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M D Grounds

Publications and source records attributed to M D Grounds.

At least 55 records · Page 3Linked to original sources
PubMed1992

Skeletal muscle regeneration after crush injury in dystrophic mdx mice: an autoradiographic study.

The X-linked dystrophic animal model, the mdx mouse, shows an extraordinary capacity for sustained muscle regeneration compared with X-linked dystrophic golden retriever dogs and humans with Duchenne muscular dystrophy. To test the hypothesis that muscles of mdx mice might have inherently superior muscle regeneration to that in nondystrophic animals, muscle regeneration in response to a crush injury was examined in mdx mice and in the nondystrophic, parental strain C57Bl/10Sn. Autoradiographic techniques were used specifically to investigate the timing of muscle precursor replication after crush injury. Little difference in the regenerative capacity, either histologically or with respect to the timing of muscle precursor replication, was found between mdx mice and C57Bl/10Sn or other nondystrophic strains of mice.

Animals↗
PubMed1992

Identification of skeletal muscle precursor cells in vivo by use of MyoD1 and myogenin probes.

The activation of mononuclear muscle precursor cells after crush injury to mouse tibialis anterior muscles was monitored in vivo by in situ hybridization with MyoD1 and myogenin probes. These genes are early markers of skeletal muscle differentiation and have been extensively studied in vitro. The role in vivo of these regulatory proteins during myogenesis of mature muscle has not been studied previously. MyoD1 and myogenin mRNA were present in occasional mononuclear cells of uninjured muscle. Increased MyoD1 and myogenin mRNA sequences in mononuclear cells were detected as early as 6 h after injury, peaked between 24 and 48 h, and thereafter declined to pre-injury levels at about 8 days. The mRNAs were detected in mononuclear cells throughout the muscle, with the majority of cells located some distance from the site of crush injury. The presence of MyoD1 and myogenin mRNA at 6 to 48 h indicates that transcription of these genes is occurring at the same time as replication of muscle precursor cells in vivo. At no time were significant levels of mRNA for these genes detected in myotubes. MyoD1 and myogenin provide precise markers for the very early identification and study of mononuclear skeletal muscle precursor cells in muscle regenerating in vivo.

Animals↗
PubMed1992

Cellular differences in the regeneration of murine skeletal muscle: a quantitative histological study in SJL/J and BALB/c mice.

Skeletal muscle regeneration in SJL/J and BALB/c mice subjected to identical crush injuries is markedly different: in SJL/J mice myotubes almost completely replace damaged myofibres, whereas BALB/c mice develop fibrotic scar tissue and few myotubes. To determine the cellular changes which contribute to these differential responses to injury, samples of crushed tibialis anterior muscles taken from SJL/J and BALB/c mice between 1 and 10 days after injury were analysed by light and electron microscopy, and by autoradiography. Longitudinal muscle sections revealed about a 2-fold greater total mononuclear cell density in SJL/J than BALB/c mice at 2 to 3 days after injury. Electron micrographs identified a similar proportion of cell types at 3 days after injury. Autoradiographic studies showed that the proportions of replicating mononuclear cells in both strains were similar: therefore greater absolute numbers of cells (including muscle precursors and macrophages) were proliferating in SJL/J muscle. Removal of necrotic muscle debris in SJL/J mice was rapid and extensive, and by 6 to 8 days multinucleated myotubes occupied a large part of the lesion. By contrast, phagocytosis was less effective in BALB/c mice, myotube formation was minimal, and fibrotic tissue conspicuous. These data indicate that the increased mononuclear cell density, more efficient removal of necrotic muscle, together with a greater capacity for myotube formation in SJL/J mice, contribute to the more successful muscle regeneration seen after injury.

Animals↗
PubMed1992

The transcription of MyoD1 and myogenin genes in thymic cells in vivo.

The skeletal muscle specific genes MyoD1 and myogenin are closely associated with commitment of cells to the myogenic lineage and differentiation of skeletal muscle precursor cells. The transcription of these genes was studied in the thymus where mononuclear cells termed myoid cells appear to closely resemble skeletal muscle precursors. In thymus from adult SJL/J and BALB/c mice, in situ hybridization with either MyoD1 or myogenin riboprobes showed probe-positive cells concentrated in the medullary region. In neonatal thymus, mRNA for these genes was not detected. These data are the first demonstration in a higher vertebrate of MyoD1 and myogenin expression in a tissue other than skeletal muscle. The sustained expression of MyoD1 and myogenin genes in thymi of adult mice shows that myoid cells are not equivalent to quiescent stem cells of mature skeletal muscle. In addition, studies with antistriational antibodies indicate that myoid cells do not continue to differentiate within the normal murine thymic environment. This arrested differentiation process presents an unusual model for investigating conditions regulating myogenesis in vivo.

Animals↗
PubMed1992

Survival and migration of transplanted male glia in adult female mouse brains monitored by a Y-chromosome-specific probe.

A Y-chromosome-specific probe and in situ hybridization technology have been used to monitor the survival and migration of neonatal male glia isografted to the left cerebral hemisphere of adult female mice. More than 95% of the cultured donor glia were glial fibrillary acidic protein (GFAP)-positive astrocytes. By 4 weeks, large numbers of transplanted glia were found in both cerebral hemispheres; the extent of glial migration was greatest in white matter tracts. This method provides a new way of identifying all surviving donor cells within the brains of immunologically compatible hosts.

Animals↗
PubMed1992

Nonspecific binding of nucleic acid probes to Paneth cells in the gastrointestinal tract with in situ hybridization.

Nonspecific binding of a number of unrelated nucleic acid probes to cells in the crypts of Lieberkuhn was observed in the small intestine of mice with the in situ hybridization technique. Hybridization signal was localized to cells which, by virtue of their histological position, represented Paneth cells. This signal could not be removed by RNAse, DNAse, or proteinase K treatment, and was not removed after high-stringency washing conditions. This report indicates that caution must be exercised in the interpretation of in situ hybridization data when looking for nucleic acid sequences in the gastrointestinal tract.

Animals↗
PubMed1992

Elucidation of aspects of murine skeletal muscle regeneration using local and whole body irradiation.

To investigate the role of proliferating local and emigrating circulatory leucocytes in skeletal muscle regeneration in mice, their bone marrow was ablated with whole body irradiation and compared with the effects of local irradiation. The results indicate that (1) the sealing of damaged myofibres is a function of local cells and is not dependent on the presence of infiltrating leucocytes; (2) the formation of sarcoplasmic projections at the ends of damaged myofibres is dependent on leucocyte infiltration; (3) nuclei in the sarcoplasmic projections are probably derived from fusion of muscle precursor cells; (4) most muscle precursor cells in vivo replicate at least once before fusion; and (5) both replication and fusion of muscle precursors can occur in the absence of infiltrating leucocytes. These results are discussed with respect to the interaction of various cell populations during regeneration of skeletal muscle, and are of clinical significance to pathological changes seen in many myopathies.

Animals↗
PubMed1991

Towards understanding skeletal muscle regeneration.

Factors which effect proliferation and fusion of muscle precursor cells have been studied extensively in tissue culture, although little is known about these events in vivo. This review assesses the tissue culture derived data with a view to understanding factors which may control the regeneration of mature skeletal muscle in vivo. The following topics are discussed in the light of recent developments in cell and molecular biology: 1) Injury and necrosis of mature skeletal muscle fibres 2) Phagocytosis of myofibre debris 3) Revascularisation of injured muscle 4) Activation and proliferation of muscle precursor cells (mpc) in vivo Identification of mpcs; Satellite cell relationships; Extracellular matrix; Growth factors; Hormones; Replication. 5) Differentiation and fusion of muscle precursor cells in vivo Differentiation; Fusion; Extracellular matrix; Cell surface molecules: Growth factors and prostaglandins 6) Myotubes and innervation.

Animals↗
PubMed1990

Myogenic cell replication in minced skeletal muscle isografts of Swiss and BALBc mice.

The onset and pattern of muscle precursor replication in minced skeletal muscle isografts were examined autoradiographically in 22 BALBc and 23 Swiss mice. Tritiated thymidine was injected into mice at various times after grafting to label replicating muscle precursors and regenerated muscle isografts removed 14 days after grafting when labeled precursors had fused into myotubes. Analysis of labeled myotube nuclei in regenerated minced isografts showed a difference between the onset of DNA synthesis in muscle precursors of the two strains, although precursor proliferation peaked around day 5 and was greatly reduced by day 8 in both strains. The onset and duration of muscle precursor replication was similar to that seen in isografts of intact whole muscles: however, precursor proliferation was delayed and protracted compared with injured muscles. This autoradiographic model enables quantitative investigations of muscle precursor behavior in vivo, with clinical potential for improving muscle regeneration after severe injury, transplantation, and some myopathies.

Animals↗
PubMed1990

The process of new plasmalemma formation in focally injured skeletal muscle fibers.

The major ultrastructural events in murine skeletal muscle fibers were examined 3 to 24 hr after segmental injury induced by painting with aldehyde fixative. At 3 hr the viable stump of injured myofibers was separated from the necrotic segment by a zone of supercontracted myofibrils. No demarcating membrane was evident at this time, although occasionally collapsed segments of plasmalemma partially covered the viable stump. By 12 hr after injury myonuclei near the viable stump were centrally placed and numerous whorls of membrane material appeared in the vicinity of the Golgi apparatus. At this stage a convoluted, tortuous membrane exhibiting extensive interdigitations has sealed the structurally normal part of the injured fiber. The myoplasm immediately within this demarcating membrane possessed few myofilaments but numerous vesicles and tubules, several of which were continuous with the demarcating membrane; most degraded sarcoplasmic organelles remained external to the demarcating membrane and leukocytes were observed internalizing the debris. It appears that after segmental injury to skeletal muscle fibers, active production of new sarcoplasmic membranes occurs, which contributes to the formation of the part of the plasmalemma that demarcates the viable portion of the muscle fiber from the injured area.

Animals↗
PubMed1989

Initiation and duration of myogenic precursor cell replication in transplants of intact skeletal muscles: an autoradiographic study in mice.

Skeletal muscle fibers are capable of regeneration following ischemia, traumatic injury, or transplantation. Although the time course of the regenerative process has been studied in detail histologically, little is known about the time of activation of myogenic precursor cells which are primarily responsible for muscle regeneration. This study was designed to determine the initiation, peak proliferative activity, and cessation times of muscle precursor replication in small skeletal muscle transplants. Forty-eight young male BALB/c mice had the extensor digitorum longus muscles of both hind legs autotransplanted to a different site in the same leg. At various time intervals after transplantation (from 24 hours to 14 days), mice were injected once with a small dose of tritiated thymidine in order to label proliferating myogenic precursor cells. The transplants were allowed to regenerate for 14 days, before being removed, processed for autoradiography, and analysed by light microscopy. The presence of labelled myotube nuclei in regenerated transplants showed that myogenic precursors had been replicating at the time of tritiated thymidine injection. Myogenic precursor replication was initiated late on the second day (42-48 hours) after transplantation, peaked after 6 days, and was complete within 10 days.

Animals↗
PubMed1989

A comparison of muscle precursor replication in crush-injured skeletal muscle of Swiss and BALBc mice.

Muscle precursor replication in Swiss mice, in which muscle regeneration is exceptionally vigorous, was compared with previous data for regeneration in BALBc mice. The tibialis anterior muscles of 23 male and 15 female inbred Swiss SJL/J mice were crush injured, and tritiated thymidine injected into mice at various times after injury to label replicating muscle precursors. Lesion samples were taken 10 days after injury, processed for autoradiography, and grain counts of myotube nuclei analysed. Muscle regeneration was more vigorous in male compared with female Swiss mice, and in both was strikingly greater than that in BALBc mice in which there was extensive fibrous connective tissue throughout the lesions. Autoradiographic analysis showed that muscle precursor replication started at 24 hours in Swiss mice, 6 hours earlier than the onset at 30 hours in BALBc mice. Muscle precursor replication appeared to be more active 96 hours after injury in female Swiss compared with male BALBc and male Swiss mice respectively, although numbers of precursor cells replicating at other times were similar. It is not known whether the slight difference in onset of muscle precursor replication can alone account for the more complete muscle regeneration seen in Swiss mice. Similar studies were carried out in 11 male and 10 female F1 hybrid (SJL/J x BALBc) mice. Analysis of labelled myotube nuclei showed that muscle precursors did not synthesise DNA prior to 30 hours after injury, and regeneration resembled that of the parental BALBc strain.

Animals↗
PubMed1989

Muscle precursor replication after repeated regeneration of skeletal muscle in mice.

We propose that when skeletal muscle regenerates after injury, myogenic precursor cell replication commences earlier if the muscle has undergone a recent previous cycle of regeneration. To test this a series of muscles in mice were crush-injured and allowed to regenerate. Then either 7 or 28 days after the initial injury, the muscles were reinjured. The onset of DNA synthesis in myogenic precursor cells was determined by injecting each mouse once with tritiated thymidine at a specific time after the second injury. All reinjured muscles were left for 10 days to regenerate to the myotube stage. The presence of autoradiographically labelled myotube nuclei indicated that these nuclei were the progeny of myogenic precursors labelled at the time of injection of tritiated thymidine. Thus the onset of muscle precursor cell replication was determined. A similar series of experiments was conducted on muscle autotransplants, injured at 28 days after transplantation and sampled 10 days later. In none of these situations did muscle precursor cell replication occur earlier than in control muscles, which were injured only once, where myogenesis commenced between 24 and 30 h after injury. The autoradiographic data do not support our hypothesis. We conclude that the increased numbers of muscle precursors reported (by various authors) after repeated cycles of regeneration, are not due to the earlier initiation of DNA synthesis in myogenic precursor cells.

Animals↗
PubMed1989

Myogenic cells of regenerating adult chicken muscle can fuse into myotubes after a single cell division in vivo.

Autoradiographic studies were carried out on regenerating muscles of adult chickens. Three different muscles of hens were injured, and tritiated thymidine (1 microCi/g) was injected at various times after injury to label replicating muscle precursors. Detailed comparisons of grain counts over premitotic nuclei in samples removed one hour after injection of tritiated thymidine, and of postmitotic myotube nuclei in samples removed 10 days after injury (when labeled precursors had fused to form myotubes), revealed how many times some labeled precursors had divided before fusing into myotubes. DNA synthesis in muscle precursors was initiated 30 h after injury. Grain counts of myotube nuclei indicated that many muscle precursors labeled at the onset of myogenic cell proliferation had divided only once, or twice, before fusing into myotubes. The relationship of these in vivo results to the cell lineage model of myogenesis is discussed.

Aging↗
PubMed1989

The onset of myogenesis in denervated mouse skeletal muscle regenerating after injury.

Denervation of skeletal muscle stimulates increased turnover of muscle nuclei and connective tissue cells. The present investigation tests whether denervation "primes" myogenic precursor cells, so that the onset of DNA synthesis in muscle precursors after traumatic injury occurs earlier than in innervated muscle. The left legs of 29 male BALBc mice were denervated, and 1 week later small incisions were made in the tibialis anterior muscles of both legs (denervated and innervated). At specific times after injury each mouse was injected once with tritiated thymidine to label replicating muscle precursors. Muscle lesions were sampled 10 days after injury (when all precursors had fused to form myotubes) and prepared for auto-radiography. The presence of labelled myotube nuclei showed that muscle precursors had been synthesizing DNA at the time when [3H]thymidine had been injected. Our data suggest that very few precursors were proliferating in denervated muscle within 30 h after injury, and the onset of myogenesis at 30 h was essentially the same in denervated and innervated muscle. The retrospective analysis indicates that there were also similar proportions of muscle precursors proliferating at different times after injury, in regenerating lesions of both denervated and innervated muscle. Thus, denervation does not stimulate an earlier regenerative response in injured skeletal muscle.

Animals↗
PubMed1987

Phagocytosis of necrotic muscle in muscle isografts is influenced by the strain, age, and sex of host mice.

In grafts of skeletal muscle the implanted muscle becomes necrotic, is phagocytosed and replaced by new muscle cells. This study investigates the hypothesis that removal (phagocytosis) of necrotic implanted muscle is impaired in grafts made into old Swiss mice. Isografts (154) of minced muscle were made between young (20 day) and old (140 day) mice of the strain Swiss, AKR, BALBc, C3H and C57BL. Grafts were examined histologically after 7 days. A relationship between impaired phagocytosis and increasing host age was confirmed for male Swiss mice but was not seen with female Swiss mice or the other four strains. The proposal that ageing of bone marrow was responsible for diminished phagocytosis in old Swiss mice was investigated by replacing the marrow of 33 lethally irradiated male Swiss mice with marrow cells from mice of different ages (20 and 140 day), before isografting minced muscle. The results clearly show that macrophage stem cell function is unimpaired with age. Testosterone levels might account for the impaired phagocytosis seen in many sexually mature male Swiss mice. Support for this proposal came from experiments in which 15 mice were castrated before implanting muscle isografts. This study shows that genetic factors rather than the age of mice influenced phagocytosis and muscle formation in grafts.

Aging↗