Contralateral Control Muscles Research Articles

An ultrastructural study of the stretch-induced hypertrophy of skeletal muscle

The teres minor muscle of the adult chicken was studied ultrastructurally following tonic stretch-induced hypertrophy. The contralateral control muscle fibres showed compact myofibrils and proliferation of normal Z-bands. Myofibrils of the hypertrophied muscle however, showed Z-band alterations as Z-band expansions and Z-band streaming. Thus Z-band is a highly responsive structure to tonic stretch. Since a number of neuro-muscular conditions display Z-band anomolies, the latter occurring in response to a variety of metabolic and physiologic stimuli, including tonic stretch as shown here, represents a non-specific phenomenon.

Healing of experimental muscle strains and the effects of nonsteroidal antiinflammatory medication.

The healing process of muscle strains and the effect of nonsteroidal antiinflammatory medication were studied using an experimental animal model. A standardized strain of the tibialis anterior muscle in adult male rats was produced by a controlled stretch of the muscle. Groups I and II underwent a unilateral strain of the tibialis anterior muscle and were immobilized in the postinjury period. The rats in Group II were fed piroxicam in the postinjury period. Group III underwent a sham procedure and were also immobilized. At 0, 2, 4, and 11 days postinjury both injured and contralateral control muscles were evaluated by determining tensile strength characteristics and histologic appearance. Group I showed a significant drop in maximum failure load to 25.7% of the control leg at Day 2 with a gradual return to the level of Group III at Days 4 and 11 (40.9% and 50.1%). Group II showed a similar drop but was still stronger than Group I at 2 days with 40.8% of the control leg and continued to drop until 4 days postinjury (33.7%). Histology showed a delay in inflammatory reaction and muscle regeneration in Group II. At 11 days both Groups I and II showed regenerated muscle fibers bridging the entire defect and an increase in endomyseal fibrosis. It is concluded that muscle strains continue to weaken in the early postinjury period. Non-steroidal antiinflammatory medication, such as piroxicam, might delay muscle regeneration.

Delayed use of hyperbaric oxygen for treatment of a model anterior compartment syndrome

This study examines the effect of delayed exposure to hyperbaric oxygen on muscle necrosis and edema development following compartment syndromes in the canine hindlimb. Compartment syndromes (100 mm Hg for 8 h) were generated in one anterolateral compartment of six anesthetized dogs. After a 2-h delay, three 1-h hyperbaric oxygen treatments (2 atm absolute pure oxygen) were given during the next 12 h. Two days later, technetium-99m stannous pyrophosphate (99mTc Sn-PYP) was injected intravenously; 3 h later, samples were obtained from the pressurized and contralateral control muscles, weighed for edema development, counted for 99mTC Sn-PYP uptake, and evaluated histologically. Hyperbaric oxygen treatments, even when delayed 2 h, reduced muscle necrosis and intramuscular edema to negligible levels (p less than 0.05) compared with untreated animals. In addition, muscle morphology remained essentially normal in all hyperbaric oxygen-treated animals. We conclude that even if hyperbaric oxygen treatments are delayed 2 h, edema and muscle necrosis are reduced significantly in a model compartment syndrome.

Myotrophic effects on denervation atrophy of hindlimb muscles of mice with systemic administration of nerve extract

Atrophy was assessed in denervated hindlimb muscles of adult mice which either were not otherwise treated or received daily intraperitoneal injections of extract of rats' sciatic nerves. After 7 days, the denervated muscles of injected animals exhibited significantly smaller decreases in wet weight, total protein and cross-sectional areas of muscle fibers relative to innervated contralateral control muscles. The effects of denervation and nerve extract on different muscles varied.

Biochemistry of rat single muscle fibres in newly assembled motor units following nerve crush.

A partial crush was applied surgically to the common peroneal nerves of rats, producing motor deficits lasting 4 weeks; the tibialis anterior muscles supplied by the crushed nerves were removed 5 weeks after recovery along with the contralateral control muscles. Myosin ATPase staining following pre-incubation at pH 4.5 was used to determine fibre types and to demonstrate areas of fibre-type grouping in the reinnervated areas of the muscles. Enzyme activities of lactate dehydrogenase (LDH), adenylokinase (AK) and malate dehydrogenase (MDH) were measured using micro-analytical techniques on the individual fibres within the histochemically identical groups and on fibres of the same types selected from areas of the test muscle or the contralateral control which appeared normal. The results show that the degree of enzymatic variation among single fibres reinnervated by a common axon is very small when compared to the general fibre population and, moreover, to fibres of the same histochemical type. Enzyme variability within the newly formed motor units was only slightly greater than the variability reported for normal motor units (Nemeth, Pette & Vrbová, 1981). The results indicate that skeletal muscle fibres originally having great differences in levels of enzyme activity, as demonstrated in the general fibre population, acquire considerable enzymatic similarity following reinnervation by a common motor neurone.

Stretch-induced growth in chicken wing muscles: nerve-muscle interaction in muscular dystrophy.

Skeletal muscle growth following denervation and denervation plus passive stretch was characterized in the patagialis muscle of normal and dystrophic chicks until 8 wk of age. In both genotypes, muscles denervated at 1 wk of age grew at reduced rates compared with contralateral control muscles whether or not they were passively stretched. Histograms of fiber size distributions as well as morphological criteria showed that passive stretch of denervated dystropic muscles substantially delayed the development of pathology. Denervation alone provided less protection. There was no evidence of fiber necrosis in any denervated dystrophic muscle, although many fibers did exhibit extreme hypertrophy and abnormal morphology. When denervated dystrophic muscles were allowed to reinnervate, growth and development of pathology was rapid. Because denervation, denervation with passive stretch, or passive stretch alone retards, but does not prevent, the development of pathology, it is concluded that dystrophy in the chick is a myogenic defect that is exacerbated by neurally mediated contractile activity.

Myotrophic effects of anabolic steroids.

An anabolic steroid, nandrolone decanoate, was shown to produce increases in the weight, cross-sectional area, tension-generating capacity and mean fibre diameter of a limb muscle, tibialis anterior (TA), in female rabbits. Despite suggestions in the literature of an exerciserelated effect of such drugs, hypertrophy was not observed in TA muscles subjected to chronic electrical stimulation, but was seen in the contralateral control muscles and in the muscles of both hind limbs in unoperated sedentary animals. The effect was confirmed in the TA of female guinea pigs, rats and mice, and could not be explained in terms of an increase in body weight. Compared to TA some other muscles, like EDL, plantaris and soleus in the rabbit, were less sensitive to treatment; others, like pubocaudalis in the rat and mouse, and temporalis in the guinea pig, were more responsive. The myotrophic effects were undiminished in adrenalectomised female rats, and could not therefore have been mediated by interference with the catabolic actions of circulating glucocorticoids, as had been proposed in an earlier hypothesis.

Transmitter release during normal and altered growth of identified muscle fibres in the crayfish.

During growth of identified crayfish muscle fibres from a diameter of 20 to 400 micron, the excitatory junctional potential (e.j.p.) amplitude was found to be independent of diameter. Thus, e.j.p. amplitude was maintained during growth in spite of a 21-fold decrease in miniature excitatory junctional potential (m.e.j.p.) amplitude previously reported (Lnenicka & Mellon, 1983). The maintenance of e.j.p. amplitude was found to be partially due to a 5-fold increase in quantal release at 'active sites' during growth. In order to determine whether the increase in transmitter release can be regulated by the rate of muscle fibre growth, the rate of growth was experimentally reduced. By decreasing the resting length of the muscle during growth, the rate of increase in the diameter was reduced by approximately 50% compared with the contralateral control muscle fibres. The input resistance and the m.e.j.p. were appropriately larger in the smaller-diameter experimental fibres. However, e.j.p. amplitude in the experimental fibres was not significantly different from that in the contralateral control fibres. This was apparently due to the significantly smaller quantal release at active sites on the experimental fibres compared with control fibres. Thus, experimental alteration of the rate of muscle fibre growth results in regulation of transmitter release, suggesting that the muscle fibre may control the increase in transmitter release seen during normal growth.

Motor unit size and synaptic competition in rat lumbrical muscles reinnervated by active and inactive motor axons.

The size of motor units has been measured in adult rat muscles reinnervated by active and inactive motor axons. The results suggest that active nerve terminals have a competitive advantage over inactive terminals during neuromuscular synapse elimination. The experiments were done using the fourth deep lumbrical muscle in the rat hind foot, which receives its motor innervation from the lateral plantar nerve (l.p.n.) and the sural nerve (s.n.). The muscles were denervated by a nerve crush close to the muscle. Five to ten days later, nerve impulse conduction in the l.p.n. was blocked for 1-2 weeks by chronic superfusion of the nerve with tetrodotoxin (Betz, Caldwell & Ribchester, 1980 b). After 2 weeks of l.p.n. block, the isometric tetanic tension of s.n. motor units increased about two-fold, compared with contralateral control muscles. This was due to an increase in the number of muscle fibres innervated by s.n. motor axons. Intracellular recordings showed that more fibres were innervated by the s.n. than in normal muscles. In some animals, the blocked l.p.n. was cut 1-2 weeks later. The l.p.n. terminals were allowed to degenerate for 1-2 days. There were more s.n. terminals in zinc iodide-osmium stained preparations of these muscles than in normal muscles. Calculation of tetanic tension overlap between l.p.n. and s.n. motor units, and the amount of mono-neuronal innervation seen in intracellular recordings suggested that a larger fraction of the muscles was innervated only by s.n. motor nerve terminals than in controls. This fraction increased with time, ultimately reaching about 14% of the muscle per s.n. motor unit. The expansion of the s.n. motor units appeared to take place by terminal and preterminal sprouting of motor axons. The l.p.n.-evoked tetanic tension decreased in parallel with the increase in the s.n. tetanic tension. The decrease in the l.p.n. twitch tension did not parallel the increase in the s.n. twitch tension. At least part of this discrepancy was due to repetitive firing of the regenerated, inactive l.p.n. terminals when the nerve was stimulated electrically. The results support the notion that modifications in connectivity between pre- and post-synaptic cells can come about by growth or withdrawal of terminals, as a result of differences in the level of activity in the presynaptic cells (Hebb, 1949).

Local and systemic effects of tetrodotoxin on the formation and elimination of synapses in reinnervated adult rat muscle.

1. Polyneuronal innervation of normal and reinnervated fourth deep lumbrical muscle fibres was studied with tension measurements and intracellular recordings. From the tenth day after a complete crush of the muscle nerve, some of the reinnervated muscles were completely paralysed for up to 15 days by local application of tetrodotoxin (TTX) to the sciatic nerve. Other animals received only systemic infusion of TTX during the muscle reinnervation.2. Measurements of tetanic-tension overlap suggested that about 6% of the muscle fibres in the normal lumbrical muscle were polyneuronally innervated, while intracellular recordings suggested that the percentage was as high as 25%. This discrepancy was mainly due to the presence of one small, sub-threshold end-plate potential (e.p.p.) and one large, suprathreshold e.p.p. in almost all polyneuronally innervated muscle fibres.3. Intracellular recordings during muscle reinnervation showed that the extent of polyneuronal innervation reached a maximum of 50% 10-15 days after denervation and that by 16-20 days this had decreased to a level similar to that found in normal muscle.4. After a week of total muscle paralysis the extent of polyneuronal innervation had increased to about 80%, estimated by both tension measurements and intracellular recordings. Subsequently, there was no sign of any net elimination of the polyneuronal innervation, even in muscles paralysed for up to two weeks. Many of the polyneuronally innervated fibres were innervated by at least two motor axons. each producing suprathreshold e.p.p.s.5. In muscles contralateral to the paralysed muscles, the extent of polyneuronal innervation reached a maximum of 50% 10-15 days after denervation as in reinnervated muscles not exposed to TTX. But in contrast to the subsequent decrease in the extent of polyneuronal innervation in animals which received no TTX, this level of polyneuronal innervation persisted in muscles contralateral to the paralysed muscles. The same was true for reinnervated muscles in animals which only received TTX systemically.6. The increased level of polyneuronal innervation after TTX application was not caused by differences in the number of motor units or in number of muscle fibres.7. Paralysed muscles relaxed much more slowly than non-paralysed muscles at the end of a fused tetanic contraction. The tetanus/twitch ratio of these muscles was also smaller than in contralateral control muscles and the rise time of the twitch was greater.8. It is concluded that a substantial fraction of the fibres in the normal lumbrical muscle of young rats is polyneuronally innervated. After reinnervation, the normal innervation pattern is re-established, but no net elimination of the polyneuronal innervation occurs unless either nerve or muscle or both are active. A net elimination of synapses is also prevented when TTX is present systemically in low concentrations.

Phospholipid distribution and stimulation of methylation during denervation and reinnervation in skeletal muscle

Denervation of the rat soleus and extensor digitorum longus muscles was induced by nerve crush. Functional signs of denervation were noted within 48 h with recovery beginning about the 12th day following denervation. There was also a marked decrease in muscle weight but only a small decrease in protein content per mg of muscle, subsequent to denervation. At 1, 2 and 3 weeks following nerve crush there was a relative decrease in muscle phosphatidylethanolamine (PE) and a corresponding increase in phosphatidylcholine (PC). The proportion of the other phospholipids did not significantly change. The levels of PC and PE returned to, or in some cases slightly overshot, control values at 4 and 5 weeks following nerve crush, i.e. during the period of reinnervation. Levels in non-denervated contralateral muscles did not significantly change. At 1 and 3 weeks following nerve crush a marked increase was observed in the activities of the enzymes PE-methyltransferases I and II, as measured by [(3)H]methyl group incorporation from S-adenosyl methionine into phosphatidylmonomethylethanolamine, phosphatidyldimethylethanolamine and PC. Increased activity of these methylases was seen in the contralateral control muscle, although less than in the denervated muscle. These enzymatic changes could be responsible for the changes in PE and PC distribution which we observed. Methylation of PE might also decrease the microviscosity of the membrane, thereby leading to other changes associated with denervation. Activation of this system might be another form of supersensitivity induced by denervation.

Ability of motoneurons to regulate quantal release and terminal growth after reduction in motor unit size

Experiments were performed to test the hypothesis that motoneurons are programmed to produce fixed amounts of growth and transmitter release substrates and are unable to regulate production to match the number of nerve terminals they support. The size of the average motor unit in mouse tensor fascia latea muscles was approximately halved by cutting out the distal half of the muscle. Surviving terminals were assessed 100–110 days later for level of quantal output and percentage of terminals with sprouts. Both quantal output and sprout percentage were the same as in contralateral control muscles. Both parameters have been reported to be elevated 1–9 days after a similar operation 4. We conclude that mouse motoneurons can down-regulate their production of growth and release substrates but that the process takes more than 9 days to become effective.

Generation of phosphodiesters during fast-to-slow muscle transformation A 31P-NMR study

During rabbit fast-to-slow twitch muscle transformation, in response to electrical stimulation, the compound glycerophosphocholine can be detected in these muscles by 31P-NMR. This compound is not detectable in contralateral control muscles but is present in slow twitch soleus.

Neuromuscular transmission at terminals of sprouted mammalian motor neurones

Motor nerve sprouting was induced in the tensor fasciae latae muscle of mice by partial denervation produced either by cutting (to prevent reinnervation) or crushing (to allow subsequent reinnervation) spinal nerve L4 unilaterally. The quantum content (m) of endplate potentials recorded intracellularly in vitro in the presence of high-Mg2+ and low-Ca2+ ion concentrations was determined up to 400 days later in non-reinnervated, reinnervated and contralateral control muscles. The muscles were then either fixed and stained with silver and cholinesterase for light microscopy, or fixed and examined in the electron microscope. The average value of m in control muscles increased by 4-5-fold as the animals matured in the 4 months following the operations. The average value of m at terminals of sprouted motor neurones in the absence of reinnervation also increased with time after partial denervation but was always less than the value in the corresponding control muscle. In electron micrographs of muscles following L4 section the nerve terminals closely apposed on average only two-thirds of the proportion of junctional folds apposed to terminals in control muscles. When muscles were reinnervated following L4 crush the average value of m at terminals of sprouted and reinnervating motor neurones equalled and sometimes exceeded m in contralateral control muscles. A proportion of muscle fibres had endplate potentials from reinnervating and sprouted axons, and the silver stain showed that these muscle fibres were innervated at the site of the original endplate. At these endplates the fraction of the total quantum content contributed by presumed sprout terminals fell significantly in the 4 months following L4 crush. It is concluded that: (i) in the absence of reinnervation, sprout terminals grow in size but a significant number never occupy all endplate site available to them; and (ii) in the presence of reinnervation axons terminals share some endplates with sprout terminals and grow at the expense of the sprout terminals which are eventually withdrawn from some shared endplates.

Biocompatibility of a silicon based peripheral nerve electrode.

The biocompatibility of a silicon neuroelectric interface for chronic use in mammalian peripheral nerves was investigated. New Zealand white rabbits were used as the animal model. The implant was made of (110) silicon coated with one micron of silicon dioxide. An anisotropic etch was used to form a grid of ten silicon bars each 40 microns wide and spaced 160 microns apart. A Silastic nerve cuff was molded onto each side of the grid. Using microsurgical techniques, the nerve was transected and sutured into the implant cuff. One implanted rabbit was completely analyzed and is reported here. By 32 days post operatively, the EMG of the affected muscles had partially recovered. The EMG of the affected muscles was indistinguishable from the contralateral control muscles after 150 days. At 332 days, the conduction properties of the implanted nerve confirmed that the nerve was capable of conduction through the silicon grid. Histological observations were consistent with normal peripheral nerve regeneration following microsurgical neurrorhaphy. Seven additional rabbits have been implanted and will be fully analyzed in the future. It was concluded that the silicon peripheral nerve implant described here should be pursued as a substrate for a chronic neuroelectric interface.

Role of degenerating axon pathways in regeneration of mouse soleus motor axons.

1. The recovery of tension in mouse soleus was assayed 1-5 days after crushing the extramuscular nerve in muscles which had been previously either denervated by nerve crush, partly denervated by spinal nerve root section, or paralysed by I.M. injection of botulinum toxin. Recovery of tension following nerve crush in contralateral control muscles from the same mice was also measured. The muscles were then stained with zinc iodide-osmium and examined in the light microscope. 2. Recovery in control muscles began at about 50 hr after crush and was nearly complete by 5 days. Recovery began at about 50 hr after crush and was nearly complete by 5 days. Recovery began about 10 hr earlier and was more rapid in muscles denervated by crushing the muscle nerve 4 days before recrushing at the same site. 3. Paralysis 12 days earlier by intramuscular injection of botulinum toxin did not enhance recovery after nerve crush. The axons remained following partial denervation 6 days before nerve crush also regenerated at a rate similar to controls. 4. It is concluded that (1) nerves regenerate more quickly down a pre-degenerated pathway, (2) chromatolysis does not significantly enhance reinnervation, and (3) each motor axon regenerating after a crush is constrained to follow its own denervated pathway back into the muscle. 5. Histology was consistent with these conclusions, and also showed that end-plates in control muscles reinnervated after short periods of denervation were normal in appearance and possessed little "escaped' nerve growth. This was in contrast to end-plates which had been regenerated in muscle after a preceding nerve crush, botulinum toxin paralysis or partial denervation. This suggests that growth from nerve terminals is controlled locally within a muscle.

Polyamine accumulation in normal and denervated neonatal muscle

Polyamines were monitored in normal and denervated neonatal rat gastrocnemius muscle as markers of the degeneration-regeneration processes in muscle characteristic of progressive neuromuscular disorders. The muscle was denervated within 6 h of birth. The highest polyamine concentrations were present at day 2 of birth and remained elevated during the first week, the period of most rapid muscle growth. Denervation did not alter the concentration of any of the polyamines compared with normal or contralateral controls during the first 3 weeks postparturition. These data suggest that neonatal polyamine synthesis, an index of extent of cell growth processes, is not affected by denervation. However, prolonged denervation did alter the polyamine accumulation patterns, with denervated muscle having significantly elevated spermine at 21 days, putrescine and spermidine concentrations at 28 days, and elevated spermidine at 56 days of age. Within 56 days, denervated muscle compared with normal innervated contralateral control muscle contained fourfold and twofold more spermidine and spermine per milligram protein. In conclusion, it is likely that the continued elevation of polyamines in denervated muscle represents the conservation of a metabolic pattern characteristic of immature muscle, as it is known that neonatal denervation results in failure of muscle maturation and differentiation. However, fibroblast proliferation also may be a contributing factor to the markedly altered polyamine concentrations found in denervated muscle.

Muscular enlargement and number of fibers in skeletal muscles of rats.

The effect of muscular enlargement produced by surgical ablation of a synergist and the combination of synergist ablation and exercise on the number of fibers in the soleus (S), plantaris (P), and extensor digitorum longus (EDL) muscles of the rat was studied. The number of fibers per muscle was determined by direct counts of individual fibers dissected from HNO3-treated muscles. Ablation of a synergist produced average enlargements of about 25, 45, and 29% for the S, P, and EDL muscles, respectively. Exercise and synergist ablation produced increases in wet weight to about 44 and 88% for the S and P muscles, respectively, whereas no further increases were observed in the EDL muscles. Intra-animal comparisons revealed that no differences existed for total fiber number or the incidence of fibers with bifurcations between the enlarged and contralateral control muscles. The difference in dry weight of fibers from the enlarged as compared with control muscles was closely correlated to differences in total muscle wet weight. These data demonstrate that hypertrophy rather than hyperplasia was responsible for increases from 10 to over 100% in the weight of skeletal muscles.

New muscle fiber production during compensatory hypertrophy

Morphological changes exhibited by satellite cells during compensatory hypertrophy have been observed through a scanning electron microscope on m. plantaris of young, adult rats. Compensatory hypertrophy was induced by ablation of the synergistic m. gastrocnemius. Muscles were observed 15, 30, and 60 days post-operative. A consistent increase in wet-weight of m. plantaris (60.3,77.2, and 93.7% more than the contralateral control muscle) indicated the degree of developing hypertrophy. The satellite cells exhibited the following successive changes: (1) cells enlarged and became freed of connective network sheath, (2) cell distance from the associated fibers increased though still attached to the latter, (3) subsequent cell division, giving rise to rows of cells, that with time-lapse formed elongated structures with a common sheath, (4) elongated structures developed into new muscle fibers.

Developmental patterns of glycolytic enzymes in regenerating skeletal muscle after autogenous free grafting

Extensor digitorum longus muscles of rats were removed and injected with a solution of Marcaine plus hyaluronidase. After incubation in Marcaine solution for 10 min, the muscles were grafted into their original beds. The grafts and the contralateral control muscles were removed from the rats at 0, 1–5, 7, 11, 36, and 69 days postoperatively. The muscles were then frozen in dry ice and isopentane and subsequently homogenized and centrifuged. The supernatant was analyzed for a number of enzymes, the regenerative patterns of which can be classified into 3 groups: (1) early increase in activity: hexokinase, glucose-6-phosphate dehydrogenase; (2) early decrease in activity with failure to recover to control levels: phosphorylase, phosphofructokinase, α-glycerophosphate dehydrogenase; and (3) early decrease followed by return to control levels: lactate dehydrogenase, pyruvate kinase, creatine phosphokinase, adenylate kinase. These patterns are not identical to those reported for embryogenesis of muscle. The data are discussed with regard to correlative histological studies of muscle regeneration.