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Results for “Gravity, Altered”

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At least 217 records · Page 12Linked to original sources

PubMed1999

[The growth movements of moss protonemata under clinostatic and microgravity conditions].

Populations of dark-grown protonemata of moss Ceratodon purpureus wt-4 (Germany) and wt-U (Ukraine) were rotated on clinostat or flown in space (experiment "Protonema" aboard Bion-11, December 24, 1996-January 7, 1997) to determine the effects of altered gravity on orientation of protonemata growing filaments. Protonemata had been cultivated 8 days in vertical stationary position at dark to be transported to microgravity or placed in clinostat for the period of 14 days. In the ground control, protonemata demonstrated the negatively gravitropic growth (straight upwards in a bundle of compact filaments). The horizontal or circular rotation in clinostat and exposure to microgravity made filaments grow every each way within the substrate plane but with an apparent trend to rightward curling resulting in "spiral galaxies".

Bryopsida↗

PubMed2000

Adaptive effects of spaceflight as revealed by short-term partial weight suspension.

BACKGROUND: Human performance and adaptation to altered loading levels is investigated. A previous astronaut jumping study demonstrated significantly altered landing performance following spaceflight, complementing reports of postflight postural and gait instabilities. A dynamic model indicated that leg stiffness changes accounted for the kinematic differences due to adaptation in open-loop modulation of leg impedance. Muscular atrophy or altered stretch reflexes and vestibular sensing could not be discounted. HYPOTHESIS: We hypothesize that partial weight unloading can cause modulation of leg impedance and altered jump landing performance similar to longer-term microgravity exposure, while controlling for muscle atrophy and altered graviceptor inputs. Lower-body impedance changes after partial weight unloading support the hypothesis that postflight differences result primarily from modulation of leg impedance due to reduced postural control demands in microgravity. METHODS: Six subjects performed six baseline 30-cm downward jumps from a platform, followed by 10 jumps under 60% body weight unloading (the adaptation sequence), and then six additional jumps under full-body loading (termed "adapted jumps"). Joint and mass center kinematics were compared for the baseline and adapted jump landings. A second order model evaluated changes in vertical leg impedance. RESULTS: Three subjects exhibited significant increased joint angles and rates. Vertical ground reaction forces showed more heavily damped responses after adaptation. Model fits to mass center motion indicated reduced leg stiffness. CONCLUSIONS: Post-adaptation performance is similar to that of four astronaut subjects who demonstrated reduced postflight leg stiffness. The new study strongly suggests adaptive control of lower limb impedance to accommodate altered gravity levels which can be induced by minimal unloading exposure. Partial weight unloading provides a simple, inexpensive analog to spaceflight for certain postural and movement studies.

Adaptation, Physiological↗

PubMed2001

A virtual environment for simulated rat dissection.

Animal dissection for the scientific examination of organ subsystems is a delicate procedure. Performing this procedure under the complex environment of microgravity presents additional challenges because of the limited training opportunities available that can recreate the altered gravity environment. Traditional crew training often occurs several months in advance of experimentation, provides limited realism, and involves complicated logistics. We have developed an interactive virtual environment that can simulate several common tasks performed during animal dissection. In this paper, we describe the imaging modality used to reconstruct the rat in virtual space, provide an overview of the simulation environment and briefly discuss some of the techniques used to manipulate the virtual rat.

Animals↗

PubMed1996

Enhanced root production in Haplopappus gracilis grown under spaceflight conditions.

The production and growth of roots in two aseptically maintained clonal populations of Haplopappus gracilis (family Compositae), each with a distinctive pattern of root production, were studied after they had been exposed to space for 5 days aboard a NASA Space Shuttle. Total root production of both populations was 67-95% greater when compared with their Earth-grown controls. Roots were generated: (1) laterally from pre-formed roots, the tips of which had been severed at the time of plantlet insertion into a "horticultural foam" substrate supplied with a nutrient solution; (2) adventitiously from the basal or cut-end portion of shoots; (3) de novo, i.e. from primordial which were non-existent at the outset of the experiment. Roots grew in all directions in space but were uniformly positively gravitropic in ground controls. In space and on Earth, both clonal populations maintained their clone-specific root formation and growth characteristics and produced an equivalent amount of tissue when compared to each other. As on Earth, and as expected, there were fewer and shorter roots on plantlets that formed floral buds. The significance of altered moisture distribution in the "horticultural foam" substrate in space for root growth and the significance of our findings for growing plants in altered gravity environments are discussed.

Computer Simulation↗

PubMed1997

Clinorotation affects the state of photosynthetic membranes in Arabidopsis thaliana (L.) Heynh.

Photosynthesis is known to provide nearly all the carbon and chemical energy needed for plant growth, it depends on many environmental factors and alternates when these factors fluctuate. The degree of the chloroplast membrane system development can be, to a certain extent, an indicator of the organelles' photosynthetic activity. To-date, changes in chloroplast size and ultrastructure as well as starch and pigment content in leaf mesophyll cells in microgravity have been found in variety of the angiosperm species investigated in this respect. However, available data are very limited and contradictory. Taking into account the importance of studying the photosynthesis process to elucidate the possibilities of plant physiological adaptation in altered gravity that is the basis for working out the technologies of space planting in controlled ecological life-support systems, we conducted the investigations of ultrastructure and state of the photosynthetic apparatus in Arabidopsis thaliana leaf mesophyll cells at the different stages of plant development under clinorotation.

Arabidopsis↗

PubMed1992

Prevention of bone loss and muscle atrophy during manned space flight.

This paper reviews the biomedical literature concerning human adaptation to nonterrestrial environments, and focuses on the definition of practical countermeasures necessary for long-term survival on the Moon, Mars and during long-term space missions and exploration. Of particular importance is the development of clinically relevant countermeasures for prevention of pathophysiological changes in the musculoskeletal and cardiopulmonary systems under these conditions. The countermeasures which are proposed are based upon a combination of biomechanical and theoretical analyses. The biomechanical analyses are based upon clinical measurements of human skeletal density changes associated with weight lifting as well as clinical studies of human strength and fitness currently being conducted using an isoinertial trunk dynamometer. The theoretical analysis stems from a mathematical model for bone loss in altered gravity environments that we have begun to develop. These analyses provide guidelines for the development of practical therapeutic treatments (exercise, artificial gravity) designed to minimize musculoskeletal deconditioning associated with less than Earth gravity environments. Our findings suggest that very intensive exercise, which impose high loads on the musculoskeletal system for brief periods, may be more efficient in preserving bone and skeletal muscle conditioning within "safe" limits for longer periods than low intensity activities such as treadmill running and bicycling. A 1/6 to 1/7-g gravitational environment is predicted to be sufficient to preserve bone strength above the fracture risk level. Basic biomedical support of manned space missions, Moon and Mars bases should include routine assessment of skeletal density, muscle strength, cardiac output and total energy expenditure. This information can be used to periodically re-evaluate exercise programs and or artificial gravity requirements for crew members.

Adaptation, Physiological↗

PubMed1998

Clinorotation affects mesophyll photosynthetic cells in leaves of pea seedlings.

Experiments with autotrophs in altered gravity condition have a grate significant for development of space biology. The main results of investigation in the photosynthetic apparatus state under microgravity condition have based on the experiments with maturity plants and their differentiated cells. The structural and functional organization of photosynthetic cells in seedlings is poor understandable still. Along with chloroplasts preserving a native membrane system in palisade parenchyma cells of the 29-day pea plant leaves in microgravity, chloroplasts with fribly packed or damaged granae, whose thylakoids appeared as vesicles with an electrontransparent content, were also observed. The investigation of preceding process induced these effects have a sense. That is why, the goal of our experiments was to perform the study of a structural organization of the photosynthetic cells of 3-d pair of pea seedlings leaves under the influence of clinorotation.

Chlorophyll↗

PubMed1999

Electron-cytochemical study of Ca2+ in cotyledon cells of soybean seedlings grown in microgravity.

Microgravity and horizontal clinorotation are known to cause the rearrangement of the structural-functional organization of plant cells, leading to accelerated aging. Altered gravity conditions resulted in an increase in the droplets volume in cells and the destruction of chloroplast structure in Arabidopsis thaliana plants, an enhancement of cytosolic autophagaous processes, an increase in the respiration rate and a greater number of multimolecular forms of succinate- and malate dehydrogenases in cells of the Funaria hygrometrica protonema and Chlorella vulgaris, and changes in calcium balance of cells. Because ethylene is known to be involved in cell aging and microgravity appears to speed the process, and because soybean seedlings grown in space produce higher ethylene levels we asked: 1) does an acceleration of soybean cotyledon cell development and aging occur in microgravity? 2) what roles do Ca2+ ions and the enhanced ethylene level play in these events? Therefore, the goal of our investigation was to examine of the interaction of microgravity and ethylene on the localization of Ca2+ in cotyledon mesophyll of soybean seedlings.

Calcium↗

PubMed2000

The actin cytoskeleton may control the polar distribution of an auxin transport protein.

The gravitropic bending of plants has long been linked to the changes in the transport of the plant hormone auxin. To understand the mechanism by which gravity alters auxin movement, it is critical to know how polar auxin transport is initially established. In shoots, polar auxin transport is basipetal (i.e., from the shoot apex toward the base). It is driven by the basal localization of the auxin efflux carrier complex. One mechanism for localizing this efflux carrier complex to the basal membrane may be through attachment to the actin cytoskeleton. The efflux carrier protein complex is believed to consist of several polypeptides, including a regulatory subunit that binds auxin transport inhibitors, such as naphthylphthalamic acid (NPA). Several lines of experimentation have been used to determine if the NPA binding protein interacts with actin filaments. The NPA binding protein has been shown to partition with the actin cytoskeleton during detergent extraction. Agents that specifically alter the polymerization state of the actin cytoskeleton change the amount of NPA binding protein and actin recovered in these cytoskeletal pellets. Actin-affinity columns were prepared with polymers of actin purified from zucchini hypocotyl tissue. NPA binding activity was eluted in a single peak from the actin filament column. Cytochalasin D, which fragments the actin cytoskeleton, was shown to reduce polar auxin transport in zucchini hypocotyls. The interaction of the NPA binding protein with the actin cytoskeleton may localize it in one plane of the plasma membrane, and thereby control the polarity of auxin transport.

Actins↗

PubMed2001

[Effect of clinorotation on the intensity of lipid peroxidation and superoxide dismutase activity in pea chloroplasts].

The lipid peroxidation intensity and the antioxidant enzyme superoxide dismutase (SOD) activity were studied in chloroplasts of Pisum sativum under clinorotation (for 7 and 14 days) for elucidating mechanisms of biological effect of altered gravity. In comparison with the control, increased LP levels in chloroplasts were established during both the terms of clinorotation. The SOD activity rose in the chloroplasts of plants clinorotated for 7 days, which has a significant protective effect. However, under a longer clinorotation (for 14 days) the SOD activity fell, being, however, higher than in the control samples. In accordance with the Selye oxidative stress theory, plants clinorotated for 7 days are in the phase of growing stability, while plants clinorotated for 14 days are in the phase of decreasing stability.

Chloroplasts↗

PubMed2000

Survival and growth of developing rats during centrifugation at 2G.

We studied the effects of 2G hypergravity on the survival, body mass and growth of postnatal rats (Rattus norvegicus). Nursing litters comprised of either neonatal (Postnatal day [P]7) or pre-weanling (P14) rats and their mothers were exposed to 16 days of continuous centrifugation. All of the offspring survived and gained body mass, indicating that mothers nursed their young. Following the onset of centrifugation, neonatal and pre-weanling rats showed a reduction in growth relative to age-matched environmental controls (EC). At the completion of testing, body mass of the hypergravity (HG) groups was significantly less than that of controls (p<0.05). Over the course of the test, the HG-exposed P7 group showed an overall 55% gain in body mass as compared to a 71% increase in controls, while the HG-exposed P14 group showed a 62% increase relative to 75% in controls. Neonatal offspring (P7) gained body mass during centrifugation, but at significantly slower rates as compared to EC controls (p<0.05). In contrast, growth rates of pre-weanling (P14) rats were not reduced relative to controls, possibly related to the initiation of weaning, around P18 in the rat. These findings raise key issues relevant to studies of nursing mammals reared in altered gravity.

Age Factors↗

PubMed2001

Effect of clinorotation on growth and pigment biosynthesis in etiolated barley plants.

Altered gravity conditions (hyper- or hypogravity) leads to changes in metabolic processes in living organisms (Kordyum, 1997). One important subject of plant space biology is the investigation of the effects of microgravity conditions on the development of the photosynthetic apparatus. The impact of microgravity on the photosynthetic apparatus of plants has been studied in a number of space-flight experiments. Particularly, the Chl (a+b) content and Chl a/b ratio were determined in several experiments, however the results did not allow understanding how microgravity affects pigment apparatus of the plants since presented contradictory results [Laurinavichius et al. 1984; Volovik et al, 1999]. To elucidate how clinorotation affects pigment apparatus formation in etiolated plants, we studied morphological characteristics and pigment (chlorophyll and carotenoids) biosynthesis in the first period of greening of barley plants.

Carotenoids↗

PubMed2001

The interaction of microgravity and ethylene on the ultrastructure cell and Ca2+ localization in soybean hook hypocotyl.

Calcium ions are secondary messenger in numerous cellular processes of plant grown at 1 g. Ca2+ are connected with oxygen atoms, of pectin carboxy groups and/or with H(+)-groups of protein (Roux and Slocum, 1982; Hepler and Wayne, 1985). The influence of altered gravity on the calcium balance in some cells is established. The increased synthesis of ethylene in plant grown in microgravity caused the change of the structural-functional organization of cell (Hensel and Iversen, 1980; Hilaire et al., 1996). Available data put the new question: how do high ethylene level and microgravity influence on the redistribution of Ca2+ in cell of seedling in early stage of growth? Therefore, the goal of our data was the comparable study of the cell ulltrastructure and localization of Ca2+ in hook hypocotyl of soybean seedling under interaction of microgravity and ethylene.

Calcium↗

PubMed2001

Model of statoconia accumulation in gravireceptors of mollusks.

The kinetics of formation and accumulation of statoconia are different for Aplysia californica and Biomphalaria glabrata. In Aplysia californica, the fast growth of statoconia number occurs after the critical size (approximately 45 micrometers) of statocyst is reached; then the increase of statoconia number is proceeding with the nonmonotonic rate during the life of an animal. In Biomphalaria the growth of statoconia number occurs only in the initial phase. Then long-term evolution of statoconia in the absence of their generation is the result of their growth in the cyst lumen. In the case of Aplysia californica it is not clear whether a temporal change of the statoconia size distribution (SSD) is caused by statoconia growth in the cyst lumen similar to that in Biomphalaria (Model 1) or statoconia growth takes place in supporting cells until their release into the cyst lumen occurs. (Model 2). This problem is of practical importance because the majority of experiments related to the development of molluscan gravireceptors in altered gravity dealt with an initial phase of statoconia evolution in Aplysia californica and Biomphalaria glabrata. The purpose of the present work is the application of mathematical modeling to the analysis of mechanisms of statoconia formation by supporting cells.

Animals↗

PubMed2002

[Research plan to study allelopathy under microgravity].

Living organisms interact each others and form ecological system on the earth. Such interactions between organisms and species have been long known, and studied at a global scale. Allelopathy is a phenomenon observed in many plants that emit specific chemicals acting on other organisms, including animals and microorganisms, in either inhibitory or excitatory ways. We propose to study whether phenomena of allelopathy are modified under altered gravity or not. If biosynthesis, emission and sensing mechanism of allelopathic substances would be affected by gravity, many organisms and ecological system might show different behaviors based on the inter-organisms and species interactions under microgravity. In the macroscopic scale, transport of the substances between organisms is largely affected by convection induced by gravity. Furthermore, the fate of allelopathic substances in confined environment differs from that seen on the earth, because of lacking sink compartment for removal and producing exotic bio-active substances by man-made system. We design basic ground experiment to evaluate gravitational effects on allelopathy applying pseudo-microgravity. Our study contributes to the synthesis of ecological system and its control on spacecrafts and extraterrestrial bodies. It also makes possible to sustain qualitative human life even on the ground under confined artificial environment that dominates in many scenes.

Agriculture↗

PubMed2002

The influence of 2.5 g exposure on the morphology of rat vestibular epithelia.

Several studies have shown that altered gravity causes changes in vestibular induced reflexes and behaviour, and in vestibular morphology. How the level of gravity affects the morphology of vestibular epithelia, however, is largely unknown. Vestibular epithelia of hypergravity (HG) exposed animals and control animals were histochemically labeled for actin and tubulin (two characteristic proteins for specific cytoskeletal structures in hair cells and supporting cells). Cellular organization, cytoskeletal structure and apical cross-sectional area were investigated.

Research Support, N.I.H., Extramural↗

PubMed2002

Hypergravity impairs angiogenic response of in vitro cultured human primary endothelial cells.

A variety of evidence suggest that cardiovascular system functions are impaired in altered gravity conditions. In this study we investigated the influence of hypergravity environment (3g) on endothelial cell proliferation, endothelial vasoactive compound production and on in vitro angiogenesis. We found that cultured primary human endothelial cells were very sensitive to mild hypergravity conditions. Even if we did not record changes in cell viability and apoptosis, we found significant differences in cell proliferation, prostacyclin (PGI2) synthesis, nitric oxide (NO) synthesis, and in angiogenic responses. Using western blotting technique we detected an increased expression of cycloxygenase-2 (COX-2) in primary endothelial cells exposed for 48 hours to hypergravity, in comparison to those exposed to normal gravity.

Journal Article↗

PubMed2004

Velocity of head movements and sensory-motor adaptation during and after short spaceflight.

To investigate to time course of sensory-motor adaptation to microgravity, we tested spatially-directed voluntary head movements before, during and after short spaceflight. We also tested the re-adaptation of postural responses to sensory stimulation after space flight. The cosmonaut performed in microgravity six cycles of voluntary head rotation in pitch, roll and yaw directions. During the first days of weightlessness the angular velocity of head movements increased. Over the next days of microgravity the velocity of head movements gradually decreased. On landing day a significant decrease of head rotation velocity was observed compared to the head movement velocity before spaceflight. Re-adaptation to Earth condition measured by body sway on soft support showed similar time course, but re-adaptation measured by postural responses to vestibular galvanic stimulation was prolonged. These results showed that the angular velocity of aimed head movements of cosmonauts is a good indicator of sensory-motor adaptation in altered gravity conditions.

Adaptation, Physiological↗