Biomedical subjects

R R Roy

Publications and source records attributed to R R Roy.

At least 127 records · Page 7Linked to original sources

PubMed1996

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.

Adaptation, Physiological↗

PubMed1995

Succinate dehydrogenase activity and soma size relationships among cat dorsal root ganglion neurons.

A large range in succinate dehydrogenase (SDH) activity and soma size among neurons in the dorsal root ganglion (DRG) and the dorsolateral region of the ventral horn (DLVH) at spinal cord level L7 was observed. Mean soma sizes were similar for the two populations. DLVH, but not DRG, neurons showed an inverse relationship between SDH activity and soma size. DRG neurons had a higher mean SDH activity than DLVH neurons, reflecting the observation that there was a population of DRG neurons with a higher oxidative capacity than DLVH neurons.

Animals↗

PubMed1995

Three-dimensional structure of cat tibialis anterior motor units.

The motor unit is the basic unit for force production in a muscle. However, the position and shape of the territory of a motor unit within the muscle have not been defined precisely. The territories of five motor units in the cat tibialis anterior muscle were reconstructed three-dimensionally (3-D) from tracings of the glycogen-depleted fibers belonging to each unit. The motor unit territories did not span the entire length of the muscle and their cross-sectional areas tapered along the proximodistal axis producing a conical shape. In addition, the position of the territory of each unit shifted in an anterior-posterior plane along the longitudinal axis of the muscle, presumably as a consequence of the pinnation of the fibers. The area of the motor unit territory at any given level along the proximodistal axis was highly correlated with the number of fibers within the territory at that level. Connective tissue boundaries (outlining fascicles) appeared to have a strong influence on the shape of the territory, territories showed abrupt changes at connective tissue boundaries as groups of motor unit fibers within a fascicle often terminated together while motor unit fibers in neighboring fascicles did not terminate. It is likely that the mechanical impact of the recruitment of a motor unit is affected by the location and shape of motor units within the same muscle area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Response of mouse plantaris muscle to functional overload: comparison with rat and cat.

Functional overload (FO) of a muscle by removing its synergists results in a compensatory hypertrophy of the muscle. However, the extent of the response appears to be dependent, at least in part, on the activity and/or loading levels of the muscle following surgery. Thus, differences in the inherent physical activity levels across species may be an important factor to consider. In the present study, the effects of 8 weeks of FO on the isometric mechanical properties of the plantaris of mice (highly active) were determined and the findings compared with the results from previous studies performed on the plantaris of rats (highly active) and cats (less active). FO resulted in approximately a doubling of the mass, the physiological cross-sectional area and the maximum tetanic tension per unit cross-sectional area, was similar in the plantaris of control and FO mice. Isometric twitch speed properties were unaffected, but the tension enhancement in response to an increase in the rate of stimulation showed the pattern of a "faster" muscle following FO. The fatigue resistance of the plantaris in FO mice was significantly higher than in control mice. Although the degree of hypertrophy that occurred in the mouse plantaris was similar to that observed after FO in rats and in cats that are exercised intermittently at high intensities, there were differences in the mechanical properties that may be related to the adaptability of species and/or the behavioral responses to the overload.

Animals↗

PubMed1995

Succinate dehydrogenase activity and soma size of motoneurons innervating different portions of the rat tibialis anterior.

The spatial distribution, soma size and oxidative enzyme activity of gamma and alpha motoneurons innervating muscle fibres in the deep (away from the surface of the muscle) and superficial (close to the surface of the muscle) portions of the tibialis anterior in normal rats were determined. The deep portion had a higher percentage of high oxidative fibres than the superficial portion of the muscle. Motoneurons were labelled by retrograde neuronal transport of fluorescent tracers: Fast Blue and Nuclear Yellow were injected into the deep portion and Nuclear Yellow into the superficial portion of the muscle. Therefore, motoneurons innervating the deep portion were identified by both a blue fluorescent cytoplasm and a golden-yellow fluorescent nucleus, while motoneurons innervating the superficial portion were identified by only a golden-yellow fluorescent nucleus. After staining for succinate dehydrogenase activity on the same section used for the identification of the motoneurons, soma size and succinate dehydrogenase activity of the motoneurons were measured. The gamma and alpha motoneurons innervating both the deep and superficial portions were located primarily at L4 and were intermingled within the same region of the dorsolateral portion of the ventral horn in the spinal cord. Mean soma size was similar for either gamma or alpha motoneurons in the two portions of the muscle. The alpha motoneurons innervating the superficial portion had a lower mean succinate dehydrogenase activity than those innervating the deep portion of the muscle. An inverse relationship between soma size and succinate dehydrogenase activity of alpha, but not gamma, motoneurons innervating both the deep and superficial portions was observed. Based on three-dimensional reconstructions within the spinal cord, there were no apparent differences in the spatial distribution of the motoneurons, either gamma or alpha, associated with the deep and superficial compartments of the muscle. The data provide evidence for an interdependence in the oxidative capacity between a motoneuron and its target muscle fibres in two subpopulations of motoneurons from the same motor pool, i.e. the same muscle.

Animals↗

PubMed1995

Further evidence of incomplete neural control of muscle properties in cat tibialis anterior motor units.

To examine the influence of a motoneuron in maintaining the phenotype of the muscle fibers it innervates, myosin heavy chain (MHC) expression, succinate dehydrogenase (SDH) activity, and cross-sectional area (CSA) of a sample of fibers belonging to a motor unit were studied in the cat tibialis anterior 6 mo after the nerve branches innervating the anterior compartment were cut and sutured near the point of entry into the muscle. The mean, range, and coefficient of variation for the SDH activity and the CSA for both motor unit and non-motor unit fibers for each MHC profile and from each control and each self-reinnervated muscle studied was obtained. Eight motor units were isolated from self-reinnervated muscles using standard ventral root filament testing techniques, tested physiologically, and compared with four motor units from control muscles. Motor units from self-reinnervated muscles could be classified into the same physiological types as those found in control tibialis anterior muscles. The muscle fibers belonging to a unit were depleted of glycogen via repetitive stimulation and identified in periodic acid-Schiff-stained frozen sections. Whereas muscle fibers in control units expressed similar MHCs, each motor unit from self-reinnervated muscles contained a mixture of fiber types. In each motor unit, however, there was a predominance of fibers with the same MHC profile. The relative differences in the mean SDH activities found among fibers of different MHC profiles within a unit after self-reinnervation and those found among fibers in control muscles were similar, i.e., fast-2 < fast-1 < or = slow MHC fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Prominence of myosin heavy chain hybrid fibers in soleus muscle of spinal cord-transected rats.

The effect of a midthoracic spinal cord transection (ST) on myosin heavy chain (MHC) isoform expression in the rat soleus muscle was studied. Electrophoretic analyses demonstrated that 15 days after ST there were significant proportional increases in type IIx, decreases in type IIa, and no change in type I MHC composition. Thirty days after ST, some type IIb MHC was expressed, there were further proportional increases in type IIx, an increase in type IIa (compared with 15-day ST), and a decrease in type I MHC. At both time periods after ST, many fibers expressed multiple MHCs, as demonstrated by immunohistochemistry where a battery of monoclonal antibodies specific to MHC isoforms was used. Fibers were observed containing types I and II together or multiple type II MHC isoforms. These data suggest that the expression of the normal complement of MHC isoforms in the adult rat soleus muscle is dependent, in part, on normal neuromuscular activation.

Animals↗

PubMed1995

Human fiber size and enzymatic properties after 5 and 11 days of spaceflight.

Biopsies from the vastus lateralis muscle were obtained from three astronauts before and after two 5-day flights and from five astronauts before and after one 11-day flight (space shuttle flights: STS-32, -33, and -34). Muscle fibers from two separate samples from each biopsy were classified as type I and II or as type I, IIA, and IIB by using qualitative myofibrillar adenosinetriphosphatase (ATPase) staining. Cross-sectional area (CSA), number of capillaries per fiber, and the activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar ATPase were determined from one sample of fibers of each myofibrillar ATPase type. Postflight biopsies had 6-8% fewer type I fibers than preflight. Mean fiber CSAs were 16-36% smaller after the 11-day flight with the relative effect being type IIB > IIA > I. Mean fiber CSAs were 11 and 24% smaller in type I and II fibers after 5 days of flight. Myofibrillar ATPase activities increased in type II but not in type I fibers after flight, whereas SDH activity was unaffected in either fast or slow fibers. GPD activity in type I fibers was approximately 80% higher (P > 0.05) postflight compared with preflight. Myofibrillar ATPase/SDH ratios in type II fibers were higher after than before flight, suggesting that some fast fibers were more susceptible to fatigue after flight. The GPD/SDH ratios were elevated in some type I fibers after spaceflight. The number of capillaries per fiber was 24% lower after than before flight, whereas the number of capillaries per unit CSA of muscle tissue was unchanged. These data suggest that adaptations in the size, metabolic properties, and vascularity of muscle fibers can occur rapidly in the space environment. These adaptations were qualitatively similar to those observed in animals after actual or simulated spaceflight conditions for short periods.

Adenosine Triphosphatases↗

PubMed1995

Myosin heavy chain isoforms of human muscle after short-term spaceflight.

The influence of microgravity on the myosin phenotype of skeletal muscle fibers in the vastus lateralis of eight crew members was studied before and after 5-day (n = 3) and 11-day (n = 5) spaceflights (space shuttle flights: STS-32, -33 and -34). Single-fiber electrophoresis analyses showed that the proportion of fibers expressing only slow (type I) myosin heavy chain (MHC) in the vastus lateralis was significantly lower after than before 11 days of spaceflight. Although the family of type II MHC isoforms was elevated post- compared with preflight, the distribution among the isoforms of type II MHC was not statistically different. Based on monoclonal and polyclonal antibodies specific for three adult MHC isoforms and single-fiber electrophoresis, approximately 3% of the fibers analyzed coexpressed all three adult MHC isoforms. The results from immunohistochemical staining with two different sets of antibodies indicate a reduction in the percentage of fibers expressing type I MHC as a result of spaceflight. The mean difference, however, was significant only when the fibers were categorized simply as type I or II. These changes appeared to be highly individualized among the astronauts. These results suggest that a rapid change in MHC isoform expression can occur in some muscle fibers after a relatively brief exposure to spaceflight.

Adult↗

PubMed1995

Plasticity of myonuclear number in hypertrophied and atrophied mammalian skeletal muscle fibers.

Although a mammalian skeletal muscle fiber may contain thousands of myonuclei, the importance of this number or the potential to modulate it in adult muscle has not been clearly demonstrated. Using immunohistochemistry and confocal microscopy, we examined the plasticity of myonuclear number and fiber size in isolated fast and slow fiber segments from adult cat hindlimb muscles in response to chronic alterations in neuromuscular activity and loading. Compared with slow fibers in the soleus of control cats, myonuclear number in presumably transformed fast fibers was 32% lower and fiber size was decreased 73% after elimination of neuromuscular activation for 6 mo by spinal isolation. Slow fibers in the soleus of spinal-isolated cats had smaller cross-sectional areas, whereas myonuclear number was not significantly different than that in the control cats. Myonuclear number in fast plantaris fibers was more than threefold higher and fiber size was 2.8-fold higher after 3 mo of functional overload compared with the plantaris of control cats. Compared with control slow plantaris fibers, myonuclear number and fiber size also increased in overloaded slow plantaris fibers. These results demonstrate that changes in myonuclear number are associated with changes in myosin type and suggest that modulations in the amount of available DNA may be a factor in regulating cytoplasmic volume of muscle fibers in response to chronic changes in neuromuscular activity.

Animals↗

PubMed1995

Myofibrillar ATPase activity of feline muscle fibers expressing slow and fast myosin heavy chains.

The interrelationships among myofibrillar ATPase activity (Quant-mATPase), qualitative myofibrillar ATPase staining after acid (Acid-mATPase) and alkaline (Alk-mATPase) preincubations, and myosin heavy chain (MHC) composition were determined in frozen sections of soleus (Sol) and medial gastrocnemius (MG) muscle fibers from adult control cats and cats 6 months after complete spinal cord transection (Sp). Fibers were categorized as either fast, slow, or fast and slow (Fast-Slow) based on monoclonal antibody labeling. Slow fibers had low Quant-mATPase activity and stained lightly with Alk-mATPase and darkly with Acid-mATPase. Fast fibers had high Quant-mATPase activity (approximately twice that of slow fibers) and stained darkly with Alk-mATPase and lightly with Acid-mATPase. Fast-Slow fibers had intermediate Quant-mATPase activity and stained intermediately for Acid-mATPase and darkly for Alk-mATPase. There was a positive linear relationship between Alk-mATPase and Quant-mATPase for all fibers of Sol and MG from control and Sp cats. There was a negative linear relationship between Acid-mATPase and Quant-mATPase for all fibers of Sol and MG. However, within the fast fiber population of the MG there was a positive relationship between these two measures of mATPase. In summary, quantitative and qualitative measures of mATPase are highly correlated with the types of MHC expressed by single fibers from control and Sp cat muscles.

Animals↗

PubMed1995

Adaptations of human skeletal muscle fibers to spaceflight.

Human skeletal muscle fibers seem to share most of the same interrelationships among myosin ATPase activity, myosin heavy chain (MHC) phenotype, mitochondrial enzyme activities, glycolytic enzyme activities and cross-sectional area (CSA) as found in rat, cat and other species. One difference seems to be that fast fibers with high mitochondrial content occur less frequently in humans than in the rat or cat. Recently we have reported that the type of MHC expressed and the size of the muscle fibers in humans that have spent 11 days in space change significantly. Specifically, about 8% more fibers express fast MHCs and all phenotypes atrophy in the vastus lateralis (VL) post compared to preflight. In the present paper we examine the relationships among the population of myonuclei, MHC type and CSA of single human muscle fibers before and after spaceflight. These are the first data that define the relationship among the types of MHC expressed, myonuclei number and myonuclei domain of single fibers in human muscle. We then compare these data to similar measures in the cat. In addition, the maximal torque that can be generated by the knee extensors and their fatigability before and after spaceflight are examined. These data provide some indication of the potential physiological consequences of the muscle adaptations that occur in humans in response to spaceflight.

Adaptation, Physiological↗

PubMed1995

Adaptations in myosin heavy chain profile in chronically unloaded muscles.

In this review, myosin heavy chain (MHC) adaptations in response to several models of decreased neuromuscular activity (i.e. electrical activation and loading of a muscle) are evaluated. In each of these "reduced-activity" models it is important to: a) quantify the changes in electrical activation of the muscle as a result of the intervention; b) quantify the forces generated by the muscle; and c) determine whether the neuromuscular junction remains normal. Most of the models, including spaceflight, hindlimb suspension, spinal cord isolation, spinal cord transection, denervation, and limb immobilization in a shortened position, result in increases in the percentage of fast MHCs (or fast MHC mRNA) in normally slow rat muscles. It also can be inferred from histochemical data that increases in fast MHCs occur with TTX application and bed rest. The only "reduced-activity" model to consistently increase slow muscle myosin mRNA, and slow fibers is limb immobilization in a stretched position; however, this model results in at least a temporary increase in tension. It appears that the most common feature of these models that might induce MHC adaptations is the modification in loading rather than a change in the neuromuscular activity.

Animals↗

PubMed1994

Extensor- and flexor-like modulation within motor pools of the rat hindlimb during treadmill locomotion and swimming.

EMG activity was recorded from the vastus lateralis (VL, knee extensor), rectus femoris (RF, hip flexor and knee extensor), tibialis anterior (TA, ankle flexor and digit extensor) and either the lateral or medial gastrocnemius (LG, MG, knee flexors and ankle extensors) muscles of 7 adult rats during treadmill locomotion and swimming. Most flexors and extensors are activated as a single burst but each is known to be modulated differently during locomotion. For example, the extensor EMG bursts are shortened and amplitude elevated as speed increases, whereas little change occurs in the EMG duration and amplitude in flexors. The RF and VL displayed a double burst of EMG activity per cycle during treadmill locomotion and a single burst during swimming. Kinematic and EMG analyses showed that during running, one of these EMG bursts occurred primarily during swing while the other burst occurred primarily during stance. Modulation of the burst occurring during swing approximated a flexor pattern, while the second burst was modulated like a typical extensor when running over a range of speeds and grades on a treadmill. These data suggest that motoneurons within a motor pool of a uniarticular (VL) as well as a biarticular (RF) muscle can be modulated by more than one cyclical input, probably of central origin, and that under some conditions several motor pools may share the same central commands.

Activity Cycles↗

PubMed1994

Regional and age variations in growing tendon.

Gastrocnemius tendons of 10 White Leghorn chickens at 6, 8, and 12 weeks of age were divided into proximal, middle, and distal portions to assess regional variability in composition and growth. Body weight increases approximately 150% during the period examined, whereas the lateral gastrocnemius muscle and tendon increase approximately 193% and 227%, respectively. No significant changes in cellularity (DNA concentration) or hydroxypyridinium (OHP) crosslinks occur with increasing age. Hydroxyproline (HYP) concentration increases by 12 weeks of age, as hexuronate, glucosamine, and galactosamine decrease. Composition shows some regional variation: the distal region of the tendon has a lower HYP concentration and increased GAGs and OHP crosslinks compared to either the proximal or middle regions, which do not differ from each other. The mean collagen fibril diameter increases with age, but the oldest tendons also contain more small diameter fibrils (< 40 nm). There is a unimodal fibril distribution at all three ages, although this has broadened by 12 weeks. The data from this study suggest that rapid tendon growth occurs throughout the time period examined and that changes characteristic of mature tendon, such as increased OHP crosslink concentration, have not yet developed in hatchlings because of the large amount of new tissue being produced. Whereas all three regions of the tendon are similar in size, composition of the distal region differs from that of the proximal and middle regions, suggesting that this portion of the tendon should be avoided when sampling a tendon.

Aging↗

PubMed1994

Level of independence of motor unit properties from neuromuscular activity.

Neuromuscular activity was eliminated in the tibialis anterior muscle of adult cats for 6 months by spinal isolation (SI), i.e., complete spinal cord transections at T-12-13 and at L-7-S-1, plus bilateral dorsal rhizotomy between the two transection sites. One motor unit from each muscle was isolated using ventral root teasing procedures and physiologically tested. The fibers belonging to each motor unit were visualized in PAS-stained sections by the loss of glycogen following prolonged repetitive stimulation. Qualitatively, the normal enzymatic interrelationships among fibers identified by myosin heavy chain composition were unchanged by SI. Generally, each motor unit from SI cats were of a single myosin immunohistochemical type. The same physiological motor unit types that typify control muscles were found in SI cats. In SI compared to control cats, there was approximately a 10% increase in the number of muscle fibers expressing fast myosin. Mean fiber activity levels of ATPase and SDH for a given fiber type (based on MHC antibody reactions) decreased by approximately 10% and 25%, whereas GPD activity increased approximately 35%. It is concluded that differential levels or patterns of activity are not essential to maintain the range of histochemical and physiological motor unit types found in the tibialis anterior of normal adult cats.

Action Potentials↗

PubMed1994

Neuromuscular adaptation to actual and simulated weightlessness.

The chronic "unloading" of the neuromuscular system during spaceflight has detrimental functional and morphological effects. Changes in the metabolic and mechanical properties of the musculature can be attributed largely to the loss of muscle protein and the alteration in the relative proportion of the proteins in skeletal muscle, particularly in the muscles that have an antigravity function under normal loading conditions. These adaptations could result in decrements in the performance of routine or specialized motor tasks, both of which may be critical for survival in an altered gravitational field, i.e., during spaceflight and during return to 1 G. For example, the loss in extensor muscle mass requires a higher percentage of recruitment of the motor pools for any specific motor task. Thus, a faster rate of fatigue will occur in the activated muscles. These consequences emphasize the importance of developing techniques for minimizing muscle loss during spaceflight, at least in preparation for the return to 1 G after spaceflight. New insights into the complexity and the interactive elements that contribute to the neuromuscular adaptations to space have been gained from studies of the role of exercise and/or growth factors as countermeasures of atrophy. The present chapter illustrates the inevitable interactive effects of neural and muscular systems in adapting to space. It also describes the considerable progress that has been made toward the goal of minimizing the functional impact of the stimuli that induce the neuromuscular adaptations to space.

Adaptation, Physiological↗

PubMed1994

Interactive effects of growth hormone and exercise on muscle mass in suspended rats.

Measures to attenuate muscle atrophy in rats in response to stimulated microgravity [hindlimb suspension (HS)] have been only partially successful. In the present study, hypophysectomized rats were in HS for 7 days, and the effects of recombinant human growth hormone (GH), exercise (Ex), or GH+Ex on the weights, protein concentrations, and fiber cross-sectional areas (CSAs) of hindlimb muscles were determined. The weights of four extensor muscles, i.e., the soleus (Sol), medial (MG) and lateral (LG) gastrocnemius, and plantaris (Plt), and one adductor, i.e., the adductor longus (AL), were decreased by 10-22% after HS. Fiber CSAs were decreased by 34% in the Sol and by 17% in the MG after HS. In contrast, two flexors, i.e., the tibialis anterior (TA) and extensor digitorum longus (EDL), did not atrophy. In HS rats, GH treatment alone maintained the weights of the fast extensors (MG, LG, Plt) and flexors (TA, EDL) at or above those of control rats. This effect was not observed in the slow extensor (Sol) or AL. Exercise had no significant effect on the weight of any muscle in HS rats. A combination of GH and Ex treatments yielded a significant increase in the weights of the fast extensors and in the CSA of both fast and slow fibers of the MG and significantly increased Sol weight and CSA of the slow fibers of the Sol. The AL was not responsive to either GH or Ex treatments. Protein concentrations of the Sol and MG were higher only in the Sol of Ex and GH + Ex rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗