Search

Currently, there is no established technique to directly measure extrinsic tongue muscle activation during selective hypoglossal stimulation therapy (sHNS) in patients with obstructive sleep apnea syndrome (OSAS) in a simple, non-invasive clinical setting. Ultrasound shear-wave elastography (US-SWE) enables quantitative measurement of tissue stiffness. We investigated whether US-SWE is able to detect changes in muscle stiffness of the tongue during sHNS. Patients with OSAS treated with sHNS were prospectively enrolled. A standardized US-SWE protocol was used to selectively measure tissue stiffness of the geniohyoid muscle (GH) and genioglossus (GG) muscles on the side of stimulator implantation (sGH, sGG) and on the contralateral side (nGH, nGG) without and with sHNS. Eighteen patients were included (median age = 62 years, interquartile range: 56-65, 83.3% male). Median shear-wave velocity (SWV) increased during contraction with each patient's clinically prescribed therapeutic regimen in the sGH (+19%, p = 0.020) and sGG (+81%, p0.001) and decreased during contraction in the nGH (-8%, p = 0.107) and nGG (-8%, p = 0.396). Differences in SWV during contraction were significant only on the side of stimulation (sGG +81%, sGH +19%). SWE measurements had excellent reliability as reflected by a Cronbach α value ≥0.9 for all target muscles pre- and post-contraction and an item-total correlation ≥0.5. US-SWE allows reliable measurement of SWV as an indicator of muscle stiffness of extrinsic tongue muscles. This non-invasive method provides new possibilities to distinguish and characterize responders from non-responders in hypoglossal stimulation therapy. Compared with the regular visual assessment of tongue movement, US-SWE of individual muscle groups provides a new non-invasive imaging tool in patients with OSAS.

Alzheimer's disease (AD) is a progressive neurodegenerative condition disturbing major brain networks, including those pivotal to the motor control of breathing. The aim of this study was to examine respiratory control in the TgF344-AD transgenic rat model of AD. At 8-11 months of age, basal minute ventilation and ventilatory responsiveness to chemostimulation were equivalent in conscious wild-type (WT) and TgF344-AD rats. Under urethane anesthesia, basal diaphragm and genioglossus EMG activities were similar in WT and TgF344-AD rats. The duration of phenylbiguanide-induced apnoea was significantly shorter in TgF344-AD rats compared with WT. Following bilateral cervical vagotomy, diaphragm and genioglossus EMG responsiveness to chemostimulation were intact in TgF344-AD rats. Amyloid precursor protein C-terminal fragments were elevated in the TgF344-AD brainstem, in the absence of amyloid-β accumulation or alterations in tau phosphorylation. Brainstem pro-inflammatory cytokine concentrations were not increased in TgF344-AD rats. We conclude that neural control of breathing is preserved in TgF344-AD rats at this stage of the disease.

Genioglossus was stimulated intramuscularly to determine the effect of regional activation of the muscle on tongue movement in eight healthy adults. Stimulation at motor threshold was delivered with a needle electrode inserted to different depths in the anterior and posterior regions of genioglossus. The current amplitude that induced muscle contraction was ∼80% higher for anterior than posterior sites. Evoked tongue movements were determined from stimulus-triggered averages (150 pulses) of the outputs from an accelerometer fixed to the posterosuperior surface of the tongue. The median amplitude [95% confidence intervals] for the resultant acceleration was 0.0 m/s2 [0.0, 0.2] for anterior and 0.6 m/s2 [0.1, 2.8] for posterior sites. There was a positive relationship between acceleration amplitude and stimulation depth in the posterior of genioglossus (p < 0.001), but acceleration amplitude did not vary with stimulation depth in the anterior region (p = 0.83). This heterogeneity in acceleration responses between muscle regions may contribute to differences in collapsibility of the upper airway.

Genioglossus activity maintains the patency of the upper airway. 5-HT neurons in the raphe nucleus regulate genioglossus activity. In order to study the influence of 5-HT1A receptors in dorsal raphe nucleus (DRN) on genioglossus EMG during normoxia, adult male Wistar rats were randomly divided into four groups: the artificial cerebrospinal fluid group (ACSF group), the low-concentration of 5-HT1A receptors agonist 8-OH-DPAT group (0.1 mM group), the mid-concentration 8-OH-DPAT group (0.4 mM group) and the high-concentration 8-OH-DPAT group (1.0 mM group). Rats received 0.1 μl ACSF/8-OH-DPAT microinjections into the DRN. EMG activity of the genioglossus was recorded at 5 min, 15 min and 30 min after microinjection. In three 8-OH-DPAT groups, genioglossus EMG activity significantly decreased at 5 min after microinjection and persisted for 30 min. The significantly decreased EMG activity was more pronounced in the mid- and high-concentration groups than in the low-concentration group, indicating that 5-HT1A receptors in the DRN could rapidly and continuously inhibit genioglossus EMG activity during normoxia.

Our aim was to find out first whether the extrinsic muscles of the tongue are histologically identifiable, and secondly to what degree the use of the new criteria in the 8th editions of the American Joint Committee on Cancer(AJCC)/Union for International Cancer Control (UICC) manuals (which have recognised the importance of depth of invasion of tumour, rather than invasion of the extrinsic muscles of the tongue and extranodal extension), will alter staging of lingual squamous cell carcinoma (SCC). The histological sections from 165 patients who had had primary resection of lingual SCC were reviewed, and one or more extrinsic muscles of the tongue was identified in 100 patients (61%), with the genioglossus seen the most often (in 96). By contrast, the hyoglossus was identified in only eight patients, the styloglossus in two, and the palatoglossus in none. Identification was straightforward only in extensive resections. Applying the criteria from the 8th edition increased the number of pT3 SCC with a simultaneous reduction in pT4a tumours. The number of pN2b SCC was also reduced, but the new category of pN3b meant that overall 53% of tumours were upstaged. The kappa scores for agreement between the two sets of criteria were 0.221 (weighted 0.410) for the pT values, 0.508 (0.713) for pN values (but 0.227, weighted 0.386, if the pN0 values were removed before calculation), and 0.243 (0.514) for overall stage, indicating poor to fair agreement. We conclude that the removal of invasion of extrinsic muscles of the tongue as a criterion for a pT4a SCC is justified, and that many SCC of the tongue will be upstaged as a result of implementation of the 8th editions.

Neural mechanisms of obstructive sleep apnea, a common sleep-related breathing disorder, are incompletely understood. Hypoglossal motoneurons, which provide tonic and inspiratory activation of genioglossus (GG) muscle (a major upper airway dilator), receive catecholaminergic input from medullary A1/C1 neurons. We aimed to determine the contribution of A1/C1 neurons in control of GG muscle during sleep and wakefulness. To do so, we placed injections of a viral vector into DBH-cre mice to selectively express the hMD4i inhibitory chemoreceptors in A1/C1 neurons. Administration of the hM4Di ligand, clozapine-N-oxide (CNO), in these mice decreased GG muscle activity during NREM sleep (F1,1,3=17.1, p

In the cat four different types of vocalization, mews, howls, cries, and hisses were generated by microstimulation in different parts of the periaqueductal gray (PAG). While mews imply positive vocal expressions, howls, hisses, and cries represent negative vocal expressions. In the intermediate PAG, mews were generated in the lateral column, howls, and hisses in the ventrolateral column. Cries were generated in two other regions, the lateral column of the rostral PAG and the ventrolateral column of the caudal PAG. In order to define the specific motor patterns of the mews, howls, and cries, the following muscles were recorded during these vocalizations; larynx (cricothyroid, thyroarytenoid, and posterior cricoarytenoid), tongue (genioglossus), jaw (digastric), and respiration muscles (diaphragm, internal intercostal, external, and internal abdominal oblique). During these mews, howls, and cries we analyzed the frequency, intensity, activation cascades power density, turns, and amplitude analysis of the electromyograms (EMGs). It appeared that each type of vocalization consists of a specific circumscribed motor coordination. The nucleus retroambiguus (NRA) in the caudal medulla is known to serve as the final premotor interneuronal output system for vocalization. Although neurochemical microstimulation in the NRA itself also generated vocalizations, they only consisted of guttural sounds, the EMGs of which involved only small parts of the EMGs of the mews, howls, and cries generated by neurochemical stimulation in the PAG. These results demonstrate that positive and negative vocalizations are generated in different parts of the PAG. These parts have access to different groups of premotoneurons in the NRA, that, in turn, have access to different groups of motoneurons in the brainstem and spinal cord, resulting in different vocalizations. The findings would serve a valuable model for diagnostic assessment of voice disorders in humans.

Surgical intervention for obstructive sleep apnea (OSA) is a complex topic. The discussion involves intricate procedures targeting specific areas of the upper airway. Because of the wide variety of physiologic and anatomic causes of this disorder it is important to tailor the treatment to offer the patient the best possible outcome. Genioglossus, hyoid, and tongue base procedures should be considered among theses treatment options.

Surgical interventions for the upper airway have long been a part of treatment algorithms for sleep-disordered breathing. Genioglossus advancement is one such procedure designed to specifically treat obstructed breathing related to hypopharyngeal collapse. The procedure involves surgical manipulation of the genioglossus muscleʼs attachment to the mandible. The result is reducing obstruction at the hypopharynx and tongue base by displacing this musculature anteriorly. The last 30 years have introduced variations of the procedures and further explored the relevant anatomy. Although there is a paucity of high-level evidence, studies have shown promising outcomes when the procedure is tailored to those with appropriate anatomy and pathophysiology.

Imaging and quantification of tongue anatomy is helpful in surgical planning, post-operative rehabilitation of tongue cancer patients, and studying of how humans adapt and learn new strategies for breathing, swallowing and speaking to compensate for changes in function caused by disease, medical interventions or aging. In vivo acquisition of high-resolution three-dimensional (3D) magnetic resonance (MR) images with clearly visible tongue muscles is currently not feasible because of breathing and involuntary swallowing motions that occur over lengthy imaging times. However, recent advances in image reconstruction now allow the generation of super-resolution 3D MR images from sets of orthogonal images, acquired at a high in-plane resolution and combined using super-resolution techniques. This paper presents, to the best of our knowledge, the first attempt towards automatic tongue muscle segmentation from MR images. We devised a database of ten super-resolution 3D MR images, in which the genioglossus and inferior longitudinalis tongue muscles were manually segmented and annotated with landmarks. We demonstrate the feasibility of segmenting the muscles of interest automatically by applying the landmark-based game-theoretic framework (GTF), where a landmark detector based on Haar-like features and an optimal assignment-based shape representation were integrated. The obtained segmentation results were validated against an independent manual segmentation performed by a second observer, as well as against B-splines and demons atlasing approaches. The segmentation performance resulted in mean Dice coefficients of 85.3%, 81.8%, 78.8% and 75.8% for the second observer, GTF, B-splines atlasing and demons atlasing, respectively. The obtained level of segmentation accuracy indicates that computerized tongue muscle segmentation may be used in surgical planning and treatment outcome analysis of tongue cancer patients, and in studies of normal subjects and subjects with speech and swallowing problems.

Maximal voluntary protrusion force of the human tongue has not been examined in positions beyond the incisors or at different lung volumes. Tongue force was recorded with the tongue tip at eight positions relative to the incisors (12 and 4mm protrusion, neutral and 4, 12, 16, 24 and 32mm retraction) at functional residual capacity (FRC), total lung capacity (TLC) and residual volume (RV) in 15 healthy subjects. Maximal force occurred between 12mm and 32mm retraction (median 16mm). Maximum force at FRC was reproducible at the optimal tongue position across sessions (P=0.68). Across all positions at FRC the average force was highest at 24mm retraction (28.3±5.3N, mean±95% CI) and lowest at 12mm protrusion (49.1±4.6% maximum; P

A 43-year-old man was admitted to our department for the acute onset of unilateral right throbbing headache. Neurologic examination revealed right ocular myosis and ptosis, left displacement of the uvula, dysphonia, weak left-turning of the head, right scapular winging on arm abduction and right tongue deviation, suggesting 9th through 12th cranial nerve palsy and Horner’s syndrome. Neurophysiologic examination confirmed the unilateral involvement. EMG showed loss of motor unit recruitment and denervation activity in the right sternocleidomastoid, trapezius and genioglossus muscles. MEPs and C-MAP were not excitable from those muscles. MRI demonstrated a crescent-shaped hyperintense T1 and T2 signal within the wall of the distal extracranial portion of the right internal carotid artery (ICA), suggesting an intramural hematoma causing mass effect upon the internal jugular vein. A diagnosis of spontaneous extracranial carotid dissection was made. An extended CT angiogram showed extensive luminal irregularities in the main renal arteries, with aneurysm formation at its bifurcation. Ibromuscular dysplasia was hypothesized and genetic counseling for connective tissue was carried on. Cranial nerve palsy is an unusual presentation of extracranial ICA dissection, likely mediated by compression or stretching of the nerve by the expanded artery. Neurophysiological testing provides useful information to localize the damage and to better understand the pathophysiology of the disease.

Introduction In patients with OSA, substantial increases in genioglossus (GG) activity during hypopneas/apneas usually fail to restore normal airflow. The present study was undertaken to evaluate if this phenomenon can be explained by reduced activation of other peri-pharyngeal muscles. Methods We recorded EMGs of the GG and four other peri-pharyngeal muscles (accessory dilators, AD), in 8 patients with OSA and 12 healthy subjects, during wakefulness and sleep. Repetitive events of flow limitation were induced during sleep. The events with the highest increases in AD activity were evaluated, to assess if combined activation of both the GG and AD to levels higher than while awake ameliorate airflow reduction during sleep. Results Flow limitation triggered large increases in GG-EMG, but only modest augmentation in AD activity. Nevertheless, phasic EMG activity was present in 40 % of the ADs during sleep. In multiple events, increases of both GG and AD activity to levels substantially higher than while awake were not associated with improvement in airflow. Conclusions We conclude that sleep-induced reduction in AD response to airway obstruction cannot completely explain the failure of upper airway dilators to maintain pharyngeal patency. We speculate that reduction in dilator muscle efficacy may be due to the alterations in motor units recruitment patterns during sleep.

The base of tongue plays an important role in the pathophysiology of obstructive sleep apnea (OSA), and addressing the tongue base can be an alternative for continuous positive airway pressure and some surgeries done such as uvulopalatopharyngoplasty to treat OSA. One of the options to address the tongue base to treat the OSA is stimulation of human hypoglossal nerve with implantable devices. Thus, one needs to know the physiology of the human hypoglossal nerve to understand the mechanism of such devices. The human hypoglossal nerve is the primary motor nerve that innervates 7 of the 8 extrinsic and intrinsic muscles of the tongue on each side, except palatoglossus muscle, which is innervated by the ipsilateral vagus nerve. At the level of the hyoid bone, the human hypoglossal nerve (the proximal and midthird) is normally unfasciculated, becoming fascicular only in its distal third where it branches. The lateral branch has many small, independent branches that supply the styloglossus, hyoglossus, and inferior longitudinalis muscles. The medial branch innervates the genioglossus, superior longitudinalis, transversalis, and verticalis muscles.

The pathogenesis of obstructive sleep apnea–hypopnea syndrome (OSAHS) is summarized as the narrow anatomic structure of upper airway (UA) and the defective function of UA dilator muscles. Up to now, there have been no specific treatments for the UA dilator muscle deficiency. We previously found that some estrogen-like compounds exert protective effects on genioglossus, but this protection tends to be less satisfactory. A novel phytoestrogen derivative was synthesized in recent years and was verified to have some cytoprotective activity. This study was designed to compare the effects of natural estrogens and the synthetic resveratrol dimer on genioglossus contraction and expression of estrogen receptors (ERs) under chronic intermittent hypoxia (CIH) condition. Genioglossus myoblasts of rat were isolated and cultured in a culture medium with different agents (estradiol, genistein, resveratrol, and resveratrol dimer, respectively) under hypoxia condition, and ERs expressions were detected. In vivo study, 48 ovariectomized female rats were randomized into six groups. After CIH exposure and agents injection, rats were tested for genioglossus contractile properties and further analysis of ERs expression. Estradiol up-regulated ERα level and exerted the best protective effect of fatigue resistance. Genistein, resveratrol and resveratrol dimer primarily up-regulated the expression of ERβ. Resveratrol dimer exhibited better protection of fatigue resistance than genistein and resveratrol, and expressed higher binding affinity for ERβ than for ERα. Besides estrogenic effects, there may be some other mechanisms for the fatigue resistance improvement contributed by phytoestrogens and their derivatives.

The TNM classification for oral malignancies has been criticized for its upstaging to T4a when tumour involves styloglossus, hyoglossus, palatoglossus and genioglossus. The aims of this study were to (1) create an anatomical computer atlas of extrinsic tongue musculature, and (2) reassess the original staging of pre-treatment archived magnetic resonance images (MRI) of tongue carcinomas using the strict extrinsic muscle criteria. The anatomy of the extrinsic tongue muscles was mapped using images from the Visible Human Project (VHP) to create a computer model of the extrinsic tongue muscles. This was co-registered with 87 archived pre-staging MRI scans of tongue carcinomas to assess tumour ingress of the extrinsic tongue muscles. Of the 87 image sets reviewed, 16 were of superficial tumours not visible on MRI. In the remaining 71 cases that showed positive extrinsic muscle tumour ingress, 52% were upstaged from T1/2/3 tumours to cT4a based upon this finding. Extrinsic lateral and genioglossus muscle invasion did not predict occult cervical lymph node invasion or disease-related survival. In conclusion, tumour invasion of styloglossus or hyoglossus would result in the majority of lateral tongue tumours being staged T4a. Such stratification is of little clinical relevance, and an alternative more reliable method is required.

In obstructive sleep apnea (OSA) patients, inspiratory activation (IA) of lingual muscles protects the upper airway from collapse. We aimed to determine when rats’ lingual muscles exhibit IA. In 5 Sprague-Dawley and 3 Wistar rats, we monitored cortical EEG and lingual, diaphragmatic and nuchal electromyograms (EMGs), and identified segments of records when lingual EMG exhibited IA. Individual segments lasted 2.4–269 s (median: 14.5 s), most (89%) occurred during slow-wave sleep (SWS), and they collectively occupied 0.3–6.1% of the total recording time. IA usually started to increase with a delay after SWS onset and ended with an arousal, or declined prior to rapid eye movement sleep. IA of lingual EMG was not accompanied by increased diaphragmatic activity or respiratory rate changes, but occurred when cortical EEG power was particularly low in a low beta-1 frequency range (12.5–16.4 Hz). A deep SWS-related activation of upper airway muscles may be an endogenous phenomenon designed to protect the upper airway against collapse.

Obstructive sleep apnea (OSA) is a prevalent disorder that may cause cardiovascular disease and fatal traffic accidents but the pathophysiology remains incompletely understood. Increased fatigability of the genioglossus (the principal upper airway dilator muscle) might be important in OSA pathophysiology but the existing literature is uncertain. We hypothesized that the genioglossus in OSA subjects would fatigue more than in controls. In 9 OSA subjects and 9 controls during wakefulness we measured maximum voluntary tongue protrusion force (Tpmax). Using surface electromyography arrays we measured the rate of decline in muscle fiber conduction velocity (MFCV) during an isometric fatiguing contraction at 30% Tpmax. The rate of decline in MFCV provides an objective means of quantifying localized muscle fatigue. Linear regression analysis of individual subject data demonstrated a significantly greater decrease in MFCV in OSA subjects compared to control subjects (29.2 ± 20.8% [mean ± SD] versus 11.2 ± 20.8%; p=0.04). These data support increased fatigability of the genioglossus muscle in OSA subjects which may be important in the pathophysiology of OSA.

Previous studies have demonstrated that functional plasticity in the primary motor cortex (M1) is related to motor-skill learning and changes in the environment. Increased occlusal vertical dimension (iOVD) may modulate mastication, such as in the masticatory cycle, and the firing properties of jaw-muscle spindles. However, little is known about the changes in motor representation within the face primary motor cortex (face-M1) after iOVD. The purpose of the present study was to determine the effect of iOVD on the face-M1 using intracortical microstimulation (ICMS). In an iOVD group, the maxillary molars were built-up by 2mm with acrylic. The electromyographic (EMG) activities from the left (LAD) and right (RAD) anterior digastric (AD), masseter and genioglossus (GG) muscles elicited by ICMS within the right face-M1 were recorded 1, 2 and 8 weeks after iOVD. IOVD was associated with a significant increase in the number of sites within the face-M1 from which ICMS evoked LAD and/or GG EMG activities, as well as a lateral shift in the center of gravity of the RAD and LAD muscles at 1 and 2 weeks, but not at 8 weeks. These findings suggest that a time-dependent neuroplastic change within the rat face-M1 occurs in association with iOVD. This may be related to the animal's ability to adapt to a change in the oral environment.

Background The therapeutic value of transcutaneous electrical stimulation of the genioglossus muscle in patients with obstructive sleep apnea (OSA) to reduce sleep-disordered breathing is unclear. Methods Contraction of the genioglossus muscles during transcutaneous stimulation was investigated using ultrasonography in 11 healthy subjects (seven men, mean [SD] age 30 [6] years; BMI, 24.2 [3.5] kg/m 2 ). Esophageal and gastric pressures were measured with balloon catheters, and transesophageal diaphragm electromyogram (EMGdi) was recorded during polysomnography in 11 patients with OSA (eight men, aged 51 [16] years; BMI, 42.0 [9.7] kg/m 2 ) while transcutaneous electrical stimulation of the genioglossus was applied in non-rapid eye movement sleep (stage N2). Results Ultrasonography measurements showed a significant increase in tongue diameter during stimulation (sagittal: 10.0% [2.8%]; coronal: 9.4 % [3.7%]). The measurements were reproducible and repeatable. In patients with OSA, snoring decreased during stimulation ( P P = .001); the respiratory disturbance index (RDI) fell from 28.1 (26.3) to 10.2 (10.2) events per hour during stimulation ( P = .002), returning to 26.6 (26.0) events per hour after stimulation was stopped. Transdiaphragmatic pressure swing decreased from 24.1 (13.5) cm H 2 O to 19.7 (7.1) cm H 2 O ( P = .022), increasing to 24.2 (10.8) cm H 2 O afterward, and EMGdi fell from 23.8% max (12.6% max) to 15.7% max (6.4% max) ( P Conclusions Continuous transcutaneous electrical stimulation of the genioglossus contracts the genioglossus muscle and reduces ventilatory load and neural respiratory drive in patients with OSA.

Upper airway muscles play an important role in regulating airway lumen and in increasing the ability of the pharynx to remain patent in the face of subatmospheric intraluminal pressures produced during inspiration. Due to the considerable technical challenges associated with recording from muscles of the upper airway, much of the experimental work conducted in human subjects has centered on recording respiratory-related activities of the extrinsic tongue protudor muscle, the genioglossus (GG). The GG is one of eight muscles that invest the human tongue (Abd-El-Malek, 1939). All eight muscles are innervated by the hypoglossal nerve (cranial nerve XII) the cell bodies of which are located in the hypoglossal motor nucleus (HMN) of the caudal medulla. Much of the earlier work on the respiratory-related activity of XII motoneurons was based on recordings obtained from single motor axons dissected from the whole XII nerve or from whole muscle GG EMG recordings. Detailed information regarding respiratory-related GG motor unit activities was lacking until as recently as 2006. This paper examines key findings that have emerged from the last decade of work conducted in human subjects. Wherever appropriate, these results are compared with results obtained from in vitro and in vivo studies conducted in non-human mammals. The review is written with the objective of facilitating some discussion and some new thoughts regarding future research directions. The material is framed around four topics: (a) motor unit type, (b) rate coding and recruitment, (c) motor unit activity patterns, and (d) a compartment based view of pharyngeal airway control.

This study tests the hypothesis that the surface electromyographic (EMG) activity of upper airway dilators would respond to inspiratory loading in a healthy humans model of ventilator trigger asynchrony. EMG activity was measured in levator alae-nasi, genioglossus, parasternal, scalene and diaphragm muscles in eight subjects. They breathed quietly through a face mask and then were connected to a mechanical ventilator. Recordings were performed during nasal breathing against negative pressure triggers (−2.5%, −5% and −10% of maximal inspiratory pressure) and during oro-nasal breathing with a “−10% trigger”. Scalene, alae-nasi and genioglossus EMG activity level increased with the “−10% trigger”. While no breathing route dependence was found in scalene, the significant increase was only found for nasal breathing in alae-nasi and for oro-nasal breathing in genioglossus. The dyspnea intensity was significantly correlated with the EMG activity level of these three muscles. Surface EMG of airway dilator muscles could be used as a complementary tool to assess inspiratory drive during mechanical ventilation.

To elucidate the influences of obesity on the properties and volume of lingual (genioglossus and geniohyoid) muscles in obese rats.We analysed the accumulation of triacylglycerol and the diameter of myofibres in the lingual muscles using histochemistry, and the MyHC composition using real-time PCR in rats fed a high-fat diet for 10 weeks. In the genioglossus and geniohyoid muscles, the percentage of oil droplet areas in the obesity group were 3.6 and 2.5 times greater than those in the control group, respectively (p0.025). The diameters of the slow myofibres in the genioglossus and geniohyoid muscles were approximately 20% greater in the obesity group than in the control group (p0.0001), while that of the fast myofibres in the geniohyoid muscle was approximately 10% greater in the obesity group than in the control group (p0.0001). No significant difference in the expressions of any of the MyHC isoforms studied was found in any of the muscles studied between the obesity and control groups.High-fat diet feeding induced the fat deposition in the myofibre and influenced the structure of the lingual (genioglossus and geniohyoid) muscles.

For approximately 3 decades, urethane has been (partially or solely) used as a successful anesthetic in numerous respiratory long-term facilitation (LTF) studies, which were performed on anesthetized, paralyzed, vagotomized and artificially ventilated animals of several different species. However, things become complicated when LTF of muscle activity is studied in un-paralyzed animals. For example, a commonly used acute intermittent hypoxia (AIH) protocol failed to induce muscle LTF in anesthetized, spontaneously breathing rats. But muscle LTF could be induced when hypoxic episode number was increased and/or anesthetics other than urethane were used. In these studies however, neither anesthetic nor paralysis was mentioned as a potential factor influencing AIH-induced muscle LTF. This study tested whether urethane inhibits AIH-induced genioglossal LTF (gLTF) in un-paralyzed ventilated rats, and if so, determined whether reducing urethane dose reverses this inhibition. Three groups of adult male Sprague-Dawley rats were anesthetized (Group 1: approximately 1.6 g kg(-1) urethane; Group 2: 50 mg kg(-1) alpha-chloralose +0.9-1.2 g kg(-1) urethane; Group 3: 0.9 g kg(-1) urethane +200-400 microg kg(-1) min(-1) alphaxalone), vagotomized and mechanically ventilated. Integrated genioglossus activity was measured before, during and after AIH (5 episodes of 3-min isocapnic 12% O(2), separated by 3-min hyperoxic intervals). The AIH-induced gLTF was absent in Group 1 rats (success rate was only approximately 1/7), but was present in Group 2 (in 10/12 rats) and Group 3 (in 11/11 rats) rats. The genioglossal response to hypoxia was not significantly different among the 3 groups. Collectively, these data suggest that urethane dose-dependently inhibits gLTF in un-paralyzed anesthetized rats.

Introduction Amyotrophic Lateral Sclerosis (ALS) is the most relevant motor neuron disease in adults and characterized by widespread weakness. Despite frequent bulbar involvement, little is known about clinical and electrophysiological changes in the larynx in patients with ALS. The objective of this study was to evaluate the frequency and pattern of involvement of laryngeal muscles in ALS and its functional relevance. In addition, we assessed whether laryngeal EMG (LEMG) would increase the diagnostic sensitivity for ALS. Methods Fourteen ALS patients, 13 with spinal onset and 1 with bulbar onset, underwent nasofibroscopy (NF) followed by LEMG, in which a concentric needle was used to evaluate the thyroid-arytenoid (TA), lateral crico-arytenoid (CAL), posterior crico-arytenoid (CAP) and crico-thyroid (CT) muscles, at rest and during activation. After LEMG, resting and activation of the genioglossus and masseter muscles were also studied using the same concentric needle. Results The mean age of the patients was 48.5 years and there were 6 women. The procedures were fast (30 min on average) and uneventful. Thirteen patients presented neurogenic changes in at least one laryngeal muscle. A single patient had entirely normal LEMG. We found a pattern compatible with chronic denervation (MUAPs remodeling and incomplete recruitment) with the following frequency: TA muscle in 11/14 patients (78.5%); CT in 10/14 patients (71.4%); CAP in 10/14 patients (71.4%) and CAL in 7/14 patients (50%). In 8 patients, there were fibrillations and/ or fasciculations associated with chronic neurogenic changes in the same muscle; of these, 4 had no alteration in the genioglossus muscle and 2 had only chronic alterations in the same muscle. NF revealed motor abnormalities in the larynx in 9 patients; in the remaining 5, NF was normal but LEMG identified signs of denervation in 4 of them. Conclusion LEMG is able to identify laryngeal denervation in patients with ALS. This procedure may increase diagnostic sensitivity for ALS by identifying bulbar involvement in patients without tongue denervation. Changes in LEMG may precede clinical involvement of the larynx in these patients.

To understand the role of cholinoceptive, medial pontine reticular formation (mPRF) neurons in the control of upper airway, pharyngolaryngeal reflexes, we measured activities of intrinsic laryngeal muscles (posterior cricoarytenoid, PCA; thyroarytenoid, TA), diaphragm (DIA), genioglossus (GG) and a neck muscle (trapezius) in unanesthetized, decerebrated, spontaneously breathing cats with and without mPRF carbachol injections. The ethimoidal nerve was electrically stimulated to evoke sneezing, and the superior laryngeal nerve to evoke the laryngeal reflex, swallowing, and coughing. Carbachol reduced the amplitudes of the spontaneous electromyographic activities in the neck, TA, PCA, GG, and DIA to 7%, 30%, 54%, 45% and 71% of control, respectively, reduced the respiratory rate to 53% without changes in expiratory CO(2) concentration; the magnitude of the laryngeal reflex in the TA muscle to 56%; increased its latency by 13%; and reduced the probability of stimulus-induced sneezing, swallowing, and coughing to less than 40%. These changes lasted more than 1h. These data demonstrate that important upper airway reflexes are suppressed by increasing cholinergic neurotransmission in the mPRF. Because acetylcholine release in the mPRF changes in accordance with sleep-wake cycles, the present findings are relevant to the control of upper airway reflexes during various vigilance states.

Anastomosis of the tracheal ends requires sufficient mobilization of the trachea because excessive tension is the principal cause of anastomotic insufficiency. Several mobilization and release techniques can be used to reduce some of the anastomotic tension of the trachea. Of these, Montgomery's suprahyoid release technique is a surgical method that severs three muscles above the hyoid bone: the mylohyoid, geniohyoid, and genioglossus. Of these, we present the suprahyoid release technique here because we believe that it is superior to the other mobilization techniques, particularly supralaryngeal release. This is the first report to approach this subject from both anatomical and functional perspectives. In summary, we performed a tracheoplasty requiring a suprahyoid release for a 55-year-old female with adenoid cystic carcinoma as an oncologic emergency. We should master the supralaryngeal release, particularly wide resection of the trachea, because this technique provides sufficient mobilization, with no dysphagia or complications.

Objective This study was designed to investigate the effects of genistein on genioglossal muscle function and the expression of oestrogen receptors (ERs) in the ovariectomized rats. Design Fifty female Sprague-Dawley rats were randomly divided into 5 groups: the control group (SHAM), the ovariectomized group (OVX), the ovariectomized rats receiving low genistein dosage (OVX+L), the moderate genistein dosage group (OVX+M) and the high genistein dosage group (OVX+H). Oestradiol level was detected by radioimmunity. The isometric twitch tension ( P t ) and tetanic tension ( P 0 ) of the GG muscle were measured in response to electrical field stimulation. The expression of ERs on the mRNA and protein levels was measured by real-time PCR and western blot respectively. Results Ovariectomy decreased muscle fatigue resistance and the expression of different ERs significantly. Genistein treatment resulted in a dose-dependent protective effect on muscle fatigability and a parallel dose-responsive increase in the expression of oestrogen receptors mRNA and protein levels in genioglossus, with larger effects on oestrogen receptor beta vs. alpha. In contrast to the improvements in fatigability, there was no treatment effect on isometric twitch or tetanic tensions. Conclusion The results indicated that genistein increased muscle fatigue resistance in addition to effects on receptors, and the up-regulation of receptors expression may be a possible mechanism by which genistein improved fatigue.

Mandibular advancement in conjunction with genial tubercle advancement has gained the attention of surgeons involved in the treatment of obstructive sleep apnea syndrome. 1 The principle behind this technique involves the fact that mandibular advancement along with genial tubercle advancement pulls the geniohyoid and genioglossus muscles forward, causing a forward movement of the base of the tongue and the hyoid bone. This shift enlarges the posterior airway space and avoids the collapse of its walls during the rapid eye movement phase of sleep. 2 The genioglossus muscle originates from the superior mental spine or genial tubercles and then fans posteriorly to insert at the tip of the tongue, at the dorsum of the tongue, and into the body of the hyoid bone. The superior fibers retract the tip of the tongue, whereas the middle fibers depress the dorsum of the tongue. The inferior fibers advance the hyoid antero

Obstructive sleep apnea (OSA) patients have elevated tonic and phasic inspiratory activity in the genioglossus and other upper airway muscles during wakefulness; this protects their upper airway from collapse. In this group, sleep-related decrements of upper airway motor tone result in sleep-related upper airway obstructions. We previously reported that in the rat, a species widely used to study the neural mechanisms of both sleep and breathing, lingual electromyographic activity (EMG) is minimal or absent during slow-wave sleep (SWS) and then gradually increases after the onset of rapid eye movement sleep (REMS) due to the appearance of large phasic bursts. Here, we investigated whether sleep-wake patterns and respiratory modulation of lingual EMG depend on the site of EMG recording within the tongue. In nine chronically instrumented rats, we recorded from 17 sites within the tongue and from the diaphragm across sleep-wake states. We quantified lingual EMG in successive 10s intervals of continuous 2h recordings (1-3 p.m.). We found that sleep-wake patterns of lingual EMG did not differ between the base and tip of the tongue, and that respiratory modulation was extremely rare regardless of the recording site. We also determined that the often rhythmic lingual bursts during REMS do not occur with respiratory rhythmicity. This pattern differs from that in OSA subjects who, unlike rats, have collapsible upper airway, exhibit prominent respiratory modulation of upper airway motor tone during quiet wakefulness, retain considerable tonic and inspiratory phasic activity during SWS, and show nadirs of activity during REMS.

We examined the influence of pharyngeal dilator muscle activity on upper airway extraluminal tissue pressure (ETP) distribution and upper airway patency. We studied seven anaesthetised, supine, spontaneously breathing NZ white rabbits. ETP was measured via pressure transducer tipped catheters in lateral (ETP(lat)) and anterior (ETP(ant)) pharyngeal wall tissues. Airflow (V) and tracheal pressure (P) were monitored and upper airway resistance (RUA) calculated. Genioglossus (GG) or bilateral sternohyoid (SH) muscles were electrically stimulated. Tongue protrusion (TP) during GG stimulation was measured. With GG stimulation, RUA decreased to 57.8+/-10.9% (mean+/-S.E.M.) of baseline and TP increased to 4.8+/-0.5mm (both p

This study was designed to investigate the effects of oestrogen on sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity and gene expression in ovariectomised rats under the condition of chronic intermittent hypoxia (CIH). Thirty-two female Sprague-Dawley rats were randomly divided into four groups: the normal control group (NC), the CIH group (CIH), the CIH-ovariectomised group (CIH+OVX), and the group of CIH-ovariectomised rats receiving estradiol replacement (CIH+OVX+E(2)). Rats in the latter three groups were exposed to CIH for 5 weeks. The animals were killed before genioglossus (GG) was rapidly excised, and their body and uterus mass were determined. Estradiol level was detected by radioimmunoassay. SR Ca(2+)-ATPase (SERCA) activity was observed by detecting inorganic phosphorus ion, and the SERCA mRNA level was measured using real-time quantitative polymerase chain reaction (real-time PCR). It was found that, compared with the NC group, the SERCA activity and mRNA level were remarkably reduced (p

The mechanisms contributing to worsening of obstructive sleep apnea (OSA) during rapid eye movement (REM) sleep have been minimally studied. Reduced upper-airway muscle tone may be an important contributor. Because respiratory events and the associated blood gas changes can influence genioglossus (GG) activity, we compared GG activity between OSA patients and control subjects during REM sleep using continuous positive airway pressure (CPAP) to minimize the influences of upper-airway resistance (RUA) and blood gas disturbances on GG activity.Twenty subjects (10 female subjects), 12 healthy individuals, and 8 OSA patients, were studied overnight. Sleep staging, epiglottic pressure, minute ventilation, and GG electromyogram (GGEMG) were recorded. GGEMG was compared between REM sleep with (phasic REM) and without (tonic REM) eye movements, non-REM (NREM) sleep, and wakefulness.Breathing frequency increased from stable NREM, to tonic REM to phasic REM sleep, whereas tidal volume and GGEMG decreased (ie, peak GGEMG: 3.0 +/- 0.7 vs 1.7 +/- 0.4 vs 1.2 +/- 0.3% max, respectively; p0.001). Reductions in GGEMG during REM sleep were not different between OSA patients and control subjects or between genders.When RUA and blood gas disturbances are minimized by CPAP, genioglossal activity is reduced in a stepwise manner from stable NREM, to tonic REM to phasic REM sleep to a similar extent in OSA and healthy individuals of both genders. Thus, an inherent abnormality in GG neural control in OSA patients during REM sleep is unlikely to explain the increased upper-airway collapse in this sleep stage. Rather, a generalized reduction in GG activity during REM likely renders individuals who are highly reliant on upper-airway dilator muscles vulnerable to pharyngeal collapse during REM sleep.

UNLABELLED Episodic hypoxia (EH) is followed by increased ventilatory motor output in the recovery period indicative of long-term facilitation (LTF). We hypothesized that episodic hypoxia evokes LTF of genioglossus (GG) muscle activity in humans during non-rapid eye movement sleep (NREM) sleep. We studied 12 normal non-flow limited humans during stable NREM sleep. We induced 10 brief (3 min) episodes of isocapnic hypoxia followed by 5 min of room air. Measurements were obtained during control, hypoxia, and at 5, 10, 20, 30 and 40 min of recovery, respectively, for minute ventilation (V(I)), supraglottic pressure (P(SG)), upper airway resistance (R(UA)) and phasic GG electromyogram (EMG(GG)). In addition, sham studies were conducted on room air. During hypoxia there was a significant increase in phasic EMG(GG) (202.7+/-24.1% of control, p

The motor control of the respiratory muscles differs in some ways from that of the limb muscles. Effectively, the respiratory muscles are controlled by at least two descending pathways: from the medulla during normal quiet breathing and from the motor cortex during behavioural or voluntary breathing. Neurophysiological studies of single motor unit activity in human subjects during normal and voluntary breathing indicate that the neural drive is not uniform to all muscles. The distribution of neural drive depends on a principle of neuromechanical matching. Those motoneurones that innervate intercostal muscles with greater mechanical advantage are active earlier in the breath and to a greater extent. Inspiratory drive is also distributed differently across different inspiratory muscles, possibly also according to their mechanical effectiveness in developing airway negative pressure. Genioglossus, a muscle of the upper airway, receives various types of neural drive (inspiratory, expiratory and tonic) distributed differentially across the hypoglossal motoneurone pool. The integration of the different inputs results in the overall activity in the muscle to keep the upper airway patent throughout respiration. Integration of respiratory and non-respiratory postural drive can be demonstrated in respiratory muscles, and respiratory drive can even be observed in limb muscles under certain circumstances. Recordings of motor unit activity from the human diaphragm during voluntary respiratory tasks have shown that depending on the task there can be large changes in recruitment threshold and recruitment order of motor units. This suggests that descending drive across the phrenic motoneurone pool is not necessarily consistent. Understanding the integration and distribution of drive to respiratory muscles in automatic breathing and voluntary tasks may have implications for limb motor control.

Activation of the genioglossus (GG) muscles is necessary to maintain the patency of the upper airway. In the condition of obstructive sleep apnea (OSA) this mechanism fails and the possible role of fatigue in its pathogenesis is still not fully understood. In this paper, a new electrode design for recording the genioglossus surface electromyogram (sEMG) is presented. The new design differs from a widely used GG surface electrode in both electrode configuration (unilateral rather than bilateral) and electrode material (Ag-AgCl rather than stainless steel (SS)). The separate effects of these factors were evaluated during force-varying and fatiguing contractions on normal human subjects and using GG sEMG model simulations. Unilateral sEMG was found to have lower amplitude, lower frequency content and a different rate of change of median frequency during fatiguing contractions. It was shown to overcome several disadvantages posed by the bilateral configuration and be more selective. Ag-AgCl has more favorable impedance characteristics and resulted in greater signal amplitudes. It was concluded that the new design is more suitable for detecting GG sEMG and allows more reliable interpretation of changes in sEMG due to physiological mechanisms, thus providing a new methodology for studying GG function and the role of fatigue in OSA.

We assessed upper airway responses to acute and chronic inspiratory loading. In Experiment I, 11 healthy subjects underwent T2-weighted magnetic resonance imaging (MRI) of upper airway dilator muscles (genioglossus and geniohyoid) before and up to 10 min after a single bout of pressure threshold inspiratory muscle training (IMT) at 60% maximal inspiratory mouth pressure (MIP). T2 values for genioglossus and geniohyoid were increased versus control (p < 0.001), suggesting that these airway dilator muscles are activated in response to acute IMT. In Experiment II, nine subjects underwent 2D-Flash sequence MRI of the upper airway during quiet breathing and while performing single inspirations against resistive loads (10%, 30% and 50% MIP); this procedure was repeated after 6 weeks of IMT. Lateral narrowing of the upper airway occurred at all loads, whilst anteroposterior narrowing occurred at the level of the laryngopharynx at loads ≥30% MIP. Changes in upper airway morphology and narrowing after IMT were undetectable using MRI. © 2007 Elsevier B.V. All rights reserved.

PubMedID: 17350586 The performance of tongue muscles in various feeding behaviours is not well defined. This study was undertaken to examine the role of the intrinsic and extrinsic tongue muscles during natural drinking, food ingestion and chewing. Ten 12-week-old Yucatan miniature pigs (5 in each gender) were used. Under anesthesia, fine-wire electrodes were inserted into three intrinsic (verticalis and transversus [V/T]; superior and inferior longitudinalis [SL and IL]) and two extrinsic (genioglossus [GG] and styloglossus [SG]) tongue muscles and two jaw muscles (masseter [MA] and anterior digastricus [DI]). Electromyogram (EMG) and jaw movement were recorded and synchronized when pigs were drinking water, ingesting and chewing food freely. Chewing frequency (CF), onset of activation, burst duration and integrated activity (IEMG) were assessed quantitatively, and EMG activities during drinking and ingestion were examined qualitatively. Results indicate that during chewing, the V/T and GG had one phase of activity starting at early jaw opening, and the V/T activity lasted through late of jaw closing. The SL, IL and SG had double phases with the first starting at jaw opening and the second at late jaw closing phases. The three intrinsic tongue muscles and the SG were active during 35-48% of the chewing cycle. IEMG values of the SL, IL and SG of both sides were significantly greater compared to the other muscles (p < 0.05-0.01). Both the SL and the IL showed significantly higher activities in the contralateral than ipsilateral sides (p < 0.05). The timing sequences of both extrinsic and intrinsic muscles were similar between ingestion and chewing, but amplitudes of the GG and IL were greatly enhanced and those of the MA and SL were reduced during ingestion. The simultaneous activation of the MA, GG and V/T were seen during drinking, along with major activity in the GG and V/T. These results suggested that the majority of activity in the intrinsic and extrinsic tongue muscles occurred during jaw opening and the occlusal phases of chewing. The activity of the GG and IL played a major role during ingestion, whereas simultaneous activation of jaw, extrinsic and intrinsic tongue muscles and major activity in the GG and V/T occurred during drinking. © 2007 Elsevier Ltd. All rights reserved. National Institute of Dental and Craniofacial Research The authors would like to thank Dr. Sue Herring for her invaluable advice and critical comments, Dr. Katherine Rafferty for her comments, help with experiments and English editing, and Ms. Xian-Qin Bai for her general lab assistance. Thanks also go to two anonymous reviewers and the Associate Editor for their constructive comments and suggestions on earlier versions of the manuscript. This study was supported by the grant R01DE15659 from NIDCR to Dr. Liu.

Functions of the extrinsic tongue muscles in vowel production were examined by measurements of muscle length and tongue tissue deformation using MRI (magnetic resonance imaging). Results from the analysis of Japanese vowel data suggested: (1) Contraction and relaxation of the three subdivisions of the genioglossus (GG) play a dominant role in forming tongue shapes for vowels. (2) The extra-lingual part of the styloglossus (SG), which was previously thought to cause a high-back tongue position by pulling its insertion point in the tongue, was found to be nearly constant across all vowels both in length and orientation. (3) The tongue shape for back vowels is mainly achieved by internal deformation of the tongue tissue, and the medial tissue of the tongue showed lateral expansion in front vowels, and medial compression in back vowels.

Background Upper airway (UA) patency during inspiration is determined by the balance between dilating forces generated by UA dilator muscle activity and collapsing forces related to the decreased intraluminal pressure that accompanies flow generated by inspiratory muscle activity. It is possible that the relative strengths of UA dilator and inspiratory pump muscles could be an important determinant of the susceptibility to UA collapse during sleep ( ie , obstructive sleep apnea [OSA]). Methods Measurements of tongue protrusion (TP) force and maximum inspiratory pressure (P i max) were obtained in 94 patients admitted for overnight polysomnography for suspected OSA, quantified by apnea-hypopnea index (AHI). Results There was a direct linear relationship between TP force and P i max ( r 2 = 0.37, p i max (greater than group 90th percentile, 0.027 kg/cm H 2 O) appeared to protect against OSA, as moderate-to-severe OSA (AHI > 20/h) was not observed in any individual with a ratio above this threshold. AHI was not linearly related to TP force, P i max, or the ratio of TP force to P i max. Conclusions UA muscle strength is linearly related to inspiratory pump muscle strength. The ratio of UA muscle strength (TP force) and inspiratory pump muscle strength (P i max) was not different between individuals with and without OSA; however, a high wakeful ratio of TP force to P i max appears to be associated with a reduced propensity to moderate-to-severe OSA.

Needle electromyography (EMG) and determining the motor evoked potential (MEP) of the genioglossus (tongue) are difficult to perform in evaluation of the craniobulbar region in patients with amyotrophic lateral sclerosis (ALS). Needle EMG and MEP determination in the upper trapezius were carried out in 17 consecutive ALS patients. The needle EMG parameters recorded included abnormal spontaneous activity and motor unit action potential morphology. An upper motor neuron lesion was presumed when either response to cortical stimulation was absent, or the central conduction time was delayed (>mean + 2 SD). Of the 12 patients with limb-onset ALS, using needle EMG, 11 were found to have abnormalities in the upper trapezius, and only five in the tongue. Three of the six patients with isolated limb involvement had abnormal MEP findings. In conclusion, electrophysiological studies of the upper trapezius are useful in ALS patients without bulbar symptoms.

Brainstem respiratory neurons innervate the hypoglossal motor nucleus which in turn transmits this respiratory drive signal to the genioglossus muscle of the tongue. The mechanism of this transmission is important to help maintain an open airspace for effective breathing, and is thought to rely almost exclusively on non-N-methyl-d-aspartate (non-NMDA) glutamate receptor activation during respiration. However those studies were performed in slices of medulla from neonatal animals in vitro which may have led to an underestimation of the contribution of NMDA glutamate receptors that may normally operate in intact preparations. The current study tests the hypothesis that both NMDA and non-NMDA receptors contribute to respiratory drive transmission at the hypoglossal motor nucleus in vivo. Experiments were performed in urethane-anesthetized and tracheotomized adult Wistar rats in which vagus nerves were either intact or sectioned. In the presence of augmented genioglossus activity produced by vagotomy, microdialysis perfusion of either an NMDA receptor antagonist (D-2-amino-5-phosphonovaleric acid, 0.001-10 mM) or a non-NMDA receptor antagonist (6-cyano-7-nitroquinoxaline-2, 3-dione disodium salt, 0.001-1 mM) to the hypoglossal motor nucleus reduced respiratory-related genioglossus activity in a dose-dependent manner (P < 0.001) indicating that both NMDA and non-NMDA glutamate receptors are necessary for transmission of the respiratory drive signal to genioglossus muscle in vivo. Similar effects were observed in the vagus nerve intact rats. Further experiments demonstrated that each delivered antagonist had effects that were specific to its respective receptor. Regression analysis also revealed that the activity of both NMDA and non-NMDA receptors at the hypoglossal motor nucleus is related to levels of the prevailing respiratory drive. These results show that both NMDA and non-NMDA glutamate receptors at the hypoglossal motor nucleus are involved in transmission of the respiratory drive signal to genioglossus muscle in vivo.

Postural tone is reduced during slow-wave sleep (SWS) and absent during rapid eye movement sleep (REMS). In obstructive sleep apnea subjects, upper airway dilating muscles, including those of the tongue, show a similar pattern; this contributes to sleep-related airway obstructions. However, in healthy subjects, state-dependent changes in the activity of pharyngeal muscles are variable. In seven chronically instrumented Sprague-Dawley rats, an animal model used to study sleep and sleep-disordered breathing, we quantified lingual and postural muscle activity across the sleep-wake states by measuring the root mean square levels of the electromyograms (EMG) in successive 10s intervals collected during 2h of recording at a constant circadian time (1-3p.m.). The nuchal EMG was low and steady during SWS and further reduced with occasional twitches during REMS. In contrast, the mean lingual EMG during SWS was only 5.9+/-1.6% (S.E.) of its mean in wakefulness, and during REMS, it increased to 46+/-15% (S.E.) (p

To provide direct evidence for substantia nigra pars reticulata (SNr) control of oro-facio-lingual muscle activity, high-frequency electrical microstimulation (mainly trains of 20, 333-Hz cathodal pulses at 40-60 microA) and GABA microinjection (1-5 microl of 10 mM GABA in saline) were carried out using a three-barreled microelectrode at the same SNr site in lightly anesthetized, chronically decorticated rats (n=39). Decortication eliminated the possibility that SNr microstimulation might activate corticofugal fibers descending in the adjoining cerebral peduncle. When the most ventral layer of the SNr was approached, high-amplitude electromyographic (EMG) activity of up to 6 mV with a distinctive waveform appeared synchronously with electrical stimuli in the anterior digastric, masseter, genioglossus, and levator labii superioris muscles. This EMG activity was evoked bilaterally, with an ipsilateral predominance. Eye movements, mostly rotation of the eyeball vertically down in the orbit, were noted. Infrequent blinking was also noted. Histologic examination localized the effector site to the middle third of the mediolateral extent of the caudal SNr corresponding to between 5.8 mm (level of the oculomotor nerve) and 6.5mm (caudal end of the SNr) caudal to bregma; and to the ventralmost peripeduncular region of the SNr corresponding to 7.7 mm to 8.0 mm beneath the cortical surface. We referred to this site as the substantia nigra pars reticulata oro-facio-lingual (SNr-ofl) region. GABA injection produced tonic EMG discharge with consistent amplitude in all of the four muscles studied. The GABA effect was negated by a preceding microinjection of the GABA-A receptor antagonist bicuculline, whereas saline control injection had no effect. Changes in amplitude of evoked EMG activity according to location of the stimulating microelectrode reflected somatotopic organization of the SNr-ofl region. This extremely localized electrical and receptor microstimulation in the SNr produced synchronized powerful contraction of jaw, tongue, and facial muscles with different neural innervation. These findings advance our understanding of the mechanisms of the SNr concerning oro-facio-lingual movements.

The effects of physical characteristics of foods on the coordination of extrinsic tongue muscle activities during natural mastication were evaluated. Electromyograms of tongue-retractor (styloglossus, SG) and tongue-protractor (genioglossus, GG) muscles as well as the jaw-movement trajectories were recorded during raw rice and chow pellet chewing in the freely moving rabbit. Each masticatory cycle included a jaw closing (Cl) phase consisting of a fast-closing (FC) and a slow-closing (SC) phase, and a jaw opening (Op) phase. The duration of the Cl and SC phases was found to be much larger while the duration of the FC phase was much smaller during rice chewing than pellet chewing. The jaw movements during rice chewing had smaller amplitudes of the gape and lateral excursion of the jaw as compared with those during pellet chewing. The SG muscle had a double-peaked burst activity in each masticatory cycle with one peak during the Op phase (the SG1 burst) and the other during the Cl phase (the SG2 burst). They were significantly larger during pellet chewing as compared with rice chewing, but the duration of the SG2 burst was significantly longer during rice chewing than pellet chewing. The offset of the SG2 burst was delayed during rice chewing as compared with that during pellet chewing. There was little difference in the activity pattern of the GG burst between the foods. Our present results suggest that the SG muscle activity could be modified by the sensory feedback possibly to adapt to environmental demands during chewing.

Serotonin (5-HT) from medullary raphe neurons excites hypoglossal motoneurons innervating genioglossus (GG) muscle. Since some raphe neurons also show increased activity in hypercapnia, we tested the hypothesis that serotonergic mechanisms at the hypoglossal motor nucleus (HMN) modulate GG activity and responses to CO2. Seventeen urethane-anesthetized, tracheotomized and vagotomized rats were studied. Microdialysis probes were used to deliver mianserin (5-HT receptor antagonist, 0 and 0.1 mM) or 5-HT (eight doses, 0-50 mM) to the HMN during room air or CO2-stimulated breathing. Mianserin decreased respiratory-related GG activity during room air and CO2-stimulated breathing (P

The present study was undertaken to determine the effects of intravenous L-5 hydroxytryptophan (5HTP), the immediate precursor of serotonin, on the electromyographic (EMG) activity of the genioglossus (gEMG) and diaphragm (dEMG) in the spontaneously breathing, vagotomized anesthetized male Sprague-Dawley rats (urethane 1.2-1.4 g/kg). Sequential administration of saline and 0.05-, 0.1-, 0.2-, 1-, and 5-mg/kg doses of 5HTP were given intravenously every 15 min. There was a significant increase (percent change from predrug) in both gEMG and dEMG amplitude at 1.0 and 5.0 mg/kg of 5HTP compared to saline. The percent increase in gEMG induced by 1.0 and 5.0 mg/kg 5HTP however was significantly greater than the increase in dEMG. There was no significant change in heart rate (HR), mean arterial blood pressure (MAP), or respiratory rate at any of the doses of 5HTP tested. These results suggest that intravenous 5HTP at doses of 1 and 5 mg/kg preferentially increased the gEMG in the anesthetized rat compared to the dEMG. We hypothesize that at appropriate doses serotonin precursors could increase genioglossus activity in humans during sleep and help maintain upper-airway patency.

Hypoglossal motoneurons (HMNs), which innervate the tongue muscles, are involved in several important physiological functions, including the maintenance of upper airway patency. The neural mechanisms that affect HMN excitability are therefore important determinants of effective breathing. Obstructive sleep apnea is a disorder characterized by recurrent collapse of the upper airway that is likely due to decline of pharyngeal motoneuron activity during sleep. Because cholinergic neuronal activity is closely coupled to wake and sleep states, we tested the effects and pharmacology of nicotinic acetylcholine receptor (nAChR) activation on HMNs. We made intracellular recordings from HMNs in medullary slices from neonatal rats and found that local application of the nicotinic agonist, 1,1-dimethyl-4-phenylpiperazinium iodide, excited HMNs by a Ca(2+)-sensitive, and TTX-insensitive inward current that was blocked by dihydro-beta-erythroidine (IC(50): 19+/-3 nM), methyllycaconitine (IC(50): 32+/-7 nM), and mecamylamine (IC(50): 88+/-11 nM), but not by alpha-bungarotoxin (10 nM). This is consistent with responses being mediated by postsynaptic nAChRs that do not contain the alpha7 subunit. These results suggest that nAChR activation may contribute to central maintenance of upper airway patency and that the decline in firing rate of cholinergic neurons during sleep could potentially disfacilitate airway dilator muscle activity, contributing to airway obstruction.