Differential-effects Of Neonatal Denervation On Intrafusal Muscle-fibers In The Rat
afferents; Anatomy & Morphology; denervation; Developmental Biology; expression; heavy-chain isoforms; innervation; intrafusal muscle fiber; motor denervation; muscle spindles; myosin heavy chains; neonatal rat; nerve dependence; nerve growth-factor; spindle development; spindles
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 bag, 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.
Kucera J; Walro J M; Reichler J
Anatomy and Embryology
1993
1993-04
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00185898" target="_blank" rel="noreferrer noopener">10.1007/bf00185898</a>
Expression Of Type-specific Mhc Isoforms In Rat Intrafusal Muscle-fibers
cat; Cell Biology; differentiation; fiber types; histochemistry; identification; immunocytochemistry; innervation; intrafusal; monoclonal antimyosin antibodies; monoclonal-antibody; motor; muscle fiber typing; muscle spindles; myosin heavy-chain; rat skeletal muscle; skeletal-muscle; spindles
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 anterior muscles of the rat. Among the MHC isoforms expressed in extrafusal fibers, only the slow-twitch MHC of Type 1 extrafusal fibers was expressed along much of the fibers. Monoclonal antibodies (MAb) specific for this MHC bound to the entire length of bag2 fibers and the extracapsular region of bag1 fibers. The fast-twitch MHC isoform strongly expressed by bag2 and chain fibers had an epitope not recognized by MAb to the MHC isoforms characteristic of developing muscle fibers or the three subtypes (2A, 2B, 2X) of Type 2 extrafusal fibers. Therefore, intrafusal fibers may express a fast-twitch MHC that is not expressed by extrafusal fibers. Unlike extrafusal fibers, all three intrafusal fiber types bound MAb generated against mammalian heart and chicken limb muscles. The similarity of the fast-twitch MHC of bag2 and chain fibers and the slow-tonic MHC of bag1 and bag2 fibers to the MHC isoforms expressed in avian extrafusal fibers suggests that phylogenetically primitive MHCs might persist in intrafusal fibers. Data are discussed relative to the origin and regional regulation of MHC isoforms in intrafusal and extrafusal fibers of rat hindlimb muscles.
Kucera J; Walro J M; Gorza L
Journal of Histochemistry & Cytochemistry
1992
1992-02
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1177/40.2.1552171" target="_blank" rel="noreferrer noopener">10.1177/40.2.1552171</a>
Influence Of Muscle-cell Substrates On Differentiation Of Intrafusal Fiber Types In Neonatal Rats
expression; gastrocnemius; myogenesis; myosin heavy-chain; nerve crush; Neurosciences & Neurology; spindles
Rat muscle spindles contain one nuclear bag2, one nuclear bag1, and two nuclear chain fibers. The three different types of intrafusal fiber in spindles may be a reflection of concomitant changes in proportions of slow primary, slow/fast secondary, and fast secondary myotubes during the period of spindle development. We examined whether experimentally altering the available muscle substrates would impact the intrafusal fiber type composition of spindles. De novo formation of spindles in muscles devoid of primary myotubes was induced by crushing the nerve to the medial gastrocnemius muscle in newborn rats and administering nerve growth factor for ten days afterwards. Encapsulated fibers of the reinnervated muscles examined one month after nerve crush had myofibrillar adenosine triphosphatase and myosin heavy chain profiles similar to normal bag2, bag1, or chain intrafusal fibers. However, spindles in reinnervated muscles contained fewer fibers than controls. Most experimental spindles contained chain and/or bag1 fibers, the two fiber types which ordinarily arise during secondary myogenesis. In contrast, bag2 fibers, fibers that normally form concomitant with primary myogenesis, were absent from nearly 90% of spindles in reinnervated muscles. The paucity of bag2 fibers may reflect the absence of primary myotubes, whereas the prevalence of chain and/or bag1 fibers may reflect that secondary myotubes or myofibers that descended from the secondary myotubes were the principal muscle substrates available for spindle formation in the nerve-crushed muscles. The paucity of bag2 fibers in spindles formed in muscles devoid of primary myotubes suggests that the types of muscle substrates available to afferents are an important determinant of intrafusal fiber types in muscle spindles, and that the formation of a bag2 fiber in an intrafusal bundle is not essential for the subsequent differentiation of chain and/or bag1 fibers.
Kucera J; Walro J M; Gao Y
Neuroscience
1993
1993-02
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/0306-4522(93)90546-r" target="_blank" rel="noreferrer noopener">10.1016/0306-4522(93)90546-r</a>
Transient Expression Of A Slow-tonic Mhc Isoform By Extrafusal Fibers In The Developing Rat
Anatomy & Morphology; denervation; Developmental Biology; diversity; extrafusal fibers; intrafusal fibers; intrafusal muscle-fibers; monoclonal-antibody; motor innervation; muscle; myosin heavy-chain; neonatal rats; skeletal-muscle; slow-tonic myosin; spindles
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.
Kucera J; Walro J M
Anatomy and Embryology
1993
1993-10
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00185950" target="_blank" rel="noreferrer noopener">10.1007/bf00185950</a>
Slow-tonic Mhc Expression In Paralyzed Hindlimbs Of Fetal Rats
Cell Biology; heavy-chain isoforms; innervation; intrafusal muscle-fibers; numbers; spindles
Whether nerve activity and active contraction of myotubes are essential for the assembly and initial differentiation of muscle spindles was investigated by paralyzing fetal rats with tetrodotoxin (TTX) from embryonic day 16 (E16) to E21, prior to and during the period when spindles typically form. TTX-treated soleus muscles were examined by light and electron microscopy for the presence of spindles and expression of myosin heavy chain (MHC) isoforms by the intrafusal fibers. Treatment with TTX did not inhibit the formation of a spindle capsule or the expression of a slow-tonic MHC isoform characteristic of intrafusal fibers, but did retard development of spindles. Spindles of TTX-treated E21 muscles usually consisted of one intrafusal fiber (bag2) only rather than two fibers (bag1 and bag2) typically present in untreated (control) E21 spindles. Intrafusal fibers of TTX-treated spindles also had only one sensory region supplied by multiple afferents, and were devoid of motor innervation. These features are characteristic of spindles in normal E18-E19 muscles. Thus, nerve and/or muscle activity is not essential for the assembly of muscle spindles, formation of a spindle capsule, and transformation of undifferentiated myotubes into the intrafusal fibers containing spindle-specific myosin isoforms. However, activity may promote the maturation of intrafusal bundles, as well as the maturation of afferent and efferent nerve supplies to intrafusal fibers.
Kucera J; Walro J M
Histochemistry
1991
1991
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00266761" target="_blank" rel="noreferrer noopener">10.1007/bf00266761</a>
Sequences Of Intrafusal Fiber Formation Are Muscle-dependent In Rat Hindlimbs
Anatomy & Morphology; cat; development; Developmental Biology; embryonic-development; expression; innervation; intrafusal fibers; motor; muscle; muscle spindles; myosin heavy chains; myosin heavy-chain; neonatal rats; skeletal-muscle; slow myosin; spindles; tenuissimus muscles
A rat muscle spindle typically contains four intrafusal fibers - one nuclear bag(2), one nuclear bag, and two nuclear chain fibers. We compared the sequence of formation of the three intrafusal fiber types among the tibialis anterior (TA), soleus (SOL) and medial gastrocnemius (RIG) muscles using immunocytochemistry of spindle-specific myosin heavy chain isoforms. Spindles of the TA began to differentiate earlier and acquired the full complement of intrafusal fibers sooner than spindles of the SOL or MG muscles. At the onset of spindle assembly, the intrafusal myotubes expressed myosin heavy chains similar to those expressed by extrafusal myotubes. The first intrafusal myotube then differentiated into the bag, fiber regardless of the muscle. However, the fate of the second-forming intrafusal myotube varied among the muscles studied. It usually differentiated into a chain fiber in the TA, into a bag(1) fiber in the SOL, and into either a bag(1) or a chain in the MG. The fate of the third-forminge was reciprocal to that of the second; i.e. in those spindles in which the bag(1) fiber was second to form, a chain was third, and vice versa. The fourth and last intrafusal myotube gave rise to a chain fiber. The inter- and intramuscular variability in the fate of intrafusal myotubes of the second and third generation argues against the existence of a program intrinsic to the myotubes that would mandate their differentiation along specific paths. Rather, an extrinsic regulatory factor, probably associated with the primary afferent neuron, may govern differentiation of pluripotential myotubes into particular types of intrafusal fiber. The fate of the intrafusal myotubes might then depend on the timing of the regulatory effect of afferents relative to the stage of development of the intrafusal bundle.
Kucera J; Walro J M
Anatomy and Embryology
1994
1994-09
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00234305" target="_blank" rel="noreferrer noopener">10.1007/bf00234305</a>