Vitamin A regulates mitochondrial biogenesis and function through p38 MAPK‑PGC‑1α signaling pathway and alters the muscle fiber composition of sheep

Background Vitamin A(VA)and its metabolite,retinoic acid(RA),are of great interest for their wide range of physiological functions.However,the regulatory contribution of VA to mitochondrial and muscle fiber composition in sheep has not been reported.Method Lambs were injected with 0(control)or 7,500 IU VA palmitate into the biceps femoris muscle on d 2 after birth.At the age of 3 and 32 weeks,longissimus dorsi(LD)muscle samples were obtained to explore the effect of VA on myofiber type composition.In vitro,we investigated the effects of RA on myofiber type composition and intrinsic mechanisms.Results The proportion of type I myofiber was greatly increased in VA-treated sheep in LD muscle at harvest.VA greatly promoted mitochondrial biogenesis and function in LD muscle of sheep.Further exploration revealed that VA elevated PGC-1αmRNA and protein contents,and enhanced the level of p38 MAPK phosphorylation in LD muscle of sheep.In addition,the number of type I myofibers with RA treatment was significantly increased,and type IIx myofibers was significantly decreased in primary myoblasts.Consistent with in vivo experiment,RA significantly improved mitochondrial biogenesis and function in primary myoblasts of sheep.We then used si-PGC-1αto inhibit PGC-1αexpression and found that si-PGC-1αsignificantly abrogated RA-induced the formation of type I myofibers,mitochondrial biogenesis,MitoTracker staining intensity,UQCRC1 and ATP5A1 expression,SDH activity,and enhanced the level of type IIx muscle fibers.These data suggested that RA improved mitochondrial biogenesis and function by promoting PGC-1αexpression,and increased type I myofibers.In order to prove that the effect of RA on the level of PGC-1αis caused by p38 MAPK signaling,we inhibited the p38 MAPK signaling using a p38 MAPK inhibitor,which significantly reduced RA-induced PGC-1αand MyHC I levels.Conclusion VA promoted PGC-1αexpression through the p38 MAPK signaling pathway,improved mitochondrial biogenesis,and altered the composition of muscle fiber type.

Dietary protein levels changed the hardness of muscle by acting on muscle fiber growth and the metabolism of collagen in sub-adult grass carp(Ctenopharyngodon idella)

Background:Nutrient regulation has been proven to be an effective way to improve the flesh quality in fish.As a necessary nutrient for fish growth,protein accounts for the highest proportion in the fish diet and is expensive.Although our team found that the effect of protein on the muscle hardness of grass carp was probably related to an increased collagen content,the mechanism for this effect has not been deeply explored.Moreover,few studies have explored the protein requirements of sub-adult grass crap(Ctenopharyngodon idella).Therefore,the effects of different dietary protein levels on the growth performance,nutritional value,muscle hardness,muscle fiber growth,collagen metabolism and related molecule expression in grass carp were investigated.Methods:A total of 450 healthy grass carp(721.16±1.98 g)were selected and assigned randomly to six experimen-tal groups with three replicates each(n=25/replicate),and were fed six diets with 15.91%,19.39%,22.10%,25.59%,28.53%and 31.42%protein for 60 d.Results:Appropriate levels of dietary protein increased the feed intake,percentage weight gain,specific growth rate,body composition,unsaturated fatty acid content in muscle,partial free amino acid content in muscle,and muscle hardness of grass carp.These protein levels also increased the muscle fiber density,the frequency of new muscle fibers,the contents of collagen and IGF-1,and the enzyme activities of prolyl 4-hydroxylases and lysyloxidase,and decreased the activity of matrix metalloproteinase-2.At the molecular level,the optimal dietary protein increased col-lagen type Iα1(Colα1),Colα2,PI3K,Akt,S6K1,La ribonucleoprotein domain family member 6a(LARP6a),TGF-β1,Smad2,Smad4,Smad3,tissue inhibitor of metalloproteinase-2,MyoD,Myf5,MyoG and MyHC relative mRNA levels.The levels of the myostatin-1 and myostatin-2 genes were downregulated,and the protein expression levels of p-Smad2,Smad2,Smad4,p-Akt,Akt,LARP6 and Smad3 were increased.Conclusions:The appropriate levels of dietary protein promoted the growth of sub-adult grass carp and improved muscle hardness by promoting the growth of muscle fibers,improving collagen synthesis and depressing collagen degradation.In addition,the dietary protein requirements of sub-adult grass carp were 26.21%and 24.85%according to the quadratic regression analysis of growth performance(SGR)and the muscle hardness(collagen content),respectively.

Pathophysiological changes of muscle after ischemic stroke:a secondary consequence of stroke injury

Sufficient clinical evidence suggests that the damage caused by ischemic stroke to the body occurs not only in the acute phase but also during the recovery period,and that the latter has a greater impact on the long-term prognosis of the patient.However,current stroke studies have typically focused only on lesions in the central nervous system,ignoring secondary damage caused by this disease.Such a phenomenon arises from the slow progress of pathophysiological studies examining the central nervous system.Further,the appropriate therapeutic time window and benefits of thrombolytic therapy are still controversial,leading scholars to explore more pragmatic intervention strategies.As treatment measures targeting limb symptoms can greatly improve a patient’s quality of life,they have become a critical intervention strategy.As the most vital component of the limbs,skeletal muscles have become potential points of concern.Despite this,to the best of our knowledge,there are no comprehensive reviews of pathophysiological changes and potential treatments for post-stroke skeletal muscle.The current review seeks to fill a gap in the current understanding of the pathological processes and mechanisms of muscle wasting atrophy,inflammation,neuroregeneration,mitochondrial changes,and nutritional dysregulation in stroke survivors.In addition,the challenges,as well as the optional solutions for individualized rehabilitation programs for stroke patients based on motor function are discussed.

Crosstalk among canonical Wnt and Hippo pathway members in skeletal muscle and at the neuromuscular junction

Skeletal muscles are essential for locomotion,posture,and metabolic regulation.To understand physiological processes,exercise adaptation,and muscle-related disorders,it is critical to understand the molecular pathways that underlie skeletal muscle function.The process of muscle contra ction,orchestrated by a complex interplay of molecular events,is at the core of skeletal muscle function.Muscle contraction is initiated by an action potential and neuromuscular transmission requiring a neuromuscular junction.Within muscle fibers,calcium ions play a critical role in mediating the interaction between actin and myosin filaments that generate force.Regulation of calcium release from the sarcoplasmic reticulum plays a key role in excitation-contraction coupling.The development and growth of skeletal muscle are regulated by a network of molecular pathways collectively known as myogenesis.Myogenic regulators coordinate the diffe rentiation of myoblasts into mature muscle fibers.Signaling pathways regulate muscle protein synthesis and hypertrophy in response to mechanical stimuli and nutrient availability.Seve ral muscle-related diseases,including congenital myasthenic disorders,sarcopenia,muscular dystrophies,and metabolic myopathies,are underpinned by dys regulated molecular pathways in skeletal muscle.Therapeutic interventions aimed at preserving muscle mass and function,enhancing regeneration,and improving metabolic health hold promise by targeting specific molecular pathways.Other molecular signaling pathways in skeletal muscle include the canonical Wnt signaling pathway,a critical regulator of myogenesis,muscle regeneration,and metabolic function,and the Hippo signaling pathway.In recent years,more details have been uncovered about the role of these two pathways during myogenesis and in developing and adult skeletal muscle fibers,and at the neuromuscular junction.In fact,research in the last few years now suggests that these two signaling pathways are interconnected and that they jointly control physiological and pathophysiological processes in muscle fibers.In this review,we will summarize and discuss the data on these two pathways,focusing on their concerted action next to their contribution to skeletal muscle biology.However,an in-depth discussion of the noncanonical Wnt pathway,the fibro/a dipogenic precursors,or the mechanosensory aspects of these pathways is not the focus of this review.

Study on Development Rule of Muscle Fiber in Different Duck Breeds

[Objective] The aim of this study was to investigate the development rule of muscle fiber in different duck breeds during various developmental stages. [Method] Cherry valley duck, Jinding duck, White muscory duck and Suma duck （ Cherry valley duck ♂ × Jinding duck ♀ ） were fed for 10 weeks to observe the ultrastructure of muscle fiber by electron microscope, and the myofibril diameter and sarcomere length were also determined. [Result] The myofibril diameter increased with ages. Sarcomere length and myofibril diameter did not change significantly with the increasing ages （P〉0.05）. The myofibril diameter of White muscory duck and Jinding duck were thicker, while that of Cherry valley cluck and Suma duck were thinner. Moreover, the sarcomere length of Suma duck and White muscory duck were longer, while that of Cherry valley duck and Jinding duck were shorter. Thus, the basic characteristics of ultrastructure of muscle fiber were consistent in these duck breeds.[Conclusion] The results have an important meaning for duck breeding.

Comparison of Soleus Muscle Fibers in Rats and Rabbits at Different Stages of Postnatal Development

In the present study,the effects of postnatal development on the number and distribution of skeletal muscle fibers of different types in hind leg of rat and rabbit were studied.The soleus muscles of rats aged 2 days,2,4,6,8,and 10 weeks (body weight 10,32,95,190,280,and 320 g),and rabbits aged 2 days,2,4,8,12,16,20,and 24 weeks (body weight 100,220,400,750,1 200,1 600,2 100,and 2 500 g) were stained with succinic dehydrogenase.With an image analysis system,the X-Y coordinates of fibers were used to analyze the growth-related changes.The results of present study showed that three types of fibers were found in the soleus muscles of rat and rabbit,i.e.,type Ⅰ (slow oxidative),ⅡX (fast oxidative),and ⅡA (fast oxidative glycolytic).The type Ⅰ fibers were present throughout the muscle that had a uniform distribution and tended to increase in number with aging.Type ⅡX fibers were scattered throughout the muscle and decreased markedly in number with aging.Type ⅡA fibers were located at the central and deep regions,and showed a little or no change in number and distribution with aging.While be of age,type ⅡA and ⅡX fibers became restricted to the superficial region.No type ⅡB fibers were detected.Type ⅡA fibers had the largest diameter,type Ⅰ intermediate and type ⅡX the smallest.Mean cross-sectional area of each type fibers of rabbits was larger than that of rats.The present results indicate that the number and distribution of muscle fibers of different types in hind limb of rat and rabbit change with the process of postnatal growth.

A Review on Tibetan Swine(a)——Carcass,Meat Quality,Basic Nutrition Component,Amino Acids,Fatty Acids,Inosine Monophosphate and Muscle Fiber

In this review, the carcass, meat quality, internal organs, basic nutrition component, amino acids （AAs）, fatty acids, inosine monophosphate （IMP） and mus- cle fiber of Tibetan swine were summarized for the first time. The formation mecha- nism of excellent features was analyzed from the aspects of physiological traits, ge- ographical environments and constraint reasons. Thereby, the outstanding features of Tibetan swine could be extended continuously, and the poor characteristics should be improved in the future.

Comparative Study on Muscle Fiber Characteristics and Muscle Nutritional Quality between Two Groups of Yellow River Carps

The aim was to protect the Henan Yellow River carp germplasm resources and provide a scientific basis for the meat quality improvement of Yellow River carps. With artificially farmed and wild Henan Yellow River carps as the research objects, comparative study on muscle fiber diameter and density, routine nutritional composition, calcium and phosphorus contents and amino acids composition was conducted between the two groups of carps. The results showed that the moisture content was significantly higher （P 〈0.05）, the crude fat and crude protein contents were significantly lower （P〈0.05）, the essential amino acids and total amino acids contents were lower （P〉0.05）, the phosphorus content was higher （P 〉0.05）, and the calcium content was lower （P〉0.05） in the wild group compared with those in the farming group. The analysis of muscle fiber characteristics showed that there were significant differences in the average muscle fiber diameter （P〈0.05） and muscle fiber density （P〈0.01） between the two groups of Henan Yellow River carps.

Effects of dietary protein restriction on muscle fiber characteristics and m TORC1 pathway in the skeletal muscle of growing-finishing pigs

Background： To investigate the effects of dietary crude protein（CP） restriction on muscle fiber characteristics and key regulators related to protein deposition in skeletal muscle, a total of 18 growing-finishing pigs（62.30 ± 0.88 kg）were allotted to 3 groups and fed with the recommended adequate protein（AP, 16 % CP） diet, moderately restricted protein（MP, 13 % CP） diet and low protein（LP, 10 % CP） diet, respectively. The skeletal muscle of different locations in pigs, including longissimus dorsi muscle（LDM）, psoas major muscle（PMM） and biceps femoris muscle（BFM） were collected and analyzed.Results： Results showed that growing-finishing pigs fed the MP or AP diet improved（P 〈 0.01） the average daily gain and feed： gain ratio compared with those fed the LP diet, and the MP diet tended to increase（P = 0.09） the weight of LDM. Moreover, the ATP content and energy charge value were varied among muscle samples from different locations of pigs fed the reduced protein diets. We also observed that pigs fed the MP diet up-regulated（P 〈 0.05） muscular m RNA expression of all the selected key genes, except that myosin heavy chain（My HC） IIb,My HC IIx, while m RNA expression of ubiquitin ligases genes was not affected by dietary CP level. Additionally, the activation of mammalian target of rapamycin complex 1（m TORC1） pathway was stimulated（P 〈 0.05） in skeletal muscle of the pigs fed the MP or AP diet compared with those fed the LP diet.Conclusion： The results suggest that the pigs fed the MP diet could catch up to the growth performance and the LDM weight of the pigs fed the AP diet, and the underlying mechanism may be partly due to the alteration in energy status, modulation of muscle fiber characteristics and m TORC1 activation as well as its downstream effectors in skeletal muscle of different locations in growing-finishing pigs.

A novel triple immunoenzyme staining enables simultaneous identification of all muscle fiber types on a single skeletal muscle cryosection from normal, denervated or reinnervated rats

Triple immunofluorescence staining has recently been developed to simultaneously identify all muscle fibers on a single cryosection which is helpful for clinical and basic research, but it has disadvantages such as fast photobleaching and unclear outlines of muscle fibers. Triple immunoenzyme staining（TIE） is likely to avoid these disadvantages. In this study, we aimed to establish a sensitive and specific TIE technique to identify fiber types in normal, denervated, and reinnervated rat muscles, and to develop a systematic sampling method for muscle fiber quantification. Tibialis anterior and soleus from normal, denervated, and reinnervated Lewis rat hind limbs were used. Five consecutive cryosections were cut from each muscle, including one for TIE and four for single immunoenzyme staining（SIE）. The TIE was performed using the polymerized reporter enzyme staining system for the first two antigens（A4.74 for My HC-IIA, BA-F8 for My HC-I） and alkaline phosphatase staining system for the third antigen（BF-F3 for My HC-IIB）, followed by corresponding detective systems and respective chromogens. The type of muscle fibers was quantified by systematic sampling at 12.5%, 25%, 33% and 50% of all muscle fibers, and was compared with that acquired from counting all the fibers（100%）. All muscle fiber phenotypes, including pure and hybrid, could be simultaneously identified on a single TIE cryosection with clear outlines. The fiber types on TIE slides matched well with their respective counterpart on the consecutive SIE slides with a 95% match rate. Systematic sampling of 12.5% fibers could represent the true fiber type distribution of the entire muscle section. Our results suggest that novel TIE can effectively visualize fiber types in normal, denervated or reinnervated rat muscles.

Targeted myostatin loss-of-function mutation increases type Ⅱ muscle fibers in Meishan pigs

Myostatin(MSTN) is a negative regulator of skeletal muscle growth and development. The skeletal muscle in MSTN^(-/-)mice is significantly hypertrophied, with muscle fiber type II increasing significantly while muscle fiber type I decreasing.However, it is still not clear how the skeletal muscle types change in MSTN^(-/-)pigs, and how the mechanism for MSTN regulates fiber types, especially in large animals like pigs. This study conducted a comprehensive analysis of the composition of skeletal muscle fibers in MSTN^(-/-)pigs produced in our laboratory. It was observed that, compared with wild-type(WT) pigs, both the total mass of skeletal muscle and type IIb muscle fibers increased significantly(P<0.01),while the type I and type IIa muscle fibers decreased significantly(P<0.01), in MSTN^(-/-)Meishan pigs. In addition, to explore the influence of MSTN on muscle fiber type and its regulation mechanism in the embryonic stage, this study selected a few genes(Myf5, Mef2 d, MyoD and Six1) associated with muscle fiber type and validated their expression by quantitative RT-PCR. Herein, it was found that Myh7, Myh2, Myh4 and Myh1 can be detected in the skeletal muscle of pigs at 65 days of gestation(dg). Compared with WT pigs, in MSTN^(-/-)Meishan pigs, Myh7 decreased significantly(P<0.01), while Myh4(P<0.001) and Myh1(P<0.05) increased significantly. Meanwhile, the increased expression of Myf5(P<0.05), Mef2 d(P<0.01) and Six1(P<0.05) in MSTN^(-/-)Meishan pigs suggested that MSTN should regulate the directional development of muscle fiber types in the early stage of embryonic development. Thus, at the embryonic stage, the type II muscle fibers began to increase in MSTN^(-/-)pigs. These results can provide valuable information not only for pig meat quality improvement, but also for the study of human skeletal muscle development and disease treatment.

AMPK Subunit Expression Regulates Intramuscular Fat Content and Muscle Fiber Type in Chickens

The objective of this study was to assess the role of AMPK in intramuscular fat(IMF) and fiber type in chicken muscle. The chickens were slaughtered and their muscles were collected at the ages of 4, 8, and 16 weeks so as to determine the IMF contents, as well as the expression levels of AMPK subunits, regulators of adipogenesis. In addition, the myosin heavy chains(My HCs) in thigh muscle tissues were also measured. The results showed that the IMF contents in 16-week old chickens were higher than those in 4 and 8-week-old chickens(P<0.05).The expression levels of fatty acid synthase(FAS) and fatty aicd translocase CD36(FAT/CD36) m RNA were increased significantly in samples collected at the ages of4 and 16 weeks(P<0.05). The expression levels of My HC IIa and IIb differed significantly among all the developmental stages(P <0.05). The AMPKα2, AMPKγ1,and AMPKγ3 m RNA levels were dramatically decreased with the increase of age(P <0.05). To examine the role of AMPK in adipogenesis regulation, the SV cells were cultured in an adipogenesis medium and treated with AICAR and Compound C respectively, the specific activator and inhibit of AMPK. The Compound C induced dramatically a greater expression of C/EBPβ, SREBP1 and PPARγ(P <0.05). In conclusion, the expression of AMPKα2, AMPKγ1, and AMPKγ3 m RNA is significantly correlated with the adipogenesis in skeletal muscle of chickens.

Transfer of β-hydroxy-β-methylbutyrate from sows to their offspring and its impact on muscle fiber type transformation and performance in pigs

Background： Previous studies suggested that supplementation of lactating sows with β-hydroxy-β-methylbutyrate（HMB） could improve the performance of weaning pigs, but there were little information in the muscle fiber type transformation of the offspring and the subsequent performance in pigs from weaning through finishing in response to maternal HMB consumption. The purpose of this study was to determine the effect of supplementing lactating sows with HMB on skeletal muscle fiber type transformation and growth of the offspring during d 28 and180 after birth. A total of 20 sows according to their body weight were divided into the control（CON, n = 10） or HMB groups（HMB, n = 10）. Sows in the HMB group were supplemented with β-hydroxy-β-methylbutyrate calcium（HMB-Ca） 2 g/kg feed during d 1 to 27 of lactation. After weaning, 48 mixed sex piglets were blocked by sow treatment and fed standard diets for post-weaning, growing, finishing periods. Growth performance was recorded during d 28 to 180 after birth. Pigs were slaughtered on d 28（n = 6/treatment） and 180（n = 6/treatment） postnatal and the longissimus dorsi（LD） was collected, respectively.Results： The HMB-fed sows during lactation showed increased HMB concentration（P ＆lt; 0.05） in milk and LD of weaning piglets（P ＆lt; 0.05）. In addition, offsprings in HMB group had a higher finishing BW and lean percentage than did pigs in CON group（P ＆lt; 0.05）, meanwhile, compared with pigs from sows fed the CON diet, pigs from sows fed HMB diet showed higher type Ⅱ muscle fiber cross-sectional area（CSA）, elevated myosin heavy chain（MyHC） Ⅱb and Sox6 mRNA, and fast-MyHC protein levels in LD（P ＆lt; 0.05）.Conclusions： HMB supplemented to sow diets throughout lactation increases the levels of HMB in maternal milk and skeletal muscle of pigs during d 28 after birth and promotes subsequent performance of pigs between d 28 and 180 of age by enhancing glycolytic muscle fiber transformation.

Changes in Myelinated Nerve Fibers and Skeletal Muscle of Rats Exposed to High Doses of Permethrin

Neurological signs and segmcntal demyelination in a cervical nerve were observed in rats treated orally with permethrin (300 mg/kg/day) for 5 days. Inflammatory and degenerative signals were recorded in the diaphragm muscle. These effects were more intense with the trade grade than with the technical grade product. The possible influence of the percentage of cisitrans isomers on the intensity of the observed effects is discussed. 5 imi Academic Press.Inc.

One-dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibers

A quantum chain model of multiple molecule motors is proposed as a mathematical physics theory for the microscopic modeling of classical force-velocity relation and tension transients in muscle fibers. The proposed model was a quantum many-particle Hamiltonian to predict the force-velocity relation for the slow release of muscle fibers, which has not yet been empirically defined and was much more complicated than the hyperbolic relationships. Using the same Hamiltonian model, a mathematical force-velocity relationship was proposed to explain the tension observed when the muscle was stimulated with an alternative electric current. The discrepancy between input electric frequency and the muscle oscillation frequency could be explained physically by the Doppler effect in this quantum chain model. Further more, quantum physics phenomena were applied to explore the tension time course of cardiac muscle and insect flight muscle. Most of the experimental tension transient curves were found to correspond to the theoretical output of quantum two- and three-level models. Mathematical modeling electric stimulus as photons exciting a quantum three-level particle reproduced most of the tension transient curves of water bug Lethocerus maximus.

Comparison of Muscle Fiber Growth from F1Generations of Large Yorkshire Pig andErhualian Pig by Reciprocal Cross

[ Objective] To compare the muscle fiber growth between F1 generations of large Yorkshire pig and Erhualian pig by reciprocal cross, and provide a theoretical basis for the integrated breeding of meat quality traits and growth performances by rational utilization of hybrid combination. [ Method] The hybrid pigs of large Yorkshire pig and Erhualian pig were fed and managed in the same conditions. The reciprocal combinations were Erhualian pig ♀ × Yorkshire pigd, and Yorkshire pig ♀ × Erhualian pig♂ , respectively. At the age of 20, 70, 120 and 180 d, the Iongissimus dorsi muscle and thigh muscle were collected and made into frozen sections for hematoxylin and eosin （HE） staining, and then the muscle fiber area was determined. [ Result] The muscle fiber was thickened gradually with increasing age; and the absolute growth curve of muscle fiber area was presented as ＂S＂ shape. The diameter, perimeter and area of Iongissimus dorsi muscle and thigh muscle fibers in the reciprocal combination of Yorkshire pig ♀ × Erhualian pig♂ were higher than those in the reciprocal combination of Erhualian pig ♀ × Yorkshire pig♂ （P 〈 0.01 ）. The thigh muscle grew faster than Iongissimus dorsi muscle at the age of 20 -120 d; but at the age of 120 -180 d, the growth rate of Iongissimus dorsi muscle was higher than that of thigh muscle; and at the age of 180 d, the muscle fiber area had no significant difference between the Iongissimus dorsi muscle and the thigh muscle. The muscle fiber area had extremely significant difference between the reciprocal combinations at the age of 20 d; but no significant difference was found at the age of 180 d. [ Conclusion] The reciprocal combinations can affect the muscle fiber growth of hybrid pigs of Yorkshire pig and Erhualian pig, but the affect degree reduces with the increasing age.

Investigation on the Growth and Development of Muscle Fibers in Black Goat Lambs

[Objectives]This study was conducted to analyze and study the growth and development of muscle fibers at different stages,so as to provide a theoretical basis for subsequent research on developmental biology and nutritional regulation.[Methods]The body weights of black goat lambs in groups at different month age(0-6 months old)were recorded,and the diameter,area and number of muscle fibers were measured by tissue section and hematoxylin-eosin staining.The curves of body weight and muscle fiber growth and development of black goat lambs were drawn.[Results]The black goat lambs maintained a high absolute growth intensity of 2.95-4.35 kg/30 d throughout the rearing cycle,and the body weight continued to increase significantly,while the relative growth coefficient decreased from 93.05%at the age of 30 d to 13.83%at the age of 180 d.The diameter and area of muscle fibers in black goat lambs showed obvious"three-stage"growth and development characteristics,and showed different trends of gender advantages in different stages.[Conclusions]This study will help to further optimize the key supporting technologies for production and promote the diversified and comprehensive development of the mutton sheep industry in Sichuan Province.

Key changes in denervated muscles and their impact on regeneration and reinnervation

The neuromuscular junction becomes progressively less receptive to regenerating axons if nerve repair is delayed for a long period of time. It is difficult to ascertain the denervated muscle＇s residual receptivity by time alone. Other sensitive markers that closely correlate with the extent of denervation should be found. After a denervated muscle develops a fibrillation potential, muscle fiber conduction velocity, muscle fiber diameter, muscle wet weight, and maximal isometric force all decrease; remodeling increases neuromuscular junction fragmentation and plantar area, and expression of myogenesis-related genes is initially up-regulated and then down-regulated. All these changes correlate with both the time course and degree of denervation. The nature and time course of these denervation changes in muscle are reviewed from the literature to explore their roles in assessing both the degree of detrimental changes and the potential success of a nerve repair. Fibrillation potential amplitude, muscle fiber conduction velocity, muscle fiber diameter, mRNA expression levels of myogenic regulatory factors and nicotinic acetylcholine receptor could all reflect the severity and length of denervation and the receptiveness of denervated muscle to regenerating axons, which could possibly offer an important clue for surgical choices and predict the outcomes of delayed nerve repair.

Changes following denervation to the masseter muscle

BACKGROUND： Masseter muscle nerve is often injured in mandible osteotomy. What changes in food intake and masseter muscle will be brought after masseter muscle nerve injury？ OBJECTIVE： This study was designed to selectively establish animal models of denervated masseter muscle and investigate the effects of severing masseter muscular nerve on masseter muscle and animal＇s food intake. DESIGN, TIME AND SETTING： A randomized controlled animal experiment was performed at the Laboratory Animal Center, Nanfang Hospital, Southern Medical University from September to November 2005. MATERIALS： A total of 50 healthy, adult, SPF-grade, New Zealand rabbits, of both genders, were used to develop an animal model of selectively denervated masseter muscle. METHODS： Five rabbits were randomly selected as normal controls. According to various mutilation methods, the remaining animals were randomly divided into 3 experimental groups, with 15 rabbits in each group： masseter muscular neural stem denervated, masseter muscular neural superior branch-denervated, and masseter muscular neural inferior brancb-denervated groups. Self-control comparison was performed on each animal. The right masseter muscle served as the experimental side, and the left masseter muscle served as the control side. In each group, 3 time points （2, 8, and 24 weeks post-surgery） were allotted for observation. MAIN OUTCOME MEASURES： At the pre-set time points, masseter muscular thickness was measured with a Logic 500 color Doppler ultrasonic diagnostic apparatus. Masseter muscle tissue was resected for hematoxylin eosin staining. Masseter muscular fiber diameter and area were measured with an optical microscope. Masseter muscle tissue was sectioned and nicotinamide adenine dinucleotide tetrazolium oxidoreductase （NADH-TR） and adenosine triphosphatase staining were performed. Following staining, the sections were quantitatively analyzed using an IBAS200 image analyzer. RESULTS： Post-surgery food intake： No abnormal food intake was found after surgery among the three groups. Intragroup comparison： In each experimental group, following denervation, masseter muscular thickness was decreased （P 〈 0.05） and masseter muscular fiber cross-section area was reduced in the experimental side compared to the control side （P 〈 0.05）. Inter-group comparison： There was a significant difference in masseter muscular thickness and masseter fiber cross-section area among the three experimental groups （P 〈 0.05）. There was no significant difference in masseter fiber type between the control side of the three experimental groups and the normal control group （P 〉 0.05）. CONCLUSION： Following various methods of masseter muscle denervation, masseter muscle thickness and masseter fiber cross-section area was reduced by varying degrees. Denervated masseter muscle did not influence food intake of experimental animals or alter masseter muscle fiber ratio.

Skeletal Muscle Adaptation to Endurance and Resistance Training

Endurance training in the aerobic zone of metabolism promotes a transition from type II to type I muscle fibers, influences the enzyme system of the Krebs cycle, electron transport chain, capillary supply, changes in key metabolic enzymes involved in fatty acid activation, and increased oxygen uptake in skeletal muscle. First of all, the transition process is related to the contractile apparatus. 5＇adenosine monophosphate-activated protein kinase is activated in response to endurance training and related to the metabolic adaptation of skeletal muscle. The peroxisome proliferator-activated receptor isoform δ is an important regulator of skeletal muscle endurance capacity. Resistance training improves muscle contractile function and increases muscle mass as a result of an anabolic and anti catabolic effect in fast-twitch fibers. Resistance training expands the amount of the contractile apparatus in order to enlarge fiber cross-sectional area. A concomitant alteration in proteins phenotype of contractile apparatus and metabolic enzyme levels occurs in accordance with activity-induced changes in the muscle＇s fiber-type profile. Recovery of skeletal muscle mechanical properties depends on the structural and metabolic peculiarities of muscle and the character of training.