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PubMedDate not supplied

[Gravitational sensitivity of eukaryotic unicellular organisms].

Unicellular organisms are viewed as the best suitable objects for studying environmental effects, including the field of gravity, on living beings at the cellular level. Investigations of unicellular free-living eukaryotic organisms in gravitational and space biology help resolve both theoretical problems and practical problems associated with the design and development of biological life support systems. This paper presents experimental data about the effect of hypergravity on the structure, function and behavior of unicellular organisms--Tetrahymena pyriformis and Euglena gracilis. They were centrifuged at a rate of 87, 108 or 142 rpm to produce acceleration of 2, 3 or 5 G. The following parameters were measured: time course variations in the culture growth, rate of biomass accumulation, cell shape and size. It was found that as the gravity level grew from 2 to 5 G the culture growth was first stimulated and then inhibited. Biomass accumulation as well as the cell size and volume of Tetrahymena pyriformis and Euglena gracilis also decreased. It was demonstrated that the functional activity of cells was inversely proportional to the gravity magnitude. Potential mechanisms of the effect of hypergravity on the cell structure and function are discussed.

Animals↗
PubMed1980

Piracetam and fish orientation during parabolic aircraft flight.

Goldfish were flown in parabolic Keplerian trajectories in a KC-135 aircraft to assay both the effectiveness of piracetam as an anti-motion sickness drug and the effectiveness of state-dependent training during periods of oscillating gravity levels. Single-frame analyses of infrared films were performed for two classes of responses--roll rates in hypogravity or hypogravity orienting responses (LGR) and climbing responses in hypergravity or hypergravity orienting responses (HGR). In Experiment I, preflight training with a vestibular stressor facilitated suppression of LGR by the 10th parabola. An inverse correlation was found between the magnitudes of LGR and HGR. Piracetam was not effective in a state-dependent design, but the drug did significantly increase HGR when injected into trained fish shortly before flight. In Experiment II, injections of saline, piracetam, and modifiers of gamma-aminobutyric acid (GABA)--aminooxyacetic acid (AOAA) and isonicotinic acid (INH)--did not modify LGR. AOAA did significantly increase HGR. Thus, the preflight training had a beneficial effect in reducing disorientation in the fish in weightlessness, but the drugs employed were ineffective.

Aminooxyacetic Acid↗
PubMed1980

The architecture of the avian retina following exposure to chronic 2 G.

Rhode Island REd female chicks at 2 weeks posthatch were subjected, for 7 d, to either earth gravity of 1 G or a 2-G hypergravity environment by chronic whole-body centrifugation. Animals were sacrificed at 3 weeks posthatch and the eyes were enucleated, fixed in 10% BNF, doubly embedded, sectioned at 7-8 micrometer and routinely processed with H & E for histological examination. Compared to normogravity controls, animal exposure for 1 week to the chronic effects of 2-G resulted in a significantly decreased mean width of the photoreceptor, inner nuclear, and inner plexiform retinal layers. The outer nuclear, outer plexiform, and ganglion cell layers of the retina appeared minimally affected by the hypergravity state since the mean width of these layers showed no noticeable differences from earth gravity control animals. The present anatomic findings suggest a reduction in the detection of motion or rapid changes in illumination by the avian retina when the animal is exposed to a 2-G environment.

Animals↗
PubMed1994

Joint position sense in simulated changed-gravity environments.

The proprioceptive position sense was investigated in an elbow-angle matching task in which the right forearm was moved passively by an experimenter and the left forearm actively by the subject. The right forearm could be immersed in water or loaded with a weight, to simulate micro- and hypergravity. We found that in simulated microgravity, matching performance was more variable than in normal gravity, and the right forearm deviated systematically upwards. The latter finding was limited to near-horizontal forearm positions (i.e., where the anticipated effects of gravity are strongest), and could be "reset" by intermittent visual feedback. The observed impairments of the proprioceptive position sense may adversely affect the manual performance of astronauts. In simulated hypergravity, we found no changes of variability and no systematic deviations. This outcome confirms our previous results that weight compensation is efficient even when only static (i.e., gravitational) cues are available.

Adult↗
PubMed1998

Swimming kinematics and respiratory behaviour of xenopus laevis larvae raised in altered gravity

We examined the respiratory behaviours and swimming kinematics of Xenopus laevis tadpoles hatched in microgravity (Space Shuttle), simulated microgravity (clinostat) and hypergravity (3 g centrifuge). All observations were made in the normal 1 g environment. Previous research has shown that X. laevis raised in microgravity exhibit abnormalities in their lungs and vestibular system upon return to 1 g. The tadpoles raised in true microgravity exhibited a significantly lower tailbeat frequency than onboard 1 g centrifuge controls on the day of landing (day0), but this behaviour normalized within 9 days. The two groups did not differ significantly in buccal pumping rates. Altered buoyancy in the space-flight microgravity tadpoles was indicated by an increased swimming angle on the day after landing (day1). Tadpoles raised in simulated microgravity differed to a greater extent in swimming behaviours from their 1 g controls. The tadpoles raised in hypergravity showed no substantive effects on the development of swimming or respiratory behaviours, except swimming angle. Together, these results show that microgravity has a transient effect on the development of locomotion in X. laevis tadpoles, most notably on swimming angle, indicative of stunted lung development. On the basis of the behaviours we studied, there is no indication of neuromuscular retardation in amphibians associated with embryogenesis in microgravity.

Journal Article↗
PubMed2002

CECILIA, a versatile research tool for cellular responses to gravity.

We describe a centrifuge designed and constructed according to current demands for a versatile instrument in cellular gravitational research, in particular protists (ciliates, flagellates). The instrument (called CECILIA, centrifuge for ciliates) is suited for videomonitoring, videorecording, and quantitative evaluation of data from large numbers of swimming cells in a ground-based laboratory or in a drop tower/drop shaft under microgravity conditions. The horizontal rotating platform holds up to six 8mm-camcorders and six chambers holding the experimental cells. Under hypergravity conditions (up to 15 g) chambers can be rotated about 2 axes to adjust the swimming space at right angles or parallel to the resulting gravity vector. Evaluations of cellular responses to central acceleration-- in the presence of gravitational 1 g--are used for extrapolation of cellular behaviour under hypogravity conditions. CECILIA is operated and monitored by computer using a custom-made software. Times and slopes of rising and decreasing acceleration, values and and quality of steady acceleration are supervised online. CECILIA can serve as an on-ground research instrument for precursor investigations of the behaviour of ciliates and flagellates under microgravity conditions such as long-term experiments in the International Space Station.

Acceleration↗
PubMed2001

Ion channel are sensitive to gravity changes.

The effects of gravity on alamethicin doped planar lipid bilayers and on reconstituted porins of Escherichia coli outer membrane, respectively, have been investigated in this paper. The aim of the study was to find out whether and how gravity influences the highly stratified system: membrane-ion channel, in order to provide a novel approach to the explanation of gravity effects on living systems. This is necessary, as even single cells can react to gravity changes without having perceptive organelles. The mechanism of this detection is not clear yet. One possibility might be the detection of gravity by the membrane itself, or by the interaction of integral membrane proteins with gravity. Here we show for the first time that gravity directly influences the integral open state probability of native ion channels (porins) incorporated into planar lipid bilayers. Under hypergravity, especially the open state probability of porins is increased, whereas it is decreased in the microgravity case. The dependency is sigmoidal with the steepest region at 1 to 1.3 g. In the light of these experiments, a general effect of gravity on ion channels and membranes seems to be reasonable, possibly providing an explanation for several impacts of gravity on living systems.

Alamethicin↗
PubMed2002

Effects of space flight, clinorotation, and centrifugation on the substrate utilization efficiency of E. coli.

Cultures of Escherichia coli grown in space reached a 25% higher average final cell population than those in comparably matched ground controls (p<0.05). However, both groups consumed the same quantity of glucose, which suggests that space flight not only stimulated bacterial growth as has been previously reported, but also resulted in a 25% more efficient utilization of the available nutrients. Supporting experiments performed in "simulated weightlessness" under clinorotation produced similar trends of increased growth and efficiency, but to a lesser extent in absolute values. These experiments resulted in increases of 12% and 9% in average final cell population (p<0.05), while the efficiency of substrate utilization improved by 6% and 9% relative to static controls (p=0.12 and p<0.05, respectively). In contrast, hypergravity, produced by centrifugation, predictably resulted in the opposite effect--a decrease of 33% to 40% in final cell numbers with corresponding 29% to 40% lower net growth efficiencies (p<0.01). Collectively, these findings support the hypothesis that the increased bacterial growth observed in weightlessness is a result of reduced extracellular mass transport that occurs in the absence of sedimentation and buoyancy-driven convection, which consequently also improves substrate utilization efficiency in suspended cultures.

Biological Transport↗
PubMed2003

Somatosensory graviception inhibits soleus H-reflex during erect posture in humans as revealed by parabolic flight experiment.

The purpose of this study was to investigate how gravity level affects the excitability of the soleus muscle (SOL) motoneuron pool to Ia afferent input while erect posture is maintained in humans. Three healthy male subjects participated in an experiment whereby three different gravity conditions [microgravity (MG), normal gravity (NG), and hypergravity (HG)] were imposed using a parabolic flight procedure. The SOL H-reflex was evoked every 2 s while the subjects kept an erect posture. The stimulus intensity was controlled automatically on a real-time basis by personal computer to induce the constant amplitude of M-wave (10+/-5% of maximal M-wave amplitude). The background electromyographic activity (BGA) of the SOL was largest during HG, while it was almost absent during MG. The SOL H-reflex amplitude was significantly larger during HG and MG than during NG ( P<0.05). During NG and HG, there was a linear relationship between the BGA and the H-reflex amplitude; the difference in the SOL H-reflex amplitude between both gravity conditions could be explained in terms of the BGA level. However, during MG, despite the absence of BGA, the SOL H-reflex amplitude was larger than that during NG. Furthermore, when the subjects voluntarily activated the SOL by applying a load to the lower limb joints and spine by pulling a handle upward, this H-reflex enhancement almost disappeared. These results suggest that the somatosensory systems detecting a load at the lower limbs and/or vertebral column might play a role in reducing the excitability of the SOL motoneuron pool to Ia afferent inputs by presynaptic inhibition.

Adult↗
PubMed1999

Grip forces exerted against stationary held objects during gravity changes.

In the present study, grip forces exerted against a stationary held object were recorded during parabolic flights. Such flight maneuvers induce changes of gravity with two periods of hypergravity, associated with a doubling of normal terrestrial gravity, and a 20 s period of microgravity. Accordingly, the object's weight changed from being twice as heavy as normally experienced and weightless. Grip-force recordings demonstrated that force control was seriously disturbed only during the first experience of hyper- and microgravity, with the grip forces being exceedingly high and yielding irregular fluctuations. Thereafter, however, grip force traces were smooth, the force level was scaled to the object's weight under normal and high-G conditions, and the grip force changed in parallel with the weight during the transitions between hyper- and microgravity. In addition, during weightlessness, when virtually no force was necessary to stabilize the object, a low force was established, which obviously represented a reasonable safety margin for preventing possible perturbations. Thus, all relevant aspects of grip-force control observed under normal gravity conditions were preserved during gravity changes induced by parabolic flights. Hence, grip-force control mechanisms were able to cope with hyper- and microgravity, either by incorporating relevant receptor signals, such as those originating from cutaneous mechanoreceptors, or by adequately including perceived gravity signals into control programs. However, the adaptation to the uncommon gravity conditions was not complete following the first experience; finer tuning of the control system to both hyper- and microgravity continued over the measurement interval, presumably with a longer observation period being necessary before a stable performance can be reached.

Adult↗
PubMed1991

Transition from self tilt to object tilt during maintained lateral tilt in parabolic flight.

19 young healthy subjects were subjected to parabolic rollercoaster flight. A horizontal luminous line was seen by the subjects in a headfixed goggle device. During the hypergravic phases of parabolic flight the luminous line seemed to rotate into and during the hypogravic phase against the direction of static head tilt. Ocular counter rotation and activity of the neck position receptors cannot explain these subjective rotations. We conclude that information from the otolith system, converging with visual information within the brain, dislocated the headfixed visual target line. While the retinal image of the luminous line remains unchanged, loading and unloading the otoliths in parabolic flight changes the sensation of self tilt into object tilt, hereby subjectively rotating visual targets such as the luminous line.

Eye Movements↗
PubMed1984

Effects of gravity and cosmic rays on cell proliferation kinetics in Paramecium tetraurelia.

Space flights resulted in a stimulating effect on kinetics of proliferation in Paramecium tetraurelia. Additional experiments were performed in order to determine the origin of this phenomena. Paramecia were cultivated in balloon flights or in a slow clinostat, or were exposed to different levels of hypergravity. The results suggest that changes in cell proliferation rate are related to cosmic rays and to a direct effect of microgravity.

Animals↗
PubMed1992

Understanding the organization of the amphibian egg cytoplasm: gravitational force as a probe.

A combination of hypergravity (centrifugation) and hypogravity (clinostat) studies have been carried out on amphibian (frog, Xenopus) eggs. The results reveal that the twinning caused by centrifugation exhibits substantial spawning to spawning variation. That variation can be attributed to the apparent viscosity of the egg's internal cytoplasm. Simulated hypogravity results in a relocation of the egg's third (horizontal) cleavage furrow, towards the equator. Substantial egg-to-egg variation is also observed in this "cleavage effect". For interpreting spaceflight data and for using G-forces as probes for understanding the egg's architecture the egg variation documented herein should be considered.

Animals↗
PubMed1994

Early development of Xenopus embryos is affected by simulated gravity.

Early amphibian (Xenopus laevis) development under clinostat-simulated weightlessness and centrifuge-simulated hypergravity was studied. The results revealed significant effects on (i) "morphological patterning" such as the cleavage furrow pattern in the vegetal hemisphere at the eight-cell stage and the shape of the dorsal lip in early gastrulae and (ii) "the timing of embryonic events" such as the third cleavage furrow completion and the dorsal lip appearance. Substantial variations in sensitivity to simulated force fields were observed, which should be considered in interpreting spaceflight data.

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↗
PubMed1978

Effects of gravitational and magnetic fields on transplanted neuroblastoma vascularity.

Transplanted neuroblastomas were subjected to altered neural influences and imposed gravitational and magnetic fields, either separately or in combination. In each case impaired vascularity, and greater extravasation of blood with associated tumor necrosis occurred in the experimental animals. The combination of both hypergravity and alternating magnetic field resulted in definite macroscopic but less marked microscopic changes than with either force alone. Neuroblastoma cells in vitro exposed to a magnetic field showed no definite growth changes, suggesting an effect of the field forces on the host. Exposure of a unicellular organism, not requiring a host for survival, to a similar magnetic field, did result in distinct cell division changes.

Animals↗
PubMedDate not supplied

The relative role of visual and non-visual cues in determining the perceived direction of "up": experiments in parabolic flight.

In order to measure the perceived direction of "up", subjects judged the three-dimensional shape of disks shaded to be compatible with illumination from particular directions. By finding which shaded disk appeared most convex, we were able to infer the perceived direction of illumination. This provides an indirect measure of the subject's perception of the direction of "up". The different cues contributing to this percept were separated by varying the orientation of the subject and the orientation of the visual background relative to gravity. We also measured the effect of decreasing or increasing gravity by making these shape judgements throughout all the phases of parabolic flight (0 g, 2 g and 1 g during level flight). The perceived up direction was modeled by a simple vector sum of "up" defined by vision, the body and gravity. In this model, the weighting of the visual cue became negligible under microgravity and hypergravity conditions.

Cues↗
PubMed2004

Evidence for macular gravity receptor modulation of hypothalamic, limbic and autonomic nuclei.

Mice lacking normal vestibular gravity reception show altered homeostatic, circadian and autonomic responses to hypergravity (+G) exposure. Using c-Fos as a marker of neuronal activation, the current study identifies CNS nuclei that may be critical for initiating and integrating such responses to changes in vestibular signaling. This experiment utilized the mutant C57BL/6JEi-het mouse (het), which lacks macular otoconia and thus gravity receptor function. Following 2 h of 2G (2x Earth's gravity) exposure (via centrifugation) the neuronal responses of the het mice were compared with wildtype mice similarly exposed to 2G, as well as het and wildtype 1G controls. Wildtype mice exposed to 2G demonstrated robust c-Fos expression in multiple autonomic, hypothalamic and limbic nuclei, including: the lateral septum, bed nucleus of the stria terminalis, amygdala, paraventricular hypothalamus, dorsomedial hypothalamus, arcuate, suprachiasmatic hypothalamus, intergeniculate leaflet, dorsal raphe, parabrachial and locus coeruleus. The het mice exposed to 2G demonstrated little to null c-Fos expression in these nuclei with a few exceptions and, in general, a similar pattern of c-Fos to 1G controls. Data from this study further support the existence of a complex and extensive influence of the neurovestibular system on homeostatic, circadian and possibly autonomic regulatory systems.

Animals↗