Muscle Type Research Articles

Natural Extracts Mitigate the Deleterious Effects of Prolonged Intense Physical Exercise on the Cardiovascular and Muscular Systems.

Muscle fatigue is a common symptom induced by exercise. A reversible loss of muscle force is observed with variable rates of recovery depending on the causes or underlying mechanisms. It can not only affect locomotion muscles, but can also affect the heart, in particular after intense prolonged exercise such as marathons and ultra-triathlons. The goal of our study was to explore the effect of four different natural extracts with recognized antioxidant properties on the contractile function of skeletal (locomotion) and cardiac muscles after a prolonged exhausting exercise. Male Wistar rats performed a bout of exhausting exercise on a treadmill for about 2.5 h and were compared to sedentary animals. Some rats received oral treatment of a natural extract (rosemary, buckwheat, Powergrape®, or rapeseed) or the placebo 24 h and 1 h before exercise. Experiments were performed 30 min after the race and after 7 days of recovery. All natural extracts had protective effects both in cardiac and skeletal muscles. The extent of protection was different depending on muscle type and the duration post-exercise (just after and after one-week recovery), including antiarrhythmic effect and anti-diastolic dysfunction for the heart, and faster recovery of contractility for the skeletal muscles. Moreover, the muscular protective effect varied between natural extracts. Our study shows that an acute antioxidant supplementation can protect against acute abnormal endogenous ROS toxicity, induced here by prolonged exhausting exercise.

Continuous muscle, glial, epithelial, neuronal, and hemocyte cell lines for Drosophila research.

Expression of activated Ras, RasV12, provides Drosophila cultured cells with a proliferation and survival advantage that simplifies the generation of continuous cell lines. Here we used lineage restricted RasV12 expression to generate continuous cell lines of muscle, glial, and epithelial cell type. Additionally, cell lines with neuronal and hemocyte characteristics were isolated by cloning from cell cultures established with broad RasV12 expression. Differentiation with the hormone ecdysone caused maturation of cells from mesoderm lines into active muscle tissue and enhanced dendritic features in neuronal-like lines. Transcriptome analysis showed expression of key cell-type specific genes and the expected alignment with single cell sequencing and in situ data. Overall, the technique has produced in vitro cell models with characteristics of glia, epithelium, muscle, nerve, and hemocyte. The cells and associated data are available from the Drosophila Genomic Resource Center.

Bioinspired design of stimuli-responsive artificial muscles with multiple actuation modes

Artificial muscles that can reproduce the functions and biomimetic motions of natural muscles are widely used to construct soft robots with applications in various fields. However, it is still challenging to develop stimuli-responsive artificial muscles with multiple-mode actuation. Inspired by the forearm muscles, we propose a new type of stimuli-responsive artificial muscles with multiple-mode actuation using liquid crystal elastomers (LCEs), named FILAMs (forearm muscle-inspired LCE-based artificial muscles). The proposed FILAMs consist of active LCE driving units, a passive silicone rubber flexible skeleton and two quick connectors. By selectively actuating different types of LCE driving units, the FILAMs can achieve multiple-mode actuation, such as twisting, bending, combined twisting and bending. We introduce prototypical designs for the FILAMs and demonstrate that they can be used as ‘building blocks’ to reconfigure different soft robots. Three kinds of soft robots are constructed to show extensive applications through the cooperation of a combination FILAMs, i.e. a soft assembly robot, a soft crawling robot, and a soft flexible wrist.

Flavor Development of Individually Vacuum-Packaged Beef Steaks During Extended Wet Aging

The objective of the study was to determine the effect of extended aging on the flavor development of various muscles, individually stored in vacuum rollstock packaging. Strip loins, paired tenderloins, and top sirloin butts (n=48) from USDA Low Choice carcasses (Small00 to Small100 marbling score, n=16). Subprimals were wet-aged in the absence of light for 28 d postmortem before fabrication into 2.54 cm steaks representing the longissimus lumborum (LL), psoas major (PM), and gluteus medius (GM). Steaks were individually packaged in vacuum rollstock packaging and assigned to an additional aging time of 28, 35, 42, 49, or 56 d. Cut steaks (n=240/test) were designated to trained descriptive panel analysis or volatile compound analysis. No interactions occurred for trained sensory analysis, but a main effect of days of age (P≤0.033) showed the greatest effect on negatively associated attributes, including liver-like, oxidized, fishy, bitter, and sour, after 42 d of aging. A main effect of muscle type also occurred (P≤0.040) for flavor attributes, in which GM and PM samples scored higher in off-flavor attributes compared with LL samples, including flavors such as liver-like, oxidized, and sour. An interaction between muscle type and days of age occurred for 2-pentyl-furan (P=0.021). One compound—3 hydroxy-2 butanone—was affected by muscle type (P=0.009). However, most compounds were affected by days of age (P≤0.046), in which compounds related to off-flavors increased in concentrations the most after 49 d. Additionally, discriminant function analyses were performed, suggesting the most effective aging time for individual steaks to be under 49 d when considering loadings for volatile compounds and flavor attributes corresponding with days of age. Overall, these data suggest individual packaging of GM, LL, and PM muscles is most optimal for up to 42 or49 d of age without a large impact from the presence of off-flavors, thus providing food service establishments the opportunity to individually package beef steaks for an extended period while maintaining consumer satisfaction through optimal flavor.

Effects of Acupotomy on Immobilization-Induced Gastrocnemius Contracture and Fibrosis in Rats via Wnt/β-Catenin Signaling.

To determine whether acupotomy ameliorates immobilization-induced muscle contracture and fibrosis via Wnt/β-catenin signaling pathway. Thirty Wistar rats were randomly divided into 5 groups (n=6) by a random number table, including control, immobilization, passive stretching, acupotomy, and acupotomy 3 weeks (3-w) groups. The rat model of gastrocnemius contracture was established by immobilizing the right hind limb in plantar flexion for 4 weeks. Rats in the passive stretching group received passive stretching at gastrocnemius, a daily series of 10 repetitions for 30 s each at 30-s intervals for 10 consecutive days. Rats in the acupotomy and acupotomy 3-w groups received acupotomy once and combined with passive stretching at gastrocnemius a daily series of 10 repetitions for 30 s each at 30-s intervals for 10 consecutive days. Additionally, rats in the acupotomy 3-w group were allowed to walk freely for 3 weeks after 10-day therapy. After treatment, range of motion (ROM), gait analysis [i.e., paw area, stance/swing and maximum ratio of paw area to paw area duration (Max dA/dT)], gastrocnemius wet weight and the ratio of muscle wet weight to body weight (MWW/BW) were tested. Gastrocnemius morphometric and muscle fiber cross-sectional area (CSA) were assessed by hematoxylin-eosin staining. Fibrosis-related mRNA expressions (i.e., Wnt 1, β-catenin, axin-2, α-smooth muscle actin, fibronectin, and types I and III collagen) were measured using real-time quantitative polymerase chain reactions. Wnt 1, β-catenin and fibronectin concentrations were measured by enzyme-linked immunosorbent assay. Types I and III collagen in the perimysium and endomysium were analyzed using immunofluorescence. Compared with the control group, ROM, gait function, muscle weight, MWW/BW and CSA were significantly decreased in the immobilization group (all P<0.01), while protein levels of types I and III collagen, Wnt 1, β-catenin, fibronectin and mRNA levels of fibrosis-related genes were obviously increased (all P<0.01). Treatment with passive stretching or acupotomy restored ROM and gait function and increased muscle wet weight, MWW/BW and CSA (all P<0.05), while protein expression levels of Wnt 1, β-catenin, fibronectin, types I and III collagen and mRNA levels of fibrosis-related genes were remarkably declined compared with the immobilization group (all P<0.05). Compared with passive stretching group, ROM, gait function, MWW was remarkably restored (all P<0.05), and mRNA levels of fibrosis-related genes as well as protein expression levels of Wnt 1, β-catenin, fibronectin, types I and III collagen in the acupotomy group were obviously decreased (all P<0.05). Compared with the acupotomy group, ROM, paw area, Max dA/dT, and MWW were restored (all P<0.05), and mRNA levels of fibrosis-related genes along with protein levels of Wnt 1, β-catenin, fibronectin, types I and III collagen in the acupotomy 3-w group were decreased (P<0.05). Improvements in motor function, muscle contractures, and muscle fibrosis induced by acupotomy correlates with the inhibition of Wnt/β-catenin signaling pathway.

Selective inhibition of neurogenic, but not agonist-induced contractions by phospholipase A2 inhibitors points to presynaptic phospholipase A2 functions in contractile neurotransmission to human prostate smooth muscle.

Phospholipases A2 (PLA2 ) may be involved in α1 -adrenergic contraction by formation of thromboxane A2 in different smooth muscle types. However, whether this mechanism occurs with α1 -adrenergic contractions of the prostate, is still unknown. While α1 -adrenoceptor antagonists are the first line option for medical treatment of voiding symptoms in benign prostatic hyperplasia (BPH), improvements are limited, probably by nonadrenergic contractions including thromboxane A2 . Here, we examined effects of PLA2 inhibitors on contractions of human prostate tissues. Prostate tissues were obtained from radical prostatectomy. Contractions were induced by electric field stimulation (EFS) and by α1 -adrenergic agonists in an organ bath, after application of the cytosolic PLA2 inhibitors ASB14780 and AACOCF3, the secretory PLA2 inhibitor YM26734, the leukotriene receptor antagonist montelukast, or of solvent to controls. Frequency-dependent contractions of human prostate tissues induced by EFS were inhibited by 25% at 8 Hz, 38% at 16 Hz and 37% at 32 Hz by ASB14780 (1 µM), and by 32% at 16 Hz and 22% at 32 Hz by AACOCF3 (10 µM). None of both inhibitors affected contractions induced by noradrenaline, phenylephrine or methoxamine. YM26734 (3 µM) and montelukast (0.3and 1 µM) neither affected EFS-induced contractions, nor contractions by α1 -adrenergic agonists, while all contractions were substantially inhibited by silodosin (100 nM). Our findings suggest presynaptic PLA2 functions in prostate smooth muscle contraction, while contractions induced by α1 -adrenergic agonists occur PLA2 -independent. Lacking sensitivity to montelukast excludes an involvement of PLA2 -derived leukotrienes in promotion of contractile neurotransmission.

Muscle Specific Promotors for Gene Therapy - A Comparative Study in Proliferating and Differentiated Cells.

Depending on the therapy approach and disease background, the heterogeneity of muscular tissues complicates the development of targeted gene therapy, where either expression in all muscle types or restriction to only one muscle type is warranted. Muscle specificity can be achieved using promotors mediating tissue specific and sustained physiological expression in the desired muscle types but limited activity in non-targeted tissue. Several muscle specific promotors have been described, but direct comparisons between them are lacking. Here we present a direct comparison of muscle specific Desmin-, MHCK7, microRNA206- and Calpain3 promotor. To directly compare these muscle specific promotors we utilized transfection of reporter plasmids using an in vitro model based on electrical pulse stimulation (EPS) to provoke sarcomere formation in 2D cell culture for quantification of promotor activities in far differentiated mouse and human myotubes. We found that Desmin- and MHCK7 promotors showed stronger reporter gene expression levels in proliferating and differentiated myogenic cell lines than miR206 and CAPN3 promotor. However, Desmin and MHCK7 promotor promoted gene expression also cardiac cells whereas miR206 and CAPN3 promotor expression was restricted to skeletal muscle. Our results provides direct comparison of muscle specific promotors with regard to expression strengths and specificity as this is important feature to avoid undesired transgene expression in non-target muscle cells for a desired therapy approach.

Integrated analysis of circRNA, lncRNA, miRNA and mRNA to reveal the ceRNA regulatory network of postnatal skeletal muscle development in Ningxiang pig.

Introduction: The development of skeletal muscle is regulated by regulatory factors of genes and non-coding RNAs (ncRNAs). Methods: The objective of this study was to understand the transformation of muscle fiber type in the longissimus dorsi muscle of male Ningxiang pigs at four different growth stages (30, 90, 150, and 210 days after birth, n = 3) by histological analysis and whole transcriptome sequencing. Additionally, the study investigated the expression patterns of various RNAs involved in muscle fiber transformation and constructed a regulatory network for competing endogenous RNA (ceRNA) that includes circular RNA (circRNA)/long non-coding RNA (lncRNA)-microRNA (miRNA)-messenger RNA (mRNA). Results: Histomorphology analysis showed that the diameter of muscle fiber reached its maximum at 150 days after birth. The slow muscle fiber transformation showed a pattern of initial decrease followed by an increase. 29,963 circRNAs, 2,683 lncRNAs, 986 miRNAs and 22,411 mRNAs with expression level ≥0 were identified by whole transcriptome sequencing. Furthermore, 642 differentially expressed circRNAs (DEc), 505 differentially expressed lncRNAs (DEl), 316 differentially expressed miRNAs (DEmi) and 6,090 differentially expressed mRNAs (DEm) were identified by differential expression analysis. Functions of differentially expressed mRNA were identified by gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). GO enrichment analysis indicates that 40 known genes and 6 new genes are associated with skeletal muscle development. Additionally, KEGG analysis shows that these genes regulate skeletal muscle development via MAPK, FoxO, Hedgehog, PI3K-Akt, Notch, VEGF and other signaling pathways. Through protein-protein interaction (PPI) and transcription factor prediction (TFP), the action mode of skeletal muscle-related genes was explored. PPI analysis showed that there were stable interactions among 19 proteins, meanwhile, TFP analysis predicted 22 transcription factors such as HMG20B, MYF6, MYOD1 and MYOG, and 12 of the 19 interacting proteins were transcription factors. The regulatory network of ceRNA related to skeletal muscle development was constructed based on the correlation of various RNA expression levels and the targeted binding characteristics with miRNA. The regulatory network included 31 DEms, 59 miRNAs, 667 circRNAs and 224 lncRNAs. conclusion: Overall, the study revealed the role of ceRNA regulatory network in the transformation of skeletal muscle fiber types in Ningxiang pigs, which contributes to the understanding of ceRNA regulatory network in Ningxiang pigs during the skeletal muscle development period.

Characteristics of paraspinal muscle fat infiltration in asymptomatic Chinese adults: a cross-sectional study.

Paraspinal muscle fat infiltration is closely related to the occurrence and development of lumbar spine disorders and postoperative complications. This study aimed to explore the effects of age, sex, muscle, and level on paraspinal muscle fat infiltration among Chinese adults to identify the best single level of assessing whole-level paraspinal muscle fat infiltration and to define the standardized identification thresholds for paraspinal muscle fat infiltration by means of magnetic resonance imaging. This was a single-center, cross-sectional study conducted on 336 asymptomatic Chinese volunteers aged 20 to 69 years recruited from Beijing and surrounding communities through designed advertisements from May 2022 to October 2022. The fat signal fraction of multifidus (FSFMF), erector spinae (FSFES), psoas major (FSFPM), and the sum of multifidus, erector spinae, and psoas major (FSFTotal) at lumbar levels L1-L5 were measured with magnetic resonance imaging. The Student t-test and Mann-Whitney test were performed, and Pearson correlations and intraclass correlation coefficients were determined. Subgroups were compared using analysis of variance followed by a post hoc Bonferroni test or Kruskal-Wallis test. FSFTotal (14.02%±4.71% vs. 10.34±4.08%; P<0.001), FSFMF (21.14%±6.77% vs. 16.21%±6.26%; P<0.001), and FSFES (15.97%±5.56% vs. 12.37%±4.80%; P<0.001) were higher in females than in males and increased with age and lumbar level, whereas FSFPM did not significantly differ by age (all P values >0.05) or sex (P=0.12) and showed a decreasing trend from L1 to L5. The FSFTotal at L4 showed both the strongest correlation (Pearson correlation coefficient =0.95; P<0.001) and agreement (intraclass correlation coefficient =0.92; P<0.001) with the whole-level FSFTotal. Pathological paraspinal muscle fat infiltration identification thresholds of FSFTotal, FSFMF, FSFES, and FSFPM were 10.0-33.9%, 19.2-47.4%, 16.2-43.6%, and 4.8%, respectively, in each age (range, 20-69 years) and sex group. In asymptomatic Chinese adults, paraspinal muscle fat infiltration can be influenced by age, sex, muscle type, and location. The L4 level can serve as an optimal substitution in whole-level fat infiltration measurement. We present the first data concerning the identification thresholds of pathological paraspinal muscle fat infiltration, which will provide a valuable resource for researchers in the field.

Physical Characteristics of Three Types of Muscles with Different Aging Times

The demand for premium beef continues to increase along with changes in the lifestyle of upper middle class, increasing tourists and expatriates from abroad. Local cattle usually cannot produce premium beef, but aging can improve the quality of meat. This study aimed to characterize the physical quality (pH, cooking loss, water holding capacity, and tenderness) of bali beef with different aging times. This study used three types of muscles, which is Longissimus dorsi, Gluteus medius, and Semitendinosus from bali beef aged ± 3 years and body weight of ± 350 kg. Samples were aged at cold temperatures for 1, 21, and 42 days. A completely randomized design with a 3x3x4 factorial was used in this study. Least Square Means test was applied if the data obtained is significantly different. The results showed that the three types of muscle produced relatively the same physical properties, except for cooking loss. The Longissimus dorsi and Semitendinosus muscles were aged for 21 days to show the best results ofmeat tenderness.

Differential histological features and myogenic protein levels in distinct muscles of d-sarcoglycan null muscular dystrophy mouse model.

Skeletal muscle (SkM) comprises slow and fast-twitch fibers, which differ in molecular composition, function, and systemic energy consumption. In addition, muscular dystrophies (DM), a group of diverse hereditary diseases, present different patterns of muscle involvement, progression, and severity, suggesting that the regeneration-degeneration process may differ depending on the muscle type. Therefore, the study aimed to explore the expression of proteins involved in the repair process in different muscles at an early stage of muscular dystrophy in the δ-sarcoglycan null mice (Sgcd-null), a limb-girdle muscular dystrophy 2F model. Hematoxylin & Eosin (H&E) Staining showed a high number of central nuclei in soleus (Sol), tibialis (Ta), gastrocnemius (Gas), and extensor digitorum longus (Edl) from four months Sgcd-null mice. However, fibrosis, determined by trichrome of Gomori modified staining, was only observed in Sgcd-null Sol. In addition, the number of Type I and II fibers variated differentially in the Sgcd-null muscles vs. wild-type muscles. Besides, the protein expression level of β-catenin, myomaker, MyoD, and myogenin also presented different expression levels in all the Sgcd-null muscles studied. In summary, our study reveals that muscles with different metabolic characteristics showed distinct expression patterns of proteins involved in the muscle regeneration process. These results could be relevant in designing therapies for genetic and acquired myopathy.

1643-P: Unique Signature of Circular RNA in Skeletal Muscle of Different Insulin Sensitivity

Diabetes pathologies are complex, affecting numerous organs such as liver, pancreas, and skeletal muscle. Circular RNAs (circRNA) are a class of non-coding RNAs that are characterized by a covalently closed loop structure. Functionally, they can act on cell physiology by sponging microRNAs and thus regulating gene and protein expression. The emerging function of these circRNA is not fully understood, but initial studies have recently shown that circRNA are involved in insulin secretion regulation. Therefore, deregulation of this class of RNAs may lead to metabolic disorders in pancreatic β-cells and thus be involved in the pathogenesis of type 1 (T1DM) and type 2 diabetes (T2DM). Our research is focused on the unique signature by circular RNA and the impact on skeletal muscle metabolism. We demonstrated that human skeletal muscle cells in culture maintain their gene expression phenotype. A different gene signature of the cells according to their different muscular fiber type sources (oxidative versus glycolytic versus mixt) was confirmed. Moreover, an independent microRNA composition has also been highlighted. As CircRNA can regulate microRNAs and then gene expression and proteins, we wondered whether these observed signatures could be explained by circRNA. We therefore focused on key circRNAs involved in myogenesis (such as circZNF609, circHIPK3) and we were able to see that there is a difference in expression of circRNA according to the muscle type. Moreover, we analyzed correlations between circRNA levels and insulin sensitivity (measured by PKB phosphorylation). Finally, we are currently completing our analysis with in-depth sequencing techniques to identify all expressed circRNA in muscle fiber types to potentially identify new targets in insulin metabolic pathways. Disclosure M.Yepmo: None. E.Meugnier: None. M.Pinget: Consultant; Novo Nordisk, Stock/Shareholder; ILONOV. K.Bouzakri: Consultant; Adocia, Stock/Shareholder; ILONOV.

Prognostic value of myocardial scar burden using cardiac magnetic resonance in ischemic and non-ischemic cardiomyopathy

Abstract Funding Acknowledgements Type of funding sources: None. Myocardium is a unique muscle type designed to perform a specific function; conducting electrical activity to both ventricle simultaneously to contract and relax in a synchronized manner. Therefore, evaluation of the myocardial muscle function only using left ventricular ejection fraction (LVEF) would be inaccurate. However, assessment of the myocardium on the tissue level, is expected to provide more precise data regarding the ability to conduct, contract and relax properly. Purpose is to evaluate the prognostic value of myocardial scar using CMR on the clinical outcome in patients with ischemic cardiomyopathy (ICM) and non-ischemic cardiomyopathy (NICM). Methods 154 patients with either ICM or NICM underwent CMR (using 1.5T) for assessment of LVEF, detection and quantification of any myocardial scar by calculating the percentage (%) of scar mass to the whole myocardial mass (using manual quantification of scarred tissue in each myocardial segment, summed and divided by the total myocardial mass). Patients were followed up for at least 6 months for any cardiac events. These events were scaled according to severity from 1 (asymptomatic) to 7 (most severe), including; no symptoms, mild non-acute chest pain, mild dyspnoea (NYHA I-II), hospital admission due to decompensated heart failure, syncope, documented ventricular arrhythmia and sudden cardiac arrest/death, respectively. Statistical correlation between the amount of scarred myocardium in both ICM (group I) and NICM (group II) patients and the severity of the clinical events during the period of the follow up was performed. The study included 154 patients, 56% were males, mean age of 61 years with minimal follow up duration of 6 months. Patients were divided into: group I with ICM (58%) and group II with NICM (42%). Clinical presentation was ranging from eventless (10%), chest pain (18%), heart failure (15%), hospitalization (35%), syncope (1%), ventricular tachycardia (&amp;lt;1%) and up to cardiac arrest (&amp;lt;1%). Direct relationship was observed between scar size and event severity in the two groups (P value &amp;lt; 0.001). However, inverted relationship between LVEF and event severity in group I (P value of &amp;lt; 0.001) was detected but not in group II (P value 0.128), as shown in figure 1. Low EF was mainly linked with hospitalization in both ICM and NICM. It was observed that serious cardiac events were less detected in patient with mean scar mass &amp;lt; 5.4–8.4% . However, patients who have experienced sudden cardiac arrest have a mean scar mass of 15.9 % and patients with ventricular tachycardia with mean of 9.8%. Conclusion The amount of scarred myocardium is found to be directly linked to the severity of the clinical event in both ICM and NICM. Therefore, quantification of myocardial scar could be used as a predictor for cardiac events, hospitalization and sudden cardiac death.

Physical inactivity induces insulin resistance in plantaris muscle through protein tyrosine phosphatase 1B activation in mice.

Inactivity causes insulin resistance in skeletal muscle and exacerbates various lifestyle-related diseases. We previously found that 24-h hindlimb cast immobilization (HCI) of the predominantly slow-twitch soleus muscle increased intramyocellular diacylglycerol (IMDG) and insulin resistance by activation of lipin1, and HCI after a high-fat diet (HFD) further aggravated insulin resistance. Here, we investigated the effects of HCI on the fast-twitch-predominant plantaris muscle. HCI reduced the insulin sensitivity of plantaris muscle by approximately 30%, and HCI following HFD dramatically reduced insulin sensitivity by approximately 70% without significant changes in the amount of IMDG. Insulin-stimulated phosphorylation levels of insulin receptor (IR), IR substrate-1, and Akt were reduced in parallel with the decrease in insulin sensitivity. Furthermore, tyrosine phosphatase 1B (PTP1B), a protein known to inhibit insulin action by dephosphorylating IR, was activated, and PTP1B inhibition canceled HCI-induced insulin resistance. In conclusion, HCI causes insulin resistance in the fast-twitch-predominant plantaris muscle as well as in the slow-twitch-predominant soleus muscle, and HFD potentiates these effects in both muscle types. However, the mechanism differed between soleus and plantaris muscles, since insulin resistance was mediated by the PTP1B inhibition at IR in plantaris muscle.

An information theoretic method to resolve millisecond-scale spike timing precision in a comprehensive motor program.

Sensory inputs in nervous systems are often encoded at the millisecond scale in a precise spike timing code. There is now growing evidence in behaviors ranging from slow breathing to rapid flight for the prevalence of precise timing encoding in motor systems. Despite this, we largely do not know at what scale timing matters in these circuits due to the difficulty of recording a complete set of spike-resolved motor signals and assessing spike timing precision for encoding continuous motor signals. We also do not know if the precision scale varies depending on the functional role of different motor units. We introduce a method to estimate spike timing precision in motor circuits using continuous MI estimation at increasing levels of added uniform noise. This method can assess spike timing precision at fine scales for encoding rich motor output variation. We demonstrate the advantages of this approach compared to a previously established discrete information theoretic method of assessing spike timing precision. We use this method to analyze the precision in a nearly complete, spike resolved recording of the 10 primary wing muscles control flight in an agile hawk moth, Manduca sexta. Tethered moths visually tracked a robotic flower producing a range of turning (yaw) torques. We know that all 10 muscles in this motor program encode the majority of information about yaw torque in spike timings, but we do not know whether individual muscles encode motor information at different levels of precision. We demonstrate that the scale of temporal precision in all motor units in this insect flight circuit is at the sub-millisecond or millisecond-scale, with variation in precision scale present between muscle types. This method can be applied broadly to estimate spike timing precision in sensory and motor circuits in both invertebrates and vertebrates.

Myosin Heavy-Chain Messenger Ribonucleic Acid (mRNA) Expression and Fibre Cross-Sectional Area in Masseter, Digastric, Gastrocnemius and Soleus Muscles of Young and Adult Rats.

Different demands on the muscles of mastication may influence their functional profile (size and distribution of muscle fibre types), which may change during growth and maturation, potentially influencing craniofacial growth. The aim of this study was to evaluate mRNA expression and cross-sectional area of masticatory muscle fibres compared with limb muscles in young and adult rats. Twenty-four rats were sacrificed at two different ages, namely 12 at 4 weeks (young) and 12 at 26 weeks (adult). The masseter, digastric, gastrocnemius and soleus muscles were dissected. Gene expression of myosin heavy-chain isoforms Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx) in the muscles was measured using qRT-PCR RNA analysis, and immunofluorescence staining was performed to measure the cross-sectional area of different muscle fibre types. Different muscle types and ages were compared. Significant differences were found in the functional profile between masticatory and limb muscles. For the masticatory muscles, there was an increase in Myh4 expression with age, and this change was more intense for the masseter muscles, which also presented an increase in Myh1 expression, similarly to limb muscles. The fibre cross-sectional area of the masticatory muscles was generally smaller in young rats; however, this difference was less pronounced than in limb muscles.

A dynamic calcium-force relationship model for sag behavior in fast skeletal muscle.

In vitro studies using isolated or skinned muscle fibers suggest that the sigmoidal relationship between the intracellular calcium concentration and force production may depend upon muscle type and activity. The goal of this study was to investigate whether and how the calcium-force relationship changes during force production under physiological conditions of muscle excitation and length in fast skeletal muscles. A computational framework was developed to identify the dynamic variation in the calcium-force relationship during force generation over a full physiological range of stimulation frequencies and muscle lengths in cat gastrocnemius muscles. In contrast to the situation in slow muscles such as the soleus, the calcium concentration for the half-maximal force needed to drift rightward to reproduce the progressive force decline, or sag behavior, observed during unfused isometric contractions at the intermediate length under low-frequency stimulation (i.e., 20 Hz). The slope at the calcium concentration for the half-maximal force was required to drift upward for force enhancement during unfused isometric contractions at the intermediate length under high-frequency stimulation (i.e., 40 Hz). The slope variation in the calcium-force relationship played a crucial role in shaping sag behavior across different muscle lengths. The muscle model with dynamic variations in the calcium-force relationship also accounted for the length-force and velocity-force properties measured under full excitation. These results imply that the calcium sensitivity and cooperativity of force-inducing crossbridge formation between actin and myosin filaments may be operationally altered in accordance with the mode of neural excitation and muscle movement in intact fast muscles.

Evaluation of the relationship between the attachment type of lateral pterygoid muscle and the position of temporomandibular joint disc in patients with temporomandibular joint disorders based on wireless amplified MRI detector high resolution imaging

Objective: To explore the correlation between the attachment type of lateral pterygoid muscle (LPM) and the position of temporomandibular joint (TMJ) disc in patients with temporomandibular disorders (TMD) by using wireless amplified magnetic resonance imaging detector (WAND) coupled with conventional head and neck joint coil for high resolution imaging of TMJ. Methods: Eighty-five patients with TMD diagnosed by oral and maxillofacial surgeons of Guizhou Provincial People's Hospital from October 2019 to January 2022 were collected. A total of 160 TMJ were included. There were 16 males and 69 females, aged (32.7±14.2) years. All patients were scanned with open, closed oblique sagittal and coronal WAND coupled head and neck coils with bilateral TMJ. Based on TMJ and LPM high resolution imaging, to explore the correlation between LPM attachment types and the position of TMJ disc in TMD patients, and to evaluate the potential clinical value of LPM attachment types in TMD patients. χ2 test and Pearson correlation analysis were used to evaluate the correlation between LPM attachment type and TMJ disc location. Results: There were three types of LPM attachment: type Ⅰ in 51 cases [31.9% (51/160)], type Ⅱ in 77 cases [48.1% (77/160)] and type Ⅲ in 32 cases [20.0% (32/160)]. There was a significant correlation between the type of LPM attachment and the position of articular disc (χ2=28.20, P=0.002, r=0.776). There was no statistical significance between the type of LPM attachment and the reversible displacement of articular disc (χ2=0.24, P=0.887, r=0.825). Conclusions: There is a correlation between the attachment type of LPM and the position of the disc in TMD patients. WNAD coupled with conventional head and neck joint coil TMJ high resolution scan can provide reliable imaging evidence for TMD patients in evaluating the type of LPM attachment and the location of disc.

Accessory Subscapularis muscle compressing posterior division of upper trunk: A rare presentation

Presence of additional or accessory muscles near the axilla can lead to compression of vital structures of the axilla. Opposite conventional thoughts, it seems that the subscapularis muscle (SM) is the most variable muscle of the rotator cuff group. Accessory Subscapularis muscle is one of the rare variants of the Subscapularis muscle. Presence of this variant (ASsm) can cause abnormal clinical presentation. During routine dissection of the axilla in a female cadaver in the Department of Anatomy, Muzaffarnagar Medical College, we found an additional slip or accessory subscapularis muscle, arising from the anterolateral part of the Subscapularis and running upward and medially, finally attached to the coracoid process (palpated tip). During its course, it passed through the Brachial plexus and caused compression of the posterior division of the Upper trunk. This type of accessory slip or accessory subscapular muscle can cause compression neuropathy, or this accessory slip can be used during the repair of a ruptured Subscapularis or any other adjacent muscle. Keywords: Accessory Subscapularis Muscle, Rotator Cuff Variants, Brachial Plexus Compression

Proteomics and metabolomics profiling of meat exudate to determine the impact of postmortem aging on oxidative stability of beef muscles.

The objective of this study was to characterize the major proteomes and metabolites in beef exudate and determine their relationship to color and oxidative quality of beef muscles. Beef loin (LD) and tenderloin (PM) muscles were cut into sections, individually vacuum-packaged, and aged for 9, 16 and 23days at 2°C. Following aging, beef exudates were collected and analyzed for both proteomics and metabolomics profiles. Proteome analysis indicated clustering by muscle types, while metabolomics profiling further clustered the samples based on the aging periods. The PM exudate had a greater concentration of oxidative enzymes, while the LD exudate contained more glycolytic enzymes. Greater lipid, nucleotide, carnitine and glucoside metabolites were observed in LD and 23d exudates. HSP70 and laminin proteins, together with glucosides metabolites, were correlated to muscle oxidative stability. The results indicated that meat exudate could be a viable analytical matrix to determine changes in quality attributes of meat with aging.