Fusimotor-free Spindles In Reinnervated Muscles Of Neonatal Rats Treated With Nerve Growth-factor
crush; fibers; hindlimb muscles; injury; innervation; Neurosciences & Neurology; sensory neurons; survival
Crushing the nerve to the medial gastrocnemius muscle in newborn rats and administering nerve growth factor afterwards results in a reinnervated muscle containing supernumerary muscle spindles. The structure and innervation of 88 spindles in the reinnervated muscles were reconstructed from serial thick and thin transverse sections at 30 35 days after the nerve crush, and compared to those of five control spindles. The spindles consisted of one to four small-diameter encapsulated fibers with features of nuclear chain intrafusal fibers, or infrequently a nuclear bag intrafusal fiber. Some of the spindles were located within a capsule that also contained an extrafusal fiber. Each spindle was innervated by an afferent with features of the primary afferent. The density of secondary afferents was lower in reinnervated muscles than in controls. Endplates were observed on extrafusal fibers in the experimental muscles. attesting to restoration of skeletomotor (alpha) innervation after the nerve crush. However, 78% of the experimental spindles were entirely devoid of efferent innervation. The remainder received either one or two fusimotor (gamma) axons or a skeletofusimotor (beta) axon, compared to the six to eight motor axons that innervated control spindles. The presence of supernumerary spindles composed of fibers that resemble normal intrafusal fibers in the absence of motor innervation suggests that afferents alone can induce the formation and subsequent differentiation of intrafusal fibers in nerve-crushed muscles of neonatal rats. In addition, the paucity of gamma innervation in nerve-crushed muscles suggests that immature gamma neurons are more susceptible than spindle afferents or alpha efferents to cell death after axotomy at birth.
Kucera J; Walro J M; Gao Y
Neuroscience
1993
1993-01
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/0306-4522(93)90194-k" target="_blank" rel="noreferrer noopener">10.1016/0306-4522(93)90194-k</a>
Superfluousness Of Motor Innervation For The Formation Of Muscle-spindles In Neonatal Rats
afferents; Anatomy & Morphology; Developmental Biology; efferents; expression; fibers; intrafusal muscle fiber; muscle differentiation; neonatal rat; nerve dependence; nerve lesion; spindle development
Muscle spindles form de novo in reinnervated muscles of neonatal rats treated with nerve growth factor. Whether the spindles can also form in muscle reinnervated only by afferents was investigated by removing the lumbosacral segment of the spinal cord immediately after crushing the nerve to the medial gastrocnemius muscle at birth, and administering nerve growth factor for 10 days afterwards. As predicted, the medial gastrocnemius muscles were reinnervated by afferents, but not efferents. No motor endplates were visible on any muscle fibers, and extrafusal fibers were atrophied. The reinnervated muscles contained spindle-like encapsulations of one to four fibers at 5, 7, 9 and 30 days after the nerve crush. The number of spindles as well as encapsulated fibers exceeded that of normal medial gastrocnemius muscles. The encapsulated fibers resembled typical intrafusal fibers. They had normal sensory-muscle contacts, but no motor endings. The fibers displayed equatorial clusters of myonuclei and expressed the spindle-specific slow-tonic myosin heavy chain isoform at postnatal day 30. Thus, efferents are not essential for the formation and differentiation of muscle spindles in reinnervated muscles of neonatal rats.
Kucera J; Walro J M
Anatomy and Embryology
1992
1992-09
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00185978" target="_blank" rel="noreferrer noopener">10.1007/bf00185978</a>
An Immunocytochemical Marker For Early-type-i Muscle-fibers In The Developing Rat Hindlimb
Anatomy & Morphology; Developmental Biology; expression; extrafusal; fibers; isoforms; mhc isoforms; muscle development; myosin heavy-chain; myotubes; skeletal-muscle; slow myosin; slow myosins; type i fibers
Muscle fibers develop sequentially from several generations of myotubes that express specific isoforms of myosin heavy chain (MHC). We observed that the chicken-derived monoclonal antibody (mAb) S46 binds to myotubes of the fetal rat hindlimb in a specific temporal and spatial pattern. To determine the type and fate of the S46-reactive myotubes, we immunoreacted sections of fetal, neonatal and postnatal hindlimb muscles to this antibody. The mAb S46 bound to a subpopulation of primary myotubes in the tibialis anterior, and to all primary and slow/fast secondary myotubes in the soleus muscle. The S46-reactive primary myotubes represented the oldest set of myotubes in the muscles. Reactivity to S46 was present from the earliest stages of muscle development, peaked in the late fetal period, and dissipated in the first postnatal week, suggesting that mAb S46 binds to a developmental form of slow myosin. The regional distribution of myotubes that bound S46 in fetal muscles was identical to the distribution of type I (slow-twitch) fibers in the adult, indicating that S46-reactive myotubes ultimately develop into type I extrafusal fibers. Thus, mAb S46 can be used as a marker for prospective type I extrafusal fibers in the rat hindlimb.
Kucera J; Walro J M
Anatomy and Embryology
1995
1995-08
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00186002" target="_blank" rel="noreferrer noopener">10.1007/bf00186002</a>
Formation Of Muscle-spindles In The Absence Of Motor Innervation
afferent; differentiation; efferent; fibers; intrafusal muscle fiber; muscle; nerve; Neurosciences & Neurology; rat; spindle development
Whether muscle spindles can form in muscles innervated only by afferents was investigated by removing the lumbosacral segment of the spinal cord immediately after crushing the nerve to the medial gastrocnemius (MG) muscle in newborn rats, and administering nerve growth factor for 10 days afterwards. The nerve-crushed MG muscles reinnervated by afferents in the absence of motor innervation were examined at postnatal (P) days 7, 9 and 30 for the presence of spindles by light and electron miscroscope. Reinnervated MG muscles contained spindle-like encapsulations of 1-4 fibers at 7, 9 and 30 days after the nerve crush. The number of spindles exceeded that of normal MG muscles, suggestive of de novo formation of spindles. All nerve-muscle contacts in the spindles had features of sensory endings, and intrafusal fibers expressed the spindle-specific slow-tonic myosin heavy chain (MHC) isoform at P30. No motor endplates were visible on any muscle fibers and extrafusal fibers were atrophied, as would be predicted in the absence of motor innervation. Thus, efferents are not essential for the formation and differentiation of muscle spindles in reinnervated muscles of neonatal rats.
Kucera J; Walro J M
Neuroscience Letters
1992
1992-09
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/0304-3940(92)90200-q" target="_blank" rel="noreferrer noopener">10.1016/0304-3940(92)90200-q</a>
Aggregation Of Myonuclei And The Spread Of Slow-tonic Myosin Immunoreactivity In Developing Muscle-spindles
Cell Biology; expression; fibers; heavy-chain isoforms; innervation; motor; rat; skeletal-muscle
The pattern of regional expression of a slowtonic myosin heavy chain (MHC) isoform was studied in developing rat soleus intrafusal muscle fibers. Binding of the slow-tonic antibody (ATO) began at the equator of prenatal intrafusal fibers where sensory nerve endings are located, and spread into the polar regions of nuclear bag2 and bag1 fibers but not nuclear chain fibers during ontogeny. The onset of the ATO reactivity coincided with the appearance of equatorial clusters of myonuclei (nuclear bag formations) in bag1 and bag2 fibers. Moreover, the intensity of the ATO reaction was strongest in the region of equatorial myonuclei and decreased with increasing distance from the equator of bag1 and bag2 fibers at all stages of prenatal and postnatal development. The polar expansion of ATO reactivity continued throughout the postnatal development of bag1 fibers, but ceased shortly after birth in bag2 fiber coincident with innervation by motor axons. Thus, afferents that innervate the equator might induce the slow-tonic MHC isoform in bag2 and bag1 fibers by regulating the myosin gene expression by equatorial myonuclei, and efferents or twitch contractile activity might inhibit the spread of the slow-tonic MHC isoform into the poles of bag2 but not bag1 fibers. Absence of ATO binding in chain fibers suggests that chain myotubes may not be as susceptible to the effect of afferents as are myotubes that develop into bag2 and bag1 fibers. The different patterns of slow-tonic MHC expression in the three types of intrafusal fiber may therefore result from the interaction of three elements: sensory neurons, motor neurons, and intrafusal myotubes.
Kucera J; Walro J M
Histochemistry
1991
1991
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1007/bf00315994" target="_blank" rel="noreferrer noopener">10.1007/bf00315994</a>
Axotomy Induces Fusimotor-free Muscle-spindles In Neonatal Rats
fibers; fusimotor system; intrafusal; intrafusal muscle fiber; nerve; Neurosciences & Neurology; spindle development
Crushing the nerve to the medial gastrocnemius (MG) muscle at birth and administering nerve growth factor to rats afterwards results in a reinnervated muscle with supernumerary muscle spindles, some of which must have formed de novo. Structure and innervation of spindles in the reinnervated MG muscles were studied in serial 1-mu-m transverse sections. Two types of spindle-like encapsulations were observed. The prevalent type consisted of one to three small diameter intrafusal fibers with features of nuclear chain fibers or infrequently a nuclear bag fiber. The second type of encapsulation consisted of the small-diameter fibers located in a compartment which abutted a compartment containing a large diameter extrafusal fiber. All intrafusal fibers in spindles of the experimental muscles were innervated by afferents, but most of them (85%) were devoid of efferent innervation. Thus, immature fusimotor neurons may be more susceptible than spindle afferents to cell death after axotomy at birth.
Kucera J; Walro J
Neuroscience Letters
1992
1992-03
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/0304-3940(92)90052-9" target="_blank" rel="noreferrer noopener">10.1016/0304-3940(92)90052-9</a>