Appearance of "transitional" motor units in overloaded rat skeletal muscle

1989 ◽  
Vol 67 (5) ◽  
pp. 2049-2054 ◽  
Author(s):  
E. G. Noble ◽  
F. P. Pettigrew
Keyword(s):  
Skeletal Muscle ◽  
Motor Units ◽  
Contraction Time ◽  
Rat Skeletal Muscle ◽  
Short Term ◽  
Single Motor Units ◽  
Whole Muscle ◽  
Tetanic Tension ◽  
Large Decline ◽  
Contractile Characteristics

The contractile characteristics of single motor units, isolated from rat plantaris muscles subjected to short-term (30 days) compensatory overload, were assessed to determine whether motor units in transition could be detected. In the control plantaris 88% of the motor units were classified as fast. After overload, a large decline (26.5%) in the proportion of typical fast motor units was noted. The estimated contribution of fast fatigable units to whole muscle tetanic tension (Po 200) also declined (from 55 to 25%), whereas that of fast intermediate motor units increased (from 33 to 55%). In the overloaded plantaris, motor units that exhibited unusual “sag” and contraction time characteristics were detected. These motor units, which could be further subdivided into two distinct types by a variety of indexes, exhibited characteristics intermediate to fast and slow units and therefore were termed “transitional.” Transitional units accounted for 12% of the estimated whole muscle Po200 after overload. These experiments characterize novel classifications of motor units undergoing transformation and further detail the motor unit shift that accompanies compensatory overload.

Whole-Muscle and Motor-Unit Contractile Properties of the Styloglossus Muscle in Rat

1999 ◽  
Vol 82 (2) ◽  
pp. 584-592 ◽  
Author(s):  
Thomas G. Sutlive ◽  
J. Ross McClung ◽  
Stephen J. Goldberg
Keyword(s):  
Motor Units ◽  
Contractile Properties ◽  
Contraction Time ◽  
Fusion Frequency ◽  
Single Motor Units ◽  
The Mean ◽  
Whole Muscle ◽  
Tetanic Tension ◽  
Contractile Characteristics ◽  
Stimulation Of

Investigations of whole muscle and motor-unit contractile properties have provided valuable information for our understanding of the spinal cord and extraocular motor systems. However, no previous investigation has examined these properties in an isolated tongue muscle. The purpose of this study was to determine the contractile properties and muscle fiber types of the rat styloglossus muscle. The styloglossus is one of three extrinsic tongue muscles and serves to retract the tongue within the oral cavity. Adult male Sprague-Dawley rats ( n = 19) were used in these experiments. The contractile characteristics of the whole styloglossus muscle ( n = 9) were measured in response to stimulation of the hypoglossal nerve branch to the muscle. The average twitch tension produced was 3.30 g with a mean twitch contraction time of 13.81 ms. The mean maximum tetanic tension was 19.66 g and occurred at or near the fusion frequency, which averaged 109 Hz. The styloglossus muscle was resistant to fatigue [fatigue index (F. I.) = 0.76]. In separate experiments ( n = 7), the contractile characteristics of 37 single motor units were measured in response to extracellular stimulation of hypoglossal motoneurons. The twitch tension generated by styloglossus motor units averaged 35.7 mg, and the mean twitch contraction time was 12.46 ms. The mean fusion frequency was 92 Hz. Maximum tetanic tension averaged 177.8 mg. Styloglossus single motor units were resistant to fatigue (F. I. = 0.74). The sites of stimulation that yielded a contractile response in the styloglossus muscle were consistent with the location of the styloglossus motoneuron pool reported in earlier anatomy studies. Muscle fiber typing was determined in three animals based on the myofibrillar ATPase reaction at pH 9.8, 4.6, and 4.3. The styloglossus muscle was composed of ≈99% type IIA fibers with a few scattered type I fibers present in the study sample. On the basis of the combined findings of the physiology and histochemistry experiments, the styloglossus muscle appeared to be a homogeneous muscle composed almost exclusively of fast, fatigue-resistant motor units. These properties of the styloglossus muscle and its motor units were compared with findings in other rat skeletal muscles.

Skeletal muscle nNOSμ protein content is increased by exercise training in humans

2007 ◽  
Vol 293 (2) ◽  
pp. R821-R828 ◽  
Author(s):  
Glenn K. McConell ◽  
Scott J. Bradley ◽  
Terry J. Stephens ◽  
Benedict J. Canny ◽  
Bronwyn A. Kingwell ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Protein Expression ◽  
Intense Exercise ◽  
Rat Skeletal Muscle ◽  
Short Term ◽  
Protein Levels ◽  
Oxide Synthase ◽  
Whole Muscle ◽  
Inducible Nos

The major isoform of nitric oxide synthase (NOS) in skeletal muscle is the splice variant of neuronal NOS, termed nNOSμ. Exercise training increases nNOSμ protein levels in rat skeletal muscle, but data in humans are conflicting. We performed two studies to determine 1) whether resting nNOSμ protein expression is greater in skeletal muscle of 10 endurance-trained athletes compared with 11 sedentary individuals ( study 1) and 2) whether intense short-term (10 days) exercise training increases resting nNOSμ protein (within whole muscle and also within types I, IIa, and IIx fibers) in eight sedentary individuals ( study 2). In study 1, nNOSμ protein was ∼60% higher ( P < 0.05) in endurance-trained athletes compared with the sedentary participants. In study 2, nNOSμ protein expression was similar in types I, IIa, and IIx fibers before training. Ten days of intense exercise training significantly ( P < 0.05) increased nNOSμ protein levels in types I, IIa, and IIx fibers, a finding that was validated by using whole muscle samples. Endothelial NOS and inducible NOS protein were barely detectable in the skeletal muscle samples. In conclusion, nNOSμ protein expression is greater in endurance-trained individuals when compared with sedentary individuals. Ten days of intense exercise is also sufficient to increase nNOSμ expression in untrained individuals, due to uniform increases of nNOSμ within types I, IIa, and IIx fibers.

Nonuniform fatigue characteristics of slow-twitch motor units activated at a fixed percentage of their maximum tetanic tension

1991 ◽  
Vol 66 (5) ◽  
pp. 1483-1492 ◽  
Author(s):  
T. C. Cope ◽  
C. B. Webb ◽  
A. K. Yee ◽  
B. R. Botterman
Keyword(s):  
Relaxation Time ◽  
Conduction Velocity ◽  
Motor Units ◽  
Contraction Time ◽  
Stimulation Rate ◽  
Axonal Conduction ◽  
Slow Twitch ◽  
Force Clamp ◽  
Highly Correlated ◽  
Tetanic Tension

1. The endurance of slow-twitch motor units from the soleus (SOL) and medial gastrocnemius (MG) muscles of the cat were tested by determining the length of time (endurance time, Et) that a unit could maintain its tension output at 85% of maximum. Motor-unit tension was clamped at the target level by altering the stimulation rate of a unit's motor axon through computer feedback control. Tested in this way, units of both muscles displayed a wide range of Ets, approximately 40- to 50-fold. 2. Electromyographic (EMG) waveforms of motor units subjected to force-clamp contractions were analyzed to access whether any activity-dependent changes in their waveform shape might predict Et. Three measurements of waveform shape were determined: baseline-to-baseline duration, peak-to-peak amplitude, and area. Typically, amplitude decreased and duration increased as a contraction proceeded, whereas area remained fairly constant. Because changes in each measure were very similar for units of widely different Ets, it was concluded that neuromuscular junction failure and changes in the excitability of the sarcolemma (excluding the t-tubule system) play a minor role in determining Et. 3. Et was highly correlated with the mean stimulation rate (Et/number of stimuli) used during the force-clamp contractions. Mean rate was seen to progressively decrease with increasing Et. This correlation could not be explained by measures of isometric contractile speed or relaxation (e.g., twitch contraction time or half-relaxation time) measured before the force-clamp contractions. Both contraction time and half-relaxation time were found to be unrelated to both Et and the rate used to stimulate the unit during the force-clamp contraction. 4. Among type S units of SOL and MG, maximum tetanic tension and Et were not related. A significant relation (r = -0.49) was found between axonal conduction velocity and Et for SOL units (n = 38). In addition, a significant correlation (r = 0.47) was found between conduction velocity and tetanic tension for SOL units. Perhaps because of the small sample of type S units from MG (n = 10), conduction velocity was found not be related to either Et or tetanic tension. 5. Others have shown that a motor unit's maximum tetanic tension and axonal conduction velocity are correlated with its order of recruitment among motoneurons innervating a muscle. Recent work has further shown that among type F units the order in which a motoneuron is recruited is highly correlated with the fatigue resistance of its muscle unit.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomic and physiological characteristics of the ferret lateral rectus muscle and abducens nucleus

2007 ◽  
Vol 103 (5) ◽  
pp. 1706-1714 ◽  
Author(s):  
Keith N. Bishop ◽  
J. Ross McClung ◽  
Stephen J. Goldberg ◽  
Mary S. Shall
Keyword(s):  
Motor Units ◽  
Lateral Rectus ◽  
Contraction Time ◽  
Fatigue Index ◽  
Muscle Twitch ◽  
Abducens Nucleus ◽  
Single Motor Unit ◽  
Twitch Contraction ◽  
Whole Muscle ◽  
Individual Motor

The ferret has become a popular model for physiological and neurodevelopmental research in the visual system. We believed it important, therefore, to study extraocular whole muscle as well as single motor unit physiology in the ferret. Using extracellular stimulation, 62 individual motor units in the ferret abducens nucleus were evaluated for their contractile characteristics. Of these motor units, 56 innervated the lateral rectus (LR) muscle alone, while 6 were split between the LR and retractor bulbi (RB) muscle slips. In addition to individual motor units, the whole LR muscle was evaluated for twitch, tetanic peak force, and fatigue. The abducens nucleus motor units showed a twitch contraction time of 15.4 ms, a mean twitch tension of 30.2 mg, and an average fusion frequency of 154 Hz. Single-unit fatigue index averaged 0.634. Whole muscle twitch contraction time was 16.7 ms with a mean twitch tension of 3.32 g. The average fatigue index of whole muscle was 0.408. The abducens nucleus was examined with horseradish peroxidase conjugated with the subunit B of cholera toxin histochemistry and found to contain an average of 183 motoneurons. Samples of LR were found to contain an average of 4,687 fibers, indicating an LR innervation ratio of 25.6:1. Compared with cat and squirrel monkeys, the ferret LR motor units contract more slowly yet more powerfully. The functional visual requirements of the ferret may explain these fundamental differences.

Subsarcolemmal and intermyofibrillar mitochondrial responses to short-term high-fat feeding in rat skeletal muscle

Nutrition ◽  
2014 ◽  
Vol 30 (1) ◽  
pp. 75-81 ◽  
Author(s):  
Raffaella Crescenzo ◽  
Francesca Bianco ◽  
Paola Coppola ◽  
Arianna Mazzoli ◽  
Giovanna Liverini ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
High Fat ◽  
Rat Skeletal Muscle ◽  
Short Term ◽  
Fat Feeding

scholarly journals Reconstitution of the complete rupture in musculotendinous junction using skeletal muscle-derived multipotent stem cell sheet-pellets as a “bio-bond”

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2231 ◽  
Author(s):  
Hiroyuki Hashimoto ◽  
Tetsuro Tamaki ◽  
Maki Hirata ◽  
Yoshiyasu Uchiyama ◽  
Masato Sato ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Stem Cell ◽  
Muscle Mass ◽  
Control Group ◽  
Short Term ◽  
Musculotendinous Junction ◽  
Multipotent Stem Cell ◽  
Recovery Group ◽  
Tetanic Tension

Background.Significant and/or complete rupture in the musculotendinous junction (MTJ) is a challenging lesion to treat because of the lack of reliable suture methods. Skeletal muscle-derived multipotent stem cell (Sk-MSC) sheet-pellets, which are able to reconstitute peripheral nerve and muscular/vascular tissues with robust connective tissue networks, have been applied as a “bio-bond”.Methods.Sk-MSC sheet-pellets, derived from GFP transgenic-mice after 7 days of expansion culture, were detached with EDTA to maintain cell–cell connections. A completely ruptured MTJ model was prepared in the right tibialis anterior (TA) of the recipient mice, and was covered with sheet-pellets. The left side was preserved as a contralateral control. The control group received the same amount of the cell-free medium. The sheet-pellet transplantation (SP) group was further divided into two groups; as the short term (4–8 weeks) and long term (14–18 weeks) recovery group. At each time point after transplantation, tetanic tension output was measured through the electrical stimulation of the sciatic nerve. The behavior of engrafted GFP+tissues and cells was analyzed by fluorescence immunohistochemistry.Results.The SP short term recovery group showed average 64% recovery of muscle mass, and 36% recovery of tetanic tension output relative to the contralateral side. Then, the SP long term recovery group showed increased recovery of average muscle mass (77%) and tetanic tension output (49%). However, the control group showed no recovery of continuity between muscle and tendon, and demonstrated increased muscle atrophy, with coalescence to the tibia during 4–8 weeks after operation. Histological evidence also supported the above functional recovery of SP group. Engrafted Sk-MSCs primarily formed the connective tissues and muscle fibers, including nerve-vascular networks, and bridged the ruptured tendon–muscle fiber units, with differentiation into skeletal muscle cells, Schwann cells, vascular smooth muscle, and endothelial cells.Discussion.This bridging capacity between tendon and muscle fibers of the Sk-MSC sheet-pellet, as a “bio-bond,” represents a possible treatment for various MTJ ruptures following surgery.

scholarly journals Effect of Short-Term Endurance Exercise on COX IV and PGC-1a mRNA Expression Levels in Rat Skeletal Muscle

2019 ◽  
Vol 12 (3) ◽  
pp. 1309-1316 ◽  
Author(s):  
Nova Sylviana ◽  
Christina Natalia ◽  
Hanna Goenawan ◽  
Yuni Susanti Pratiwi ◽  
Iwan Setiawan ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Mrna Expression ◽  
Endurance Exercise ◽  
Mitochondrial Biogenesis ◽  
Control Group ◽  
Muscle Adaptation ◽  
Rat Skeletal Muscle ◽  
Short Term ◽  
Expression Levels ◽  
Mrna Expression Levels

Endurance exercise induces specific skeletal muscle adaptation by increasing mitochondrial oxidative phosphorylation eficiency and mitochondrial biogenesis. Many previous studies suggesting both PGC-1a and COX IV as a potential biomarker of skeletal muscle adaptation induced by exercise. But most of them only studied the effect of long-term endurance exercise, whereas the effect of short-term exercise remains unclear. To investigate short-term physiological adaptation induced by endurance exercise on expression of COX IV and PGC-1a mRNA in rat skeletal muscle. Twenty healthy male Wistar rats (Rattus norvegicus) aged 10-11 weeks old were used in this experiment. Rats were randomly assigned into 4 groups based on the time period of exercise: 1) control (C; n=5), 2) three days of exercise (E3; n=5), 3) six days of exercise (E6; n=5), 4) fifteen days of exercise (E15; n=5). The exercise groups were run at 20m/s for 30 minutes on the rat treadmill and the stationary control group was only placed inside treadmill with the machines turned off. On the last day of exercise, the rats were sacrificed then RNA from skeletal muscle was extracted. COX IV and PGC-1a mRNA expressions were measured by Reverse Transcriptase PCR. The results showed that there were statistically significant differences of PGC-1a mRNA expression levels in both soleus (F(3,16)=3.740, ps=0.033) and gastrocnemius (F(3,16)=3.969, pg=0.027) muscles. The COX IV mRNA expression levels in soleus (F(3,16)=3.801, ps=0.031) and gastrocnemius (F(3,16)=5.429, ps=0.009) muscles were also significantly increased. There were significant increases of PGC-1a and COX IV expressions in fifteen days of exercise group compared to control group in both muscles. Short-term endurance exercise induced mitochondrial biogenesis marker and mitochondrial activity marker by increasing the PGC-1a and COX IV mRNA expression levels in rat skeletal muscle significantly following the time periods of exercise.

Velocity of shortening of single motor units from rat soleus

1992 ◽  
Vol 67 (5) ◽  
pp. 1133-1145 ◽  
Author(s):  
S. R. Devasahayam ◽  
T. G. Sandercock
Keyword(s):  
Motor Unit ◽  
Motor Units ◽  
Surrounding Tissue ◽  
Passive Tension ◽  
Contraction Time ◽  
Single Motor ◽  
Twitch Contraction ◽  
Single Motor Units ◽  
Velocity Of Shortening ◽  
Force Velocity

1. The force-velocity relationship of a motor unit can provide insight into the contractile proteins of its constituent fibers as well as fundamental information about the function and use of the motor unit. Although the force-velocity profiles of whole muscle and skinned mammalian fibers have been studied, technical difficulties have prevented similar studies on motor units. A technique is presented to directly measure the velocity of shortening of individual motor units from in vivo rat soleus muscle. 2. The soleus muscles of anesthetized rats were dissected free of surrounding tissue while their nerve and blood supplies were preserved. Both tendons were cut, and the distal tendon was attached to a servomechanism to control muscle length, whereas the proximal tendon was attached to a force transducer. Single motor units were stimulated via the ventral roots. 3. The major problem encountered in measuring the force-velocity profile of a motor unit was that the force from the large number of passive fibers and connective tissue in the soleus confounded the force produced by the small number of active fibers in the motor unit. This problem was minimized by measuring active motor unit tension during an isovelocity ramp. This allowed experimental measurement of the passive tension by shortening the muscle with an identical isovelocity ramp without, however, stimulating the motor unit. Active tension was estimated by subtracting the passive tension waveform from the waveform recorded when the motor unit was active. 4. The method substantially reduced the noise from the passive fibers; however, problems remained. The probable sources of error are discussed, with the most significant being the elasticity associated with the blood and nerve connections to surrounding tissue. The elasticity prevents uniform shortening velocities along the length of the active fibers, thereby introducing a systematic bias to measurements made at high velocities. These errors are most pronounced when the data are extrapolated to determine the maximum velocity of shortening (Vmax). Determination of velocity at peak power (Vpp) is a more robust measure; however, of the 34 motor units studied, only 19 exhibited a distinct peak in the power-force curve, indicating residual noise. 5. To assess the validity of using twitch contraction time as an index of the velocity of shortening, when possible, Vmax and Vpp of each motor unit were correlated with the inverse of its twitch contraction time. The correlation was poor (r less than 0.2), indicating that, although widely used, twitch contraction time is a poor index of contractile speed.

Physiological and histochemical characteristics of motor units in cat tibialis anterior and extensor digitorum longus muscles

1980 ◽  
Vol 43 (6) ◽  
pp. 1615-1630 ◽  
Author(s):  
R. P. Dum ◽  
T. T. Kennedy
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Extensor Digitorum Longus ◽  
Motor Units ◽  
Input Resistance ◽  
Histochemical Staining ◽  
Glycogen Depletion ◽  
Single Motor Units ◽  
The Mean ◽  
Tetanic Tension

1. Intracellular recording and stimulation techniques were used to study the normal motor-unit population of tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in the cat. Histochemical staining of the whole muscle and glycogen depletion of single motor units were performed. These results may be compared to those of their extensor antagonist, medial gastrocnemius (MG), as reported in studies by Burke and co-workers (7, 11, 13). 2. On the basis of two physiological properties, “sag” and fatigue resistance, the motor units in both TA and EDL could be classified into the same categories (types FF, F(int), FR, and S) as in MG (11). In contrast to MG, TA and EDL had nearly twice as many type-FR motor units and only half as many type-S motor units. 3. Glycogen depletion of representative single motor units of types FF and FR suggests a close correspondence between the physiological classification and a unique histochemical profile. No type-S units were depleted. 4. On the basis of histochemical staining, the muscle fibers in TA were presumed to belong to type-FF, -FR, or -S motor units. TA had a higher proportion of type-FR and a lower proportion of type-S muscle fibers than are found in MG. A striking feature was the variation in the proportion of each fiber type in different regions of TA. The anterolateral portion had mostly types FF and FR, while the posteriomedial portion had more types FR and S. 5. The twitch time to peak (TwTP) of isometric motor-unit contractions was generally quite fast with none having TwTP greater than 55 ms. The mean TwTP (not in EDL) and the mean tetanic tension of each motor-unit type were significantly different from each other. Most of the motor units exhibited significant postetanic potentiation of twitch tension and a corresponding lengthening of half-relaxation time and to a lesser degree, twitch contraction time. 6. There was a significant relationship between the inverse of motoneuronal input resistance and either tetanic tension or twitch contraction time. These relationships were not apparent when axonal conduction velocity rather than input resistance was used as an index of motoneuron size. The mean input resistances of the three major motor-unit types were significantly different while the mean conduction velocities of types FF and FR were nearly identical. A weak positive correlation was observed between the TwTP and the afterhyperpolarization of TA and EDL motoneurons. 7. In general, the mechanical characteristics and intrinsic motoneuronal properties of TA and EDL appear to parallel the organization of their extensor antagonist, MG, with some important quantitative differences that may reflect their different functional roles.

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