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Biomedical subjects

R R Roy

Publications and source records attributed to R R Roy.

At least 91 records · Page 5Linked to original sources
PubMed1998

Hypertrophy of rat plantaris muscle fibers after voluntary running with increasing loads.

There have been no systematic comparisons of skeletal muscle adaptations in response to voluntary wheel running under controlled loading conditions. To accomplish this, a voluntary running wheel for rats and mice was developed in which a known load can be controlled and monitored electronically. Five-week-old male Sprague-Dawley rats (10 rats/group) were assigned randomly to either a 1) sedentary control group (Control); 2) voluntary exercised with no load (Run-No-Load) group; or 3) voluntary exercised with additional load (Run-Load) group for 8 wk. The load for the Run-Load group was progressively increased to reach approximately 60% of body weight during the last week of training. The proportions of fast glycolytic (FG), fast oxidative glycolytic (FOG), or slow oxidative (SO) fibers in the plantaris were similar in all groups. The absolute and relative plantaris weights were greater in the Run-Load group compared with the Control and Run-No-Load groups. The mean fiber cross-sectional areas of FG, FOG, and SO fibers were 20, 25, and 15% greater in the Run-Load than in Control rats. In addition, these fiber types were 16, 21, and 12% larger in Run-Load than in Run-No-Load rats. The muscle weights and mean cross-sectional areas of each fiber type were highly correlated with the average running distances and total work performed in the Run-Load, but not the Run-No-Load, group. The slope of the relationship between fiber size and running distance and total work performed was significant for each fiber type but was higher for FG and FOG fibers compared with SO fibers. These data show that the load on a rat running voluntarily can determine the magnitude of a hypertrophic response and the population of motor units that are recruited to perform at a given loading condition.

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PubMed1998

Size constraints of telemeters in rats.

This study was designed to determine the maximum-size subcutaneous telemeter that would enable long-term and multichannel data collection in a 170-g rat for 90 days. In phase 1, rats with implants weighing 5 (2.5 cm3), 15 (7.5 cm3), 25 (12.5 cm3), 35 (17.5 cm3), or 45 (22.5 cm3) g were compared with sham-operated (SOC) and nonoperated (NOC) control animals. Severe skin lesions, seromas, and lower growth rates were observed in rats having implants >/=35 g. Thus, in phase 2, rats implanted with 23.5 g (17.5 cm3; 11-g active telemeter and 12.5-g implant) were compared with rats implanted with 11 g (6 cm3; telemeter only) and with the SOC and NOC groups. No differences were found among implanted groups in mean arterial pressure (MAP), heart rate (HR), subcutaneous temperature, or spontaneous activity under standard housing conditions. All groups were more active and had a higher MAP during the dark than the light phase of the daily cycle. During 2 h of cold exposure (3 degreesC), both telemetered groups exhibited similar changes in HR, MAP, temperature, and activity levels. Adrenal glands were larger in the 23.5-g group (51 +/- 1.6 mg) than in the SOC (46 +/- 1.0 mg) and the NOC groups (41 +/- 2.0 mg). No other significant differences were found in organ, muscle, or bone weights. These data verify the feasibility of using 23.5-g (17.5 cm3) subcutaneous telemeters for chronic recordings in young adult rats.

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PubMed1998

Locomotor capacity attributable to step training versus spontaneous recovery after spinalization in adult cats.

Locomotor performance, hindlimb muscle activity and gait patterns during stepping were studied in step-trained and non-trained female, adult spinal cats. Changes in locomotor characteristics relative to prespinalization bipedal and quadrupedal stepping patterns were used to evaluate the effects of step training on the capacity to execute full weight-bearing stepping after spinalization. Step training consisted of full weight-bearing stepping of the hindlimbs at the greatest range of treadmill speeds possible at any given stage of locomotor recovery. In the initial stages of training the limbs were assisted as needed to execute successful steps. On the basis of two behavioral criteria, the maximum speed of treadmill stepping and the number of successful steps per unit time, the ability to step was at least 3 times greater in animals trained to step versus those allowed to recover spontaneously, i.e., the non-trained. The greater success in stepping was reflected in several physiological and kinematic properties. For example, the amplitude of electromyograph (EMG) bursts in the tibialis anterior (an ankle dorsiflexor), the amount of extension at the end of both the stance (E3) and swing (E1) phases of the step cycle, and the amount of lift of the hindlimb during swing were greater in step-trained than in non-trained spinal cats. The changes that occurred in response to training reflected functional adaptations at specific phases of the step cycle, e.g., enhanced flexor and extensor function. The improved stepping capacity attributable to step training is interpreted as a change in the probability of the appropriate neurons being activated in a temporally appropriate manner. This interpretation, in turn, suggests that step training facilitated or reinforced the function of extant sensorimotor pathways rather than promoting the generation of additional pathways. These results show that the capacity of the adult lumbar spinal cord to generate full weight-bearing stepping over a range of speeds is defined, in large part, by the functional experience of the spinal cord after supraspinal connectivity has been eliminated. These results have obvious implications with regards to 1) the possibility of motor learning occurring in the spinal cord; 2) the importance of considering "motor experience" in assessing the effect of any postspinalization intervention; and 3) the utilization of use-dependent interventions in facilitating and enhancing motor recovery.

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PubMed1998

Full weight-bearing hindlimb standing following stand training in the adult spinal cat.

Behavioral and physiological characteristics of standing were studied in nontrained spinal cats and in spinal cats that received daily stand training of the hindlimbs for 12 wk. Training consisted of assisting the cats to stand with full weight support either on both hindlimbs or on one hindlimb (30 min/day, 5 days/wk). Extensor muscle electromyographic (EMG) amplitude and extension at the knee and ankle joints during full weight bearing recovered to prespinal levels in both stand-trained and nontrained spinal cats. However, full weight bearing of the hindquarters was sustained for up to approximately 20 min in the spinal cats that received bilateral stand training compared with approximately 4 min in cats that were not trained to stand. Unilateral stand training selectively improved weight bearing on the trained limb based on ground reaction forces and extensor muscle EMG activity levels measured during bilateral standing. These results suggest that the capacity of the adult lumbar spinal cord to generate full weight-bearing standing can be improved by as much as fivefold by the repetitive activation of selected neural pathways in the spinal cord after supraspinal connectivity has been eliminated. Given that stepping is improved in response to step training, it appears that the recovery of standing provides another example of training-specific motor learning in the spinal cord, i.e., the spinal cord learns to perform hindlimb standing by practicing that specific task.

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PubMed1998

Comparison of hyper- and microgravity on rat muscle, organ weights and selected plasma constituents.

BACKGROUND: Centrifugation has been proposed to be one possible countermeasure for the skeletal muscle, organ, hormonal, and plasma chemistry adaptations associated with chronic unloading (e.g., during spaceflight). HYPOTHESIS: Our hypothesis was that there would be a continuum of physiological and morphological responses from zero gravity to hypergravity. METHODS: Adult male rats were centrifuged continuously at 2G for 14 d and the weights of limb muscles and organs, and the levels of plasma constituents were compared with the same measurements from rats flown on a 14-d spaceflight (Cosmos 2044). RESULTS: Mean body weights of centrifuge rats did not change, whereas age-matched controls grew 21%. There was a sparing of muscle protein in the centrifuge rats; the absolute weights of predominantly slow muscles in the hindlimb were maintained and the relative weights (expressed relative to body weight and as a percent difference from control) of almost all muscles studied were larger than control. In contrast, spaceflight resulted in a decrease in the relative weights of most extensor, but not flexor, hindlimb muscles studied. Relative organ weights, in general, were elevated in centrifuge rats compared with control rats. Relative organ weights in flight rats were similar to control, except for a decrease in testes weight. Plasma thyroxine and testosterone levels were significantly reduced following flight, whereas only thyroxine was decreased after centrifugation. Centrifugation resulted in a decrease in most other plasma chemistry measurements, whereas flight rats showed no change or an elevation in these measures. DISCUSSION: These data indicate that the physiological responses to micro- and hypergravity are often in the opposite direction, suggesting that in general there is a continuum of physiological and morphological effects from microgravity to 1G to hypergravity. These data further suggest that the imposition of hypergravity conditions on animals that are in a microgravity environment may have a beneficial effect in maintaining some physiological systems at or near control levels.

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PubMed1997

Architectural and mechanical properties of the rat adductor longus: response to weight-lifting training.

BACKGROUND: The primary objective of this study was to determine the effects of an 8 week weight-lifting program on the mechanical, histochemical, and architectural properties of the rat adductor longus muscle, a predominantly slow adductor muscle. METHODS: The weight-lifting program was progressive such that the rats were performing three bouts of ten lifts with 300% body weight load every other day during the last 3 weeks of training. The in situ mechanical properties, fiber type composition, and architectural characteristics of the muscle were determined in control and weight-trained rats. Intramuscular electromyographic recordings were used to verify the recruitment of the adductor longus during the lifting task. RESULTS: The adductor longus was composed predominantly of slow fibers (approximately 80% slow oxidative) and had a relatively simple architectural design, i.e., one motor end-plate band near the center of the muscle, virtually no angle of pinnation of the fibers from the line of pull, and a fiber length:muscle length ratio of 0.72. The mean fiber type composition and fiber size, the total fiber number, and the mean physiological cross-sectional area of the adductor longus were similar in the two groups of rats. The mean body weight of weight-lifting rats was significantly less than control. The weight of the adductor longus relative to body weight and its fatigue resistance were higher and the maximum rate of shortening was slower in weight-lifting than in control rats. No other mechanical property was significantly affected by the training program. CONCLUSIONS: The results indicate that approximately 1 minute of over-load every other day by physiological recruitment of motor units can induce remodeling of the adductor longus of growing rats; i.e., the trained muscles were slower and less fatigable than control. Given that the effects on the architectural or force-generating properties of the muscles were small, the marked improvement in the ability to lift heavier loads as the training progressed appears to be more attributable to neurally related than to muscle-related phenomena.

Adenosine Triphosphatases↗
PubMed1997

Effects of 14 days of spaceflight and nine days of recovery on cell body size and succinate dehydrogenase activity of rat dorsal root ganglion neurons.

The cross-sectional areas and succinate dehydrogenase activities of L5 dorsal root ganglion neurons in rats were determined after 14 days of spaceflight and after nine days of recovery. The mean and distribution of the cross-sectional areas were similar to age-matched, ground-based controls for both the spaceflight and for the spaceflight plus recovery groups. The mean succinate dehydrogenase activity was significantly lower in spaceflight compared to aged-matched control rats, whereas the mean succinate dehydrogenase activity was similar in age-matched control and spaceflight plus recovery rats. The mean succinate dehydrogenase activity of neurons with cross-sectional areas between 1000 and 2000 microns2 was lower (between 7 and 10%) in both the spaceflight and the spaceflight plus recovery groups compared to the appropriate control groups. The reduction in the oxidative capacity of a subpopulation of sensory neurons having relatively large cross-sectional areas immediately following spaceflight and the sustained depression for nine days after returning to 1 g suggest that the 0 g environment induced significant alterations in proprioceptive function.

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PubMed1997

Apoptosis: a mechanism contributing to remodeling of skeletal muscle in response to hindlimb unweighting.

The role of apoptosis in the elimination of myonuclei during hindlimb unloading-induced atrophy and the inhibition of apoptosis in the prevention of muscle atrophy were examined. The number of nuclei demonstrating double-stranded DNA fragmentation seen by terminal deoxynucleotidyl transferase (TDT) histochemical staining, an indicator of apoptosis, was significantly increased after 14 days of suspension. Double staining with TDT and antilaminin immunohistochemistry revealed that some TDT-positive nuclei were within the fiber lamina and were most likely myonuclei. The number of fibers containing morphologically abnormal nuclei was also significantly greater in suspended compared with control rats. Combined treatment with growth hormone and insulin-like growth factor I (GH/ IGF-I) and resistance exercise attenuated the increase in TDT-positive nuclei (approximately 26%, P > 0.05) and significantly decreased the number of fibers with morphologically abnormal nuclei. The data suggest that 1) "programmed nuclear death" contributes to the elimination of myonuclei and/or satellite cells from atrophying fibers, and 2) GH/IGF-I administration plus muscle loading ameliorates the apoptosis associated with hindlimb unloading.

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PubMed1997

Modulation of MHC isoforms in functionally overloaded and exercised rat plantaris fibers.

The effects of 1 and 10 wk of functional overload (FO) of the rat plantaris with (FOTr) and without daily endurance treadmill training on its myosin heavy chain (MHC) composition were studied. After 1 and 10 wk of FO, plantaris mass was 22 and 56% greater in FO and 37 and 94% greater, respectively, in FOTr rats compared with age-matched controls. At 1 wk, pure type I and pure type IIa MHC fibers were hypertrophied in FO (39 and 44%) and FOTr (70 and 87%) rats. By 10 wk all fiber types comprising >5% of the fibers sampled showed a hypertrophic response in both FO groups. One week of FO increased the percentage of hybrid (containing both type I and type IIa MHC) fibers and of fibers containing embryonic MHC. By 10 wk, the percentage of pure type I MHC fibers was approximately 40% in both FO groups compared with 15% in controls, and the percentage of fibers containing embryonic MHC was similar to that in controls. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses showed an increase in type I MHC and a decrease in type IIb MHC in both FO groups at 10 wk, whereas little change was observed at 1 wk. These data are consistent with hypertrophy and transformation from faster to slower MHC isoforms in chronically overloaded muscles. The additional overload imposed by daily endurance treadmill training employed in this study (1.6 km/day; 10% incline) results in a larger hypertrophic response but appears to have a minimal effect on the MHC adaptations.

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PubMed1997

Growth hormone, IGF-I, and exercise effects on non-weight-bearing fast muscles of hypophysectomized rats.

The effects of growth hormone (GH) or insulin-like growth factor I (IGF-I) with or without exercise (ladder climbing) in countering the effects of unweighting on fast muscles of hypophysectomized rats during 10 days of hindlimb suspension were determined. Compared with untreated suspended rats, muscle weights were 16-29% larger in GH-treated and 5-15% larger in IGF-I-treated suspended rats. Exercise alone had no effect on muscle weights. Compared with ambulatory control, the medial gastrocnemius weight in suspended, exercised rats was larger after GH treatment and maintained with IGF-I treatment. The combination of GH or IGF-I plus exercise in suspended rats resulted in an increase in size of each predominant fiber type, i.e., types I, I + IIa and IIa + IIx, in the medial gastrocnemius compared with untreated suspended rats. Normal ambulation or exercise during suspension increased the proportion of fibers expressing embryonic myosin heavy chain in hypophysectomized rats. The phenotype of the medial gastrocnemius was minimally affected by GH, IGF-I, and/or exercise. These results show that there is an IGF-I, as well as a GH, and exercise interactive effect in maintaining medial gastrocnemius fiber size in suspended hypophysectomized rats.

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PubMed1997

Growth hormone/IGF-I and/or resistive exercise maintains myonuclear number in hindlimb unweighted muscles.

In the present study of rats, we examined the role, during 2 wk of hindlimb suspension, of growth hormone/insulin-like growth factor I (GH/IGF-I) administration and/or brief bouts of resistance exercise in ameliorating the loss of myonuclei in fibers of the soleus muscle that express type I myosin heavy chain. Hindlimb suspension resulted in a significant decrease in mean soleus wet weight that was attenuated either by exercise alone or by exercise plus GH/IGF-I treatment but was not attenuated by hormonal treatment alone. Both mean myonuclear number and mean fiber cross-sectional area (CSA) of fibers expressing type I myosin heavy chain decreased after 2 wk of suspension compared with control (134 vs. 162 myonuclei/mm and 917 vs. 2,076 micron2, respectively). Neither GH/IGF-I treatment nor exercise alone affected myonuclear number or fiber CSA, but the combination of exercise and growth-factor treatment attenuated the decrease in both variables. A significant correlation was found between mean myonuclear number and mean CSA across all groups. Thus GH/IGF-I administration and brief bouts of muscle loading had an interactive effect in attenuating the loss of myonuclei induced by chronic unloading.

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PubMed1997

Effects of muscle length on the response to unloading.

Muscle mass, distribution of fiber types, fiber cross-sectional areas (CSA) and selected enzyme activities were determined in rats hindlimb-suspended free of immobilization (Susp-Free), suspended with the ankle dorsiflexed (Susp-DF, soleus stretched) or plantarflexed (Susp-PF, soleus shortened) for 10 days and compared to cage-control (Con) rats. Reduction of muscle weight associated with suspension was prevented in Susp-DF rats. The mean CSAs of slow fibers were Con = Susp-DF > Susp > PF > Susp-Free and of fast and intermediate fiber tended to be Susp-DF > Con > Susp-PF = Susp-Free. Mean activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD) and myofibrillar adenosine triphosphatase (mATPase) in slow and fast fibers were similar in Con and Susp-Free rats. Mean SDH activity in slow fibers was higher in Susp-DF and Susp-PF than in Con and Susp-Free. No significant differences in SDH activities of fast fibers were observed among groups. GPD activity was higher in slow fibers of Susp-DF and Susp-PF compared to Con. The mATPase activity was higher in slow fibers of Susp-DF compared to Con and Susp-Free rats and lower in fast fibers of Susp-DF compared to Con rats. Thus, when compared to control, the patterns of adaptation were more similar in the Susp-DF and Susp-PF than in the Susp-Free. Although these results are consistent with previous studies demonstrating that the load placed on a muscle can affect protein metabolism, the direction and magnitude of the adaptive responses observed in the present study were closely associated with the chronically imposed changes in muscle length, i.e. fixed at either a shortened or a lengthened position.

Adenosine Triphosphatases↗
PubMed1997

Spindle representation relative to distribution of muscle fiber types in the cat capsularis muscle.

The spatial representation of muscle spindles (Sps) in the small (approximately 0.2 g), simply structured capsularis muscle that crosses anterior to the cat's hip joint was compared with the distribution of the slow oxidative (SO) and few (< 10%) fast oxidative-glycolytic (FOG) fibers of which it is composed to see if their distributions were consistent with a hypothesis that sensory input from Sps influences the incidence of extrafusal fiber types. In frozen sections from 4 muscles, FOG fibers were enumerated along 1-mm strips across the muscle's maximum width, and between the 'superficial' surface and the 'deep' one that contacts the joint. The locations of Sps in complete serial sections of 2 paraffin-embedded muscles, one perfused with the hip joint flexed and the other with it extended, were plotted on an outline of each muscle at its midlength, and their numbers and density in horizontal and sagittal 'strata' determined. In general, the incidence of Sps increased down the superficial-to-deep axis, while FOG fibers became fewer, as is consistent with support of SO status by Sp input. Along the craniocaudal axis, i.e. width, the numbers of FOG fibers rose toward the hip joint, but this was not associated with a monomodal gradient of Sps. In the extended muscle, however, the lengths of the axial bundle and capsular space of Sps in the half of the muscle next to the joint exceeded those in the longer, cranial half, implying that under stretch the input from Sps became higher toward the joint. In the non-extended muscle these lengths did not differ, although the lengths of extrafusal fibers isolated from 2 macerated muscles and normalized according to sarcomere length decreased linearily by approximately 50% along craniocaudal axis. It is explained that if elastic resistance of a Sp's sensory region exceeded that of an equivalent length of septal tissue in-series, the progressive shift in the ratio of compliances across this trapezoidally-shaped muscle should result in relatively greater lengthening of Sps at the shorter border as the muscle was extended. Levels of discharge conducive to transition of some motor units to the FOG type might be attained. Thus, gradients in the discharge of Sps (but not necessarily incidence) along both transverse and superficial-to-deep axes may be consistent with Sp sensory input influencing the distribution of at least these types of motor units.

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PubMed1997

Architectural and histochemical properties of cat hip 'cuff' muscles.

The architectural properties and fiber-type composition of the cat hip 'cuff' muscles, i.e. the deep layer of muscles encircling the hip joint, were determined. The muscles studied included the gluteus minimus, obturator internus and externus, gemellus superior and inferior, pyriformis, quadratus femoris and capsularis. In addition, the fiber-type composition was determined for the iliacus muscle. Compared to other lower limb muscles, the cuff muscles were small (approximately 0.2 to 2.7 g) and short (approximately 15 to 40 mm long) and had short mean fiber lengths (approximately 7 to 12 mm long), small angles of fiber pinnation (< or = 12 degrees), and small physiological cross-sectional areas (approximately 0.2 to 2.8 cm2). The percentage of the cross-sectional area comprised of slow fibers ranged from 24 to 95% with this value being over 50% in 5/9 muscles studied. The small angle of pinnation and short fiber lengths optimize force production and the relatively high percentage of slow fibers suggest a high level of activation. Both of these properties are consistent with a hip stabilization role for these muscles. In addition, the high percentage of slow fibers suggests a high spindle density and a possible role of these muscles in providing proprioceptive feedback to the central nervous system for the control of posture and locomotion.

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PubMed1997

Perineal muscles and their innervation: metabolic and functional significance of the motor unit.

Cross-sectional areas and succinate dehydrogenase (SDH) activities of muscle fibers in the rat levator ani (LA) and bulbocavernosus (BC) were determined and compared with those of the soleus (SOL) and superficial (TAs) and deep (TAd) portions of the tibialis anterior (TA). In addition, cell body sizes and SDH activities of spinal motoneurons innervating the LA and BC were examined. Histochemical myofibrillar adenosine triphosphatase (mATPase) staining reactions following alkaline and acid preincubations revealed that all the muscle fibers in the LA and BC were type IIB. Gel electrophoresis, however, showed that the LA and BC contained 2.9 and 2.4% type IIx myosin heavy chain (MHC) isoform, respectively. Immunohistochemical analyses using MHC antibodies showed that the muscle fibers in the LA and BC had types IIx / IIa (approximately 3%) or type IIb MHC isoforms. The mean fiber cross-sectional areas in the LA and BC were significantly smaller than those in the SOL, TAs, or TAd. The mean fiber SDH activities in the LA and BC were significantly lower than those in the SOL or TAd, and similar to TAs. The population of alpha motoneurons innervating the LA and BC had similar SDH activities, irrespective of their cell body sizes. These data indicate that the LA and BC are comprised of a relatively homogeneous population of small, fast and low oxidative fibers innervated by a relatively homogeneous population of spinal motoneurons. These characteristics of the muscle fibers and motoneurons are consistent with their function in short, high-intensity activities.

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PubMed1997

Mitochondrial density of ventral horn neurons in the rat spinal cord.

Mitochondrial density in neurons of the dorsolateral region of the ventral horn at the L5 spinal cord segment in rats was examined using electron microscopy. The gamma motoneurons had a higher density of mitochondria (25.1 +/- 4.2%, n = 19) in the cytoplasm compared to the alpha motoneurons which had a mitochondrial density of 19.4 +/- 4.5% (n = 38). An inverse relationship between cell body size and mitochondrial density was found for alpha (n = 38) and alpha plus gamma (n = 57), but not for gamma (n = 19), motoneuron populations. The higher densities of mitochondria in the smaller neurons correspond well with their metabolic properties since the smaller neurons have the highest oxidative enzyme activities.

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