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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Control of abdominal muscles by brain stem respiratory neurons in the cat

The nature of the control of abdominal muscles by the brain stem respiratory neurons was investigated in decerebrate unanesthetized cats. First, it was determined which of the brain stem respiratory neurons project to the lumbar cord (from which the abdominal muscles receive part of their innervation), by stimulating the neurons monopolarly. In a second part of the study, it was determined if lumbar-projecting respiratory neurons make monosynaptic connections with abdominal motoneurons; in these experiments, discriminate spontaneous spikes of antidromically acivated expiratory (E) neurons were used to trigger activity from both L1 and L2 nerves. A large projection was observed from E neurons in the caudal ventral respiratory group to the contralateral upper lumber cord. However, cross-correlation experiments found only two (out of 47 neuron pairs tested) strong monosynaptic connections between brain stem neurons and abdominal motoneurons.

Miller, Alan D.↗
NASA NTRS1988

Problems in analysis of data from muscles of rats flow in space

Comparison of hind-limb muscles of rats flown on Spacelab-3 or tail-traction-suspended showed that 11-17 h reloading postflight might have altered the results. Soleus atrophied; plantaris, gastrocnemius, and extensor digitorum longus grew slower; and tibialis anteiror grew normally. In both flight and simulated soleus and plantaris, higher tyrosine and greater glutamine/glutamate ratio indicated negative protein balance and increased glutamine production, respectively, relative to controls. Aspartate was lower in these muscles. Reloading generally decreased tyrosine, but increased aspartate and glutamine/glutamate. These data showed that 12 h of reloading after flight is characterized by reversal, to varying extents, of the effects of unloading.

Tischler, Marc E.↗
NASA NTRS1985

Regulation of protein degradation in muscle by calcium

Calcium-dependent regulation of intracellular protein degradation was studied in isolated rat skeletal muscles incubated in vitro in the presence of a large variety of agents known to affect calcium movement and distribution. The effect of different classes of protease inhibitors was tested to determine the responsible proteolytic systems involved in calcium-dependent degradation. The results suggest that nonlysosomal leupetin- and E-64-c-sensitive proteases are resposible for calcium-dependent proteolysis in muscle.

Zeman, Richard J.↗
NASA NTRS1986

Regulation of Ca(2+)-dependent protein turnover in skeletal muscle by thyroxine

Dantrolene, an agent that inhibits Ca(2+) mobilization, improved protein balance in skeletal muscle, as thyroid status was increased, by altering rates of protein synthesis and degradation. Thyroxine (T4) caused increases in protein degradation that were blocked by leupeptin, a proteinase inhibitor previously shown to inhibit Ca(2+)-dependent nonlysosomal proteolysis in these muscles. In addition, T4 abolished sensitivity to the lysosomotropic agent methylamine and the autophagy inhibitor 3-methyladenine, suggesting that T4 inhibits autophagic/lysosomal proteolysis.

Zeman, Richard J.↗
NASA NTRS1989

Effect of swim exercise training on human muscle fiber function

The effect of swim exercise training on the human muscle fiber function was investigated in swimmers trained in a typical collegiate swim-training program followed by an intensified 10-day training period. The measured parameters included the peak tension (P0), negative log molar Ca(2+) concentration (pCa)-force, and maximal shortening speed (Vmax) of the slow-twitch type I and fast-twitch type II fibers obtained by biopsy from the deltoid muscle. The P0 values were found to be not altered after either the training or the 10-day intensive program. The type I fibers from the trained swimmers showed pCa-force curves shifted to the right, such that higher free Ca(2+) levels were required to elicit a given percent of P0. The training program significantly increased the Vmax in the type I fibers and decreased that of the type II fibers, and the 10-day intensive training produced a further significant decrease of the type II fibers.

Fitts, R. H.↗
NASA NTRS1989

Changes in volume, muscle compartment, and compliance of the lower extremities in man following 30 days of exposure to simulated microgravity

To investigate the relationship between leg compliance and a reduction in the size of the leg muscle compartment due to long-duration exposure to microgravity, eight men were exposed for 30 d of continuous 6-deg headdown tilt, and changes in vascular compliance (vol pct/mm Hg x 100) of the calf and serial circumferences of the thigh and the calf were measured before, during, and after the tilt. It was found that the tilt exposure led to calculated leg volume decreases of 9.9 percent in the calf and of 4.5 in the thigh. Leg compliance was found to increase from 3.9 to about 4.9. Calf compliance measured before and after bedrest was found to be inversely related to calf-muscle compartment cross-sectional area (CSA).

Convertino, Victor A.↗
NASA NTRS1989

Characteristics and preliminary observations of the influence of electromyostimulation on the size and function of human skeletal muscle during 30 days of simulated microgravity

The effect of transcutaneous electromyostimulation (EMS) on the development of atrophy and the loss of strength in lower limb musculature in humans exposed to microgravity was determined in three subjects who received EMS twice daily in a 3-d on/1-d off cycle on their dominant leg during 30 days of bedrest. The output waveform from the stimulator was sequenced to the knee extensors, knee flexors, ankle extensors, and ankle flexors, and caused three isometric contractions of each muscle group per minute. It was found that, in the dominant leg, EMS acted to attenuate the changes caused by bedrest, such as reductions in the leg volume, muscle compartment size, cross-sectional area of slow- and fast-twitch fibers, strength, and aerobic enzyme activities, and an increase in leg compliance.

Duvoisin, Marc R.↗
NASA NTRS1989

Metabolism of branched-chain amino acids in leg muscles from tail-cast suspended intact and adrenalectomized rats

The effects of muscle unloading, adrenalectomy, and cortisol treatment on the metabolism of branched-chain amino acids in the soleus and extensor digitorum longus of tail-cast suspended rats were investigated using C-14-labeled lucine, isoleucine, and valine in incubation studies. It was found that, compared to not suspended controls, the degradation of branched-chain amino acids in hind limb muscles was accelerated in tail-cast suspended rats. Adrenalectomy was found to abolish the aminotransferase flux and to diminish the dehydrogenase flux in the soleus. The data also suggest that cortisol treatment increases the rate of metabolism of branched-chain amino acids at the dehydrogenase step.

Jaspers, Stephen R.↗
NASA NTRS1988

Contraction-free, fume-fixed longitudinal sections of fresh frozen muscle

Contraction damage occurring when longitudinal frozen sections of fresh unfixed muscles are thawed on microscope slides has limited histological examination of this tissue mainly to cross sections. Longitudinally oriented sections are advantageous for investigating properties that vary along the length of the muscle fibers. A fume fixation technique has been developed for preventing contraction of thick longitudinal frozen sections. The technique is compatible with histochemical staining of enzymes.

Riley, Danny A.↗
NASA NTRS1990

beta-adrenergic effects on carbohydrate metabolism in the unweighted rat soleus muscle

The effect of unweighting on the response of the soleus-muscle carbohydrate metabolism to a beta-adrenergic agonist (isoproterenol) was investigated in rats that were subjected to three days of tail-cast suspension. It was found that isoproterenol promoted glycogen degradation in soleus from suspended rats to a higher degree than in weighted soleus from control rats, and had no effect in unweighted digitorum longus. However, isoproterenol did not have a greater inhibitory effect on the net uptake of tritium-labeled 2-deoxy-glucose by the unweighted soleus and that isoproterenol inhibited hexose phosphorylation less in the unweighted than in the control muscle.

Kirby, Christopher R.↗
NASA NTRS1992

Eccentric and concentric muscle performance following 7 days of simulated weightlessness

Changes in skeletal muscle strength occur in response to chronic disuse or insufficient functional loading. The purpose of this study was to examine changes in muscle performance of the lower extremity and torso prior to and immediately after 7 days of simulated weightlessness (horizontal bed rest). A Biodex was used to determine concentric and eccentric peak torque and angle at peak torque for the back, abdomen, quadriceps, hamstring, soleus, and tibialis anterior. A reference angle of 0 degrees was set at full extension. Data were analyzed by ANOVA.

Hayes, Judith C.↗
NASA NTRS1991

Mechanical stimulation of skeletal muscle generates lipid-related second messengers by phospholipase activation

Repetitive mechanical stimulation of cultured avian skeletal muscle increases the synthesis of prostaglandins E2 and F2(alpha) which regulate protein turnover rates and muscle cell growth. Mechnical stimulation significantly increases the breakdown rate of (3)H-arachidonic acid labelled phospholipids, releasing free (3)H-arachidonic acid, and the rate-limiting precursor of prostaglandin synthesis. Mechanical stimulation also significantly increases (3)H-arachidonic acid labelled diacylglycerol formation and intracellular levels of inositol phosphates from myo-2-(3)H inositol labelled phospholipids. Phospholipase A2, phosphatidylinositol-specific phospholipase C (PLC), and phospholipase D (PLD) are activated by stretch. The lipase inhibitors bromophenacylbromide and RHC80267 together reduce stretch-induced prostaglandin production by 73-83 percent. The stretch-induced increases in prostaglandin production, (3)H-arachidonic acid labelled phospholipid breakdown, and (3)H-arachidonic acid labelled diacylglycerol formation occur independently of cellular electrical activity (tetrodotoxin insensitive) whereas the formation of inositol phosphates from myo-2-(3)H inositol labelled phospholipids are dependent on cellular electrical activity. These results indicate that mechanical stimulation increases the lipid-related second messengers arachidonic acid, diacylglycerol, and prostaglandins through activation of specific phospholipases such as PLA2 and PLD, but not by activation of phosphatidylinositol-specific PLC.

Vandenburgh, Herman H.↗
NASA NTRS1992

Intermittent acceleration as a countermeasure to soleus muscle atrophy

The effectiveness of using intermittent acceleration as a countermeasure to muscle atrophy was investigated in rats subjected to 7 days of hindlimb suspension interrupted by daily periods of 1.2 g acceleration, for 15-min periods evenly spaced over 12-hr interval. It was found that this regimen, when repeated for 7 days, failed to completely maintain the mass of soleus muscle, which was 84 percent of control.

D'Aunno, Dominick S.↗
NASA NTRS1992

Muscle sarcomere lesions and thrombosis after spaceflight and suspension unloading

Data obtained during Cosmos 2044 bisatellite mission are reviewed and found to be consistent with the results of previous rodent spaceflight experiments. Investigation was carried out of hindlimb muscles from flight rats killed as close to land as possible so that changes induced by spaceflight and early readaptation to weight bearing could be distinguished from the changes that resulted from the two-day postflight period during Cosmos 1887. Results presented pertain to muscle atrophy and fiber type changes, eccentric contraction-like lesions, microcirculatory changes and interstitial edema, and tissue damage.

Riley, D. A.↗
NASA NTRS1992

Altered distribution of mitochondria in rat soleus muscle fibers after spaceflight

The effect of an exposure to microgravity on the distribution of the succinate dehydrogenase (SDH) activity throughout the soleus muscle fibers was investigated by measuring SDH activity throughout the cross section of 20-30 fibers each of the slow-twitch oxidative and fast-twitch oxidative-glycolytic types of fibers in rats exposed to 12.5 days in space aboard Cosmos 1887. It was found that, after the spaceflight, the entire regional distribution of SDH activity was significantly altered (as compared to ground controls) in the slow-twitch oxidative fibers, whereas the fast-twitch oxidative-glycolytic fibers from muscles of flown rats exhibited a significantly lower SDH activity only in their subsarcolemmal region.

Bell, Gordon J.↗
NASA NTRS1992

Mechanical stimulation of skeletal muscle increases prostaglandin F2(alpha) synthesis and cyclooxygenase activity by a pertussis toxin sensitive mechanism

Repetitive mechanical stimulation of differentiated skeletal muscle in tissue culture increases the production of prostaglandin F(sub 2(alpha)), an anabolic stimulator of myofiber growth. Within 4 h of initiating mechanical activity, the activity of cyclooxygenase, a regulatory enzyme in prostaglandin synthesis, was increased 82% (P is less than .005), and this increase was maintained for at least 24 h. Kinetic analysis of the stretch-activated cyclooxygenase indicated a two to three-fold decrease in the enzyme's K(sub m) with no change in V(sub max). The stretch-induced increase in enzymatic activity was not inhibited by cycloheximide, was independent of cellular electrical activity (tetrodotoxin-insensitive), but was prevented by the G protein inhibitor pertussis toxin. Pertussis toxin also inhibited the stretch-induced increases in PGF(sub 2(alpha)) production, and cell growth. It is concluded that stretch of skeletal muscle increases the synthesis of the anabolic modulator PGF(sub 2(alpha)) by a G protein-dependent process which involves activation of cyclooxygenase by a posttranslational mechanism.

Vandenburgh, Herman H.↗
NASA NTRS1993

Mapping of electrical muscle stimulation using MRI

The pattern of muscle contractile activity elicited by electromyostimulation (EMS) was mapped and compared to the contractile-activity pattern produced by voluntary effort. This was done by examining the patterns and the extent of contrast shift, as indicated by T2 values, im magnetic resonance (MR) images after isometric activity of the left m. quadriceps of human subjects was elicited by EMS (1-sec train of 500-microsec sine wave pulses at 50 Hz) or voluntary effort. The results suggest that, whereas EMS stimulates the same fibers repeatedly, thereby increasing the metabolic demand and T2 values, the voluntary efforts are performed by more diffuse asynchronous activation of skeletal muscle even at forces up to 75 percent of maximal to maintain performance.

Adams, Gregory R.↗
NASA NTRS1993

Spaceflight on STS-48 and earth-based unweighting produce similar effects on skeletal muscle of young rats

Eight female albino rats were exposed to 5.4 days of weightlessness aboard the Space Shuttle mission STS-48 in 1991. An asynchronous ground control experiment mimicked the flight cage conditions and mission duration of the STS-48 rats, and a third group of animals underwent limb suspension for 5.4 days. The flight animals gained a greater percentage of body mass per day despite similar rates of food consumption in the three groups. The results obtained on insulin response and muscle size show that a tail-cast hindlimb-suspension model is suitable for mimicking the effects of weightlessness on rapidly growing juvenile rat muscles.

Tischler, Marc E.↗