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At least 19 recordsLinked to original sources
PubMed1999

A genetic effect of altered gravity: mutations induced by simulated hypogravity and hypergravity in microsatellite sequences of human tumor cells.

To determine the possible genetic effects of gravity alterations, we analyzed mutation induction in microsatellite sequences of human tumor cells treated with simulated hypogravity provided by a clinostat or hypergravity by a centrifuge. Microsatellite mutations were detected as changes in the size of polymerase chain reaction (PCR)-amplified allelic markers. The frequencies of mutant clones in cultures treated with simulated hypogravity for 24 or 48 h were almost the same as those of controls, but after 72 h of treatment, the mutant frequencies had increased significantly in all three microsatellite loci examined. Significantly higher mutant frequencies were similarly detected in cultures treated for 72 h with a hypergravity condition as low as 18xg, but not detected in 24 or 48 h treated cultures. These findings clearly show that gravity alterations that last for 3 days can induce microsatellite mutations in human cells. A genetic effect of gravity change, therefore, is established for the first time. Moreover, high frequencies of microsatellite mutations were induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) which activates protein kinase C-mediated signal transduction pathways and causes genetic instability. These findings suggest that gravity change induces microsatellite mutations by modulating the pattern of gene expression involved in signal transduction pathways.

DNA Primers↗
PubMed2000

Regulation of heat shock protein message in Jurkat cells cultured under serum-starved and gravity-altered conditions.

Although our understanding of effects of space flight on human physiology has advanced significantly over the past four decades, the potential contribution of stress at the cellular and gene regulation level is not characterized. The objective of this ground-based study was to evaluate stress gene regulation in cells exposed to altered gravity and environmentally suboptimal conditions. We designed primers to detect message for both the constitutive and inducible forms of the heat shock protein, HSP-70. Applying the reverse transcriptase-polymerase chain reaction (RT-PCR), we probed for HSP-70 message in human acute T-cell leukemia cells, Jurkat, subjected to three types of environmental stressors: (1) altered gravity achieved by centrifugation (hypergravity) and randomization of the gravity vector in rotating bioreactors, (2) serum starvation by culture in medium containing 0.05% serum, and (3) temperature elevation (42 degrees C). Temperature elevation, as the positive control, significantly increased HSP-70 message, while centrifugation and culture in rotating bioreactors did not upregulate heat shock gene expression. We found a fourfold increase in heat shock message in serum-starved cells. Message for the housekeeping genes, actin and cyclophilin, were constant and comparable to unstressed controls for all treatments. We conclude that gravitational perturbations incurred by centrifugal forces, exceeding those characteristic of a Space Shuttle launch (3g), and culture in rotating bioreactors do not upregulate HSP-70 gene expression. In addition, we found RT-PCR useful for evaluating stress in cultured cells.

Aerospace Medicine↗
PubMed2003

Calcium signaling in plant cells in altered gravity.

Changes in the intracellular Ca2+ concentration in altered gravity (microgravity and clinostating) evidence that Ca2+ signaling can play a fundamental role in biological effects of microgravity. Calcium as a second messenger is known to play a crucial role in stimulus-response coupling for many plant cellular signaling pathways. Its messenger functions are realized by transient changes in the cytosolic ion concentration induced by a variety of internal and external stimuli such as light, hormones, temperature, anoxia, salinity, and gravity. Although the first data on the changes in the calcium balance in plant cells under the influence of altered gravity have appeared in 80th, a review highlighting the performed research and the possible significance of such Ca2+ changes in the structural and metabolic rearrangements of plant cells in altered gravity is still lacking. In this paper, an attempt was made to summarize the available experimental results and to consider some hypotheses in this field of research. It is proposed to distinguish between cell gravisensing and cell graviperception; the former is related to cell structure and metabolism stability in the gravitational field and their changes in microgravity (cells not specialized to gravity perception), the latter is related to active use of a gravitational stimulus by cells presumebly specialized to gravity perception for realization of normal space orientation, growth, and vital activity (gravitropism, gravitaxis) in plants. The main experimental data concerning both redistribution of free Ca2+ ions in plant cell organelles and the cell wall, and an increase in the intracellular Ca2+ concentration under the influence of altered gravity are presented. Based on the gravitational decompensation hypothesis, the consequence of events occurring in gravisensing cells not specialized to gravity perception under altered gravity are considered in the following order: changes in the cytoplasmic membrane surface tension --> alterations in the physicochemical properties of the membrane --> changes in membrane permeability, ion transport, membrane-bound enzyme activity, etc. --> metabolism rearrangements --> physiological responses. An analysis of data available on biological effects of altered gravity at the cellular level allows one to conclude that microgravity environment appears to affect cytoskeleton, carbohydrate and lipid metabolism, cell wall biogenesis via changes in enzyme activity and protein expression, with involvement of regulatory Ca2+ messenger system. Changes in Ca2+ influx/efflux and possible pathways of Ca2+ signaling in plant cell biochemical regulation in altered gravity are discussed.

Calcium↗
PubMed1997

Development of gravity-sensing organs in altered gravity.

Experiments are described in which the development of the gravity-sensing organs was studied in newt larvae reared in microgravity on the IML-2 mission and in Aplysia embryos and larvae reared on a centrifuge at 1 to 5 g. In Aplysia embryos, the statolith (single dense mass on which gravity and linear acceleration act) was reduced in size in a graded fashion at increasing g. In early post-metamorphic Aplysia or even in isolated statocysts from such animals, the number of statoconia produced is reduced at high g. Newt larvae launched before any of the otoconia were formed and reared for 15 days in microgravity had nearly adult labyrinths at the end of the IML-2 mission. The otoliths of the saccule and utricle were the same size in flight and ground-reared larvae. However, the system of aragonitic otoconia produced in the endolymphatic sac in amphibians was much larger and developed earlier in the flight-reared larvae. At later developmental stages, the aragonitic otoconia enter and fill the saccule. One flight-reared larva was maintained for nine months post-flight and the size of the saccular otolith, as well as the volume of otoconia within the endolymphatic sac, were considerably larger than in age-matched, ground-reared newts. This suggests that rearing in microgravity initiates a process that continues for several months after introduction to 1-g, which greatly increases the volume of otoconia. The flight-reared animal had abnormal posture, pointing its head upward, whereas normal ground-reared newts always keep their head horizontal. This suggests that rearing for even a short period in microgravity can have lasting functional consequences in an animal subsequently reared in 1-g conditions on Earth.

Animals↗
PubMed2003

The development of gravity sensory systems during periods of altered gravity dependent sensory input.

Gravity related behavior and the underlying neuronal networks are the most suitable model systems to study basic effects of altered gravitational input on the development of neuronal systems. A feature of sensory and motor systems is their susceptibility to modifications of their adequate physical and/or chemical stimuli during development. This discovery led to the formulation about critical periods, which defines the period of susceptibility during post-embryonal development. Critical periods can be determined by long-lasting modifications of the stimulus input for the gravity sensory system (GSS). Techniques include: (1) destruction of the gravity sense organ so that the gravity cannot be detected any longer and the central neuronal network of the GSS is deprived of gravity related information, (2) loading or deloading of parts of the body by weights or counterweights, respectively, which compensates for the gravitational pull, and (3) absence or augmentation of the gravitational environment per se by the exposure of organisms to microgravity during spaceflights or to hypergravity by centrifugation. Most data came from studies on compensatory eye or head movements in the clawed toad Xenopus laevis, the cichlid fish Oreochromis mossambicus, and crickets (Acheta domesticus, Gryllus bimaculatus). The responses are induced by a roll or pitch stimulation of the gravity sense organs, but are also affected by sensory inputs from proprioreceptors and eyes. The development of these compensatory eye and head responses reveals species-specific time courses. Based on experiments using spaceflights, centrifugation, lesion and loading or deloading, all species revealed a significant susceptibility to modifications of the gravity sensory input during development. Behavioral responses were depressed (Xenopus) or augmented (Xenopus, Oreochronis) by microgravity, and depressed by hypergravity except in crickets. In Acheta, however, the sensitivity of its position sensitive neuron PSI was reduced by microgravity. After termination of the period of modified gravity sensory input, all behavioral and physiological modifications disappeared, in some preparations such as the PSI of Acheta or the eye response in Xenopus, however, delayed after exposure to hypergravity. Irreversible modifications were rare; one example were malformations of the body of Xenopus tadpoles caused by lesion induced deprivation. Several periods of life such as the period of hatching or first appearance of gravity related reflexes revealed a specific sensitivity to altered gravity. Although all studies gave clear evidences for a basic sensitivity of developing GSSs to long-lasting modifications of the gravity sensory input, clear arguments for the existence of a critical period in the development of the sense of gravity are still missing. It has to take into consideration that during long-term exposures, adaptation processes take place which are guided by central physiological and genetically determined set points. The International Space Station (ISS) is the necessary platform of excellence if biological research is focussed on the analysis of long-term space effects on organisms.

Animals↗
PubMed2003

Neurophysiology of developing fish at altered gravity: background--facts--perspectives.

During the entire evolution of life on Earth, the phylogenetic as well as the individual development of all organisms took place under constant gravity conditions, against which they achieved specific countermeasures for compensation and adaptation. On the one side, gravity represents a factor of physical restriction, which compelled the ancestors of all extant living beings to develop basic achievements to counter the gravitational force (e.g., elements of statics like any kind of skeleton--from actin to bone--to overcome gravity enforced size limits or to keep form). On the other side, already early forms of life possibly used gravity as an appropriate cue for orientation and postural control, since it is continuously present and has a fixed direction. Due to such a thorough adaptation to the Earthly gravity vector, both orientation behaviour as well as the ontogenetic development of animals is impaired, when they have to experience altered gravity (delta g; i.e., hyper- or microgravity). On this background, it is still an open question to which extent delta g affects the normal individual development, either on the systemic level of the whole organism or on the level of individual organs or even single cells. The present review provides information on these questions, focusing on developing fish as model systems. Special emphasis is being laid on the effect of delta g on the developing brain and vestibular system, comprising investigations on behaviour and plastic reactivities of the brain and inner ear. Moreover, clues and insights into the possible basic causes of space motion sickness-phenomena (SMS; a kinetosis) are provided. Overall, the results speak in favour of the following concept: short-term altered gravity (< or = 1 day) can induce transitional aberrant behaviour due to malfunctions of the inner ear, originating from asymmetric otoliths or, generally, from a mismatch between canal and otolith afferents. The vanishing aberrant behaviour is due to a reweighing of sensory inputs and neurovestibular compensation, probably on bioelectrical basis. During long-term altered gravity (several days and more), step by step neuroplastic reactivities on molecular basis (i.e., molecular facilitation) in the brain and inner ears obviously activate feedback mechanisms between the CNS and the vestibular organs for the regain of normal behaviour. Mainly, the following areas of research with animals at altered gravity need to be addressed in the future: (1) Maintenance of animals through two complete life cycles in the space environment (developmental deficiencies?). (2) Investigation of the peripheral and central vestibular system by ground-based studies (mutants, hypergravity experiments...), focusing on plasticity in developing animals as well as in adults. (3) Investigation of the effect of microgravity during critical developmental periods (imprinting phase for graviperception?). Answers to these questions may be of crucial interest for basic gravitational research.

Animals↗
PubMed1994

Soybean cotyledon starch metabolism is sensitive to altered gravity conditions.

We have demonstrated that etiolated soybean seedlings grown under the altered gravity conditions of clinorotation (1 rpm) and centrifugation (5xg) exhibit changes in starch metabolism. Cotyledon starch concentration was lower (-28%) in clinorotated plants and higher (+24%) in centrifuged plants than in vertical control plants. The activity of ADP-glucose pyrophosphorylase in the cotyledons was affected in a similar way, i.e. lower (-37%) in the clinorotated plants and higher (+22%) in the centrifuged plants. Other starch metabolic enzyme activities, starch synthase, starch phosphorylase and total hydrolase were not affected by the altered gravity treatments. We conclude that the observed changes in starch concentrations were primarily due to gravity-mediated differences in ADP-glucose pyrophosphorylase activity.

Centrifugation↗
PubMed2005

Purkinje cell loss accompanies motor impairment in rats developing at altered gravity.

We have previously reported that the developmental exposure of rats to altered gravity (1.65 g) from gestational day 8 to postnatal day 21 impacts motor functions and cerebellar structure. The present study examined whether the decrease in cerebellar mass accompanied by impaired performance on a rotorod in hypergravity-exposed rats was related to a decrease in Purkinje cell number. The total number of Purkinje cells was determined on postnatal day 21 using a stereological analysis applied to paraformaldehyde-fixed cerebellar samples subsequently embedded in celloidin. Total Purkinje cell number was decreased by 17.7-25.3%. These results imply that exposure to altered gravity during Purkinje cell birth may affect their proliferation, resulting in a decrease in Purkinje cell number, which, in turn, leads to motor impairment.

Animals↗
PubMed1998

Short-term responses of gravitaxis to altered gravity in Paramecium.

Negative gravitaxis of Paramecium almost disappeared in solutions having specific gravity about the same as that of the organisms (1.04). The taxis turned to positive in solutions of specific gravity 1.08. Using a drop shaft at the Japan Microgravity Center, Hokkaido (JAMIC) we examined how swimming behaviour in these media was modified by changing gravitational conditions before, during and after free-fall. Tracks of swimming cells recorded on videotape indicate that the swimming cells continued upward and downward shift depending on the specific gravity of the external medium under 1-g conditions and these vertical displacements disappeared immediately after the moment of launch. The effectiveness of changing gravity to induce displacement of the cells seems to depend on the orientation of the cells to gravity. These results suggest a corelation between vertical displacement of the cell through the medium and a gravitactic mechanism in Paramecium.

Animals↗
PubMed1998

Study of adaptation to altered gravity through systems analysis of motor control.

Maintenance of posture and production of functional, coordinated movement demand integration of sensory feedback with spinal and supra-spinal circuitry to produce adaptive motor control in altered gravity (G). To investigate neuroplastic processes leading to optimal performance in altered G we have studied motor control in adult rats using a battery of motor function tests following chronic exposure to various treatments (hyper-G, hindlimb suspension, chemical distruction of hair cells, space flight). These treatments differentially affect muscle fibers, vestibular receptors, and behavioral compensations and, in consequence, differentially disrupt air righting, swimming, posture and gait. The time-course of recovery from these disruptions varies depending on the function tested and the duration and type of treatment. These studies, with others (e.g., D'Amelio et al. in this volume), indicate that adaptation to altered gravity involves alterations in multiple sensory-motor systems that change at different rates. We propose that the use of parallel studies under different altered G conditions will most efficiently lead to an understanding of the modifications in central (neural) and peripheral (sensory and neuromuscular) systems that underlie sensory-motor adaptation in active, intact individuals.

Adaptation, Physiological↗
PubMed1994

The influence of altered gravity on carbohydrate metabolism in excised wheat leaves.

We developed a system to study the influence of altered gravity on carbohydrate metabolism in excised wheat leaves by means of clinorotation. The use of excised leaves in our clinostat studies offered a number of advantages over the use of whole plants, most important of which were minimization of exogenous mechanical stress and a greater amount of carbohydrate accumulation during the time of treatment. We found that horizontal clinorotation of excised wheat leaves resulted in significant reductions in the accumulation of fructose, sucrose, starch and fructan relative to control, vertically clinorotated leaves. Photosynthesis, dark respiration and the extractable activities of ADP glucose pyrophosphorylase (EC 2.7.7.27), sucrose phosphate synthase (EC 2.4.4.14), sucrose sucrose fructosyltransferase (EC 2.4.1.99), and fructan hydrolase (EC 3.2.1.80) were unchanged due to altered gravity treatment.

Bacterial Proteins↗
PubMed1992

Physical effects at the cellular level under altered gravity conditions.

Several modifications of differentiated functions of animal cells cultivated in vitro have been reported when cultures have been exposed to increased or decreased inertial acceleration fields by centrifugation, clinorotation, and orbital space flight. Variables modified by clinorotation conditions include inertial acceleration, convection, hydrostatic pressure, sedimentation, and shear stress, which also affect transport processes in the extracellular chemical environment. Autocrine, paracrine and endocrine substances, to which cells are responsive via specific receptors, are usually transported in vitro (and possibly in certain embryos) by convection and in vivo by a circulatory system or ciliary action. Increased inertial acceleration increases convective flow, while microgravity nearly abolishes it. In the latter case the extracellular transport of macromolecules is governed by diffusion. By making certain assumptions it is possible to calculate the Peclet number, the ratio of convective transport to diffusive transport. Some, but not all, responses of cells in vitro to modified inertial environments could be manifestations of modified extracellular convective flow.

Acceleration↗
PubMed1994

Protozoa as model systems for the study of cellular responses to altered gravity conditions.

The orientation behavior of Paramecium changed in a similar way after transition to conditions of free-fall in a sounding rocket and after transition to conditions of simulated weightlessness on a fast rotating clinostat. After a period of residual orientation, Paramecium cells distributed themselves randomly 80 s (120 s) after onset of free-fall (simulated weightlessness). Swimming velocity increased significantly; however, the increase was transient and subsided after 3 min in the rocket experiments, while the velocity remained enhanced even during 2 h of rotation on a fast clinostat. Trichocysts were present and without morphological changes in Paramecium cells which had been exposed to a rocket flight, as well as to fast or slow rotation on a clinostat. Regeneration of the oral apparatus of Stentor and morphogenesis of Eufolliculina proceeded normally on the clinostat. The results demonstrate that the clinostat is a useful tool to simulate the conditions of weightlessness on earth and to detect gravisensitive cellular functions.

Animals↗
PubMed1994

Effects of altered gravity on plant cell processes: results of recent space and clinostatic experiments.

Space and clinostatic experiments revealed that plant cell structure and metabolism rearrangements depend on taxonomical position and physiological state of objects, growth phase and real or simulated microgravity influence duration. It was shown that clinostat conditions reproduce only a part of microgravity biological effects. It is established that various responses occur in microgravity: 1) rearrangements of cytoplasmic organelles ultrastructure and calcium balance; 2) physical-chemical properties of the plasmalemma are changed; 3) enzymes activity is often enhanced. These events provoke the acceleration of growth and differentiation of cells and their aging as a result; at the same time some responses can be considered as cell adaptation to microgravity.

Adaptation, Physiological↗
PubMed1994

Behavioural and biochemical investigations of the influence of altered gravity on the CNS of aquatic vertebrates during ontogeny.

Quantitative data are presented on the influences of hyper-gravity (3 +/- 1g) and of simulated weightlessness (approximately 0g) during early ontogeny of cichlid fish (Oreochromis mossambicus) and clawed toad (Xenopus laevis, Daudin) demonstrating changes in the swimming behaviour and the brain energy and plasma membrane metabolism. After return to 1g conditions, hyper-g reared fish and toads express the well known "loop-swimming" behaviour. By means of a computer based video analyzing system different types of swimming movements and velocities were quantitatively determined. Analyses of the brain energy and plasma-membrane metabolism of hyper-g fish larvae demonstrated an increase in energy availability (glucose 6Pi dehydrogenase, G-6P-DH), a decrease of cellular energy transformation (creatine kinase activity, CK) but no changes in energy consumptive processes (e.g. ATPases) and cytochrome oxidase activity (Cyt.-Ox). In contrast hypo-g fish larvae showed a slight increase in brain CK activity. In addition, unlike 1g controls, hyper-g fish larvae showed pronounced variations in the composition (=polarity) of sialoglycosphingolipids (=gangliosides), typical constituents of the nerve cell membranes, and a slight increase in the activity of sialidase, the enzyme responsible for ganglioside degradation.

Animals↗
PubMed1996

Influence of altered gravity on the cytochemical localization of cytochrome oxidase activity in central and peripheral gravisensory systems in developing cichlid fish.

Cichlid fish larvae were reared from hatching to active free swimming under different gravity conditions: natural environment, increased acceleration in a centrifuge, simulated weightlessness in a clinostat and near weightlessness during space flight. Cytochrome oxidase activity was analyzed semiquantitatively on the ultrastructural level as a marker of regional neuronal activity in a primary, vestibular brainstem nucleus and in gravity receptive epithelia in the inner ear. Our results show, that gravity seems to be positively correlated with cytochrome oxidase activity in the magnocellular nucleus of developing fish brain. In the inner ear the energy metabolism is decreased under microgravity concerning utricle but not saccule. Hypergravity has no effect on cytochrome oxidase activity in sensory inner ear epithelia.

Animals↗