Motor-unit categorization based on contractile and histochemical properties: a glycogen depletion analysis of normal and reinnervated rat tibialis anterior muscle

1992 ◽  
Vol 67 (5) ◽  
pp. 1404-1415 ◽  
Author(s):  
J. E. Totosy de Zepetnek ◽  
H. V. Zung ◽  
S. Erdebil ◽  
T. Gordon
Keyword(s):  
Tibialis Anterior ◽  
Isometric Force ◽  
Tibialis Anterior Muscle ◽  
Continuous Distribution ◽  
Motor Units ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Glycogen Depletion ◽  
Time To Peak ◽  
Fast Twitch

1. Isolated and glycogen-depleted motor units (MUs) have been studied in normal and reinnervated tibialis anterior (TA) muscles of the rat to examine 1) the correspondence between physiological and histochemical classifications, 2) the extent to which unit properties cluster according to type, 3) the relation between unit force and fatigability, and 4) the extent to which reinnervated MUs recover their former properties. 2. MUs were isolated by ventral root dissection and stimulation in reinnervated and normal TA muscles, 3.5-8 mo after common peroneal (CP) nerve section and resuture and in age-matched control rats, respectively. The units were characterized physiologically for classification into four types: slow twitch (S), fast twitch, fatigue resistant (FR), fast twitch fatigue intermediate (FI), and fast twitch fatigue sensitive (FF). Four muscle fiber types were identified histochemically with the use of a modification of the techniques of Brooke and Kaiser, and Guth and Samaha to delineate fiber subtypes on the basis of the pH sensitivity of myofibrillar adenosine triphosphatase (ATPase). 3. Neither the time-to-peak twitch force development nor the profile of unfused tetanus ("sag test") was unambiguous in separating fast from slow MUs. However, all units with a time to peak greater than 22 ms were fatigue resistant, and this time was chosen to delineate fast from slow. The fast unit population was further subdivided on the basis of their fatigability. There is normally a small proportion of S units (6% S) that increased to 20% after reinnervation. Although the fast population was subdivided, there was a continuous distribution of fatigue indexes in normal and reinnervated muscles with the highest number of fast units falling into the FI category. The proportions of fast units were 28% FR, 45% FI, and 21% FF in normal muscles and 29% FR, 38% FI, and 13% FF in reinnervated muscles. 4. In normal muscles, delineation of fast and slow fibers and subdivision of fast fiber types on the basis of acid and alkali stability of myofibrillar ATPase provided a histochemical classification that showed 78% correspondence with physiological classification of the same identified units. In reinnervated muscles the correspondence between physiological and histochemical classifications was reduced to 72%. 5. The normal correlation between MU fatigability and isometric force in TA muscles was not seen in reinnervated muscles that contained more FR MUs. Mean fatigue index from normal units was significantly less at 0.55 +/- 0.03 (mean +/- SE) compared with 0.68 +/- 0.03 from reinnervated units.(ABSTRACT TRUNCATED AT 400 WORDS)

Cross-reinnervated motor units in cat muscle. I. Flexor digitorum longus muscle units reinnervated by soleus motoneurons

1985 ◽  
Vol 54 (4) ◽  
pp. 818-836 ◽  
Author(s):  
R. P. Dum ◽  
M. J. O'Donovan ◽  
J. Toop ◽  
R. E. Burke
Keyword(s):  
Muscle Fibers ◽  
Motor Units ◽  
Muscle Fiber Types ◽  
Type I ◽  
Fiber Types ◽  
Glycogen Depletion ◽  
Flexor Digitorum Longus ◽  
Wet Weight ◽  
Flexor Digitorum ◽  
Individual Motor

The properties of flexor digitorum longus (FDL) muscles and of individual motor units were studied in cats 30-50 wk after self-reinnervation by FDL motoneurons (FDL----FDL) or cross-reinnervation by soleus (SOL) motoneurons (SOL----FDL). Individual motor units were functionally isolated by intracellular recording and stimulation of identified SOL alpha-motoneurons. Glycogen-depletion methods permitted histochemical study of muscle fibers belonging to physiologically characterized muscle units. The observations were compared with data from normal cat FDL muscles and motor units (27). Intentionally self-reinnervated FDL muscles (FDL----FDL; n = 5) were normal in size and wet weight. FDL----FDL motor units could be classified into the same physiological categories found in normal FDL [types: fast contracting, fatigable (FF), fast contracting, fatigue resistant (FR), and slow (S); n = 24], with approximately the same proportions as normal. The histochemical muscle fiber types associated with these categories were also qualitatively normal although there was evidence of marked distortion of the normal histochemical mosaic. These data confirm other studies of self-reinnervation and suggest that self-reinnervation can produce complete interconversion of muscle fiber types. Cross-reinnervation of FDL muscle by SOL motoneurons (SOL----FDL; n = 12) produced muscles that were smaller (about half the normal wet weight) and more red than normal. SOL----FDL muscle contracted more slowly than normal or FDL----FDL muscles and had much higher proportions of histochemical type I muscle fibers. In those SOL----FDL muscles, in which little or no unwanted self-reinnervation could be demonstrated, greater than 95% of the muscle fibers were type I. Forty-one individual motor units in SOL----FDL muscles were isolated by intracellular penetration in functionally identified SOL alpha-motoneurons. Their muscle units were all type S by physiological criteria (absence of "sag" in unfused tetani and marked resistance to fatigue). SOL----FDL muscle units had contraction times and fatigue properties that were essentially identical to those of type S units in the normal FDL. All of the seven units, successfully studied by glycogen depletion, exhibited histochemical type I fibers. SOL motoneurons that innervated FDL muscle units had slightly shorter afterhyperpolarization durations than normal SOL cells, but axonal conduction velocities were normal.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolic variation among alpha-motoneurons innervating different muscle-fiber types. I. Oxidative enzyme activity

1984 ◽  
Vol 51 (3) ◽  
pp. 529-537 ◽  
Author(s):  
D. W. Sickles ◽  
T. G. Oblak
Keyword(s):  
Optical Density ◽  
Muscle Fiber ◽  
Enzyme Activities ◽  
Tibialis Anterior ◽  
Fiber Type ◽  
Ventral Horn ◽  
Oxidative Enzyme ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Fast Twitch

We have examined the oxidative metabolism of rat alpha-motoneurons innervating muscles composed predominantly of one muscle-fiber type. Intramuscular injections of horseradish peroxidase (HRP) into the tensor fasciae latae (TFL) (approximately 94% fast-twitch glycolytic fibers, FG), tibialis anterior (TA) (approximately 66% fast-twitch oxidative-glycolytic, FOG; 32% FG), and soleus (SOL) (approximately 84% slow-twitch oxidative, SO) muscles permitted identification of motoneurons innervating these muscles. gamma-Motoneurons (less than 25-micron average soma diameter) were eliminated from the sampling. The alpha-motoneurons innervating the TFL were considered as FG, those innervating the tibialis anterior as FOG, and those of the soleus as SO. Alternate 5-micron serial cryostat sections were processed for HRP and nicotinamide adenine dinucleotide-diapharase (NADH-D) (oxidative enzyme) activities. Controls were included to assure reliability of reaction product quantitation. Motoneuron pools of each muscle were characterized by their shape and location within the ventral horn. Cells identified on HRP sections as innervating each of the muscles were located on sections processed for NADH-D activity. The optical density of motoneurons in sections processed for NADH-D activity was measured with a Zeiss Zonax MPM 03 microdensitometer. The mean relative NADH-D activities (optical density) of alpha-motoneurons innervating the TFL (FG), TA (FOG), and SOL(SO) muscles were 0.261, 0.305, and 0.447, respectively. Although some overlap in distribution of enzyme activities was observed, statistical analysis indicated significant differences between the NADH-D activities of each type of alpha-motoneuron. This is the first report of any metabolic difference in alpha-motoneurons belonging to different motor-unit types.(ABSTRACT TRUNCATED AT 250 WORDS)

MHC composition and enzyme-histochemical and physiological properties of a novel fast-twitch motor unit type

1991 ◽  
Vol 261 (1) ◽  
pp. C93-C101 ◽  
Author(s):  
L. Larsson ◽  
L. Edstrom ◽  
B. Lindegren ◽  
L. Gorza ◽  
S. Schiaffino
Keyword(s):  
Cross Sections ◽  
Tibialis Anterior Muscle ◽  
Muscle Fibers ◽  
Relaxation Times ◽  
Motor Units ◽  
Biochemical Properties ◽  
The Other ◽  
Glycogen Depletion ◽  
Single Motor Units ◽  
Fast Twitch

Determinations of fatigue ratio, twitch and tetanus tension, and contraction and half-relaxation times of the isometric twitch were made in 21 single fast-twitch motor units from the rat tibialis anterior muscle. Single motor units were functionally isolated by microdissection of the ventral root, and the glycogen depletion technique was used to demonstrate the muscle fibers in the unit. Morphological and immuno- and enzyme-histochemical methods were applied to serial muscle cross sections to characterize the muscle fibers in the unit. Three of the units had muscle fibers of the IIa type according to staining both for myofibrillar adenosinetriphosphatase after acid preincubation and with the use of monoclonal antibodies specific for myosin heavy chains (MHCs), i.e., the IIa-MHC isoform. The other 18 units were of the IIb type according to enzyme-histochemistry, but immunohistochemistry showed that in six of these units the muscle fibers exhibited the novel type IIx-MHC isoform and in the other 12 units the IIb-MHC isoform. It was found that the IIx motor units have contraction and half-relaxation times similar to those of types IIa and IIb units but have morphological, physiological, and biochemical properties that distinguish them from the latter two types.

Myofibrillar M-band structure and composition of physiologically defined rat motor units

1987 ◽  
Vol 253 (3) ◽  
pp. C456-C468 ◽  
Author(s):  
L. E. Thornell ◽  
E. Carlsson ◽  
E. Kugelberg ◽  
B. K. Grove
Keyword(s):  
Motor Units ◽  
Volume Density ◽  
Band Pattern ◽  
Fiber Types ◽  
Contraction Time ◽  
Glycogen Depletion ◽  
Disc Width ◽  
Composition And Structure ◽  
Fast Twitch ◽  
Anterior Tibialis

The isometric contraction time of 19 fast and slow rat motor units in the soleus and the anterior tibial muscles were recorded. The motor unit fibers, subsequently distinguished by glycogen depletion, were histochemically differentiated into fiber types and analyzed immunohistochemically for high molecular weight M-band proteins, as well as ultrastructurally for M-band fine structure, Z-disc width, and volume density of mitochondria. All fibers belonging to slow-twitch motor units in both the anterior tibialis and soleus muscles were histochemically classed as type 1. They lacked the Mr 165,000 M-protein, showed ultrastructurally a four-line M-band pattern, and had broad Z-discs, whereas the volume density of the mitochondria varied considerably. Muscle fibers belonging to the fast-twitch motor units were histochemically classed as types 2A and 2B in anterior tibialis and type 2A in soleus. They contained a three- or a five-line M-band pattern and medium-to-thin Z-discs in the anterior tibialis and a five-line M-band pattern and broad Z-discs in the soleus. Furthermore, the volume density of mitochondria showed considerable variation within and in between soleus and anterior tibialis type 2 fibers. As the differences in M-band composition and structure between fiber types overrode the intragroup variability in contraction times of slow and fast units within and between the two muscles, it is concluded that the M-band composition and structure is fundamentally related to whether the fiber is innervated by a slow or fast motor neuron, whereas other parameters such as contraction time, Z-disc width, and mitochondrial content of fibers of fast and slow units are relative and vary between muscles. Thus the M-band appearance can be used as a reliable marker to distinguish between fibers of slow- and fast-twitch motor units in rat leg muscles.

Influence of exercise intensity and duration on biochemical adaptations in skeletal muscle

1982 ◽  
Vol 53 (4) ◽  
pp. 844-850 ◽  
Author(s):  
G. A. Dudley ◽  
W. M. Abraham ◽  
R. L. Terjung
Keyword(s):  
Cytochrome C ◽  
Exercise Intensity ◽  
Adaptive Response ◽  
General Pattern ◽  
Motor Units ◽  
Exercise Duration ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Work Intensity ◽  
Fast Twitch

The influence of intensity and daily duration of exercise on cytochrome c concentration in the three muscle fiber types was assessed in rats that were treadmill trained for 8 wk (5 days/wk) by 1 of 19 protocols. The importance of exercise duration was determined at six running intensities (10, 20, 30, 40, 50, and 60 m/min). Daily run times resulted in a maximal adaptive change for each running intensity. The general pattern of cytochrome c change, caused by increasing daily run times, followed a first-order manner in all fiber types. The final time-independent asymptotic values were dependent on the intensity of running. In addition, as running intensity was increased, the length of daily run time required to achieve the peak adaptive response was shortened. The intensity influence was very different between fiber types. In the fast-twitch red fiber, the maximal time-independent response at each work intensity was altered by exercise intensity at only submaximal work loads (i.e., the adaptation from 19 to 29 nmol/g was not further increased at 50 and 60 m/min). In contrast, the adaptive response in the fast-twitch white fiber began at 30 m/min (approx 80% VO2max) and increased exponentially as intensity was increased (200% increase at 60 m/min). Whether this different adaptive response between fiber types is due solely to the ordered recruitment of motor units remains to be determined.

scholarly journals lncRNA-Six1 Is a Target of miR-1611 that Functions as a ceRNA to Regulate Six1 Protein Expression and Fiber Type Switching in Chicken Myogenesis

Cells ◽  
2018 ◽  
Vol 7 (12) ◽  
pp. 243 ◽  
Author(s):  
Manting Ma ◽  
Bolin Cai ◽  
Liang Jiang ◽  
Bahareldin Ali Abdalla ◽  
Zhenhui Li ◽  
...  
Keyword(s):  
Fiber Type ◽  
Muscle Fibers ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Proliferation And Differentiation ◽  
Slow Twitch Muscle ◽  
Fast Twitch Muscle ◽  
Slow Twitch ◽  
Slow Twitch Fibers ◽  
Fast Twitch

Emerging studies indicate important roles for non-coding RNAs (ncRNAs) as essential regulators in myogenesis, but relatively less is known about their function. In our previous study, we found that lncRNA-Six1 can regulate Six1 in cis to participate in myogenesis. Here, we studied a microRNA (miRNA) that is specifically expressed in chickens (miR-1611). Interestingly, miR-1611 was found to contain potential binding sites for both lncRNA-Six1 and Six1, and it can interact with lncRNA-Six1 to regulate Six1 expression. Overexpression of miR-1611 represses the proliferation and differentiation of myoblasts. Moreover, miR-1611 is highly expressed in slow-twitch fibers, and it drives the transformation of fast-twitch muscle fibers to slow-twitch muscle fibers. Together, these data demonstrate that miR-1611 can mediate the regulation of Six1 by lncRNA-Six1, thereby affecting proliferation and differentiation of myoblasts and transformation of muscle fiber types.

Blood flow to different skeletal muscle fiber types during contraction

1983 ◽  
Vol 245 (2) ◽  
pp. H265-H275 ◽  
Author(s):  
B. G. Mackie ◽  
R. L. Terjung
Keyword(s):  
Skeletal Muscle ◽  
Blood Flow ◽  
Muscle Fiber ◽  
Fiber Type ◽  
Oxidative Capacity ◽  
Skeletal Muscle Fiber ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Blood Flows ◽  
Fast Twitch

Blood flow to fast-twitch red (FTR), fast-twitch white (FTW), and slow-twitch red (STR) muscle fiber sections of the gastrocnemius-plantaris-soleus muscle group was determined using 15 +/- 3-microns microspheres during in situ stimulation in pentobarbital-anesthetized rats. Steady-state blood flows were assessed during the 10th min of contraction using twitch (0.1, 0.5, 1, 3, and 5 Hz) and tetanic (7.5, 15, 30, 60, and 120/min) stimulation conditions. In addition, an earlier blood flow determination was begun at 3 min (twitch series) or at 30 s (tetanic series) of stimulation. Blood flow was highest in the FTR (220-240 ml X min-1 X 100 g-1), intermediate in the STR (140), and lowest in the FTW (70-80) section during tetanic contraction conditions estimated to coincide with the peak aerobic function of each fiber type. These blood flows are fairly proportional to the differences in oxidative capacity among fiber types. Further, their absolute values are similar to those predicted from the relationship between blood flow and oxidative capacity found by others for dog and cat muscles. During low-frequency contraction conditions, initial blood flow to the FTR and STR sections were excessively high and not dependent on contraction frequency. However, blood flows subsequently decreased to values in keeping with the relative energy demands. In contrast, FTW muscle did not exhibit this time-dependent relative hyperemia. Thus, besides the obvious quantitative differences between skeletal muscle fiber types, there are qualitative differences in blood flow response during contractions. Our findings establish that, based on fiber type composition, a heterogeneity in blood flow distribution can occur within a whole muscle during contraction.

Influence of training on skeletal muscle enzymatic adaptations in normal and diabetic rats

1985 ◽  
Vol 249 (4) ◽  
pp. E360-E365 ◽  
Author(s):  
E. G. Noble ◽  
C. D. Ianuzzo
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Citrate Synthase ◽  
Diabetic Rats ◽  
Muscle Fiber Types ◽  
Fiber Types ◽  
Marker Enzymes ◽  
Oxidative Potential ◽  
Hydroxyacyl Coa Dehydrogenase ◽  
Fast Twitch

Muscle homogenates representing slow-twitch oxidative, fast-twitch oxidative-glycolytic, fast-twitch glycolytic, and mixed fiber types were prepared from normal, diabetic, and insulin-treated diabetic rats. Diabetes was induced by injection of 80 mg . kg-1 of streptozotocin. The activities of citrate synthase, succinate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase were employed as markers of oxidative potential, whereas phosphorylase, hexokinase, and phosphofructokinase activities were used as an indication of glycolytic capacity. Diabetes was associated with a general decrement in the activity of oxidative marker enzymes for all fiber types except the fast-twitch glycolytic fiber. In contrast, the fast-twitch glycolytic fibers demonstrated the greatest decline in glycolytic enzymatic activity. Insulin-treated animals, either trained or untrained, exhibited enzyme activities similar to their normal counterparts. Exercise training of diabetic rats mimicked the effect of insulin treatment and caused a near normalization of the activity of the marker enzymes. These findings suggest that the enzymatic potential of all skeletal muscle fiber types of diabetic rats may be normalized by exercise training even in the absence of significant amounts of insulin.

Further evidence of incomplete neural control of muscle properties in cat tibialis anterior motor units

1995 ◽  
Vol 268 (2) ◽  
pp. C527-C534 ◽  
Author(s):  
G. A. Unguez ◽  
R. R. Roy ◽  
D. J. Pierotti ◽  
S. Bodine-Fowler ◽  
V. R. Edgerton
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Neural Control ◽  
Periodic Acid ◽  
Muscle Fibers ◽  
Motor Units ◽  
Fiber Types ◽  
Muscle Properties ◽  
Periodic Acid Schiff ◽  
The Mean

To examine the influence of a motoneuron in maintaining the phenotype of the muscle fibers it innervates, myosin heavy chain (MHC) expression, succinate dehydrogenase (SDH) activity, and cross-sectional area (CSA) of a sample of fibers belonging to a motor unit were studied in the cat tibialis anterior 6 mo after the nerve branches innervating the anterior compartment were cut and sutured near the point of entry into the muscle. The mean, range, and coefficient of variation for the SDH activity and the CSA for both motor unit and non-motor unit fibers for each MHC profile and from each control and each self-reinnervated muscle studied was obtained. Eight motor units were isolated from self-reinnervated muscles using standard ventral root filament testing techniques, tested physiologically, and compared with four motor units from control muscles. Motor units from self-reinnervated muscles could be classified into the same physiological types as those found in control tibialis anterior muscles. The muscle fibers belonging to a unit were depleted of glycogen via repetitive stimulation and identified in periodic acid-Schiff-stained frozen sections. Whereas muscle fibers in control units expressed similar MHCs, each motor unit from self-reinnervated muscles contained a mixture of fiber types. In each motor unit, however, there was a predominance of fibers with the same MHC profile. The relative differences in the mean SDH activities found among fibers of different MHC profiles within a unit after self-reinnervation and those found among fibers in control muscles were similar, i.e., fast-2 < fast-1 < or = slow MHC fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Sign in / Sign up

Export Citation Format

Share Document