Structure and variation in the hindlimb musculature of the woodcreepers (Aves: Passeriformes: Dendrocolaptinae)

The Dendrocolaptinae (woodcreepers), a clade of neotropical passerine birds, form an adaptive radiation with a spectrum of body sizes and bill shapes. Woodcreepers are scansorial, climbing vertical tree trunks supported by their forward toes and stiffened tail. The hindlimb musculature was dissected and described for 42 of the 50 species representing all genera, and for 14 outgroup species. Structural, functional, developmental and evolutionary aspects of muscular variations are analysed. Woodcreepers have extensive ossification of leg tendons. There is intraspecific variation in the degree of ossification, and interspecific variation in the occurrence of ossification between muscles. Intraspecific variation in muscle structure was apportioned according to a published classification. Nine muscles showed variation of the minor, singular, mimicking and incongruous types, but explosive variation was lacking. Some muscles are more prone to variation than others. Ten muscles showed interspecific variations of four types, for which new terms are proposed: occurrence variations; attachment variations in origins and insertions; structural variations in size, shape, or fibre arrangement; and relational variations with other muscles. Variations in the presence of a muscle component did not occur. Discrimination of intraspecific variations from interspecific variations is discussed.     

Effect of sciatectomy and induced ammonia stress on Mg2+_adenosine triphosphatase activity in frog tissues

Mg² + dependent —adenosine triphosphatase activity has been studied in the muscle, brain, kidney and liver tissues of frog,Rana hexadactyla (Lesson) after sciatectomy and induced chronic ammonia stress. The enzyme activity decreased in the tissues of the denervated frog. The activity of the enzyme increased in all the tissues of the normal and denervated frogs except in the denervated muscle when ammonium lactate was infused intraperitoneally.     

Plasticity of skeletal muscle: regenerating fibers adapt more rapidly than surviving fibers

The properties of mammalian skeletal muscle demonstrate a high degree of structural and functional plasticity as evidenced by their adaptability to an atypical site after cross-transplantation and to atypical innervation after cross-innervation. We tested the hypothesis that, regardless of fiber type, skeletal muscles composed of regenerating fibers adapt more readily than muscles composed of surviving fibers when placed in an atypical site with atypical innervation. Fast muscles of rats were autografted into the site of slow muscles or vice versa with the donor muscle innervated by the motor nerve to the recipient site. Surviving fibers in donor muscles were obtained by grafting with vasculature intact (vascularized muscle graft), and regenerating fibers were obtained by grafting with vasculature severed (free muscle graft). Our hypothesis was supported because 60 days after grafting, transposed muscles with surviving fibers demonstrated only a slight change from the contractile properties and fiber typing of donor muscles, whereas transplanted muscles with regenerating fibers demonstrated almost complete change to those of the muscle formerly in the atypical site.     

Effect of denervation on the expression of glycogen phosphorylase in mouse skeletal muscle.

After sciatectomy of the left hind-limb of C57BL/J mice, a denervation-induced muscular atrophy ensued and was accompanied by a decrease in the specific activity of glycogen phosphorylase to approx. 25% of control values. The cofactor of phosphorylase, pyridoxal 5'-phosphate, was used as a specific label in the determination of the degradation rate of the enzyme following nerve section. After a delay of 3-4 days, phosphorylase was degraded approx, twice as rapidly in the denervated gastrocnemius (0.20 day-1) as in the control muscle (0.12 day-1). The effect of denervation on phosphorylase mRNA was measured by quantitative Northern-blot analysis using a rat skeletal-muscle phosphorylase cDNA probe. After an initial rapid decline, phosphorylase mRNA levels stabilized in denervated muscle at 50% of the value measured in the contralateral control muscle.     

The recruitment of different compartments within a muscle depends on the mechanics of the movement

Muscles are commonly assumed to have uniform activations across their bellies. Yet animal studies have shown that different regions across a muscle can vary in their architecture, fibre type, levels of activation and the transfer of forces to the bones and tendons. The purpose of this study was to test whether regional variations in activity occurred across the soleus, medial gastrocnemius and lateral gastrocnemius in man, and whether these regional variations changed with altered mechanical demands on the limb. Arrays of surface electrodes were placed over these muscles and the electromyograms (EMG) measured for a range of cycling tasks where the resistance and pedal velocity was independently altered. Significant variations in the magnitude and timing of the EMG occurred across these muscles, which were most pronounced in the gastrocnemii and occurred in both the proximodistal and mediolateral directions. The patterns of variation across the muscles changed in response to the altered mechanical demands during the cycling. It is likely that the muscle fascicles in the gastrocnemii contribute varied mechanical functions to the contractions that depend on both their location within the muscle belly and on the mechanical requirements of the movement.     

Ghosts of the past I: some muscles and fasciae in the head domain

Humans alone among primates lack a superficial head of the temporalis muscle, although a complete superficial muscle is present in 1% of humans and an incomplete one in 8%. Yet the temporal fascia of normal humans contains all the fascial sheets associated with that head even though it is absent. The implication is that humans have lost the superficial temporal muscle, that this is evident from the retention of the fascial sheets, and that the muscular variations represent situations where the muscle has persisted to some degree. Molecular factors in the head domain that are responsible for the development of the muscles of mastication (myosin heavy chain 16) are likewise different in humans than in all non-human species and seem to be responsible for the reduction of those muscles in humans. Could the loss of the superficial portion of the temporalis muscle be a component of this reduction? Could the uncommon muscular variations result from some slight persistence of the prior molecular situation? Could the persistence of the fascial sheets, even when the muscle is absent, be because the molecular factors responsible for connective tissues are not the same as those responsible for muscles? How much of all this can be visualised in the fossil record? Skeletal dimensions of the temporal fossa, partly related to the temporal muscle size, imply that it may be possible to determine in which fossils temporal muscle reduction has occurred. Likewise, surface features of the bone in modern humans without a superficial muscular component but with a strong complex fibrous element suggest that it might be possible to determine, in any fossil in which the surface preservation is good enough, how far back this situation may have persisted. It is already known that myosin heavy chain molecular dating suggests that the muscle reduction may have occurred about 2.4 million years ago.     

Parasternal and external intercostal responses to various respiratory maneuvers.

Recent studies suggest that the external intercostal (EI) muscles of the upper rib cage, like the parasternals (PA), play an important ventilatory role, even during eupneic breathing. The purpose of the present study was to further assess the ventilatory role of the EI muscles by determining their response to various static and dynamic respiratory maneuvers and comparing them with the better-studied PA muscles. Applied interventions included 1) passive inflation and deflation, 2) abdominal compression, 3) progressive hypercapnia, and 4) response to bilateral cervical phrenicotomy. Studies were performed in 11 mongrel dogs. Electromyographic (EMG) activities were monitored via bipolar stainless steel electrodes. Muscle length (percentage of resting length) was monitored with piezoelectric crystals. With passive rib cage inflation produced either with a volume syringe or abdominal compression, each muscle shortened; with passive deflation, each muscle lengthened. During eupneic breathing, each muscle was electrically active and shortened to a similar degree. In response to progressive hypercapnia, peak EMG of each intercostal muscle increased linearly and to a similar extent. Inspiratory shortening also increased progressively with increasing PCO2, but in a curvilinear fashion with no significant differences in response among intercostal muscles. In response to phrenicotomy, the EMG and degree of inspiratory shortening of each intercostal muscle increased significantly. Again, the response among intercostal muscles was not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)     

Experimental investigations on hypokinesis of skeletal muscles with different functions, III. Changes in protein fractions of subcellular components

Changes occurring in the protein fractions of rabbits' immobilized skeletal muscles with different functions were studied. Disuse of the muscles resulted in a gradual reduction in the contractile proteins. The specific proteins of the tonic muscle (m. soleus) were degraded to a greater extent than those of the tetanic (white) muscles (m. gastrocnemius). Parallel with the decrease in the structural proteins the sarcoplasmic protein exhibited a relative increase. The tonic muscles underwent greater damage than the tetanic muscles, indicating that the dedifferentiation was more marked in the tonic muscle. The results are explained by the biological importance of the function and activity of the cell: disuse leads to changes in the physiological and biochemical characteristics of the muscle, and to dedifferentiation of the cells.     

Reliability of leg muscle electromyography in vertical jumping

In this study we aimed to determine the reliability of the surface electromyography (EMG) of leg muscles during vertical jumping between two test sessions, held 2 weeks apart. Fifteen females performed three maximal vertical jumps with countermovement. The displacement of the body centre of mass (BCM), duration of propulsion phase (time), range of motion (ROM) and angular velocity of the knee and surface EMG of four leg muscles (rectus femoris, vastus medialis. biceps femoris and gastrocnemius) were recorded during the jumps. All variables were analysed throughout the propulsion and mid-propulsion phases. Intraclass correlation coefficients (ICC) for the rectus femoris, vastus medialis, biceps femoris and gastrocnemius were calculated to be 0.88, 0.70, 0.24 and 0.01, respectively. BCM, ROM and time values all indicated ICC values greater than 0.90, and the mean knee angular velocity was slightly lower, at 0.75. ICCs between displacement of the BCM and integrated EMG (IEMG) of the muscles studied were less than 0.50. The angular velocity of the knee did not correlate well with muscle activity. Factors that may have affected reliability were variations in the position of electrode replacement, skin resistance, cross-talk between muscles and jump mechanics. The results of this study suggest that while kinematic variables are reproducible over successive vertical jumps, the degree of repeatability of an IEMG signal is dependent upon the muscle studied.     

Pterygoideus muscles and other jaw adductors in amphibians and reptiles

The general structural patterns of jaw adductors in all orders of extant amphibians and reptiles, and also polypteriforms, crossopterygians (coelacanth), and dipnoans, are compared. The pterygoideus muscles probably developed independently and in parallel in gymnophions and amniotes from the profound pseudotemporalis muscle, which was present in their fishlike ancestors and was retained in caudate and anuran amphibians. The functional causes of the development of pterygoideus muscles in the majority of tetrapod groups and the absence of these muscles in Urodela and Anura are discussed. The anterior pterygoideus muscle of crocodiles is homologous to the pseudotemporalis (superficial) muscle of other reptiles.     

Paradoxical absence of M lines and downregulation of creatine kinase in mouse extraocular muscle.

The M lines are structural landmarks in striated muscles, necessary for sarcomeric stability and as anchoring sites for the M isoform of creatine kinase (CK-M). These structures, especially prominent in fast skeletal muscles, are missing in rodent extraocular muscle, a particularly fast and active muscle group. In this study, we tested the hypotheses that 1). myomesin and M protein (cytoskeletal components of the M lines) and CK-M are downregulated in mouse extraocular muscle compared with the leg muscles, gastrocnemius and soleus; and 2). the expression of other cytosolic and mitochondrial CK isoforms is correspondingly increased. As expected, mouse extraocular muscles expressed lower levels of myomesin, M protein, and CK-M mRNA than the leg muscles. Immunocytochemically, myomesin and M protein were not detected in the banding pattern typically seen in other skeletal muscles. Surprisingly, message abundance for the other known CK isoforms was also lower in the extraocular muscles. Moreover, total CK activity was significantly decreased compared with that in the leg muscles. Based on these data, we reject our second hypothesis and propose that other energy-buffering systems may be more important in the extraocular muscles. The downregulation of major structural and metabolic elements and relative overexpression of two adenylate kinase isoforms suggest that the extraocular muscle group copes with its functional requirements by using strategies not seen in typical skeletal muscles.     

Structural and functional remodeling of skeletal muscle microvasculature is induced by simulated microgravity

Hindlimb unloading of rats results in a diminished ability of skeletal muscle arterioles to constrict in vitro and elevate vascular resistance in vivo. The purpose of the present study was to determine whether alterations in the mechanical environment (i.e., reduced fluid pressure and blood flow) of the vasculature in hindlimb skeletal muscles from 2-wk hindlimb-unloaded (HU) rats induces a structural remodeling of arterial microvessels that may account for these observations. Transverse cross sections were used to determine media cross-sectional area (CSA), wall thickness, outer perimeter, number of media nuclei, and vessel luminal diameter of feed arteries and first-order (1A) arterioles from soleus and the superficial portion of gastrocnemius muscles. Endothelium-dependent dilation (ACh) was also determined. Media CSA of resistance arteries was diminished by hindlimb unloading as a result of decreased media thickness (gastrocnemius muscle) or reduced vessel diameter (soleus muscle). ACh-induced dilation was diminished by 2 wk of hindlimb unloading in soleus 1A arterioles, but not in gastrocnemius 1A arterioles. These results indicate that structural remodeling and functional adaptations of the arterial microvasculature occur in skeletal muscles of the HU rat; the data suggest that these alterations may be induced by reductions in transmural pressure (gastrocnemius muscle) and wall shear stress (soleus muscle).     

Morphological and Functional Questions on the Growth and Plasticity of Mammalian and Avian Jaw Muscles

SYNOPSIS: Growth studies of mammalian jaw muscles and studiesdetermining the degree of plasticity of these muscles are few.There are questions concerning the degrees and types of morphologicaland physiological change occurring in these muscles during normalgrowth and the ability of external forces to modify this growthprocess. There are also questions on the effects of sensoryloss on muscle growth and on changes in the motor system asthese muscles change. In this report, questions are proposedand hypotheses presented that deal with these areas relativeto the jaw muscles. It is suggested that (1) changes in themorphology and function of jaw muscles during growth vary regionallyand are related to the action of the muscle and the loadingforces imposed; (2) the degree of muscle plasticity varies regionallyand varies depending on the type of loading forces and age ofthe animal; (3) loss of sensory input during the growth of thejaw muscles would produce marked changes in the histochemicalprofile, the distribution of motor neurons, and the activitypattern of these muscles; and (4) organization of the trigeminalmotor nucleus changes as the jaw muscles grow and may also changein response to sensory loss or application of different typesof loading forces. In addition, possible approaches to thesequestions are discussed.     

Calcineurin-A alpha activation enhances the structure and function of regenerating muscles after myotoxic injury

Calcineurin signaling is essential for successful muscle regeneration. Although calcineurin inhibition compromises muscle repair, it is not known whether calcineurin activation can enhance muscle repair after injury. Tibialis anterior (TA) muscles from adult wild-type (WT) and transgenic mice overexpressing the constitutively active calcineurin-A alpha transgene under the control of the mitochondrial creatine kinase promoter (MCK-CnA alpha*) were injected with the myotoxic snake venom Notexin to destroy all muscle fibers. The TA muscle of the contralateral limb served as the uninjured control. Muscle structure was assessed at 5 and 9 days postinjury, and muscle function was tested in situ at 9 days postinjury. Calcineurin stimulation enhanced muscle regeneration and altered levels of myoregulatory factors (MRFs). Recovery of myofiber size and force-producing capacity was hastened in injured muscles of MCK-CnA alpha* mice compared with control. Myogenin levels were greater 5 days postinjury and myocyte enhancer factor 2a (MEF2a) expression was greater 9 days postinjury in muscles of MCK-CnA alpha* mice compared with WT mice. Higher MEF2a expression in regenerating muscles of MCK-CnA alpha* mice 9 days postinjury may be related to an increase of slow fiber genes. Calcineurin activation in uninjured and injured TA muscles slowed muscle contractile properties, reduced fatigability, and enhanced force recovery after 4 min of intermittent maximal stimulation. Therefore, calcineurin activation can confer structural and functional benefits to regenerating skeletal muscles, which may be mediated in part by differential expression of MRFs.     

Nature of the changes in the activity of water-soluble enzymes as affected by noxious agents acting on the muscles. I. A study of the extractability of phosphofructokinase from intact and altered muscles

Binding of phosphofructokinase (PPK) in intact and thermally altered (15 minutes at 38 degrees C) skeletal muscles of frogs (Rana temporaria) the the extractability of PPK from muscles was studied. PPK activity in actomyosin was also studied. Inhibiting effect of electrolytes (KCl, NaCl, CaCl2, MgCl2) on PPK in muscle extract does not allow to use them for the decision of the question of the interprotein interactions of PPK. 5 mM Na2-EDTA extracts additional PPK from homogenates of intact and altered muscles in comparison with PPK extracted in the media without Na2-EDTA (for intact muscles and altered muscles--509 and 729%). Under alteration of muscle, the binding of PPK increases. Among the structural components of muscle which bind PPK, proteins of actomyosin complex have been found.     

Reproducibility of eight lower limb muscles activity level in the course of an incremental pedaling exercise.

Despite the wide use of surface electromyography (EMG) recorded during dynamic exercises, the reproducibility of EMG variables has not been fully established in a course of a dynamic leg exercise. The aim of this study was to investigate the reproducibility of eight lower limb muscles activity level during a pedaling exercise performed until exhaustion. Eight male were tested on two days held three days apart. Surface EMG was recorded from vastus lateralis, rectus femoris (RF), vastus medialis, semimembranosus, biceps femoris, gastrocnemius lateral, gastrocnemius medianus and tibialis anterior during incremental exercise test. The root mean square, an index of global EMG activity, was averaged every five crank revolutions (corresponding to about 3 s at 85 rpm) throughout the tests. Despite inter-subjects variations, we showed a high reproducibility of the activity level of lower limb muscles during a progressive pedaling exercise performed until exhaustion. However, RF muscle seemed to be the less reproducible of the eight muscles investigated during incremental pedaling exercise. These results suggest that each subject adopt a personal muscle activation strategy in a course of an incremental cycling exercise but fatigue phenomenon can induce some variations in the most fatigable muscles (RF).     

Skeletal muscle HIF-1alpha expression is dependent on muscle fiber type

Oxygen homeostasis is an essential regulation system for cell energy production and survival. The oxygen-sensitive subunit alpha of the hypoxia inducible factor-1 (HIF-1) complex is a key protein of this system. In this work, we analyzed mouse and rat HIF-1alpha protein and mRNA expression in parallel to energetic metabolism variations within skeletal muscle. Two physiological situations were studied using HIF-1alpha-specific Western blotting and semiquantitative RT-PCR. First, we compared HIF-1alpha expression between the predominantly oxidative soleus muscle and three predominantly glycolytic muscles. Second, HIF-1alpha expression was assessed in an energy metabolism switch model that was based on muscle disuse. These two in vivo situations were compared with the in vitro HIF-1alpha induction by CoCl(2) treatment on C(2)C(12) mouse muscle cells. HIF-1alpha mRNA and protein levels were found to be constitutively higher in the more glycolytic muscles compared with the more oxidative muscles. Our results gave rise to the hypothesis that the oxygen homeostasis regulation system depends on the fiber type.     

Combined kinematic and electromyographic analyses of proleg function during crawling by the caterpillar Manduca sexta

The planta retractor muscles in the prolegs of Manduca sexta caterpillars are a frequently-used model system for investigating a number of problems in neurobiology. We have combined kinematic and electromyogram analysis of proleg movements during crawling to examine the roles of these muscles during normal behavior. We found that retractor muscle activity is highly stereotyped, and that the primary function of these muscles is to disengage the crochets at the tip of the proleg for the swing phase of crawling. The duration of activity of the muscles was tightly coupled to the phasing of crawling behavior. The stepping patterns of animals changed to accommodate variations in the substrate, but the relative timing of retractor muscle activity was unaffected. There were no clear correlations between the various properties of motoneuronal input to the muscle (duration of activity, number of spikes, peak frequency of spikes) and the resulting muscle length change. Perhaps because it functions partially as a hydrostat, this may represent a neuromuscular system in which a significant part of the control algorithm is embedded in its morphology.     

Sarcomere length-joint angle relationships of seven frog hindlimb muscles.

The sarcomere length-joint angle relationship was measured in 7 different muscle-joint complexes (n = 43 muscles) of the frog hindlimb (Rana pipiens). Muscles studied included the cruralis, iliacus internus, gastrocnemius, gluteus magnus, gracilis major, semimembranosus and the semitendinosus. Muscle-joint complexes were mounted in a jig and submerged in chilled Ringer's solution. Joints were rotated throughout their range of motion, while sarcomere length was measured by laser diffraction. Muscles were then formalin fixed and architectural properties determined by microdissection of individual muscle fibers. Sarcomere length change per degree of joint rotation (dLs/d theta) ranged from a low of 3.7 nm/degree for the cruralis muscle acting at the knee to a high of 12.5 nm/degree for the semitendinosus muscle acting at the hip. Values for dLs/d theta were significantly different between all muscles (p < 0.001), and dLs/d theta values for muscles acting at the hip were significantly greater than those for muscles acting at the knee (p < 0.005). dLs/d theta was negatively correlated with fiber length, suggesting a balance between fiber length and moment arm in most muscle-joint systems. However, many exceptions to this generalization were noted. These data suggest that different muscle-joint systems are 'designed' for differential contribution of muscle force production to the joint torque profile. The low variability of these data also suggests that sarcomere number is tightly regulated in these muscle-joint systems but not simply as a result of the total in vivo muscle excursion.     

Automatic segmentation of surface EMG images: Improving the estimation of neuromuscular activity

Surface electromyograms (EMGs) recorded with a couple of electrodes are meant to comprise representative information of the whole muscle activation. Nonetheless, regional variations in neuromuscular activity seem to occur in numerous conditions, from standing to passive muscle stretching. In this study, we show how local activation of skeletal muscles can be automatically tracked from EMGs acquired with a bi-dimensional grid of surface electrodes (a grid of 8 rows and 15 columns was used). Grayscale images were created from simulated and experimental EMGs, filtered and segmented into clusters of activity with the watershed algorithm. The number of electrodes on each cluster and the mean level of neuromuscular activity were used to assess the accuracy of the segmentation of simulated signals. Regardless of the noise level, thickness of fat tissue and acquisition configuration (monopolar or single differential), the segmentation accuracy was above 60%. Accuracy values peaked close to 95% when pixels with intensity below ～70% of maximal EMG amplitude in each segmented cluster were excluded. When simulating opposite variations in the activity of two adjacent muscles, watershed segmentation produced clusters of activity consistently centered on each simulated portion of active muscle and with mean amplitude close to the simulated value. Finally, the segmentation algorithm was used to track spatial variations in the activity, within and between medial and lateral gastrocnemius muscles, during isometric plantar flexion contraction and in quiet standing position. In both cases, the regionalization of neuromuscular activity occurred and was consistently identified with the segmentation method.