The muscle spindle in cortisone-induced muscular atrophy

The muscle spindles in serially sectioned rat extensor digitorum longus (EDL) and soleus (SOL) muscles were studied histologically and histochemically after chronic cortisone administration. Nuclear chain fibers were found to be significantly atrophied in the EDL but not in the SOL. Nuclear bag fibers were not significantly affected in either muscle. Nuclear chain fibers all stained darkly with the pH 9.4 myofibrillar adenosine triphosphatase (ATPase) reaction (type II) and also stained darkly with the succine dehydrogenase (SDH) reaction. Nuclear bag fibers showed mostly light ATPase staining (type I) and dark, light, or intermediate SDH staining. Extrafusal fibers showed preferential type II fiber atrophy in EDL with relative sparing of type II fibers in SOL. The results suggest that histochemical characteristics that we have evaluated are alone insufficient to explain the differential susceptibility of skeletal muscle fibers to corticosteroids and, therefore, do not in themselves define either a myopathic or neurogenic etiology for the observed muscle wasting.     

Effects of tenotomy on muscles reinnervated by a foreign nerve

Tenotomy of the rat soleus (SOL) and gastrocnemius (MG) muscles produces a central degeneration in slow fatigue-resistant fibers, but not in similar fibers of muscles in the extensor and peroneal compartments. To investigate the part that innervation plays in rendering a particular fiber type in a particular muscle susceptible to this degeneration, the SOL, extensor digitorum longus (EDL), and MG muscles were experimentally reinnervated by foreign nerves and tenotomized. When the SOL was reinnervated by the common peroneal nerve, slow fatigue-resistant fibers showed lesions, but when the EDL was reinnervated by the nerve to the SOL, no lesions were found after tenotomy. When the MG was reinnervated by the nerve to the SOL, slow fatigue-resistant fibers that had differentiated in regions normally occupied almost entirely by fast fatigable fibers showed characteristic lesions. These results show that the failure of tenotomy to produce lesions in the EDL is not due to the nature of its innervation and that a fiber type not normally susceptible to the degenerative change will become susceptible when transformed to the slow fatigueresistant type.     

Core myofibers and related alterations induced in rats' soleus muscle by immobilization in shortened position

Experimental induction of core myofibers by tenotomy or local tetanus suggests that mechanical factors such as muscle tension loss, shortening or immobilization may play a role in core fiber formation. To test this hypothesis, we investigated the morphologic alterations induced in soleus (SOL) and extensor digitorum longus (EDL) muscles following immobilization of rats' hindlimb in various positions. The SOL and EDL muscles were immobilized in either shortened or lengthened state by applying wire-meshed plaster cast for 1, 2 and 3 weeks. The muscles were dissected out, measured, weighed and examined by histochemistry and electron microscopy. Gross atrophy was noted in all muscles but was greatest in shortened SOL. The SOL atrophy was diffuse and associated with relative increase in type 2 fibers. In EDL, the atrophy selectively involved fibers with low oxidative enzyme activity. Core myofibers were seen mainly in shortened SOL and consisted of myofibrillar derangement, loss of myofilaments and streaming of Z bands. The preferential involvement of shortened SOL (tonic, fatigue-resistant, slow-twitch muscle) suggests that the functional length, loss of tension subsequent to shortening and intrinsic biochemical properties of the muscle are important in core fiber formation.     

Expression of myosin heavy chain isoforms in stimulated fast and slow rat muscles

The expression of 4 myosin heavy chain (MHC) isoforms was analyzed in the rat soleus (SOL) and extensor digitorum longus (EDL) muscles after denervation and chronic electric stimulation. The stimulation frequencies used were 20 and 150 Hz and the amount of stimulation was either large (20 Hz), intermediate (150 Hz), or small (150 Hz). These patterns resemble some features of normal motor unit activity in SOL and EDL of freely moving rats (Hennig and L?mo, 1985). The relative expression of each MHC isoform depended strongly on the stimulation pattern. Furthermore, for any particular stimulation pattern, fibers in SOL and EDL expressed different MHCs. Coexistence of different MHC types in the same fiber was frequently observed in stimulated muscles. 20-Hz stimulation preserved normal expression of type 1-MHC in SOL but failed to induce type 1-MHC in type 2 fibers of the EDL, where type 2A- and 2X-MHC expression dominated and type 2B-MHC expression was completely suppressed. 150-Hz low-amount stimulation preserved nearly normal 2B-MHC expression in many type 2 fibers of the EDL but failed to induce type 2B-MHC expression in the SOL, where 2X-MHC became predominant. 150-Hz high-amount stimulation differed from 150-Hz small amount stimulation by suppressing almost all type 2B-MHC expression in EDL and by inducing considerable type 2A-MHC expression in the SOL. Scattered fibers in EDL that were probably the original type 1 fibers responded differently from both type 2 fibers in the EDL and from type 1 fibers in the SOL to stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the cholinergic system of rat sciatic nerve and skeletal muscle following suspension-induced disuse

Muscle disuse-induced changes in the cholinergic system of sciatic nerve, slow-twitch soleus (SOL), and fast-twitch extensor digitorum longus (EDL) muscles were studied in rats. Rats with hind limbs suspended for 2 to 3 weeks showed marked elevation in the activity of choline acetyltransferase in sciatic nerve (38%), in the SOL (108%), and in the EDL (67%). Acetylcholinesterase (AChE) activity in the SOL increased 163% without changing the molecular forms pattern of 4S, 10S, 12S, and 16S. No significant (P greater than 0.05) changes in the activity and molecular forms pattern of AChE were seen in the EDL or in AChE activity of sciatic nerve. Nicotinic receptor binding of [3H]acetylcholine was increased in both muscles. When measured after 3 weeks of hind limb suspension the normal distribution of type I fibers in the SOL (87%) was reduced (to 58%) and a corresponding increase in types IIa and IIb fibers occurred. In the EDL no significant change in fiber proportion was observed. Muscle activity, such as loadbearing, appeared to have a greater controlling influence on the characteristics of the slow-twitch SOL muscle than on the fast-twitch EDL muscle.     

Changes of myosin and its ATPase in "neuronally" and "mechanically" contralateral muscles after cross-reinnervation in normal and capsaicin-treated rats

The extensor digitorum longus (EDL) muscle was cross-reinnervated by the soleus (SOL) nerve in normal and neonatally capsaicin-treated rats. After 5 months the muscles were investigated for their myofibrillar ATPase reaction and their myosin light and heavy chain composition. Besides the well known transformation of the cross-reinnervated EDL toward a slow muscle, muscular changes were also found in the contralateral leg. Although these changes were hardly detectable in the EDL muscle, a remarkable (70 to 100%) reduction of the fast type IIA fiber population was found in the SOL. The decrease of the number of IIA fibers (compared with time-matched controls) was paralleled by corresponding changes in the myosin light and heavy chain patterns. After the cross-reinnervation of a muscle, two kinds of contralaterality must be distinguished. In the experiments reported the cross-reinnervated EDL muscle remains "mechanically" contralateral to the EDL muscle of the other leg, while it becomes "neuronally" contralateral to the SOL muscle. Our results are interpreted as a symmetric "slowing down" of these "neuronally" contralateral muscles. Neonatal capsaicin treatment that decreased considerably the number of unmyelinated group IV afferent fibers did not influence the outcome of these experiments.     

Electrophysiologic differences between mouse extensor digitorum longus and soleus

Miniature end-plate potentials (MEPPs) and indirectly elicited action potentials were recorded in vivo at 37°C from surface fibers of the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus (SOL) muscles of 3- to 4-month-old Bar Harbor 129 mice. The EDL MEPPs exhibited a significantly higher frequency, smaller amplitude, and shorter duration than the MEPPs of the SOL. Action potentials of EDL fibers exhibited a significantly greater amplitude and shorter duration than SOL fibers. A single stimulus elicited several action potentials from an EDL fiber but only one action potential from a SOL fiber. Fast- and slow-twitch muscle fibers can thus be identified and distinguished on the basis of these electrophysiologic parameters. There was no significant difference in resting membrane potentials between EDL and SOL fibers.     

Contractile properties, fiber types, and myosin isoforms in fast and slow muscles of hyperactive Japanese waltzing mice

This study focuses on the effects of neuromuscular hyperactivity on the contractile properties, fiber type composition, and myosin heavy chain (MHC) isoform expression of fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus (SOL) muscles in Japanese waltzing mice (JWM) of the C57BL/6J-v2J strain. The same properties were studied in the homologous muscle of control CBA/J mice (CM). In comparison to CM, the JWM exhibited (i) longer activity periods, prolonged bouts of running and a higher food intake, (ii) slower twitch and tetanic contractions of both EDL and SOL muscles, decreased cold and post-tetanic potentiation of the EDL, as well as increased cold and post-tetanic depressions of the SOL. Electrophoretic analyses of MHC isoform revealed a shift toward slower isoforms in both EDL and SOL muscles of JWM as compared to the homologous muscles of CM, namely, a shift from the fastest MHCIIb to the MHCIId/x isoform in the EDL muscle and a shift from MHCIIa to MHCI in the SOL muscle. The latter also contained a higher percentage of type I fibers and displayed a higher capillary density than the SOL muscle of CM. These findings show that the inherently enhanced motor activity of the JWM leads to fiber type transitions in the direction of slower phenotypes. JWM thus represent a suitable model for studying fast-to-slow fiber transitions under the influence of spontaneous motor hyperactivity.     

Effect of hind-limb suspension on young and adult skeletal muscle. II. Dystrophic mice

Disuse atrophy induced by limb immobilization reportedly protects dystrophic mouse muscle from histopathological changes. This study was conducted to determine whether disuse atrophy induced by hind-limb suspension (HS) limits the histopathology and contractile abnormalities typically observed in the dystrophic mouse. Two weeks of hind-limb suspension were applied to dystrophic mice (line 129B6F1) at two ages, 4 weeks (6 mice) and 12 weeks (8 mice). Thirty-one untreated dystrophics served as controls. In general, HS exaggerated the dystrophic signs, especially in the younger mice; it reduced animal weight, muscle weight, maximum tetanic and twitch tensions, and rates of tetanic and twitch tension development. HS further slowed the contractile properties of soleus (SOL) and extensor digitorum longus (EDL) muscles, and increased their fatigue resistance. HS reduced the size of type I and IIA fibers in the 6-week SOL and EDL, but not in the 14-week muscles. HS produced a preferential atrophy of SOL type I fibers, with a parallel increase in type IIA fibers. However, it did not alleviate the fiber size variability, degree of necrosis, central nucleation, inflammation, or muscle fibrosis in dystrophic muscles. These data demonstrate that disuse by hind-limb suspension does not prevent the histopathological deterioration or loss of muscle function in 6- and 14-week dystrophic mice.     

Temperature dependence of contraction characteristics in developing rat muscles

Contractions of rat extensor digitorum longus (EDL, a fast muscle) and soleus (SOL, a slow muscle) muscles of different ages (1-4 weeks) were recorded in vitro with direct stimulation and at different temperatures (range 35-10 degrees C). Twitch tension in 4-week-old EDL muscle increased in cooling from 35 to 20 degrees C (cooling potentiation); the tension decreased in further cooling below 20 degrees C. This pattern of temperature dependence of twitch tension was seen in fast muscles of all ages (1-4 weeks). Twitch tension in 4-week-old SOL muscle decreased monotonically in cooling from 35 to 10 degrees C (cooling depression). This pattern of cooling depression was not clearly evident in younger SOL muscles. There was a marked hysteresis in the temperature dependence of twitch tension in the 1-week-old SOL muscles. Tetanic tension was depressed by low temperature in both EDL and SOL muscles at 1 week and at 4 weeks of age. Results show that the processes concerned with contractile activation are nearly fully developed in the fast muscle fibers at an early age (1 week), whereas they develop later in the slow muscle fibers.     

Putative effects of nerve extract on carbonic anhydrase III expression in rat muscles

Carbonic anhydrase III (CA III), the predominant CA isoform in skeletal muscle is very sensitive to neuronal influences. We aimed to determine whether CA III expression could be influenced by neurotrophic factor(s) present in sciatic nerve extract (SNE). Intact muscles were thus compared with denervated soleus (SOL), extensor digitorum longus (EDL), and tibialis anterior (TA) muscles injected daily for 7 days with saline solution (SS) or with SNE. CA III activity was significantly increased in SS-treated EDL and TA muscles compared to control (CTR), while SNE injections partially prevented this increase. There was no significant difference for CA III activity in the SOL between CTR, SS, and SNE groups. The CA III mRNA increase observed in response to denervation was reduced by 40% in SNE-treated EDL and TA muscles. While SOL CA III mRNA level was not affected by denervation, a 52% decrease was observed with SNE. We concluded that neuronal modulation of CA III expression in type II fibers may involve a neurotrophic component. © 1994 John Wiley & Sons, Inc.     

Comparison of contractile properties between developing and regenerating soleus muscle: Influence of external calcium concentration upon the contractility

In newborn rat skeletal extensor digitorum longus (EDL) muscle, it has been found that an influx of calcium from the extracellular medium is necessary for contraction, in contrast to the situation observed in adult EDL muscle. The aim of the present study was to determine the influence of the extracellular calcium concentration ([Ca]o) upon the contractile responses elicited in developing as well as in regenerating (notexin-injected) soleus (SOL) muscle. A morphological study was performed to follow the steps of postnatal development and regeneration in SOL muscle. In nominally calcium-free solution, the amplitudes of the twitch and tetanic tensions were greatly reduced in 1–14-day-old developing SOL muscles, as well as in notexin-injected SOL muscles. With longer times after birth, twitch and tetanic tensions of SOL muscle were less affected by the absence of calcium. This contrasts with notexin-injected SOL muscle in which the amplitudes of the contractions remained strongly dependent on [Ca]o. The present finding suggests that some functional characteristics are different in regenerating muscle fibers and may be of interest in the evaluation of the contractile properties of muscles in which injections of genetically engineered or not autologous myoblasts or viral vector have been performed. © John Wiley & Sons, Inc.     

Satellite cells in slow and fast rat muscles differ in respect to acetylcholinesterase regulation mechanisms they convey to their descendant myofibers during regeneration

The hypothesis of satellite cell diversity in slow and fast mammalian muscles was tested by examining acetylcholinesterase (AChE) regulation in muscles regenerating (1) under conditions of muscle disuse (tenotomy, leg immobilization) in which the pattern of neural stimulation is changed, and (2) after cross-transplantation when the regenerating muscle develops under a foreign neural stimulation pattern. Soleus (SOL) and extensor digitorum longus (EDL) muscles of the rat were allowed to regenerate after ischemic-toxic injury either in their own sites or had been cross-transplanted to the site of the other muscle. Molecular forms of AChE in regenerating muscles were analyzed by velocity sedimentation in linear sucrose gradients. Neither tenotomy nor limb immobilization significantly affected the characteristic pattern of AChE molecular forms in regenerating SOL muscles, suggesting that the neural stimulation pattern is probably not decisive for its induction. During an early phase of regeneration, the general pattern of AChE molecular forms in the cross-transplanted regenerating muscle was predominantly determined by the type of its muscle of origin, and much less by the innervating nerve which exerted only a modest modifying effect. However, alkali-resistant myofibrillar ATPase activity on which the separation of muscle fibers into type I and type II is based, was determined predominantly by the motor nerve innervating the regenerating muscle. Mature regenerated EDL muscles (13 weeks after injury) which had been innervated by the SOL nerve became virtually indistinguishable from the SOL muscles in regard to their pattern of AChE molecular forms. However, AChE patterns of mature regenerated SOL muscles that had been innervated by the EDL nerve still displayed some features of the SOL pattern. In regard to AChE regulation, muscle satellite cells from slow or fast rat muscles convey to their descendant myotubes the information shifting their initial development in the direction of either slow or fast muscle, respectively. The satellite cells in fast or slow muscles are, therefore, intrinsically different. Intrinsic information is expressed mostly during an early phase of regeneration whereas later on the regulatory influence of the motor nerve more or less predominates. © 1994 Wiley-Liss, Inc.     

Muscle-specific beta-enolase concentrations after cross- and random innervation of soleus and extensor digitorum longus in rats

The concentration of beta-enolase, a highly specific marker of the skeletal muscle of rats, was determined in a slow-twitch muscle, the soleus (SOL) and a fast-twitch muscle, the extensor digitorum longus (EDL) after cross-innervation, random reinnervation, or denervation. The beta-enolase concentration is normally high in EDL and low in SOL. When the nerves entering into these muscles were cross-sutured, the beta-enolase concentration in EDL decreased and that in SOL increased to reach an almost equal value in 20 weeks and by the 35th week the SOL ultimately had a higher beta-enolase concentration than the EDL. When the sciatic nerve trunk was completely transected and sutured immediately, the beta-enolase concentration in EDL decreased and that of SOL increased; in 20 weeks SOL had a beta-enolase concentration similar to that of the EDL. When these muscles were denervated by cutting the sciatic nerve trunk, their beta-enolase concentrations were markedly lowered, but EDL still retained on the 12th week a beta-enolase value comparable to the normal SOL. Possible mechanisms behind the observed changes in beta-enolase concentration are discussed.     

Histochemical and morphometrical analysis of skeletal muscle in spontaneous diabetic WBN/Kob rat

Spontaneous diabetic WBN/Kob rats develop diabetic peripheral neuropathy characterized by primary segmental demyelination and secondary axonal degeneration. The objective of this study was to evaluate the histochemical and morphometric characteristics of the lesions of skeletal muscles innervated by the affected nerves in diabetic rats. The following groups of rats were investigated: 24-month-old males that had been diabetic for less than 12 months, 10-month-old pre-diabetic males, 24-month-old non-diabetic females, and 10-month-old nondiabetic females. The soleus (SOL), extensor digitorum longus (EDL) and biceps femoris (BF) muscles were studied by light and electron microscopy, including histochemical and morphometric analyses. Muscle weight was reduced with age to a remarkable degree in diabetic BF and EDL. Dispersed atrophy of muscle fiber was observed in type 2a fibers of BF and EDL, and type 2c fibers of SOL, and the incidence was higher in diabetic rats. Multi-core, myofibrillar disorientation and an increased number of central nucleus of SOL, along with connective tissue proliferation of BF perimysium were noted in diabetic rats. The fiber population and type of composition varied with age, but no remarkable changes attributable to diabetic conditions were observed. Electron microscopically, an abnormal arrangement of myofibrils, a number of myelin figures, mitochondrial swelling and lysis of mitochondrial cristae were seen in diabetic rats. However, the neuromuscular junction and capillaries were intact. These findings indicate that the diabetic skeletal muscle lesion in WBN/Kob rats was mainly myogenic in nature, and was aggravated by the age-related change.     

A maturational defect in passive membrane properties of dystrophic mouse muscle

Electrical properties, component ionic conductances, and histochemical characteristics of normal and dystrophic (dy^2J/dy^2J) mouse extensor digitorum longus (EDL) and soleus (SOL) muscles were studied between 1 and 6 months of age. Normal EDL and SOL membrane electrical parameters were indistinguishable at 1 month. Between 1 and 3 months, membrane resistance (R_m) in normal EDL decreased progressively to a mature value one-half that found in SOL muscles. Measurements of component conductances indicated that this decrease in R_m was due to a specific increase in membrane chloride conductance (G_C1) in EDL fibers. During the same time membrane capacitance increased slightly in both EDL and SOL. Dystrophic EDL failed to develop fully the changes in membrane resistance seen in controls, showing significant deviation at all time points beyond 1 month. An abnormal high-resistance subpopulation was evident in R_m histograms of mature dystrophic EDL. Average membrane properties of dystrophic SOL appeared normal during the 6-month interval studied but significant changes in R_m histograms were found. Histochemical analysis of normal and dystrophic EDL showed that both contained almost exclusively type II fibers (> 95%); normal and dystrophic SOL contained a nearly equal mixture of type I and type II fibers. Progressive degenerative changes were seen in both dystrophic muscles with age but were more severe in the SOL. The depressed average G_C1 in the dystrophic EDL was due to a subpopulation of fibers (30% of total) having a high membrane resistance. Denervation was ruled out as a cause for this subpopulation by a lack of correlation between membrane resistance and resting potential. Histochemical evidence eliminated the possibility that this subpopulation was composed of slow-twitch fibers. Data are presented indicating that the subpopulation represents a group of dystrophic EDL fibers which fail to undergo normal maturation.     

Long-term effects of estrogen on rat skeletal muscle

The long-term effects of estrogen on the development of rat extensor digitorum longus (EDL) and soleus (SOL) muscles were examined using physiological and histochemical methods. The rats were in three groups: group 1, ovariectomized; group 2, sham-operated; and group 3, ovariectomized followed by estradiol administration. Isometric twitch and tetanic tensions of both the EDL and SOL obtained from 10-week-old rats were evoked by electrical stimulation. The isometric twitch tensions of the EDL in groups 2 and 3 were significantly lower than in group 1, however, there was no significant differences in isometric twitch tensions of the SOL among the three groups. The isometric tetanic tensions of the EDL in groups 2 and 3 were also significantly lower than in group 1, and the isometric tetanic tension of the SOL in group 3 was significantly lower than in group 1. There were no changes in the total number of muscle fibers or in the ratios of fiber types. But the mean fiber diameter of all fiber types (particularly in types IIA and IIB) was significantly lower in group 3 than in groups 1 and 2. Therefore, the possibility that estrogen may play an inhibitory role in the development of skeletal muscle fibers has to be considered.     

Effect of hind-limb suspension on young and adult skeletal muscle. I. Normal mice

The purpose of this study was to determine the effect of hind-limb suspension (HS) on morphometric, histologic, and contractile characteristics of fast extensor digitorum longus (EDL) and slow soleus (SOL) twitch muscles in adult and immature mice. Hind-limb suspension for 2 weeks was used to produce atrophy in two groups of mice, ages 4 and 12 weeks, with nonsuspended animals serving as controls. Young HS mice exhibited marked decreases in SOL weight, length, cross-sectional area (CSA), twitch and tetanic tensions, and rates of tension development and relaxation, with increases in fatigue resistance. HS reduced the diameter of both type I and IIA fibers, increased the percentage of type I fibers, and decreased the percentage of type IIA fibers in both young and adult SOL. Muscle weight, length, CSA, IIA and IIB fiber areas, and maximum rate of tetanic tension development were decreased in EDL of young HS mice; fatigue resistance and EDL half-relaxation times were increased. For most parameters evaluated, slow twitch muscle was more affected than fast twitch. HS affected contractile characteristics less than morphometric or histologic parameters. Rates of tension development and relaxation were the contractile parameters most affected by HS, and the time parameters of contraction were least affected. For all measurements young mice were more affected than adult mice.     

Morphology of stable muscle grafts of rats: effects of gender and muscle type

Our purpose was to quantify morphological characteristics of extensor digitorum longus (EDL) and soleus (SOL) muscle grafts in female (N = 8) and male (N = 8) rats. Muscles were grafted orthotopically, with the nerve remaining intact, and were studied 56 days later. The mass of EDL and SOL grafts and control muscles of females was 60% to 65% of male values; this difference was directly related to gender differences in body mass. The fiber composition of EDL and SOL grafts did not differ from control, and no gender effects were noted. The mean fiber area (MFA) of control EDL and SOL muscles of females averaged 65% of male values. The MFA of grafts did not differ due to gender, and averaged 60% of control value for SOL and 70% for EDL grafts. We conclude there are no substantial differences in the regenerative capacity of EDL and SOL muscles grafted with the nerve intact.     

Fiber type susceptibility in the dystrophic mouse

Slow-twitch soleus (SOL) and fast-twitch extensor digitorum longus (EDL) muscles from young normal and dystrophic ( ) mice were examined histochemically. Counts were made of total fiber content and of the proportions of various fiber types in whole cross sections. By 3 weeks of age the number of fibers in the SOL of dystrophic mice decreased by 16%. The proportions of both type I and type II_ox fibers decreased approximately equal amounts. Even at this relatively early stage of the disease process, almost 20% of the fibers appeared abnormal and could not be clearly identified as belonging to a specific fiber type. Very few type I fibers with dystrophic characteristics were seen. However, this may simply reflect an alteration in staining characteristics which preceded structural changes in involved fibers. In 6- to 7-week-old EDL muscles the most marked change occurred in the proportion of type II_glyc fibers. The percentage of these fibers in dy^2J mice was 8.4% compared with 57.3% in control animals. At this stage the total number of fibers in dy^2J EDL had decreased by 30%, although the number of type II_ox fibers remained virtually constant. Various explanations for these findings are considered.