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PubMed1981

Calcium transients in normal and denervated slow muscle fibres of the frog.

1. Intracellular changes in free Ca2+ concentration were recorded from slow muscle fibres in the pyriformis muscle of Rana temporaria, using the dye arsenazo III. Fibres were voltage clamped, and arsenazo signals were recorded in response to depolarizing pulses. 2. The size of the arsenazo response to depolarizing pulses of 100 msec duration was a sigmoid function of membrane potential over the range -45 to 0 mV, and remained constant with further depolarizations up to +100 mV. 3. The peak size of the arsenazo signal to supramaximal depolarizations increased with increasing pulse length. The initial rising phase during a pulse was much slower than in twitch fibres, and this phase was followed by an even slower rise. Following short pulses the decay of the response was exponential, with a time constant of about 1.4 sec, while after long pulses the decline became much slower. 4. Decreasing free Ca2+ concentration in the bathing medium to very low levels, using EGTA , did not affect the responses to short (100 msec) depolarizations. 5. Slow fibres bathed in Ringer's solution containing 12 mM-Ca2+ showed a well maintained arsenazo response to supramaximal depolarizations lasting over 1 min. Reduction of external Ca2+ to 1.8 and (nominally) 0 mM caused the response to become progressively more transient. 6. After denervation, slow fibres developed action potentials, but non of the parameters of the arsenazo response was significantly changed. During the early phase of reinnervation by a mixed nerve, when fast conduction axons begin to innervate slow fibres, the ability to give a maintained response during long depolarizations was reduced. 7. It is concluded that intracellular Ca2+ transients in slow muscle fibres are probably generated by a similar mechanism as in twitch fibres and entry of external Ca2+ is not an appreciable factor. The slow time course of the transients may be important in determining the time courses of tension development and relaxation.

Animals↗
PubMed1993

Proliferation of mast cells in the smooth muscle of denervated rat jejunum.

Mast cell hyperplasia and changes in phenotypic characteristics subsequent to myenteric and extrinsic denervation of a segment of rat jejunum were studied. The myenteric plexus and extrinsic nerves were ablated by serosal application of the cationic surfactant benzyldimethyltetradecylammonium chloride. There was a four-fold increase in the number of mast cells in the smooth muscle layers 15 days after denervation. This increase was sustained for at least 90 days after treatment. No increase in mast cell number was observed in the villus-crypt axis of the jejunum. Berberine sulfate fluorescent detection of heparin-containing mast cells demonstrated that a change in mast cell phenotype occurred between 20 and 90 days after the denervation procedure. The fact that myeloperoxidase activity was the same in denervated and control tissue within 5 days of denervation demonstrates the lack of a chronic inflammatory reaction. Our results suggest that mast cells might play a role in the gut wall re-modeling processes.

Animals↗
PubMed1990

Denervation-induced alterations of acetylcholinesterase in denervated and nondenervated muscle.

The influence of denervation on acetylcholinesterase (AchE) molecular forms in rat skeletal muscle for durations up to 30 days is examined in denervated anterior tibialis, the innervated contralateral muscle, and diaphragm. Denervated rats at a common age of 8.5 weeks are compared with age-matched, nondenervated animals. The results indicate that time-dependent losses of AchE in denervated muscle occur more rapidly than loss of muscle mass and are not uniform among the different molecular forms. Loss of the 4 S and 16 S forms is rapid and essentially complete within 3.5 days of denervation, while during this same period the 10.5 S form undergoes a transient twofold increase and its presence in denervated muscle is never abolished. Within 30 days of denervation, all forms of AchE including the 16 S species reappear. A salient finding of these studies is that the effects of denervation are evident also in anatomically remote, innervated muscle such as anterior tibialis of the contralateral limb and in diaphragm. These alterations appear as pronounced reductions in 4 S AchE and increases in 10.5 S AchE; the asymmetric collagen-tailed 16 S form is unaltered. Treatment of primary cultures of embryonic chick pectoral muscle with sera from denervated but not nondenervated rat causes reductions in AchE. These results indicate that the appearance and retention of AchE, in particular the 16 S form, occur in the absence of functional innervation. The effects of denervation on AchE metabolism in remote, innervated tissue are consistent with the action of a diffusible factor released from severed nerve or muscle, or both.

Acetylcholinesterase↗
PubMed1998

Motoneurons innervating partially denervated rat hindlimb muscles remain susceptible to axotomy-induced cell death.

Tibialis anterior and extensor digitorum longus muscles were partially denervated by cutting the L4 spinal nerve in three-day-old rats. The ultrastructure of the intact axons to these muscles in the L5 spinal nerve was examined in nine-day-old rats. In the control L5 spinal nerve, myelinated and unmyelinated axons were intermingled throughout the cross-section of the nerve, while on the operated side the nerve contained areas with predominantly small unmyelinated immature axons. The number of motoneurons innervating the partially denervated muscles was established by retrograde labelling with Diamidino Yellow. In nine- and 21-day-old rats, the number of labelled motoneurons on the partially denervated side, expressed as a percentage of the control side, was 26.1 +/- 5.5% and 20.7 +/- 3.0%, respectively. The response of these uninjured motoneurons to axotomy was tested. The axons of the motoneurons to the partially denervated muscles were crushed at nine days and the numbers of labelled motoneurons in the spinal cord of these rats counted at 21 days of age. Only 4.9 +/- 2.0% labelled motoneurons were seen on the operated side, as opposed to 20.7 +/- 3.0% present in animals without sciatic nerve injury. In normal animals, nerve injury at nine days does not cause motoneuron death. Thus, motoneurons to partially denervated muscles (i) have axons with several immature features and (ii) remain susceptible to axotomy-induced death for much longer than normal.

Animals↗
PubMed2006

Induction of neuregulin signaling in mouse schwann cells in vivo mimics responses to denervation.

Neuregulins play crucial roles in early development of Schwann cells (SCs), but their roles in the activities of SCs during denervation and reinnervation of muscle are less clear. In the present study, the Tet-On system has been used in transgenic mice to enable inducible expression of a mutant, constitutively active neuregulin receptor (ErbB2) in SCs. This induction simulates neuregulin signaling to these cells. Reporter transgenes were used to show a tightly regulated, SC-selective expression in muscle. Induction leads to a number of changes in SCs at neuromuscular junctions that mimic the response to muscle denervation/reinnervation. These include process extension, soma migration, and proliferation. SCs also come to express nestin, a protein characteristic of their reaction to muscle denervation. This activation of SCs results in the sprouting of nerve terminals, and these sprouts follow the extensions of the SCs. However, these sprouts and their associated SCs disappear after the removal of the inducer. Last, induction of the active receptor is sufficient to rescue SCs in neonatal muscle from denervation-induced apoptosis. These findings show that the responses of SCs in muscle to denervation can be explained by induction of an autocrine/paracrine neuregulin signaling cascade suggested by previous molecular studies.

Animals↗
PubMed2004

mRNA expression of fibroblast growth factors and hepatocyte growth factor in rat plantaris muscle following denervation and compensatory overload.

We addressed the question of whether hypertrophy induced by compensatory overload differs according to innervation status, and how fibroblast growth factors (FGF) and hepatocyte growth factor (HGF) mRNAs are expressed in the rat plantaris muscle during overload (OL) and/or denervation. Male Wistar rats were divided into four groups (Normal-Cont, Normal-OL, Denervated-Cont, and Denervated-OL). according to the plantaris denervation and/or overload. Three weeks later, plantaris weight in Denervated-Cont and Denervated-OL was significantly lower than in the Normal-Cont. The muscle weights in the Normal-OL were higher than in the Normal-Cont. The muscle weights in the Denervated-OL were higher than in the Denervated-Cont. Three days after the treatment, FGF-2, FGF-6, FGF-7 and HGF mRNAs in the Normal-OL were significantly higher than those in the Normal-Cont. FGF-2, FGF-6, FGF-7 and HGF mRNAs in the Denervated-OL were also significantly higher after 3 days than those in the Denervated-Cont. After 7 days, FGF-2, FGF-5, FGF-6, FGF-7 and HGF mRNAs were significantly higher in the Normal-OL than those in the Normal-Cont. At 21 days, FGF-1, FGF-6 and HGF mRNA levels were significantly increased. In the Denervated-OL, FGF-2, FGF-7 and HGF mRNAs at 7 days, and FGF-2 mRNA at 21 days were significantly higher than those in the Denervated-Cont. FGF-2 and FGF-6 mRNA levels decreased significantly following denervation; however, FGF-1, FGF-5, FGF-7 and HGF mRNA levels increased and maintained this increase for the 21-days treatment period. Muscle hypertrophy was thus induced by compensatory overload irrespective of innervation status, possibly in association with certain FGFs and HGF. The differential mRNA expression patterns of FGFs and HGF observed following compensatory overload and/or denervation suggest distinct roles for individual FGFs and HGF in muscle hypertrophy and/or atrophy.

Animals↗
PubMed1986

[Formation and repression of neuromuscular endplates in neurogenic and muscular lesions].

The motor endplates and intramuscular nerves of rat and rabbit masticatory muscle were preferentially demonstrated using an acetylcholinesterase reaction followed by silver staining. The regeneration of the neuromuscular unit was followed serially at the site of an earlier biopsy. Using observations concerning the sproutings of neuronal fibers in normal and operated animals, a hypothetical generalization of the phenomenon is proposed and evaluated in the light of the literature. Intramuscular sprouts of motor axons are detectable both in normal and partially denervated muscle. These can be regarded as the precondition of the muscle's ability to adapt to an altered stress situation. Single muscle fibers and synapses are multiply innervated by different alpha-motor neurons with subsequent fiber transformation via an intermediary stage, the 2C fiber. Following neurogenic damage a trigger is released from the denervated muscle tissue and damaged nerve parenchyma which stimulates the reinnervation of surviving motor endplates by axon sprouting and new synapse formation. Collateral, nerve stem, and terminal sprouts may occur singly or multiply. As long as denervated muscle fibers are present triggers for synapse formation and axon sprouting, as opposed to repression, continue to be released, resulting in a period of poly-innervation. The degree of sprouting correlates with the extent of nerve damage. The period of innervation is not affected by muscle damage alone. Complete or partial fiber regeneration products will survive only if they reach an innervation zone where neurotransmission is insured by the presence of sprouts and synapses. The period of poly-innervation is followed by a period of synapse repression whereby the redundant sprouts and synapses are reabsorbed. The length of the axon determines the sprouts resistance to reabsorption. The connections which survive are those which are the shortest between the endplate and the stem nerve. Intramuscular sprouting can be experimentally stimulated by, among other factors, partial denervation, oxygen deficiency, toxic inactivation, an altered stress situation and exogenous gangliosides.

Animals↗
PubMedDate not supplied

[Mechanism of the inhibitory effect of acetylcholine and its analogs on sarcolemma Na, K-ATPase].

Effect of acetylcholine on Na, K-ATPase from cardiac and skeletal rabbit muscles is studied. The inhibition of the enzyme by acetylcholine was shown to depend on the Na+/K+ ratio and Mg2+ concentration in the incubation medium. The sensitivity of Na, K-ATPase to acetylcholine and its analogues decreased as follows: acetylcholine, propionylcholine butyrylcholine, arecoline, carbacholine, choline. Muscle denervation resulted in 20-fold increase of the enzyme sensitivity to acetylcholine. Preparations of Na, K-ATPase from different muscles have the increasing sensitivity to acetylcholine in the following order: white, mixed, cardiac, denervated muscles.

Acetylcholine↗
PubMed1985

Three-dimensional computer reconstruction of the neuromuscular junction distribution in the human posterior cricoarytenoid muscle.

Recent studies have indicated that in a denervated muscle highly specific interactions occur between regenerating axons and the basal lamina of the myofiber precisely at the original synaptic sites. Since these findings suggest that synapse regeneration is facilitated at the original synaptic sites, a knowledge of the distribution of neuromuscular junctions in the human posterior cricoarytenoid (PCA) muscle may guide reinnervation procedures in this muscle. We, therefore, have used histochemical and computer graphics techniques to reconstruct the three-dimensional distribution of neuromuscular junctions in the human PCA taken fresh at autopsy. The results indicated a more localized pattern of neuromuscular junctions as compared to the human thyroarytenoid muscle. The results will be discussed with respect to their implications for procedures for reinnervation of the posterior cricoarytenoid muscle.

Computers↗
PubMed2000

Direct muscle neurotization in rat soleus muscle.

An experimental study was conducted using rat soleus muscles to characterize reinnervation of the denervated muscles by direct muscle neurotization. Also studied was whether there is any difference in the regeneration process between original (tibial) and foreign (peroneal) nerve neurotization. For functional evaluation, an electrophysiologic study was carried out by analyzing pattern, latency, amplitude, and duration of compound motor action potential. In a histochemical study, both hematoxylin-eosin stain and nicotineamide adenin dehydrogenase stain were used to identify the morphology and the change in the type of muscle fiber. Combined silver-acetylcholinesterase stain was utilized to identify reinnervated motor endplates and axonal sprouting. Evidence of regeneration of the denervated muscle by direct muscle neurotization could be confirmed. Regenerating muscles showed type grouping of muscle fibers. The newly-formed ectopic motor endplate was connected with axonal sprouting. The giant motor endplate composed of mature axon sprouting and several new ectopic motor endplates appeared in the neurotization group. There was no specific difference in the regeneration process between original and foreign nerve neurotization.

Animals↗
PubMed2006

Myonuclei and satellite cells in denervated rat muscles: an electron microscopy study.

The study and description of a separated cell type have been dependent on the evolution of the electron microscope. There have been few experiments designed to induce changes in myonucleus and satellite-cell populations in vivo without physically injuring muscle. In this regard, the most practical method to experimentally alter myonucleus and satellite-cell populations is denervation. The sciatic nerve was sectioned in order to observe myonuleus and satellite-cell behavior. After 7, 16, and 38 weeks postdenervation, the soleus and extensor digitorum longus muscles were observed under electron microscopy. In each studied period, the pattern, distribution, and possible cellular alterations were observed in the studied muscles. Myonuclei exhibited alterations such as shrinkage, nuclear membrane separation, condensed chromatin, ghost nuclei as well as normal ones, and disorganized myofibrils. The maximum and minimum myonucleus diameters were measured in each studied period. In both muscles, the maximum diameters decreased. On the other hand, the minimum myonucleus diameters did not show any differences. Regarding satellite cells, activation characteristics were observed. In both muscles, the satellite cells were located distant of capillary after denervation. Characterization of the different types of nuclei abnormalities, especially in chromatin condensation, should provide useful information for future morphological studies.

Animals↗
PubMed1993

Selective reinnervation of the rat serratus anterior muscle following denervation and partial target removal.

The rat serratus anterior (SA) muscle is reinnervated by cervical roots C6 and C7 with a topographic bias following transection or freezing of the long thoracic nerve. The study reported here was undertaken to determine the specificity of regenerating motoneurons when the size of the target SA muscle was reduced. After crush and removal of the caudal half of the muscle, a rostrocaudal map was reestablished that was no different from control or crush alone. Rostral (C6) axons dominated the innervation of muscles deprived of their caudal sectors. Input from caudal (C7) axons was significantly reduced. These results may be explained by preferential pathways or a competitive advantage held by rostral axons reinnervating rostral sectors to the detriment of caudal axons.

Animals↗
PubMed2000

Direct muscle neurotization in rat soleus muscle.

The authors carried out an experimental study using rat soleus muscles to evaluate reinnervation of the denervated muscles by direct muscle neurotization. They also attempted to determine whether there is any difference in the regeneration process between original (tibial) and foreign (peroneal) nerve neurotization. For functional evaluation, they did an electrophysiologic study by analyzing pattern, latency, amplitude, and duration of compound motor action potential. For histochemical studies, both hematoxyline-eosin stain and nicotineamide adenin dehydrogenase stainings were used to identify the morphology and the change of the type of muscle fiber. Combined silver-acetylcholinesterase stain was performed to identify reinnervated motor endplate and axonal sprouting. They confirmed evidence of regeneration of the denervated muscle by direct muscle neurotization. Regenerating muscles showed type groupings of muscle fibers. The newly-formed ectopic motor endplate was connected with axonal sprouting. The giant motor endplate composed of mature axon sprouting and several new ectopic motor endplates, appeared in the neurotization group. There was no significant difference in the regeneration process between original and foreign nerve neurotization.

Animals↗
PubMed1998

Neurite outgrowth-promoting factors in extracts of denervated chick skeletal muscle.

1. An extract of denervated skeletal muscle contained activity for promotion of neurite outgrowth from telencephalic neurons, as well as that from neurons in the spinal cord. A factor responsible for the activity was characterized in cultures of dissociated neurons. 2. The factor acted on neurons only when they were attached to the surface of culture dishes. Since treatments with proteases and lectins reduced the outgrowth-promoting activity, the factor was thought to be a glycoprotein. 3. Among the monoclonal antibodies raised against the partially purified extract, five antibodies were found to inhibit the activity for spinal and telencephalic neurons. The most potent antibody, 4D2a, recognized mainly a 63-kD protein and other minor proteins in the extract. Although the 63-kD protein was confirmed to be chick serum albumin by analysis of amino acid sequence, the purified albumin exhibited no activity. 4. From these observations, the factor was found to be a glycoprotein recognized by the neutralizing antibody as one of the minor components of the extract. This factor exhibits its activity in a substrate-bound form but not in a diffusible one.

Amino Acid Sequence↗
PubMed1989

Terminal cisternae of denervated rabbit skeletal muscle: alterations of functional properties of Ca2+ release channels.

Terminal cisternae (TC) of skeletal muscle represent the specialized compartment from which Ca2+ is released into the myoplasm after a propagated action potential. In this study we have investigated the morphology, protein composition, and Ca2+ release properties of TC isolated from rabbit gastrocnemius muscle 2 wk after nerve sectioning. Thin-section electron microscopy showed that TC vesicles from denervated muscle were enriched in calsequestrin (CS) and contained a larger fraction of the junctional sarcoplasmic reticulum (SR), as judged by membrane profiles with morphologically intact feet structures. Accordingly, the yield of junctional SR from denervated muscle was twice that of control muscle, and the protein pattern of TC vesicles exhibited an increase in junctional protein components, e.g., CS and the 350-kDa protein. The larger content of the 350-kDa protein, or ryanodine receptor (F.A. Lai, H. Erickson, E. Rousseau, Q.-Y. Liu, and G. Meissner, Nature Lond. 331: 315-319, 1988; T. Imagawa, J. S. Smith, R. Coronado, and K. P. Campbell. J. Biol. Chem. 262: 10636-10643, 1987; L. Hymel, M. Inui, S. Fleischer, and H. Schindler, Proc. Natl. Acad. Sci. USA 85:441-445, 1988) was paralleled by an increased binding site density (Bmax) for ryanodine binding in denervated muscle TC. The effects of ruthenium red, a Ca2+ release blocker, on Ca2+ loading rate and Ca2+-ATPase activity suggested that TC from denervated muscle were less permeable to Ca2+. After active Ca2+ loading, both doxorubicin and caffeine induced Ca2+ release from isolated TC, yet Ca2+ release rates were reduced in denervated muscle TC.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

Electrophysiological study of the denervated orbicularis oculi muscle in dogs.

This study investigated the electrophysiology of the denervated orbicularis oculi muscle and its clinical application. Orbicularis oculi muscle denervation was achieved by complete transection of the seventh nerve in ten dogs. The parameters studied were the electrical requirements needed to cause a minimal perceptible contraction (twitch) and a complete eyelid closure (blink). Twitch and blink curves were generated. The findings are summarized as follows: (1) Minimum intensities for direct twitch of denervated orbicularis oculi muscle were significantly lower than intensities of normal orbicularis oculi muscle twitch (p less than 0.01) when long stimulus duration (5 to 400 ms) was used. (2) Minimum intensities for direct blink of denervated orbicularis oculi muscle were not significantly different from stimulus intensities for blink of normal orbicularis oculi muscle if long stimulus duration (5 to 400 ms) was used. Twitch and blink curves could be used to clinically follow the orbicularis oculi muscle movement return after operations performed in patients affected by lagophthalmos.

Animals↗
PubMed1989

Sensitivity of rodent skeletal muscles to dicholines: dependence on innervation and age.

Depolarizations provoked by acetylcholine (ACh) and three dicholines, succinylcholine (SCh), glutarylcholine (GCh) and azelainylcholine (AzCh) were measured in normal and 3-7 days denervated muscles of adult, and in normal muscles of 0-27 days old mice and rats. Soleus and flexor digitorum superficialis muscles were mainly used. To prevent movement during measurement of the membrane potential by microelectrodes, the muscles were bathed in solutions containing 30 mM K+. At the adult endplate region of muscles of the mouse, the -log concentrations required for 7 mV depolarization were 6.5 for AzCh and approximately 5.9 for SCh, GCh and ACh. In extrajunctional areas of denervated muscles the values were 7.1, 6.4, 5.9 and 5.6 for AzCh, ACh, GCh and SCh, respectively. In non-denervated soleus muscles of 1-3 days-old mice, the average difference in sensitivity (estimated as mentioned above) to AzCh and SCh was approximately 2.0 log units, not significantly different from that found in denervated adult muscles. Between days 3 and 24 this difference decreased to about 0.8 at the endplate region but it remained greater in the periphery of soleus muscles. The AzCh-SCh sensitivity differences were smaller in muscles from juvenile rats than in juvenile mice. Sensitivity to ACh and AzCh, but not that to SCh, was by 0.6-0.8 log units greater in the presence than in the absence of anticholinesterases in endplates at any age of the animals. The blocking effectiveness of d-tubocurarine was low in newborn animals (similar to that observed in denervated adult muscles) and it increased with age.

Aging↗
PubMed2001

Motion-specific laryngeal reinnervation using muscle-nerve-muscle neurotization.

There is no current treatment method that can reliably restore physiologic movement to a paralyzed vocal fold. The purposes of this study were to test the hypotheses that 1) muscle-nerve-muscle (M-N-M) neurotization can be induced in feline laryngeal muscles and 2) M-N-M neurotization can restore movement to a paralyzed vocal fold. Muscle-nerve-muscle neurotization can be defined as the reinnervation of a denervated muscle via axons that are induced to sprout from nerves within an innervated muscle and that then traverse a nerve graft interposed between it and the target denervated muscle. A paralyzed laryngeal muscle could be reinnervated by axons from its contralateral paired muscle, thus achieving motion-specific reinnervation. Eighteen adult cats were divided into sham, hemilaryngeal-denervated, and M-N-M-reinnervated thyroarytenoid muscle groups. Five of the 6 reinnervated animals had histologic evidence of axons in the nerve graft, 4 of the 6 had evoked electromyographic evidence of crossed reinnervation, and 1 of the 6 had a return of appropriately phased adduction. This technique has great potential and should be further investigated.

Animals↗