Comparative histology, histochemistry and innervation of striated muscle fibers of the greater pectoralis muscle and supracoracoid muscle in birds

The morphology of the pectoralis major muscle and the supracoracoideus muscle was compared in three Galliformes and five Passeriformes, in relation to partial behavioral characteristics. In all species, two fibres types are observed. The frequencies of these fibres are different, especially between Galliformes and Passeriformes, but also between Coturnix and other Galliformes. All fibres show phasic innervation. A relation of the extent between synaptic gutters and muscle activity is suggested.     

Molecular forms of acetylcholinesterase in the slow muscle and the fast muscle of the chicken]

Five molecular forms of AChE are present in the slow (ALD) and twitch (PLD) muscles of the chick. These forms have 4 S, 7 S, 11 S, 15 S and 20 S sedimentation coefficient in sucrose gradient. The heaviest forms, the 20 S and 15 S of AChE are absent in uninnervated muscles and present in innervated muscles. In innervated muscles, the 20 S and 15 S AChE are present in both nerve-free segments and end-plates zones. The 20 S and 15 S which are not specifically associated with the end-plate zones in the chick could be considered as a biochemical "marker" of neuromuscular interactions.     

Postsynaptic currents in phasic and tonic muscle fibers of the rat extraocular muscle

Focal extracellular recordings were made of postjunctional currents produced at synapses of the inferior rectus eye muscle fibers by the spontaneous release of quanta of transmitter. These consisted of miniature endplate currents, or MEPC, in phasic fibers and miniature postjunctional currents, or MPJC, in tonic fibers. Open time of ionic channels (_chan) was also registered. In tonic fibers, MPJC lasted considerably longer than MEPC did in phasic fibers: rising time, decay time, and _chan in the former measured respectively 2.5, 4–5, and 2.2 times higher than in the latter. Acetylcholinesterace (AChE) inhibition produced a much greater (4.4-fold extension of current decay in phasic than in tonic fibers, where a 1.8-fold increase was seen, thereby reducing the gap between the decay time of currents in these fibers to a difference of 1.6 times. The more protracted decay of MPJC in tonic fibers compared with MEPC in phasic fibers is determined by the lower functional activity of AChE as well as the higher value of _chan. Duration of MEPC and magnitude of _chan in the "slow" phasic fibers of rat skeletal muscles fell well below the same parameters measured in the tonic fibers of the ocular muscle.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 120–129, January–February, 1987.     

Colocalization of muscle FBPase and muscle aldolase on both sides of the Z-line

Previously we have reported that in vitro muscle aldolase binds to muscle FBPase [Biochem. Biophys. Res. Commun. 275 (2000) 611-616] which results in the changes of regulatory properties of the latter enzyme. In the present paper, the evidence that aldolase binds to FBPase in living cell is presented. The colocalization experiment, in which aldolase was diffused into skinned fibres that had been pre-incubated with FBPase, has shown that aldolase in the presence of FBPase binds predominantly to the Z-line. The existence of a triple aldolase-FBPase-alpha-actinin complex was confirmed through a real-time interaction analysis using the BIAcore biosensor. The colocalization of FBPase and aldolase on alpha-actinin of the Z-line indicates the existence of glyconeogenic metabolon in vertebrates' myocytes.     

Role of nerve and muscle factors in the development of rat muscle spindles

The soleus muscles of fetal rats were examined by electron microscopy to determine whether the early differentiation of muscle spindles is dependent upon sensory innervation, motor innervation, or both. Simple unencapsulated afferent-muscle contacts were observed on the primary myotubes at 17 and 18 days of gestation. Spindles, encapsulations of muscle fibers innervated by afferents, could be recognized early on day 18 of gestation. The full complement of spindles in the soleus muscle was present at day 19, in the region of the neuromuscular hilum. More afferents innervated spindles at days 18 and 19 of gestation than at subsequent developmental stages, or in adult rats; hence, competition for available myotubes may exist among afferents early in development. Some of the myotubes that gave rise to the first intrafusal (bag2) fiber had been innervated by skeletomotor (alpha) axons prior to their incorporation into spindles. However, encapsulated intrafusal fibers received no motor innervation until fusimotor (gamma) axons innervated spindles 3 days after the arrival of afferents and formation of spindles, at day 20. The second (bag1) intrafusal fiber was already formed when gamma axons arrived. Thus, the assembly of bag1 and bag2 intrafusal fibers occurs in the presence of sensory but not gamma motor innervation. However, transient innervation of future bag2 fibers by alpha axons suggests that both sensory and alpha motor neurons may influence the initial stages of bag2 fiber assembly. The confinement of nascent spindles to a localized region of the developing muscle and the limited number of spindles in developing muscles in spite of an abundance of afferents raise the possibility that afferents interact with a special population of undifferentiated myotubes to form intrafusal fibers.     

Columellar muscle of neogastropods: muscle attachment and the function of columellar folds

Malacologists often assume that ornamentation on snail shells is functional, and therefore adaptive. I conducted the first comprehensive test of the widely accepted hypothesis that columellar folds, a type of internal ornamentation, enhance the performance of the columellar muscle, which attaches the snail to its shell. Careful dissections of live, non-relaxed specimens reveal that the physical attachment between the columellar muscle and the columella is not restricted to a small, circular patch located deep within the shell. Instead, the attachment is long and narrow, extending approximately a full whorl along the length of the columella. I developed a novel technique for preparing three-dimensional reconstructions from photographs documenting the dissections. These reconstructions were then used to measure four parameters that describe the muscle: (1) the surface area of the physical attachment between the muscle and columella, (2) the total contact area between the muscle and the columella, (3) the depth of attachment, and (4) the length of attachment. None of these parameters differed significantly between species with and without folds. In light of the biomechanics of muscular hydrostats, values of the first parameter indicate that columellar folds probably do not guide the columellar muscle as the animal moves in and out of its shell. Values of the other parameters indicate that columellar folds neither increase an animal's ability to maneuver its shell nor facilitate deeper withdrawal. These results, and the fact that folds have evolved convergently several times, might indicate that folds are an easily evolvable solution to many functional problems, none of which are currently understood.     

Contralateral muscle activity and fatigue in the human first dorsal interosseous muscle.

During effortful unilateral contractions, muscle activation is not limited to the target muscles but activity is also observed in contralateral muscles. The amount of this associated activity is depressed in a fatigued muscle, even after correction for fatigue-related changes in maximal force. In the present experiments, we aimed to compare fatigue-related changes in associated activity vs. parameters that are used as markers for changes in central nervous system (CNS) excitability. Subjects performed brief maximal voluntary contractions (MVCs) with the index finger in abduction direction before and after fatiguing protocols. We followed changes in MVCs, associated activity, motor-evoked potentials (MEP; transcranial magnetic stimulation), maximal compound muscle potentials (M waves), and superimposed twitches (double pulse) for 20 min after the fatiguing protocols. During the fatiguing protocols, associated activity increased in contralateral muscles, whereas afterwards the associated force was reduced in the fatigued muscle. This force reduction was significantly larger than the decline in MVC. However, associated activity (force and electromyography) remained depressed for only 5-10 min, whereas the MVCs stayed depressed for over 20 min. These decreases were accompanied by a reduction in MEP, MVC electromyography activity, and voluntary activation in the fatigued muscle. According to these latter markers, the decrease in CNS motor excitability lasted much longer than the depression in associated activity. Differential effects of fatigue on (associated) submaximal vs. maximal contractions might contribute to these differences in postfatigue behavior. However, we cannot exclude differences in processes that are specific to either voluntary or to associated contractions.     

Correlation between the distribution of smooth muscle or non muscle myosins and alpha-smooth muscle actin in normal and pathological soft tissues

The distribution of smooth muscle (SM) and non muscle myosins was compared with that of alpha-SM actin in various normal and pathological tissues and in cultured cells by means of indirect immunofluorescence using a monoclonal antibody specific for alpha-SM actin [anti-alpha sm-1, Skalli et al., 1986b] and two polyclonal antibodies raised against bovine aortic myosin (ABAM) and human platelet myosin (AHPM), respectively. In normal tissues ABAM stained vascular and parenchymal smooth muscle cells (SMC), myoepithelial cells and myoid cells of the testis in a pattern similar to that reported by other authors with antisera raised against non vascular SM myosin. Cells stained with ABAM were always positive for anti-alpha sm-1. In human and experimental atheromatous plaques, most cells were positive for AHPM; a variable proportion was also stained for ABAM plus anti-alpha sm-1. Myofibroblasts from rat granulation tissue, Dupuytren's nodule and stroma from breast carcinoma were constantly positive for AHPM and negative for ABAM; however, myofibroblasts from Dupuytren's nodule and breast carcinoma were anti-alpha sm-1 positive. Early primary cultures of rat aortic SMC were positive for ABAM and anti-alpha sm-1 and became negative for ABAM and positive for AHPM after a few days in culture. They remained positive for AHPM and anti-alpha sm-1 after passages; the staining of AHPM and anti-alpha sm-1 appeared to be colocalized along the same stress fibers. These results may be relevant for the understanding of SMC function and adaptation, and show that in non malignant SMC proliferation, alpha-SM actin represents a more general marker of SM origin than SM myosin.     

Smoking impairs muscle protein synthesis and increases the expression of myostatin and MAFbx in muscle

Smoking causes multiple organ dysfunction. The effect of smoking on skeletal muscle protein metabolism is unknown. We hypothesized that the rate of skeletal muscle protein synthesis is depressed in smokers compared with non-smokers. We studied eight smokers (> or =20 cigarettes/day for > or =20 years) and eight non-smokers matched for sex (4 men and 4 women per group), age (65 +/- 3 and 63 +/- 3 yr, respectively; means +/- SEM) and body mass index (25.9 +/- 0.9 and 25.1 +/- 1.2 kg/m(2), respectively). Each subject underwent an intravenous infusion of stable isotope-labeled leucine in conjunction with blood and muscle tissue sampling to measure the mixed muscle protein fractional synthesis rate (FSR) and whole body leucine rate of appearance (Ra) in plasma (an index of whole body proteolysis), the expression of genes involved in the regulation of muscle mass (myostatin, a muscle growth inhibitor, and MAFBx and MuRF-1, which encode E3 ubiquitin ligases in the proteasome proteolytic pathway) and that for the inflammatory cytokine TNF-alpha in muscle, and the concentration of inflammatory markers in plasma (C-reactive protein, TNF-alpha, interleukin-6) which are associated with muscle wasting in other conditions. There were no differences between nonsmokers and smokers in plasma leucine concentration, leucine rate of appearance, and plasma concentrations of inflammatory markers, or TNF-alpha mRNA in muscle, but muscle protein FSR was much less (0.037 +/- 0.005 vs. 0.059 +/- 0.005%/h, respectively, P = 0.004), and myostatin and MAFBx (but not MuRF-1) expression were much greater (by approximately 33 and 45%, respectivley, P < 0.05) in the muscle of smokers than of nonsmokers. We conclude that smoking impairs the muscle protein synthesis process and increases the expression of genes associated with impaired muscle maintenance; smoking therefore likely increases the risk of sarcopenia.     

Relationship between muscle fiber types and sizes and muscle architectural properties in the mouse hindlimb

Skeletal muscle fiber and architectural properties both contribute to the functional behavior of a muscle. This study uses discriminant analysis and mathematical modeling to identify the structurally and functionally significant properties. The architectural properties of fiber length, muscle length, and pennation angle are found to be the most structurally significant parameters, whereas fiber length, muscle length, and fiber type distribution are found to be most functionally determining. Architectural speed and fiber type do not appear to be complimentary (i.e., the architectural determinant of sspeed, fiber length, is not associated with fibers of high intrinsic velocity). However, there does seem to be a synergistic relation between the two property classes and force production. Muscles with large physiological cross sectional areas (PCSAs) tend to contain a greater proportion of larger, faster fibers. Structurally or morphologically significant parameters are not always found to have a large functional effect. Pennation angle, though one of the most structurally significant variables, was found to have very little functional effect. © 1994 Wiley-Liss, Inc.     

Mechanomyographic and electromyographic responses of the vastus medialis muscle during isometric and concentric muscle actions

The purpose of this study was to examine the patterns for the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) vs. torque relationships during submaximal to maximal isometric and isokinetic muscle actions. Seven men (mean +/- SD age, 22.4 +/- 1.3 years) volunteered to perform isometric and concentric isokinetic leg extension muscle actions at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex II dynamometer. A piezoelectric MMG recording sensor was placed between bipolar surface EMG electrodes on the vastus medialis. Polynomial regression and separate 1-way repeated-measures analysis of variance were used to analyze the EMG amplitude, MMG amplitude, EMG MPF, and MMG MPF data for the isometric and isokinetic muscle actions. For the isometric muscle actions, EMG amplitude (R(2) = 0.999) and MMG MPF (R(2) = 0.946) increased to MVC, mean MMG amplitude increased to 60% MVC and then plateaued, and mean EMG MPF did not change (p > 0.05) across torque levels. For the isokinetic muscle actions, EMG amplitude (R(2) = 0.988) and MMG amplitude (R(2) = 0.933) increased to PT, but there were no significant mean changes with torque for EMG MPF or MMG MPF. The different torque-related responses for EMG and MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric vs. dynamic muscle actions. These results support the findings of others and suggest that isometric torque production was modulated by a combination of recruitment and firing rate, whereas dynamic torque production was modulated primarily through recruitment.     

Regeneration fo the completely excised gastrocnemius muscle in the frog and rat from minced muscle fragments

In 85 frogs and 29 rats, the entire gastrocnemius muscle was removed. After removal of as much connective tissue as possible, about two-thirds of the remaining muscle was finely minced with a scissors. These minced fragments were orthotopically re-implanted, and the overlying skin was sutured. As the implanted muscle fragments degenerate, new muscle fibers appears in the regenerate. The proportion of connective tissue to muscle is usually greater than normal especially in the frog. Grossly, normal relationships are established with the cut ends of the Achilles and proximal tendons, as well as with the blood vessels and nerves. The total diameter of the regenerated muscle is almost always less than half of that seen in normal muscles. Regeneration of muscle is much more extensive in the rat than in the frog, and it occurs almost twice as rapidly. The histology of the regenerative process is described for both the frog and the rat.