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PubMed1995

Gravity effects on connective tissue biosynthesis by cultured mesenchymal cells.

Quantitative and qualitative aspects of collagen synthesis under microgravity, normal gravity and hypergravity conditions were investigated during the spacelab D-2 mission by incubating human fibroblast cultures with [3H]-proline for 0, 4, 7, 10 and 20 hours. Quantitative analysis revealed an increase of collagen synthesis under microgravity conditions, being 40% higher than 1g controls. Hypergravity samples at 1.44g, 6.6g and 10g showed a decrease in collagen synthesis with increasing g, being down to about 15% at 10g. The relative proportion of collagen from total protein synthesized, the secretion of collagen by the cells, proline hydroxylation of individual collagen alpha-chains and the relative proportions of collagens I, III and V synthesized were not affected at any of the applied conditions.

Cells, Cultured↗
PubMed2000

Fos expression in the rat brain after exposure to gravito-inertial force changes.

The immediate-early genes constitute useful neurobiological tools for mapping brain functional activity after sensory stimulation. We immunohistochemically investigated Fos protein expression in the brain of rats exposed to gravito-inertial force changes. Experiments were performed in hypergravity rats born and housed for 60 days in terrestrian gravity (1xg) and thereafter exposed for 90 min to 2xg or 4xg in a centrifuge, and in hypogravity rats born and housed for 60 days at 2xg and submitted for 90 min to 1xg. Data from these two experimental groups were quantified by light microscopy and compared to those from two groups of control rats born and permanently housed in either 1xg or 2xg environments that never had to adapt to novel gravito-inertial environments. Results showed a low basal Fos expression in the controls and a strong Fos staining in the experimental rats. Only the hypergravity rats displayed Fos-positive cells in vestibular-related brainstem regions (medial, inferior, and superior vestibular nuclei (VN); group y; dorsomedial cell column (DMCC) of the inferior olive (IO)). By contrast, many suprabulbar areas were strongly labeled in both the hyper- and hypogravity rats, as shown by the numerous Fos-positive cells in mesencephalic (colliculus, laterodorsal periaqueductal gray, autonomic nuclei), diencephalic (hypothalamic and thalamic nuclei), and telencephalic (parietal, temporal, entorhinal and visual cortices) structures. These spatial patterns of Fos expression suggest that an increase in gravito-inertial force activates otolith-vestibulo-olivar pathways and various suprabulbar structures underlying the corticovestibular interactions, which govern the multiple representations of vestibular information in the cortex. A decrease in gravito-inertial force has the opposite effects on the vestibulo-olivar structures as a result of otolith system disfacilitation which, in turn, modifies the activity of complex neural pathways. Exposure to both hyper- and hypogravity environments likely induces neurovegetative and/or stress effects that could account for Fos labeling in autonomic nuclei and in nervous structures involved in the hypothalamo-pituitary-adrenal axis.

Animals↗
PubMed2001

Leaf senescence under various gravity conditions: relevance to the dynamics of plant hormones.

Effects of simulated microgravity and hypergravity on the senescence of oat leaf segments excised from the primary leaves of 8-d-old green seedlings were studied using a 3-dimensional (D) clinostat as a simulator of weightlessness and a centrifuge, respectively. During the incubation with water under 1-g conditions at 25 degrees C in the dark, the loss of chlorophyll of the segments was found dramatically immediately after leaf excision, and leaf color completely turned to yellow after 3-d to 4-d incubation. In this case kinetin (10 micromolar) was effective in retarding senescence. The application of simulated microgravity conditions on a 3-D clinostat enhanced chlorophyll loss in the presence or absence of kinetin. The loss of chlorophyll was also enhanced by hypergravity conditions (ca. 8 to 16 g), but the effect was smaller than that of simulated microgravity conditions on the clinostat. Jasmonates (JAs) and abscisic acid (ABA) promoted senescence under simulated microgravity conditions on the clinostat as well as under 1-g conditions. After 2-d incubation with water or 5-d incubation with kinetin, the endogenous levels of JAs and ABA of the segments kept under simulated microgravity conditions on the clinostat remained higher than those kept under 1-g conditions. These findings suggest that physiological processes of leaf senescence and the dynamics of endogenous plant hormone levels are substantially affected by gravity.

Abscisic Acid↗
PubMed2002

Adaptation of the macular vestibuloocular reflex to altered gravitational conditions in a fish (Oreochromis mossambicus).

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days, or to hypergravity (hg) for 9 days. For several weeks after termination of micro g and hg, the roll-induced static vestibuloocular reflex (rVOR) was recorded. In stage 11/12-fish, the rVOR amplitude (angle between the maximal up and down movement of an eye during a complete 360 degree lateral roll) of micro g-animals increased significantly by 25% compared to 1 g-controls during the first post-flight week but decreased to the control level during the second post-flight week. Microgravity had no effect in stage 14/16 fish on the rVOR amplitude. After 3 g-exposure, the rVOR amplitude was significantly reduced for both groups compared to their 1 g-controls. Readaptation to 1 g-condition was completed during the second post-3 g week. We postulate a critical period during which the development of the macular vestibuloocular reflex depends on gravitational input, and which is limited by the first appearance of the rVOR. At this period of early development, exposure to microgravity sensitizes the vestibular system while hypergravity desensitizes it.

Adaptation, Physiological↗
PubMed2006

Swimming Paramecium in magnetically simulated enhanced, reduced, and inverted gravity environments.

Earth's gravity exerts relatively weak forces in the range of 10-100 pN directly on cells in biological systems. Nevertheless, it biases the orientation of swimming unicellular organisms, alters bone cell differentiation, and modifies gene expression in renal cells. A number of methods of simulating different strength gravity environments, such as centrifugation, have been applied for researching the underlying mechanisms. Here, we demonstrate a magnetic force-based technique that is unique in its capability to enhance, reduce, and even invert the effective buoyancy of cells and thus simulate hypergravity, hypogravity, and inverted gravity environments. We apply it to Paramecium caudatum, a single-cell protozoan that varies its swimming propulsion depending on its orientation with respect to gravity, g. In these simulated gravities, denoted by f(gm), Paramecium exhibits a linear response up to f(gm) = 5 g, modifying its swimming as it would in the hypergravity of a centrifuge. Moreover, experiments from f(gm) = 0 to -5 g show that the response is symmetric, implying that the regulation of the swimming speed is primarily related to the buoyancy of the cell. The response becomes nonlinear for f(gm) >5 g. At f(gm) = 10 g, many paramecia "stall" (i.e., swim in place against the force), exerting a maximum propulsion force estimated to be 0.7 nN. These findings establish a general technique for applying continuously variable forces to cells or cell populations suitable for exploring their force transduction mechanisms.

Animals↗
PubMed2000

Effects of vestibular cerebellum lesion on motion sickness in rats.

The importance of the vestibular apparatus in the development of motion sickness is widely accepted, although the role of the vestibular cerebellum remains controversial. We examined the effects of vestibular cerebellum lesion on the development of motion sickness in rats. Rats do not vomit, but the behaviour known as "pica", the eating of non-nutritive substances, such as kaolin, can be used as an index of motion sickness. A 2 h load of hypergravity induced pica in rats, indicating that they suffered from motion sickness. Pica was induced by hypergravity load even after surgical lesion to the bilateral cerebellar flocculus or to the cerebellar vermis. We concluded that the vestibular cerebellum was not essential in the development of motion sickness in rats.

Animals↗
PubMed2001

Effects of changing gravity on anticipatory grip force control during point-to-point movements of a hand-held object.

We investigated the quality of predictive grip force control during gravity changes induced by parabolic flight maneuvers. During these maneuvers gravity varied: There were 2 periods of hypergravity, in which terrestrial gravity nearly doubled, and a 20-s period of microgravity, during which a manipulated object was virtually weightless. We determined grip and load forces during vertical point-to-point movements of an instrumented object. Point-to-point movements were a combination of static (stationary holding) and dynamic (continuous movements) task conditions, which were separately analyzed in our previous studies. Analysis of the produced grip forces revealed that grip adjustments were closely linked to load force fluctuations under each gravity condition. In particular, grip force maxima coincided closely in time with load force peaks, although these occurred at different phases of the movement depending on the gravity level. However, quantitative analysis of the ratio of maximum grip force to the corresponding load force peak revealed an increased force ratio during microgravity when compared to that during normal and hypergravity. We hypothesize that the impaired precision of force coupling with respect to force magnitude during microgravity results from reduced feedback information about the object's mass during the stationary holding of the object in between each movement. The results indicate that the temporal grip force regulation is highly automatized and stable, whereas economical planning of force magnitude is more flexible and might reflect changes of the external loading condition.

Adaptation, Physiological↗
PubMed1998

Gravity effects on upper airway area and lung volumes during parabolic flight.

We measured upper airway caliber and lung volumes in six normal subjects in the sitting and supine positions during 20-s periods in normogravity, hypergravity [1.8 + head-to-foot acceleration (Gz)], and microgravity ( approximately 0 Gz) induced by parabolic flights. Airway caliber and lung volumes were inferred by the acoustic reflection method and inductance plethysmography, respectively. In subjects in the sitting position, an increase in gravity from 0 to 1. 8 +Gz was associated with increases in the calibers of the retrobasitongue and palatopharyngeal regions (+20 and +30%, respectively) and with a concomitant 0.5-liter increase in end-expiratory lung volume (functional residual capacity, FRC). In subjects in the supine position, no changes in the areas of these regions were observed, despite significant decreases in FRC from microgravity to normogravity (-0.6 liter) and from microgravity to hypergravity (-0.5 liter). Laryngeal narrowing also occurred in both positions (about -15%) when gravity increased from 0 to 1.8 +Gz. We concluded that variation in lung volume is insufficient to explain all upper airway caliber variation but that direct gravity effects on tissues surrounding the upper airway should be taken into account.

Adult↗
PubMed2000

Altered gravity downregulates aquaporin-1 protein expression in choroid plexus.

Aquaporin-1 (AQP1) is a water channel expressed abundantly at the apical pole of choroidal epithelial cells. The protein expression was quantified by immunocytochemistry and confocal microscopy in adult rats adapted to altered gravity. AQP1 expression was decreased by 64% at the apical pole of choroidal cells in rats dissected 5.5-8 h after a 14-day spaceflight. AQP1 was significantly overexpressed in rats readapted for 2 days to Earth's gravity after an 11-day flight (48% overshoot, when compared with the value measured in control rats). In a ground-based model that simulates some effects of weightlessness and alters choroidal structures and functions, apical AQP1 expression was reduced by 44% in choroid plexus from rats suspended head down for 14 days and by 69% in rats suspended for 28 days. Apical AQP1 was rapidly enhanced in choroid plexus of rats dissected 6 h after a 14-day suspension (57% overshoot, in comparison with control rats) and restored to the control level when rats were dissected 2 days after the end of a 14-day suspension. Decreases in the apical expression of choroidal AQP1 were also noted in rats adapted to hypergravity in the NASA 24-ft centrifuge: AQP1 expression was reduced by 47% and 85% in rats adapted for 14 days to 2 G and 3 G, respectively. AQP1 is downregulated in the apical membrane of choroidal cells in response to altered gravity and is rapidly restored after readaptation to normal gravity. This suggests that water transport, which is partly involved in the choroidal production of cerebrospinal fluid, might be decreased during spaceflight and after chronic hypergravity.

Animals↗
PubMed2002

Enhanced expression of the LDH-A gene after gravity-changing stress in human RSa cells.

A major issue in radiation and space biology is whether gene expression levels are altered in cells exposed to gravity-changing stress. In the present study, genes up- or down-regulated in radiation-sensitive human RSa cells cultured under gravity-changing conditions, were identified using a PCR-based mRNA differential display method. Exposure of cells to gravity-changing stress was performed by free-fall with a drop-shaft facility or by an airplane-conducted parabolic flight. Among the candidates for gravity-changing stress-responsive genes obtained by the differential display analysis, the lactate dehydrogenase A gene (LDH-A) was confirmed by Northern blotting analysis to exhibit increased expression levels. The gravity-changing stress consisted of a combination of microgravity and hypergravity. However, exposure of the cells to hypergravity produced by centrifuge only slightly affected the LDH-A mRNA expression. Thus, LDH-A was found to be a candidate for the genes which play a role in the cellular response to gravity-changing stress, and mainly to microgravity.

Cell Line↗
PubMed1999

Gravitational changes affect tibial growth plates according to Hert's curve.

BACKGROUND: Microgravity significantly affects chondrocyte differentiation within the tibial epiphyseal growth plate of space flown rats. The changes produced in height and number of cells in different zones of the plate are associated with ultrastructural changes in the extracellular matrix. Given the importance of the growth plate in endochondral ossification, we began to assess the response of the plate to hypergravity, and the countermeasure value of excess G. METHODS: Rats of the strain used in Cosmos biosatellite missions were housed under conditions similar to Cosmos flights and subjected to continuous hypergravity (2 G) for 14 d, in a 12-ft radius centrifuge. RESULTS: Histomorphometrical analyses of tibial growth plates from these rats found the hypertrophic/calcification zone to be significantly reduced in both height and cell number, and the proliferation zone in cell number. CONCLUSIONS: These results, along with those of spaceflight and of studies using suspension-centrifugation, indicate that rat growth plate responds to gravitational changes according to Hert's curve: i.e., a) an increased baseline (minimal) loading reduces cartilage differentiation; and b) a reduced baseline loading may lead to increased cartilage differentiation but only within a range, beyond which lack of differentiation results. The plasticity of the plate, i.e., its ability to increase or decrease its activity in response to changes in gravity suggests the possibility of a range of G that will produce the load necessary to maintain normal growth of the plate, i.e., possible countermeasures to the effects of either hypo- or hyper-gravity.

Animals↗
PubMed1999

The effects of roll vs. pitch rotation in humans under orthostatic stress.

BACKGROUND: It has been known since 1953 that pre-exposure to less than +1 Gz will reduce subsequent +Gz-tolerance. With few exceptions, during operational flying, the transition from hypogravity to hypergravity involves roll as well as pitch rotation. We examined the effect of roll vs. pitch rotation while undergoing transition from hypogravity to +1 Gz on a tilt table. METHODS: Twelve subjects (28-47 yr old) were rotated at 45 degrees x s(-1) from head-up (HU) at 15 degrees relative to gravitational vertical to 135 degrees head-down (HD) and back to the HU position after different HD dwell times. HD dwell times were set at 7, 15, and 30 s. The subject was rotated about the interaural axis (pitch) and about the naso-occipital axis (roll). Both the HD dwell times and axes of rotation were randomized within and across subjects. BP and heart rate were recorded during the HU-HD-HU maneuver. RESULTS: Analysis of variance, repeated measure design revealed that the rate and magnitude of BP decrease induced by the HD to HU maneuver is significantly higher (p < 0.01) in roll than in pitch during all HD dwell times. The decrease of BP at 7s is significantly (p < 0.01) higher than at 15s and 30s. Heart rate increases significantly higher (p < 0.01) in pitch than in roll at 7s-dwell time. CONCLUSION: Our results suggest that the compensatory mechanism to orthostatic stress is more efficient in response to pitch than roll rotation. This is reflected from the findings that the mean magnitude of OH (orthostatic hypotension) and the rate of BP decrease induced by the HD-HU maneuver is significantly greater in roll rotation than pitch rotation. The mean HR increase post HD-HU rotation is significantly higher in the pitch than the roll rotation. The significant rate of BP decrease during HD-HU roll rotation could have important implications for maintaining G-tolerance and spatial orientation during subsequent exposure to hypergravity.

Adaptation, Physiological↗
PubMed1998

Reduction of pituitary AVP and OT contents in rats following spaceflight.

BACKGROUND: Responses of pituitary concentrations of vasopressin (AVP) and oxytocin (OT) during spaceflight have been variable, possibly due to differences in flight conditions or in age and strain of flight animals. METHODS: We reviewed findings of three space-flights of varying flight and recovery durations in which rats of different ages and strains were used. Male rats ranging in weight from 248-396 g were flown in space for 7-14 d. Flight animals were then compared with vivarium controls and synchronous controls. Parallel ground-based studies (hypergravity and simulated hypogravity) were conducted. RESULTS: Pituitary content of AVP was significantly (p < or = 0.05) decreased by spaceflight (6.3 +/- 0.3 micrograms.mg-1 protein in flight vs. 8.3 +/- 0.5 micrograms.mg-1 protein in vivarium). OT content was also reduced during spaceflight (4.3 +/- 0.2 micrograms.mg-1 protein in flight vs. 6.1 +/- 0.3 micrograms.mg-1 protein in vivarium). Vivarium and synchronous control rats showed no difference in pituitary contents. Flight duration or recovery times did not appear to influence pituitary hormone contents. Strain of rat had an effect on content but not on responses to spaceflight. Age of animals confounded the response to spaceflight: pituitary contents of AVP and OT were not altered in young animals (< or = 60 d old). Hindlimb suspended animals showed no difference in AVP but OT content was decreased. Ground-based exposure to hypergravity (2 G) did not alter content of AVP or OT in young animals. CONCLUSIONS: Decreases in pituitary content of AVP and OT with spaceflight may be due to a variety of factors unique to the microgravity environment. Differences between studies may be due in part to differences in size and age of rats used.

Age Factors↗
PubMed1999

Gravisensing, apoptosis, and drug recovery in Taxus cell suspensions.

Haploid and diploid cell suspensions of Taxus spp. were examined for their adaptive plasticity in response to simulated microgravity, unit gravity, and hypergravity. Cell suspensions produced the taxane, paclitaxel, (TAXOL (R)), which is useful for the treatment of various cancers. Amyloplasts contributed to taxane ring biosynthesis and to drug release at the cell wall. Drug-producing cells reacted as gravisensing osmotic tensiometers. In stressed cells, amyloplasts docked and fused in clusters to sites on the plasmalemma before taxane discharge into the culture medium. In simulated microgravity and compared to all other treatments, taxane production was reduced nearly 100-fold. The percent paclitaxel of total taxanes remained 3-to 6-fold greater, and biomass doubled. When p53-independent programmed cell death was induced, taxanes were released into the culture medium as free molecules (soluble and insoluble) or bound to membranes, nuclear fragments, xylan residues, and other particulate materials. Unit gravity and especially hypergravity promoted xylogenesis and significant drug overproduction. A model relating families of >touch = (TCH), taxane early response (TER), nuclear cycling, and apoptosis-regulating genes to gravisensing, cell wall modifications, and to taxane recovery accounted for most but not all of the observations.

Apoptosis↗
PubMed1997

Body mass change during altered gravity: spaceflight, centrifugation, and return to 1 G.

To assess the effect of gravity on growth, immature rats (130-200 g) were studied during chronic altered gravity exposure and while transitioning between gravity fields. Body mass gain of rats (n = 12) exposed to 14 days of microgravity (spaceflight) was evaluated and compared to mass gain of 1 G controls. Spaceflight did not affect mass gain. Six rats exposed to 1 G following spaceflight, when compared to controls, experienced a significant (0 < 0.05) post-flight mass loss over 48 h of 13 g. Over subsequent days, however, this loss was compensated for, and no difference from 1 G controls was noted after 5 days. Exposure to hypergravity (2 G) for 16 days was evaluated [(n = 6/group): Centrifuge (C); On Center Control (OCC); Centrifuge Control (CC)]. Body mass of centrifuged and OCC rats was reduced within 24 h, with OCCs regaining control mass within 13 days. The mass difference (44 g) in centrifuged animals persisted, however, with no subsequent difference in rate of mass gain between centrifuged animals and controls over Days 3-16 (3.7 +/- 0.1 vs. 3.9 +/- 0.1 g/day, respectively). Transitioning from 2 G to 1 G resulted in a mass increase within 48 hours for centrifuged animals. Over Days 3-16 at 1 G, the rate of gain for centrifuged animals continued to increase (3.1 +/- 0.1 g/day compared to 2.1 +/- 0.1 g/day for controls); differences from control, however, were still noted on Day 16. Transitioning to an increase in a gravity field causes acute losses in body mass. In hypergravity, the acute reduction in body mass persists but the rate of mass gain is normal. Animals returning to 1 G, after acute changes, adjust to attain control mass.

Adaptation, Physiological↗
PubMed1999

Detection of apoptosis in chloroplasts and nuclei in different gravitational environments.

Plant cells either die by "accident" (traumatic cell death) or by "design" (programmed cell death; PCD). There is clear evidence that cell death during plant development and interactions with the environment involves PCD (in Gray and Johal, 1998). K. daigremontiana reproduces asexually by forming plantlets from leaf indentations which fall to soil and convert into adult plants. In nature, its entire plant body except leaf-plantlets senesces as consequence of floral differentiation or stressful environmental conditions. At unit gravity, PCD precedes plantlet detachment from the mother-leaf, leading to an abscission scar after plantlet fall. Earlier experiments have shown that leaf-plantlet formation and asexual reproduction increased with short duration hypergravity treatments and decreased in simulated hypergravity (Pedroso and Durzan, 1998). The present experiments were designed to determine if and what type of cell death occurs following gravitational changes, and the sequence of events leading to it. Our study shows that changes in gravitational environment cause a burst in nitric oxide, followed by a sequence of events that may ultimately led to programmed cell death by apoptosis.

Apoptosis↗
PubMed2000

Survival and growth of developing rats during centrifugation at 2G.

We studied the effects of 2G hypergravity on the survival, body mass and growth of postnatal rats (Rattus norvegicus). Nursing litters comprised of either neonatal (Postnatal day [P]7) or pre-weanling (P14) rats and their mothers were exposed to 16 days of continuous centrifugation. All of the offspring survived and gained body mass, indicating that mothers nursed their young. Following the onset of centrifugation, neonatal and pre-weanling rats showed a reduction in growth relative to age-matched environmental controls (EC). At the completion of testing, body mass of the hypergravity (HG) groups was significantly less than that of controls (p<0.05). Over the course of the test, the HG-exposed P7 group showed an overall 55% gain in body mass as compared to a 71% increase in controls, while the HG-exposed P14 group showed a 62% increase relative to 75% in controls. Neonatal offspring (P7) gained body mass during centrifugation, but at significantly slower rates as compared to EC controls (p<0.05). In contrast, growth rates of pre-weanling (P14) rats were not reduced relative to controls, possibly related to the initiation of weaning, around P18 in the rat. These findings raise key issues relevant to studies of nursing mammals reared in altered gravity.

Age Factors↗
PubMed2003

Effects of gravity on early embryogenesis [correction of embryogeneis] in Caenorhabditis elegans.

The embryonic development of the nematode Caenorhabditis elegans was examined under different gravitational conditions. The embryos after fertilization normally hatched under hypergravity (200 G) or 3D-clinorotation, whereas the number of eggs laid from an adult hermaphrodite decreased and their hatching rate was reduced under the hypergravity condition. The first cleavage plane in the 1-cell embryo was slid to some extent by re-orientation of liquid culture vessel, but the pattern and timing of cleavages were not affected.

Animals↗