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At least 379 records · Page 21Linked to original sources
PubMed2003

Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans.

Both in normal subjects exposed to hypergravity and in patients with acute respiratory distress syndrome, there are increased hydrostatic pressure gradients down the lung. Also, both conditions show an impaired arterial oxygenation, which is less severe in the prone than in the supine posture. The aim of this study was to use hypergravity to further investigate the mechanisms behind the differences in arterial oxygenation between the prone and the supine posture. Ten healthy subjects were studied in a human centrifuge while exposed to 1 and 5 times normal gravity (1 G, 5 G) in the anterioposterior (supine) and posterioanterior (prone) direction. They performed one rebreathing maneuver after approximately 5 min at each G level and posture. Lung diffusing capacity decreased in hypergravity compared with 1 G (ANOVA, P = 0.002); it decreased by 46% in the supine posture compared with 25% in the prone (P = 0.01 for supine vs. prone). At the same time, functional residual capacity decreased by 33 and 23%, respectively (P < 0.001 for supine vs. prone), and cardiac output by 40 and 31% (P = 0.007 for supine vs. prone), despite an increase in heart rate of 16 and 28% (P < 0.001 for supine vs. prone), respectively. The finding of a more impaired diffusing capacity in the supine posture compared with the prone at 5 G supports our previous observations of more severe arterial hypoxemia in the supine posture during hypergravity. A reduced pulmonary-capillary blood flow and a reduced estimated alveolar volume can explain most of the reduction in diffusing capacity when supine.

Acceleration↗
PubMed1995

Effects of sustained acceleration on the morphological properties of otoconia in hamsters.

We investigated the effect of prolonged hypergravity on the otoconial layer of the maculae utriculi and the maculae sacculi in hamsters. The animals were placed in a centrifuge under conditions of 2.5 G, and remained there for 6 months. We then determined the calcium contents of the otoconia with energy dispersive X-ray element analysis, and recorded the size, shape and distribution of the otoconia. Scanning electron microscopy was used to make photos to determine the effects of hypergravity on the shape and size of the otoconia, and on the distribution of smaller and larger otoconia. No differences were found in the calcium content, shape, size or distribution of otoconia between centrifuged hamsters and control animals. Our findings indicate that structural adaptation to hypergravity does not take place at the otoconial level, at least not in animals subjected to hypergravity after the vestibular system was fully matured.

Animals↗
PubMed1998

Comparison of hyper- and microgravity on rat muscle, organ weights and selected plasma constituents.

BACKGROUND: Centrifugation has been proposed to be one possible countermeasure for the skeletal muscle, organ, hormonal, and plasma chemistry adaptations associated with chronic unloading (e.g., during spaceflight). HYPOTHESIS: Our hypothesis was that there would be a continuum of physiological and morphological responses from zero gravity to hypergravity. METHODS: Adult male rats were centrifuged continuously at 2G for 14 d and the weights of limb muscles and organs, and the levels of plasma constituents were compared with the same measurements from rats flown on a 14-d spaceflight (Cosmos 2044). RESULTS: Mean body weights of centrifuge rats did not change, whereas age-matched controls grew 21%. There was a sparing of muscle protein in the centrifuge rats; the absolute weights of predominantly slow muscles in the hindlimb were maintained and the relative weights (expressed relative to body weight and as a percent difference from control) of almost all muscles studied were larger than control. In contrast, spaceflight resulted in a decrease in the relative weights of most extensor, but not flexor, hindlimb muscles studied. Relative organ weights, in general, were elevated in centrifuge rats compared with control rats. Relative organ weights in flight rats were similar to control, except for a decrease in testes weight. Plasma thyroxine and testosterone levels were significantly reduced following flight, whereas only thyroxine was decreased after centrifugation. Centrifugation resulted in a decrease in most other plasma chemistry measurements, whereas flight rats showed no change or an elevation in these measures. DISCUSSION: These data indicate that the physiological responses to micro- and hypergravity are often in the opposite direction, suggesting that in general there is a continuum of physiological and morphological effects from microgravity to 1G to hypergravity. These data further suggest that the imposition of hypergravity conditions on animals that are in a microgravity environment may have a beneficial effect in maintaining some physiological systems at or near control levels.

Animals↗
PubMed1996

Altered gravitational experience during early periods of life affects the static vestibulo-ocular reflex of tadpoles of the southern clawed toad, Xenopus laevis Daudin.

The effects of altered gravitational forces (AGF) on the development of the static vestibulo-ocular reflex (VOR) were investigated in Xenopus laevis tadpoles exposed to hypergravity (1.4g; 3g) or microgravity conditions (German spacelab mission D-2) for 9-10 days. The effects of light conditions during development were also tested by exposing tadpoles to either complete darkness (DD) or 12:12 h light-dark conditions (LD). The static VOR was induced by lateral roll. The efficacy of the VOR circuit after termination of AGF conditions was described by the peak-to-peak amplitude of the sinusoidal VOR characteristics (i.e. amplitude). The static VOR was first observed at stage 41 for both LD and DD tadpoles. Its further development was retarded in the DD tadpoles compared with the LD tadpoles up to stage 48. Microgravity as well as hypergravity exposure caused a significant (P < 0.05, at least) decrease in the static VOR amplitude during the first week after termination of the AGF period. The decreases were 39.4% in the microgravity group, 16.2% in the 1.4g group and 24.9-42.9% in the 3g group compared with the 1g ground-reared siblings at the same developmental stages. The response deficits usually disappeared but persisted for at least 2 weeks in animals whose development was retarded by hypergravity exposure. It is postulated (i) that gravity exerts an important influence on the normal development of the roll-induced static VOR; (ii) that hypergravity exposure decreases the sensitivity of the gravity-sensitive system so that recordings under 1g conditions cause a weaker static VOR; and (iii) that the vestibulo-spinal pathway possesses a higher degree of plasticity than the vestibulo-ocular pathway.

Adaptation, Physiological↗
PubMed2002

Changes of decartograms under gravitational acceleration and microgravity.

The Decarto technique was used to study the orthogonal ECGs recorded in 23 subjects during parabolic flights (44 records). A parameter of the instantaneous decartograms, namely the activation area (AA), which is the total area of the depolarization front projection on the image sphere, was analyzed. We compared the values of AA during the periods of horizontal flight, upward parts of all parabolas, and the initial 10 s of microgravity of all parabolas. According to the characteristics of the vectorcardiograms and AA, all subjects were subdivided into 3 groups: with increased electric activity of the right ventricle (I), the left ventricle (II) and both ventricles (III). Changes of AA with change of gravitational levels in these groups showed some differences. In groups I and II, the AA of the initial part of the QRS complex increased during microgravity and decreased during hypergravity. In group III it decreased during microgravity and changed variously during hypergravity. The AA of the middle part of the QRS complex decreased during microgravity and increased during hypergravity, and these changes were more pronounced in group III. The changes of AA in groups I and II may be explained by the Brody effect. In group III, AA seems to be influenced by some additional factors, possibly by changes in the intramyocardial or intraventricular blood volume. The AA of the last part of the QRS complex increased during microgravity and decreased during hypergravity in all groups. This may be explained by an effect of mutual neutralization of depolarization fronts related to the changes of the QRS duration.(Fig. 3, Ref. 4)

Acceleration↗
PubMed2000

Effect of different gravity environments on DNA fragmentation and cell death in Kalanchoe leaves.

Different gravity environments have been shown to significantly affect leaf-plantlet formation and asexual reproduction in Kalanchoë daigremontiana Ham. and Perr. In the present work, we investigated the effect of gravity at tissue and cell levels. Leaves and leaf-plantlets were cultured for different periods of time (min to 15 d) in different levels of gravity stimulation: simulated hypogravity (1 rpm clinostats; 2 x 10(-4) g), 1 g (control) and hypergravity (centrifugation; 20 and 150 g). Both simulated hypogravity and hypergravity affected cell death (apoptosis) in this species, and variations in the number of cells showing DNA fragmentation directly correlated with nitric oxide (NO) formation. Apoptosis in leaves was more common as gravity increased. Apoptotic cells were localized in the epidermis, mainly guard cells, in leaf parenchyma, and in tracheary elements undergoing terminal differentiation. Exposures to acute hypergravity (up to 60 min) showed that chloroplast DNA fragmentation occurred prior to nuclear DNA fragmentation, marginalization of chromatin, nuclear condensation, and nuclear blebbing. Addition of sodium nitroprusside (NO donor) mimicked centrifugation. NO and DNA fragmentation decreased with N(G)-monomethyl-L-arginine (NO-synthase inhibitor). The variations in NO levels, nucleoid DNA fragmentation, and cell death show how chloroplasts, cells and leaves may respond (and adapt) to gravity changes.

Apoptosis↗
PubMed2006

Effects of altered gravity on the actin and microtubule cytoskeleton of human SH-SY5Y neuroblastoma cells.

Human SH-SY5Y neuroblastoma cells were used to study the effects of altered gravity on the actin and microtubule cytoskeleton dynamics. A cholinergic stimulation of the cells during a 6 min period of changing gravity (3 parabolas) resulted in an enhanced actin-driven protrusion of evoked lamellipodia. Likewise, the spontaneous protrusive activity of nonactivated cells was promoted during exposure to changing gravity (6 up to 31 parabolas). Ground-based experiments revealed a similar enhancement of the spontaneous and evoked lamellar protrusive activity when the cells were kept at 2 g hypergravity for at least 6 min. This gravity response was independent of the direction of the acceleration vector in respect to the cells. Exposure of the cells to "simulated weightlessness" (clinorotation) had no obvious influence on this type of lamellar actin cytoskeleton dynamics. A 20 min exposure of the cells to simulated weightlessness or to changing gravity (6 to 31 parabolas) - but not to 2 g (hypergravity, centrifugation) - resulted in an altered arrangement of microtubules indicated by bending, turning, and loop formation. A similar altered arrangement was shown by microtubules which had polymerized into lamellipodia after release from a taxol block at simulated weightlessness (clinorotation) or during changing gravity (5 parabolas). Our data suggest that in human SH-SY5Y neuroblastoma cells, microgravity affects the dynamics and spatial arrangement of microtubules but has no influence on the Rac-controlled lamellar actin cytoskeleton dynamics and cell spreading. The latter, however, seems to be promoted at hypergravity.

Acetylcholine↗
PubMed2006

Microgravity-related changes in gene expression after short-term exposure of Arabidopsis thaliana cell cultures.

Cell cultures of Arabidopsis thaliana (cv. Columbia) were used to screen for early alterations in gene expression as a response to altered gravitational fields. Genes of interest were selected from a larger group whose expression was altered under hypergravity (microarray study; M. Martzivanou and R. Hampp, Physiol. Plant. 118: 221-231, 2003). Transcriptional changes of these genes were studied within a time frame of up to 10 min of exposure to microgravity in a sounding-rocket experiment, to clinorotation (random positioning machine), and to hypergravity (8 g). We could identify a set of nine genes (mainly components of signaling chains) with increased transcript levels after about 6 min of exposure to microgravity. As clinorotation and hypergravity treatment did not alter the respective transcript amounts, we assume that the identified genes could be involved in a microgravity-related response.

Arabidopsis↗
PubMed2006

Indications for acceleration-dependent changes of membrane potential in the flagellate Euglena gracilis.

The effects of the calcium sequester EGTA on gravitactic orientation and membrane potential changes in the unicellular flagellate Euglena gracilis were investigated during a recent parabolic-flight experiment aboard of an Airbus A300. In the course of a flight parabola, an acceleration profile is achieved which yields subsequently about 20 s of hypergravity (1.8 g(n)), about 20 s of microgravity, and another 20 s of hypergravity phases. The movement behavior of the cells was investigated with real-time, computer-based image analysis. Membrane potential changes were detected with a newly developed photometer which measures absorption changes of the membrane potential-sensitive probe oxonol VI. To test whether the data obtained by the oxonol device were reliable, the signal of non-oxonol-labelled cells was recorded. In these samples, no absorption shift was detected. Changes of the oxonol VI signals indicate that the cells depolarize during acceleration (very obvious in the step from microgravity to hypergravity) and slightly hyperpolarize in microgravity, which can possibly be explained with the action of Ca-ATPases. These signals (mainly the depolarization) were significantly suppressed in the presence of EGTA (5 mM). Gravitaxis in parallel was also inhibited after addition of EGTA. Initially, negative gravitaxis was inverted into a positive one. Later, gravitaxis was almost undetectable.

Acceleration↗
PubMed2003

Adaptations of the vestibular system to short and long-term exposures to altered gravity.

Long-term space flight creates unique environmental conditions to which the vestibular system must adapt for optimal survival of a given organism. The development and maintenance of vestibular connections are controlled by environmental gravitational stimulation as well as genetically controlled molecular interactions. This paper describes the effects of hypergravity on axonal growth and dendritic morphology, respectively. Two aspects of this vestibular adaptation are examined: (1) How does long-term exposure to hypergravity affect the development of vestibular axons? (2) How does short-term exposure to extremely rapid changes in gravity, such as those that occur during shuttle launch and landing, affect dendrites of the vestibulocerebellar system? To study the effects of longterm exposures to altered gravity, embryonic rats that developed in hypergravity were compared to microgravity-exposed and control rats. Examination of the vestibular projections from epithelia devoted to linear and angular acceleration revealed that the terminal fields segregate differently in rat embryos that gestated in each of the gravitational environments.To study the effects of short-term exposures to altered gravity, mice were exposed briefly to strong vestibular stimuli and the vestibulocerebellum was examined for any resulting morphological changes. My data show that these stimuli cause intense vestibular excitation of cerebellar Purkinje cells, which induce up-regulation of clathrin-mediated endocytosis and other morphological changes that are comparable to those seen in long-term depression. This system provides a basis for studying how the vestibular environment can modify cerebellar function, allowing animals to adapt to new environments.

Adaptation, Physiological↗
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↗
PubMed2003

Gravity influences the development of inputs from the brain to lumbar motoneurons in the rat.

We investigated the influence of gravity on the maturation of electrical properties of lumbar motoneurons and the development of their inputs from ventral descending pathways, which are important for the control of posture and locomotion. Using electrophysiological approaches in the in vitro brain stem-spinal cord preparation of neonatal rats born and reared in hypergravity field we demonstrate that: (1) the postnatal development of descending inputs to lumbar enlargement was reduced in animals submitted to hypergravity; (2) similar developmental pattern of basic electrical properties observed between motoneurons of hypergravity and control animals could not account for the changes in descending inputs. We concluded that gravity was critical to shape development of the supraspinal afferents in the lumbar spinal cord throughout the postnatal period.

Animals↗
PubMed2006

The molecular chaperone HSP47 rapidly senses gravitational changes in myoblasts.

Skeletal muscle unloading induced by spaceflight or bed rest leads to muscle atrophy. It is unclear how muscle atrophy is caused and how muscles respond to microgravity. We addressed the response of collagen and its chaperone system to gravitational forces. We show here that expression of HSP47, a collagen-specific molecular chaperone, responds to gravitational changes, including microgravity and hypergravity in vitro and in vivo. By using the method hindlimb suspension of rats, which mimics microgravity conditions, we demonstrated that the expression of Hsp47 mRNA decreased within 1 day and the mRNA levels of collagen types I and IV were subsequently reduced. In contrast, hypergravity stimulated HSP47 expression. HSP47 and collagen types I and IV were localized intracellularly in the endoplasmic reticulum and/or Golgi apparatus of myoblasts, as expected. Intriguingly, Hsp47 mRNA levels in cultured myoblasts increased significantly with hypergravity treatment at 40G for 2 h, and decreased with microgravity treatment at almost 0G for 1-2 h. Collagen mRNA levels were also altered, although changes were slower and less pronounced compared with those for HSP47. The gravity-regulated HSP47 may play a role in the maintenance of the extracellular matrix by modulating collagen production at the primary stage of adaptation.

Animals↗
PubMed2004

Exposure of mouse to high gravitation forces induces long-term potentiation in the hippocampus.

The central nervous system is highly plastic and has been shown to undergo both transient and chronic adaptive changes in response to environmental influences. The purpose of this study was to investigate the effect of hypergravic field on long-term potentiation (LTP) in the mouse hippocampus. Exposure of mice to 4G fields for 48 h had no effect on input-output coupling during extracellular stimulation of Schaffer collaterals and paired pulse facilitation, suggesting that the hypergravic exposure had no detrimental effect on basal neurotransmission in the hippocampus. However, the exposure to 4G fields for 48 h significantly induced LTP compared with the control mouse hippocampus. In contrast, no significant changes of late-phase LTP (L-LTP) were found in the hippocampi of mice exposed to the hypergravic field. Exposure of mice to 4G fields for 48 h enhanced AMPA receptor phosphorylation but not cyclic AMP-responsive element binding protein (CREB) phosphorylation. These results suggest that exposure to hyperdynamic fields influences the synaptic plasticity in the hippocampus.

Adaptation, Physiological↗
PubMed1999

Shift in arm-pointing movements during gravity changes produced by aircraft parabolic flight.

It has been shown that target-pointing arm movements without visual feedback shift downward in space microgravity and upward in centrifuge hypergravity. Under gravity changes in aircraft parabolic flight, however, arm movements have been reported shifting upward in hypergravity as well, but a downward shift under microgravity is contradicted. In order to explain this discrepancy, we reexamined the pointing movements using an experimental design which was different from prior ones. Arm-pointing movements were measured by goniometry around the shoulder joint of subjects with and without eyes closed or with a weight in the hand, during hyper- and microgravity in parabolic flight. Subjects were fastened securely to the seat with the neck fixed and the elbow maintained in an extended position, and the eyes were kept closed for a period of time before each episode of parabolic flight. Under these new conditions, the arm consistently shifted downward during microgravity and mostly upward during hypergravity, as expected. We concluded that arm-pointing deviation induced by parabolic flight could be also be valid for studying the mechanism underlying disorientation under varying gravity conditions.

Adult↗
PubMed2000

Increases in body mass of rats during spaceflight: models and measurements.

To test the hypothesis that the body mass of rats is increased during spaceflight, we developed two models from the literature and obtained mass measurements during spaceflight. From studies of centrifugation (hypergravity), there is a reduction in body mass of rats dependent on the exposure gravity level. From data in 18 publications on rats subjected to hypergravity by centrifugation, we developed a model that predicted a 27% increase in body mass during the microgravity of spaceflight. Following spaceflight, with an increase in gravity on return to Earth, there is a reduction in body mass of rats for over 3 d. We related the reduction in body mass after spaceflight to the time after landing that mass measurements were made. From data in 23 publications on rats returning from spaceflight, we developed a model that predicted a 19% increase in body mass during spaceflight. Measurement of body mass of rats on days 6 and 10 of spaceflight found a 7 and 9% increase compared with ground control animals. The increase in body mass during spaceflight suggests that the rat may provide a viable model for metabolic studies in which changes during spaceflight may be predicted in part by ground-based hypergravity studies.

Analysis of Variance↗
PubMed1999

Changes in muscle sympathetic nerve activity and effects of breathing maneuvers in humans during microgravity induced by parabolic flight.

The mechanism of cardiovascular deconditioning, such as an orthostatic intolerance after space flight, has not been well clarified. Several studies to investigate that mechanism have focused mainly on hemodynamic changes including heart rate, arterial blood pressure, cardiac output, etc., but no studies have yielded a direct insight into changes in the sympathetic nervous system. Among ground-based experiments, parabolic flight is the only maneuver to expose human subjects to actual microgravity although it lasts for only a short duration of approx. 20 sec. Using microneurography, the present study aimed to analyze the involvement of the sympathetic nervous system in regulating the acute effects of fluid shift induced by parabolic flight during the transitional changes from 1 G to hypergravity, hypergravity to microgravity, and microgravity to hypergravity by direct measurement of sympathetic outflow to the muscles. Some parts of the study were published elsewhere. We also investigated how the sympathetic outflow to muscle is modified during microgravity with elimination of the breathing effect by comparing the cardiovascular parameters under controlled and uncontrolled respiration.

Adult↗
PubMed2002

Heart rate variability during gravity transitions.

During parabolic flight short periods of microgravity and hypergravity are created. During standing position time domain analysis showed higher vagal modulation of the autonomic nervous system in microgravity compared to hypergravity. We hypothesised that this behaviour could better be unravelled by analysis of frequency domain heart rate variability (HRV) techniques. During parabolic flights a subject is exposed to 20-25 sec periods of microgravity (at the top of the parabola), preceded and followed by 20 sec duration episodes of hypergravity. No significant differences were found in the frequency parameters in supine position for each of the phases. In standing position higher values for Total Power, high frequency (HF), low frequency (LF), LF/HF and HF% in 0 g phase were found in comparison with the 3 other phases. LF% was significant lower in standing position at 0 g compared with 1.8 g. These results show that despite the time window limitations, frequency analysis is still possible on ultra short data segments.

Adult↗