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PubMed1986

Gradient of extrajunctional acetylcholine receptors early after denervation of mammalian muscle.

After denervation, the number of acetylcholine receptors (AChR) found within the endplate band of skeletal muscle increases transiently by about twofold. In this study, we used EM autoradiography to show that this increased endplate band label is not due to an elevated site density of receptors at the junctional folds. Rather, AChR site density within 500 microns of the endplate was found to be 4 X higher than in non-endplate areas defined as greater than 2 mm from the endplate. This nonuniform distribution of extrajunctional AChR early after denervation could represent a transient gradient, similar to that reported shortly after innervation during development.

Animals↗
PubMed1978

Neural neurotization.

Controlled experimentation using dogs has demonstrated that free nerve-end insertion into a denervated muscle that has lost its motor nerve at the point of entry into that muscle can sprout axons at its implanted end to unite with neuromuscular endplates, either preexisting or new, and result in a functioning muscle. Clinical applications can be found in the treatment of facial paralysis and traumatically induced avulsions of large muscles.

Animals↗
PubMed2000

Endogenous BDNF is required for myelination and regeneration of injured sciatic nerve in rodents.

Following a peripheral nerve injury, brain-derived neurotrophic factor (BDNF) and the p75 neurotrophin receptor are upregulated in Schwann cells of the Wallerian degenerating nerves. However, it is not known whether the endogenous BDNF is critical for the functions of Schwann cells and regeneration of injured nerve. Treatment with BDNF antibody was shown to retard the length of the regenerated nerve from injury site by 24%. Histological and ultrastructural examination showed that the number and density of myelinated axons in the distal side of the lesion in the antibody-treated mice was reduced by 83%. In the BDNF antibody-treated animals, there were only distorted and disorganized myelinated fibres in the injured nerve where abnormal Schwann cells and phagocytes were present. As a result of nerve degeneration in BDNF antibody-treated animals, subcellular organelles, such as mitochondria, disappeared or were disorganized and the laminal layers of the myelin sheath were loosened, separated or collapsed. Our in situ hybridization revealed that BDNF mRNA was expressed in Schwann cells in the distal segment of lesioned nerve and in the denervated muscle fibres. These results indicate that Schwann cells and muscle fibres may contribute to the sources of BDNF during regeneration and that the deprivation of endogenous BDNF results in an impairment in regeneration and myelination of regenerating axons. It is concluded that endogenous BDNF is required for peripheral nerve regeneration and remyelination after injury.

Animals↗
PubMed1996

[The possibilities for the surgical treatment of neurogenic fecal incontinence in children].

Treatment of anal incontinence in children with a pathology of the distal portion of the spine is a serious problem. We observed 36 children aged from 3 to 6 years with the 3rd degree of fecal incontinence. Twenty patients had spina bifida, 12 had meningocele, 4 children had the following symptoms: disturbed formation of the arches, sacrum agenesia, deformity of the distal portion of the spine. The conservative treatment was effective but in children without concomitant neurological disorders (motor disorders of the lower extremities, disturbance of the perineum sensitivity). Great increase of the ano-rectal angle and decreased pressure in the anal canal were found in 12 patients with meningocele and in 4 children with severe defects of the vertebral column. They were subjected to operation of free transplantation of the preliminarily denervated muscle by the Hakelius method. Good effects were obtained in 10 cases of 12 operations.

Anal Canal↗
PubMed1996

[The surgical treatment of fecal incontinence in children].

Based on his experience with treatment of 112 children the author considers that severe and various disturbances of the rectum abturative apparatus function arising from surgical interventions in the anorectal area require the differentiated approach to choice of the method of surgical correction of the incontinence. The transplantation of the denervated muscle, transplantation of the vascular-nervous thoraco-dorsal flap, a lavsan band were used to make a pubo-rectal loop, plasty of the outer and inner sphincters being performed mainly with local tissues.

Anal Canal↗
PubMed1997

Nerve terminal withdrawal from rat neuromuscular junctions induced by neuregulin and Schwann cells.

Schwann cells (SCs) that cap neuromuscular junctions (nmjs) play roles in guiding nerve terminal growth in paralyzed and partially denervated muscles; however, the role of these cells in the day-to-day maintenance of this synapse is obscure. Neuregulins, alternatively spliced ligands for several erbB receptor tyrosine kinases, are thought to play important roles in cell-cell communication at the nmj, affecting synapse-specific gene expression in muscle fibers and the survival of terminal SCs during development. Here we show that application of a soluble neuregulin isoform, glial growth factor II (GGF2), to developing rat muscles alters terminal SCs, nerve terminals, and muscle fibers. SCs extend processes and migrate from the synapse. Nerve terminals retract from acetylcholine receptor-rich synaptic sites, and their axons grow, in association with SCs, to the ends of the muscle. These axons make effective synapses only after withdrawal of GGF2. These synaptic alterations appear to be induced by the actions of neuregulin on SCs, because SC transplants growing into contact with synaptic sites also caused withdrawal of nerve terminal branches. These results show that SCs can alter synaptic structure at the nmj and implicate these cells in the maintenance of this synapse.

Age Factors↗
PubMed1998

Effects of dantrolene sodium on fibrillation potentials in denervated rat muscles.

To examine whether a decrease in cytosolic Ca2+ affects fibrillation potentials, we studied effects of dantolene on these potentials in denervated rat muscle. Administered intraperitoneally, dantrolene sodium (12-22 mg/kg) abolished fibrillation potentials and subthreshold oscillating potentials over 2.5-6 h without affecting excitability of the muscle to electrical stimulation. Fibrillation potentials reappeared 36-96 h after administration of dantrolene. We suggest that cytosolic Ca2+ has a specific role in generating fibrillations.

Animals↗
PubMed1995

Persistent polyneuronal innervation in partially denervated rat muscle after reinnervation and recovery from prolonged nerve conduction block.

The contribution of activity to the long-term stability of synaptic connections is a subject of ongoing debate. In the present study we examined the effects of recovery from chronic disuse on the pattern of reinnervation of partially denervated adult rat skeletal muscles, using tension measurements, intracellular recordings, and observations of vital staining with activity-dependent styryl dyes. Fourth deep lumbrical muscles were partially denervated by crushing the lateral plantar nerve (LPN) bilaterally. Denervated muscle fibers became innervated by sprouts from the sural nerve (SN); 17-23 d after LPN crush, conduction in the right sciatic nerve was blocked by connecting an osmotic minipump containing tetrodotoxin to a cuff placed around the nerve. Distal muscles remained continuously paralysed for 10-19 d. After 2 weeks of nerve block the tension produced by stimulating the regenerated LPN axons had reached about 70% of the total. Regenerating axons in contralateral muscles reinnervated only about 55% of the muscle fibers. The level of dual innervation by both regenerating and intact axons reached about 50% of the total muscle fibers after 2 weeks of paralysis, but only about 20% in contralateral controls. We then measured the rate and amount of decline in motor unit tension and polyneuronal innervation in reinnervated muscles during an eight week period of recovery from nerve block. Some LPN and SN connections regressed within 2-4 weeks, but about 35% of the muscle fibers still retained convergent inputs from LPN and SN motor axons 8 weeks after activity had resumed. This was about twice the level observed in contralateral reinnervated muscles. Vital staining with the styryl dyes FM1-43 and RH414 confirmed that many of the reinnervated motor end-plates were convergently supplied by both SN and LPN axons. Intracellular recordings showed that most of the dually innervated fibers in paralyzed muscles were supplied by suprathreshold inputs from both LPN and SN axons. The increased excitability of these muscle fibers was partly explained by their two-fold increased input resistance. Input resistance recovered to control levels within 4 weeks of resumption of activity, but dually innervated fibers in previously blocked muscles still gave mostly suprathreshold responses to stimulation of both the LPN and the SN. We conclude that chronic nerve conduction block generates or sustains a local environment which allows some convergent synaptic inputs on reinnervated muscle fibers to become consolidated and strengthened, independent of subsequent neuromuscular activity.

Animals↗
PubMed2001

A novel role of neuregulin in skeletal muscle. Neuregulin stimulates glucose uptake, glucose transporter translocation, and transporter expression in muscle cells.

Neuregulins regulate the expression of acetylcholine receptor genes and induce development of the neuromuscular junction in muscle. In studying whether neuregulins regulate glucose uptake in muscle, we analyzed the effect of a recombinant neuregulin, (r)heregulin-beta1-(177-244) (HRG), on L6E9 muscle cells, which express the neuregulin receptors ErbB2 and ErbB3. L6E9 responded acutely to HRG by a time- and concentration-dependent stimulation of 2-deoxyglucose uptake. HRG-induced stimulation of glucose transport was additive to the effect of insulin. The acute stimulation of the glucose transport induced by HRG was a consequence of the translocation of GLUT4, GLUT1, and GLUT3 glucose carriers to the cell surface. The effect of HRG on glucose transport was dependent on phosphatidylinositol 3-kinase activity. HRG also stimulated glucose transport in the incubated soleus muscle and was additive to the effect of insulin. Chronic exposure of L6E9 cells to HRG potentiated myogenic differentiation, and under these conditions, glucose transport was also stimulated. The activation of glucose transport after chronic HRG exposure was due to enhanced cell content of GLUT1 and GLUT3 and to increased abundance of these carriers at the plasma membrane. However, under these conditions, GLUT4 expression was markedly down-regulated. Muscle denervation is associated with GLUT1 induction and GLUT4 repression. In this connection, muscle denervation caused a marked increase in the content of ErbB2 and ErbB3 receptors, which occurred in the absence of alterations in neuregulin mRNA levels. This fact suggests that neuregulins regulate glucose transporter expression in denervated muscle. We conclude that neuregulins regulate glucose uptake in L6E9 muscle cells by mechanisms involving the recruitment of glucose transporters to the cell surface and modulation of their expression. Neuregulins may also participate in the adaptations in glucose transport that take place in the muscle fiber after denervation.

Animals↗
PubMed1997

Motor nerve transplantation.

The motor nerve transplantation (MNT) technique is used to transfer an intact nerve into a denervated muscle by harvesting a neurovascular pedicle of muscle containing motor endplates from the motor endplate zone of a donor muscle and implanting it into a denervated muscle. Thirty-six adult New Zealand White rabbits underwent reinnervation of the left long peroneal (LP) muscle (fast twitch) with a motor nerve graft from the soleus muscle (slow twitch). The right LP muscle served as a control. Reinnervation was assessed using microstimulatory single-fiber electromyography (SFEMG), alterations in muscle fiber typing and grouping, and isometric response curves. Neurofilament antibody was used for axon staining. The neurofilament studies provided direct evidence of nerve growth from the motor nerve graft into the adjacent denervated muscle. Median motor endplate jitter was 13 microsec preoperatively, and 26 microsec at 2 months, 29.5 microsec at 4 months, and 14 microsec at 6 months postoperatively (p < 0.001). Isometric tetanic tension studies showed a progressive functional recovery in the reinnervated muscle over 6 months. There was no histological evidence of aberrant reinnervation from any source outside the nerve pedicle. Isometric twitch responses and adenosine triphosphatase studies confirmed the conversion of the reinnervated LP muscle to a slow-type muscle. Acetylcholinesterase studies confirmed the presence of functioning motor endplates beneath the insertion of the motor nerve graft. It is concluded that the MNT technique achieves motor reinnervation by growth of new nerve fibers across the pedicle graft into the recipient muscle.

Acetylcholinesterase↗
PubMed1995

Barium resistant potassium current in mammalian skeletal muscle following denervation.

Inward rectifier potassium channels are thought to be related to resting membrane potential and in innervated skeletal muscle they are specially sensitive to the blocking action of Ba2+ ions. After denervation other channels are known to become resistant to their blockers. We study the effect of Ba2+ upon the inward rectifier potassium channels after denervation. Rat extensor digitorum longus fibers were equilibrated for 150 minutes in 150 mM KCl; when they were returned to 5 mM KCl the resting potential went back to its original level with a half time of 35 minutes. This repolarization was blocked by 5 mM BaCl2 in innervated muscles and in muscles denervated for 7 days, but failed to do so after 14 days of denervation. Voltage-clamp experiments performed in lumbricalis denervated muscle showed a lack of effect of Ba2+ upon potassium current after 18 days of denervation. This results suggest that the inward rectifier potassium channels become resistant to Ba2+ ions after denervation, indicating a neural influence.

Animals↗
PubMed1985

Receptor-mediated uptake of horseradish peroxidase in innervated and denervated skeletal muscle.

The in vitro uptake of [3H]inulin and horseradish peroxidase (HRP) has been studied in innervated and 6 days denervated extensor digitorum longus muscle of the mouse. Both markers were taken up at a higher rate in denervated muscle. The increase in uptake after denervation was, however, larger for HRP than for [3H]inulin. After 2 h incubation at 37 degrees C, pH 7.3, in the presence of equimolar concentrations of HRP and [3H]inulin (approx. 2.1 microM), the uptake of HRP was approx. 8 times as great as the uptake of [3H]inulin in the same innervated muscles. In denervated muscle the HRP uptake was approx. 19 times as great as the [3H]inulin uptake in the same muscles. Various possible explanations of these differences in uptake have been considered and tested experimentally. [3H]Inulin uptake in skeletal muscle has previously been shown to obey bulk kinetics. The present investigation shows the HRP uptake to obey saturation kinetics. The HRP uptake shows dependency on divalent cations and is reduced if incubation is carried out at pH 6.4. The uptake of HRP, when used at a low, non-saturating concentration (10 micrograms/ml approx. 0.25 microM), is inhibited greater than or equal to 60% by yeast mannan (0.1 mg/ml), ribonuclease B (0.1 mg/ml, approx. 7.4 microM), mannose (30 mM), monodansylcadaverine (1 mM), chloroquine (100 microM), trifluoperazine (25 microM) or maleic acid (2 mM). It is concluded that HRP is taken up in innervated and denervated skeletal muscle by a process of receptor-mediated endocytosis and that this uptake is under neurotrophic control.

Animals↗
PubMed1990

Phosphorylase kinase isozymes and phosphorylase in denervated skeletal muscles.

The effects of motor denervation on levels of phosphorylase kinase isozymes and phosphorylase were investigated in rat epitrochlearis, hemidiaphragm, and soleus muscles. Amounts of the proteins were measured after quantitative immunoprecipitation and found to be decreased by as much as 70% 2 weeks after denervation. Unexpectedly, denervation had little, if any, effect on the relative proportions of the two phosphorylase kinase isozymes. Phosphorylase and phosphorylase kinase were decreased by essentially the same extent after denervation, and the effects of denervation were comparable in all three muscles. The decreases in these enzymes explain, at least in part, the marked alterations in glycogen metabolism that occur after motor denervation.

Animals↗
PubMed2006

Effects of a nerve-muscle pedicle on the denervated rat thyroarytenoid muscle.

OBJECTIVES: To evaluate the effects of the nerve-muscle pedicle (NMP) method on the rat thyroarytenoid (TA) muscle after transection of the recurrent laryngeal nerve (RLN). STUDY DESIGN: Quantitative histologic assessment of the TA muscle after NMP implantation. METHODS: Thirty-six Wistar rats were divided into two groups: animals subjected to transection of the left RLN alone (DNV group) and animals subjected to transection of the left RLN followed by immediate transplantation of a NMP flap containing the sternohyoid (SH) muscle and ansa cervicalis nerve branch (NMP group). Animals were killed 2, 4, and 10 weeks after the treatments. The TA muscle stained with hematoxylin-eosin was evaluated quantitatively. The pre- and postsynaptic structures of the neuromuscular junction (NMJ) in the TA muscle were analyzed histochemically. The myosin heavy chain (MyHC) isoforms were evaluated using immunohistochemistry and reverse-transcriptase polymerase chain reaction (RT-PCR). RESULTS: In the NMP group, the TA muscle fiber recovered to almost normal at 10 weeks, and the ratio of the number of synaptophysin-positive nerve terminals to that of alpha-bungarotoxin-positive acetylcholine receptors recovered to 79.8 +/- 11.8% (P < .05, compared with the control). Immunohistochemistry and the RT-PCR method after laser capture microdissection revealed the expression of MyHC isoforms type 2B and type 2A; the latter was detected in the SH muscle but not in the normal or denervated TA muscle. CONCLUSION: The NMP method was effective for recovering from the atrophic changes of the TA muscle after transection of the RLN. This was attributed to successful reinnervation by reconstruction of the NMJ, which might change MyHC isoform expression.

Animals↗
PubMed1988

Activity-dependent and -independent synaptic interactions during reinnervation of partially denervated rat muscle.

1. Reinnervation of adult rat fourth deep lumbrical muscles was studied, following extensive partial denervation of the hindfoot by crushing the lateral plantar nerve (LPN). Most muscles remained innervated by between one and five motor axons supplied by the sural nerve (SN). Intact SN motor units expanded as a result of collateral sprouting. Virtually complete collateral reinnervation occurred in muscles containing more than two SN motor units. Twitch tension measurements from isolated muscles suggested that most of the sprouts evoked suprathreshold responses from the muscle fibres they innervated. Intracellular recordings suggested that only a small percentage of sprouts evoked subthreshold end-plate potentials. 2. Lateral plantar nerve motor axons returned to the lumbrical muscles within 15-18 days and subsequently reinnervated muscle fibres already innervated by SN motor nerve terminals. Nerve conduction in the regenerating axons was then blocked for 7-15 days by chronic superfusion with tetrodotoxin. In both LPN-blocked and control (LPN crushed but not blocked) animals, isometric tetanic tension overlap and intracellular recordings showed that some lumbrical muscle fibres became innervated exclusively by regenerating LPN motor axons. 3. With time, the tension evoked by stimulating regenerating motor axons increased and there was a parallel fall in the tension produced by stimulating the intact motor units. The extent of reinnervation by LPN motor axons was inversely related to the number of remaining SN motor units. In comparable muscles, regenerated LPN-blocked motor units produced only about half the tension of the controls. Selective glycogen depletion of motor units and intracellular recordings of end-plate potentials indicated that this was due to reduced numbers of muscle fibres innervated by the blocked motor axons. 4. Nerve conduction block prolonged the time course of the isometric twitch in regenerated motor units, and increased the duration of the end-plate potential in muscle fibres innervated only by the regenerating axons. LPN block did not affect the recovery of the latency of the end-plate potential. The regenerated motor units were more resistant to fatigue caused by continuous 4 Hz nerve stimulation than intact SN units, but the resistance to fatigue of LPN-blocked motor units was no different from the controls.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1977

Physiological properties of dissociated muscle fibres obtained from innervated and denervated adult rat muscle.

1. Adult rat flexor digitorum brevis muscles were dissociated by treatment with collagenase and trituration. Several hundred isolated fibres were obtained from each muscle. 2. Most isolated fibres appeared to be intact as judged by some morphological and physiological criteria, although resting membrane potentials were about -60 mV, which is somewhat lower than normal. 3. A small percentage of the muscle fibres were branched. 4. Acetylcholine sensitivity was measured iontophoretically. The sensitivity fell abruptly outside the margin of the end-plate. Extrajunctional sensitivty was detected on all fibres, and declined smoothly away from the end-plate to an undetectable level over a distance of about 200 micron. On a few fibres, ACh sensitivity was mapped circumferentially from the end-plate. It appeared to decline with distance in a manner similar to the longitudinal sensitivity gradient. 5. Fibres dissociated from muscles denervated a week earlier were sensitive to ACh everywhere on their surfaces.

Acetylcholine↗
PubMed1998

Distinct location and prevalence of alpha-, beta-catenins and gamma-catenin/plakoglobin in developing and denervated skeletal muscle.

We studied the distribution of alpha-catenin, beta-catenin and gamma-catenin/plakoglobin in developing, adult and denervated mouse skeletal muscle. During primary myogenesis, all three catenins present a subsarcolemmal distribution within primary myotubes. During secondary myogenesis they accumulate at myotube-myotube contacts. In contrast to the other catenins, gamma-catenin is strongly expressed in the sarcoplasm. In adult muscle, all three catenins are localized on the presynaptic elements of the neuromuscular junction. In denervated muscles, alpha- and beta-catenins are upregulated like N- and M-cadherin, while the levels of gamma-catenin/plakoglobin remain unchanged. The developmental changes in localization and regulation of alpha- and beta-catenins in muscle compared to gamma-catenin/plakoglobin are suggestive of a privileged association of alpha- and beta-catenins with N- and M-cadherins, while gamma-catenin/plakoglobin appears to be expressed quite independently and must assume a different role during myogenesis.

Animals↗
PubMedDate not supplied

Effect of in vivo electrical stimulation on the carbohydrate metabolism of control and denervation atrophied muscle of dog, Canis domesticus.

The standardized programme of electrical stimulation was applied to the control and denervation atrophied muscle of dog, Canis domesticus and the pattern of changes in the carbohydrate metabolism was analysed in the control (C), denervated control (DC), control stimulated (CS) and denervated stimulated (DS) gastrocnemius muscles. The programme of electrical stimulation of the control muscle has elevated glycogenolysis, glycolysis and increased the level of operation of TCA cycle with decreased mobilization of carbohydrates into hexose monophosphate pathway, indicating the setting in of trained condition. Sciatectomy, on the other hand, lowered the level of operation of glycogenolysis and decreased the utilization of carbohydrates through hexose-mono and di-phosphate pathways and TCA cycle. The programme of electrical stimulation applied to the denervated muscle has restored the utilization of carbohydrates through hexose mono and diphosphate pathways and oxidative metabolism indicating the applicability of this programme of electrical stimulation in the treatment of muscular atrophy.

Animals↗