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At least 901 records · Page 50Linked to original sources
PubMed1996

Graviresponse of cress roots under varying gravitational forces.

During the spacelab mission IML-2 threshold values concerning gravity controlled growth processes have been estimated in order to test the reciprocity law (dose = stimulus x time = constant) for the first time under exact physiological conditions. Cress seedlings have been cultivated from dry seeds under conditions of microgravity and on a 1 x g-centrifuge in the ESA-BIORACK. With the help of NIZEMI--the slow rotating centrifuge microscope--these seedlings have been stimulated by different doses ranging from 12 to 60 x g x s. Two different values of acceleration--0.1 x g and 1 x g--have been used. Graviresponses of the roots have been documented by video recording for 60 min under conditions of microgravity. The response of roots to accelerations of 0.1 x g was remarkably less than to 1 x g in spite of the same doses being applied to the seedlings. Roots cultivated under conditions of microgravity showed a higher sensitivity than those grown on the 1 x g-centrifuge. Displacement of statoliths in gravity perceiving cells was mainly less than 1 micron under the different stimulation procedures. These results together with results from former space flights do not confirm the validity of the reciprocity law. They indicate that transformation of the gravistimulus has to occur in close vicinity to the statoliths, probably mediated by the ground cytoplasm and the cytoskeleton suspended therein.

Acceleration↗
PubMed1981

Human adaptation to simulated gravitational fields.

We present the results of manned studies in which test subjects were exposed to simulated zero g (water immersion or head-down tilt at -6 degrees) and head-to-feet acceleration. The findings give evidence that humans have different individual tolerances to an acceleration of +3 Gz after exposure to zero g, whether simulated by immersion or by head-down tilt. The paper discusses the functional relationship between water balance and cardiac output in the establishment of adaptive reactions to simulated zero g.

Adaptation, Physiological↗
PubMed1974

Metabolic responses of monkeys to increased gravitational fields.

A depletion of body fat has been reported by several investigators for various species of homoiotherms exposed to chronic acceleration. Generally the effect is proportional to field strength, and over the size range examined (0.25-5 kg) it becomes more severe in larger animals. There is some evidence that this may be the result of increased secretion of a pituitary hormone, the fat mobilizing substance (FMS). An exception to the defatting effect of chronic acceleration was observed in mature pig-tailed monkeys (Macaca nemestrina)--although they exhibited other changes generally found in homoiotherms exposed to hyperdynamic environments. It is considered that this unusual primate response to chronic acceleration may result from a different geometry of the central nervous system, and its effect upon gravity load distribution in the lower part of the brain.

Acceleration↗
PubMed2001

Gravitational force regulates elongation growth of Arabidopsis hypocotyls by modifying xyloglucan metabolism.

Growth of dark-grown Arabidopsis hypocotyls was suppressed under hypergravity conditions (300 g), or was stimulated under microgravity conditions in space (Space Shuttle STS-95). The mechanical extensibility of cell walls decreased and increased under hypergravity and microgravity conditions, respectively. The amounts of cell wall polysaccharides (pectin, hemicellulose-I, hemicellulose-II and cellulose) per unit length of hypocotyls increased under hypergravity conditions, and decreased under microgravity conditions. The amount and the molecular mass of xyloglucans also increased under the hypergravity conditions, while those decreased under microgravity conditions. The activity of xyloglucan-degrading enzymes extracted from hypocotyl cell walls decreased and increased under hypergravity and microgravity conditions, respectively. These results indicate that the amount and the molecular mass of xyloglucans are affected by the magnitude of gravity and that such changes are caused by changes in xyloglucan-degrading activity. Modifications of xyloglucan metabolism as well as the thickness of cell walls by gravity stimulus may be the primary event determining the cell wall extensibility, thereby regulating the growth rate of Arabidopsis hypocotyls.

Arabidopsis↗
PubMed2003

Kinetics of amyloplast movement in cress root statocytes under different gravitational loads.

In order to investigate the movement of a statolith complex along the longitudinal axis of root cap statocytes under different mass accelerations, a series of experiments with Lepidium sativum L. in an automatically operating centrifuge during the Bion-11 satellite flight and on a centrifuge-clinostat have been performed. During spaceflight, roots were grown for 24 h under root-tip-directed centrifugal 1-g acceleration, then exposed to microgravity for 6, 12 and 24 min and chemically fixed. During the first 6 min of microgravity, the statoliths moved towards the cell center with a mean velocity of 0.31 +/- 0.04 micrometers/min, which decreased to 0.12 +/- 0.01 micrometers/min within subsequent 12-24 min period. The mean relative position of the statolith complex in respect to the distal cell wall (% of total cell length) increased from 24.0 +/- 0.5% in 1 g-grown roots to 38.8 +/- 0.8% in roots exposed for 24 min to microgravity, but remained smaller than in roots grown continuously in microgravity (48.0 +/- 0.7%). The properties of the statolith movement away from the distal pole of the statocyte were studied in roots grown for 24 h vertically under 1 g and then placed for 6 min on a fast rotating clinostat (50 rpm) or 180 degrees inverted. After 2 min of both treatments, the mean relative position of the statoliths increased by about 10% versus its initial position. Later on, the proximal displacement of amyloplasts slowed down under simulated weightlessness, while it proceeded at a constant velocity under 1 g inversion. In roots grown on the clinostat and then exposed to 1 g in the longitudinal direction, amyloplast sedimentation away from the central region of statocyte was similar at the beginning of distal and proximal 6-min 1-g stimulation. However, at the end of this period statolith displacement was more pronounced in proximal direction as compared to distal. It is proposed that statolith position in the statocyte of a vertical root is controlled by the force of gravity, however, the intracellular forces, first of all those generated by the network of the cytoskeleton, are manifested when an usual orientation of the organ is changed or the statocytes are exposed to microgravity and clinorotation.

Centrifugation↗
PubMed2003

Changes in gravitational force induce alterations in gene expression that can be monitored in the live, developing zebrafish heart.

Little is known about the effect of microgravity on gene expression, particularly in vivo during embryonic development. Using transgenic zebrafish that express the gfp gene under the influence of a beta-actin promoter, we examined the affect of simulated-microgravity on GFP expression in the heart. Zebrafish embryos, at the 18-20 somite-stage, were exposed to simulated-microgravity for 24 hours. The intensity of GFP fluorescence associated with the heart was then determined using fluorescence microscopy. Our measurements indicated that simulated-microgravity induced a 23.9% increase in GFP-associated fluorescence in the heart. In contrast, the caudal notochord showed a 17.5% increase and the embryo as a whole showed only an 8.5% increase in GFP-associated fluorescence. This suggests that there are specific effects on the heart causing the more dramatic increase. These studies indicate that microgravity can influence gene expression and demonstrate the usefulness of this in vivo model of 'reporter-gene' expression for studying the effects of microgravity.

Animals↗
PubMed2002

Short-term (Fos) and long-term (FRA) protein expression in rat locus coeruleus neurons during the neurolab mission: contribution of altered gravitational fields, stress, and other factors.

Changes in immediate-early gene (IEG) expression during and after space flight were studied in the rat locus coeruleus (LC) during the NASA Neurolab mission. The LC sends widespread projections throughout the brain and releases the neuromodulator norepinephrine. LC neurons respond to natural vestibular stimulation; their firing rate also increases during waking and decreases or ceases during sleep. LC neurons express IEGs such as c-fos after activation. Adult male albino Fisher 344 rats were killed at four mission time points, and the number of Fos- and Fos-related antigen (FRA)-positive LC cells were counted in flight and ground-based control rats. Half of the subjects at each time point were exposed to light for 60 min prior to killing to standardize their sleep-waking state. FRA-expressing cells were more numerous than Fos-expressing cells in both flight- and ground-based subjects. The difference between FRA- and Fos-expressing cells within individuals was significantly larger 24 h after landing in subjects exposed to both space flight and light pulse than in all other subjects at any mission time point. Fos and FRA responses scaled in proportion to the maximum response observed in any single individual showed similar patterns of variation. Analysis of the scaled and combined responses showed that LC IEG levels responded to both gravity changes and light pulses. Subjects exposed to either single stimulus had equivalent responses, significantly greater than those of control subjects maintained in dim light. The combination of gravity change and light pulse gave significantly higher LC responses than either stimulus alone 24 h after takeoff, and to a lesser extent after 12 days in space; the highest responses were obtained 24 h after landing. By 14 days after landing, animals exposed to space flight and light pulse responded no differently than ground-based subjects. No difference in LC IEG expression was clearly attributable to changes in the sleep-waking state of subjects. Activity of noradrenergic LC neurons has been previously shown to modulate IEG expression in target structures. The increased IEG LC activity (seen most especially 24 h after landing) may reflect large-scale activation of noradrenergic neurons that may serve as a trigger for molecular changes in target structures, and be critical for adaptation to gravity changes.

Adaptation, Physiological↗
PubMed2001

Experimental design methodology applied to the study of channel dimensions on the elution of red blood cells in gravitational field flow fractionation.

Field flow fractionation (FFF) separation techniques have gained considerable success with micron-sized species. Living red blood cells (RBCs) of any origin have emerged as ideal models for cell separation development. Their elution mode is now described as "Lift-Hyperlayer". Certain separator dimension parameters are known to play a key role in the separation and band spreading process. Systematic studies of channel dimensions effects on RBC retention, band spreading, peak capacity and on a novel parameter described as "Particle Selectivity" were set up by means of a two-level factorial experimental design. From experimental results and statistical calculations it is confirmed that channel thickness plays a major role in retention ratio, peak variance, peak capacity and particle selectivity. Channel breadth strongly influences plate height, with lower impact on peak capacity and particle selectivity. Retention ratio, peak variance and peak capacity observed results are modulated by second-order interactions between channel dimensions. Preliminary rules for channel configurations are therefore set up and depend on separation goals. It is shown that a very polydisperse population is best disentangled in a thin and narrow channel whatever its length. If a mixture of many different micron-sized species is considered (each of limited polydispersities); a thick and broad channel should be preferred, with length modulating peak capacity to disentangle this polymodal mixture.

Cell Separation↗
PubMedDate not supplied

Glutamatergic transmission in the rat brain and gravitational stress.

The effects of hypergravity stress on L-[14C]-glutamate release from synaptosomes obtained from the rat brain and on the kinetic parameters of high-affinity glutamate transport activity were investigated. We found that hypergravity stress affected only the Ca(2+)-dependent component of L-[14C]-glutamate release. It did not modify the transporter affinity, but the maximum rate of uptake dropped from 12.5 +/- 3.2 to 5.6 +/- 0.9 nmol/min/mg of protein (in control rats and in animals subjected to hypergravity, respectively).

Animals↗