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PubMed1983

Intraabdominal pressure and trunk muscle activity during lifting--effect of abdominal muscle training in healthy subjects.

Isometric training of the abdominal muscles is recommended as a preventive measure against low back complaints in the hope that the increased strength of the abdominal muscles should result in an increased intraabdominal pressure when lifting. There is, however, neither experimental nor clinical proof of this hypothesis. Twenty healthy young men went through intense isometric training of the abdominal muscles for five weeks. Before and after training the subjects were put through a standardized test programme, measuring the strength of abdominal and back muscles, and a series of lifts, 10, 25, and 40 kg, leg lifts and back lifts. The intraabdominal pressure (IAP), and the EMG activity of the oblique abdominal muscles, and of the erector spinae muscle were recorded. It was found that: The strength of the trunk flexors increased markedly after training. The activity of the oblique abdominal muscles when lifting decreased after training, i.e. motor unit recruitment was not improved. The IAP at lifting was not affected by training. The activity of the oblique abdominal muscles was of no decisive importance to the IAP. The strength of the back muscles increased, but the activity of the back muscles at lifts was not affected by training. In back lifts there was no detectable activity of the back muscles during the beginning of the lifting and during a great part of the lowering. In back lifts the maximum activity of the abdominal muscles appeared long before the peak of the IAP which may be of importance with regard to the pathogenesis of inguinal hernia. Further investigation is needed, both to study the effect of training on patients with back complaints, and to study the factors determining the IAP.

Abdomen↗

PubMed1984

[Experimental study on free muscle transplantation--histological changes and functional recovery of transplanted muscles in relation to the duration of ischemia and denervation].

UNLABELLED: The purpose of this study was to clarify the influence of temporary ischemia and denervation on the characteristics of transplanted muscles. MATERIALS AND METHODS: The rectus femoris brevis muscle of white rabbit was used. Under an operating microscope, this muscle was mobilized preserving its feeding vessels, and the innervating nerve was severed at 1 cm proximal to the entrance of the muscle. Six groups were made as follows. Group D: The severed nerve was left as it was. Group S: The nerve was sutured immediately after severance. No treatment was made on the feeding vessels. Group SI: The artery and vein were clamped for 1, 2, 3 and 4 hours (group SI-1, 2, 3 and 4) after nerve repair. The proximal and distal tendon were reattached to their original place in every group. Examination I: Transplanted muscles were examined histologically and histochemically from 48 hours to 6 months. Motor end-plate was one of the targets of observation. RESULTS: Main patho-histological changes observed on the muscle and motor end-plates at one week were thought due to denervation, and the longer ischemic time caused more severe change in the group SI-3 and 4. Phagocytosis, destruction of muscle fibers and edema in the interstitial tissue were seen in these long ischemic time groups. A few motor end-plates in the group SI-3 and many of them in the group SI-4 were atrophic and their acetylcholinesterase (AChE) activity was low. Reduced nicotinamide-adenine dinucleotide-tetrazolium reductase (NADH-TR) and phosphorylase activity were reduced in all groups at one week. At 3 weeks, muscle atrophy was pronounced and was found earlier in type II fibers than in type I as a result of denervation. Pathological changes such as elongation, atrophy or segmentation and low AChE activity were observed in the motor end-plates of all groups at 3 and 6 weeks. These findings were more pronounced in the group SI-3 and 4. In all groups at 6 weeks, phosphorylase activity was found to be generally low but NADH-TR reaction stained a few regenerated muscle fibers. Although muscle atrophy was still observed at 9 weeks, recovery in size and shape and histochemical reaction was seen in all groups at this stage. These findings became more manifest at 15 weeks and almost normal appearance of muscle fibers was observed at 6 months. Interstitial connective tissue, however, increased, and necrotized muscle fibers were seen extensively in the group SI-3 and 4.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholinesterase↗

PubMed1995

Influence of muscle length on work from trabecular muscle of frog atrium and ventricle

The work capacity of segments of atrial and ventricular muscle from the frog Rana pipiens was measured as a function of muscle length using the work loop technique. Both the work done during shortening and the work required to re-lengthen the muscle after shortening increased with muscle length. Net work increased with length up to a maximum, beyond which work declined. The optimum sarcomere length for work output was 2.52.6 µm for both atrial and ventricular muscle. Isometric force increased with muscle length to lengths well beyond the optimum for work output. Thus, the decline in work at long lengths is not simply a consequence of a reduction in the capacity of heart muscle to generate force. It is proposed that it is the non-linear increase in work required to re-lengthen muscle with increasing muscle length which limits net work output and leads to a maximum in the relationship between net work and muscle length. Extension of the results from muscle strips to intact hearts suggests that the work required to fill the ventricle exceeds that available from atrial muscle at all but rather short ventricular muscle lengths.

Journal Article↗

PubMed1982

Differentiation of muscle fiber types in aneurogenic brachial muscles of the chick embryo.

Cross-reinnervation studies performed ex ovo with newly hatched chicks demonstrate that peripheral motor neurons control the phenotypic characteristics of avian muscles. The present experiments were designed to determine whether or not nerves play a similar role during the initial expression of muscle fiber types. Previous experiments indicated that differentiation of specific fiber types occurs during the first week of embryogenesis, temporally coincident with the penetration of nerves within muscle masses. These observations suggested that peripheral nerves may be associated with the initial differentiation of fiber types. To test this hypothesis directly, anterior limb buds of the chick embryo were rendered aneurogenic by deletion of the brachial segment of the neural tube. To ensure a completely aneurogenic environment for developing brachial muscles, surgery was performed at day 2 in ovo before the exit of ventral root fibers. Experimental and control embryos from Stage (St) 25 (4.5 d) through St 45 (19d) were analyzed histochemically by a silver-cholinesterase reaction to detect nerves and by the myosin ATPase reaction, following alkali and acid preincubation, to determine the fiber type composition of the muscles. In addition, the total volume of aneurogenic and control muscles was compared. Results demonstrate that the characteristic myosin ATPase profiles of individual aneurogenic and innervated (control) muscles were identical throughout the entire period analyzed. Therefore, we conclude that these enzymic profiles are endogenously expressed and are not under neuronal control during early embryogenesis. Furthermore, the entire sequence of events from the migration of myogenic cells to the anterior limb bud through the division of the primary muscle masses to form individual brachial muscles proceeded on schedule in the absence of nerves. Since the growth of aneurogenic muscles was impaired, we conclude that during embryogenesis peripheral motor nerves are necessary initially for the proper growth of muscles and ultimately, for their survival. They are not involved, however, with either the initial formation or initial differentiation of individual brachial muscles.

Adenosine Triphosphatases↗

PubMed2000

Identification and purification of an intrinsic human muscle myogenic factor that enhances muscle repair and regeneration.

The limited ability of damaged muscle to regenerate after gross injuries is a major clinical problem. To date, there is no effective therapeutic treatment for muscle injuries. In the present study, we have examined the ability of crude and fractionated human skeletal muscle extracts to promote myogenic cell proliferation and differentiation. It was found that the crude muscle extract could significantly stimulate BrdU incorporation in C2C12 myogenic cell line. In addition, the extract also promoted myogenic cell alignment and fusion. Using electrophoresis techniques, in conjunction with in vitro refolding technique, a protein with molecular weight of approximately 40 kDa was identified that could produce the same effects as the crude muscle exdtract. We also tested the ability of semipurified (30-50 kDa) muscle extract to promote muscle repair in adult rats. Surgical intervention was used to induce muscle damage in the tibialis anterior. The semipurified muscle extract (fraction H) was injected subcutaneously over the tibialis anterior for a period of 5 days. It was found that the damaged muscle fibers were replaced by newly regenerated muscle fibers. These newly regenerated fibers originated from the fusion of differentiated satellite cells as revealed by BrdU-labeling analysis. In contrast, the injury site of muscles treated with BSA control protein contained mainly fibroblasts.

Adult↗

PubMed1998

Eye muscle antibodies in patients with ocular myasthenia gravis: possible mechanism for eye muscle inflammation in acetylcholine-receptor antibody-negative patients.

Myasthenia gravis is an organ-specific autoimmune disorder generally thought to be caused by an antibody-mediated attack against the skeletal muscle nicotinic acetylcholine (Ach) receptor (AchR) at the neuromuscular junction. Extraocular muscle weakness and double vision are present in about 90% of patients with myasthenia gravis and are the predominant complaints in about 20% of patients, when the condition is called ocular myasthenia gravis (OMG). While serum antibodies against the AchR are detected in most patients with generalized myasthenia gravis (GMG), they are not found in about one-third of patients with the ocular variety, and epidemiological, clinical, and serological studies suggest that OMG and GMG are two separate diseases. Both forms of myasthenia gravis are sometimes associated with thyroid autoimmunity or thyroid-associated ophthalmopathy (TAO). We have therefore tested the sera of patients with GMG and OMG by Western blotting for antibodies against porcine eye muscle membrane proteins in general, and by enzyme-linked immunosorbent assays (ELISA) specifically for reaction with two skeletal muscle antigens which are prominent marker antigens for TAO, namely, the calcium-binding protein calsequestrin and the so-called "64-kDa protein." The 64-kDa protein has recently been identified as the flavoprotein subunit of mitochondrial succinate dehydrogenase. Patients with ophthalmopathy and myasthenia were excluded. Nine of the patients had associated Graves' hyperthyroidism without evident ophthalmopathy and one had Hashimoto's thyroiditis. Antibodies against porcine eye muscle membrane antigens of M(r) 15-110 kDa were detected in patients with GMG or OMG, one or more antibodies being detected in 100% of patients with GMG and in 88% of those with OMG. The most frequently found antibodies were those targeting eye muscle membrane proteins of 15, 67, and 110 kDa. Antibodies reactive with purified calsequestrin (63 kDa) were detected in 21% of patients with OMG but in no patient with GMG. Antibodies recognizing purified succinate dehydrogenase (67 kDa) were found in 42% of patients with OMG, in 100% (5 of 5) of patients with GMG, and in 48% of all patients with myasthenia gravis not associated with Graves' hyperthyroidism. There was no close correlation between any eye muscle-reactive antibody and antibodies against the AchR in either group of myasthenic patients. The findings support the notion that immunoreactivity against skeletal muscle proteins other than the AchR may play a role in the development of the muscle weakness in AchR antibody-negative patients with OMG and GMG, although it is unlikely that any of the antibodies demonstrated in this study are directly implicated. Similarly, while the demonstration of antibodies reactive with eye muscle antigens associated with TAO in patients with OMG raises the possibility that the link between the ocular lesions of myasthenia gravis and Graves' disease may be autoimmunity against a common antigen(s), it is more likely that both disorders are mediated by cytotoxic T cells recognizing another cell membrane antigen, such as the novel thyroid and eye muscle shared protein G2s, and that serum antibodies reactive with succinate dehydrogenase Fp subunit and calsequestrin are markers of an immune-mediated eye muscle reaction.

Animals↗

PubMed2006

Muscle fiber orientation in muscles commonly injected with botulinum toxin: an anatomical pilot study.

The endplate zone is assumed to be at about the midpoint of a muscle fiber. This study was designed to locate the middle of the muscle fibers of commonly injected muscles, thus identifying the endplate zone of these muscles. The proximal and distal musculotendinous junctions in muscles of the upper and lower extremities were identified. Orientation of muscle fibers was determined. Measurements using common surface landmarks were used to determine the relationship of these muscles with the landmarks (e.g., biceps muscle bulk extends from the upper fourth to the lower fourth of the humerus). Figures were developed using these measurements so as to be able to extrapolate these measurements to other patients of varying sizes. Illustrations of muscle fiber orientation were done and the assumed location of motor endplate bands marked. Color illustrations will be shown. With the thought that the endplate zone is at the middle of the muscle fiber, this detailed study of muscle fibers helps identify assumed location of motor endplates of specific muscles, thereby improving technique and efficacy of botulinum toxin injections.

Adult↗

PubMed1999

Vibration sensitivity of cat muscle spindles at short muscle lengths.

Experiments are described in which the vibration sensitivity was tested for primary and secondary endings of soleus muscle spindles of the anaesthetised cat. The vibratory stimulus was applied longitudinally to the muscle tendon and, after locating the site of the spindle in the muscle, applied transversely to muscle fibres directly overlying the spindle. All measurements were made with the muscle slack, at 20 mm shorter than its maximum physiological length (Lm-20 mm). Spindles were separated into two groups: spontaneous spindles, which maintained background activity at this length, and silent spindles, which did not. Two forms of muscle conditioning were used: hold-long, in which the muscle was stretched by 5 mm, contracted and then returned to the test length, and hold-test, in which a conditioning contraction was given at the test length. After hold-test, most spindles responded to longitudinal vibration; after hold-long, most did not. This difference in responsiveness was attributed to the presence or absence of slack in intrafusal and extrafusal fibres, due to the muscle's thixotropic property. When the vibration was applied transversely, at a site directly overlying the spindle, responses of silent spindles continued to show thixotropic behaviour, whereas responses of spontaneous spindles were almost independent of the form of muscle conditioning. It is proposed that the ability of spontaneous spindles to maintain background activity at short muscle lengths is due to connective tissue or elastic fibre links between the sensory ending and the spindle capsule. The vibratory stimulus, applied transversely, reaches the sensory ending via these strands which, as non-muscle tissue, do not alter their mechanical state as a result of muscle conditioning.

Animals↗

PubMedDate not supplied

Morphometric analysis of mdx diaphragm muscle fibres. Comparison with hindlimb muscles.

Histological, histochemical and morphometric characteristics of diaphragm muscles from mdx and control mice were compared with those of hindlimb muscles [extensor digitorum longus (EDL), tibialis anterior (TA) and soleus (SA) muscles]. In contrast to mdx limb muscles, regeneration after muscle necrosis does not restore diaphragm muscle structure. In mdx mice at 270 days of age, 70-80% of fibres in hindlimb muscles had central nuclei, compared with only 35% in diaphragm muscle. At 270 days of age, mdx diaphragm muscle was characterized by perimysial and endomysial fibrosis; this latter feature was absent from mdx hindlimb muscles. Fibre diameter remained smaller than the control in mdx diaphragm muscle. We suggest that the similarity in muscle pathology between the diaphragms of mdx mice and in patients suffering from Duchenne muscular dystrophy (DMD) makes these an appropriate model for DMD, since respiratory failure is the leading cause of death in DMD patients.

Aging↗

PubMed2005

Efferent and afferent innervations of Mueller's muscle related to involuntary contraction of the levator muscle: important for avoiding injury during eyelid surgery.

Because stretching of Mueller's muscle induces involuntary contraction of the levator muscle, we hypothesised that Mueller's muscle functions as a serial kind of muscle spindle of the levator muscle. To confirm the presence and location of efferent and afferent innervations of Mueller's muscle, cadavers' eyelids were microscopically and macroscopically examined, and the resultant findings were physiologically confirmed in patients' eyelids during surgery. Fine neural myelinated structures acting as a mechanoreceptor were found in the proximal Mueller's muscle. Mueller's muscle is doubly innervated by the unmyelinated sympathetic efferent nerve and the myelinated trigeminal proprioceptive afferent nerve, both of which run transversely on the proximal Mueller's muscle to join the lacrimal nerve. Electrical stimulation of the transverse nerve fibres induced involuntary contraction of both the levator muscle as the Hoffmann reflex and Mueller's muscle. Surgical injury to these nerve fibres should be avoided to preserve involuntary contraction of the levator muscle.

Cadaver↗

PubMed2006

Passive muscle-tendon amplitude may not reflect skeletal muscle functional excursion.

PURPOSE: To quantify the gain in muscle mobility with progressive release of surrounding connective-tissue structures and to compare this property with the known architecture of each muscle. METHODS: Each of 5 different muscle tendon units (extensor carpi radialis brevis, extensor carpi radialis longus, flexor carpi ulnaris, flexor digitorum superficialis, pronator teres) was released from its insertion and secured into the jaws of a clamp attached to a servomotor that could be operated under length or force control to simulate the load placed on the tendon by a surgical assistant. A constant load of 5 N was applied to the tendon while the muscle-tendon unit was released surgically from the surrounding tissue in 1-cm increments. Mobility was plotted against release distance and analyzed by linear regression to yield mobility gain, the slope of the regression equation. One-way analysis of variance was used to compare mobility gain among muscles. RESULTS: In contrast to previous results from the brachioradialis muscle in which the mobility gain was large and highly nonlinear, mobility gain was small, consistent, and linear for all muscles studied. The smallest mobility gain was for the flexor digitorum superficialis and was highly linear. The largest gain was for the pronator teres and again was highly linear. In general, the mobility gain for the extensor carpi radialis brevis was similar to that of the extensor carpi radial longus. The flexor carpi ulnaris muscle was difficult to mobilize, and its gain was modest. There was no significant correlation between mobility gain of the forearm muscles during progressive release and the length of their fibers. CONCLUSIONS: The small mobility and complete lack of correlation with fiber length provide strong evidence that mobility gain does not accurately reflect muscle excursion as it is typically described. This calls into question the general practice of tensioning muscles by first passively extending the muscle and then choosing the attachment length as a particular portion of that passive relationship.

Aged, 80 and over↗

PubMed1998

Muscle fiber type compartmentalization and expression of an immature myosin isoform in the sternocleidomastoid muscle of rabbits and primates.

The sternocleidomastoid muscle is located in the neck and is both a neck rotator and flexor. Cervical dystonia, a focal dystonia disorder, is characterized by forceful involuntary contraction of a group of neck muscles, usually including the sternocleidomastoid. Little is known about the fiber type composition, fiber type compartmentalization and innervation patterns in this muscle in rabbit and primates. Sternocleidomastoid muscles from rabbit and monkey were analyzed for muscle fiber type composition and number, muscle fiber cross-sectional area and patterns of innervation. The sternocleidomastoid muscle was composed of two distinct regions, or compartments, with different fiber type compositions: an outer or superficial region composed of mostly type 2 myofibers and an inner deep region composed of both type 2 and type 1 myofibers. Neonatal myosin heavy chain isoform was detected in approximately 25% of the myofibers in both regions of the muscle. Neuromuscular junctions were located in seven endplate bands approximately 1-3 cm apart throughout the length of the muscle. There is clear evidence of anatomical subdivisions within this muscle. Not only is there variation in fiber type composition between superficial and deep regions of the muscle, but unlike most other mature skeletal muscles, it continues to express neonatal myosin heavy chain isoform in the adult. The motor program for neck movements is extremely complex, and the histological complexity plays a role in allowing for a continuum of movements of the head and neck, from maintenance of posture to rapid head movements.

Adenosine Triphosphatases↗

PubMed1998

Age-related muscle atrophy does not affect all muscles and can partly be compensated by physical activity: an ultrasound study.

In adults, the volume of quadriceps femoris muscle decreases with age, whereas the impact of increasing age on the size of other extremity muscles was hardly studied. This study was conducted to examine whether age-related muscle atrophy is a general phenomenon, whether it is accompanied by increasing subcutaneous fat and whether physical activity can compensate age-related muscle atrophy. One hundred and two female and 101 male subjects (aged 19-86 years), with common physical activity, as well as 29 women and 38 men (aged 20-81 years) regularly performing sports at least 3 h per week for several years (mean, 10 years in women and 14 years in men, respectively), were examined. Both in athletes and control subjects, the thickness of thigh muscles significantly decreased with age (-15(-)-21% from age 20 to age 70), whereas diameter of upper arm muscles remained nearly unchanged. Diameters of the calf muscle decreased with advancing age only in the control group. In male control subjects, the tibialis anterior muscle shrunk as well. Except for the vastus lateralis muscle in women, the relative loss of muscle thickness was more evident in control subjects than in athletes. Thickness of the subcutaneous fat layers remained almost unchanged. In summary, not all extremity muscles exhibit age-related decrease in size. Regular physical activity can ease off muscle atrophy.

Adipose Tissue↗

PubMed2000

Cervical muscle response during whiplash: evidence of a lengthening muscle contraction.

OBJECTIVE: To assess the potential for cervical muscle injury from a rear-end automobile collision. DESIGN: Experimental design in which human subjects were exposed to low-speed rear-end collisions. The influence of independent variable (gender, speed change, muscle group, and motion phase) on dependent variables (kinematic response, muscle onset and muscle activation level) was examined using repeated-measures analysis of variance. BACKGROUND: Injuries to various tissues of the cervical spine have been proposed, yet little attention has been focused on the cervical muscles as a site of injury. METHODS: 42 subjects (21 males, 20-40 yr) were exposed to collisions of 4 and 8 km/h speed change while measuring kinematic response of the head and torso and electromyography of the sternocleidomastoid and cervical paraspinal muscles. RESULTS: Muscle activation occurred earlier in females and in the 8 km/h speed change. Sternocleidomastoid onset preceded paraspinal onset. Muscle activation level varied significantly with speed change, motion phase and muscle group. Initial rearward retraction of the head relative to the torso resulted in lengthening of the activated sternocleidomastoid, consistent with a contraction-induced muscle injury. CONCLUSIONS: The cervical muscles contract rapidly in response to impact and the potential exists for muscle injury due to lengthening contractions. RELEVANCE: The clinician should recognize the role of cervical retraction in the mechanism of whiplash injury and avoid aggressive motion in that plane during diagnosis and treatment. An understanding of whiplash injury mechanisms should improve patient education and preventative measures.

Accidents, Traffic↗

PubMed2002

Effect of muscle electrostimulation on afferent activities from tibialis anterior muscle after nerve repair by self-anastomosis.

Numerous previous studies were devoted to the regeneration of motoneurons toward a denervated muscle after nerve repair by self-anastomosis but, to date, few investigations have evaluated the regeneration of sensory muscle endings. In a previous electrophysiological study (Decherchi et al., 2001) we showed that the functional characteristics of tibialis anterior muscle afferents are affected after self-anastomosis of the peroneal nerve even when the neuromuscular preparation was not chronically stimulated. The present study examines the regeneration of groups I-II (mechanosensitive) and groups III-IV (metabosensitive) muscle afferents by evaluating the recovery of their response to different test agents after self-anastomosis combined or not with chronic muscle stimulation for a 10-weeks period. We compared five groups of rats: C, control; L, nerve lesion without suture; LS, nerve lesion with suture; LSE(m): nerve lesion plus chronic muscle stimulation with a monophasic rectangular current; and LSE(b): nerve lesion plus chronic stimulation with a biphasic current with modulations of pulse duration and frequency, eliciting a pattern of activity resembling that delivered by the nerve to the muscle. Compared to the control group, (1) muscle kept only its original weight in the LSE(b) group, (2) in the LS group the response curve to tendon vibration was shifted toward the highest mechanical frequencies and the response of groups III-IV afferents after fatiguing muscle stimulation lowered, (3) in the LSE(m) group, the pattern of activation of mechanoreceptors by tendon vibrations was altered as in the LS group, and the response of metabosensitive afferents to KCl injections was markedly reduced, (4) in the LSE(b) group, the response to tendon vibration was not modified and the activation of metabosensitive units by increased extracellular potassium chloride concentration was conserved. Both LSE(b) and LSE(m) conditions were ineffective to maintain the post muscle stimulation activation of metabosensitive units as well as their activation by injected lactic acid solutions. Our data indicate that chronic muscle electrostimulation partially favors the recovery of mechano- and metabosensitivity in a denervated muscle and that biphasic modulated currents seem to provide better results.

Action Potentials↗

PubMed2003

Muscle fibre type adaptation in the elderly human muscle.

This short review discusses changes in the fibre type distribution, myosin heavy chain isoform composition and histological appearance of the very elderly human skeletal muscle. Point of origin of the discussion comes from data that we have obtained from muscle biopsies from the vastus lateralis muscle of a group of frail very elderly subjects (age: 88 +/- 3 years, range 85-97). Myosin heavy chain composition of muscle homogenates and single fibres, fibre type distribution, fibre size and capillary density were examined and compared with muscle biopsies from the young vastus lateralis muscle. Histological preparations of the muscle biopsies from our elderly subjects showed extended "grouping" (Nygaard & Sanchez, Anat Rec 1992: 202: 451-459) of the fibre types as well as significant changes in the appearance and size of the individual muscle fibres. On average, the fibre type composition of our very elderly subjects do not seem to be different to what is observed in a corresponding young group when examined with ATPase histochemistry. Likewise, the MHC composition of the muscle homogenates is comparable to what is observed in young subjects. Nevertheless, a detailed examination of the MHC composition of single fibres from the old subjects revealed that the most prominent phenotype was fibres co-expressing MHC I and MHC IIA. This is very different from what is observed in the young muscle. Detailed investigation of longitudinally cut fibres indicated that some fibres in the very old muscle, in contrast to the young muscle, switch fibre type along the length of the fibre or contain areas or nuclear domains in which the MHC expression is different from the remaining part of the fibre.

Adaptation, Physiological↗

PubMed1999

A substituted dextran enhances muscle fiber survival and regeneration in ischemic and denervated rat EDL muscle.

Ischemia and denervation of EDL muscle of adult rat induce a large central zone of degeneration surrounded by a thin zone of peripheral surviving muscle fibers. Muscle regeneration is a complex phenomenon in which many agents interact, such as growth factors and heparan sulfate components of the extracellular matrix. We have shown that synthetic polymers, called RGTA (as regenerating agents), which imitate the heparan sulfates, are able to stimulate tissue repair when applied at the site of injury. In crushed muscles, RGTA were found to accelerate both regeneration and reinnervation. In vitro, RGTA act as protectors and potentiators of various heparin binding growth factors (HBGF). It was postulated that in vivo their tissue repair properties were due in part to an increase of bioavailability of endogenously released HBGF. In the present work, we show that ischemic and denervated EDL muscle treated by a unique injection of RGTA differs from the control after 1 wk in several aspects: 1) the epimysial postinflammatory reaction is inhibited and the area of fibrotic tissue among fibers is reduced; 2) the peripheral zone, as measured by the number of intact muscle fibers, was increased by more than twofold; and 3) In the central zone, RGTA enhances the regeneration of the muscle fibers as well as muscle revascularization. These results suggest that RGTA both protects muscle fibers from degeneration and preserves the differentiated state of the surviving fibers. For the first time it is demonstrated that a functionalized polymeric compound can prevent some of the damage resulting from muscle ischemia. RGTA may therefore open a new therapeutic approach for muscle fibrosis and other postischemic muscle pathologies.

Animals↗

PubMed2000

The effect of muscle transplantation after unilateral partial facial paralysis on craniofacial growth and development: relationship between muscle and nerve histomorphometric findings.

Muscle transplantation has become an indispensable tool to restore the smile in patients with long-standing or congenital facial paralysis. However, little is known of the effect of this surgical intervention on craniofacial growth and development or of the adaptation of the transplant to its recipient site under circumstances of growth. The present study investigates these phenomena in the rabbit model. Twelve-day-old New Zealand White rabbits were randomly assigned to three experimental groups. The control group was used to study normal craniofacial growth and development (n = 15). In the nerve ablation group, unilateral paralysis of the buccal branches of the facial nerve was surgically induced (n = 15). In the transplant group, the surgically induced unilateral paralysis of the buccal branches was immediately followed by a neuromuscular graft (n = 12). All animals were operated on at the age of 12 days, and follow-up evaluations were performed at the ages of 2 months and 6 months. Computerized dorsoventral roentgencephalometric and computed tomography investigations were performed at both ages. Nerve and muscle histomorphometric measurements were performed at the age of 6 months to relate the quality of nerve and muscle regeneration to the growth parameters. The roentgencephalometric measurements revealed that analogous disturbed parameters were present in the nerve ablation and the transplant groups. However, in the transplant group, an additional significant effect of time between 2 and 6 months was seen for some parameters. This resulted in significant differences between the nerve ablation and transplant groups at 6 months for these parameters. Computed tomography measurements showed no significant differences in maxillary or mandibular volume in the transplant group compared with the control or nerve ablation groups. However, a significantly diminished increase in bone volume existed in the transplant group for the time period between 2 and 6 months in comparison with the control and nerve ablation groups. Muscle histomorphometric findings revealed a significant change in muscle fiber composition in the graft compared with the normal latissimus dorsi muscle; this was due to a major decrease in type IIB fibers, with an increase in type I and type IIA fibers. Compared with the normal zygomaticoauricular muscle, the amount of type I fibers was significantly increased. No fiber atrophy was found. Macroscopically, the transplanted muscle failed to increase its length during growth. Nerve histomorphometric findings demonstrated a normal amount of nerve fibers; however, they had significantly decreased diameters and reduced myelin areas. The nerve histomorphometric parameters were related to the muscle histomorphometric findings, which in turn were related to craniofacial growth disturbances. These findings suggested that the main growth differences between the transplant group and the control group may have been due to altered nerve function influencing muscle function. Scar tissue formation and the development of more intense muscle activity later are suggested as the causes of the additional effect of time between 2 and 6 months for the several parameters in the transplant group. Reasons for the failure of complete conversion of the graft to a fast muscle and the failure of the transplant to elongate during growth are discussed.

Animals↗