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The formation of synapses in amphibian striated muscle during development.

1. A study has been made of the formation of synapses in developing reinnervated and cross-reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques. 2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon. 3. The short iliofibularis and sartorius myofibres of young tadpoles (800 mum long) possessed only a single synapse and the iliofibularis myofibres did not receive any further innervation during development. However the sartorius myofibres received further transient innervation on the new muscle laid down during development at the fast growing pelvic insertion, until the distance between the original synapse formed on the myofibres and the synapse at the pelvic end of the muscle was about 12 mm. 4. During development synapses possessed either skewed, multimodal, or unimodal m.e.p.p. amplitude-frequency distributions; the intervals between m.e.p.p.s. were not distributed randomly according to a Poisson process, as m.e.p.p.s. of similar amplitudes tended to be separated by very short intervals; the unit-size e.p.p. had a similar amplitude-frequency distribution as the m.e.p.p.s. if these had a unimodal distribution. 5. Reinnervation or cross-reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs. 6. These observations on synapse formation in amphibia are consistent with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross-reinnervation of adult muscles this refractory property constrains synapse formation to these sites.

Amphibians↗

Temporal distributions of red cell supply rate to individual capillaries of resting skeletal muscle, in frog and rat.

Microvascular red cell (RBC) supply in resting skeletal muscle fluctuates with time and varies from capillary to capillary. Our aim was to quantitate this heterogeneity in two species (frog, rat) with very different oxygen requirements. Video recordings were made of RBC flow in capillaries associated with superficial fibers of frog sartorius and rat gracilis muscles, for periods of 2-10 min. RBC supply rate (cell/s) to individual capillaries was computed as the product of RBC 'content' (measured as lineal density, cells/mm, by a video-densitometric method) and RBC velocity (mm/s, measured by a spatial correlation technique). The videotapes were analyzed at rates of 6 to 15 samples per second. Regression analysis of the mean data showed little or no correlation between RBC content and RBC velocity (r2: frog 0.095, rat 0.002), both parameters contributing equally to variations in RBC supply rate. Temporal distributions of the three supply parameters demonstrate (1) the wide range of values present within each capillary, and (2) the symmetry of the distributions at high mean values versus a pronounced skewness as mean values approached zero. The wide range of mean values of each parameter, found in both species, suggests considerable 'spatial' heterogeneity of RBC supply among capillaries in resting muscle. Temporal heterogeneity of RBC supply rate to individual capillaries increased markedly as either velocity or content (or both) approached zero (overall mean coefficient of variation: frog, 62%; rat, 100%). Both species show remarkably similar rates of convective transport of RBCs per capillary in resting muscle (e.g. mean supply rates 3.2 and 6.2 RBCs/s in frog and rat, respectively).

Animals↗

[Mechanism of potentiation of contraction in glycerol-treated muscles].

The glycerol was shown to lead to a considerable though transient increase in the contractile amplitude of the m. sartorius. Prolonged incubation of the muscle in the Ringer and Ca-free solutions in presence of glycerol led to a decrease in the response following potentiation. The potentiation due to glycerol seems to be caused by Ca2+ release which, in its turn, is due to the glycerol effect on membranes of SR and T-systems.

Animals↗

Effects of toxin II from the sea anemone Anemonia sulcata on contractile and electrical responses of frog skeletal muscle fibres.

The effects of Anemonia sulcata toxin II (ATX-II) were studied on mechanical and electrical activities of frog muscle fibres isolated from semitendinosus or tibialis anterior muscles of Rana temporaria (2.8-7.7 degrees C). In concentrations ranging between 7.7 and 100 microM, ATX-II greatly potentiated the isometric twitch of single muscle fibres in a time-dependent manner. Increase in twitch amplitude by ATX-II was associated with an increase in time to peak tension and time from peak tension to half relaxation. ATX-II caused no change in maximum force production during fused tetanus, but the tension was maintained for several seconds after the cessation of stimulation. Such long tetanic contractions were also obtained in low-Na Ringer solution, but their duration was somewhat shorter. No specific action of ATX-II was detected on relaxation kinetics during a tetanus. The twitch potentiating effect of ATX-II was markedly increased by 3,4-diaminopyridine. Action potentials recorded from single muscle fibres in the presence of ATX-II showed a delayed onset of repolarization with a reduced rate of fall. In addition, ATX-II caused repetitive spontaneous firing of action potentials after the cessation of tetanic stimulation. ATX-II (3.3 - 10 microM) also increased action potential duration by reducing the rate of repolarization in surface fibres of formamide-treated sartorius or cutaneous pectoris muscles (20 degrees C) stimulated indirectly or directly. The potentiation of twitch force and the prolongation of contractions caused by tetanic stimulation can be attributed to the membrane action of ATX-II, which leads to prolongation of action potentials, to repetitive muscle firing and to the appearance of plateau potentials.

4-Aminopyridine↗

Characteristics of membrane channels induced by acetylcholine at frog muscle-tendon junctions.

The membrane at the tendinous ends of frog muscle fibres has acetylcholine (ACh) receptors that are blocked by alpha-bungarotoxin. The properties of ACh-activated channels in the myotendinous region were investigated by noise analysis. These channels displayed the same characteristics in normal, denervated and reinnervated muscles. The mean lifetime and conductance of ACh-induced channels at the myotendinous junction resembled those of channels at the normal neuromuscular junction. Both channels opened with a lifetime shorter than that of extrajunctional receptors. Channels of short lifetime could be detected at distances of several hundred micrometres from the tendon junction. The similarity of ACh-activated channels at neuromuscular and myotendon junctions was found both in the fast, 'singly' innervated sartorius and cutaneous pectoris muscle and in the intermediate, multiply innervated submaxillaris muscle.

Acetylcholine↗

[Effect of veratrine on the hyoglossus and the sartorius of frogs].

We have investigated how veratrine does act on the contraction elicited by the motor nerve of a quick muscle on one side, the frog's sartorius, and of a slow muscle on the other side, the frog's hyoglossus. We have found that the contraction of the slow muscle is increased and lengthened and that its graphic has the shape of the veratrine intoxication, whereas the contraction of the quick muscle does not show the slightest alteration.

Animals↗

Chemical Energetics of contraction in mammalian smooth muscle.

Measurements of high-energy phosphate utilization during isometric tetanic contractions were made on a rabbit taenia coli preparation that had been treated so that respiration and glycolysis were blocked without altering the mechanical response to the muscle. At 18 C the first sign of high-energy phosphate usage after electrical stimulation was a net breakdown of ATP with a subsequent net resynthesis when the rate of phosphocreatine breakdown was high. The average rate of chemical energy usage was more than four times as high during the period of initial force development compared to that during maximum force maintenance. This initial high rate of energy usage was not due only to the internal work done against the series elasticity during force development. Comparison of energetics and mechanics data for the rabbit taenia coli and frog sartorius showed that smooth muscle was 100-fold more economical in maintaining isometric force and probably had a cross-bridge cycle time that was about 150-fold slower. The rate of energy usage during relaxation from an isometric tetanus in smooth muscle was very low, and force was exerted with a lower expenditure of energy during relaxation than during maximum force maintenance. Phosphorylation of the 20,000-dalton light chain of myosin occurred to the extent of 32% during a maximally activated isometric tetanus and was not proportional to the rate of energy usage during different stages of the tetanus. During isometric relaxation, the degree of phosphorylation, rate of energy usage, and active state all decreased more quickly than did active force output.

Adenosine Triphosphate↗

An anatomic evaluation of T-Fix suture device placement for arthroscopic all-inside meniscal repair.

This investigation documented the locations of endoscopically applied T-Fix suture devices (Acufex Microsurgical, Mansfield, MA) placed in six fresh-frozen cadaveric knees (age, 60 to 72 years) in relationship to the joint capsule, and adjacent neurovascular and musculotendinous structures. Five T-Fix devices were placed in the posterior meniscal regions at approximately 20 degree intervals. Gross dissection enabled T-Fix bar and suture placement identification. Fifty total devices were placed (23 medially and 27 laterally). Lateral: None of the devices penetrated more superficially than the deepest capsular layer (layer III). Six of the 27 devices placed at the posterior horn of the lateral meniscus pierced the popliteus tendon. None of the bars pierced the lateral collateral ligament (layer III). All devices placed at the posterolateral knee were outside the arcuate ligament (layer III) but inside the fabellofibular ligament (layer II). Medial: Seven of the 23 devices pierced the deep medial collateral ligament (MCL, layer III), and 4 pierced the superficial MCL (layer II). Three devices pierced the sartorius tendon (layer I) and one pierced the gracilis tendon (layer II). None of the medial devices created a plicating effect on the posterior capsule. None of the devices were placed near neurovascular structures. Devices placed within the posterior meniscal horns had a > or =1.5-cm buffer zone from the popliteal neurovascular bundle. Most bars (36 of 50) were anchored to the capsular layer (layer III) after piercing the meniscocapsular junction (layer II). T-Fix devices simulating arthroscopic all-inside meniscal repair provided well-positioned, solid suture anchorage through the junction with no neurovascular involvement. Care needs to be taken when placing lateral (popliteus muscle) and medial (gracilis, sartorius tendons and superficial MCL) devices to avoid possible soft tissue tenodesis.

Aged↗

Masses of inositol phosphates in resting and tetanically stimulated vertebrate skeletal muscles.

The masses of inositol phosphates have been determined in isolated skeletal muscles from Xenopus laevis (sartorius, tibialis anterior and iliofibularis) and rat (gastrocnemius and soleus) which were quick-frozen in the resting state and at different stages of an isometric (Xenopus) or isotonic (rat) tetanus. The isomeric spectrum of inositol phosphates detected was similar to that in other tissues and cell types. The total sarcoplasmic concentrations of the isomers Ins-(1,4,5,6)P4/Ins(3,4,5,6)P4 (0.2-0.9 microM), Ins(1,3,4,6)P4 (not detectable), Ins(1,3,4,5,6)P5 (about 1 microM) and InsP6 (3.2-4.6 microM) were lower than in other cell types. Variations in these concentrations were due to the muscle type rather than to the donor species. The putative second messenger Ins(1,4,5)P3, as well as its dephosphorylation product Ins(1,4)P2, were present at surprisingly high total myoplasmic resting concentrations, ranging from 1.2 to 2.5 microM and 3.5 to 6.9 microM respectively. Upon tetanic stimulation these two inositol phosphates in particular exhibited significantly increased total sarcoplasmic concentrations, up to 4.2 microM and 11.3 microM respectively, with a time scale of seconds. From the initial rate of increase in the total sarcoplasmic concentrations of Ins(1,4,5)P3 and its rapidly formed metabolic products, a minimal phosphoinositidase C (PIC) activity in tetanically activated Xenopus skeletal muscle of about 1.7-2.6 microM/s can be estimated. This PIC activity observed in vivo seems to be far too low to account for a functional role for Ins(1,4,5)P3 as a chemical transmitter in the fast excitation-contraction coupling (ECC) process in skeletal muscle. The presence of Ins(1,3,4,5)P4 in all muscle types is indicative of a Ca(2+)-activated Ins(1,4,5)P3 3-kinase activity. The rapid transient increases in Ins(1,3,4)P3 and Ins(1,3)P2 in isometrically contracting Xenopus muscles suggest that corresponding Ins(1,3,4,5)P4 phosphatases are operating in skeletal muscle as well. In all muscles investigated except rat soleus, the fructose 1,6-bisphosphate [Fru(1,6)P2] concentration increased substantially during a tetanus, up to about 2 mM. This increase is correlated with a simultaneous decrease in phosphocreatine, whereas the energy charge of the muscles was essentially unaffected by the applied tetani. The time course of the rise in Fru(1,6)P2 was used to model changes in the free concentrations of high-affinity aldolase-binding inositol phosphates during the course of a tetanus. These calculations demonstrate that the free concentration of Ins(1,4,5)P3 and other aldolase-bound inositol phosphates can increase much faster and to a larger extent than the corresponding total concentrations as a result of their competitive displacement from aldolase-binding sites by the rapidly rising concentration of Fru(1,6)P2.

Animals↗

The occurrence of post-denervation hypertrophy in chick slow muscle fibres after complete elimination of stretch and tension.

With the slow muscle fibres in the pure slow muscle ALD as well as in two mixed muscles, flexor metacarpi ulnaris and sartorius, it is demonstrated that the phenomenon of postdenervation hypertrophy still occurs under conditions preventing stretch of muscle after denervation or even in tenotomized muscles in shortened state relieved of tension. Striking differences between the slow fibres of the ALD and those of the mixed muscles are seen, both with respect to their histochemical property and to the degree of development of post-denervation hypertrophy. The slow fibres in the mixed muscles show the phenomenon of post-denervation hypertrophy in a much more striking form than the ALD fibres and should be made more use of in further studies on the phenomenon.

Animals↗

Functionally complex muscles of the cat hindlimb. I. Patterns of activation across sartorius.

The cat sartorius (SA) can be divided functionally into an anterior (SAa), knee extensor portion and a medial (SAm), knee flexor portion; it can be further subdivided anatomically by multiple nerve branches into parallel longitudinal columns that terminate in a distributed insertion at the knee with a continuous range of moment arms. Thus, SA may be controlled by a discrete number of motoneuron task groups reflecting a small number of central command signals or by a continuum of activation patterns associated with a continuum of moment arms. To resolve this question, the activation patterns across the width of the SA were recorded with an electrode array during three kinematically different movements--treadmill locomotion, scratching and paw shaking, in awake, unrestrained cats. Uniformity of activation along the longitudinal axis was also examined because individual muscle fibers do not extend the length of the SA. In addition, the cutaneous reflex responses were recorded throughout all regions of the SA during locomotion. Two fascial surface-patch arrays, each carrying 4-8 pairs of bipolar EMG electrodes, were sutured to the inner surface of the SA, one placed proximally and the other more distally. Each array sampled separate sites across the anterior to medial axis of SA. During locomotion, two basic EMG patterns were observed: the two burst-per-step-cycle pattern typical of SAa and the single burst pattern typical of SAm. There was an abrupt transition in the pattern of activation recorded in the two parts of SA during locomotion, and no continuum in the activation pattern was observed. Stimulation of both sural and saphenous cutaneous nerves during locomotion produced reflex responses that were uniformly distributed throughout SA, in contrast to the regional differences noted during unperturbed walking. Similarly, during scratching and paw shaking all parts of the SA were active simultaneously but with regional differences in EMG amplitude. The abrupt functional border between SAa and SAm coincided with the division of the SA into a knee flexor vs. a knee extensor. In all cases, the quantitative and qualitative differences in SAa and SAm EMGs were uniformly recorded throughout the entire extent of SAa or SAm; i.e., there was no segregation of activity within either SAa or SAm. Furthermore, the time course of EMG from each proximal recording site was nearly identical to the corresponding distal site, indicating no segregation of function along the longitudinal axis of SA. These results indicate that SAa and SAm constitute the smallest functional modules that can be recruited in SA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Relative EMG levels in training exercises for abdominal and hip flexor muscles.

The main purpose of our study was to compare systematically EMG levels in sub-maximal training exercises for the trunk and hip flexor muscles with those voluntarily attainable in corresponding situations. Six healthy subjects performed three types of standardized training exercises, whose static positions, movement velocity and range of motion were reproduced during maximal voluntary isokinetic strength tests. EMG was recorded with wire electrodes from the iliacus muscle and with surface electrodes from the rectus femoris, sartorius, rectus abdominis, obliquus externus and internus muscles. The relative EMG values demonstrated a task dependency which could differ between individual muscles. The maximal voluntary activation levels were relatively constant across conditions. Exceptions were present, particularly for the rectus femoris and iliacus muscles. These findings highlight the consequences of using different methods of normalizing EMG. The relative EMG values presented may serve as guidelines when selecting training exercises for specific trunk and hip flexor muscles in sports and rehabilitation.

Abdominal Muscles↗

Ultrasonographic assessment of the prevalence of fasciculations in lesions of the peripheral nervous system.

In previous studies, ultrasonography was a very sensitive method in detecting fasciculations. The present study was intended to examine the prevalence of ultrasonographically visible fasciculations in patients with neuromuscular diseases affecting the lower extremities. Ultrasonography of 9 muscles (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis, sartorius, semitendinosus, tibialis anterior, gastrocnemius, and soleus muscles) was performed bilaterally in 70 adult healthy subjects and 172 patients with various neuromuscular diseases. Fasciculations were detected in 109 (63%) of 172 patients. The median value of affected muscles was 10 (range 1-18). Patients with spinal muscular atrophy (37/38, p < 0.001), hereditary motor and sensory neuropathy (24/25, p < 0.001), and lumbosacral radiculopathy with motor deficits (24/29, p < 0.001) exhibited fasciculations more frequently than did healthy volunteers. Radiculopathy with sensory deficits, lesions of either plexus or peripheral nerves, compartment syndrome, and myopathy were not associated with a significantly enhanced prevalence of fasciculations in the patient group compared to the control group. In summary, fasciculations are a frequent ultrasonographic sign in neuromuscular diseases. They are almost regularly found in patients with spinal muscular atrophy and those with hereditary motor and sensory neuropathy. Thus, the absence of fasciculations in ultrasonographic assessment should give cause for reconsidering these diagnoses.

Adolescent↗

Excision of quadriceps muscle group.

Excision of the quadriceps muscle group may be selected for definitive treatment of intracompartmental soft tissue sarcomas within this muscle group. After a skin incision is made from anterosuperior iliac spine to the patella, skin flaps are dissected superficial to the fascia lata to the flexor muscles laterally and to the gracilis muscle medially. The superficial femoral artery is dissected free of the quadriceps muscles over the entire thigh. The origins of the sartorius, tensor fascia lata, and rectus femoris muscles are transected from their origins on the pelvis, and the vastus lateralis, vastus medialis, and vastus intermedius muscles are transected from their origins on the femur. To free the specimen, the quadriceps femoris tendon is divided just proximal to its attachment to the patella. The gracilis muscle medially and the short head of the biceps muscle laterally are transected at their insertions and secured to the patella. The subcutaneous tissue and skin are closed over generous suction drains. After operation an ankle-foot orthosis is used to provide for relatively unrestricted ambulation.

Humans↗

Of post-denervation hypertrophy in chick slow muscle fibres after complete elimination of stretch and tension.

For the slow muscle fibres in the pure slow muscle ALD as well as in two mixed muscles, flexor metacarpi ulnaris and sartorius, it is demonstrated that the phenomenon of post-denervation hypertrophy still occurs under conditions preventing stretch of muscle after denervation or even in tenotomized muscles in shortened state relieved of tension. Striking differences between the slow fibres of the ALD and those of the mixed muscles are seen, both with respect to their histochemical property and to the degree of development of post-denervation hypertrophy. The slow fibres in mixed muscles show the phenomenon of post-denervation hypertrophy in a much more striking form than do the ALD fibres, and should be used in further studies of the phenomenon.

Animals↗

Splayleg: a spontaneous limb defect in rabbits. Genetics, gross anatomy, and microscopy.

A limb defect in rabbits known as splayleg arose in a closed breeding colony of Dutch rabbits. Since the causes of this postural deformity are not fully understood, an effort was made to clarify the mode of inheritance and the etiology of the disease. Pedigree analysis and genetic mating tests showed that, in contrast to published reports, the disease is not determined by a single recessive gene with complete expressivity. The underlying genetic system is composed of one recessive gene with reduced expressivity or of more genes with the probable involvement of environmental factors. Femurs of abnormal limbs displayed endotorsion of the shaft and anteversion of the neck as the main features. Endotorsion of the femur was associated with exotorsion of the tibia. Dislocation of the hip was not observed. There was no abnormnal laxity of the joint capsule or the ligamentaum teres. Only minor differences in the acetabulum between control and splayleg rabbits were observed. Enzyme histochemistry and electron microscopy of the gluteus medius, adductor longus- and magnus, sartorius, gracilis, and semitendinosus muscles and the femoral, peroneal, and tibial nerves did not reveal any qualitative differences between splayleg and control rabbits. A study on muscle fiber diameter showed that fibers of splayleg animals were in general smaller, particularly in the semitendinosus. Atypical mitochondria of muscles were observed in all rabbits, but more frequently in splayleg animals. A hypothesis is presented in which imbalanced development of the neural, muscular and skeletal systems of the limb is the primary defect. This results in torsion of the femur. It depends on the degree of femoral torsion and the capacity of the young rabbit for compensation by exorotation of the limb in the hip whether a persistent splayleg posture will develop.

Animals↗

Relation between work and power calculated from force-velocity curves to that done during oscillatory work.

The force-velocity relation during oscillatory work was compared with that measured in the traditional way with quick release and force clamps using toad sartorius, frog sartorius, and mouse soleus muscles. Plotting the force and corresponding velocity data in this way produces a 'power-loop'. The 'power-loop' has less intuitive value than the frequently reported 'work-loops' but it is useful because it permits comparison with the force-velocity curve produced using traditional methods. The force/velocity combinations for oscillatory work during a contraction often exceed those that would be predicted from the force-velocity curve. Although it has been known for many years that more force is developed by stimulated muscle when it is being stretched than can be developed during an isometric contraction, my results show that the increase in force is of importance at stretch velocities that probably occur in vivo during locomotion.

Animals↗