significantly higher than the LTA across all age groups.

CONCLUSIONS

The regenerative capacity of the TA muscle is impaired with increasing age.

Effects of aging and levodopa on the laryngeal adductor reflex in rats

Dopaminergic neurotransmission plays an essential role in sensorimotor function, and declines with age. Previously, we found the laryngeal adductor reflex (LAR) was increased in excitation by a dopamine receptor antagonist. If this airway-protective reflex is similarly affected by aging, it will interfere with volitional control in older adults. The current study tested whether the LAR was affected by aging, and whether such deficits were reversed by levodopa administration in aging rats. We recorded thyroarytenoid (TA) muscle activity at rest and during elicitation of LAR responses by stimulation of the internal branch of the superior laryngeal nerve (iSLN) in 6-, 18- and 30-month-old rats under alpha-chloralose anesthesia. Using paired stimuli at different inter-stimulus intervals (ISIs), LAR central conditioning, resting muscle activity, and reflex latency and amplitudes were quantified. Numbers of dopaminergic neurons in the substantia nigra pars compacta (SNpc) were measured using tyrosine hydroxylase staining. We found: (1) increased resting TA muscle activity and LAR amplitude occurred with fewer dopaminergic neurons in the SNpc in 18- and 30-month-old rats; (2) decreases in LAR latency and increases in amplitude correlated with reduced numbers of dopaminergic neurons in the SNpc; (3) test responses were greater at 1000ms ISI in 18-month-old rats compared with 6-month-old rats; and (4) levodopa administration further increased response latency but did not alter muscle activity, response amplitude, or central conditioning. In conclusion, increases in laryngeal muscle activity levels and reflex amplitudes accompanied age reductions in dopaminergic neurons but were not reversed with levodopa administration.

Nerve-muscle pedicle implantation in the denervated thyroarytenoid muscle of aged rats

CONCLUSION

Nerve-muscle pedicle (NMP) implantation was effective in the recovery of atrophic changes in the denervated thyroarytenoid (TA) muscle in aged rats.

OBJECTIVES

To evaluate the effects of NMP implantation on the denervated TA muscle in aged rats.

METHODS

Wistar rats aged 20 months and 8 weeks were respectively divided into two groups in which the left recurrent laryngeal nerve (RLN) was transected without (aged/young DNV group) or with (aged/young NMP group) NMP implantation. The aged DNV and NMP groups were further divided into two subgroups, based on the period after RLN transection (10 or 20 weeks). In the DNV groups, we assessed the area of muscle and the number of neuromuscular junctions (NMJs) histologically. In the NMP groups, we performed electromyography and histological assessments. For electromyography, we stimulated the transferred nerve and evaluated the muscle action potentials (MAPs) of the TA muscle.

RESULTS

The muscle areas in the aged NMP groups were significantly larger than those in the aged DNV groups. More NMJs were found in aged NMP groups compared with aged DNV groups. MAPs were seen in all NMP animals. No significant differences were observed between the aged and young NMP groups in histological and physiological assessments.

Subglottal pressure, tracheal airflow, and intrinsic laryngeal muscle activity during rat ultrasound vocalization

Vocal production requires complex planning and coordination of respiratory, laryngeal, and vocal tract movements, which are incompletely understood in most mammals. Rats produce a variety of whistles in the ultrasonic range that are of communicative relevance and of importance as a model system, but the sources of acoustic variability were mostly unknown. The goal was to identify sources of fundamental frequency variability. Subglottal pressure, tracheal airflow, and electromyographic (EMG) data from two intrinsic laryngeal muscles were measured during 22-kHz and 50-kHz call production in awake, spontaneously behaving adult male rats. During ultrasound vocalization, subglottal pressure ranged between 0.8 and 1.9 kPa. Pressure differences between call types were not significant. The relation between fundamental frequency and subglottal pressure within call types was inconsistent. Experimental manipulations of subglottal pressure had only small effects on fundamental frequency. Tracheal airflow patterns were also inconsistently associated with frequency. Pressure and flow seem to play a small role in regulation of fundamental frequency. Muscle activity, however, is precisely regulated and very sensitive to alterations, presumably because of effects on resonance properties in the vocal tract. EMG activity of cricothyroid and thyroarytenoid muscle was tonic in calls with slow or no fundamental frequency modulations, like 22-kHz and flat 50-kHz calls. Both muscles showed brief high-amplitude, alternating bursts at rates up to 150 Hz during production of frequency-modulated 50-kHz calls. A differentiated and fine regulation of intrinsic laryngeal muscles is critical for normal ultrasound vocalization. Many features of the laryngeal muscle activation pattern during ultrasound vocalization in rats are shared with other mammals.

Cytochrome c oxidase deficiency in human posterior cricoarytenoid muscle

BACKGROUND

Mitochondrial alterations occur in skeletal muscle fibers throughout the normal aging process, resulting from increased accumulation of reactive oxide species (ROS). These result in respiratory chain abnormalities, which decrease the oxidative capacity of muscle fibers, leading to decreased contractile force, sarcopenia, or fiber necrosis. Intrinsic laryngeal muscles are a cranial muscle group that possesses some distinctive genotypic, phenotypic, and physiologic properties. Their susceptibility to mitochondrial alterations resulting from biological processes that increase levels of oxidative stress may be one of these distinctive characteristics.

OBJECTIVES

The incidence of cytochrome c oxidase (COX) deficiency (COX(-)) was determined in human posterior cricoarytenoid (PCA) muscle when compared with the human thyrohyoid (TH) muscle, an extrinsic laryngeal muscle that served as "control" muscle. Ten PCA and 10 TH muscles were harvested postlaryngectomy from 10 subjects ranging in age from 55 to 86 years. Differences in COX(-) were compared within and between muscle types using tissue section staining and standard morphometric analysis.

RESULTS AND CONCLUSIONS

COX(-) fibers were identified in both the PCA and TH muscles. The PCA muscle had 10 times as may affected fibers as the TH muscle, with significant differences in COX(-) found between muscle type and fiber type (P=0.003). Almost all of this effect was the result of elevated levels of COX(-) in type I fibers from the PCA muscle (P=0.002) that showed a strong positive correlation with increased age. These results suggest that increased mitochondrial alterations may occur in the PCA muscle during normal aging.

Chronic stimulation-induced changes in the rodent thyroarytenoid muscle

PURPOSE

Therapies for certain voice disorders purport principles of skeletal muscle rehabilitation to increase muscle mass, strength, and endurance. However, applicability of limb muscle rehabilitation to the laryngeal muscles has not been tested. In this study, the authors examined the feasibility of the rat thyroarytenoid muscle to remodel as a consequence of increased activity instantiated through chronic electrical stimulation.

METHOD

Twenty adult Sprague-Dawley rats (Rattus norvegicus), assigned to a 1-week or 2-week stimulation group, were implanted with a nerve cuff electrode placed around the right recurrent laryngeal nerve and were fitted with a head connector. All animals were placed under anesthesia twice a day for 1 hr each time. Following the training, rats were killed, and thyroarytenoid muscles were isolated for histology and immunohistochemistry.

RESULTS

Mean muscle fiber area decreased, neuromuscular junction density increased, mitochondrial content increased qualitatively, and glycogen-positive fibers increased, demonstrating exercise-induced changes similar to those seen in limb muscles after endurance training.

CONCLUSION

Rat thyroarytenoid muscles are capable of remodeling in response to chronic electrical stimulation.

Challenges and opportunities in the management of the aging voice

Presbyphonia, or age-related dysphonia, is a diagnosis of exclusion, and other comorbidities must be considered in a complete evaluation of elderly patients with dysphonia. The aging voice can have a significant effect on the quality of life of the patient. In addition to the molecular effects of aging on the laryngeal tissues, the etiology of presbyphonia is often multifactorial because of comorbidities in the other organ systems involved in phonation. After a comprehensive evaluation, presbyphonia may be treated conservatively with voice therapy or with a range of interventions. Research into tissue engineering and electrical reanimation offers future options for treatment of presbyphonia. Currently, a multidisciplinary approach offers the most complete improvement in the vocal quality of life in this patient population.

Doxorubicin causes diaphragm weakness in murine models of cancer chemotherapy

Doxorubicin is a chemotherapeutic agent prescribed for a variety of tumors. While undergoing treatment, patients exhibit frequent symptoms that suggest respiratory muscle weakness. Cancer patients can receive doxorubicin chemotherapy through either intravenous (IV) or intraperitoneal (IP) injections. We hypothesized that respiratory muscle function would be depressed in a murine model of chemotherapy. We tested this hypothesis by treating C57BL/6 mice with a clinical dose of doxorubicin (20 mg/kg) via IV or IP injection. Three days later we measured contractile properties of muscle fiber bundles isolated from the diaphragm. Doxorubicin consistently depressed diaphragm force with both methods of administration (P < 0.01). Doxorubicin IP exaggerated the depression in diaphragm force and stimulated tissue inflammation and muscle fiber injury. These results suggest that clinically relevant doses of doxorubicin cause respiratory muscle weakness and that the loss of function depends, in part, on the route of administration.

Translating Exercise Science Into Voice Care

The basic principles of exercise training for skeletal muscle adaptations have been applied to voice training for some time. To date, the use of the basic principles of muscle training for designing a voice rehabilitation program or advising voice clients about the role of voice rest and modified voice use following surgical intervention has not been well developed. Voice training is a complex process of skill acquisition through application of motor learning principles and the concurrent coordinated use of many physiologic systems. However, the translation of exercise science literature to voice training and recovery needs to be undertaken with caution, because the function and performance of laryngeal skeletal muscle can be different from those of skeletal muscles used for other types of movement. This discussion will be confined to the basic adaptations of the muscle tissue itself. A brief review of basic principles of muscle training as understood for skeletal muscle will be followed by a more extensive discussion of the neurologic, metabolic, and physiologic adaptations of muscle training and detraining. Translation of this body of literature will be considered in the contexts of post-surgical voice recovery, voice rehabilitation, and maintenance of professional voice requirements.

Quantitative PCR analysis of laryngeal muscle fiber types

Voice and swallowing dysfunction as a result of recurrent laryngeal nerve paralysis can be improved with vocal fold injections or laryngeal framework surgery. However, denervation atrophy can cause late-term clinical failure. A major determinant of skeletal muscle physiology is myosin heavy chain (MyHC) expression, and previous protein analyses have shown changes in laryngeal muscle fiber MyHC isoform with denervation. RNA analyses in this setting have not been performed, and understanding RNA levels will allow interventions better designed to reverse processes such as denervation in the future. Total RNA was extracted from bilateral rat thyroarytenoid (TA), posterior cricoarytenoid (PCA), and cricothyroid (CT) muscles in rats. Primers were designed using published MyHC isoform sequences. SYBR Green real-time reverse transcription-polymerase chain reaction (SYBR-RT-PCR) was used for quantification. The electropherogram showed a clear separation of total RNA to 28S and 18S subunits. Melting curves illustrated single peaks for all type MyHC primers. All MyHC isoforms were identified in all muscles with various degrees of expression. Quantitative PCR is a sensitive method to detect MyHC isoforms in laryngeal muscle. Isoform expression using mRNA analysis was similar to previous analyses but showed some important differences. This technique can be used to quantitatively assess response to interventions targeted to maintain muscle bulk after denervation.

LEARNING OUTCOMES

(1) Readers will be able to describe the relationship between myosin heavy chain expression and muscle contractile properties. (2) Readers will be able to separate myosin heavy chain isoforms into slow and fast twitch phenotypes. (3) Readers will be able to describe differential muscle isoform expression between different laryngeal muscles. (4) Readers will be able to compare this study to other modalities of determining muscle fiber type.

Lesions in the Larynx of Wistar RccHan: WIST Rats

Specific regions in the rat larynx exhibit cellular changes in response to inhaled xenobiotics. These regions include the base of the epiglottis, ventral pouch, and medial surfaces of the vocal processes of the arytenoid cartilages. 1 , 2 In order to collect information on the usefulness of trimming techniques, the influence of different vehicles, the impact of different application routes in toxicity studies, and differences between induced vs. spontaneous lesions, the data obtained from a large number of inhalation and non-inhalation studies performed in Wistar RCCHan^TM: Wist rats at Harlan Laboratories Ltd Switzerland, all evaluated or reviewed by the same pathologist, were compiled for a detailed review. The value of different trimming techniques was deemed to be greatest for transverse and sagittolongitudinal section techniques, as compared to horizontolongitudinally section techniques. The comparison of lesions encountered in control rats of inhalation studies treated with different vehicles did not reveal differences in the type, distribution pattern, incidence and/or severity of spontaneous lesions. The types of lesions were also independent of different application routes in non-inhalation studies compared to inhalation studies. The pattern of spontaneous lesions in the rodent larynx was determined by degenerative and inflammatory lesions starting most often in the submucosal glands by desiccated secretion followed by mineralization and local inflammation or were induced by impacted foreign bodies. Squamous metaplasia was recorded in the respiratory epithelium overlaying the ventral gland as a spontaneous lesion in male Wistar rats from inhalation studies with a maxim of 20.0% in an inhalation oncogenicity study. Induced metaplastic changes recorded in the larynx were reversible. Other induced lesions in inhalation studies consisted of submucosal edema, necrosis, inflammation and/or granuloma. Induced lesions in non-inhalation studies were found to be exclusively related to reflux laryngitis or food impaction. It is concluded, that in rodents induced lesions of the larynx differ in type, distribution pattern, severity and incidence from spontaneous lesions.

Doxorubicin acts through tumor necrosis factor receptor subtype 1 to cause dysfunction of murine skeletal muscle

Cancer patients receiving doxorubicin chemotherapy experience both muscle weakness and fatigue. One postulated mediator of the muscle dysfunction is an increase in tumor necrosis factor-alpha (TNF), a proinflammatory cytokine that mediates limb muscle contractile dysfunction through the TNF receptor subtype 1 (TNFR1). Our main hypothesis was that systemic doxorubicin administration would cause muscle weakness and fatigue. Systemic doxorubicin administration (20 mg/kg) depressed maximal force of the extensor digitorum longus (EDL; P < 0.01), accelerated EDL fatigue (P < 0.01), and elevated serum TNF levels (P < 0.05) 72 h postinjection. Genetic TNFR1 deficiency prevented the fall in specific force caused by systemic doxorubicin, without protecting against fatigue (P < 0.01). These results demonstrate that clinical doxorubicin concentrations disrupt limb muscle function in a TNFR1-dependent manner.

Diminished contraction-induced intracellular signaling towards mitochondrial biogenesis in aged skeletal muscle

The intent of this study was to determine whether aging affects signaling pathways involved in mitochondrial biogenesis in response to a single bout of contractile activity. Acute stimulation (1 Hz, 5 min) of the tibialis anterior (TA) resulted in a greater rate of fatigue in old (36 month), compared to young (6 month) F344XBN rats, which was associated with reduced ATP synthesis and a lower mitochondrial volume. To investigate fiber type-specific signaling, the TA was sectioned into red (RTA) and white (WTA) portions, possessing two- to 2.5-fold differences in mitochondrial content. The expression and contraction-mediated phosphorylation of p38, MKK3/6, CaMKII and AMPKalpha were assessed. Kinase protein expression tended to be higher in fiber sections with lower mitochondrial content, such as the WTA, relative to the RTA muscle, and this was exaggerated in tissues from senescent, compared to young animals. At rest, kinase activation was generally similar between young and old animals, despite the age-related variations in mitochondrial volume. In response to contractile activity, age did not influence the signaling of these kinases in the high-oxidative RTA muscle. However, in the low-oxidative WTA muscle, contraction-induced kinase activation was attenuated in old animals, despite the greater metabolic stress imposed by contractile activity in this muscle. Thus, the reduction of contraction-evoked kinase phosphorylation in muscle from old animals is fiber type-specific, and depends on factors which are, in part, independent of the metabolic milieu within the contracting fibers. These findings imply that the downstream consequences of kinase signaling are reduced in aging muscle.

Establishing a new animal model for the study of laryngeal biology and disease: an anatomic study of the mouse larynx

PURPOSE

Animal models have contributed greatly to the study of voice, permitting the examination of laryngeal biology and the testing of surgical, medical, and behavioral interventions. Various models have been used. However, until recently, the mouse (Mus musculus) has not been used in laryngeal research, and features of the mouse larynx have not been defined. Therefore, the purpose of this study was to qualitatively describe mouse laryngeal anatomy in relation to known human anatomy.

METHODS

Larynges of 7 C57BL mice were examined and photographed under stereotactic and light microscopy.

RESULTS

The authors found that mouse laryngeal organization was similar to that of humans. The hyoid bone and epiglottal, thyroid, cricoid, and arytenoid cartilages were identified. An additional cartilage was present ventrally. Thyroarytenoid, posterior cricoarytenoid, lateral cricoarytenoid, and cricothyroid muscles were grossly positioned as in humans. Interarytenoid muscles were not present; however, a functional counterpart was identified.

CONCLUSIONS

The authors provide an initial description of mouse laryngeal anatomy. Because of its amenability to genetic engineering, the mouse is the premiere model for the study of disease and the testing of interventions. Introduction of the mouse model for laryngeal study offers a tool for the study of normal laryngeal cell biology and tissue response to disease processes.

Functional and morphological evidence of age-related denervation in rat laryngeal muscles

Laryngeal muscle dysfunction compromises voice, swallowing, and airway protection in elderly adults. Laryngeal muscles and their motor neurons and their motor neurons communicate via the neuromuscular junction (NMJ). We tested the hypothesis that aging disrupts NMJ organization and function in the laryngeal thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles We determined NMJ density and size and acetylcholine receptor (AChR) subunit mRNAs in TA and PCA muscles from 6-, 18-, and 30- month old-rats. NMJ function was determined with tubocurarine (TC) and contractions during nerve and muscle stimulation. NMJ size, abundance, and clustering decreased in 30-month TA and PCA muscles. AChRe mTNA and protein increased with age in both muscles. AChRg mRNA increased with age in both muscles while protein content increased in TA only. Aging PCA and TA were more sensitive to TC, demonstrating functional evidence of denervation. These results demonstrate that NMJs become smaller and less abundant in aging TA and PCA muscles.

Laryngeal muscles are spared in the dystrophin deficient mdx mouse

PURPOSE

Duchenne muscular dystrophy (DMD) is caused by the loss of the cytoskeletal protein, dystrophin. The disease leads to severe and progressive skeletal muscle wasting. Interestingly, the disease spares some muscles. The purpose of the study was to determine the effects of dystrophin deficiency on 2 intrinsic laryngeal muscles, the posterior cricoarytenoid and the thyroarytenoid, in the mouse model.

METHOD

Larynges from dystrophin-deficient mdx and normal mice were examined histologically.

RESULTS

Results demonstrate that despite the absence of dystrophin in the mdx laryngeal muscles, membrane damage, inflammation, necrosis, and regeneration were not detected in the assays performed.

CONCLUSIONS

The authors concluded that these muscles are 1 of only a few muscle groups spared in this model of dystrophin deficiency. The muscles may count on intrinsic and adaptive protective mechanisms to cope with the absence of dystrophin. Identifying these protective mechanisms may improve DMD management. The study also highlights the unique aspects of the selected laryngeal skeletal muscles and their dissimilarity to limb skeletal muscle.

Effect of aging on blood flow in rat larynx

OBJECTIVE/HYPOTHESIS

Age-associated muscular changes and fatigue have been shown to affect phonatory function. Reductions in blood flow with aging could translate to reductions in oxidative capacity within laryngeal muscles and increased fatigability. We tested the hypothesis that there would be increased capillary red blood cell (RBC) velocity and a reduction of capillary density in the thyroarytenoid (TA) muscle of senescent rats.

STUDY DESIGN/METHODS

Ten male Fisher 344/Brown Norway rats in two age groups were used: young adult (9 mo) and old (28-30 mo). Sixteen additional young and old rats were used in a fluorescent microsphere experiment that examined blood flow rates before and after a surgical manipulation. With use of a specially equipped intravital microscope, in vivo measurements of capillary geometry and flow were obtained, including RBC velocity, capillary density, tortuosity, and number of branch points.

RESULTS

There was an age-related reduction in capillary surface area as evidenced by reduced lineal density of capillaries. In addition, reduced RBC transit time was suggested by the reduction in branch points found with age. There was no change in RBC velocity with aging. The surgical method used to expose the TA muscle for blood flow recordings did not significantly affect resultant blood flow measurements.

CONCLUSIONS

We developed a method to evaluate in vivo laryngeal microvasculature. We found age-related changes in microvascular geometry within the TA muscle of the rat that could affect blood flow to this critical muscle of phonation and airway protection. These microvascular changes could contribute to age-related laryngeal dysfunction.

Effect of aging on tongue protrusion forces in rats

The purpose of this study was to ascertain the effect of aging on muscle contractile properties associated with tongue protrusion in a rat model. Fischer 344/Brown Norway hybrid rats, ten young (9 months old) and ten old (32 months old), were used to measure protrusive contractile properties. Results showed a significant reduction in tetanic forces in the old animals. The following measures of muscle contraction were not different between age groups: mean twitch contraction force, twitch contraction time, twitch contraction half-decay time, and a calculated measure of fatigability. In conclusion, aging influenced protrusive tongue muscle contractions in a rat model such that tetanic forces were reduced. The reduction of tetanus force may parallel findings in human subjects relative to isometric tongue force generation and may be associated with age-related disorders of swallowing.

Aging thyroarytenoid and limb skeletal muscle: lessons in contrast

Voice production is vital throughout life because it allows for the communication of basic needs as well as the pursuit and enjoyment of social encounters. Unfortunately, for many older individuals the ability to produce voice is altered. Structural and functional declines in the neuromuscular system occur with aging and likely contribute to the modification of voice. One specific target of the aging process is the thyroarytenoid (TA) muscle, the primary muscle of voice production. The objectives of this overview article are to (1) share current findings related to the aging of limb skeletal muscle, (2) identify age-related morphological and physiological features of TA muscle, (3) compare and contrast age-related changes in TA with those in limb skeletal muscle, and (4) describe therapies for reversing sarcopenia in limb muscle and consider the applicability of these therapies for addressing vocal fold atrophy and age-related voice changes. The article shares current knowledge from the basic sciences related to skeletal muscle aging and compares/contrasts typical muscle aging to TA aging. Current evidence suggests that (1) the TA muscle undergoes notable remodeling with age, (2) aging of the TA is multifactorial, resulting from a myriad of neurologic, metabolic, and hormonal changes, many of which are distinct from the age-related processes of typical limb skeletal muscle, (3) investigation of the aging of the TA and its role in the aging of voice is in its infancy, and (4) potential behavioral and nonbehavioral therapies for reversing aging of the TA must be further examined.