Physiological and histochemical properties of the soleus muscle after denervation of its antagonists

A comparison of the effects of denervation on the mechanical properties of rat and guinea-pig skeletal muscle

1. A fast (extensor digitorum longus) and slow (soleus) twitch muscle were denervated in rats and guinea-pigs and isometric and isotonic contractions were followed for periods of up to 6 months after. 2. The decay of tetanic tension with time could be described as exponential. The rate of decay of tension was greatest in rat soleus and least in guinea-pig soleus by a factor of more than three. The fast muscles atrophied at intermediate rates. 3. The contraction and relaxation times of soleus and extensor digitorum longus of rat, initially prolonged by denervation, became shorter after 3 weeks. There was no such reversal in either guinea-pig muscle, indeed extensor digitorum longus twitch became even more prolonged. Guinea-pig muscles often showed signs of repetitive response to a single stimulus, resulting in distortion of relaxation of the twitch. 4. There was a slowing of isotonic shortening velocity in the late stage of denervation of guinea-pig extensor digitorum longus, accompanied by a fall in the rate of development of isometric tetanic tension. There was a just-significant (P less than 0.1) increase in the shortening velocity of rat soleus. None of the other muscles showed any change in either rate characteristic. 5. In guinea-pig extensor digitorum longus the type I fibres atrophied less than type II fibres; in all other muscles the atrophy was more uniform, possibly faster in type II. Guinea-pig soleus remained pure type I contrasting with an increase in the numbers of type II fibres in rat soleus. There was a possible increase in the number of type I fibres in guinea-pig fast muscle and no change in the rat.

Is the myosin type altered in the aging platysma?

The myosin light chains of platysma samples originating from 2 to 86 year old patients of the maxillo-facial surgery clinic were investigated. The platysma contained both fast and slow myosin. No change in the proportion of myosin type in relation to age was found. Female patients often displayed less fast myosin than male patients. Each time when the platysma muscle activity has been reduced a decrease in the amount of slow myosin light chains was observed. In the reported study, variations of the fast and slow myosin light chains resulted mainly from the platysma activity level, i.e. from the pathology requiring the surgery, rather than from the patients' age.

Section of fibular nerve affects activity pattern and contractile properties of soleus motor units in adult rats

Transection of the common fibular (FIB) nerve caused an immediate reduction in the total amount of soleus (SOL) motor unit activity, which declined further during the following 10 days and then remained stable at less than half of normal values. In addition, there was an immediate reduction in median impulse rate from about 20.0 to 14.9 Hz followed by a return to normal values during the first 10 days. Short interval (3-4 ms) double discharges, occurring either in isolation or at the same regular intervals as single impulses, were observed 2-5 days after FIB nerve section in a few motor units. Brief, high frequency impulse bursts with interspike intervals of 12-16 ms were observed in a few units from the third day and until the end of the experiment (up to 31 days). It was not established whether the high frequency discharge pattern occurred only in a fixed population of the SOL motor units, or whether the units could switch between high and low frequency activity. Two months after FIB nerve section, the SOL muscle in the same leg contracted faster than normal (mean isometric twitch contraction time 29.6 ms, n = 4; vs. 38.7 ms, n = 8), contained a larger than normal percentage of type II fibres (13-36 vs. 0-0.2%) and weighed less than the contralateral SOL muscles (180 vs. 206 mg). SOL muscles (n = 4) in the opposite leg were comparable to normal SOL muscles except for a small reduction in mean isometric twitch contraction time (35.5 ms).

Central core degeneration after tenotomy in soleus muscles of hyperthyroid rats

Tenotomy of the rat soleus muscle is followed by a central degeneration of slow, fatigue-resistant muscle fibers. Previous experiments showed that fast, fatigable fibers of the gastrocnemius when transformed to slow, fatigue-resistant fibers by cross-reinnervation also develop lesions after tenotomy. The experiments described in this communication were carried out to discover whether the susceptibility of fibers to lesions was determined by their fiber type or the nature of their innervation. Rats were rendered hyperthyroid by the administration of sodium 3,3',5-triiodo-L-thyronine (T3) for 7 to 10 weeks. Tenotomy of the soleus muscles was then carried out and the experimental and contralateral muscles were removed and stained for myosin ATPase activity after a further 2 weeks. The hyperthyroid state of each animal was confirmed by the assay of succinate dehydrogenase activity of liver and the contralateral muscle. After acid preincubation, whole muscle fiber type counts of contralateral muscles showed a statistically significant change from a predominantly acid-stable population of fibers to acid-labile fibers. In addition, many fibers of intermediate staining properties were seen. When the experimental muscles were examined, all three varieties of fiber showed central degeneration. The nature of the fiber type change induced by T3 and the role that innervation might play in this is discussed. It was concluded that the susceptibility of fibers to the lesions that follow tenotomy is dependent on the nature of their innervation rather than their fiber type.

Modification of the atrophic effects of tenotomy on mouse soleus muscles by various hind limb nerve lesions and different levels of voluntary motor activity

The response of mouse soleus muscles to transection of the proximal tendon was examined in a variety of circumstances which might be expected to modify the amount of activation of soleus motoneurons. (i) Denervation of ankle flexors antagonistic to the soleus produced slight atrophy of intact muscles but protected soleus to some extent from the effects of concurrent tenotomy. The onset of changes in tenotomized fibers was delayed several days. (ii) Tenotomy of the soleus soon after reinnervation of the muscle fibers (following tibial nerve transection) resulted in little loss of mass and no degenerative changes. (iii) Denervation during the first few days after tenotomy halted the progress of muscle shortening and alleviated the atrophic changes at the stage reached at the time of denervation. Anesthesia without surgical intervention at the same period after tenotomy also halted the atrophic changes, despite subsequent muscle shortening. (iv) Oral administration of diazepam (approximately 1 mg/kg/day) or chlorpromazine (approximately 12 mg/kg/day), which decreased motor activity during the early posttenotomy period, reduced the amount of muscle shortening and the degree of atrophy. The results suggest that both reflex and voluntary activation of soleus motoneurons contribute to the development of atrophy after tenotomy. The response in soleus muscle seems to be particularly sensitive to the pattern of motor activity during the first 2 to 3 days after tenotomy.

Fiber type changes in denervated soleus muscles of the hyperthyroid rat

The thyroid status of rats is known to influence the histochemical and biochemical myosin adenosine triphosphatase (M-ATPase) activity of the soleus muscle. In the hypothyroid state, denervated soleus muscles are not subject to that influence. Our experiments indicated that in the hyperthyroid state fibers of the denervated soleus muscle show a profound change from acid-stable M-ATPase positive to acid-stable M-ATPase negative. We concluded that this change was induced by the hyperthyroid state and was not neurally mediated.

Histological changes of muscle in a patient with pyruvate dehydrogenase deficiency

Histological changes of muscle from a 17-month-old boy with pyruvate dehydrogenase deficiency are presented. The patient had muscle hypotonia, mental retardation, seizures, lactic acidosis and hyperalaninemia. Deficient activity of the pyruvate dehydrogenase complex was found in his platelets (about 25% of normal) and of pyruvate dehydrogenase in his biopsied muscle (about 5% of normal). A muscle biopsy specimen showed an increased proportion of type IIC fibers (24%), fiber-type grouping and lipid droplet accumulation.

Rapid atrophy of mouse soleus muscles after tenotomy depends on an intact innervation

Changes in length and mass of mouse soleus muscles have been determined during the first 14 days after division of the Achilles tendon and/or the tibial nerve. Muscle atrophy and associated histological changes were detectable 24 h after tenotomy, and increased progressively over the first week. These changes were less marked in muscles which had also been denervated, and were rapidly reversed if the tendon became reattached. An attempt is made to distinguish the role of the nerve supply from the effects of reduced longitudinal tension in the production of atrophy after tenotomy.

Histochemical and morphometric evaluation of skeletal muscle of cachectic sheep

Skeletal muscle of sheep was examined histochemically in an attempt to define muscle fiber populations capable of distinctive biological behavior. ATPase at alkaline and acid pH, NADH-TR, and succinic dehydrogenase showed at least 12 fiber types, but only three often enough to be considered biologically important muscle fiber populations. The proportions of the three major types altered during early life, but not perceptibly during adult life. Proportions of Type I and Type II fibers were different, sometimes significantly, from breed to breed. Histochemical techniques and morphometric analyses of fiber cross-sectional area were used to study muscle fiber changes in moderate to marked cachectic atrophy. Progressive reduction of gross muscle volume was attended by complex interrelationships between the two major muscle fiber types, including alternate episodes of atrophy and hypertrophy, resulting in marked inequality of mean fiber size between the fiber types. The patterns appeared to be different but characteristic for each muscle. The usual pattern of cachectic atrophy shows atrophy resistance of Type I fibers, but here a Type II-dominant atrophy also was seen. It is concluded that the large muscle fibers often seen in advanced cachectic atrophy are those Type I fibers that are most labile in both atrophy and hypertrophy than most.

The adaptive response of skeletal muscle to increased use

Skeletal muscle undergoes profound changes in morphological, physiological, and biochemical character when subjected to prolonged periods of increased use. Although increased use may be brought about in a variety of ways, the results show consistent features. In particular, endurance exercise and chronic stimulation differ only in degree: the properties which change in response to exercise are also those which change at an early stage of stimulation; the properties which are resistant to change under exercise conditions change only after prolonged stimulation. There is therefore a hierarchy of stability in the properties of skeletal muscle which is revealed in its response to changing functional demands. The adaptive potential of muscle provides a logical framework for understanding neural influences on the emergence of fiber types during muscle development. It is also relevant to the study of pathological conditions which may involve a sustained departure from normal postural and locomotor patterns of activity.

Patterns of abnormal histochemical fibre type differentitation in human muscle biopsies

The histochemical profile of individual human skeletal muscle fibres was analysed by correlating mitochondrial oxidative enzyme activity and that of myofibrillar ATPase at pH 9.5 and after pre-incubation at pH 4.3 and pH 4.6. In normal control muscle, only a small percentage of fibres did not conform to one or other of the normal variants of Type I and Type II fibres. In biopsies from early cases of Werdnig-Hoffmann disease, the denervated fibre populations contained many abnormal Type I and Type II fibres, including "IIc" fibres, but the basic distinction between Type I and Type II was preserved. However, in infantile spinal muscular atrophy patients aged two years and over, this distinction was progressively lost, leading to the total dedifferentiation of the atrophied fibres. In the Kugelberg-Welander form of spinal muscular atrophy, many of the constituent fibres of re-innervated groups displayed normal or near-normal histochemical profiles, but chronically denervated fibres became totally dedifferentiated. In Duchenne dystrophy, the spectrum of histochemical types appeared to be more continuous due to the emergence of fibres with properties intermediate between those of the normal variants, but the basic distinction between Type I and Type II fibres was preserved in the majority of cases. The percentage of severely abnormal fibres was higher in Type II than Type I and probably contributed to the observed decrease in the overall proportion of Type II fibres. Although very small atrophied fibres were observed in biopsies from cases of Becker and Duchenne dystrophy, these did not show the total dedifferentiation seen in the chronically denervated fibres in cases of spinal muscular atrophy.

Adaptive transformation of rat soleus motor units during growth

Soleus motor units of 5 and 34 week-old rats, weighing 150 and 520 g respectively, were examined for contraction time at 36 degrees C, innervation ratio as well as cross-sectional area, ATPase and SDH activity of fibres. The muscle was continuously adjusted to the growth of the animal. Between 5 and 34 weeks the proportion of Type II fibre units with 15-26 msec contraction time decreased from 33% to 10% and Type I fibre units with 27-40 msec contraction time thus increased from 67 to 90%. This was parallelled by approximately the same relative changes in number of Type II and Type I fibres.

Analysis of fiber types in the pigeon's metapatagialis muscle. II. Effects of denervation

The pigeon's metapatagialis muscle consists of three slips, two twitch and one tonic, and these slips are distinguishable at the gross anatomical level. Comparative studies of denervation are facilitated because the two fiber types are under the same mechanical forces, can be denervated as one muscle, and can be distinguished after denervation. Both fiber types atrophied after denervation, with the twitch fibers having a more variable response. Pathological alterations observed by light microscopy suggested that the twitch fibers were more affected by denervation than the tonus fibers. Ultrastructurally, both fiber types showed the same changes, with the twitch fibers again being more consistently altered. Proliferation of the transverse tubular system and sarcoplasmic reticulum were more marked in the tonus than twitch fibers, and the sarcoplasmic reticulum proliferated prior to the transverse tubules. Filament and fibril degeneration, peripheral and central degeneration, lysosomes and their derivatives, and satellite cell proliferation were common to both fiber types. Contracture knots were common to the denervated fibers, and were suggested to be characteristic of degenerating fibers. Degenerating motor end plates were observed, and most neurons in the fibers were naked, lacking myelin sheaths. The results are discussed in relation to the function of the neuron in maintaining the muscle, and the possibility of denervation inducing a transformation of tonic to twitch fibers.