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Alfred Maier - One of the best experts on this subject based on the ideXlab platform.
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proportions of slow myosin heavy chain positive fibers in muscle spindles and adjoining Extrafusal fascicles and the positioning of spindles relative to these fascicles
Journal of Morphology, 1999Co-Authors: Alfred MaierAbstract:Chicken leg muscles were examined to calculate the percentages of slow myosin heavy chain (MHC)-positive fibers in spindles and in adjacent Extrafusal fascicles, and to clarify how the encapsulated portions of muscle spindles are positioned relative to these fascicles. Unlike mammals, in chicken leg muscles slow-twitch MHC and slow-tonic MHC are expressed in intrafusal fibers and in Extrafusal fibers, suggesting a close developmental connection between the two fiber populations. In 8-week-old muscles the proportions of slow MHC-positive Extrafusal fibers that ringed muscle spindles ranged from 0–100%. In contrast, proportions of slow MHC-positive intrafusal fibers in spindles ranged from 0–57%. Similar proportions in fiber type composition between intrafusal fibers and surrounding Extrafusal fibers were apparent at embryonic days 15 and 16, demonstrating early divergence of Extrafusal and intrafusal fibers. Muscle spindles were rarely located within single fascicles. Instead, they were commonly placed where several fascicles converged. The frequent extrafascicular location of spindles suggests migration of intrafusal myoblasts from developing clusters of Extrafusal fibers toward the interstitium, perhaps along a neurotrophic gradient established by sensory axons that are advancing in the connective tissue matrix that separates adjoining fascicles. J. Morphol. 242:157–165, 1999. © 1999 Wiley-Liss, Inc.
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Proportions of slow myosin heavy chain‐positive fibers in muscle spindles and adjoining Extrafusal fascicles, and the positioning of spindles relative to these fascicles
Journal of morphology, 1999Co-Authors: Alfred MaierAbstract:Chicken leg muscles were examined to calculate the percentages of slow myosin heavy chain (MHC)-positive fibers in spindles and in adjacent Extrafusal fascicles, and to clarify how the encapsulated portions of muscle spindles are positioned relative to these fascicles. Unlike mammals, in chicken leg muscles slow-twitch MHC and slow-tonic MHC are expressed in intrafusal fibers and in Extrafusal fibers, suggesting a close developmental connection between the two fiber populations. In 8-week-old muscles the proportions of slow MHC-positive Extrafusal fibers that ringed muscle spindles ranged from 0–100%. In contrast, proportions of slow MHC-positive intrafusal fibers in spindles ranged from 0–57%. Similar proportions in fiber type composition between intrafusal fibers and surrounding Extrafusal fibers were apparent at embryonic days 15 and 16, demonstrating early divergence of Extrafusal and intrafusal fibers. Muscle spindles were rarely located within single fascicles. Instead, they were commonly placed where several fascicles converged. The frequent extrafascicular location of spindles suggests migration of intrafusal myoblasts from developing clusters of Extrafusal fibers toward the interstitium, perhaps along a neurotrophic gradient established by sensory axons that are advancing in the connective tissue matrix that separates adjoining fascicles. J. Morphol. 242:157–165, 1999. © 1999 Wiley-Liss, Inc.
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Proportions of slow-twitch and fast-twitch Extrafusal fibers in receptive fields of tendon organs in chicken leg muscles.
The Anatomical Record, 1998Co-Authors: Alfred MaierAbstract:Golgi tendon organs are mechanoreceptors that monitor the contractile force produced by motor units. Receptors are most responsive to contractions of Extrafusal muscle fibers that terminate closest to them and on them. Three anterior and four posterior chicken leg muscles were examined. Proportions of immunohistochemically identified slow-twitch Extrafusal fibers and fast-twitch Extrafusal fibers were calculated for 374 tendon organ receptive fields. Tendon organs were observed in muscle regions occupied either by slow-twitch fibers or fast-twitch fibers only, but most were found in regions that contained both slow-twitch and fast-twitch Extrafusal fibers. The frequency with which each fiber type occurred near tendon organs approached the frequency with which it occurred in more inclusive regions. In receptive fields with mixed fiber populations, fast-twitch fibers were the predominant type, especially in the anterior leg muscles. Distribution patterns of Extrafusal fiber types adjacent to and farther removed from tendon organs suggest that afferent discharges from tendon organs are by and large unbiased measures of the contractile activity of the Extrafusal fiber population of the muscle portion in which the tendon organs are located. In mixed muscle regions, slow-twitch fibers and fast-twitch fibers attach on given tendon organs, enabling them to monitor forces produced by slow motor units and by fast motor units. Most tendon organs are situated in mixed Extrafusal fiber fields with high fast-twitch fiber content, indicating that in chicken leg muscles sensory feedback from tendon organs is largely one from fast motor units.
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Extracellular matrix and transmembrane linkages at the termination of intrafusal fibers and the outer capsule in chicken muscle spindles.
Journal of morphology, 1996Co-Authors: Alfred MaierAbstract:Attachments of intrafusal fibers and of the outer spindle capsule at the far polar region were examined by immunohistochemistry in serially sectioned chicken leg muscles. Patterns of distribution of connective tissues and intracellular filaments suggest that, in this segment of the muscle spindle, intrafusal fibers bind laterally with the capsule. Contrary to Extrafusal fibers at myotendinous junctions, folded plasmalemmas at the ends of intrafusal fibers were rare. Thus, there was little end-to-end interlocking between intrafusal fibers and the extracellular matrix. The tapered contours of terminating intrafusal fibers resembled those of Extrafusal fibers which end in fascicles without tendinous connections. At points where the distal portions of intrafusal fibers closely adjoined and overlapped Extrafusal fibers, alpha-actinin, vinculin, filamin, talin, beta 1 integrin, spectrin, and dystrophin occurred with moderate to great frequency. It is generally accepted that these compounds are links in molecular chains that extend from the intracellular space across cell membranes to the extracellular matrix. Their location along substantial lengths of Extrafusal fibers, distal capsule, and terminating intrafusal fibers suggests the presence of numerous transverse connections between elements of the terminal portion of the spindle and nonspindle tissues. Hence, it is likely that forces monitored by chicken spindles in muscles undergoing length changes are transferred from Extrafusal fibers and extracellular matrix to the receptors in large part via lateral shear instead of by longitudinal tension.
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Transient expression of a ventricular myosin heavy chain isoform in developing chicken intrafusal muscle fibers
Histochemistry, 1993Co-Authors: Alfred MaierAbstract:Sections of chicken tibialis anterior and extensor digitorium longus muscles were incubated with monoclonal antibodies against myosin heavy chains (MHC). Ventricular myosin was present in developing secondary intrafusal myotubes when they were first recognized at embryonic days (E) 13–14, and in developing Extrafusal fibers prior to that date. The reaction in intrafusal fibers began to fade at E17, and in 2-week-old postnatal and older muscles the isoform was no longer recognized. Only those intrafusal fibers which also reacted with a monoclonal antibody against atrial and slow myosin contained ventricular MHC. Intrafusal myotubes which developed into fast fibers did not express the isoform. Hence, based on the presence or absence of ventricular MHC, two lineages of intrafusal fiber are evident early in development. Strong immunostaining for ventricular MHC was observed in primary Extrafusal myotubes at E10, but the isoform was already downregulated at E14, when secondary intrafusal myotubes were still forming and expressed ventricular MHC. Only light to moderate and transient immunostaining was observed in coexisting secondary Extrafusal myotubes, most of which developed into fast fibers. Thus at the time when nascent muscle spindles are first recognized, differences in MHC profiles already exist between prospective intrafusal and Extrafusal fibers. If intrafusal fibers stem from a pool of primordial muscle cells, which is common to intrafusal and Extrafusal myotubes, they diverged from it some time prior to E13.
Chris Boulias - One of the best experts on this subject based on the ideXlab platform.
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Intrafusal effects of botulinum toxin injections for spasticity: revisiting a previous paper.
Neuroscience letters, 2013Co-Authors: Chetan P. Phadke, Yesim Kirazli, Farooq Ismail, Chris BouliasAbstract:a b s t r a c t Botulinum toxin, frequently used to manage focal limb spasticity, has been reported to affect both extra- fusal and intrafusal fibers of the injected muscle. Since most studies have used spinal reflexes, it is difficult to isolate the intrafusal effects from Extrafusal and central effects. In a paper by On et al. (7), both stretch and H-reflexes were used to examine the intrafusal effects of botulinum toxin injections. Revisiting the data from On et al. (7) presented a unique opportunity to describe a novel method of measuring the effect of botulinum toxin-A on muscle spindle activity in patients with spasticity. H-reflex, maximum M-wave, and Achilles tendon reflex were serially assessed in ten patients with stroke pre-, 2, 4, and 12 weeks post-botulinum. In order to assess the intrafusal effects, we subtracted the %change in H- reflex amplitude from baseline (representing Extrafusal and central effects) from the %change in Achilles tendon reflex amplitude from baseline (representing intrafusal, Extrafusal and central effects). Using this formula, our results suggest that botulinum induces significant chemodenervation of the intrafusal muscle fibers (33% decreases). Intrafusal effects were greatest at 2 weeks, but tapered off by 12 weeks post-botulinum (p < 0.017). We found a significant positive correlation between the intrafusal effects of botulinum toxin and changes in modified Ashworth scale. Our method of assessing the effects of botulinum toxin shows significant effect on intrafusal fibers, which correlates with clinical manifesta- tion of spasticity. Future studies need to investigate ways to maximize intrafusal effects and minimize Extrafusal effects of botulinum therapy.
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Intrafusal effects of botulinum toxin injections for spasticity: revisiting a previous paper.
Neuroscience letters, 2013Co-Authors: Chetan P. Phadke, Yesim Kirazli, Farooq Ismail, Chris BouliasAbstract:Abstract Botulinum toxin, frequently used to manage focal limb spasticity, has been reported to affect both Extrafusal and intrafusal fibers of the injected muscle. Since most studies have used spinal reflexes, it is difficult to isolate the intrafusal effects from Extrafusal and central effects. In a paper by On et al. [7] , both stretch and H-reflexes were used to examine the intrafusal effects of botulinum toxin injections. Revisiting the data from On et al. [7] presented a unique opportunity to describe a novel method of measuring the effect of botulinum toxin-A on muscle spindle activity in patients with spasticity. H-reflex, maximum M-wave, and Achilles tendon reflex were serially assessed in ten patients with stroke pre-, 2, 4, and 12 weeks post-botulinum. In order to assess the intrafusal effects, we subtracted the %change in H-reflex amplitude from baseline (representing Extrafusal and central effects) from the %change in Achilles tendon reflex amplitude from baseline (representing intrafusal, Extrafusal and central effects). Using this formula, our results suggest that botulinum induces significant chemodenervation of the intrafusal muscle fibers (33% decreases). Intrafusal effects were greatest at 2 weeks, but tapered off by 12 weeks post-botulinum (p
Jan Kucera - One of the best experts on this subject based on the ideXlab platform.
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Why adult mammalian intrafusal and Extrafusal fibers contain different myosin heavy-chain isoforms.
Trends in neurosciences, 1999Co-Authors: J Walro, Jan KuceraAbstract:Multiple isoforms of the contractile protein myosin are present in mammalian skeletal muscles. The diversity of the heavy-chain subunits of myosin (MyHCs) in intrafusal fibers is thought to reflect a pathway of differentiation that is unique to muscle spindles. In fact, intrafusal MyHCs are developmental isoforms expressed by the prenatal precursors of both intrafusal and Extrafusal fibers. In adult limbs, developmental MyHCs persist in intrafusal, but not Extrafusal fibers principally due to the afferent neurons that arrest their maturational replacement by MyHCs associated with faster shortening velocities. The slow shortening velocities that are characteristic of developmental MyHCs might be adaptive for precise calibration of muscle spindles as sense organs.
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Origin of intrafusal fibers from a subset of primary myotubes in the rat.
Anatomy and embryology, 1995Co-Authors: Jan Kucera, J WalroAbstract:S46, a monoclonal antibody (mAb) specific for the SM-1 and SM-2 isoforms of avian slow myosin heavy chains (MHC), was used to study the earliest stages of development of intrafusal fibers in muscle spindles of the rat hindlimb. Spindles formed only in the regions of fetal muscles that contained primary myotubes reactive to mAb S46, such as the axial region of the tibialis anterior muscle. The first intrafusal fiber to form, the nuclear bag2 fiber, originated from within the population of S46-reactive primary myotubes. Binding of mAb S46 by myotubes giving rise to the bag2 fibers preceded the appearance of encapsulated spindles in the muscles by electron microscopy. However, reactivity to S46 intensified in the myotubes transforming into bag2 fibers after the innervation of the fibers by afferents, and dissipated in myotubes differentiating into slow-twitch (type I) Extrafusal fibers. Thus, afferents may enhance intrafusal expression of the MHC isoform reactive to mAb S46. The pattern of S46 binding to nuclear bag and chain intrafusal fibers in both developing and adult spindles was the same as that reported for the mAb ALD19, suggesting that both antibodies bind to the same MHC isoform. This isoform is probably a developmental form of slow myosin, because it was transiently expressed during the development of type I Extrafusal fibers. The origin of bag2 intrafusal and type I Extrafusal fibers from a bipotential subpopulation of primary myotubes reactive to mAb S46 correlates with the location of muscle spindles in the slow regions of muscles in adult rat hindlimbs.
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differential effects of neonatal denervation on intrafusal muscle fibers in the rat
Anatomy and Embryology, 1993Co-Authors: Jan Kucera, J Walro, Judith ReichlerAbstract:The response of developing muscle spindles to denervation was studied by sectioning the nerve to the medial gastrocnemius muscle of rats at birth. The denervated spindles were examined daily throughout the first postnatal week for changes in ultrastructure and expression of several isoforms of myosin heavy chain (MHC). Each of the three different types of intrafusal muscle fiber exhibited a different response to denervation. Within 5 days after the nerve section nuclear bag2 fibers degenerated completely; nuclear bag1 fibers persisted, but ceased to express the ‘spindle-specific’ slow-tonic MHC isoform and thereby could not be differentiated from Extrafusal fibers; nuclear chain fibers did not form. The capsules of spindles disassembled, hence spindles or their remnants could no longer be identified 1 week after denervation. Neonatal deefferentation has little effect on these features of developing spindles, so removal of afferent innervation is presumably the factor that induces the loss of spindles in denervated muscles. Degeneration of the bag2 fiber, but not bag1 or Extrafusal fibers, reflects a greater dependence of the bag2 fiber than the bag1 fiber on afferent innervation for maintenance of its structural integrity. This difference in response of the two types of immature bag fiber to denervation might reflect an origin of the bag2 fibers from a lineage of myogenic cells distinct from that giving rise to bag1 or Extrafusal fibers, or a difference in the length of contact with afferents between the two types of bag fiber prior to nerve section.
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Transient expression of a slow-tonic MHC isoform by Extrafusal fibers in the developing rat.
Anatomy and embryology, 1993Co-Authors: Jan Kucera, J WalroAbstract:ALD 19, a monoclonal antibody that recognizes the slow-tonic myosin heavy chain (MHC) isoform, has been used extensively as a marker for nuclear bag intrafusal fibers of muscle spindles in developing and adult rats. Extrafusal fibers of adult rat hindlimb muscles do not express slow-tonic MHC. However, while using ALD 19 to trace the fate of intrafusal fibers following neonatal denervation, we noted that some Extrafusal fibers of neonates also bound this antibody. The immunolabeled Extrafusal fibers were a subset of slow fibers located in the deep axial regions of crural muscles. The same fiber subset transiently displayed a weak affinity for ALD 19 during the first postnatal week in normal muscles. Denervation at birth increased the intensity of ALD 19 immunolabelling by these Extrafusal fibers and extended the duration of the slow-tonic immunoreactivity into the 2nd postnatal week, after which expression diminished or ceased. Demonstration that some developing Extrafusal fibers have a nerve-independent capacity for transiently expressing slow-tonic MHC, an MHC previously thought to be expressed only by intrafusal fibers, raises the possibility that both types of fiber originate from a subset of bipotential slow primary myotubes in rat hindlimbs.
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Expression of type-specific MHC isoforms in rat intrafusal muscle fibers.
The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society, 1992Co-Authors: Jan Kucera, J Walro, L. GorzaAbstract:Myosin heavy chain (MHC) expression by intrafusal fibers was studied by immunocytochemistry to determine how closely it parallels MHC expression by Extrafusal fibers in the soleus and tibialis ante...
William K. Ovalle - One of the best experts on this subject based on the ideXlab platform.
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Distribution of dystrophin and neurofilament protein in muscle spindles of normal and mdx‐dystrophic mice: An immunocytochemical study
The Anatomical Record, 1993Co-Authors: Patrick C. Nahirney, William K. OvalleAbstract:Dystrophin is a high molecular weight protein localized under the sarcolemma of normal Extrafusal muscle fibers but absent in skeletal muscle of Duchenne muscular dystrophy patients and mdx mice. Muscle spindles in the soleus of 32-week-old normal and age-matched mdx mice were examined by immunocytochemical methods to determine the localization of dystrophin in polar and equatorial regions of the intrafusal fibers. Spindles were serially sectioned in transverse and longitudinal planes, and were double-labelled with an antibody to dystrophin and with an antibody to a 200 kD neurofilament protein, which revealed their sensory innervation. By fluorescence microscopy, intrafusal fibers in the soleus of mdx mice were deficient in dystrophin throughout their lengths, whereas their sensory nerve terminals stained intensely with the nerve-specific antibody and appeared unaltered in dystrophy. In the normal soleus, intrafusal fibers displayed a regional variability in the distribution of dystrophin. Polar regions of bag and chain fibers exhibited a peripheral rim of sarcolemmal staining equivalent to that seen in the neighboring Extrafusal fibers. Dystrophin labelling in equatorial regions of normal intrafusal fibers, however, showed dystrophin-deficient segments alternating in a spiral fashion with positive-staining domains along the sarcolemma. Double-labelling for dystrophin and neurofilament protein showed that these dystrophin-deficient sites were subjacent to the annulospiral sensory nerve wrappings terminating on the intrafusal fibers. These findings suggest that dystrophin is not an integral part of the subsynaptic sensory membrane in equatorial regions of normal intrafusal fibers and thus is not directly related to sensory signal transduction. The complete absence of this protein in mdx intrafusal fibers indicates that these fibers exhibit the same primary defect in muscular dystrophy as seen in the Extrafusal fibers. However, because of their small diameters, capsular investment, and relatively low tension outputs, dystrophic intrafusal fibers may be less prone to the sarcolemmal membrane disruption that is characteristic of Extrafusal fibers in this disorder.
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Morphometry and histoenzymology of the hamster tenuissimus and its muscle spindles.
The Anatomical record, 1992Co-Authors: Robert M. Patten, William K. OvalleAbstract:Muscle spindles and Extrafusal fibers in the tenuissimus muscle of mature golden Syrian hamsters were studied morphologically and quantitatively using several light microscopic techniques. Muscle spindles were identified in serial-transvere frozen-sections of whole muscles stained with hematoxylin and eosin. Five tenuissimus muscles were examined from origin to insertion, and the locations of individual receptors were plotted in camera-lucida reconstructions. Spindles were found in proximity to the main neurovascular bundle in the central core of each muscle. A range of 16–20 receptors was noted per muscle. The mean muscle spindle index (the total number of spindles per gram of muscle weight) was 503 and the average spindle length was 7.5 mm. Oxidative enzyme and myosin adenosine-triphosphatase (ATPase) staining profiles were also evaluated in the intrafusal and Extrafusal fibers in each muscle. Even numbers of type I and type IIA Extrafusal fibers were distributed homogeneously throughout all muscle cross-sections. Histochemical staining patterns varied along the lengths of the three intrafusal fiber types. Nuclear chain fibers possessed staining properties similar to the type IIA Extrafusal fibers and exhibited no regional variations. Bag1 fibers displayed staining variability, particularly when treated for myosin ATPase under acid preincubation conditions. Some spindles were isolated under darkfield illumination and then either treated with 7-nitrobenz-2-oxa-1, 3-diazole (NBD)-phallacidin to detect filamentous actin by fluorescence microscopy, or prepared for conventional scanning electron microscopy (SEM). By fluorescence microscopy, a registered actin banding-pattern was observed in the sarcomeres of the intrafusal fibers, and variations in the intensity of banding were noted amongst different fibers. SEM revealed punctaie sensory nerve endings that adhered intimately to the surfaces of underlying intrafusal fibers in the equatorial and juxtaequatorial regions. By transmission electron microscopy (TEM) these endings appeared crescent-shaped and were enveloped by external laminae. Each profile contained numerous mitochondria and cytoskeletal organelles. The high spindle density observed in this muscle suggests that the hamster tenuissimus may function in hindlimb proprioception.
J Walro - One of the best experts on this subject based on the ideXlab platform.
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Why adult mammalian intrafusal and Extrafusal fibers contain different myosin heavy-chain isoforms.
Trends in neurosciences, 1999Co-Authors: J Walro, Jan KuceraAbstract:Multiple isoforms of the contractile protein myosin are present in mammalian skeletal muscles. The diversity of the heavy-chain subunits of myosin (MyHCs) in intrafusal fibers is thought to reflect a pathway of differentiation that is unique to muscle spindles. In fact, intrafusal MyHCs are developmental isoforms expressed by the prenatal precursors of both intrafusal and Extrafusal fibers. In adult limbs, developmental MyHCs persist in intrafusal, but not Extrafusal fibers principally due to the afferent neurons that arrest their maturational replacement by MyHCs associated with faster shortening velocities. The slow shortening velocities that are characteristic of developmental MyHCs might be adaptive for precise calibration of muscle spindles as sense organs.
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Origin of intrafusal fibers from a subset of primary myotubes in the rat.
Anatomy and embryology, 1995Co-Authors: Jan Kucera, J WalroAbstract:S46, a monoclonal antibody (mAb) specific for the SM-1 and SM-2 isoforms of avian slow myosin heavy chains (MHC), was used to study the earliest stages of development of intrafusal fibers in muscle spindles of the rat hindlimb. Spindles formed only in the regions of fetal muscles that contained primary myotubes reactive to mAb S46, such as the axial region of the tibialis anterior muscle. The first intrafusal fiber to form, the nuclear bag2 fiber, originated from within the population of S46-reactive primary myotubes. Binding of mAb S46 by myotubes giving rise to the bag2 fibers preceded the appearance of encapsulated spindles in the muscles by electron microscopy. However, reactivity to S46 intensified in the myotubes transforming into bag2 fibers after the innervation of the fibers by afferents, and dissipated in myotubes differentiating into slow-twitch (type I) Extrafusal fibers. Thus, afferents may enhance intrafusal expression of the MHC isoform reactive to mAb S46. The pattern of S46 binding to nuclear bag and chain intrafusal fibers in both developing and adult spindles was the same as that reported for the mAb ALD19, suggesting that both antibodies bind to the same MHC isoform. This isoform is probably a developmental form of slow myosin, because it was transiently expressed during the development of type I Extrafusal fibers. The origin of bag2 intrafusal and type I Extrafusal fibers from a bipotential subpopulation of primary myotubes reactive to mAb S46 correlates with the location of muscle spindles in the slow regions of muscles in adult rat hindlimbs.
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differential effects of neonatal denervation on intrafusal muscle fibers in the rat
Anatomy and Embryology, 1993Co-Authors: Jan Kucera, J Walro, Judith ReichlerAbstract:The response of developing muscle spindles to denervation was studied by sectioning the nerve to the medial gastrocnemius muscle of rats at birth. The denervated spindles were examined daily throughout the first postnatal week for changes in ultrastructure and expression of several isoforms of myosin heavy chain (MHC). Each of the three different types of intrafusal muscle fiber exhibited a different response to denervation. Within 5 days after the nerve section nuclear bag2 fibers degenerated completely; nuclear bag1 fibers persisted, but ceased to express the ‘spindle-specific’ slow-tonic MHC isoform and thereby could not be differentiated from Extrafusal fibers; nuclear chain fibers did not form. The capsules of spindles disassembled, hence spindles or their remnants could no longer be identified 1 week after denervation. Neonatal deefferentation has little effect on these features of developing spindles, so removal of afferent innervation is presumably the factor that induces the loss of spindles in denervated muscles. Degeneration of the bag2 fiber, but not bag1 or Extrafusal fibers, reflects a greater dependence of the bag2 fiber than the bag1 fiber on afferent innervation for maintenance of its structural integrity. This difference in response of the two types of immature bag fiber to denervation might reflect an origin of the bag2 fibers from a lineage of myogenic cells distinct from that giving rise to bag1 or Extrafusal fibers, or a difference in the length of contact with afferents between the two types of bag fiber prior to nerve section.
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Transient expression of a slow-tonic MHC isoform by Extrafusal fibers in the developing rat.
Anatomy and embryology, 1993Co-Authors: Jan Kucera, J WalroAbstract:ALD 19, a monoclonal antibody that recognizes the slow-tonic myosin heavy chain (MHC) isoform, has been used extensively as a marker for nuclear bag intrafusal fibers of muscle spindles in developing and adult rats. Extrafusal fibers of adult rat hindlimb muscles do not express slow-tonic MHC. However, while using ALD 19 to trace the fate of intrafusal fibers following neonatal denervation, we noted that some Extrafusal fibers of neonates also bound this antibody. The immunolabeled Extrafusal fibers were a subset of slow fibers located in the deep axial regions of crural muscles. The same fiber subset transiently displayed a weak affinity for ALD 19 during the first postnatal week in normal muscles. Denervation at birth increased the intensity of ALD 19 immunolabelling by these Extrafusal fibers and extended the duration of the slow-tonic immunoreactivity into the 2nd postnatal week, after which expression diminished or ceased. Demonstration that some developing Extrafusal fibers have a nerve-independent capacity for transiently expressing slow-tonic MHC, an MHC previously thought to be expressed only by intrafusal fibers, raises the possibility that both types of fiber originate from a subset of bipotential slow primary myotubes in rat hindlimbs.
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Expression of type-specific MHC isoforms in rat intrafusal muscle fibers.
The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society, 1992Co-Authors: Jan Kucera, J Walro, L. GorzaAbstract:Myosin heavy chain (MHC) expression by intrafusal fibers was studied by immunocytochemistry to determine how closely it parallels MHC expression by Extrafusal fibers in the soleus and tibialis ante...
