Embryonic growth and innervation of rat skeletal muscles. - III. Neural regulation of junctional and extra-junctional acetylcholine receptor clusters

The number and distribution of acetylcholine (ACh) receptors on muscle cells was studied during development of normal, paralysed and aneural embryonic rat diaphragm muscles. (i) ACh receptors initially are dispersed over the surface of rat embryo myotubes. At day 15| of gestation junctional receptor clusters (‘J-clusters’) form in a well ordered band across the midline of the diaphragm muscle; these also form in denervated and paralysed muscles. At about day 18 of gestation additional ‘EJ-clusters’ develop to either side of the midpoint of treated muscles. (ii) If a nerve terminal is present, J-clusters increase in length with time. The time course of generation of new endplates calculated from frequency distributions of J-cluster lengths accurately predicts the muscle growth curve established from muscle fibre counts. (iii) The mean length of J-clusters in paralysed muscles was greater than in controls, due to small new-formed clusters failing to appear. In muscles allowed to recover from paralysis the mean length was less, due to a preponderance of small, new-formed clusters. These observations show that development of new endplates, which is thought to reflect the development of new muscle cells, is halted in paralysed muscles, and recovery from paralysis is associated with the generation of many new endplates. (iv) J-clusters appeared, but failed to grow, in aneural muscles. In muscles denervated during the later stages of gestation, analysis of the distribution of J-cluster lengths shows that new clusters failed to appear, and existing clusters showed little or no increase in length after the time of removal of the nerve. (v) EJ-clusters form by aggregation of dispersed receptors, and their mean length increases with time. They do not appear to be stable entities, and are removed within 2 d of recovery from paralysis. In paralysed muscles, with both J-clusters and EJclusters present, only J-clusters attract nerve sprouts or become innervated. (vi) A curve is derived showing development of the total number of synaptic terminals in a muscle. This number increases during days 13-18 of gestation, reaching a peak of about 170 % of the adult value during dl8 and d l9 of gestation. There are two episodes of terminal elimination, one during days 19-21 of gestation, and another about 2 weeks postnatally. During the first postnatal week the number of terminals remains constant at about 140% of the adult number, while the average number of inputs per fibre goes down and the number of muscle fibres increases. (vii) Innervation is essential for muscle development. Motoneurons cannot regulate the number of muscle fibres by requiring a simple one-to-one relation between nerve terminal and muscle fibre, and if their role is regulatory as well as supportive of muscle development then some more complex relationship between nerve terminals and developing myotubes must be postulated.

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The effect of maternal undernutrition on muscle fibre type in the newborn lamb

Proceedings of the British Society of Animal Science ◽

10.1017/s1752756200012199 ◽

2003 ◽

Vol 2003 ◽

pp. 60-60

Author(s):

A.J. Fahey ◽

J.M. Brameld ◽

T. Parr ◽

P.J. Buttery

Keyword(s):

Muscle Fibre ◽

Meat Quality ◽

Fibre Type ◽

Muscle Development ◽

Nutrient Supply ◽

Muscle Fibre Type ◽

Growth Potential ◽

Muscle Fibres ◽

General Hypothesis ◽

Maternal Undernutrition

Muscle fibre type can influence meat quality (Maltinet al1997). Muscle fibre formation occurs during gestation and in the sheep the total number of fibres in a muscle is essentially fixed at birth. (Ashmereet al1972). Postnatal growth of muscle is entirely due to elongation and widening of the existing muscle fibres. Therefore the gestational period is important in the long-term growth potential of the animal. By investigating changes in muscle fibre type, the aim of this study was to test the general hypothesis that the poor carcass quality sometimes seen in ruminant animals may be due to poor nutrition at strategic time points during the animal’s development. As agricultural practices continue to become more extensive, variation in the nutrient supply to the animal is becoming more common. Therefore it is important to understand the effect of any changes in nutrient supply to the mother, during gestation on the subsequent muscle development of the fetus and ultimately the effects on meat quality.

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Visualization of satellite cells in living muscle fibres of the frog

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1980.0113 ◽

1980 ◽

Vol 209 (1177) ◽

pp. 563-568 ◽

Cited By ~ 9

Keyword(s):

Electron Microscopy ◽

Horseradish Peroxidase ◽

Muscle Fibre ◽

Satellite Cells ◽

Light Microscope ◽

Muscle Cells ◽

Fibre Axis ◽

Muscle Fibres ◽

Single Fibres

Satellite cells were visualized in living muscle fibres of the frog. Single fibres or bundles consisting of a few fibres were isolated after treatment with collagenase, and viewed under the light microscope. Subsequent electron microscopy of identified cells confirmed that they were satellite muscle cells. Under the light microscope, satellite cells appear as fusiform cells, tapering into long fine processes usually orientated parallel to the muscle fibre axis. Horseradish peroxidase injected into the muscle fibre was not transferred to the satellite cells.

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Distribution of acetylcholine receptors in the vicinity of nerve terminals on skeletal muscle of the frog

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1972.0060 ◽

1972 ◽

Vol 181 (1065) ◽

pp. 431-440 ◽

Cited By ~ 29

Keyword(s):

Skeletal Muscle ◽

Connective Tissue ◽

Neuromuscular Junction ◽

Muscle Fibre ◽

Nerve Terminal ◽

Acetylcholine Receptors ◽

Postsynaptic Membrane ◽

Muscle Membrane ◽

Muscle Fibres ◽

Nerve Terminals

1. The acetylcholine (ACh) sensitivity of muscle fibres at the neuromuscular junction of the frog was investigated in preparations in which the nerve terminals could be clearly seen. 2. ACh released iontophoretically from a micropipette that was precisely positioned at various points along the muscle fibre in the vicinity of the synapse showed that the peak chemosensitivity (up to 1900 mV/nC) is confined to an area of postsynaptic membrane within a few micra of the nerve terminal; a tenfold decline in sensitivity was obtained when the ACh was released only 5 to 10 μm from the terminal’s edge. It is estimated that most of the response obtained when ACh is released within 40 μm from the terminal (the area covered in this study) is due to diffusion to the immediate postsynaptic area. The extrasynaptic chemosensitivity of the muscle membrane was too low to be measured with the present methods. 3. The accuracy with which micropipettes could be positioned in synaptic areas and the clarity of viewing nerve terminals were improved by bathing the tissue in collagenase, which reduced the amount of connective tissue. The distribution of chemosensitivity remained unchanged by such treatment. The ACh response was not detectably altered when nerve terminals were lifted off the muscle, exposing the subsynaptic muscle surface.

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Number of conceptuses in utero affects porcine fetal muscle development

Reproduction ◽

10.1530/rep.1.00069 ◽

2004 ◽

Vol 128 (4) ◽

pp. 443-454 ◽

Cited By ~ 83

Author(s):

S C Town ◽

C T Putman ◽

N J Turchinsky ◽

W T Dixon ◽

G R Foxcroft

Keyword(s):

Muscle Fibre ◽

Muscle Development ◽

Weight Ratio ◽

In Utero ◽

Muscle Fibres ◽

Semitendinosus Muscle ◽

Muscle Weight ◽

Cross Sectional ◽

Fetal Organ ◽

Muscle Cross Sectional Area

Unmodified, third parity, control sows (CTR; n = 30) or sows subjected to unilateral oviduct ligation before breeding (LIG; n = 30), were slaughtered at either day 30 or day 90 of gestation and used to determine the effects of numbers of conceptuses in utero on prenatal, and particularly muscle fibre, development. Ovulation rate, number of conceptuses in utero, placental and fetal size, and (day 90 sows) fetal organ and semitendinosus muscle development were recorded. Tubal ligation reduced (P < 0.05) the number of viable embryos at day 30 and fetuses at day 90. Placental weight at day 30 and day 90, and fetal weight at day 90, were lower (P < 0.05) in CTR sows. All body organs except the brain were lighter, and the brain:liver weight ratio was higher in CTR fetuses (P < 0.05), indicative of brain sparing and intrauterine growth restriction in fetuses from CTR sows. Muscle weight, muscle cross-sectional area and the total number of secondary fibres were also lower (P < 0.05) in CTR fetuses. The number of primary fibres, the secondary:primary muscle fibre ratio, and the distribution of myosin heavy chain-Iβ, -IIa, fetal and embryonic isoforms did not differ between groups. Thus, even the relatively modest uterine crowding occurring naturally in CTR sows negatively affected placental and fetal development and the number of secondary muscle fibres. Consequences of more extreme crowding in utero on fetal and postnatal development, resulting from changing patterns of early embryonic survival, merit further investigation.

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Inhibition of capillary endothelial cell growth by pericytes and smooth muscle cells.

The Journal of Cell Biology ◽

10.1083/jcb.105.3.1455 ◽

1987 ◽

Vol 105 (3) ◽

pp. 1455-1462 ◽

Cited By ~ 419

Author(s):

A Orlidge ◽

P A D'Amore

Keyword(s):

Smooth Muscle ◽

Endothelial Cell ◽

Epithelial Cells ◽

Smooth Muscle Cells ◽

Culture System ◽

Time Course ◽

Muscle Cells ◽

Cell Type ◽

3T3 Cells ◽

The Mean

Morphological studies of developing capillaries and observations of alterations in capillaries associated with pathologic neovascularization indicate that pericytes may act as suppressors of endothelial cell (EC) growth. We have developed systems that enable us to investigate this possibility in vitro. Two models were used: a co-culture system that allowed direct contact between pericytes and ECs and a co-culture system that prevented physical contact but allowed diffusion of soluble factors. For these studies, co-cultures were established between bovine capillary ECs and the following growth-arrested cells (hereafter referred to as modulating cells): pericytes, smooth muscle cells (SMCs), fibroblasts, epithelial cells, and 3T3 cells. The modulating cell type was growth arrested by treatment with mitomycin C before co-culture with ECs. In experiments where cells were co-cultured directly, the effect of co-culture on EC growth was determined by comparing the mean number of cells in the co-cultures to the mean for each cell type (EC and modulating cell) cultured separately. Since pericytes and other modulating cells were growth arrested, any cell number change in co-cultures was due to EC growth. In the co-cultures, pericytes inhibited all EC proliferation throughout the 14-d time course; similar levels of EC inhibition were observed in SMC-EC co-cultures. Co-culture of ECs with fibroblasts, epithelial cells, and 3T3 cells significantly stimulated EC growth over the same time course (30-192% as compared to EC cultured alone). To determine if cell contact was required for inhibition, cells were co-cultured using Millicell chambers (Millipore Corp., Bedford, MA), which separated the cell types by 1-2 mm but allowed the exchange of diffusible materials. There was no inhibition of EC proliferation by pericytes or SMCs in this co-culture system. The influence of the cell ratios on observed inhibition was assessed by co-culturing the cells at EC/pericyte ratios of 1:1, 2:1, 5:1, 10:1, and 20:1. Comparable levels of EC inhibition were observed at ratios from 1:1 to 10:1. When the cells were co-cultured at a ratio of 20 ECs to 1 pericyte, inhibition of EC growth at 3 d was similar to that observed at other ratios. However, at higher ratios, the inhibition diminished so that by the end of the time course the co-cultured ECs were growing at the same rate as the controls. These results suggest that pericytes and SMCs can modulate EC growth by a mechanism that requires contact or proximity. We postulate that similar interactions may operate to modulate vascular growth in vivo.

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Histology of Muscle Development in Pigs, Epigenetics from Myotubes to Tapered Fibres

Asian Journal of Agriculture and Food Sciences ◽

10.24203/ajafs.v9i6.6800 ◽

2021 ◽

Vol 9 (6) ◽

Author(s):

Howard J. Swatland

Keyword(s):

Connective Tissue ◽

Muscle Fibre ◽

Radial Growth ◽

Muscle Development ◽

Transverse Section ◽

Longitudinal Growth ◽

Sartorius Muscle ◽

Muscle Fibres ◽

Peroneus Longus ◽

Peripheral Position

Pre-natal muscle development in pigs starts with myotubes (axial nuclei in a tube of myofibrils) and secondary fibres (peripheral nuclei on an axial strand of myofibrils). By the time of birth, the nuclei of myotubes move to a peripheral position like secondary fibres. As pre-natal secondary fibres grow in length, the number of fibres in a transverse section may appear to increase. This stereology may also occur in post-natal muscles that have tapered fibres anchored in endomysial connective tissue around adjacent fibres and with one or both ends not reaching the end of their fasciculus. Up to 100 days gestation, Peroneus longus (no tapered fibres) had larger (P < 0.001) diameter secondary fibres than Longissimus thoracis (with tapered fibres). Up to 100 days gestation, no radial growth of secondary fibres was detected, but myotubes decreased in diameter (P < 0.001). From a curve showing the relative numbers of myotubes and secondary fibres, it was deduced that approximately 80% of muscle fibres in pigs are derived from secondary fibres. In post-natal Sartorius muscle there was an increase (P < 0.005) in the apparent number of muscle fibres attributed to longitudinal growth of tapered fibres. Myotubes located centrally within their fasciculi had the same position as slow-contracting fibres with a high myoglobin content in adult muscle. Post-natal changes in muscle fibre histochemistry were achieved through transitional types, probably neurally regulated rather than by differential longitudinal growth of tapered endings. Secondary fibres are important – they give rise to both the majority of muscle fibres in adult pigs and affect subsurface optical pathways and pork colourimetry.

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Fusimotor innervation in the cat

Philosophical Transactions of the Royal Society of London Series B Biological Sciences ◽

10.1098/rstb.1970.0038 ◽

1970 ◽

Vol 258 (825) ◽

pp. 315-346 ◽

Cited By ~ 86

Keyword(s):

Electron Microscopy ◽

Muscle Fibre ◽

High Frequency ◽

Light And Electron Microscopy ◽

Spindle Pole ◽

Muscle Fibres ◽

Flexor Hallucis Longus ◽

Spindle Poles ◽

Fusimotor Innervation ◽

The Mean

The motor innervation of cat spindles was examined in hindlimb muscles using a variety of techniques employed in light and electron microscopy. Observations were made on teased, silver preparations of 267 spindles sampled from the peroneal, flexor hallucis longus, and soleus muscles, hereafter referred to as the PER /FHL /SOL series. The y innervation . Trail endings are almost invariably present, and innervate both bag and chain muscle fibres. T rail fibres accounted for 64.6 to 74.8 % of the total fusimotor supply to samples of spindle poles in the PER/FHL /SOL series, the m ean num ber of fibres per pole varying from 2.7 to 5.0 in the different muscles, and the mean number of ramifications (areas of synaptic contact) per fibre being 3.7. By contrast, the p 2 innervation of a spindle pole generally consists of a single fibre supplying only one plate. In the above samples p 2 fibres accounted for 4.1 to 28.0% of the total fusimotor supply, and the mean number of fibres per pole varied from 0.3 to 1.2 in the different muscles. Ninety per cent of p 2 plates innervate bag fibres. The α innervation . The structure of p 1 plates as seen in both light and electron microscopy compares very closely with that of extrafusal plates. After nerve section p 1 plates degenerate at the same time as extrafusal plates, being the first of the three types of fusimotor ending to disappear. The frequency of the p x innervation is similar to that of the p 2 innervation. In the same samples of P E R /F H L /S O L spindle poles as above p x fibres accounted for 6.0 to 28.8 % of the total fusimotor supply, the mean number of fibres per pole varying from 0.25 to 2.1 in the different muscles. The majority of p 1 fibres enter a pole to terminate in one plate only. Seventy-five per cent of the plates innervate bag fibres. The three types of fusimotor ending are thus not selectively distributed to the two types of intrafusal muscle fibre. All three types of fusimotor fibre may branch within the spindle so as to innervate both bag and chain fibres. Bag fibres receive both types of plate ending as well as trail endings. Most chain fibres receive trail endings only; the rest receive either a p 1 or a p 2 plate innervation in addition, 25 % of the p 1 and 10% of the p 2 innervation being distributed to chain fibres. The significance of this nonselective innervation is interpreted as indicating that the type of contraction elicited by stimulating a fusimotor fibre depends upon the type of ending initiating it rather than upon the type of muscle fibre executing it. Reasons are given for concluding that the dynamic response is controlled via the p 1 and p 2 plates, and that the static response is controlled by the trail endings. The participation of the a fibres in mammalian fusimotor innervation, previously regarded as a vestigial feature, proved to be widespread in the muscles studied and more prevalent in fast muscles (FHL, peroneus digiti quinti) than slow (soleus). A low frequency of p 1 innervation is offset by a high frequency of p 2 (as in peroneus longus), and vice versa (as in FHL). It is unlikely that collaterals from slow a fibres innervating type B muscle fibres are wholly responsible for the high frequency of the p 1 innervation in FHL, and it is suggested that collaterals may also be derived from fast a fibres innervating type C muscle fibres. The possibility of there being some motor fibres of a conduction velocity and with an exclusively fusimotor distribution is also taken into account.

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Aminergic and peptidergic modulation of motor function at an identified neuromuscular junction in Helisoma

Journal of Experimental Biology ◽

10.1242/jeb.142.1.225 ◽

1989 ◽

Vol 142 (1) ◽

pp. 225-243

Author(s):

M. J. Zoran ◽

P. G. Haydon ◽

P. J. Matthews

Keyword(s):

Muscle Fibre ◽

Muscle Cells ◽

Muscle Contractions ◽

Interactive Effects ◽

Muscle Fibres ◽

Buccal Ganglion ◽

Motor Pathway ◽

Peripheral Muscle ◽

Electrophysiological Studies

Electrophysiological studies suggest that motoneurone B19 in the buccal ganglia of Helisoma makes monosynaptic, cholinergic connections with the supralateral radular tensor (SLT) muscle of the buccal mass. Serotonin (5-HT) and small cardioactive peptide B (SCPB) were found to have peripheral modulatory effects on this motor pathway that are consistent with their previously described central facilitatory effects. Both neurotransmitters, when applied exogenously (10(−6) mol l-1) to isolated buccal ganglion-buccal muscle preparations, potentiated the magnitude of motoneurone B19-evoked muscle contractions (6.3 and 2.7 times, respectively) without affecting excitatory junctional potential (EJP) amplitudes. When applied to single dissociated SLT muscle fibres in cell culture, these modulators had similar effects on acetylcholine (ACh)-evoked muscle fibre shortening, demonstrating that these neuromodulators exert direct actions on the muscle cells. The cardioactive peptide FMRFamide (10(−6) mol l-1), although slightly potentiating muscle contractions in reduced neuromuscular preparations, significantly decreased both ACh-evoked muscle fibre shortening and depolarizing potentials in cultured SLT muscle cells. The differential effects of FMRFamide may, in part, be due to the elimination of interactive effects between multiple neurotransmitters that might exist in semi-intact preparations and in vivo. These results demonstrate that 5-HT, SCPB and FMRFamide in Helisoma can directly modulate the peripheral muscle targets of buccal motoneurones involved in the generation of cyclical feeding behaviour.

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EARLY VARIATIONS OF PLASMA CORTISOL AFTER PULSE INTRAVENOUS INJECTION OF DIBUTYRYL CYCLIC ADENOSINE 3′,5′-MONOPHOSPHATE IN NORMAL SUBJECTS

Acta Endocrinologica ◽

10.1530/acta.0.0720753 ◽

1973 ◽

Vol 72 (4) ◽

pp. 753-761 ◽

Cited By ~ 3

Author(s):

Alberto Angeli ◽

Giuseppe Boccuzzi ◽

Roberto Frajria ◽

Daniela Bisbocci ◽

Franco Ceresa

Keyword(s):

Intravenous Injection ◽

Plasma Cortisol ◽

Time Course ◽

Healthy Adult ◽

Normal Subjects ◽

Adult Women ◽

Healthy Women ◽

Adrenal Steroidogenesis ◽

The Mean ◽

Zero Time

ABSTRACT 10 mg/kg of dibutyryl cyclic adenosine 3′,5′-monophosphate (Db-cAMP) was iv pulse injected into twelve healthy adult women. The plasma cortisol levels were determined as 11-OHCS at zero time and then at 2.5, 5, 7.5, 10, 15, 30, 60 and 180 min after the injection. The data were compared with those obtained at the corresponding times in two groups of eleven and seventeen healthy women after the injection of 250 ng and 250 μg of synthetic β-1-24 corticotrophin performed in the same manner as the injection of the nucleotide. The mean increments in plasma cortisol were significantly lower after Db-cAMP than after ACTH. Differences were noted by analyzing the time course of the responses. In the case of stimulation with Db-cAMP the 11-OHCS levels rose progressively to a maximum at 15–30 min. By contrast, a peak of plasma cortisol was evident in most cases within a few min after the injection of ACTH; after a fall, a later rise was then observed starting from 15 min. The differences in the plasma 11-OHCS responses after the two stimuli may also be of interest clinically for the investigation of some aspects of adrenal steroidogenesis.

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