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PubMed1990

Effect of reinnervation on the degradation rate of junctional acetylcholine receptors synthesized in denervated skeletal muscles.

Two populations of ACh receptors (AChRs) with different degradation rates have been shown to coexist in the postsynaptic membrane after denervation of the neuromuscular junction (NMJ). One population, consisting of the slowly degrading original AChRs inserted into the plasma membrane prior to denervation, has a degradation half-life (t1/2) of approximately 8 d. This degradation rate accelerates after denervation (to a t1/2 approximately 3 d), but can be decelerated back to the predenervation rate by reinnervation. The second population, the rapidly degrading new AChRs, which replace the degrading original AChRs at the NMJ after denervation, resembles embryonic AChRs, with a t1/2 of approximately 1 d. In the present study, we report that the degradation rate of these new junctional AChRs is unaltered for 3-6 half-lives after reinnervation. We further report that a small amount (less than 10%) of slowly degrading AChRs (t1/2 approximately 3 d) may also be synthesized in denervated muscle. We suggest that, unlike its effect on the original, slowly degrading AChRs, reinnervation does not modulate the degradation rate of the rapidly degrading new junctional AChRs. It merely regulates the ratio of rapidly to slowly degrading AChRs being synthesized and inserted at the NMJ.

Animals↗
PubMedDate not supplied

Phosphorylation of the sarcolemma of dystrophic and normal hamster muscle following denervation.

The rapid phosphorylation at 0 degree C of sarcolemma preparations of hamster leg muscle was compared with (Na+,K+)-ATPase activity in sham-operated and 7-day denervated muscle. The phosphorylation appeared to be under the trophic influence of the sciatic nerve since the denervated preparations exhibited a markedly reduced phosphorylation. In similar studies using dystrophic hamsters the sarcolemma preparations from sham-operated and denervated leg muscle both exhibited the same degree of phosphorylation.

Animals↗
PubMed1989

Sustained cell proliferation in denervated skeletal muscle of mice.

Cellular proliferation in skeletal muscle was measured throughout the first 4 weeks after denervation. Twenty four mice had one leg denervated, and 4 groups of 6 of these mice were injected with tritiated thymidine once daily for 7 days, either during the first, second, third or fourth week after denervation. Autoradiographic labelling of muscle and connective tissue nuclei in denervated muscles was compared with innervated muscles from the opposite innervated legs of the same mice. Labelling of connective tissue and muscle (myonuclear and satellite cell) nuclei was significantly higher in denervated muscles, compared with innervated muscles on the unoperated side. There were no significant differences among labelling of nuclei in muscles denervated for 1, 2, 3 or 4 weeks. However, connective tissue labelling after 1 week of denervation was significantly higher than at later times. This study shows that nuclei of muscle and connective tissue cells proliferate and turnover at high levels for at least one month after denervation.

Animals↗
PubMed1982

Size plasticity of intact motoneurons as reaction to partial denervation of muscle.

It is known that partial denervation of muscle leads to the enlargement of the intact motor units by collateral sprouting of the intramuscular axons. After partially denervating the hind limb muscles in the frog, its effect on the intact motoneuron cell size was investigated. It was found that motoneurons increase in size when their motor unit territory expanded. This increase indicates size plasticity and the dynamic nature of motoneuron size. It is proposed that there are two distinct, but interacting states relating to motoneuron size (the stable in equilibrium labile states). The implications of size plasticity of motoneuron on synaptogenesis/synaptic reorganization on its membrane surface is discussed.

Animals↗
PubMed1993

[Effect of endurance running training on the structural and metabolic properties of partially denervated soleus muscle in rats].

To estimate the influence of partial denervation on the skeletal muscle, a histochemical and biochemical study was performed on the soleus muscle. Partial denervation was carried out by cutting the proximal root of the nerve innervating the soleus muscle. Further, the effect of endurance running training on the recovery of the partially denervated muscle was examined. Partial denervation did not cause apparent diminution of the number of muscle fibers, nor the muscle weight. Four weeks after denervation, histological changes such as grouping atrophy, fiber splittings, and invasive phagocytes were observed in the denervated portion of the muscle. In the non-running group, mean cross-sectional fiber area of each muscle fiber type increased significantly at 4 weeks after denervation. On the other hand, mean cross sectional fiber area of type II fibers increased at 8 weeks after denervation in the running group. The oxidative enzyme activities were significantly increased in the partially denervated muscle by endurance running training after 4 weeks of denervation. The results indicate that the influence of partial denervation gradually extends over the whole muscle. Furthermore, the running exercise appears to add a good effect to a recovery of the function and the maintenance of muscle structures.

Animals↗
PubMed1984

Gangliosides in rabbit and human skeletal muscle with denervation atrophy.

In experimental denervation of rabbit skeletal muscle, an increase of gangliosides has been reported. Ganglioside, DNA, total lipid and protein levels were studied in experimental denervation of rabbit gastrocnemius muscle and in human skeletal muscle with denervation atrophy. In severe human denervation atrophy total ganglioside, DNA and total lipid levels were increased, and protein levels decreased as compared with controls. The ganglioside pattern was changed in severe human denervation atrophy and showed a significant increase of a GT1b-like and moderate decrease of a GM1-like compound. Findings in experimentally denervated rabbit muscle resembled results obtained in human denervation atrophy, showing a significant increase of total ganglioside levels as well as a moderate increase of GT1b-like and decrease of GM1-like compounds.

Adult↗
PubMed1981

A correlation of the alpha-bungarotoxin binding sites (acetylcholine receptors) and intramembranous particles in denervated skeletal muscle of rat.

A quantitative distribution of alpha-bungarotoxin (alpha-BGT) binding sites i.e. acetylcholine receptors (AchR) has been investigated and correlated with the distribution of intramembranous particles (approximately 15 nm in diameter) observed on the freeze-fractured face (P-face) of the non-synaptic sarcolemma of denervated muscle. By both light and electron microscopy autoradiography, randomly distributed clusters of alpha-BGT sites are visualized on the plasma membrane of the denervated muscle. Such distributions of the toxin binding sites correspond with that of the 15 nm particles on the P-face of the denervated muscle. Quantitative studies suggest that upon denervation the toxin binding sites increase approximately 60-fold in the non-synaptic sarcolemma. However, the density of these alpha-BGT sites is 4--5 times more than the density of the 15 nm particles. On the basis that there are two alpha-BGT binding sites per AchR molecule, these results suggest that each 15 nm particle is composed of more than one AchR receptor. In addition to the increase in toxin binding sites on the non-synaptic sarcolemma, a notable increase in the number of silver grains is observed in the peripheral sarcoplasm and is speculated to be part of the intracellular pool of receptors.

Animals↗
PubMed1998

Increased activity improves recovery of partially denervated fast rat muscles.

Partial denervation of the neonatal rat extensor digitorum longus muscles by removing the L4 spinal nerve and thus 80% of its innervation [A.L. Connold, T.J. Fisher, S. Maudarbocus, G. Vrbová, Response of developing fast muscles to partial denervation, Neuroscience 46 (1992) 981-988; F. Tyc, G. Vrbová, The effect of partial denervation of developing rat fast muscles on their motor unit properties, J. Physiol. 482 (1995) 651-660] results in its permanent weakness. The possibility that the weakness that follows partial denervation is due to the effects of reducing activity of the muscle during a critical stage of development was studied here. Partial denervation was carried out in 3-day-old pups by removing the L4 spinal nerve. To enhance motor activity two days later some animals had injections of l-Dopa twice a day for 8 days. This treatment induced locomotor activity for at least 2 h/day. The muscles from treated and untreated animals were examined 2 months later. There was a significantly smaller reduction of weight and force production in the muscles from l-Dopa treated animals. Both twitch and tetanic force developed by the EDL muscle from the treated group was twice that of the control untreated group. This effect was due mainly to the larger size of the motor units (MUs) in the l-Dopa treated muscles compared to the controls. The mean motor unit force in the untreated group was 69% of that in the control muscle, whereas this value was 127% in the l-Dopa treated animals. Thus it appears that the activity induced by treatment with l-Dopa could to some extent prevent the loss of weight and force output seen after partial denervation of young fast muscles.

Animals↗
PubMed1960

The effect of temperature on the direct muscle twitch response and the action of drugs on the isolated denervated rat diaphragm.

The effect of temperature on the direct twitch response of the normal and denervated rat diaphragm, and the sensitivity of the contractural response of the denervated muscle to acetylcholine, suxamethonium, decamethonium, and potassium salts, was studied. Cooling the normal diaphragm from 39 to 20 degrees increased the size of the direct twitch, but below this temperature the twitch response of the muscle was progressively depressed. The denervated muscle twitch was, by contrast, maximal at 39 degrees and decreases as the temperature was lowered. This property of the denervated muscle first appeared about the third day after denervation. The contractural response of the denervated diaphragm to applied acetylcholine was enhanced by cooling, while the response to potassium salts was depressed. The depression of the contracture induced by potassium followed closely the depression of the direct muscle twitch of the denervated muscle over the same temperature range.

Acetylcholine↗
PubMed1983

Fiber type changes in denervated soleus muscles of the hyperthyroid rat.

The thyroid status of rats is known to influence the histochemical and biochemical myosin adenosine triphosphatase (M-ATPase) activity of the soleus muscle. In the hypothyroid state, denervated soleus muscles are not subject to that influence. Our experiments indicated that in the hyperthyroid state fibers of the denervated soleus muscle show a profound change from acid-stable M-ATPase positive to acid-stable M-ATPase negative. We concluded that this change was induced by the hyperthyroid state and was not neurally mediated.

Adenosine Triphosphatases↗
PubMed1982

[Effect of verapamil and manganese ions on the acetylcholine sensitivity of the membrane of innervated and denervated frog muscle fibers].

Experiments on frogs were made to examine the effect of verapamil and Mn2+ on acetylcholine sensitivity of the postsynaptic membrane of intact and denervated muscle fibers. The inhibitory action of verapamil on acetylcholine sensitivity of denervated muscle fibers was found to be more pronounced than that on intact ones. Ca2+ replacement by Mn2+ in a solution slightly lowered acetylcholine sensitivity of the membrane of denervated and intact muscle fibers. It is concluded that the synaptic and extrasynaptic cholinoreceptors of the frog muscle membrane differ as regards the effect produced on them by verapamil. At the same time the effect of verapamil on the cholinoreceptors is not reduced to the drug property to restrict the ingress of Ca2+ to muscle fibers.

Acetylcholine↗
PubMed1991

Effect of denervation on the expression of two glucose transporter isoforms in rat hindlimb muscle.

Denervation rapidly (within 24 h) induces insulin resistance of several insulin-responsive pathways in skeletal muscle, including glucose transport; resistance is usually maximal by 3 d. We examined the effect of denervation on the expression of two glucose transporter isoforms (GLUT-1 and GLUT-4) in rat hindlimb muscle; GLUT-4 is the predominant species in muscle. 1 d postdenervation, GLUT-1 and GLUT-4 mRNA and protein concentrations were unchanged. 3 and 7 d postdenervation, GLUT-4 mRNA and protein (per microgram DNA) were decreased by 50%. The minor isoform, GLUT-1 mRNA increased by approximately 500 and approximately 100%, respectively, on days 3 and 7 while GLUT-1 protein increased by approximately 60 and approximately 100%. The data suggest that the insulin resistance of glucose transport early after denervation does not reflect a decrease in total glucose transporter number; however, decreased GLUT-4 expression may contribute to its increased severity after 3 d. Parallel decreases in GLUT-4 mRNA and GLUT-4 protein postdenervation are consistent with pretranslational regulation; GLUT-1 expression may be regulated pre- and posttranslationally. The cell type(s) which overexpress GLUT-1 postdenervation need to be identified. Nervous stimuli and/or contractile activity may modulate the expression of GLUT-1 and GLUT-4 in skeletal muscle tissue.

Animals↗
PubMed1977

Nerve-muscle interaction: changes in the cellular organization of a skeletal muscle upon denervation.

The alterations in the organization of lumbrical muscle of the rat have been investigated following denervation, with emphasis on the structure of cytoplasmic constituents, sarcolemma in the synaptic and non-synaptic regions and acetylcholinesterase activity. The appearance of 15--18 nm intramenbranous particles in the non-synaptic sarcolemma is thought to be related to the known acetylcholine extrajunctional sensitivity which is manifested after denervation. The acetylcholinesterase activity is greatly reduced in the synaptic region in the denervated muscle. These changes are discussed in relation to the known physiological and biochemical data.

Acetylcholinesterase↗
PubMed1994

Denervated skeletal muscle stimulates migration of Schwann cells from the distal stump of transected peripheral nerve: an in vivo study.

We have tested the stimulation of Schwann cell migration from the distal stump of a 1 week transected sciatic nerve of adult rats by denervated skeletal muscle. Migrating Schwann cells were distinguished by the presence of non-specific cholinesterase (nChE) activity and glial fibrillary acidic protein (GFAP) at a distance of about 6 mm among denervated muscle fibres 4 weeks after insertion of the distal stump. In addition, the distal stump was introduced into the open end of a silicone chamber packed with artificial fibrin sponge (Gelaspon) soaked in homogenate from intact or denervated muscles. A larger amount of migrated Schwann cells was observed in the chambers filled with homogenate from denervated muscles. An alteration in the amounts of Schwann cells migrating into the silicone chambers observed after histochemical staining (nChE or GFAP) was supported by biochemical measurements of the nChE activity. The biochemical assessment of the nChE activity revealed the increased amounts of migrated Schwann cells in proportion to the protein contents of homogenates from the denervated muscles. In addition, heating of homogenate from the denervated muscles resulted in a diminution of Schwann cell migration. Bromodeoxyuridine incorporation did not show an increased proliferation of Schwann cells inside the chambers following application of homogenate from the denervated muscles in comparison with the homogenate from the innervated muscles. Our results suggest a stimulation of Schwann cell migration from the distal stump of the transected sciatic nerve by soluble factor(s) produced by denervated skeletal muscles.

Animals↗
PubMed2005

Abortive myogenesis in denervated skeletal muscle: differentiative properties of satellite cells, their migration, and block of terminal differentiation.

Little is known about the biological properties of myogenic satellite cells during post-denervation muscle atrophy. The present study investigated the differentiative capacity of satellite cells and their involvement in the compensatory regenerative process in long-term denervated rat muscle. Electron microscopy and immunocytochemical labeling of muscle tissue 1-18 months following denervation demonstrated that despite activation of satellite cells, myogenesis in denervated muscle is abortive and does not lead to the formation of normal muscle fibers. Small sizes, poor development of the contractile system in newly formed denervated myotubes, and the absence of satellite cells on the surface indicate that their differentiation typically does not progress to terminal stages. Many immature myotubes degenerate, and others survive but are embedded in a collagen lattice near their parent fibers. Interestingly, newly formed myotubes located on the surface of parent muscle fibers beneath the basal lamina typically did not contain developed myofibrils. This suggests that the contacts of daughter and parent muscle fibers block myofibrillogenesis. Assembly of sarcomeres in most cases occurs following complete spatial separation of daughter and parent muscle fibers. Another manifestation of the involvement of myogenic precursors in abortive myogenesis is the formation of clusters of underdeveloped branching myotubes surrounded by a common basal lamina. We found that myoblasts can also fuse directly with differentiated muscle fibers. The presence of satellite cells near the openings in the basal lamina and in the interstitial space indicates that myogenic precursors can migrate through the basal lamina and form myotubes at a distance from parent fibers. Our data may explain why long-term denervated skeletal muscle has a poor capacity for regeneration and functional restoration.

Animals↗
PubMed1989

On the effect of muscle activity on the end-plate membrane in denervated mouse muscle.

1. Mouse soleus muscles were denervated and some of them were chronically stimulated. Sixteen to twenty-one days later, the number of junctional acetylcholine receptors (AChR) and their metabolic stability were examined by measuring binding of 125I-alpha-bungarotoxin, their gating properties by analysis of acetylcholine-induced current fluctuations and the ultrastructure of the end-plate membrane by electron microscopy. 2. In agreement with other studies on inactive muscles, no effect of denervation on junctional AChR number could be resolved. However, some of the fast-gating 'adult' AChR channels had been replaced by slowly gating fetal AChRs, their half-life was lowered to 38 h and the folding of the end-plate membrane was reduced. 3. These changes were prevented in denervated but stimulated active muscles: the junctional AChR population remained homogeneously 'adult', the half-life of junctional AChRs was 13 days and folding of the end-plate membrane remained comparable to that in control muscles. 4. The significance of these results is discussed with respect to the role of muscle activity in end-plate development.

Animals↗