Three-Dimensional Architecture of the Mouse Tongue Muscles Using Micro-CT with a Focus on the Transverse, Vertical, and Genioglossus Muscles

Background: The suitability of micro-computed tomography (CT) for soft tissue applications has been well documented. Although the application of micro-CT to the three dimensional (3D) structure of the tongue muscle has been reported, a 3D rendering and/or a schematic view of the tongue muscle has yet to be published. Material and Method: First, muse tongues were fixed and decalcified, and then the vertical muscle (Ve), the transverse muscle (Tr), and/or the genioglossus muscle of the mouse tongue (Ge) were analyzed using micro-CT and are shown in this report in rendered images and pattern diagrams. Results: 1) The Tr is classified into three parts: the first part extends from the middle to the apical part of the tongue;the second part is strongly connected to the superior longitudinal muscles of the tongue (Lo);the third part fans out from the middle to the root of the tongue. 2) The Ve is classified into two main groups: the first group joins the dorsal and the lateral parts of the tongue;the second group joins the dorsal part and the floor of the tongue. 3) Ge is classified into four parts: three parts comprise the Ge apical and middle parts of the tongue, with one part in the inferior longitudinal muscles of the tongue, one joining the lingual septum of the tongue (LS), and the other joining the sub-surface of the dorsal part of the Lo. The remaining Ge exits in a fan-like manner through the root of the tongue and then joins the Tr.

Changes in genioglossus and their association with serum adiponectin levels in rats subjected to chronic intermittent hypoxia

Background The genioglossus （GG） is involved in the maintenance of an open airway for effective breathing.Although the pathogenesis of obstructive sleep apnea hypopnea syndrome （OSAHS） was closely associated with GG dysfunction,its causes and possible treatment have not been elucidated.The aim of the study was to investigate the effects of chronic intermittent hypoxia （CIH） on serum adiponectin levels, electromyograph （EMG） activity and ultrastructure of GG, as well as the effect of an adiponectin supplement in anesthetized rats.Methods Forty-two healthy male Wistar rats were randomly divided into normal control （A）, CIH （B） and adiponectin treatment （C） groups, 14 rats in each group.CIH was performed eight hours per day for five weeks in both groups B and C.Group C received transvenous injection of adiponectin at the dosage of 10 μg per injection, twice a week for five weeks.At the end of the 5th week the GG EMG voltage was measured and compared among the three groups.Transmission electron microscope was used to observe the ultrastructure of the GG.Results CIH caused significant hypoadiponectinemia, weakened activity of GG EMG at both baseline and hypoxia stimulation, and induced ultrastructural pathological changes, such as, myofibril discontinuities, lysis of myofilament,edema of mitochondria and disruption of cristae, vacuolus and lysis of some mitochondria.Venous supplement of adiponectin improved the above pathological changes resulting from CIH.Conclusion CIH resulted in pathological changes in GG＇s EMG and ultrastructure, which could be improved by supplement of adiponectin and be associated with hypoadiponectinemia caused by ClH.

Effects of 5-hydroxytryptamine and 5-hydroxytryptamine 2A/2C agonist on the genioglossus activity and sleep apnea in rats

Background 5-hydroxytryptamine （5-HT） is a common neurotransmitter in the brain which plays an important role in the pathogenesis of sleep apnea.Dysfunction of 5-HT and 5-HT2 receptors may lead to the collapse of the upper airway and the instability of respiratory control, which in turn produce apnea.Genioglossus （GG） is one of the most important oropharyngeal muscles maintaining the upper airway open.The present study aimed to investigate the effects of 5-HT and 5-HT2 receptor on GG activity and the sleep apnea in Sprague-Dawley （SD） rats.Methods Microinjection probes were placed within the fourth ventricle of sixteen SD rats.After recovery for a week, the electromyogram （EMG） of GG was recorded in the anesthetized and vagotomized rats.The changes of GG activity before and after the microinjection of 5-HT or 5-HT2A/2c agonist -2,5-dimethoxy-4-iodoamphetamine hydrochloride （DOI）were observed.Probes were also laid in another eight SD rats.Electroencephalogram （EEG）, EMG of neck muscle and respiration were recorded at the same time a week later.The effects of DOI on the occurrence of sleep apnea were explored.Results Both 5-HT and DOI significantly enhanced the activity of GG just 3 minutes after the completion of injection.The effect of 5-HT disappeared quickly and the effect of DOI lasted for more than 27 minutes.DOI also significantly decreased the post-sigh apnea index in non-rapid-eye-movement （NREM） and rapid-eye-movement （REM） sleep and decreased the spontaneous apnea index only in NREM sleep （P 〈0.05, respectively）.Conclusion 5-HT and 5-HT2A/2c system correlated closely with the pathogenesis of the sleep apnea syndrome and 5-HT receptors may become the target of the drug treatment.

Adiponectin protects the genioglossus of rats against chronic intermittent hypoxia-induced injury via inhibition of endoplasmic reticulum stress

Background Obstructive sleep apnea hypopnea syndrome, characterized by chronic intermittent hypoxia （CIH）, is closely correlated with genioglossus dysfunction. CIH has been identified to mediate mitochondrial damage in genioglossus. It has been reported that endoplasmic reticulum stress （ERS） could be induced by mitochondrial dysfunction. This study aimed to investigate the role of ERS in CIH-induced genioglossus injury, as well as the possible intervention effect of adiponectin （Ad） supplement in rats. Methods Forty-five male Wistar rats were randomly divided into three groups and submitted to room air （group A, n=15） as a control or CIH （groups B and C, n=15, respectively）. Throughout the exposure period, intravenous Ad was given in group C; while intravenous normal saline was simultaneously given in groups A and B. After 35-day exposure, genioglossus samples were obtained from the pentobarbital-anaesthetized rats via surgical dissection, following blood sampling. Western blotting was applied to detect expressions of ERS signals and associated apoptotic pathways in genioglossus. Serum adiponectin levels were assessed via enzyme-linked immunosorbent assay （ELISA）. Results Significant hypoadiponectinemia was revealed in group B only （P 〈0.05）. Compared to those in groups A and C, expressions of markers involved in ERS, such as glucose regulated protein 78 （GRP78）, p-PERK, phosphorylated eukaryotic initiation factor 2α （p-elF2α）, phosphorylated inositol-requiring transmembrane kinase/endoribonuclease 1α （p-IRE1α）, spliced X-Box binding protein 1 （XBPls） and activating transcription factor 6 （ATF6）, were significantly enhanced in group B （all P 〈0.01）; while no significant difference was shown between groups A and C （all P 〉0.05）. ERS- associated apoptotic pathways were remarkably activated in group B. The involved markers detected as the expression of CCAAT/enhancer binding protein homologous protein （CHOP）, B-cell lymphoma/leukemia associatied X protein （BAX） and caspase-12 were significantly elevated （all P 〈0.01）. Transvenous adiponectin supplement improved the above CIH- induced pathological changes in group C. Conclusion Beyond hypoadiponectinemia, CIH could enhance ERS and induce activation of ERS-associated apoptotic pathways in genioglossus, which could be significantly improved by adiponectin supplement.

Adiponectin alleviates contractile dysfunction of genioglossus in rats exposed to chronic intermittent hypoxia

Background Genioglossal dysfuntion takes an important role in pathogenesis of obstructive sleep apnea hypopnea syndrome （OSAHS） in which chronic intermittent hypoxia （CIH） is the major pathological origin. Recent studies have suggested genioglossal injury induced by CIH might be improved by adiponectin. The aim of this study was to investigate the effects of adiponectin on genioglossus contractile properties in rats exposed to CIH. Methods Thirty-nine healthy male Wistar rats were randomly divided into three groups： normal control （NC）, CIH and adiponectin supplement （CIH＋Ad） with 13 rats in each. Rats in NC were kept breathing normal air, while rats in CIH and CIH＋Ad experienced the same CIH environment eight hours per day for 35 successive days. Rats in CIH＋Ad were given intravenous adiponectin of 10 IJg twice a week for 30 successive days. Rats in the NC and CIH were injected with normal saline as a control. After 35 days＇ CIH exposure, the levels of serum adiponectin and genioglossus contractile properties were compared. Results Serum adiponectin level was significantly lower in CIH than in NC （1210 ng/ml vs. 2236 ng/ml）. Serum adiponectin level in CIH＋Ad （1844 ng/ml） was significantly higher than CIH but lower than NC. Twitch tension, time to peak tension, half relaxation time and tetanic tension were significantly lower in CIH than NC and improved in CIH＋Ad. All mean tetanic fatigue indices decreased more rapidly in the first 20 seconds than during the subsequent 100 seconds. Tetanic fatigue indices in NC and CIH＋Ad were significantly higher compared to CIH. Conclusions CIH could lead to hypoadiponectinaemia, impaired genioglossus contractile properties and decreased fatigue resistance in rats. Such changes could be partially offset by supplementation of adiponectin.

A Transcriptomic Analysis of Physiological Significance of Hypoxia-inducible Factor-1α in Myogenesis and Carbohydrate Metabolism of Genioglossus in Mice

Background： Chronic intermittent hypoxia is the most remarkable feature of obstructive sleep apnea/hypopnea syndrome and it can induce the change of hypoxia-inducible factor-1α （H IF-1α） expression and contractile properties in the genioglossus. To clarify the role of HIF-lot in contractile properties of the genioglossus, this study generated and compared high-throughput RNA-sequencing data from genioglossus between HIF-1α conditional knockout （KO） mice and littermate wild-type （WT） mice. Methods： KO mice were generated with cre-loxP strategy. Gene expression profile analysis was performed using gene enrichment analysis. Gene ontology （GO） and Kyoto Encyclopedia of Genes and Genomes （KEGG） pathway analyses of differently expressed messenger RNAs were performed to identify the related pathways and biological lhnctions. Six differentially expressed genes （DEGs） were validated by qualitative reverse transcription polymerase chain reaction. Results： A total of 142 （77 upregulated and 65 downregulated） transcripts were found to exhibit statistically significant difference between the HIF-la-KO and WT mice. GO and KEGG analyses indicated that DEGs included genes involved in ＂skeletal muscle cell differentiation,＂ ＂muscle organ development,＂ ＂glucose metabolic process,＂ ＂glycogen biosynthetic and metabolic process,＂ etc. Conclusion： This study might provide evidence that H IF-lot affects the expression of multiple genes involved in the myogenesis, muscle developrnent, and carbohydrate metabolism through transcriptome analysis in conditional HIE-1α-KO mice.

Blockage of the habenular nucleus can eliminate dyspnea induced by electrostimulation of the insular cortex

BACKGROUND： The insular cortex and habenular nucleus may be a regulatory center for obstructive sleep apnea syndrome, and dyspnea may be caused by insular cortex activity. The insular cortex is a cortical representation of obstructive sleep apnea syndrome. The habenular nucleus is a station for descending insular cortex activity. OBJECTIVE： Through actively stimulating the rat insular cortex, to observe rat respiratory movement, myoelectric activities of genioglossus, arterial partial pressure of oxygen, partial pressure of carbon dioxide and acidity-alkalinity, and to verify a hypothesis that the insular cortex is a superior-position regulation center, and the habenular nucleus is an inferior-position nervous nuclei of the insular cortex in patients with obstructive sleep apnea syndrome. DESIGN, TIME AND SETTING： The randomized, controlled animal study was performed at the Laboratory of Electrophysiology, Department of Physiology, Norman Bathune College of Medicine, Jilin University, China from September 2004 to June 2008. MATERIALS： We used L-glutamic acid （Dingguo Biological Product Research Center, Beijing, China）, lidocaine hydrochloride （Seventh Pharmacy Co., Ltd., Wuxi, China）, electric stimulator （Nihon Kohden, Japan）, and an AVL-OPTI blood gas analyzer （AVL Scientific Co., Roswell, GA, USA）. METHODS： The insular cortex of healthy adult Wistar rats underwent electrostimulation and L-glutamic acid stimulation to record changes in the myoelectric activity of genioglossus and respiratory movement. Some rats were injected with lidocaine to block the habenular nucleus before electrostimulation or L-glutamic acid stimulation. L-glutamic acid and lidocaine were injected by microelectrodes embedded in nuclear groups. MAIN OUTCOME MEASURES： Myoelectric activities of genioglossus, arterial partial pressure of oxygen, partial pressure of carbon dioxide and acidity-alkalinity were measured following apnea in rats undergoing electrostimulation in the insular cortex and following blockade of the habenular nucleus. RESULTS： Following electrostimulation and L-glutamic acid stimulation, rats developed apnea or respiratory rhythm disorders. Simultaneously, the amplitude of myoelectric activity of the genioglossus was reduced （P 〈 0.01 ）, and the electromyogram integral was decreased （P 〈 0.01）. Arterial blood gas analysis showed arterial blood acidosis, a decrease in pH （P 〈 0.05）, and an increase in the negative value of alkaline reserve （P 〈 0.01）. Lidocaine in the habenular nuclear blocked respiratory and other index changes after insular cortex stimulation. CONCLUSION： Dyspnea induced by stimulating the insular cortex may require the habenular nucleus. Paralysis of the habenular nucleus can completely eliminate insular cortex stimulation-induced dyspnea.

5-hydroxytryptamine-mediated apnea caused by the habenular nucleus

5-hydroxytryptamine contributes to the control of activities of the dilator muscle in the upper respiratory tract, and is derived from the raphe nuclei, in which the habenular nucleus exerts a sustaJned inhibitory effect. In the present study, respiratory motion curve of the genJoglossus muscle and peripheral 5-hydroxytryptamine changes were observed following L-glutamate stimulation of the habenular nucleus of adult Wistar rats. Results showed that the rats had apnea and decreased plasma 5-hydroxytryptamine content after the neurons in habenular nucleus were excited. Genioglossus muscle electromyogram amplitude and integral were significantly reduced. The genioglossus myoelectric activity and respiratory motion curve were similar to obstructive sleep apnea syndrome, thus confirming that the habenular nucleus is the key nucleus involved in the pathogenesis of obstructive sleep apnea syndrome, and is the primary regulated center in the raphe nuclei. Stimulation of the habenular nucleus may suppress 5-hydroxytryptamine release and result in apnea, which is similar to obstructive sleep apnea syndrome.