Fiber type composition of abdominal muscles in Japanese macaques (Macaca fuscata)

The muscle fiber composition and cross-sectional area of muscle fiber types were investigated histochemically in the abdominal muscles (rectus abdominis muscle, obliquus externus abdominis muscle, obliquus internus abdominis muscle and transversus abdominis muscle) of three Japanese macaques (Macaca fuscata). Muscle fibers were classified into three fiber types (Type I, II A and II B) by myosin ATPase activity and succinate dehydrogenase activity. Each abdominal muscle in Japanese macaques contained high proportion of Type II B fibers and there were no large differences in the fiber type composition between the abdominal muscles. The range of mean fiber type percent was 26-32% Type I, 21-22% Type II A, and 46-52% Type II B fibers. Thus, based on the histochemical fiber type composition, the separate abdominal muscles appear to have a similar functional capacity. The cross-sectional area was larger for Type II than for Type I fibers, and the areas were similar in Type II A and Type II B fibers in each muscle. The rectus abdominis showed larger fibers of each type compared to the lateral abdominal muscles. The high proportion of Type II B fibers and large fiber size for Type II B fibers suggest that the abdominal muscles of Japanese macaques have properties similar to the propulsive and locomotory muscles in the limbs.     

Remarks on the structure and course of renal efferent glomerular arterioles

Patients with chronic heart failure have structural and metabolic changes in skeletal muscle, which may be of importance for symptomatology. The origin of these changes are still unknown. The relationship between fiber composition and capillarization in skeletal muscle with exercise capacity and central hemodynamic variables was examined. Biopsies from the lateral vastus muscle were taken in 12 patients with chronic heart failure. Samples from eight normal subjects served as control samples. All patients underwent maximal exercise tests. Central hemodynamic variables were measured during exercise in five patients. The patients had a higher percentage of type II B fibers (P = .03) and fewer capillaries per fiber (P = .02) than the controls subjects. VO2 max correlated with the percentage of type I fibers, whereas the correlation with the type II A fibers was inverse. Cardiac index and pulmonary capillary wedge pressure at submaximal and maximal exercise were related to fiber type composition and relative fiber areas. Skeletal muscle fiber type composition and capillarization was changed in patients with chronic heart failure. These changes might influence exercise capacity. There were relationships between central hemodynamic variables and skeletal muscle changes. What the cause and effects were need further investigation.     

Type II muscle fibers are stained by anti-Fas antibody

To examine whether apoptosis related proteins are present in skeletal muscles we studied biopsied muscles immunohistochemically and by Western blot analysis. Biopsied muscles from patients with several disorders were studied with anti-Fas antibody and anti-BCL2 antibody. Type II muscle fibers identified by ATPase staining were positively stained by anti-Fas antibody in both normal control and diseased muscles. Anti-BCL2 antibody did not stain any muscle fibers. Western blot analysis using anti-Fas antibody showed a single band at 45 kDa in both skeletal muscle and lymphocytes. Anti-Fas antibody has been reported to induce apoptosis in the cells. The presence of anti-Fas antibody reactive materials in type II muscle fibers might be related to type II fiber atrophy in muscular disorders.     

Self-reinnervated cat medial gastrocnemius muscles. II. analysis of the mechanisms and significance of fiber type grouping in reinnervated muscles

1. The technique of glycogen depletion was used to determine whether regenerating motor axons reestablish the normal regionalization of motor units (MUs) in the cat medial gastrocnemius (MG) muscle, 2) whether the extent of clumping between MU fibers and/or type grouping of muscle fibers progressively increases with a decrease in reinnervated MU numbers, and 3) whether the pattern of innervation can explain why MUs fail to increase significantly in size when the cut nerve is sutured directly to the muscle, even when few axons make functional connections. 2. Distributions of MU fibers were analyzed in 5 normal and 14 reinnervated cat MG muscles 4.5-16 mo after sectioning of its nerve and suturing of the proximal end to the distal nerve sheaths (N-N suture) or directly to the muscle fascia (N-M suture). Muscle unit distributions were quantified according to location, territory size, density, and extent of clumping between fibers from the same MU. 3. Normal MU fibers were regionalized within five regions along the muscle's longitudinal and transverse axes. Reinnervated MUs were located within similar regions, indicating that regenerating axons follow the major proximal nerve branches to restore normal compartmentalization. 4. Muscle unit fibers were diffusely scattered within discrete MU territories in normal muscles. Territory size tended to increase with MU size, whereas density of muscle unit fibers within the territory decreased. 5. Territories increased with MU size after N-N suture but were smaller and showed little size variation after N-M suture. The extent of muscle unit fiber clumping was inversely related to the number of reinnervated MUs. On average, the extent of clumping was substantially higher in muscles reinnervated after N-M suture. These results indicate that distal nerve sheaths facilitate proximal axon branching, which establishes MU territory size. Once the territory is established, motor axons branch distally to increase MU size, which in turn compensates for reduced MU numbers. 6. Muscles reinnervated by < 80% of the MUs exhibited fiber type grouping of type I fibers, and on average the extent of clumping was substantially higher in muscles reinnervated after N-M suture. With less innervation, type grouping increased inversely with the number of reinnervated MUs. However, for a similar number of MUs, type I fiber type grouping was substantially higher in muscle reinnervated after N-M suture. Type grouping therefore reflects muscle unit fiber clumping under conditions where MU size increased (N-N suture) or MU territory size decreased (N-M suture).     

Evaluation of specific stabilizing exercise in the treatment of chronic low back pain with radiologic diagnosis of spondylolysis or spondylolisthesis

STUDY DESIGN: A randomized, controlled trial, test--retest design, with a 3-, 6-, and 30-month postal questionnaire follow-up. OBJECTIVE: To determine the efficacy of a specific exercise intervention in the treatment of patients with chronic low back pain and a radiologic diagnosis of spondylolysis or spondylolisthesis. SUMMARY OF BACKGROUND DATA: A recent focus in the physiotherapy management of patients with back pain has been the specific training of muscles surrounding the spine (deep abdominal muscles and lumbar multifidus), considered to provide dynamic stability and fine control to the lumbar spine. In no study have researchers evaluated the efficacy of this intervention in a population with chronic low back pain where the anatomic stability of the spine was compromised. METHODS: Forty-four patients with this condition were assigned randomly to two treatment groups. The first group underwent a 10-week specific exercise treatment program involving the specific training of the deep abdominal muscles, with co-activation of the lumbar multifidus proximal to the pars defects. The activation of these muscles was incorporated into previously aggravating static postures and functional tasks. The control group underwent treatment as directed by their treating practitioner. RESULTS: After intervention, the specific exercise group showed a statistically significant reduction in pain intensity and functional disability levels, which was maintained at a 30-month follow-up. The control group showed no significant change in these parameters after intervention or at follow-up. SUMMARY: A "specific exercise" treatment approach appears more effective than other commonly prescribed conservative treatment programs in patients with chronically symptomatic spondylolysis or spondylolisthesis.     

Morphological fiber types of retractor bulbi muscle in mouse and rat

Retractor bulbi muscles of mouse and rat were examined by light and electron microscopy. Two morphological fiber types were observed, analogous to Type I and Type II cells of skeletal musculature and comparable to fibers observed in the global region of the rectus extraocular muscles of these species.     

Electromyographic responses of back and limb muscles associated with spinal manipulative therapy

STUDY DESIGN: Ten young, asymptomatic male subjects underwent 11 clinically relevant spinal manipulative treatments along the length of the spine to test the magnitude and extent of reflex responses associated with the treatments. OBJECTIVES: To determine the magnitude and extent of reflex responses elicited by spinal manipulative treatments. SUMMARY OF BACKGROUND DATA: Spinal manipulative treatments have been associated with a reflexogenic relief of pain and a loss of hypertonicity in muscles within the treatment area. However, there is no study in which results show the probability of occurrence or the extent of reflex responses during spinal manipulative treatments. METHODS: Asymptomatic subjects received spinal manipulative treatments on the cervical, thoracic, and lumbar levels and on the sacroiliac joint. Reflex activities were measured using 16 pairs of bipolar surface electrodes placed on the back and proximal limb musculature. The percentage of occurrence and the extent of reflex responses in the back and proximal limb musculature were determined. RESULTS: Each treatment produced consistent reflex responses in a target-specific area. The reflex responses occurred within 50-200 msec after the onset of the treatment thrust and lasted for approximately 100-400 msec. The responses were probably of multireceptor origin and were elicited asynchronously. CONCLUSIONS: This is the first study in which results show a consistent reflex response associated with spinal manipulative treatments. Because reflex pathways are evoked systematically during spinal manipulative treatment, there is a distinct possibility that these responses may cause some of the clinically observed beneficial effects, such as a reduction in pain and a decrease in hypertonicity of muscles.     

Inefficient muscular stabilization of the lumbar spine associated with low back pain. A motor control evaluation of transversus abdominis

STUDY DESIGN: The contribution of transversus abdominis to spinal stabilization was evaluated indirectly in people with and without low back pain using an experimental model identifying the coordination of trunk muscles in response to a disturbances to the spine produced by arm movement. OBJECTIVES: To evaluate the temporal sequence of trunk muscle activity associated with arm movement, and to determine if dysfunction of this parameter was present in patients with low back pain. SUMMARY OF BACKGROUND DATA: Few studies have evaluated the motor control of trunk muscles or the potential for dysfunction of this system in patients with low back pain. Evaluation of the response of trunk muscles to limb movement provides a suitable model to evaluate this system. Recent evidence indicates that this evaluation should include transversus abdominis. METHODS: While standing, 15 patients with low back pain and 15 matched control subjects performed rapid shoulder flexion, abduction, and extension in response to a visual stimulus. Electromyographic activity of the abdominal muscles, lumbar multifidus, and the surface electrodes. RESULTS: Movement in each direction resulted in contraction of trunk muscles before or shortly after the deltoid in control subjects. The transversus abdominis was invariably the first muscle active and was not influenced by movement direction, supporting the hypothesized role of this muscle in spinal stiffness generation. Contraction of transversus abdominis was significantly delayed in patients with low back pain with all movements. Isolated differences were noted in the other muscles. CONCLUSIONS: The delayed onset of contraction of transversus abdominis indicates a deficit of motor control and is hypothesized to result in inefficient muscular stabilization of the spine.     

Regeneration of adrenal cortical tissue after adrenal autotransplantation

OBJECTIVE: This study examined the muscle fiber type distribution within the normal adult levator veli palatini muscle. METHODS: Levator veli palatini muscle tissue was harvested from the palates of 12 (seven female, five male) adult noncleft cadavers. Adjacent sections were stained for adenosine triphosphatase at pH 10.4 or 4.2. After mounting, magnifying, and photographing, Type I versus Type II fiber types were differentiated by the intensity of, or by the inhibition of, staining of matched fibers at each pH level. Type I fibers stained light at pH 10.4 and dark at pH 4.2, while Type II fibers stained light at pH 4.2 and dark at pH 10.4. MAIN OUTCOME MEASURES: The number of fibers counted for each specimen ranged from 60 to 616. The numbers of Type I and Type II stained fibers appearing in each muscle tissue sample were determined and expressed as a percentage of the total number of fibers identified. A few identified fibers could not be labelled as either Type I or Type II. RESULTS: The overall proportion of Type I fibers, averaged across all specimens, was 59.8%. Male specimens had 67.4% Type I fibers and 31.8% Type II fibers, while female specimens had 54.4% Type I fibers and 44.4% Type II fibers. CONCLUSIONS: Observed fiber type distributions were similar to those reported for other articulatory muscles, but differed slightly from previously reported distributions for normal levator veli palatini. The distributions observed in this study provide a baseline against which to relate fiber type data from the levator veli palatini of cleft palates to the functional status of the velopharyngeal mechanism.     

Extracapsular spread in the clinically negative neck (N0): implications and outcome

The myotomal muscle of Synbranchus marmoratus was investigated using histochemical and immunohistochemical reactions. This musculature is composed of a superficial red compartment, uniformly distributed around the trunk circumferentially and also in the lateral line. The red compartment fibers are small in diameter and have an oxidative metabolism, a high rate of glycogen and a negative reaction to alkaline and acid myofibrillar ATPase (mATPase). The white muscle forms the bulk of the muscle mass. Its fibers are large in diameter and have a glycolytic metabolism, a negative reaction to glycogen, a strong reaction to alkaline mATPase and a negative reaction to acid mATPase. Between these two compartments there is an intermediate layer of fibers presenting a mosaic metabolism pattern with a high rate of glycogen. These fibers stained moderately for alkaline and acid m-ATPase. Several clusters of red muscles were observed inside the white muscle. Each cluster is composed of three fiber types, with a predominance of red and intermediate fibers. Reactivity to anti-MHC BA-D5 was positive only in the intermediate fibers. Reactivity to anti-MHC SC-71 was negative in all fiber types.     

Chronic low back pain

Most episodes of low back pain are mechanical in origin and resolve within a 12-week period. These acute episodes of back pain are associated with muscle strain and intervertebral disc herniation with radiculopathy. A smaller proportion of individuals have back pain with a duration greater than 12 weeks. These patients have back pain secondary to a wide variety of mechanical and nonmechanical disorders. The mechanical disorders associated with chronic low back pain include osteoarthritis and lumbar spinal stenosis; the nonmechanical disorders include infectious, neoplastic, rheumatologic, endocrinologic, vascular, and gynecologic. The clinical symptoms associated with each variety of disorder helps guide the appropriate diagnostic evaluation. Plain roentgenograms are useful in documenting the presence of spinal stenosis, benign or malignant tumors, osteoporosis, sacroiliitis, and spondylitis. CT scan is helpful in defining the bony alterations associated with malignant tumors and the vascular abnormalities associated with aneurysms. MR imaging is the technique of choice to document the extent of malignant processes and the presence of endometriosis in the pelvis. The therapy of these entities are specific for the disease entity causing the chronic low back pain. Although most of the disorders that cause chronic low back pain cannot be cured, therapy can decrease pain and improve function of the symptomatic patient.     

Decreased proportion of type I myofibers in skeletal muscle of dogs with chronic heart failure

BACKGROUND: Whether biochemical and histological abnormalities of skeletal muscle (SM) develop in patients with chronic heart failure (HF) remains controversial. In the present study, dogs with chronic HF were used to examine potential alterations of SM fiber type, fiber size, number of capillaries per fiber (C/F), beta-adrenergic receptor density (Bmax), and fiber ultrastructural integrity. METHODS AND RESULTS: HF was produced in 17 dogs by sequential intracoronary microembolizations. Biopsies of the lateral head of the triceps muscle were used in all studies. Type I and type II fibers were differentiated by myofibrillar ATPase (pH 9.4 or 4.2). Bmax was assessed by radioligand binding and SM ultrastructure by transmission electron microscopy. Comparisons were made with biopsies obtained from nine control dogs. The percentage of SM type I fibers was reduced in HF dogs compared with control dogs (19 +/- 2% versus 32 +/- 5%) (p < 0.001), whereas the percentage of SM type II fibers was increased (81 +/- 2% versus 68 +/- 5%) (p < 0.001). The change in fiber type composition was not associated with a preferential atrophy or hypertrophy of either fiber type. There was no difference in SM Bmax (198.9 +/- 14.3 versus 186.8 +/- 17.3 fmol/mg protein) or in C/F (5.37 +/- 0.26 versus 5.84 +/- 0.21) between HF dogs and control dogs. No ultrastructural abnormalities were present in SM fibers of HF dogs. CONCLUSIONS: In dogs with HF, there is a decrease in the relative composition of the slow-twitch type I SM fibers and an increase in fast-twitch type II fibers. The shift in fiber type composition is not associated with preferential atrophy of either fiber type or with a reduction in C/F, beta-adrenergic receptor density, or structural abnormalities of the myofibers.     

Lumbar strengthening in chronic low back pain patients. Physiologic and psychological benefits

The effects of exercise for isolated lumbar extensor muscles were examined in 54 chronic low-back pain patients. Subjects were randomly assigned to a 10-week exercise program (N = 31) or a wait-list control group (N = 23). Results indicated a significant increase in isometric lumbar extension strength for the treatment group and a significant reduction in reported pain compared with the control group (P 0.05). Treated subjects reported less physical and psychosocial dysfunction whereas the control group increased in pain, and physical and psychosocial dysfunction. There were no concomitant changes in reported daily activity levels. These results show that lumbar extension exercise is beneficial for strengthening the lumbar extensors and results in decreased pain and improved perceptions of physical and psychosocial functioning in chronic back pain patients. However, these improvements were not related to changes in activities or psychological distress.     

Size and myosin heavy chain profiles of rat hindlimb extensor muscle fibers after 2 weeks at 2G

METHOD: The effects of 14 d of continuous centrifugation at approximately 2G on the hindlimb extensor musculature of male rats were studied. RESULTS: The mean body mass of centrifuged rats was 17% smaller than age-matched controls. In centrifuged rats, the mean absolute masses of the soleus and medial gastrocnemius (MG) were similar to control, while the mean relative masses (expressed as milligram muscle mass/gram of body mass) were larger than control. Based on a battery of monoclonal antibodies for specific myosin heavy chains (MHC), the soleus of centrifuged rats had a lower percentage (68 vs. 74%) of fibers expressing type I MHC only and a higher percentage (15 vs. 10%) that co-expressed type I and IIa MHC's. The MHC composition of fibers from the deep portion of the MG was unaffected by centrifugation. The MHC compositions based on SDS-PAGE gel electrophoresis for each muscle were similar in the two groups. Mean fiber size of each fiber type in the soleus was unaffected by centrifugation. In the MG, the fibers, expressing only type IIb MHC were smaller in the centrifuge compared to control rats. CONCLUSION: Although 2 weeks of chronic centrifugation at 2G resulted in a cessation of body growth, there was essentially no effect on the muscle masses or fiber size in either a slow or fast extensor muscle. These data suggest that periods of centrifugation may be beneficial in maintaining extensor muscle mass in an animal that is not growing at a normal rate e.g., during chronic unloading.     

Effects of adrenalectomy or RU-486 on rat muscle fibers during hindlimb suspension

The purpose of this study was to investigate the effects of a glucocorticoid antagonist, RU-486, and of adrenalectomy (ADX) on rat skeletal muscle structural properties after 3, 7, and 14 days of hindlimb suspension (H). After H, a significant loss in muscle weight was observed as early as 3 days in soleus (SOL; -10%) and adductor longus (AL; -14%) muscles. In SOL, after only 7 days, a reduction (-14%) in type I fiber percent distribution occurred, accompanied by an increase (+129%) in intermediate type I fibers. Fiber type changes increased depending on the duration of H. In AL muscle, no change occurred after H in the fiber type composition despite a similar degree of muscle atrophy. Treatment with RU-486 or ADX significantly reduced the loss of SOL weight observed after 14 days (-42 and -44%, respectively, vs. -50% for H rats), delayed the SOL atrophy (from 3 to 7 days), and normalized the shift in fiber type distribution induced by H. In SOL, administration of RU-486 (but not ADX) partly prevented the reduction in size induced by H of all the fibers. In AL, neither treatment affected the extent of muscle atrophy, even though the reduction in type IIa fiber size was prevented by RU-486 but not by ADX after 14 days of suspension. ADX or RU-486 administration did not prevent the extensor digitorum longus weight loss observed after 14 days of suspension but allowed a recovery of its normal fiber type composition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in myosin expression in denervated laryngeal muscle

The effects of chronic denervation on the myosin heavy chain (MyHC) content and muscle fiber type composition of rat laryngeal muscles are described. The posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were removed 3 weeks, 3 months, and 6 months after recurrent laryngeal nerve sectioning. Myofibrillar adenosine triphosphatase staining of cryostat sections was performed, and fiber type percentages were determined. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used to separate MyHC isoforms, and densitometry was subsequently used for quantitative analysis. Unoperated animals served as controls. In the PCA muscle, denervation resulted in a progressive reduction in type I MyHC (the slow-contracting isoform) to an almost complete loss at 6 months, with a concomitant increase in type II MyHCs (fast-contracting isoforms, excluding type IIL). Type IIL MyHC (laryngeal-specific isoform) remained relatively constant up to 6 months after denervation. The myosin expression in the TA muscle, which contained only type II MyHCs, remained relatively constant with denervation. Changes in fiber type composition of the muscles described from tissue staining correlated with MyHC content. These findings in laryngeal muscle confirm the dependence of type I MyHC expression upon neural input, as has been found previously in limb skeletal muscles. Since the expression of all MyHCs except the IIL was modified after denervation in the PCA muscle, it is possible that the IIL isoform is maintained by factors that differ from those in the other skeletal myosins.     

One-footed and externally disturbed two-footed postural control in patients with chronic low back pain and healthy control subjects. A controlled study with follow-up

STUDY DESIGN: A study of postural control during one-footed and externally disturbed two-footed stance among healthy control subjects and patients with chronic low back pain at the beginning of a functional back restoration program and 6 months later at follow-up examination. OBJECTIVES: To study postural control cross-sectionally among control subjects and patients with low back pain, and to evaluate the effects of functional restoration on the postural control parameters in a follow-up examination. SUMMARY OF BACKGROUND DATA: Deficits of motor skills and coordination have been reported in association with musculoskeletal disorders. It has been found that patients with chronic low back pain have impaired psychomotor control, but the impairment is reversible with successful low back rehabilitation. It is insufficiently known how functional activation and intensive physical training affect postural control. METHODS: Sixty-one healthy volunteers (32 men, 29 women) and altogether 99 patients with low back pain participated in the study. Sixty-eight patients (33 men, 35 women) had moderate and 31 (18 men, 13 women) had severe low back pain. Postural stability was measured with a force platform. In two-footed stance, vibration stimulation on calf and back muscles was used to disturb the balance. Center point of force-velocity (cm/sec), average position shift in anteroposterior direction (cm), and maximal position shift in lateral direction (cm) were used as the parameters. RESULTS: Reliability of all tests was acceptable. Center point of force-velocity was the most sensitive parameter and the one-footed measurement the most sensitivetest for evaluating postural stability. At the beginning, the patients with severe low back pain had poorer one-footed postural control compared with the control subjects (P = 0.0003). The subgroup of patients with moderate low back pain participated in the restoration program. The outcome of the restoration program was considered good if the disability because of low back pain (Oswestry index) decreased during the restoration program and poor if the disability increased or did not change. The one-footed postural stability remained primarily at the same level as the initial results in the control and good outcome groups, but became significantly poorer in the poor outcome group. The difference between poor outcome and control groups was statistically significant (P = 0.04). CONCLUSIONS: Impaired postural stability seems to be one factor in multidimensional symptomatology of patients with chronic low back trouble. Postural stability is easily disturbed in case of impairment in strength, coordination, or effective coupling of muscles in the lumbar and pelvic area. Patients with chronic low back pain seem to experience impairment in these functions, which should be taken into consideration when back rehabilitation programs are planned.     

Expression of myosin isoforms in denervated, cross-reinnervated, and electrically stimulated rabbit muscles

The expression of myosin heavy (MyHC) and light (MyLC) chain isoforms was analyzed after denervation and cross-reinnervation by a fast nerve of the slow-twitch Semimembranosus proprius (SMp) muscle, and after denervation and electrical stimulation at low frequency of the fast-twitch Semimembranous accessorius (SMa) muscle of the rabbit. The control SMp (100% type I fibers) expressed 100% type I MyHC and 100% slow-type (1S', 1S and 2S) MyLC isoforms. Five month denervation did not alter significantly the MyHC expression of the muscle, but induced the expression of a new type 1 MyLC corresponding most probably to an embryonic MyLC. Five-month cross-reinnervation of the SMp by the fast SMa nerve induced a large change of its fiber type properties. As shown by immunocytochemistry, almost all fibers were stained by fast myosin antibody, but a high proportion of them co-expressed slow myosin. This result was in agreement with biochemical data showing that fast MyHC and MyLC isoforms became predominant. The control SMa (nearly 100% type II fibers) expressed almost 100% type II MyHC (70% type IIb and 22% IIx/d) and 100% fast-type (1F, 2F and 3F) MyLC isoforms. Five month denervation of the SMa induced a shift in its MyHC, with 98% type IIx/d and 2% type IIb isoforms, and no change in the proportions of its MyLC. Three month electrical stimulation at 10 Hz of the SMa transformed its fiber type composition. All fibers reacted with the slow myosin antibody and a minor proportion of them were stained by the fast myosin antibody. These observations were in agreement with the biochemical analysis showing a large predominance of the slow-type MyHC and MyLC isoforms. Taken together, these results obtained from rabbit muscles which are normally homogeneous in either fast-twitch or slow-twitch fiber types, further support the idea that the different myosin isoforms, particularly the MyHC, are differentially regulated by motor innervation. Type I MyHC is maintained in denervated SMp muscle, but is not expressed in denervated SMa. Type IIb isoform is the most sensitive to neural influence, as it disappears rapidly in denervated and electrically stimulated fast-twitch SMa muscle, and is barely expressed in cross-reinnervated slow-twitch SMp muscle. In contrast, type IIa and type IIx/d are less dependent upon motor innervation. In addition to the previous studies of d'Albis et al. analysis of these results leads us to conclude that, in the rabbit, sensitivity to motor innervation increases from the glycolytic to the oxydative types of fibers, in the order IIB > IIX/IID > IIA > I.     

Mechanism of increasing dystrophin-positive myofibers by myoblast transplantation: study using mdx/beta-galactosidase transgenic mice

Female mdx/mdx mice were crossed with non-dystrophic transgenic males expressing the beta-galactosidase (beta-gal) gene under a muscle-specific promoter (TnILacZ1/29). All male offspring were mdx mice and about 50% of them also expressed the beta-gal gene. The beta-gal/mdx mice were selected as recipients for the transplantation of myoblasts from non-transgenic normal BALB/c mice. When host muscles were not irradiated before myoblast transplantation, 4.6% of the muscle fibers in host muscles were dystrophin positive 1 month after transplantation. Most of these dystrophin-positive muscle fibers were also beta-gal positive. About one quarter of these fibers are the result of reverse mutations; most of them have, however, been produced by fusion of donor myoblasts with host muscle fibers or with host myoblasts. The virtual absence of beta-gal-negative fibers indicates that there were no exclusively donor-donor fusions. When host muscles were irradiated before myoblast transplantation, roughly the same percentage (5.5%) of dystrophin-positive fibers were formed in the injected muscle, but 42% of them were beta-gal negative. These beta-gal-negative dystrophin-positive muscle fibers were formed by the exclusive fusion of donor myoblasts with one another rather than with host cells. This clearly indicates that myoblast transplantation can form completely new muscle fibers or muscle fiber segments when host satellite cell proliferation is reduced by irradiation. These newly formed muscle fibers had, however, a small diameter and additional myoblast transplantation may be required to increase their size. This situation has some similarities with findings in Duchenne muscular dystrophy patients of more than 6 years of age, who also have a limited proliferation capacity of their satellite cells.     

Spectral pattern of neonatal cerebral blood flow velocity: comparison with spectra from blood pressure and heart rate

BACKGROUND: Extrafusal muscle fibers of human striated skeletal muscles are known to have a uniform innervation pattern. Motor endplates (MEP) of the "en plaque" type are located near the center of muscle fibers and distributed within the muscles in a narrow band. The aim of this study was to evaluate the innervation pattern of human facial muscles and compare it with that of skeletal muscles. METHODS: Ten facial muscles from 11 human cadavers were dissected, the nerve entrance points located, and the dimensions measured. All muscles were stained in toto for MEPs using Acetylcholinesterase (AChE) and examined under the microscope to determine their location. Single muscle fibers were teased to evaluate the stained MEPs. RESULTS: The length of the different facial muscles varied from 29 to 65 mm, which correlated to the length of the corresponding muscle fibers. MEP zones were found on the muscles in the immediate vicinity of the nerves' entrance points and located eccentrically. Numbers and locations varied from muscle to muscle. Three MEP zone distribution patterns were differentiated: numerous small MEP zones were evenly spread over the muscle, a predominant MEP zone and two to three small zones were spread at random, and two to four MEP zones of equal size were randomly scattered. One MEP of the "en plaque" type was found in 73.8% of the muscle fibers and two to five MEPs were found in 26.2%. The distances between the multiple MEPs on one muscle fiber varied from 10 to 500 microm. CONCLUSIONS: This study suggests that facial muscles differ from skeletal muscles regarding distribution and number of MEPs. The eccentric location of MEP zones and multiple MEPs suggests there is an independent mechanism of neural regulation in the facial muscle system.