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PubMed1993

Neurotrophin 3 supports the survival of developing muscle sensory neurons in culture.

Target-dependent cell death of different sub-populations of sensory neurons may be regulated by different trophic factors. To investigate this possibility, we have taken advantage of the fact that the fractions of muscle sensory and cutaneous sensory neurons in chicken dorsal root ganglia (DRG) are probably different at different segmental levels, and we have compared the responses of chicken DRG from levels that do and do not innervate limb tissue to various growth factors in vitro. Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) both supported neurite outgrowth from DRG explanted from all segmental levels. In contrast, neurotrophin 3 (NT-3) supported robust neurite growth only from DRG explanted from the cervical or lumbar levels, which innervate limb muscles. Similarly, NGF and BDNF both promoted survival of dissociated neurons from limb and nonlimb segmental levels, whereas NT-3 promoted survival of more neurons from limb compared to nonlimb levels. This suggests that muscle sensory neurons, which are probably more prevalent at the cervical and lumbar levels, may be specifically affected by NT-3. To evaluate this possibility directly, we compared the survival of retrogradely labeled muscle and cutaneous neurons in NGF, BDNF, and NT-3. Identified muscle sensory neurons survived best in vitro in the presence of NT-3, while the survival of identified cutaneous sensory neurons was greatest in NGF. This work provides direct evidence for a potential role of NT-3 versus NGF in the survival of a specific subpopulation of DRG neurons.

Animals↗
PubMed1977

Effects of innervation on acetylcholine sensitivity of developing muscle in vitro.

1. Chick embryo skeletal muscle fibres were grown in culture. The acetylcholine (AACh) sensitivity of non-innervated fibres was compared with that of fibres innervated in vitro by chick embryo ciliary ganglion neurones. 2. The general pattern of ACh sensitivity was unchanged by innervation: ACh hot spots were superimposed on a background of uniform ACh sensitivity. 3. Quantitative comparisons revealed two differences between non-innervated and innervated fibres. First, hot spots were encountered about one third more often on innervated fibres. Secondly, about one-third of the hot spots on innervated fibres had significantly higher ACh sensitivities than the remainder, which were similar to those on control fibres. 4. Apossible explanation of these results is that nerves which form synapses induce the appearanceof end-plates which have higher ACh sensitivities than the pre-existing ACh hot spots.

Acetylcholine↗
PubMed1990

Stretch-sensitive channels in developing muscle cells from a mouse cell line.

1. Recordings of single-channel activity were made from cell-attached patches on mouse C2 muscle cells at morphologically identifiable stages of myogenesis in vitro. We have identified Ca2(+)-permeable, cation-selective channels that are gated by applying suction to the patch electrode and by changes in membrane potential and have analysed single-channel properties as well as channel expression during myogenesis. 2. Single-channel activity could be detected when the membrane was held at steady negative potentials. With monovalent cations in the electrode, the single-channel current-voltage (i-V) relations were linear. The channel is permeable to Li+, Na+, K+, Rb+ and Cs+, but is not strongly selective among the monovalent cations as judged by measurements of single-channel conductance and reversal potential. 3. With 110 mM of either CaCl2 or BaCl2 as the only inward change carrier, slope conductances were approximately 13 and 24 pS and currents reversed at approximately +22 and +17 mV, respectively. The relative permeability of Ca2+ to K+ calculated from the constant-field equation was PCa/PK = approximately 2. 4. Channel openings occurred as bursts of brief openings and closings separated by much longer closed periods. Closed-time histograms were best fitted with three exponential components, while histograms of burst duration were best fitted with two exponential components, reflecting the short and long bursts in the single-channel records. 5. Applying suction to the patch electrode while recording at steady negative membrane potentials produced channel openings to discrete current levels. Mean channel open probability depended linearly on the square of the applied pressure and was greater at positive membrane potentials. The permeability of the channel to monovalent and divalent cations was indistinguishable from the spontaneous activity recorded at steady negative potentials. 6. Channel activity recorded from cell-attached patches in the absence of applied pressure depended on membrane potential increasing approximately e-fold per 38 mV with depolarization. Analysis of the kinetics of the response to membrane potential showed that the depolarization reduced the duration of the slowest component of the closed-time distribution. 7. The lanthanide cation gadolinium (Gd) reduced the amplitude of the unitary currents in a concentration-dependent manner. The amplitudes of both inward and outward currents were reduced to the same extent suggesting block is voltage-independent. Gd produced half-maximal inhibition of the unitary current at approximately 6 microM.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

The potential value and toxicity of chromium picolinate as a nutritional supplement, weight loss agent and muscle development agent.

The element chromium apparently has a role in maintaining proper carbohydrate and lipid metabolism in mammals. As this role probably involves potentiation of insulin signalling, chromium dietary supplementation has been postulated to potentially have effects on body composition, including reducing fat mass and increasing lean body mass. Because the supplement is absorbed better than dietary chromium, most studies have focused on the use of chromium picolinate [Cr(pic)(3)]. Cr(pic)(3) has been amazingly popular with the general public, especially with athletes who may have exercise-induced increased urinary chromium loss; however, its effectiveness in manifesting body composition changes has been an area of intense debate in the last decade. Additionally, claims have appeared that the supplement might give rise to deleterious effects. However, over a decade of human studies with Cr(pic)(3) indicate that the supplement has not demonstrated effects on the body composition of healthy individuals, even when taken in combination with an exercise training programme. Recent cell culture and in vivo rat studies have indicated that Cr(pic)(3) probably generates oxidative damage of DNA and lipids and is mutagenic, although the significance of these results on humans taking the supplement for prolonged periods of time is unknown and should be a focus for future investigations. Given that in vitro studies suggest that other forms of chromium used as nutritional supplements, such as chromium chloride, are unlikely to be susceptible to generating this type of oxidative damage, the use of these compounds, rather than Cr(pic)(3), would appear warranted. Potential neurological effects (both beneficial and deleterious) from Cr(pic)(3) supplementation require further study.

Animals↗
PubMed1986

Blood vessel ontogeny in upper extremity of man as related to developing muscles.

Vascular bed and its relationship to differentiating muscular tissue was studied in a set of 104 upper limbs of human embryos and foetuses, gradually increasing from 10 to 120 mm C-R length. Knowledge obtained on the ontogeny of vascular bed was supplemented by findings in 75 limbs of adults treated by preparation technique. Embryonic and foetal material was treated histochemically a--to demonstrate vascular bed reaction for alkaline phosphatase (AP), ATPase, and dipeptidylpeptidase IV (DPP IV), b--to study differentiating muscular tissue for enzyme--ATPase and tetrazoliumreductase (NaDH2, c--to distinguish muscular tissue elements with toluidine blue staining for degree of maturity. Observations concerned several items, namely a--the ontogeny of main arterial trunks in the forearm and hand, b--muscle fibre type differentiation in antebrachial muscular primordia, c--formation of vascular bed as related to differentiating muscular tissue in the forearm and hand. Therefore our results are grouped as follows: ad a--Arterial trunks differentiate along with other limb structures in 12-18 mm C-R length embryos. Thus in embryos above 18 mm C-R length antebrachial and hand trunks are fully formed. Vascular trunks differentiate from deep vascular network via gradual reduction and magistralization in conformity with the general laws of haemodynamics. All arterial trunks forming in the limb during the ontogeny branch off the original axial artery in regio cubiti. In a. radialis trunk it has been ascertained that this blood vessel does not originate from a. brachialis superficialis, as generally reported, but its formation conforms to the same general principles as blood vessel trunks. So it branches off the original axial artery, as other trunks do. A. mediana formed during vascular trunks differentiation later in the ontogeny does not obliterate but changes into the constant a. comitans n. mediani. ad b--First involved in differentiation in antebrachial muscular primordia are the "fast" type fibres (according to Peter et al., 1972) (fast glycolytic-FG-type fibres followed by fast oxidative glycolytic-FOG-type fibres) in 27-30 mm C-R length embryos. "Slow" type fibres (slow oxidative-SO-type fibres) may not be demonstrated histochemically in antebrachial muscles earlier than 45 mm C-R length foetuses. The maturity of muscular elements may be demonstrated by staining with toluidine blue on cytoplasm basophilia of cells. Sarcolytic myotubes in muscular primordia histochemically display typical features which distinguish them markedly from other differentiating muscle fibres.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphatases↗
PubMed1999

Fetal myoblast clones contribute to both fast and slow fibres in developing rat muscle.

Retroviral cell lineage marking was used to investigate the role of cell lineage in fetal and neonatal rat muscle development. Clusters of infected cells, presumably myoblast clones, contribute cells to both slow primary and fast secondary fibres. Moreover, single clusters of marked cells contain both slow and fast primary fibres, suggesting that, at least during fetal life, single clones contribute nuclei to both fibres that are committed to remain slow and those that convert to a fast phenotype. The majority of fibres in individual fascicles of fetal muscle could be infected by a self-inactivating retroviral vector. Retroviral gene expression was markedly lower in non-muscle tissues, suggesting that fetal retroviral infection might target exogenous genes to mammalian muscle fibres during later life.

Age Factors↗
PubMed1993

Regulation and activity-dependence of N-cadherin, NCAM isoforms, and polysialic acid on chick myotubes during development.

Muscle development in vivo involves a complex sequence of cell-cell interactions in which secondary myotubes first form in association with primary myotubes and subsequently separate from them. We show here that during this process N-cadherin and the different structural forms of NCAM are regulated in a pattern that involves both temporal changes in expression and localization to particular regions of the muscle cell surface. In particular, levels of N-cadherin on maturing myotubes are decreased, and the form of NCAM synthesized by the muscle changes from a transmembrane non-polysialylated to a lipid-linked polysialylated membrane protein. Moreover, while NCAM was distributed on all myotube surfaces, the polysialyated form of NCAM was restricted to regions of the myotube surface that had recently separated from neighboring cells. We previously found that blockade of nerve-induced activity by d-Tubocurarine perturbed muscle cell interactions, resulting in a failure of myotubes to separate. We now show that this activity blockade also alters adhesion molecule expression. First, N-cadherin was no longer down-regulated in maturing myotubes, and its persistence on the surfaces of mature myotubes may partly explain their failure to separate. Secondly, the developmental switch from transmembrane to lipid-linked NCAM did not occur, and polysialylated NCAM was no longer formed. As the unusual physical properties of PSA have been proposed to impede cell-cell interactions, this alteration would also be expected to compromise cell separation. Together, these results suggest that the regulated expression of both N-cadherin and NCAM isoforms including their polysialylation, is an essential mechanism for the normal separation of secondary myotubes from primary myotubes.

Animals↗
PubMed2003

Erbb2 regulates neuromuscular synapse formation and is essential for muscle spindle development.

Neuregulins and their Erbb receptors have been implicated in neuromuscular synapse formation by regulating gene expression in subsynaptic nuclei. To analyze the function of Erbb2 in this process, we have inactivated the Erbb2 gene in developing muscle fibers by Cre/Lox-mediated gene ablation. Neuromuscular synapses form in the mutant mice, but the synapses are less efficient and contain reduced levels of acetylcholine receptors. Surprisingly, the mutant mice also show proprioceptive defects caused by abnormal muscle spindle development. Sensory Ia afferent neurons establish initial contact with Erbb2-deficient myotubes. However, functional spindles never develop. Taken together, our data suggest that Erbb2 signaling regulates the formation of both neuromuscular synapses and muscle spindles.

Actins↗
PubMed1991

[The embryonic development of iridial muscles].

Development of iridial muscles was observed in 116 fetal eyes (72 human embryos 7 weeks to full gestation). Bundles of microfilaments with local high density spots appeared in the cytoplasm of the anterior pigment epithelium early in 10 week embryos. The high density spots later grew to be the dense-bodies in the myofilaments, the original structure of the pupillary sphincter. In embryos of 4 1/2 months, blood capillaries grew into the sphincter, which was fully developed in the 6th month, and myofilaments of the dilator muscles began to appear in the cytoplasm of peripheral anterior pigment epithelium, with villous protrusions toward the stroma. Many myofilaments with scattered dense-bodies were seen in the protrusions. It was thus confirmed that both the sphincter and dilator muscles originated from the iridial anterior pigment epithelium of neuro-ectoderm; however, the former developed fully to form independent smooth muscle bundles, while the latter was less developed and remained part of the pigment epithelium (myo-epithelium). The appearance of both muscles was earlier than previously reported.

Actin Cytoskeleton↗
PubMed1988

Functional significance of myosin transitions in single fibers of developing soleus muscle.

The maximal velocity of shortening and myosin heavy chain (MHC) composition of single, chemically skinned fibers from neonatal and adult rat soleus muscles were examined to determine the relationship between these parameters during slow muscle development in the rat. In addition, the MHC composition of bundles of fibers from soleus muscles at the same ages was studied. The MHC compositions were examined using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The results from the bundles of fibers indicate that from 3 days to 5 mo postnatal, the rat soleus contains predominantly MHCs that migrate in the vicinity of the MHC from adult slow muscle. From 14 days to 2 mo postnatal, there are also significant amounts of additional MHCs that comigrate on SDS gels with those characteristic of adult rat fast muscle. All the fibers studied at 3 and 7 days postnatal and at 5 mo and the majority of fibers from 14 days to 2 mo postnatal had relatively low shortening velocities. A few fibers from the latter group had significantly higher velocities. The faster fibers at each age had greater amounts of the MHCs that comigrate with the adult fast-type MHC on SDS gels. Thus the velocity of shortening of single fibers from the rat soleus muscle appears to be related to MHC composition during postnatal development.

Animals↗