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At least 919 records · Page 51Linked to original sources
PubMed1988

Innervation of developing intrafusal muscle fibers in the rat.

The chronology of development of spindle neural elements was examined by electron microscopy in fetal and neonatal rats. The three types of intrafusal muscle fiber of spindles from the soleus muscle acquired sensory and motor innervation in the same sequence as they formed--bag2, bag1, and chain. Both the primary and secondary afferents contacted developing spindles before day 20 of gestation. Sensory endings were present on myoblasts, myotubes, and myofibers in all intrafusal bundles regardless of age. The basic features of the sensory innervation--first-order branching of the parent axon, separation of the primary and secondary sensory regions, and location of both primary and secondary endings beneath the basal lamina of the intrafusal fibers--were all established by the fourth postnatal day. Cross-terminals, sensory terminals shared by more than one intrafusal fiber, were more numerous at all developmental stages than in mature spindles. No afferents to immature spindles were supernumerary, and no sensory axons appeared to retract from terminations on intrafusal fibers. The earliest motor axons contacted spindles on the 20th day of gestation or shortly afterward. More motor axons supplied the immature spindles, and a greater number of axon terminals were visible at immature intrafusal motor endings than in adult spindles; hence, retraction of supernumerary motor axons accompanies maturation of the fusimotor system analogous to that observed during the maturation of the skeletomotor system. Motor endings were observed only on the relatively mature myofibers; intrafusal myoblasts and myotubes lacked motor innervation in all age groups. This independence of the early stages of intrafusal fiber assembly from motor innervation may reflect a special inherent myogenic potential of intrafusal myotubes or may stem from the innervation of spindles by sensory axons.

Animals↗
PubMed2004

Lamprey contractile protein genes mark different populations of skeletal muscles during development.

Agnathan lampreys retain ancestral characteristics of vertebrates in the morphology of skeletal muscles derived from two mesodermal regions: trunk myotomes and unsegmented head mesoderm. During lamprey development, some populations of myoblasts migrate via pathways that differ from those of gnathostomes. To investigate the evolution of skeletal muscle differentiation in vertebrates, we characterize multiple contractile protein genes expressed in the muscle cells of the Japanese lamprey, Lethenteron japonicum. Lamprey actin gene LjMA2, and myosin heavy chain (MyHC) genes LjMyHC1 and LjMyHC2 are all expressed in the developing skeletal muscle cells of early embryos. However, LjMyHC1 and LjMyHC2 are expressed only in cells originating from myotomes, while LjMA2 is expressed in both myotomal and head musculature. Thus, in lampreys, myotomes and head mesoderm differ in the use of genes encoding contractile protein isoforms. Phylogenetic tree analyses including lamprey MyHCs suggest that the variety of muscle MyHC isoforms in different skeletal muscles may correspond to the morphological complexity of skeletal muscles of different vertebrate species. Another lamprey actin gene LjMA1 is likely to be the first smooth muscle actin gene isolated from non-tetrapods. We conclude that, in vertebrate evolution, the different regulatory systems for striated and smooth muscle-specific genes may have been established before the agnathan/gnathostome divergence.

Actins↗
PubMed1989

Developing skeletal muscle: the importance of the physical properties of water.

We are proposing that cellular water becomes organized through its interaction with the various macromolecular (particularly protein) matrices of the cell. And a physical consequence of this interaction results in an orderly exclusion of solutes from the aqueous cytoplasm. This orderly solute exclusion, dependent on physical properties of each solute, along with selective electrostatic adsorption of ions determine the total cellular solute concentration in mature cells. We are proposing further that during early postnatal development the water-macromolecular interaction induces less order and high concentrations of sodium can occur. Finally, our current view of cell water may have been in Albert Szent-Gyorgyi's mind when he stated in 1972 that: "Sixty years of research has taught me to look upon water as part and parcel of the living machinery, if not the hub of life. Water is the most extraordinary substance! Partically all its properties are anomalous, which enabled life to use it as building material for its machinery. Life is water dancing to the tune of solids".

Animals↗
PubMed2000

Regulation of myosin expression in developing and regenerating extrafusal and intrafusal muscle fibers with special emphasis on the role of thyroid hormones.

Expression of the muscle phenotype is the result of interaction between intrinsic and extrinsic factors, the latter including innervation, mechanical influences and hormonal signals. This minireview summarizes some of the current knowledge regarding the regulation of myosin heavy chain (MHC) isoform transitions during muscle development and regeneration. It describes the role of genetic factors, neural and mechanical influences and it focuses on the contribution of thyroid hormones to the differentiation of muscle fiber phenotypes as shown by the regulation of the expression of MHC isoforms and development of myofibrillar ATPase activity. Finally, it shortly summarizes results regarding the differentiation of MHC isoforms in regenerated muscle fibers of the graft after heterochronous isotransplantation in rats with different thyroid status.

Animals↗
PubMed1994

The structural and functional development of muscle spindles and their connections in fetal sheep.

In this paper we have studied the structural and functional development of hindlimb muscle receptors and the connections of their afferent fibres in fetal sheep (n = 26) from 67-143 days of gestation (term = 146 days). By recording extracellular discharges in dorsal root ganglia (L7, S1) we have shown that muscle spindle afferents first respond to a ramp-and-hold stretch at mid-gestation (approximately 75 days). Silver-stained preparations of muscle spindles revealed that afferent fibres are just beginning to form annulospiral windings at this age. It therefore appears that the annulospiral formation is not a necessary requirement for the generation of the response. By 87-92 days some receptors had developed a discharge at resting muscle length. Discharges were generally more robust and easier to elicit and static and dynamic components could be identified in the response to stretch. Although static sensitivity was generally low it was more evident than dynamic sensitivity. By 107-115 days it was possible to clearly distinguish between muscle and tendon afferents and to tentatively classify muscle responses as originating from primary or secondary afferent spindle endings. With increasing gestational age there was a progressive increase in the length and complexity of the spindle innervation in parallel with the maturation of functional activity. Biocytin injections into the dorsal root ganglia revealed afferent projections to the motoneuron pools by 67 days. Silver-staining of muscles showed that innervation of extrafusal fibres was also present by this age. We therefore conclude that the neural pathways necessary for reflex activity involving muscle spindles are present and functional from early in gestation and could contribute to early fetal movements.

Afferent Pathways↗
PubMed1998

The endomysium of human embryonic hyoid muscle during development.

A computer analysis was performed on the endomysium of the hyoid muscle in human fetuses, which ranged in gestational week from 12 to 32 weeks. During development of the human hyoid muscle a level of intramuscular connective tissue as reticular fibers displays a specific change in morphology. We examined quantitates and distributions of endomysium in human hyoid muscles from 12 to 32 weeks. The endomysium of the hyoid muscles formed complex structures, and volume rates increased from 20 weeks gestation. On the other hand, the cross sectional area (CSA) of muscle fibers had almost the same profile. The reticular fibers increased during development from 16 to 28 weeks gestation.

Connective Tissue↗
PubMed1990

Comparative phenotypes in rhabdomyosarcomas and developing skeletal muscle.

The morphological and immunohistochemical phenotypes of 51 rhabdomyosarcomas from young people have been described and contrasted with phenotypes in developing skeletal muscle from 20 fetuses and neonates. The tumours express markers in a cumulative and consistent sequence--vimentin, desmin, fast myosin, myoglobin--which evolves pari passu with morphological differentiation and follows the same pattern found in normal myogenesis. Changes in immunohistochemical phenotype are documented in residual and recurrent tumours excised after chemotherapy. The presumptive rhabdomyoblastic nature of some primitive tumours, marking with vimentin alone, is discussed.

Adolescent↗
PubMed1983

Development of muscles in the dorsal foreleg of rat embryos. A light microscopic study with the in situ cholinesterase staining technique.

The development of muscles from the dorsal side of the forelegs from 13- to 21-day-old rat embryos was investigated under a light microscope. The muscle blastemata and individual muscles were stained in situ with the cholinesterase technique. The first muscle blastemata are visible on the early day 13. It appears that mainly myotubes are stained. The antebrachial and brachial extensor muscles form separated anlagen which connect on the late day 13 in the proximal region of the extensor carpi ulnaris muscle. The individualization of the muscles in a muscle blastema takes place on days 13 and 14. On day 15 all extensor muscles are visible. However, at this time the inserting points of some of these muscles are not yet visible after staining with alcian blue. On the early day 16 the motor end-plates are conspicuous. Due to the content of unspecific cholinesterase in rat embryos the tendons are also stained on day 16. Muscles and tendons remain stainable until birth. In addition to the muscles also the nerves, especially the epifascial nerves, stain very well with the acetylcholinesterase reaction.

Animals↗
PubMed1997

Quantitative PCR analysis reveals novel expression of prothrombin mRNA and regulation of its levels in developing mouse muscle.

Precise determination of mRNA levels is an essential element in any investigation of complex regulatory systems. Classical methodologies such as Northern hybridization suffer from requirements for significant samples of material and also a degree of nonspecificity. Recently, quantitative techniques involving PCR amplification have been devised. We have developed and applied such procedures to the determination of prothrombin messages in skeletal muscle cells during development. In addition to its role in the blood coagulation cascade, the serine protease thrombin has been shown to participate in several signaling events in the neuromuscular system. The inactive precursor, prothrombin, primarily produced in the liver, has also been shown to be synthesized and developmentally-regulated in the brain. In skeletal muscle, thrombin is a mediator of activity-dependent polyneuronal synapse elimination (ADPSE) which occurs in early postnatal development. Recent experiments showing that thrombin is released from myotubes in culture under the influence of acetylcholine suggest that locally-synthesized prothrombin may be the source of this Hebbian synaptic interaction. We have determined that prothrombin is expressed in skeletal muscle, as the likely source of thrombin involved in ADPSE, and the current results show the quantitative expression of muscle prothrombin during this time of intense synapse remodeling.

Animals↗
PubMed2005

Adult myogenesis in Drosophila melanogaster can proceed independently of myocyte enhancer factor-2.

Myocyte enhancer factor-2 (MEF2) is a transcription factor that is necessary for embryonic muscle development in Drosophila and vertebrates; however, whether this factor is required during later muscle development remains largely unknown. Using heteroallelic combinations of different Mef2 mutant alleles, we isolated and characterized a temperature-sensitive combination. Through temperature-shift experiments, we obtained adult animals that were lacking proper MEF2 function. Many of these individuals died as mature pupae, and those that eclosed showed poor locomotion and an inability to fly. Histological analysis of these animals revealed a requirement for MEF2 in skeletal muscle patterning, although these animals had strikingly normal amounts of muscle tissue. Using quantitative polymerase chain reaction, we determined that expression of the MEF2-regulated actin gene Act57B was severely reduced in these animals. By contrast myofibrillar actin genes unique to the adult stage were only mildly affected. Since MEF2 mutant adults were still capable of forming muscle tissue, we conclude that MEF2 is required for the expression of only a subset of muscle structural genes in the adult. These results indicate that additional muscle-specific factors function to control the myogenesis of complex and diverse muscle in the adult.

Alleles↗
PubMed1988

Integration of carbohydrate and lipid metabolism in skeletal muscle during postnatal development.

In the adult, muscle metabolism represents a large drain of energetic substrates. The newborn has to provide additional energy to its muscles in order to ensure a rapid growth. However, since during the neonatal period the newborn is fed with a high-fat low-carbohydrate diet, i.e., milk, the newborn must also spare glucose for organs which are obligatory glucose consumers such as the brain. Thus, regulation of energetic substrate utilisation by muscle is of upmost importance for postnatal metabolic homeotasis. In the human, fibre types at birth can already be histochemically classified as adult types and the proportional distributions of each fibre-type approximate those seen in the adult. On the other hand, glycolytic and oxidative maximal enzyme activities are lower than adult levels. In the rat, the capacity for glucose utilisation in muscles is low at birth, reaches a peak at weaning and subsequently decreases. During the suckling period, the concentration of lipid-derived substrates is high as well as the muscle capacity for their oxidation; moreover, insulin concentration is low and insulin sensitivity of muscle glucose utilization is also reduced. Thus, during the suckling period, fuel availability and insulin concentrations, as well as tissue sensitivity towards the hormone, favour the limitation of glucose utilisation by skeletal muscles.

Animals↗
PubMed1998

Neurotrophin-3 and trkC in muscle are non-essential for the development of mouse muscle spindles.

Neurotrophin-3 (NT3) or TrkC null mutant mice were examined for the presence of muscle spindles. Muscles of mastication, but not limbs, contained spindles in newborn and adolescent mutants. The intramuscular distribution and morphological properties of spindles in mutant masticatory muscles were indistinguishable from those of wild-type spindles. Intrafusal fibers of NT3- or trkC-deficient spindles-expressed the slow-tonic isoform of myosin heavy chains, characteristic of wild-type spindles. Sensory nerve endings were observed in spindles of mutants by electron microscopy. Thus, NT3 or trkC, which is expressed in wild-type spindles, may serve functions other than those related to spindle assembly. Presumably, proprioceptive neurons innervating jaw muscles are dependent on factors other than NT3 for survival and maintenance.

Animals↗
PubMed1987

Diaphragmatic muscle fiber type development in swine.

Diaphragmatic muscle fiber types were determined in the costal and crural segments of swine diaphragm at 4 postnatal ages (1 day, 1 month, 6 months, and between 3-6 yr of age). Fiber types were differentiated by enzyme histochemistry for adenosine triphosphatase and reduced nicotinamide adenine dinucleotide. A progressive increase in the number of type I fibers occurred in both costal and crural segments from birth to 6 months of age. The number of type IIA fibers decreased and type IIB fibers increased over the same time period. Type IIC fibers were present through 1 month of age, were rarely observed at 6 months, and were not found in older animals. Type I fibers were more numerous in the crural portion of the diaphragm. The cross-sectional area of all fiber types in both costal and crural segments increased significantly with age. No preferential fiber type growth was noted in either segment of the diaphragm. These data suggest that the pig diaphragmatic muscle is differentiated into its adult form by 6 months of postnatal age, but fiber cross-sectional area growth continues along with body growth.

Adenosine Triphosphatases↗
PubMed2005

The effect of maternal undernutrition before muscle differentiation on the muscle fiber development of the newborn lamb.

There is a need to improve the lean tissue content of ruminant animals destined for meat production. Muscle fiber number is set during fetal development. The effect of undernutrition of pregnant ewes on subsequent muscle fiber characteristics of their offspring was investigated. The trial involved 32 pregnant ewes carrying twins. The ewes were allocated randomly to one of four groups: three different treatment groups (n = 8) and a control group (n = 8). The diet of the treatment groups was dropped to 50% of their daily requirement to support the ewe and allow for conceptus growth for varying periods before being returned to 100% of their daily requirement until term. Group d 30-70 ewes were fed 100% of their daily requirement until d 30, the diet was then decreased to 50% until d 70; it was then returned to 100% of their daily requirement until term. Group d 55-95 ewes were similarly restricted from d 55 through 95, and Group d 85-115 ewes were restricted from d 85 through 115. The control group was fed 100% of their daily requirement to support the ewe and allow for conceptus growth throughout gestation. After parturition, the lactating ewes were fed a normal commercial diet. On d 14 (after parturition), the lambs were slaughtered and the LM, semitendinosus (ST), and vastus lateralis (VL) were dissected and snap frozen. The immunochemical determination of myosin heavy-chain slow (MHC-slow) and myosin heavy-chain fast (MHC-fast) proteins was measured by immunoprobing of Western blots. The number of fast and slow fibers and the diameter of these fibers also were measured in each muscle sample by histochemical techniques. Decreased maternal nutrition before fiber formation (d 30 through 70) was observed to change the muscle characteristics of the newborn lambs. These lambs had significantly fewer fast fibers (P < 0.001) and significantly more slow fibers (P < 0.001) in both the LM and VL compared with the other groups. Maternal nutrient restriction at the other periods had no effect on the number of muscle fibers in the newborn lambs; however, a decrease (LM, P < 0.05; VL, P < 0.01; ST, P = 0.08) in muscle weight was observed in the lambs born to the ewes restricted between d 85 and 115 of gestation compared with the other groups. This study has shown that decreased maternal diet before muscle fiber formation will alter the muscle fiber development in the fetus.

Animal Feed↗
PubMedDate not supplied

Comparative development in captive and migratory populations of the barnacle goose.

The development of the locomotory muscles and associated skeletal structures of goslings and adults from a captive population of barnacle geese (Branta leucopsis) was compared with that from a wild migratory population. There was no significant difference between flight-muscle development of wild and captive goslings up to 7 wk of age, when the birds are first able to fly. In contrast, mass-specific citrate-synthase activity in the semimembranosus leg muscle of the captive goslings was significantly lower than that of wild goslings by 5 wk of age. During the postfledging premigratory period, captive geese showed significantly higher values for both mass and mass-specific citrate-synthase activity of the leg muscles than those of wild birds. Premigratory wild geese had significantly higher citrate-synthase activity in the pectoralis muscles and larger cardiac ventricular mass (by ca. 20%-25%) than both wild postmoulting and captive premigratory adults. Total flight-muscle mass was only slightly reduced (by ca. 10%) in long-term captive adults compared with wild premigratory adults. Most of the differences between these two populations appear primarily to reflect their relative levels of activity and/or differences in their ambient environment, rather than any intrinsic differences in developmental or adult physiology.

Animals↗
PubMed2001

Amyopathic dermatomyositis in children: a diagnostic and therapeutic dilemma.

Juvenile dermatomyositis is an inflammatory disease of unknown etiology that primarily affects skin and muscles. The pathognomonic Gottron's sign consists of symmetric macules and papules on the dorsal aspect of the interphalangeal joints and exterior areas of the big joints. A periorbital violaceous (heliotrope) skin rash is also characteristic. There may be a discordance in time of presentation of the skin and muscle disease, and a small subset of patients apparently do not develop muscle disease at all. The absence of muscle involvement is termed 'amyopathic dermatomyositis.'We describe two children who presented with the characteristic rash of juvenile dermatomyositis but with no clinical evidence of muscle involvement. One developed muscle weakness 3 years later. Neither patient had a full muscle work-up at the onset of the disease, which left questions about diagnoses and whether or not there may have been subtle muscle involvement. On the basis of our literature review, the outcome of these patients is uncertain, although it appears that myositis develops in many, maybe most, affected children. We suggest that in the absence of muscle disease, application of sunscreen and administration of hydroxychloroquine sulfate may ameliorate the rash. More aggressive treatment will need to be given when muscle involvement can be demonstrated.

Journal Article↗
PubMed1997

Nucleic acid concentrations and ornithine decarboxylase activity in tissues from three lines of turkeys.

Developmental patterns in turkeys of tissue ornithine decarboxylase (ODC) activity and nucleic acid concentrations were studied in a randombred control (RBC2), in a subline of RBC2 selected for increased 16-wk BW (F), and in a commercial sire line (C). Lines F and C were similar in BW, but Line C had greater breast weight than Line F. Lines F and C were heavier and had greater breast weights than the RBC2 population. Tissue ODC activity reached its highest level on Day 2 posthatch, declined rapidly through 13 d of age, and remained relatively low through 144 d of age. The ODC activity of liver tissue was greater than that of either breast or leg muscle. Line C had greater tissue ODC activity at 2 and 8 d of age than the RBC2 population, but Line F was not different from C or RBC2. There were no line differences for ODC activity at the other ages tested, resulting in a age by line interaction. The DNA content of muscle tissue was greatest at hatch and declined to baseline values by 55 d of age. The DNA content of breast muscle was higher than for leg muscle at hatch, but this pattern was reversed following Day 8. Muscle tissue from Lines F and C had a lower DNA content than that of the RBC2 population. Although the RNA content of muscle tissue was similar across lines, the RNA content of breast muscle was greater than for leg muscle during the early posthatch period just prior to the onset of rapid growth in this tissue. Results of the present experiment demonstrate changes in muscle functional cellularity during the growth phase in association with genetic increases in BW, but not breast muscle development. In contrast, tissue ODC activity was increased in association with genetic increases in breast muscle development, but not BW.

Aging↗
PubMed1984

Fully rectified, integrated, band (FRIB-) EMG analysis in quantifying muscle activity. Development of a new field equipment.

A new approach for the study of muscular activity applicable in field and laboratory conditions has been developed. The instrument is portable (375 g) and battery operated. The signals are obtained through a surface electrode attached to the skin above the muscle. A reference electrode is applied to a bony area close by. The third electrode, to remove 50 Hz disturbance, is attached at a distance from the muscle to be registered. A time domain band EMG signal is fully rectified and integrated. The isolation of the device is done with an optocoupler. The EMG activity to be thus registered is not hampered by other external or internal (ECG) electrical signals. The recordings can also be made when the person is working quite freely. The recorded values correlate linearly (up to r = 0.99) with the load of the muscle. The angular coefficients obtained with different loads correlate inversely with the strength of the persons. When muscle fatigue develops during a static loading, the registered EMG tends to decrease while simultaneously oscillating. During the recovery from the fatigued state the response to intermittent loadings indicates that the electrical activity pattern varies with time. With the method developed it is possible to detect locally increased electrical activity at rest or during muscle function testing, and it permits the followup of therapeutic measures.

Adult↗