Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Weightlessness Simulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,135 records · Page 63Linked to original sources
PubMed2004

Electron microscopic study of left ventricular cardiomyocyte mitochondriom in rats subjected to head-down tilt.

The mitochondriom of left-ventricular cardiomyocytes in rats subjected to head-down tilt was studied at the electron microscopic level. The ultrastructure of individual mitochondria was disturbed and the number of intermitochondrial contacts in the perinuclear zone increased after 30-day head-down tilt. These parameters did not return to normal over 30 days after 30-day tilt. Repeated 14-day head-down tilt led to a more pronounced increase in the number of intermitochondrial contacts, mitochondria with abnormal ultrastructure were still observed.

Animals↗
PubMed2004

Effects of deafferentation on the size and myosin phenotype of muscle fibers on stretching of the rat soleus muscle in conditions of gravitational unloading.

The aim of the present work was to assess the contributions of the reflex and local components to preventing decreases in the size and changes in the ratio of fibers containing the slow and fast isoforms of myosin heavy chains during chronic stretching of a postural muscle in rats in conditions of gravitational unloading. A unilateral surgical deafferentation method was used. The results demonstrated that deafferentation of the hindlimb had no effect on preventing reductions in muscle fiber size in conditions of chronic muscle stretching in conditions of gravitational unloading. The results obtained from these experiments did not support the hypothesis that the predominant contribution to preventing the development of atrophic changes comes from activation of muscle afferents in chronic stretching of the unloaded muscle. Deafferentation of both suspended animals and those with normal motor activity led to increases in the proportion of soleus muscle fibers containing the slow isoforms of myosin heavy chain.

Animals↗
PubMed1999

Changes in hormonal balance and meristematic activity in primary root tips on the slowly rotating clinostat and their effect on the development of the rapeseed root system.

The morphometry of the root system, the meristematic activity and the level of indole-3-acetic acid (IAA), abscisic acid (ABA) and zeatin in the primary root tips of rapeseed seedlings were analyzed as functions of time on a slowly rotating clinostat (1 rpm) or in the vertical controls (1 rpm). The fresh weight of the root system was 30% higher throughout the growth period (25 days) in clinorotated seedlings. Morphometric analysis showed that the increase in biomass on the clinostat was due to greater primary root growth, earlier initiation and greater elongation of the secondary roots, which could be observed even in 5-day-old seedlings. However, after 15 days, the growth of the primary root slowed on the clinostat, whereas secondary roots still grew faster in clinorotated plants than in the controls. At this time, the secondary roots began to be initiated closer to the root tip on the clinostat than in the control. Analysis of the meristematic activity and determination of the levels in IAA, ABA and zeatin in the primary root tips demonstrated that after 5 days on the clinostat, the increased length of the primary root could be the consequence of higher meristematic activity and coincided with an increase in both IAA and ABA concentrations. After 15 days on the clinostat, a marked increase in IAA, ABA and zeatin, which probably reached supraoptimal levels, seems to cause a progressive disturbance of the meristematic cells, during a decrease of primary root growth between 15 and 25 days. These modifications in the hormonal balance and the perturbation of the meristematic activity on the clinostat were followed by a loss of apical dominance, which was responsible for the early initiation of secondary roots, the greater elongation of the root system and the emergence of the lateral roots near the tip of the primary root.

Abscisic Acid↗
PubMed2001

Effects of chair restraint on the strength of the tibia in rhesus monkeys.

To determine the effects of the relative inactivity and unloading on the strength of the tibias of monkeys, Macaca mulatta, we used a non-invasive test to measure bending stiffness, or EI (Nm2), a mechanical property. The technique was validated by comparisons of in vivo measurements with standard measures of EI in the same bones post-mortem (r2 = 0.95, P < 0.0001). Inter-test precision was 4.28+/-1.4%. Normative data in 24 monkeys, 3.0+/-0.7 years and 3.6+/-0.6 kg, revealed EI to be 16% higher in the right than left tibia (4.4+/-1.6 vs. 3.7+/-1.6 Nm2, P < 0.05). Five monkeys, restrained in chairs for 14 days, showed decreases in EI. There were no changes in EI in two chaired monkeys that lost weight during a 2-week space flight. The factors that account for both the decreases in bone mechanical properties after chair restraint at 1 g and lack of change after microgravity remain to be identified. Metabolic factors associated with body weight changes are suggested by our results.

Adaptation, Physiological↗
PubMed2000

Characterisation of gravity-induced facial skin oedema using biophysical measurement techniques.

BACKGROUND/AIMS: In humans, the microgravity environment can be expected to induce swelling of facial tissues and shrinking of the tissues in the lower limbs, together with a loss in body weight. To evaluate fluid shifts in skin, the head-down bed-rest model was used. The aim of the present study was to evaluate the appearance of facial oedema in subjects undergoing anti-orthostatic bed-rest at an angle of -10 degrees. METHODS: The forehead of each of four subjects was measured before and after 1, 10 and 24 h in this head-down tilt position. At these time points, interstitial fluid migration and facial oedema were assessed using a high resolution B-scan ultrasound and a device for measuring the skin's mechanical properties. RESULTS: The results obtained showed a progressive increase in dermal thickness and initial stress, and a reduction in stiffness and elasticity of the skin during the study period. CONCLUSIONS: This preliminary study has demonstrated the feasibility of the method in measuring fluid displacement and retention in the skin. Furthermore, it highlights the influence of fluids on the mechanical behaviour of the skin. These techniques could be used for studying the redistribution of liquid masses during periods spent in space.

Aerospace Medicine↗
PubMed2002

Nutrition beyond nutrition: plausibility of immunotrophic nutrition for space travel.

BACKGROUND AND AIMS: Microgravity has adverse effects on the immune system. We examined the effects of supplemental dietary nucleotides on immune function in ground-based in vivo anti-orthostatic tail-suspended (AOS) mice and in vitro (bioreactor-BIO) analogs of microgravity. METHODS: BALB/c mice were divided into the following three groups: group housed, single isolation, and AOS. Mice were fed either control chow or chow supplemented with RNA or uracil. Immune function was assessed by in vivo popliteal lymph node proliferation (PLN), in vitro PHA-stimulated proliferation of splenocytes and cytokine production. BIO splenocytes were cultured in vitro with/without PHA, a nucleoside-nucleotide mixture (NS/NT) or uridine. The cell proliferation and scanning electron microscopic examination for cells were carried out. RESULTS: PLN response was significantly suppressed in AOS mice (P<0.05) and was restored by RNA and uracil diets. Splenocytes from AOS mice had decreased phytohemagglutinin (PHA)-stimulated proliferation, decreased IL-2 and IFN-gamma cytokine levels (P<0.05). These responses were restored by RNA and uracil diets. In BIO cultures, PHA response was suppressed significantly, and uridine and NS/NT restored the proliferative responses. Scanning electron microscopic analysis of cells cultured in BIO revealed cells with pinched, distorted and eroded membranes. Nucleotide supplementation especially uridine restored normal activated cell surface appearance and ruffling. CONCLUSION: In the microgravity analog environment of AOS and BIO, supplemental nucleotides and especially uracil/uridine have up-regulating and immunoprotective effects with potential as a countermeasure to the observed immune dysfunction in true microgravity.

Animals↗
PubMedDate not supplied

Post-suspension hypotension is attenuated in Sprague-Dawley rats by prostacyclin synthase inhibition.

Cardiovascular deconditioning, sometimes manifested in astronauts during standing postflight, may be related to the impairment of autonomic function and/or excessive production of endothelium-dependent relaxing factors. In the present study, we examined the cardiovascular responses to 7-day 30 degrees tail-suspension and a subsequent 6-h post-suspension period in conscious male Sprague-Dawley rats to determine the role of prostacyclin in the observed post-suspension reduction in mean arterial pressure (MAP). The specific prostacyclin synthase inhibitor U-51605 (0.3 mg/kg), or saline, was administered intravenously prior to release from suspension and at 2 and 4 h post-suspension. During 7 days of suspension, MAP did not change, however, there was a post-suspension reduction in MAP which was associated with significant increases in plasma prostacyclin and nitric oxide. U-51605 attenuated the observed post-suspension hypotension and reduced plasma prostacyclin levels, but not nitric oxide levels. The baroreflex sensitivity for heart rate was modified by U-51605: increased MAP threshold and effective MAP range. Thus, the post-suspension reduction in mean arterial pressure may be due to overproduction of prostacyclin and/or other endothelium-dependent relaxing factors and alteration in baroreflex activity.

Animals↗
PubMed2005

Two reference frames for visual perception in two gravity conditions.

The processing and storage of visual information concerning the orientation of objects in space is carried out in anisotropic reference frames in which all orientations are not treated equally. The perceptual anisotropies, and the implicit reference frames that they define, are evidenced by the observation of 'oblique effects' in which performance on a given perceptual task is better for horizontally and vertically oriented stimuli. The question remains how the preferred horizontal and vertical reference frames are defined. In these experiments cosmonaut subjects reproduced the remembered orientation of a visual stimulus in 1g (on the ground) and in 0g, both attached to a chair and while free-floating within the International Space Station. Results show that while the remembered orientation of a visual stimulus may be stored in a multimodal reference frame that includes gravity, an egocentric reference is sufficient to elicit the oblique effect when all gravitational and haptic cues are absent.

Analysis of Variance↗
PubMed2000

Microtubule self-organization is gravity-dependent.

Although weightlessness is known to affect living cells, the manner by which this occurs is unknown. Some reaction-diffusion processes have been theoretically predicted as being gravity-dependent. Microtubules, a major constituent of the cellular cytoskeleton, self-organize in vitro by way of reaction-diffusion processes. To investigate how self-organization depends on gravity, microtubules were assembled under low gravity conditions produced during space flight. Contrary to the samples formed on an in-flight 1 x g centrifuge, the samples prepared in microgravity showed almost no self-organization and were locally disordered.

Animals↗
PubMed2002

Microarray analysis identifies Salmonella genes belonging to the low-shear modeled microgravity regulon.

The low-shear environment of optimized rotation suspension culture allows both eukaryotic and prokaryotic cells to assume physiologically relevant phenotypes that have led to significant advances in fundamental investigations of medical and biological importance. This culture environment has also been used to model microgravity for ground-based studies regarding the impact of space flight on eukaryotic and prokaryotic physiology. We have previously demonstrated that low-shear modeled microgravity (LSMMG) under optimized rotation suspension culture is a novel environmental signal that regulates the virulence, stress resistance, and protein expression levels of Salmonella enterica serovar Typhimurium. However, the mechanisms used by the cells of any species, including Salmonella, to sense and respond to LSMMG and identities of the genes involved are unknown. In this study, we used DNA microarrays to elucidate the global transcriptional response of Salmonella to LSMMG. When compared with identical growth conditions under normal gravity (1 x g), LSMMG differentially regulated the expression of 163 genes distributed throughout the chromosome, representing functionally diverse groups including transcriptional regulators, virulence factors, lipopolysaccharide biosynthetic enzymes, iron-utilization enzymes, and proteins of unknown function. Many of the LSMMG-regulated genes were organized in clusters or operons. The microarray results were further validated by RT-PCR and phenotypic analyses, and they indicate that the ferric uptake regulator is involved in the LSMMG response. The results provide important insight about the Salmonella LSMMG response and could provide clues for the functioning of known Salmonella virulence systems or the identification of uncharacterized bacterial virulence strategies.

Biomechanical Phenomena↗
PubMed2004

Effect of microgravity on spatial orientation and posture regulation during Coriolis stimulation.

OBJECTIVE: To elucidate spatial orientation and posture regulation under conditions of microgravity. MATERIAL AND METHODS: Coriolis stimulation was done with five normal subjects on the ground (1 g) and onboard an aircraft (under conditions of microgravity during parabolic flight). Subjects were asked to tilt their heads forward during rotation at speeds of 0, 50, 100 and 150 degrees/s on the ground and 100 degrees/s during flight. Body sway was recorded using a 3D linear accelerometer and eye movements using an infrared charge-coupled device video camera. Flight experiments were performed on 5 consecutive days, and 11-16 parabolic maneuvers were done during each flight. Two subjects boarded each flight and were examined alternately at least five times. RESULTS: Coriolis stimulation at 1 g caused body sway, nystagmus and a movement sensation in accordance with inertial inputs at 1 g. Neither body sway, excepting a minute sway due to the Coriolis force, nor a movement sensation occurred in microgravity, but nystagmus was recorded. CONCLUSIONS: Posture, eye movement and sensation at 1 g are controlled with reference to spatial coordinates that represent the external world in the brain. Normal spatial coordinates are not relevant in microgravity because there is no Z-axis, and the posture regulation and sensation that depend on them collapse. The discrepancy in responses between posture and eye movement under conditions of microgravity may be caused by a different constitution of the effectors which adjust posture and gaze.

Adult↗
PubMed2005

Modelled microgravity does not modify the yield of chromosome aberrations induced by high-energy protons in human lymphocytes.

The aim was to evaluate the effect of modelled microgravity on radiation-induced chromosome aberrations (CAs). G0 peripheral blood lymphocytes were exposed to 60 MeV protons or 250 kVp X-rays in the dose range 0-6 Gy, and allowed to repair DNA damage for 24 h under either normal gravity or microgravity modelled by the NASA-designed rotating-wall bioreactor. Cells were then stimulated to proliferate by phytohaemagglutinin (PHA) under normal gravity conditions and prematurely condensed chromosomes were harvested after 48 h. CAs were scored in chromosomes 1 and 2 by fluorescence in-situ hybridization. Proliferation gravisensitivity was examined by cell growth curves and by morphological evaluation of mitogen-induced activation. Cell replication rounds were monitored by bromodeoxyuridine labelling. Modelled microgravity markedly reduced PHA-mediated lymphocyte blastogenesis and cell growth. However, no significant differences between normal gravity and modelled microgravity were found in the dose-response curves for the induction of aberrant cells or total interchromosomal exchange frequency. Rotating-wall bioreactor-based microgravity reproduced space-related alterations of mitogen stimulation in human lymphocytes but did not affect the yield of CAs induced by low-linear energy transfer radiation.

Cell Proliferation↗
PubMed1996

A high protein diet does not improve protein synthesis in the nonweight-bearing rat tibialis anterior muscle.

We recently demonstrated that a high protein intake partially prevented the decrease in protein synthesis in the atrophied dark soleus muscle of rats that were hindlimb suspended (HS) for 21 d. To study the possible role of protein intake in a muscle more representative of the whole musculature, we measured the effect of a high protein (HP) (30%) and a medium protein (MP) (15%) diet on protein synthesis in the pale fast-twitch tibialis anterior muscle of HS rats. The HS animals were suspended by the tail for 21 d so that only their front legs were able to rest on the floor. The fractional rate of protein synthesis (Ks) was determined in vivo using a flooding dose method. A significantly lower Ks (24-25%) was found in both HS-MP and HS-HP rats compared with their pair-fed control groups. Reduced Ks in HS-MP rats relative to their pair-fed controls resulted from a decrease in the translational efficiency (KRNA, 23%, P < 0.01), while the ratio of RNA to protein (Cs) was unaffected. In contrast, the decrease in KRNA was prevented in the HS-HP animals compared with their pair-fed controls (P < 0.05). Hindlimb suspension did not alter fiber type distribution in the tibialis anterior muscle. However, a higher proportion of intermediate and Type I fibers with a concomitant decrease in Type II fibers was observed in both CT and HS animals fed the HP diet compared with those fed the MP diet (P < 0.05). These data clearly establish that depressed protein synthesis contributes to altered protein accretion in fast-twitch muscles during long-term hindlimb suspension. Although the HP diet prevented the decrease in translational efficiency in muscles from HS rats, it neither sustained protein synthesis nor prevented the reduction in muscle growth. Thus, it seems very unlikely that a high protein diet had any beneficial effect on the overall musculature during weightlessness in rats.

Animals↗
PubMed1990

How effectively does a clinostat mimic the ultrastructural effects of microgravity on plant cells?

Columella cells of seedlings of Zea mays L. cv. Bear Hybrid grown in the microgravity of orbital flight allocate significantly larger relative-volumes to hyaloplasm and lipid bodies, and significantly smaller relative-volumes to dictyosomes, plastids, and starch than do columella cells of seedlings grown at 1 g. The ultrastructure of columella cells of seedlings grown at 1 g and on a rotating clinostat is not significantly different. However, the ultrastructure of cells exposed to these treatments differs significantly from that of seedlings grown in microgravity. These results indicate that the actions of a rotating clinostat do not mimic the ultrastructural effects of microgravity in columella cells of Z. mays.

Cell Compartmentation↗
PubMed1990

Comparative effectiveness of a clinostat and a slow-turning lateral vessel at mimicking the ultrastructural effects of microgravity in plant cells.

The object of this research was to determine how effectively the actions of a clinostat and a fluid-filled, slow-turning lateral vessel (STLV) mimic the ultrastructural effects of microgravity in plant cells. We accomplished this by qualitatively and quantitatively comparing the ultrastructures of cells grown on clinostats and in an STLV with those of cells grown at 1 g and in microgravity aboard the Space Shuttle Columbia. Columella cells of Brassica perviridis seedlings grown in microgravity and in an STLV have similar structures. Both contain significantly more lipid bodies, less starch, and fewer dictyosomes than columella cells of seedlings grown at 1 g. Cells of seedlings grown on clinostats have significantly different ultrastructures from those grown in microgravity or in an STLV, indicating that clinostats do not mimic microgravity at the ultrastructural level. The similar structures of columella cells of seedlings grown in an STLV and in microgravity suggest that an STLV effectively mimics microgravity at the ultrastructural level.

Brassica↗