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PubMed1980

Sprouting of active nerve terminals in partially inactive muscles of the rat.

1. Certain muscles in the hind foot of rats were partially paralysed by applying tetrodotoxin to part of their motor innervation. In these muscles motor nerve sprouting occurred from the terminals of the unblocked axons. The extent of sprouting was compared with that seen in totally paralysed and in partially denervated muscles. 2. Action potentials were blocked in the medial and lateral plantar nerves of adult rats for 5-13 days by continuous superfusion with a solution containing tetrodotoxin. The drug was delivered through a tube and nerve cuff from an osmotic pump placed intraperitoneally. Control experiments showed that nerve block was complete and that signs of nerve damage were absent in the animals included in the study. 3. Two muscles (the second lumbrical and flexor digitorum brevis), which received innervation only from the medial plantar nerve, were totally paralysed by the nerve block. Two different muscles (the fourth lumbrical and flexor digitorum quinti brevis) were only partially paralysed, since they received their innervation from the lateral plantar nerve and, in addition, from the sural nerve which was not blocked. One day before the final experiment, the lateral plantar nerve was cut, and its terminals degenerated. Thus in the partially paralysed muscles only the unblocked terminals from the sural nerve remained. These terminals were observed after staining with zinc iodide and osmium tetroxide. Similarly, terminals from the medial plantar nerve were examined in the totally blocked muscles from the same animal. 4. In other experiments, muscles were partially denervated by cutting the lateral plantar nerve in order to compare effects of nerve block and nerve section. 5. Sprouting occurred under all three conditions. Active terminals in the muscles partially paralysed for 5-7 days sprouted to the same extent as terminals in muscles totally blocked during the same period: about 35% of the terminals had sprouts, and their average length was about 13 micron. Sprouting was more pronounced in partially denervated muscles: about 65% of the terminals had sprouts and they averaged 24 micron in length. Collateral (preterminal) sprouts were seen only after partial denervation. 6. Physiological and histological observations suggested that sprouts in paralysed muscles, unlike those in partially denervated muscles, seldom if ever made new synapses on neighbouring muscle fibres, even after 12-13 days of nerve block. 7. The results show that inactive muscle fibres cause active nerve terminals on neighbouring fibres to sprout, perhaps by releasing a diffusible, sprout-promoting factor, which is part of the stimulus for motor nerve sprouting in partially denervated muscles.

Action Potentials↗
PubMed1993

Differential effects of neonatal denervation on intrafusal muscle fibers in the rat.

The response of developing muscle spindles to denervation was studied by sectioning the nerve to the medial gastrocnemius muscle of rats at birth. The denervated spindles were examined daily throughout the first postnatal week for changes in ultrastructure and expression of several isoforms of myosin heavy chain (MHC). Each of the three different types of intrafusal muscle fiber exhibited a different response to denervation. Within 5 days after the nerve section nuclear bag2 fibers degenerated completely; nuclear bag1 fibers persisted, but ceased to express the 'spindle-specific' slow-tonic MHC isoform and thereby could not be differentiated from extrafusal fibers; nuclear chain fibers did not form. The capsules of spindles disassembled, hence spindles or their remnants could no longer be identified 1 week after denervation. Neonatal deefferentation has little effect on these features of developing spindles, so removal of afferent innervation is presumably the factor that induces the loss of spindles in denervated muscles. Degeneration of the bag2 fiber, but not bag1 or extrafusal fibers, reflects a greater dependence of the bag2 fiber than the bag1 fiber on afferent innervation for maintenance of its structural integrity. This difference in response of the two types of immature bag fiber to denervation might reflect an origin of the bag2 fibers from a lineage of myogenic cells distinct from that giving rise to bag1 or extrafusal fibers, or a difference in the length of contact with afferents between the two types of bag fiber prior to nerve section.

Animals↗
PubMed1990

Long-term persistence of enlarged motor units in partially denervated hindlimb muscles of cats.

1. It was the aim of this study to determine the effect that regenerating motor axons would have on enlarged or sprouted motor units that had been established for a relatively long time. 2. The fast-twitch flexor digitorum longus (FDL) and slow-twitch soleus were partially denervated by unilateral section of the L7 ventral root in 12-wk-old kittens. After 200+ days single motor units were isolated, and their isometric contractile properties were determined. FDL units were also tested for their resistance to fatigue and categorized as fast-twitch-fatigable (FF), fast-twitch-fatigue-resistant (FR), and slow-twitch-fatigue-resistant (S). 3. It had been established previously that regenerating motor axons via L7 returned to the experimental muscles by approximately 100 days. Therefore from 100 to 200 days it was assumed that the sprouted units would be in competition with the regenerating axons. The extent of the original denervations was variable and was estimated from the contralateral side. In soleus most denervations ranged from 83 to 99%; in FDL, from 37 to 81%. 4. In both soleus and FDL there was no evidence that the motor units had sprouted to any less extent than found previously. Within some soleus muscles the largest motor units were developing substantially more force than was expected. However, determination of mean fiber cross-sectional area from muscles frozen, sectioned, and prepared for histochemical analysis showed that this was attributable to increased mean cross-sectional area of the type I fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1970

Calcium uptake and bioelectrical activity of denervated and myotonic muscle.

Calcium uptake on muscle microsomal fraction has been investigated in connection with bioelectrical activity in some muscle diseases. The findings showed a significant increase of calcium uptake in denervated muscle, which exhibited spontaneous bioelectrical activity (fibrillations). In myotonias, a low calcium uptake was peculiar to Steinert's disease but not to myotonia congenita. In other muscle diseases, such as progressive muscular dystrophy (Duchenne's type) or Charcot-Marie-Tooth's disease, the ability of muscle microsomal fraction to bind calcium was not changed. Starting with the key role of calcium in excitation-contraction coupling, the implications of calcium uptake disturbances in muscle electrogenesis are discussed.

Biopsy↗
PubMed1988

Long-term retention of regenerative capability after denervation of skeletal muscle, and dependency of late differentiation on innervation.

The present study examines the influence of denervation on the regenerative ability of skeletal muscle in rats. Muscle denervation was achieved by transecting and ligating the cut ends of the sciatic nerve. Four to 48 weeks after denervation, the extensor digitorum longus (EDL) muscle was autotransplanted to induce muscle regeneration. The transplanted EDL muscles were examined at 1-12 weeks. Normal (i.e., no prior denervation) EDL muscle autotransplants were also examined for comparison. Denervation resulted in progressive atrophy of muscle, marked by a reduction in the size of myofibers and an increase in endomysialperimysial connective tissue. In spite of these alterations, typical events of muscle regeneration were invariably observed after transplantation. Initial myofiber degeneration and subsequent regeneration of myotubes occurred in a manner similar to normal muscle transplants. However, only a partial maturation of myotubes was observed in denervated muscles. These results show that extended denervation does not abolish the capability for muscle regeneration. The precursor myosatellite cells, proposed to be responsible for muscle regeneration, retain their regenerative potential after denervation. It is concluded, however, that the presence of intact innervation is crucial for the terminal differentiation and maturation of regenerating muscle.

Animals↗
PubMed1988

Dependence of acetylcholine receptor channel conversion on muscle activity at denervated neonatal rat endplates.

During the development of the motor endplate, the apparent mean open time of the junctional acetylcholine (AChR) channels decreases during the first 3 weeks of postnatal life from about 4 to about 1 ms. This decrease is prevented by early denervation of the muscle, suggesting a neural control of subsynaptic AChR channel properties. To further examine the nature of this neural influence, neonatal rat soleus muscles were now denervated at an early stage of endplate development and the muscles were kept active by chronic stimulations in vivo for 4 days. The gating properties of AChR channels at the denervated endplates and at control endplates of similar age were then examined by analysis of acetylcholine-induced endplate current fluctuations and of the time course of miniature endplate currents, respectively. The results indicate, that stimulation restores the maturation of 'adult' AChR channel properties even in the absence of the nerve, suggesting an important role of muscle activity in synapse development.

Action Potentials↗
PubMed1976

An analysis of the mode of action of carbachol on the chick biventer cervicis nerve--muscle preparation.

The mechanism of contracture evoked by carbachol in the isolated chick biventer cervicis nerve--muscle preparation was studied. At concentrations lower than 11 muM, carbachol progressively induced contracture at a rate much slower than did acetylcholine. A spontaneous increase of the response to carbachol, but not to acetylcholine, was observed 2-4 hr after isolation of the muscle. By contrast, no change of the response occurred in the denervated muscle. Anticholinesterase treatment shifted the dose-response curve for carbachol markedly to the left as far as the contracture attained after 4-6 min incubation was concerned. The shift was much less marked for the dose-response curve plotted against the initial rate of response defined as the contracture obtained after 1 min incubation. No enhancement of response was detected by inhibition of acetylcholinesterase in the denervated muscle. beta-Bungarotoxin which blocked neuromuscular transmission within 30 min, caused a transient enhancement of the response to carbachol. After 2-3 hr treatment, however, the spontaneous increase of response to carbachol was counteracted by the toxin. No potentiation of the response by anticholinesterase agents was observed after toxin treatment. When added in the presence of physostigmine or echothiophate, beta-bungarotoxin reduced the response to carbachol to the control level in 2 hr. The response to carbachol in the muscle treated with alpha-bungarotoxin and washed subsequently was also not potentiated by anticholinesterase treatment. Repetitive nerve stimulation in the presence of hemicholinium-3 caused a neuromuscular blockade but did not appreciably antagonize the response to carbachol more than that to acetylcholine either in the absence or presence of physotigmine. When calcium ion in the medium was decreased from 2.7 to 0.54 mM, ther response to nerve stimulation was nearly completely inhibited, but the response to carbachol was not affected and could still be potentiated by anticholinesterase. It is concluded that carbachol has both direct and indirect effects on the chick biventer cervicis muscle. At a low concentration, particularly in the presence of an anticholinesterase and if sufficient time of incubation is allowed, the indirect effect caused by release of acetylcholine may become more prominent than the direct action on the post-synaptic receptor. Both the mechanism and the store of acetylcholine for this indirect action appear to be different from those for the nerve impulse.

Acetylcholine↗
PubMed1986

Diabetes mellitus-induced hypersensitivity of mouse skeletal muscles to acetylcholine and succinylcholine.

The myopathy in skeletal muscles of genetically diabetic male KK-CAy mice or alloxan-induced diabetic mice was investigated. In these diabetic mice, nerve-stimulated twitch tensions of in situ sciatic nerve-gastrocnemius muscle preparations were inhibited by intraarterially administered succinylcholine (SuCh) to a greater extent than in normal (non-diabetic) ones. Despite the high blood glucose level, at one week after alloxan administration, no hypersensitivity to SuCh was induced in mice, but mice at 2 weeks and 4 weeks after alloxan showed greater sensitivities. In isolated diaphragm muscles of diabetic KK-CAy mice, the acetylcholine (ACh, iontophoretically applied) potential amplitude was greater than in KK-CAy prediabetic muscles. SuCh in diabetic KK-CAy muscles inhibited ACh potentials to a greater extent than in normal ddY muscles. Hill coefficients obtained from the inhibition curve by SuCh of the nerve-stimulation response were decreased by the diabetic state. The sensitivities to d-tubocurarine and alpha-bungarotoxin were the same in both kinds of muscles. Both extrajunctional ACh receptors in denervated muscles of normal ddY and diabetic KK-CAy mice revealed the lower sensitivity to SuCh than junctional receptors in non-denervated normal muscles. In conclusion, diabetic muscles showed the hypersensitivity restricted to SuCh. These phenomena are neither due to glycosylation nor to denervation supersensitivity.

Acetylcholine↗
PubMed1995

High endocytotic activity occurs periodically in the endplate region of denervated mouse striated muscle fibers.

High endocytotic activity after denervation of skeletal muscle occurs in a proportion of muscle fibers (both slow and fast fiber types) in the endplate region. The present study was performed in order to examine if a periodicity in the endocytotic activity could explain why the process is not observed in all fibers at a given time. Three markers, horseradish peroxidase (HRP), rhodamine B isothiocyanate-labeled dextran, and fluorescein isothiocyanate-labeled dextran were used to demonstrate endocytotic activity of muscle fibers of the denervated mouse hemidiaphragm in vivo. Acetylcholine esterase staining was used in conjunction with HRP uptake to determine the proportion of denervated muscle fibers with endocytotic activity in the endplate region at any one time. The results show that 25-50% of the muscle fibers display high endocytotic activity in the endplate region at a given time 10 days after denervation. The existence of a periodicity in this endocytotic activity is suggested by results obtained using two different endocytotic markers administered at time intervals of 0-7 days. We conclude that loss of contact with the innervating motorneuron induces a high endocytotic activity which occurs periodically in the perisynaptic region of skeletal muscle fibers.

Animals↗
PubMed1992

Response of developing rat fast muscles to partial denervation.

The changes of motor unit size following partial denervation of the extensor digitorum longus muscles in rat neonates (at five to six days) and later in development (at 18-20 days) were studied. Extensor digitorum longus muscle is innervated mainly by axons from L4 ventral ramus and to a lesser extent by axons from L5 ventral ramus. In neonates the motor units in extensor digitorum longus are large, and they become restricted to their adult size during the first two weeks of life. Six to 10 weeks after removing the major input to extensor digitorum longus, i.e. L4 ventral ramus at five to six days, the motor unit sizes of axons in the remaining L5 ventral ramus decrease from their expanded neonatal territory to their adult smaller size. In spite of partial denervation the motor units remain small throughout the animal's life and the denervated muscle fibres do not become "occupied" by sprouts from the remaining axons of L5 ventral ramus motor nerves. Partial denervation of extensor digitorum longus muscles at 18-20 days by section of the L4 ventral ramus leads to the expected two- to three-fold increase in the size of motor units of L5 ventral ramus. These results are taken to show that fast motor units of neonatal rats are unable to maintain their enlarged peripheral field, while later in development their axons can sprout and occupy an expanded peripheral field.

Aging↗
PubMed1992

Effect of ibuprofen upon denervated skeletal muscle resistance and compliance vessels during endotoxemia.

The primary aim of these studies was to specifically evaluate the non-neural role of the cyclooxygenase products on the peripheral vascular decompensation associated with endotoxemia. The constant-flow perfused, vascularly isolated, denervated double-canine gracilis muscle preparation in which one muscle is used as a control for the contralateral side was employed. The experimental muscle (GMi) received ibuprofen while the control (GMc) was infused with the vehicle. The results of these studies suggest that endotoxin increases the arterial conductance (i.e., arterial dilation) by 100% and venous compliance (i.e., venoconstriction) by 40%. These observations, which are consistent with venous pooling, were not significantly altered by the continuous intra-arterial infusion of ibuprofen at a peripheral blood concentration of 160 microM. Ibuprofen caused a small but statistically significant increase in the conductance/compliance ratio at 60, 75, and 90 min post endotoxin, suggesting that cyclooxygenase products may play a minor role in the non-neural regulation of capillary fluid dynamics during endotoxemia. Consequently, these studies do not provide convincing evidence that would support a non-neural cyclooxygenase role in the peripheral vascular decompensation reported to occur during systemic endotoxemia.

Animals↗
PubMed1999

Specific and innervation-regulated expression of the intermediate filament protein nestin at neuromuscular and myotendinous junctions in skeletal muscle.

The intermediate filament proteins nestin, vimentin, and desmin show a specific temporal expression pattern during the development of myofibers from myogenic precursor cells. Nestin and vimentin are actively expressed during early developmental stages to be later down-regulated, vimentin completely and nestin to minimal levels, whereas desmin expression begins later and is maintained in mature myofibers, in which desmin participates in maintaining structural integrity. In this study we have analyzed the expression levels and distribution pattern of nestin in intact and denervated muscle in rat and in human. Nestin immunoreactivity was specifically and focally localized in the sarcoplasm underneath neuromuscular junctions (NMJs) and in the vicinity of the myotendinous junctions (MTJs), ie, in regions associated with acetylcholine receptors (AChRs). This association prompted us to analyze nestin in neurogenically and myogenically denervated muscle. Immunoblot analysis disclosed a marked overall increase of accumulated nestin protein. Similar to the extrajunctional redistribution of AChRs in denervated myofibers, nestin immunoreactivity extended widely beyond the NMJ region. Re-innervation caused complete reversion of these changes. Our study demonstrates that the expression levels and distribution pattern of nestin are regulated by innervation, ie, signal transduction into myofibers.

Adult↗
PubMed1983

[Effects of denervation of the soleus muscle of rats].

Histological aspects and changes in wet weight were studied on rat soleus muscles after denervation by cutting the sciatic nerve. The muscles were removed after a variable period of time from the third to the fiftieth day. There was a progressive fall off in wet weight and after the third week the muscles underwent 50% atrophy. Histological changes were most striking on sarcolemmal nuclei; they became vesicular, enlarged with prominent nucleolus and there was an apparent increase in their number. The muscle fibres changed their shape, becoming rounded and there was a 50% reduction in muscle fibre diameter after 50 days. Connective tissue abnormalities were minimal after 50 days and the striations remained intact.

Animals↗