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PubMed2001

Nerve control of type 2A MHC isoform expression in regenerating slow skeletal muscle.

Bupivacaine-induced regeneration was studied in rat soleus muscle under several conditions, with the focus on type 2A and type 1 myosin heavy chain (MHC) isoform expression. In denervated muscles, type 1 was absent, whereas type 2A was widely expressed, a pattern of regeneration which appeared to be independent of fibrillation activity of the muscle. Both type 1 and type 2A isoforms were absent in muscles regenerated during tetrodotoxin (TTX) block of impulse conduction in the sciatic nerve, but type 2A was still present when the TTX block was associated with the vinblastine block of axoplasmic flow; vinblastine block alone caused the coexpression of type 1 and type 2A isoforms in the majority of fibers. These results suggest that axoplasmic flow carries some chemical factor that inhibits 2A MHC isoform expression. The results are also of clinical interest, contributing to the understanding of factors controlling muscle differentiation and adaptation.

Anesthetics, Local↗
PubMed1989

Changes in tetrodotoxin-resistant action potentials after passive transfer of myasthenia gravis patient sera.

Muscle electrical activity has been studied in mice after intraperitoneal injection of sera from myasthenia gravis (MG) patients. Myasthenic serum did not modify the electrical properties of innervated muscle fibres. The resting membrane potential and the action potential parameters remained unchanged. However, tetrodotoxin (TTX)-resistant action potentials of denervated muscles were reduced by myasthenic serum, possibly in association with receptor endocytosis induced by the immunoglobulin. However, a direct effect of MG serum on TTX-resistant sodium channels cannot be ruled out.

Action Potentials↗
PubMed1995

Mechanism of tongue protraction during prey capture in the spadefoot toad Spea multiplicata (Anura: Pelobatidae).

Recent studies have used muscle denervation experiments to examine the function of muscles during feeding in frogs. By comparing the results of denervation experiments among taxa, it is possible to identify evolutionary changes in muscle function. The purpose of this study was to examine the function of jaw and tongue muscles during prey capture in Spea multiplicata, a representative of the superorder Mesobatrachia. All members of this group possess a disjunct hyoid apparatus. We predicted that Spea would possess a novel mechanism of tongue protraction on the basis of its hyoid morphology. High-speed video motion analysis and muscle denervation were used to study the feeding behavior and mechanism of tongue protraction in Spea. Although Spea possesses a relatively long tongue, its feeding behavior is similar to that of short-tongued frogs of similar body size. Denervation of the m. submentalis had no effect on feeding behavior. When the m. geniohyoideus was denervated, the tongue pad was raised and moved forward slightly, but did not leave the mouth. When the m. genioglossus was denervated, the tongue pad was raised slightly, but no forward movement of the tongue occurred. A similar result was obtained after the mm. genioglossus and geniohyoideus were denervated simultaneously. Thus, both the mm. genioglossus and geniohyoideus are necessary for normal tongue protraction in Spea. In contrast, only the m. genioglossus is necessary for normal tongue protraction in archaeobatrachians and neobatrachians. We hypothesize that the disjunct hyoid is responsible for the greater role of hyoid movement during feeding in mesobatrachians.

Animals↗
PubMed1986

Membrane potential and intracellular potassium and sodium activities after denervation of soleus muscles of neonatal rats.

Potassium and sodium ion-selective microelectrodes were used in vitro to investigate the depolarization of slow-twitch skeletal muscle fibers (soleus) following denervation at 5 to 6 days of age. The normal increase in intracellular potassium ion activity and decrease in sodium ion activity which occurs during the first 3 weeks of life were delayed or prevented by denervation. The results are compared with those found after similar periods of denervation of neonatal rat fast-twitch muscle.

Animals↗
PubMed1982

Neural plasticity: Part 3. Responses to lesions in the peripheral nervous system.

This paper describes some of the remarkable recuperative responses that neurons of the peripheral nervous system have to injury of their axons. The initial response is a sealing of the cut ends of the axons, followed by orderly degenerative and phagocytic events in the segments lying distal and proximal to the lesion. The chromatolytic changes occurring in the cell body are adaptive responses involving the morphological, physiological, and biochemical properties of the neuron. The cell loses dendrites and synapses, its electrophysiological properties are altered, and its biochemistry is altered to prepare the neuron for synthesizing proteins needed for formation of growth cones and regeneration of the axon. During this period, the denervated muscle undergoes dramatic atrophic changes that not only modify the electrical nd chemical properties of its membrane but also reduce the diameter and weight of its fibers. This denervation atrophy of muscle is reversible if reinnervation occurs before muscle material has been replaced by connective tissue. Responses to injury of sensory axons depend on the site of the lesion. Cutting a dorsal root causes Wallerian degeneration of the primary afferents' central processes. Collateral sprouts from neighboring uncut root fibers are thought to take over the vacant synapses on the second-order neurons in the dorsal horn. Cutting a sensory axon peripherally eliminates the receptive field of the primary afferent initially, but in time, collaterals from neighboring skin afferents provide the second-order neurons with a new receptive field. Synaptic reclamation and receptive field reorganization are but two dramatic examples of neuronal plasticity that lead to "rewired" neural circuitry.

Atrophy↗
PubMed2002

Muscle reinnervation with delayed or immediate transplant of embryonic ventral spinal cord cells into adult rat peripheral nerve.

Muscle denervation is common in various neuromuscular diseases and after trauma. It induces skeletal muscle atrophy. Only muscle reinnervation leads to functional recovery. In previous studies, denervated adult rat muscles were rescued by transplantation of embryonic day 14-15 (E14-15) ventral spinal cord cells into a nearby peripheral nerve. In the present study, changes were made in the environment into which the cells were placed to test whether reinnervation was improved by: 1) prior nerve degeneration, induced by sciatic nerve transection 1 week before cell transplantation; 2) transplantation of 1 million versus 5 million cells; 3) addition of nerve growth factor (NGF) to the transplant. Ten weeks after cell transplantation, axons had grown from all of the transplants. The numbers of myelinated axons that regenerated into the tibial, medial (MG), and lateral gastrocnemius-soleus (LGS) nerves were similar across treatments. The mean diameters of large LGS axons (>6 microm) were significantly larger with nerve degeneration before transplantation. The mean diameters of MG and LGS axons were significantly larger with transplantation of 1 million versus 5 million cells. Silver-stained experimental and control lateral gastronemius (LG) muscles showed axons that terminated at motor end plates. Nodal and terminal sprouts were more common in reinnervated muscles (45-63% of all end plates) than in control muscles (10%). Electrical stimulation of the transplants induced weak contractions in 39 of 47 MG muscles (83%) and 33 of 46 LG muscles (72%) but at higher voltages than needed to excite control muscles. The threshold for MG contraction was lower with transplantation of 1 million cells, while LG thresholds were lower without NGF. The cross-sectional area of whole LG muscles was significantly larger with cell transplantation (immediate or delayed) than with media alone, but all of these muscle areas were reduced significantly compared with control muscle areas. These data suggest that delayed transplantation of fewer cells without NGF assists regeneration of larger diameter axons and prevents some muscle atrophy.

Animals↗
PubMed1978

Differential effects of perhydrohistrionicotoxin on neurally and iontophoretically evoked endplate currents.

Perhydrohistrionicotoxin, at concentrations of 10(-12)-10(-7) M, depressed the current generated by iontophoretic application of acetylcholine to endplate regions of soleus and extensor digitorum longus muscles of rats. However, no changes in the amplitude or time course of spontaneous miniature endplate potentials or currents were seen with these concentrations of toxin. Evoked endplate currents were also unaffected by the toxin. Similarly, the responses to iontophoretic acetylcholine were depressed by these concentrations of perhydrohistrionicotoxin in chronically denervated muscles. Depression of responses in both normal and chronically denervated muscles developed gradually, was greater at higher concentrations, and was reversible. The different effects of the toxin on neurally evoked currents and currents produced by iontophoretic application of acetylcholine raise the possibility of the existence of two different population of receptor complexes.

Acetylcholine↗
PubMed1982

Elimination of inappropriate axonal branches of regenerating cockroach motor neurons as detected by the retrograde transport of horseradish peroxidase conjugated wheat germ agglutinin.

A procedure is described for identifying the motor neurons innervating individual cockroach muscles by use of the retrograde transport of extracellularly injected horseradish peroxidase and the staining of cells in whole mount preparations. A modification of this procedure using wheat germ agglutinin covalently conjugated to horseradish peroxidase is required in order to identify regenerating motor neurons that have an axonal process that had regrown into a particular leg muscle at various times after axotomy. At early stages of regeneration 23 out of 31 axotomized motor neurons with axons leaving the metathoracic ganglion through nerve root 5 send an axonal process into muscle 178. In intact animals this muscle receives innervation from only one motor neuron, Df. At later stages of regeneration these inappropriate axonal branches become eliminated until this muscle is again innervated only by Df. These results indicate that the specificity required for the reformation of the original innervation pattern of the leg muscles does not come from factors which are components of paths along the nerve root or which are being released from denervated muscles which could selectively control the direction of growth of axons of particular motor neurons.

Animals↗
PubMed1992

Human muscle cell denervation: the results of a 31-phosphorus magnetic resonance spectroscopy study.

The results presented here demonstrate that there is a major abnormality of high and low energy phosphate metabolism in muscle following peripheral nerve damage. Using 31-phosphorus magnetic resonance spectroscopy the changes in phosphocreatine, adenosine triphosphate, inorganic phosphate and metabolites of membrane metabolism could be observed in vivo in human subjects. The data indicate that there may be a metabolic myopathy in the muscle cells after nerve injury. Further, the metabolic changes did not always return to the control level, indicating a persistence of the abnormality. This failure of the metabolic function of the cells may be important in determining the ultimate outcome of peripheral nerve surgery.

Adenosine Triphosphatases↗
PubMed2003

Localization of the RNA-binding proteins Staufen1 and Staufen2 at the mammalian neuromuscular junction.

Staufen is an RNA-binding protein, first identified for its role in oogenesis and CNS development in Drosophila. Two mammalian homologs of Staufen have been identified and shown to bind double-stranded RNA and tubulin, and to function in the somatodendritic transport of mRNA in neurons. Here, we examined whether Staufen proteins are expressed in skeletal muscle in relation to the neuromuscular junction. Immunofluorescence experiments revealed that Staufen1 (Stau1) and Staufen2 (Stau2) accumulate preferentially within the postsynaptic sarcoplasm of muscle fibers as well as at newly formed ectopic synapses. Western blot analyses showed that the levels of Stau1 and Stau2 are greater in slow muscles than in fast-twitch muscles. Muscle denervation induced a significant increase in the expression of Stau1 and Stau2 in the extrasynaptic compartment of both fast and slow muscles. Consistent with these observations, we also demonstrated that expression of Stau1 and Stau2 is increased during myogenic differentiation and that treatment of myotubes with agrin and neuregulin induces a further increase in the expression of both Staufen proteins. We propose that Stau1 and Stau2 are key components of the postsynaptic apparatus in muscle, and that they contribute to the maturation and plasticity of the neuromuscular junction.

Agrin↗
PubMed2006

Adaptive changes in structure of skeletal muscles from adult Sod1 homozygous knockout mice.

Cu/Zn superoxide dismutase (SOD1), which is localized cytoplasmically and in the mitochondrial intermembrane space, is an enzyme that is critically important for superoxide free-radical elimination. Compared with age-matched wild-type littermates (Sod1 ( +/+ )), SOD1 homozygous knockout (Sod1 ( -/- )) mice have smaller body masses, heart and skeletal muscle masses, and muscle cross-sectional areas. At the light-microscopic level, cross sections of skeletal muscles from Sod1 ( -/- ) mice show no gross structural abnormalities. Following the staining of muscles of Sod1 ( -/- ) mice for succinate dehydrogenase (SDH) enzymatic activity, a grouping of SDH-positive fibers has been observed. Immunostaining for neural cell adhesion marker in the gastrocnemius muscle of Sod1 ( -/- ) mice has revealed a small number of atrophic denervated muscle fibers. No denervated fibers are observed in extensor digitorum longus (EDL), tibialis anterior, or plantaris muscles. An increase in mRNA expression levels of myogenin and acetylcholine receptor alpha has been detected in muscles in Sod1 ( -/- ) mice, but no changes in MyoD expression occur. Compared with fast oxidative fibers in EDL muscles of Sod1 ( +/+ ) mice, those of Sod1 ( -/- ) mice show increased accumulations of sub-sarcolemmal mitochondria. We conclude that the lack of SOD1 in adult Sod1 ( -/- ) mice does not result in extensive denervation of skeletal muscle fibers, although the distribution of fiber types is modified, and that fast oxidative fibers develop alterations in the amount and spatial distribution of sub-sarcolemmal mitochondria.

Adaptation, Physiological↗
PubMed1983

Effects of steroid hormones on muscle reinnervation after nerve crush in rabbit.

The ability of an association of three steroid hormones to influence the reinnervation process and the trophism of rabbit muscles denervated by crush of the sciatic nerve was investigated. The beginning of reinnervation was established with electromyographic recordings from the tibialis anterior muscle. The distance from the site of crushing to the point where the motor nerve enters the tibialis anterior muscle was then measured in each animal, and the nerve regeneration velocity (mm/day) was calculated: a slightly but significantly higher (P less than 0.001) mean value was found in treated animals compared with untreated ones. When soleus and extensor digitorum longus (EDL) muscles were histochemically examined 50 days after lesion, a larger mean diameter of type 2c fibers was found in treated than in untreated animals, pointing out a possible useful effect of the treatment. On the contrary, the size reduction of EDL type 2b fibers was more pronounced in treated rabbits, indicating a catabolic influence of the drugs on this fiber type.

Animals↗
PubMed2004

Myf5 expression in satellite cells and spindles in adult muscle is controlled by separate genetic elements.

The myogenic regulatory factor Myf5 is integral to the initiation and control of skeletal muscle formation. In adult muscle, Myf5 is expressed in satellite cells, stem cells of mature muscle, but not in the myonuclei that sustain the myofibre. Using the Myf5(nlacZ/+) mouse, we now show that Myf5 is also constitutively expressed in muscle spindles-stretch-sensitive mechanoreceptors, while muscle denervation induces extensive reactivation of the Myf5 gene in myonuclei. To identify the elements involved in the regulation of Myf5 in adult muscle, we analysed reporter gene expression in a transgenic bacterial artificial chromosome (BAC) deletion series of the Mrf4/Myf5 locus. A BAC carrying 140 kb upstream of the Myf5 transcription start site was sufficient to drive all aspects of Myf5 expression in adult muscle. In contrast, BACs carrying 88 and 59 kb upstream were unable to drive consistent expression in satellite cells, although expression in muscle spindles and reactivation of the locus in myonuclei were retained. Therefore, as during development, multiple enhancers are required to generate the full expression pattern of Myf5 in the adult. Together, these observations show that elements controlling adult Myf5 expression are genetically separable and possibly distinct from those that control Myf5 during development. These studies are a first step towards identifying cognate transcription factors involved in muscle stem cell regulation.

Animals↗
PubMed1994

Neuromuscular contacts of expanded motor units in rat soleus muscles are rescued by leupeptin.

In the soleus muscle of the rat following section of the L5 ventral ramus (partial denervation) the remaining motor axons increase their territory by sprouting. Nerve sprouts are first seen two to three days after the operation, their number peaks at 10-14 days and subsequently remains at this level. The time course of the initial sprouting in partially denervated muscles is not altered by paralysing the muscles with alpha-bungarotoxin, and the initial extent of the sprouting is, if anything, greater in the paralysed muscles. However, unlike in controls, this level of sprouting is not maintained and neuromuscular contacts are lost when muscles recover from the paralysis. The loss of these contacts can be prevented by treatment of these partially denervated paralysed muscles with leupeptin, an inhibitor of calcium-activated neutral protease. Interestingly, more contacts are rescued when leupeptin is applied 10 days after alpha-bungarotoxin treatment, when sprouting has reached high levels, than at three days, when sprouting has just begun. The neuromuscular connections rescued by leupeptin are functional. Maximum tetanic tension produced by untreated soleus muscles two to five months after partial denervation is 66 +/- 9% of contralateral control muscles, but only 39 +/- 8% when the muscles were paralysed with alpha-bungarotoxin for 12-14 days after partial denervation. However, when partially denervated paralysed muscles were treated with leupeptin three and 10 days after alpha-bungarotoxin treatment their tension output is 74 +/- 3% and 81 +/- 8%, respectively. After partial denervation alone, motor units are twice their normal size. Short-term paralysis with alpha-bungarotoxin prevents this increase in motor unit territory. However, the application of leupeptin to the paralysed muscles rescues neuromuscular contacts, allowing motor unit size to remain expanded, at around 2-2.5-fold. Thus, following recovery from temporary paralysis with alpha-bungarotoxin, there is a sudden withdrawal of neuromuscular contacts and these can be rescued by treatment with leupeptin.

Amino Acid Sequence↗
PubMed2006

Study of skeletal muscle glycogenolysis and glycolysis in chronic steroid myopathy, non-steroid histochemical type-2 fiber atrophy, and denervation.

OBJECTIVE: Muscle biopsies from chronic steroid (glucocorticoid) myopathy, non-steroid histochemical type-2 fiber atrophy, and muscle denervation patients were studied to determine if their glycogen contents, or enzymes involved in glycogenolysis and glycolysis might be related to their fiber atrophy. DESIGN AND METHODS: Fast frozen muscle biopsies from the above patients and from patients later judged by histochemistry to be normal were assayed enzymatically for glycogen content, for enzymes involved in glycogenolysis, and for 6 of the enzymes involved in glycolysis. RESULTS AND CONCLUSION: All three groups of patients had glycogen content, but only the chronic steroid myopathy muscle had statistically less glycogen content than did normal human muscle. All 3 groups had statistically low mean values compared to normal muscles for glycogen phosphorylase activity. This suggests that the biosynthesis and phosphorolysis of glycogen are not involved in muscle fiber atrophy, and glucocorticoid administration does not activate muscle glycogen biosynthesis. Histochemical type-2 fiber atrophy muscles were low compared to normal muscles in three glycogenolysis enzyme activities plus four glycolysis enzyme activities. Muscles from denervation patients were low compared to normal muscles in three glycogenolysis enzyme activities plus five glycolysis enzyme activities. This suggests that muscle denervation may lower the rate of glycolysis enough to fail to provide sufficient pyruvate for mitochondrial ATP biosynthesis, resulting in insufficient protein biosynthesis in both fiber types.

Adult↗
PubMed1991

Nerve-muscle pedicle reinnervation of the paralyzed vocal cord.

Reinnervation offers great potential for the rehabilitation of the paralyzed larynx, a potential that has yet to be realized. The nerve-muscle pedicle (NMP) technique is one method of reinnervation that attempts to transfer a nerve with a portion of its muscle intact to a denervated muscle. The selection of the nerve to incorporate into a NMP is examined in the first part of this article. Experimental data that argue for and against the use of a NMP, a description of the indications and the techniques for the procedure, and a review of the clinical results are detailed.

Animals↗
PubMed1985

Potassium movements in denervated frog sartorius muscle.

The movement of 42K+ across the sarcolemma and the resting membrane potential (VM) of normal and denervated frog sartorius muscle were studied under several experimental conditions in preparations initially equilibrated in 100 mM K+ and 219 mM Cl-. The results can be summarized as follows. In the absence of any driving force on K+, i.e., when the difference between VM and the K+ equilibrium potential (EK) is zero (VM - EK = 0), the K+ conductance (gK) was 368 microseconds . cm-2 in control and 282 microseconds. in denervated muscle. The reduced gK of denervated muscles results from the addition of the opposite changes in the conductances of a Rb+-sensitive inward rectifying pathway (gIR), which decreases, and a Rb+-insensitive linear channel (gL), which increases. Thus in control muscles gK (368 microseconds . cm-2) equals gIR (359 microseconds . cm-2) plus gL (9 microseconds . cm-2), while in denervated muscles gK (282 microseconds . cm-2) equals gIR (198 microsecond . cm-2) plus gL (84 microseconds . cm-2). Denervation significantly reduces the inward rectifying properties of the resting K+ permeability system. In the presence of outward driving forces on K+ (VM - EK greater than 0) of 35-50 mV, the Rb+-sensitive inward rectifier channel appears to close completely in both control and denervated muscles. In the latter, however, the effect was not as well maintained as in the former, suggesting that its closing mechanism might be altered by denervation. No changes were observed during the first 2 wk after denervation.

Animals↗