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PubMed2000

Fiber types in the mouse levator auris longus muscle: a convenient preparation to study muscle and nerve plasticity.

The histochemical composition of the levator auris longus (LAL) muscle has been investigated in adult NMRi mice. Histochemical reaction for myofibrillar adenosine triphosphatase (ATPase) after preincubation in alkaline and acidic media, nicotine amideadenine-dinucleotide dehidrogenase (NADH-dehydrogenase), and alpha-glycerophosphate dehydrogenase were performed on cryosections of LAL muscle. Expression of myosin heavy chain (MyHC) isoforms was detected with the immunoperoxidase method applying monoclonal antibodies against MyHC isoforms -1, -2a, -2x/d, and -2b, as well as by sodium dodecylsulfate (SDS) glycerol gel electrophoresis. The muscle was proven to be a pure fast-twitch muscle. The most numerous fibers in LAL muscles contained MyHC-2b and some MyHC-2a. Histochemically, pure IIA fibers with oxidative metabolism and pure IIB fibers with glycolytic metabolism were detected. In contrast to the majority of mature control muscles, numerous hybrid fibers coexpressing MyHC-2x/d with MyHC-2a or MyHC-2b were present. Both hybrids were oxidative-glycolytic; additionally, some hybrids containing MyHC-2a were oxidative. In one out of six muscles, traces of MyHC-1 were detected both with immunoperoxidase staining and with SDS glycerol gel electrophoresis. Rare fibers that exceptionally expressed small amounts of MyHC-1 always coexpressed MyHC-2a, which is an additional proof that pure type I fibers do not exist in LAL. Due to these histochemical characteristics and to its previously described morphological features, the use of the LAL muscle as a model for various studies, particularly muscle and nerve interactions, is emphasized.

Animals↗

PubMed1996

Levator ani muscle in women with genitourinary prolapse: indirect assessment by muscle histopathology.

The objective of this study was to assess the state of innervation in levator ani muscle sites using muscle histopathology. Asymptomatic women and patients with genitourinary prolapse were included. Histopathologic analysis allows indirect assessment of a muscle's innervation. Therefore, levator ani muscle was collected in a standardized fashion during abdominal surgery and frozen in the operating room using isopentane slush cooled by liquid nitrogen. Serial sections of levator ani muscle in cross-section were studied with standard histochemical and immunohistochemical techniques. The staining patterns from these histochemical techniques allowed quantitative determination of the ratios of fiber types I, IIA, and IIB and their fiber diameters. Objective assessment of fiber type grouping was performed. The distribution of both fiber type percentage and diameter were non-parametric. Therefore, the Mann-Whitney U-test was used to analyze the data for statistical differences between the means for these variables. There was no statistical difference in levator ani muscle fiber type percentage and diameter in patients with prolapse and/or urinary incontinence when compared to asymptomatic women. Levator ani muscles have a higher proportion of slow fibers (66%) than found in other human female muscle (48%). There was no evidence for denervation/reinnervation in any of the biopsy specimens. In this study, levator ani muscle biopsies from incontinent and/or prolapse patients were neither denervated nor reinnervated.

Adult↗

PubMed1983

Differences in muscle spindle structure between pigeon muscles used in aerial and terrestrial locomotion.

Muscle spindle density (number of spindles per gram of muscle) of all 29 muscles of the forearm and leg of the domestic pigeon was evaluated by counting receptors in van Gieson-stained serial cross sections. Extra- and intra-fusal fiber-type profiles were determined from histochemical preparations. Muscles of the leg had on the average significantly more avian slow-twitch oxidative extrafusal fibers (22.5 vs. 0.8%) and slower contraction times than muscles of the forearm, but fiber-type profiles and gross actions of muscles showed no consistent relation to the relative abundance of receptors. Differences in intrafusal fiber-type composition among spindles were sought because of their potential effect on the quality of the afferent discharge. The number of intrafusal fibers per spindle was on the average significantly less (4.57 vs 5.99) in the muscles of the leg than in those of the forearm; and of spindles with the same number of intrafusal fibers, those in the leg had smaller periaxial spaces. Distribution of intrafusal fiber types identified with the myofibrillar adenosine triphosphatase reaction differed among spindles of varying sizes. An acid- and alkali-labile type occurred most frequently (P = 0.05) in spindles with one to three intrafusal fibers, and an acid-labile and alkali-stable type was most often seen (P = 0.05) in spindles with 4 to 7 intrafusal fibers. The smaller receptors were more abundant in the leg, while the larger ones were about equally distributed between the two extremities. Muscle fibers with dimensions that sometimes approached small extrafusal fibers were present in about 3% of the axial bundles examined, most of them in the forearm. The selective morphological variation of avian muscle spindles may represent the structural basis for qualitatively different afferent discharges that relate to the characteristic types of locomotion served by the two extremities.

Animals↗

PubMed1994

Appearance of complex branched fibers following repetitive muscle trauma in normal rat skeletal muscle.

BACKGROUND: To examine whether the complex branched fibers observed in mdx mutant mice were formed in normal skeletal muscles, long-term repetitive muscle trauma was applied to muscle of normal Wistar male rats. METHODS: Three kinds of artificial muscle trauma--crush injury, bupivacaine hydrochloride treatment, and forced stretching of contracting muscle (eccentric contraction)--were performed once a week for 10 weeks to achieve a state of repetitive degeneration and regeneration in the muscles. Two weeks after the final treatment, numerical, histochemical, and three-dimensional analyses by scanning electron microscopy were performed. RESULTS: Mean numbers of total branched fibers of the three groups were increased compared with normal control values, especially in the bupivacaine treatment group (three- to fivefold greater than in the other two groups). Aggregations of fibers of the same type which usually appear in mdx mice were observed in various parts of histological sections of the bupivacaine treatment group and only in a part of the crush injury group. No aggregations were observed in sections of the forced stretching group. In the three-dimensional analysis, complex branched fibers appearing as an "anastomosing syncytial reticulum" were observed only in the bupivacaine treatment group. CONCLUSIONS: These findings suggest that the formation of an anastomosing syncytial reticulum is one of the adaptation mechanisms of normal skeletal muscle rather than a specific event in mdx mutant mice, and long-term repeated trauma of the same fiber is necessary for this formation. Adaptive changes in the muscles with the three different types of muscle trauma are discussed.

Animals↗

PubMed2001

Aberrant muscle between the temporalis and the lateral pterygoid muscles: M. pterygoideus proprius (Henle).

During examination of the positional relationships between the lateral pterygoid and the temporalis muscles and the innervating nerves, an aberrant muscle was observed in three of 66 head halves. The aberrant muscle originated from the medial surface of the anteromedial muscle bundle of the temporalis (Shimokawa et al. 1998, Surg. Radiol. Anat. 20:329-334) and inserted into the inferolateral surface of the lower head of the lateral pterygoid. Due to its location, origin and insertion this aberrant muscle slip is considered to correspond to the pterygoideus proprius described by Henle (1858, Handbuch der Anatomie des Menschen). Based on the innervation findings, the present aberrant muscle might be considered as a remnant muscle bundle between the anteromedial muscle bundle of the temporalis and the lateral pterygoid during differentiation of the lateral masticatory muscle anlage.

Adult↗

PubMed2006

Dual roles of tropomyosin as an F-actin stabilizer and a regulator of muscle contraction in Caenorhabditis elegans body wall muscle.

Tropomyosin is a well-characterized regulator of muscle contraction. It also stabilizes actin filaments in a variety of muscle and non-muscle cells. Although these two functions of tropomyosin could have different impacts on actin cytoskeletal organization, their functional relationship has not been studied in the same experimental system. Here, we investigated how tropomyosin stabilizes actin filaments and how this function is influenced by muscle contraction in Caenorhabditis elegans body wall muscle. We confirmed the antagonistic role of tropomyosin against UNC-60B, a muscle-specific ADF/cofilin isoform, in actin filament organization using multiple UNC-60B mutant alleles. Tropomyosin was also antagonistic to UNC-78 (AIP1) in vivo and protected actin filaments from disassembly by UNC-60B and UNC-78 in vitro, suggesting that tropomyosin protects actin filaments from the ADF/cofilin-AIP1 actin disassembly system in muscle cells. A mutation in the myosin heavy chain caused greater reduction in contractility than tropomyosin depletion. However, the myosin mutation showed much weaker suppression of the phenotypes of ADF/cofilin or AIP1 mutants than tropomyosin depletion. These results suggest that muscle contraction has only minor influence on the tropomyosin's protective role against ADF/cofilin and AIP1, and that the two functions of tropomyosin in actin stability and muscle contraction are independent of each other.

Actins↗

PubMed1985

Trigeminal mesencephalic neurons innervating functionally identified muscle spindles and involved in the monosynaptic stretch reflex of the lateral pterygoid muscle of the guinea pig.

Location of the neurons in the trigeminal mesencephalic nucleus innervating stretch receptors of the lateral pterygoid muscle and the mode of their synaptic connection on the lateral pterygoid motoneurons of the guinea pig were studied physiologically as well as morphologically, in comparison with the trigeminal mesencephalic neurons innervating muscle spindles in the superficial masseter muscle, with the following results: stimulation of the caudal half of the trigeminal mesencephalic nucleus evoked monosynaptic excitatory postsynaptic potentials in the ipsilateral lateral pterygoid motoneurons. Stimulation of the lateral pterygoid nerve directly evoked spike potentials in the neurons located in the caudal half of the ipsilateral trigeminal mesencephalic nucleus, which responded with increased firing to stretch, and with silent period to twitch, of the ipsilateral lateral pterygoid muscle. Averaging of intracellular potentials of the lateral pterygoid motoneurons with extracellular spike potentials of these trigeminal mesencephalic neurons revealed excitatory postsynaptic potentials after a monosynaptic latency, but no inhibitory postsynaptic potentials. Injection of horseradish peroxidase into the lateral pterygoid muscle labeled 15-20 cells in the caudal half of the ipsilateral trigeminal mesencephalic nucleus, while 174-228 cells retrogradely labeled by horseradish peroxidase were found throughout the whole rostrocaudal extent of the ipsilateral trigeminal mesencephalic nucleus following injection of horseradish peroxidase into the masseter muscle. It was concluded that neurons in the caudal half of the trigeminal mesencephalic nucleus send their peripheral processes to stretch receptors, presumably muscle spindles, in the ipsilateral lateral pterygoid muscle and that their central processes have excitatory synapses on ipsilateral lateral pterygoid motoneurons, thus comprising the afferent limb of a monosynaptic stretch reflex arc of the lateral pterygoid muscle of the guinea pig.

Animals↗

PubMed1989

Regeneration of muscle axons in the frog is directed by diffusible factors from denervated muscle and nerve tubes.

In the frog, peripheral muscle axons regenerate after a lesion to reinnervate the original synaptic sites on muscle fibers. Previous experiments in the frog have shown that satellite cells of the nerve tube direct the outgrowth of regenerating muscle axons over distances of many millimeters. In the present experiments, denervated muscle was used as a target for regenerating muscle axons. Muscle and satellite cells of the nerve tube also were placed in filters to determine if their influence on axonal outgrowth was exerted by diffusible factors. Filters were used with a pore size of 0.22 micron. With this pore size, target cells were isolated from physical contact with the surrounding cells; yet an exchange of fluids--and therefore of molecules released by the target cells--could occur across the filter. In the presence of denervated muscle or satellite cells of the nerve tube in filters, regenerating axons turn and grow toward the target cells. This influence on the direction of axonal outgrowth was produced over distances of 6 mm by muscles and 4 mm by cells of the nerve tubes. This directed outgrowth is in marked contrast to the random pattern of outgrowth in the absence of the targets. The present findings set the stage for tissue culture experiments in which the phenomena observed in vivo can be analyzed in terms of mechanisms. The present finding that denervated muscle attracts regenerating axons means that sufficient material may be available for the characterization and isolation of the relevant molecules.

Animals↗

PubMed1987

Distribution and innervation of short, interdigitated muscle fibers in parallel-fibered muscles of the cat hindlimb.

The cat hindlimb contains several long, biarticular strap muscles composed of parallel muscle fascicles that attach to short tendons. Three of these muscles--sartorius, tenuissimus, and semitendinosus--were studied by dissecting individual gold-stained fibers and determining the surface distribution of acetylcholinesterase-stained end-plate zones. In each muscle, fascicles were composed of muscle fibers that ran only part of the fascicle length and tapered to end as fine strands that interdigitated with other tapering fibers within the muscle mass. Most muscle fibers measured 2-3 cm in length. Fascicles of muscle fibers were crossed by short transverse bands of endplates (1 mm wide by 1-5 mm long) that were spaced at fairly regular intervals from the origin to the insertion of the muscle. The endplate pattern suggested that the fiber fascicles were organized into multiple longitudinal strips. In the sartorius, the temporospatial distribution of electromyographic (EMG) activity evoked by stimulating fine, longitudinal branches of the parent nerve confirmed that each strip was selectively innervated by a small subset of the motor axons. These axons appeared to distribute their endings throughout the entire length of the fascicles, providing for synchronous activation of their in-series fibers.

Action Potentials↗

PubMed2001

Physiological assessment of muscle strength in vitro after direct injection of doxorubicin into rabbit sternocleidomastoid muscle.

Doxorubicin chemomyectomy is a potent method for the permanent removal of a muscle or group of muscles after direct local injection, and has been used successfully to treat blepharospasm and hemifacial spasm patients. The efficacy of doxorubicin chemomyectomy on reducing muscle strength after direct injection of doxorubicin into rabbit sternocleidomastoid muscle was tested. One- and 6-month postinjection force assessment was performed in vitro to measure alterations in peak twitch and tetanic force generation, as well as fatigue responses for the treated muscles compared to control. There were significant reductions of both twitch and tetanic peak amplitudes in the doxorubicin-treated muscles. One month after treatment, the decreases in force were greater after 2 mg doxorubicin injections than after 1 mg doxorubicin. While there was a significant reduction in force generation after doxorubicin treatment, fatigue resistances for the doxorubicin-treated muscles were increased compared to the controls. There were significant reductions in muscle mass after doxorubicin treatment, and by 6 months, the myosin heavy chain isoform distribution was similar to normal sternocleidomastoid, except for an increase in slow myosin-positive fibers. Doxorubicin chemomyectomy resulted in a significant reduction in functional force generation in the treated sternocleidomastoid muscles. These findings suggest a potential clinical use of doxorubicin chemomyectomy to treat cervical dystonia patients.

Animals↗

PubMed2002

Effects of experimental muscle pain on electromyographic activity of masticatory muscles in the rat.

The aim of the present study was to investigate the effects of noxious chemical stimulation of a jaw muscle on postural electromyographic (EMG) activity from several masticatory muscles in lightly anesthetized rats. Unilateral injection of a substance known to induce acute muscle pain (5% NaCl) or longer duration of pain with inflammation (mustard oil) was made into the masseter muscle. The changes in EMG activity following the injection were recorded from the injected and contralateral masseter muscles and the ipsilateral digastric muscle. The algesic chemicals produced a significant but transient increase in EMG activity in all three muscles. The data from the present study and similar observations from clinical and experimental human studies suggest that increased activity from muscle nociceptors is not sufficient to produce a prolonged increase in postural EMG activity. Therefore, the development and maintenance of chronic jaw muscle pain does not appear to result from a feedback cycle mechanism.

Action Potentials↗

PubMed2003

Muscle fiber number in the biceps brachii muscle of young and old men.

We have compared the number of muscle fibers in the biceps brachii muscle (BB) of six old men (82.3 +/- 4.3 years) and six young men (21.2 +/- 1.9 years). Muscle fiber number was estimated by dividing the maximal area of the BB, determined with magnetic resonance imaging, by the mean fiber area of the BB determined in a muscle biopsy. The percentage of type II fibers in the BB ( approximately 60%) and the type I fiber area were not different between the groups. The BB area (-26%), type II fiber area (-24%), mean fiber area (-20%), and maximal voluntary contraction strength (MVC) of the elbow flexor muscles (-27%) were lower in the old than young group. However, the estimated number of muscle fibers was not significantly different between the young (253000) and old (234000) men. Consequently, the smaller BB area of the old men could be explained primarily by a smaller type II fiber size. These findings suggest that old age is not associated with a reduced number of muscle fibers in the BB. The relative contribution of a reduction in fiber number to age-related muscle atrophy may be muscle-dependent.

Adult↗

PubMed1992

Muscle fatigue measured with evoked muscle vibrations.

Skeletal muscle vibrates laterally during voluntary and evoked muscle contractions. We hypothesized that the vibration amplitude from evoked muscle twitches is directly related to evoked twitch force from fatiguing muscle. To test the hypothesis, vibrations produced by evoked muscle twitches were recorded during short (5-second) rest periods as the muscle was intermittently exercised with voluntary contractions. Trials were performed at 30%, 50%, and 70% of maximal voluntary contraction. Evoked muscle twitches eliminated the problems of motivation and tremor that complicate sound and vibration measurements during voluntary contractions. Results from the first dorsal interosseus hand muscle in 11 normal adult volunteers revealed that the vibration amplitude is highly correlated (r2 = 0.93, at 70% MVC, r2 = 0.97, at 50% MVC; r2 = 0.85, at 30% MVC) with force. Both potentiation and reduction of force with exercise were accompanied by parallel changes in vibration amplitude, as measured with an accelerometer. Compound muscle action potentials did not increase with exercise-induced twitch potentiation, and did not correlate as highly with force during fatigue.

Action Potentials↗

PubMed1995

Site-dependent pathological differences in smooth muscles and skeletal muscles of the adult mdx mouse.

This study presents a survey of the morphometric characteristics, the regeneration rate, and the extent of muscle dystrophy in several smooth and skeletal muscles from adult mdx mice, an animal model of the Duchenne muscular dystrophy (DMD). Smooth muscles from adult mdx mice showed neither cell necrosis nor fibrosis. As compared to control C57 mice, the thickness of the mdx smooth muscle was normal in the vascular and urogenital layers but significantly reduced in the digestive layers, a finding relevant to clinical reports of gastrointestinal dilatation in DMD patients, and suggesting that gastrointestinal dysfunctions should be systemically searched for in DMD patients. Adult mdx skeletal muscles, however, presented different patterns of muscle suffering: either absent (esophagus); very mild (trunk and limb muscles); or severe (diaphragm). In these three conditions we studied the fiber diameters, the nuclei locations, and the regeneration rate. From this comparative study, it seems that severe dystrophy occurs in muscle tissues showing large fiber diameter and peripheral location of the nuclei. We showed that this combination occurs in the mouse diaphragm which is thus a realistic model for human DMD muscles.

Animals↗

PubMed1996

Gap junctions are found between iris sphincter smooth muscle cells but not in the ciliary muscle of human and monkey eyes.

Physiological studies indicate that in primate ciliary muscle there is little or no spread of electrical activity from cell to cell. To clarify to what extent primate intraocular smooth muscles express the structural correlate of electrical coupling, the localization of gap junctions in the ciliary and the iris sphincter muscle of human and monkey (Macaca fascicularis) eyes was analysed using electronmicroscopy and connexin43 immunocytochemistry. With both methods, numerous gap junctions were identified in the iris sphincter of both species, while no such junctions were observed between individual smooth muscle cells in the ciliary muscle. Both ciliary and iris sphincter smooth muscle cells were connected by numerous adherens-type junctions. These results further underline that primate ciliary muscle is an atypical smooth muscle which shares many common features with striated skeletal muscle.

Aged↗

PubMed1994

[Electromyographic activity of the external anal sphincter muscle and the puborectal muscle in the defecation test in patients with obstructive defecation disorders].

In a prospective electromyographic and manometric study on 23 women (average age 52 years) with obstructive defecation disorder the activity of the external anal sphincter muscle and the puborectal muscle was investigated at rest and during contraction and straining. The control group consisted of 22 healthy women with an average age of 53 years. The main aim of the study was to investigate the functioning of the two muscles during simulated defecation (maximum strain) and to examine any changes in the pressure ratio in the rectum and the anal canal during this stimulation. There were no significant differences in the resting pressure, the contraction pressure and the straining pressure (in the rectum and the anal canal) between the two groups. The functioning of the puborectal muscle and the external anal sphincter muscle was largely the same in both the study group and the control group. No statistically significant differences were found between the two groups except in the amplitude of contraction. When we tried to list the change in the activity of the muscle as an index of anism, we were not able to objectify such a change for either the external anal sphincter muscle or the puborectal muscle. We therefore conclude that the increase in the activity of the voluntary muscle of the pelvic floor observed on electromyography during defecation does not indicate a pathologic condition but is a functional state.

Adult↗

PubMed1987

Muscle damage and repair in voluntarily running mice: strain and muscle differences.

Soleus, extensor digitorum longus and tibialis anterior muscles of mice voluntarily running in wheels for periods of 5 to 120 days were studied in spaced serial and serial cross-sections. Shortly after the onset of running and during the next 2 weeks, degeneration, necrosis, phagocytosis and regeneration of muscle fibers, satellite cell proliferation and cellular infiltration were found in soleus muscles of mice from all strains investigated (CBA/J, NMRI, C57bl, NIH, SWS and Balb/c). Tibialis anterior but not extensor digitorum longus muscles were also damaged. Predominantly high-oxidative fibers were affected (both slow-oxidative and fast oxidative glycolytic in soleus, fast-oxidative glycolytic in tibialis anterior). Denervated soleus muscles that had been passively stretched during running were not damaged. Evidence was found that, during the early period of running, split fibers form by myogenesis within (regeneration) or outside (satellite cell proliferation) necrotic muscle fiber segments. Split fibers persisted in solei of long-term (2 to 3 months) exercised CBA/J but not NMRI mice. In 6 out of 20 solei of CBA/J runners exercised for 2 months or longer, fiber-type grouping was observed in the areas where extensive damage usually occurred in the early periods. The results show that different muscles are damaged and repaired to varying degrees and that marked interstrain and inter-individual differences are present. It appears that acute muscle injury occurring upon onset of voluntary running is a usual event in the adaptation of muscles to altered use.

Animals↗

PubMed1991

The effect of muscle vibration on human position sense during movements controlled by lengthening muscle contraction.

Muscle vibration studies suggest that during voluntary movement limb position is coded by muscle spindle information derived from the lengthening, antagonist muscle. However, these investigations have been limited to movements controlled by shortening contractions. This study further examined this property of kinesthesia during movements controlled by lengthening contraction. Subjects performed a horizontal flexion of the right forearm to a mechanical stop randomly positioned at 30, 50 and 70 degrees from the starting position. The movement was performed against a flexor load (1 kg) requiring contraction of the triceps muscle. Vision was occluded and movements were performed under three conditions: no vibration, vibration of the right biceps and vibration of the right triceps. The perceived position of the right forearm was assessed by instructing subjects to simultaneously match the right limb position with the left limb. Vibration of the shortening biceps muscle had no effect on limb matching accuracy. However, triceps vibration resulted in significant overestimation of the vibrated limb position (10-13 degrees). The variability in movement distance was uninfluenced by muscle vibration. During movements controlled by lengthening contraction, there is a concurrent gamma dynamic fusimotor input that would enhance primary afferent discharge. Despite this additional regulating input to the muscle spindle, it appears that muscle spindle information from the lengthening muscle is important for the accurate perception of limb movement and/or position.

Adult↗