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Results for “Hypergravity”

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At least 127 records · Page 7Linked to original sources

PubMed2000

The behavioral response of zebrafish to hypergravity conditions.

Previous reports of the behavior of aquatic organisms in the microgravity environment of space (~10(-6) g) or during the brief weightless period of parabolic flight indicate that most species display a dramatic "looping" or "circling" response (De Jong et al. 1996, Anken, Ibsch and Rahmann 1998). However, the behavior of aquatic species under hypergravity conditions is less clear. Our objectives in the present study were to examine the behavioral response of adult zebrafish (Danio rerio) to hypergravity conditions (2-g), quantify changes in adult swimbladder volume, and to determine if the larvae of zebrafish are capable of accessing the air-water interface for initial swimbladder inflation under hypergravity conditions.

Air Sacs↗

PubMed2002

Hypergravity-induced immunomodulation in a rodent model: lymphocytes and lymphoid organs.

The major goal of this study was to quantify changes in lymphoid organs and cells over time due to centrifugation-induced hypergravity. C57BL/6 mice were exposed to 1, 2 and 3 G and the following assays were performed on days 1, 4, 7, 10, and 21: spleen, thymus, lung, and liver masses; total leukocyte, lymphocyte, monocyte/macrophage, and granulocyte counts; level of splenocyte apoptosis; enumeration of CD3+ T, CD3+/CD4+ T helper, CD3+/CD8+ T cytotoxic, B220+ B, and NK1.1+ natural killer cells; and quantification of cells expressing CD25, CD69, and CD71 activation markers. The data show that increased gravity resulted in decreased body, spleen, thymus, and liver, but not lung, mass. Significant reductions were noted in all three major leukocyte populations (lymphocytes, granulocytes, monocyte/macrophages) [correction of macrphages] with increased gravity; persistent depletion was noted in blood but not spleen. Among the various lymphocyte populations, the CD3+/CD8+ T cells and B220+ B cells were the most affected and NK1.1+ NK cells the least affected. Overall, the changes were most evident during the first week, with a greater influence noted for cells in the spleen. A linear relationship was found between some of the measurements and the level of gravity, especially on day 4. These findings indicate that hypergravity profoundly alters leukocyte number and distribution in a mammalian model and that some aberrations persisted throughout the three weeks of the study. In certain cases, the detected changes were similar to those observed after whole-body irradiation. In future investigations we hope to combine hypergravity with low-dose rate irradiation and immune challenge.

Animals↗

PubMed2006

Hypergravity susceptibility of ventral root activity during fictive swimming in tadpoles (Xenopus laevis).

1. Fictive swimming is an experimental model to study early motor development. As vestibular activity also affects the development of spinal motor projections, the present study focused on the question whether in Xenopus laevis tadpoles, the rhythmic activity of spinal ventral roots (VR) during fictive swimming revealed age-dependent modifications after hypergravity exposure. In addition, developmental characteristics for various features of fictive swimming between stages 37/38 and 47 were determined. Parameters of interest were duration of fictive swimming episodes, burst duration, burst frequency (i.e., cycle length), and rostrocaudal delay. 2. Ventral root recordings were performed between developmental stage 37/38, which is directly after hatching and stage 47 when the hind limb buds appear. The location of recording electrodes extended from myotome 4 to 17. 3. Hypergravity exposure by 3 g-centrifugation lasted 9 to 11 days. It started when embryos had just terminated gastrulation (stage 11/19-group), when first rhythmical activity in the ventral roots appeared (stage 24/27-group), and immediately after hatching (stage 37/41-group). Ventral root recordings were taken for 8 days after termination of 3 g-exposure. 4. Between stage 37/38 (hatching) and stage 47 (hind limb bud stage) burst duration, cycle length and rostrocaudal delay recorded between the 10th and 14th postotic myotome increased while episode duration decreased significantly. In tadpoles between stage 37 and 43, the rostrocaudal delay in the proximal tail part was as long as in older tadpoles while in caudal tail parts, it was shorter. During this period of development, there was also an age-dependent progression of burst extension in the proximal tail area that could not be observed between the 10th and 14th myotome. 6. After termination of the 3 g-exposure, the mean burst duration of VR activity increased significantly (p < 0.01) when 3 g-exposure started shortly after gastrulation but not when it started thereafter. Other parameters for VR activity such as cycle length, rostrocaudal delay and episode duration were not affected by this level of hypergravity. 7. It is postulated that (i) functional separation of subunits responsible for intersegmental motor coordination starts shortly after hatching of young tadpoles; and that (ii) gravity exerts a trophic influence on the development of the vestibulospinal system during different periods of embryonic development leading to the formation of more rigid neuronal networks earlier in the spinal than in the ocular projections.

Action Potentials↗

PubMed2004

Hypergravity decreases carbonic anhydrase-reactivity in inner ear maculae of fish.

Previous investigations revealed that fish inner ear otolith growth depends on the amplitude and the direction of gravity. Both otolith total size, otolith bilateral size-asymmetry and the total and bilateral calcium-incorporation are also affected by gravity. Hypergravity, e.g., slows down otolith growth and diminishes bilateral otolith asymmetry as compared to 1 g control specimens raised in parallel. Since the enzyme carbonic anhydrase (CA) plays a prominent role in otolithic calcification, the reactivity of inner ear CA during otolith growth under hypergravity was investigated. CA-reactivity was demonstrated histochemically and densitometrically on sections of inner ear maculae of larval cichlid fish (Oreochromis mossambicus), that were kept for 6 hrs in a 3 g hypergravity centrifuge. The total unilateral macular CA-reactivity and the bilateral difference in CA between the left and the right maculae were significantly lower in 3 g animals than in 1g controls. The result is in complete agreement with previous studies indicating that a regulatory mechanism, which adjusts otolith size and asymmetry towards the gravity vector, acts via activation/deactivation of macular CA.

Acoustic Maculae↗

PubMed2001

Stimulation of DNA polymerase alpha by hypergravity generated by centrifugal acceleration.

Gravity alteration is known to influence cell proliferation. Here we tested the effects of hypergravity on the action of DNA polymerase alpha, one of the DNA replication enzymes in eukaryotes. Hypergravity was produced by horizontal centrifugal acceleration with a hand-made rotator. The reaction rate of DNA polymerase alpha in centrifuge tubes increased along with the acceleration up to 4g, when a plateau was reached. In contrast, no stimulation was observed with primase, DNA polymerase epsilon, and the E. coli DNA polymerase I Klenow fragment. Kinetic analysis of DNA polymerase alpha reactions revealed that, under high gravity conditions, the K(m) value for template DNA decreased while the V(max) stayed constant. In contrast, the centrifugal acceleration did not affect the K(m) values for deoxyribonucleoside triphosphates. These results suggest that the hypergravity enhances the activity of DNA polymerase alpha by increasing the affinity of the enzyme for template DNA. Such enhancement was more prominent with a low concentration of DNA polymerase alpha under low ionic conditions.

Animals↗

PubMed1991

Hypergravity signal transduction in HeLa cells with concomitant phosphorylation of proteins immunoprecipitated with anti-microtubule-associated protein antibodies.

We have shown that hypergravity (35g) stimulates production of inositol 1,4,5-trisphosphate (IP3) and decreases adenosine 3',5'-cyclic monophosphate (cAMP) levels in HeLa cells. IP3 production rapidly increased 1.5- and 2.1-fold greater (P less than 0.05) than the control after 2- and 5-min exposures to 35g, respectively. The intracellular cAMP levels, determined in the presence of isobutylmethylxanthine, were decreased by 11% (P less than 0.05) and 16% (P less than 0.01) relative to the control after 10- and 20-min exposures to 35g, respectively. The phosphorylation of proteins which were immunoprecipitated by antibodies recognizing microtubule-associated proteins (ipMAPs) was also apparent after exposure of these cells to hypergravity. In the detergent-insoluble fraction, phosphorylation of a 115-kDa protein was significantly enhanced compared to the control after a 5-min exposure to 35g. In the detergent-soluble fraction, phosphorylation of a 200-kDa protein was observed served after a 20-min exposure to 35g. Our study suggests that IP3 and cAMP may act as second messengers in hypergravity signal transduction. Phosphorylation of ipMAPs in both the detergent-soluble and -insoluble fractions suggests that cytoskeletal structures may be influenced by gravity.

1-Methyl-3-isobutylxanthine↗

PubMed1989

Effects of hypergravity environment on the parathyroid gland of the propranolol-treated golden hamster.

The fine structure of the parathyroid glands of propranolol-treated hamsters subjected to 5 x gravity environment was studied. In the parathyroid glands of the propranolol-treated hamsters exposed to hypergravity environment, the volume density occupied by the Golgi complexes and cisternae of the granular endoplasmic reticulum was increased as compared to that of propranolol-treated hamsters and was decreased as compared to that of hamsters exposed to a hypergravity environment but was almost similar to that of control hamsters. In addition, many chief cells contained rich free ribosomes, abundant mitochondria and some secretory granules located in the peripheral cytoplasm. These findings suggest that the parathyroid gland which may be suppressed by treatment of propranolol and stimulated in response to a hypergravity environment indicates the secretory activity of the control parathyroid gland.

Animals↗

PubMed1991

Electron-microscopic study of the parathyroid gland of epinephrine-treated golden hamsters subjected to hypergravity environment.

The ultrastructure of the parathyroid glands of golden hamsters subjected to 5-gravity environment after administration of epinephrine was studied. In the epinephrine-treated animals exposed to a hypergravity environment, the Golgi complexes associated with numerous prosecretory granules were significantly increased compared with those of the control, centrifuged and epinephrine-treated animals, as well as the cisternae of the granular endoplasmic reticulum compared with those of the control and centrifuged animals. In addition, many secretory granules were situated close to the the plasma membrane of the chief cells in the epinephrine-treated animals exposed to a hypergravity environment. Those observations suggest that the secretory activity of the parathyroid gland may be markedly stimulated in the epinephrine-treated animals exposed to a hypergravity environment.

Animals↗

PubMed1992

Stereological studies of the parathyroid gland of phosphate-treated golden hamsters subjected to a hypergravity environment.

The ultrastructure of the parathyroid glands of phosphate-treated golden hamsters exposed to a 5-G environment was studied. In the phosphate-treated animals exposed to a hypergravity environment, the Golgi complexes associated with numerous prosecretory granules, and the enlarged intercellular spaces containing floccular or finely particulate material showed a significant increase compared to those of the control, centrifuged, and phosphate-treated groups, and the cisternae of the granular endoplasmic reticulum showed a significant increase compared to those of the control and phosphate-treated groups. In addition, numerous secretory granules were situated close to the plasma membrane of chief cells in the phosphate-treated animals exposed to a hypergravity environment. These findings suggest that the synthesis, and to a greater extent the release of secretory granules may be markedly stimulated, in the parathyroid glands of phosphate-treated animals exposed to a hypergravity environment.

Animals↗

PubMed1992

Hypergravity and aging in Drosophila melanogaster. 4. Climbing activity.

Drosophila melanogaster flies climb up the sides of their vial after having been submitted to a mechanical stimulation; that ability is impaired at older ages. The climbing activity (CLI) of flies kept at various gravity levels (1, 3 and 5 g) has been measured throughout life, in cross-sectional studies. Hypergravity had no effect on CLI at young age, but older flies kept in hypergravity displayed lower scores than flies kept at 1 g. Results are discussed in relation with the hypothesis of increased aging rate in hypergravity.

Aging↗

PubMed2002

Artificial gravity and functional plasticity of nerve system. L-[14C]-glutamate uptake by nerve terminals from rat cerebellum and cerebral hemispheres under hypergravity stress.

We have investigated the effects of altered gravity on the kinetic parameters of glutamate transport activity. We observed no differences in Km values for cerebellum and cerebral hemisphere nerve terminals (synaptosomes) between control rats- 18,2 +/- 7,6 micromoles (cerebellum), 10,7 +/- 2,5 micromoles (cerebral hemispheres) and animals exposed to hypergravity- 23,3 +/- 6,9 micromoles (cerebellum), 6,7 +/- 1,5 micromoles (cerebral hemispheres). The similarity of this parameter for the two studied groups of animals showed that affinity of glutamate transporter to substrate in cerebellum and cerebral hemispheres was not sensitive to hypergravity stress. The maximal velocity of L-[14C]-glutamate uptake (Vmax) reduced for cerebellum synaptosomes from 9,6 +/- 3,9 nmol/min/mg of protein in control group to 7,4 +/- 2,0 nmol/min/mg of protein in animals, exposed to hypergravity stress. For cerebral hemisphere synaptosomes the maximal velocity significantly decreased from 12,5 +/- 3,2 nmol/min/mg of protein to 5,6 +/- 0,9 nmol/min/mg of protein, respectively.

Journal Article↗

PubMed2002

Hypergravity exposure affects ventral root activity in tadpoles (Xenopus laevis).

In tadpoles, it is possible to observe the rhythmical, burstlike activity of spinal motoneurons by extracellular recordings from the ventral roots. We examined the effects of hypergravity on tadpole locomotion by using a model of fictive swimming in paralysed larvae of Xenopus laevis. Hypergravity (3g) treatment lasted 10 or 11 days. After the 3g-exposure, the mean burst duration of the 3g-animals was significantly (p < or = 0.01) increased compared to the 1g-controls. Readaptation was observed for 8 days after the end of the 3g-period. Burst duration also increases with the age of the tadpoles. Therefore, we postulate that hypergravity has a reversible effect on motor development, probably caused by a neurotrophic effect of a tonic base activity of the vestibular nuclei.

Journal Article↗

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↗

PubMed1990

Effects of hypergravity on lung carcinoma cells maintained in continuous organotypic culture.

The effects of hypergravity levels ranging from 1 to 15 g were studied on A549 lung adenocarcinoma cell line, cultivated as nodules. This organotypic culture model preserves as closely as possible the cellular structures and differentiation functions of the in vivo situation. Nodules submitted to hypergravity conditions for 27 d did not show any change of cell growth, protein and DNA contents, compared with controls. Also, cellular differentiation, as regards intracellular phospholipid composition and more particularly phosphatidylcholine content, appeared undisturbed. The only obvious effect of hypergravity was a modification of the structural organization, with a disappearance of the large alveoli present at the surrounding of control nodules and the development of a dense cellular mass instead.

Adenocarcinoma↗

PubMed1984

The unresponsiveness of the immune system of the rat to hypergravity.

The immune response in rats exposed to simulated hypergravity (2.1 G and 3.1 G) by chronic centrifugation was assessed. Rats were immunized with sheep red blood cells (SRBC), either on the day of initial exposure to hypergravity (hyper-G), or after being centrifuged for 28 d and remaining on the centrifuge thereafter. Pair-fed and ad libitum fed noncentrifuged controls were used. Although there were some alterations in leukocyte counts, hyper-G did not systematically affect the primary or secondary anti-SRBC response, hematocrits, or the sizes of the liver, spleen, kidneys, thymus, or adrenal glands. The immune system is thus remarkably homeostatic under hypergravity conditions which do affect other physiologic parameters.

Adaptation, Physiological↗

PubMed1976

Hypergravity effects on normal and avulsed developing avian radii.

Rhode Island Red female chicks were subjected to complete closed fracture of the right radius at 2 weeks post-hatching. The animals were allowed to heal for 1 week at either earth gravity or 2 G hypergravity state with control and estrogen-injected groups. Intact and fractured radial length, weight, average epiphysial-diaphysial diameters, and length, width, and weight of healing fracture callus were measured. Daily 2000 IU estrogen administration for 7 d increased intact radial length. Estrogen augments the effects of the 2-G state by inhibiting growth and depleting the mass of both intact and fractured radii and by decreasing the average distal epiphysial diameter of fractured bones. Animals exposed to the hypergravity state without hormonal treatment showed decreased fractured radial length, weight, and smaller proximal epiphysial diameters. The measurable parameters of the fracture callus (width, length, and weight) were depressed by the hypergravity state regardless of whether the animal was untreated or supplemented with estrogen.

Animals↗

PubMed1976

Accumulative effects of 2 weeks' exposure to a 2-G hypergravity state and estrogen treatment upon intact and fractured radii of young female birds.

Female birds were subjected to closed fractured of the right radius at 2 weeks post-hatching and allowed to heal for 14 d. The animals were maintained at either earth gravity or a 2-G hypergravity state with control and 2000 and 4000 IU Estrone-(estrogen) injected groups. Intact and fractured radii were measured for length, weight, average epiphysial-diaphysial diameters, and length, width and weight of fracture callus. Animals receiving 2000 IU estrogen treatment showed decreased intact and fractured bone weight, as well as smaller diaphysial diameters. Fractured, but not intact, bone length was decreased by the two estrogen levels without affecting the callus parameters. Bone weight and average epiphysial diameters of both intact and fractured radii were decreased by the hypergravity state. Intact bone diaphysis and fractured bone length were similarly affected. Large, 4000 IU, estrogen levels potentiated the hypergravity state and reduced distal epiphysial diameter of intact radii.

Animals↗

PubMed1998

Effects of hypergravity on optokinetic after-nystagmus and perceived direction of optokinetic stimulation.

BACKGROUND: Previous observations made in parabolic flight and centrifuge studies have shown the presence of a vertical nystagmus (Lz-nystagmus) induced by changes in gravitoinertial forces, and its interaction with oculomotor reflexes. HYPOTHESIS: This Lz-nystagmus is also responsible for the changes in optokinetic after-nystagmus (OKAN) and the subjective perception of optokinetic stimulation direction during hypergravity. METHODS: OKAN was recorded during the 1.8-g phase of parabolic flight after exposure to horizontal or vertical optokinetic stimulation during the preceding 1.0-g or 0-g phases. Changes in the apparent direction of image motion in subjects presented with an optokinetic stimulus were investigated in another experiment where longer exposure to hypergravity was generated by flying an airplane along a spiral path. RESULTS: In upright subjects, the time constant of OKAN with slow phase up decreased during 1.8 g, whereas the horizontal OKAN showed no change in 1.8 g compared with OKAN recorded in 1.0 g. When the subjects were lying on their left side, the OKAN with slow phase right (slow phase up with respect to gravity) decreased in 1.8 g. The subjects tested showed larger error in setting the optokinetic stimulus in a pure horizontal plane in 1.8 g than in 1.0 g. The error was also larger for oblique stimulus in 1.8 g than in 1.0 g, but no differences were seen for the vertical stimulation. CONCLUSION: The changes in OKAN can be explained by an interaction between slow phase eye movements generated by OKAN and the Lz-nystagmus generated by change in the gravitational force level. The error of the perceived direction of the optokinetic stimulus measured during horizontal and oblique stimulation is also presumably due to the interaction between the visual system and the Lz-nystagmus generated by hypergravity.

Aerospace Medicine↗