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At least 559 records · Page 31Linked to original sources
PubMed2006

Effects of simulated microgravity on male gametophyte of Prunus, Pyrus, and Brassica species.

In this study we evaluated the effect of simulated microgravity on pollen germination of both herbaceous and woody species in order to investigate the possibility of applying gametophytic selection for plant growth in the space environment. The behaviour of gametophytes exposed to the stress of clinostat rotation could be used to screen the degree of tolerance of the sporophyte to simulated microgravity. The use of male gametophyte selection overcomes the problems generally encountered by sporophytic selection in space especially for woody plants: the large size of plants and their long juvenile phase. In this experiment, pollen collected from just bloomed flowers of Prunus persica, P. avium, P. domestica, Pyrus communis, and Brassica rapa was subjected to tests assessing its viability by techniques such as fluorochromatic reaction. Once pollen viability was ascertained by fluorescence microscopy, pollen was placed on the growth medium in petri dishes both at 1 g and on the clinostat. After incubating for 1 day at room temperature, pollen was observed under a light microscope in order to detect parameters such as the percentage of germination and the growth direction. Then histochemical analyses were performed in order to verify the presence and distribution of nuclei, cytoplasm, and storage substances. Moreover, the presence, size, and morphology of callose plugs were observed. Results showed that the response of gametophytes to simulated microgravity is dependent on the species, some showing altered metabolism, others being unaffected.

Brassica↗
PubMed1998

Muscle sympathetic nerve activity and plasma norepinephrine during 6 degrees head-down bed rest.

Alterations in autonomic function are evident during spaceflight. These conditions are also simulated by ground-based experimental models of a microgravity environment such as 6 degrees head-down bed rest (BR). They include a reduction in baroreflex function, a decrease in vagal tone and a loss of circulatory blood volume during weightlessness. However, it is not clear whether vasomotor sympathetic outflow, which controls peripheral vascular tone neurally, and plasma norepinephrine concentration will change or not during weightlessness. The purpose of the present study is to examine changes in vasomotor sympathetic nerve activity during six days of 6 degrees head-down BR. Vasomotor sympathetic nervous activity was evaluated by the direct recording of muscle sympathetic nerve activity (MSNA) by a use of microneurographic technique. MSNA on the sixth day during BR was the same as that in a horizontally supine position before BR (before BR; 15.4 +/- 1.6 bursts/min, during BR; 16.7 +/- 3.5 bursts/min), though plasma norepinephrine concentrations during BR were reduced by 25% compared with those before BR (before BR; 263 +/- 33 pg/ml, during BR; 193 +/- 79 pg/ml, p < 0.05). This dissociation cannot be determined precisely, but it suggests the possibility of peripheral changes in terminal sympathetic nerve endings, etc.

Adult↗
PubMed2001

Clinostats and bioreactors.

The environment created on Earth within a clinostat or Rotating Wall Vessel (RWV) bioreactor is often referred to as "simulated microgravity". Both devices utilize constant reorientation to effectively nullify cumulative sedimentation of particles. Neither, however, can fully reproduce the concurrent lack of structural deformation, displacement of intercellular components and/or reduced mass transfer in the extracellular fluid that occur in actual weightlessness. Parameters including density, viscosity, and even container geometry must each be considered to determine the overall gravity-dependent effects produced by either a clinostat or the RWV bioreactor; in addition, the intended application of these two devices differs considerably. A state of particle "motionlessness" relative to the surrounding bulk fluid, which is nearly analogous to the extracellular environment encountered under weightless conditions, can theoretically be achieved through clinorotation. The RWV bioreactor, on the other hand, while similarly maintaining cells in suspension as they continually "fall" through the medium under 1 g conditions, can also purposefully induce a perfusion of nutrients to and waste from the culture. A clinostat, therefore, is typically used in an attempt to reproduce the quiescent, unstirred fluid conditions achievable on orbit; while the RWV bioreactor ideally creates a low shear, but necessarily mixed, fluid environment that is optimized for suspension culture and tissue growth. Other techniques for exploring altered inertial environments, such as freefall, neutral buoyancy and electromagnetic levitation, can also provide unique insight into how gravity affects biological systems. Ultimately, all underlying biophysical principles thought to give rise to gravity-dependent physiological responses must be identified and thoroughly examined in order to accurately interpret data from flight experiments or ground-based microgravity analogs.

Acceleration↗
PubMed1996

Cardiovascular and hormonal changes induced by isolation and confinement.

The cardiovascular changes induced by microgravity are in general described as the result of the loss of hydrostatic pressure. Other factors are also important: restricted environment with 1) elimination of mobility, action and 2) isolation always found in space environment or during simulation studies. Several studies indicate an analogy between microgravity and confinement. The results of simulation studies could be misinterpreted without a control confinement study present in the protocol.

Cardiovascular Physiological Phenomena↗
PubMedDate not supplied

Closed-loop, estimator-based model of human posture following reduced gravity exposure.

A computational and experimental method is employed to provide an understanding of a critical human space flight problem, posture control following reduced gravity exposure. In the case of an emergency egress, astronauts' postural stability could be life saving. It is hypothesized that muscular gains are lowered during reduced gravity exposure, causing a feeling of heavy legs, or a perceived feeling of muscular weakness, upon return to Earth's 1 g environment. We developed an estimator-based model that is verified by replicating spatial and temporal characteristics of human posture and incorporates an inverted pendulum plant in series with a Hill-type muscle model, two feedback pathways, a central nervous system estimator, and variable gains. Results obtained by lowering the variable muscle gain in the model support the hypothesis. Experimentally, subjects were exposed to partial gravity (3/8 g) simulation on a suspension apparatus, then performed exercises postulated to expedite recovery and alleviate the heavy legs phenomenon. Results show that the rms position of the center of pressure increases significantly after reduced gravity exposure. Closed-loop system behavior is revealed, and posture is divided into a short-term period that exhibits higher stochastic activity and persistent trends and a long-term period that shows relatively low stochastic activity and antipersistent trends.

Adult↗
PubMedDate not supplied

[Alterations of nucleolar DNA localization caused by simulated microgravity].

The functions of the nucleolus responsible for the biosynthesis of ribosomes in altered gravity are still unclear. The location of nucleolar DNA both in control and simulated microgravity has been investigated using fluorescent and immunogold cytochemistry. We have determined the redistribution of rDNA in the nucleolar components accompanied by their ultrastructure changes. According to this the lowering of rDNA transcription level under simulated microgravity was supposed.

Cell Nucleolus↗
PubMed2000

Effects of simulated microgravity on immunoreactivity of conjugated-ubiquitin of muscle spindles of soleus in rats.

It is well known that the muscle spindle is a receptor of muscle's tension and length, it plays an important role in maintaining the muscle's tension. The aim of the present study is to compare the cross-section area (CSA) and the immunoreactivity of conjugated-ubiquitin in soleus extrafusal and intrafusal fibers after simulated-microgravity in order to demonstrate the role of muscle spindle in muscle atrophy induced by simulated microgravity.

Animals↗
PubMed2004

Is HSP70 upregulation crucial for cellular proliferative response in simulated microgravity?

Astronauts are susceptible to a variety of conditions such as motion sickness, muscular atrophy, bone demineralization and cardiovascular deconditioning. These findings suggest that the adaptation to the absence of gravity is due, at least in part, to the effects exerted by microgravity at the cellular level. Indeed, a number of studies have indicated that gravity affects mammalian cell growth and differentiation through the modulation of gene expression. We have characterized the behaviour of endothelial cells and of the human monocytic cell line U937 cultured in the NASA-developed bioreactor to simulate microgravity, the Rotating Wall Vessels (RWV). In simulated microgravity endothelial cells showed a different behavior which was dependent from the species and from the district of origin, while U937 in the RWV proliferated slower than the controls. All the effects we observed were promptly reversible upon return to normal culture conditions. It is noteworthy that all the cells which maintained the capability to proliferate in microgravity upregulated the stress protein HSP70. We therefore propose that only the cells which sense microgravity as a stressful condition and, consequently, overexpress HSP70 maintain their proliferative potential in simulated microgravity.

Animals↗
PubMed1994

Changes of pulmonary function in humans during exposure to +Gx acceleration after simulated and real microgravity.

An important goal of space medicine is preserving high tolerance and performance of cosmonauts an ring exposure to acceleration at the final flight stage given varying mission duration. Among physiological mechanisms limiting +Gx acceleration tolerance, an important role is played by disturbances of external respiration resulting from alterations of respiratory biomechanics, pulmonary gas exchange conditions, and arterial hypoxemia. However, at present data on external respiration changes during exposure to +Gx acceleration after simulated and real microgravity of varying duration, are extremely scanty.

Bed Rest↗
PubMed1994

Contractile characteristics of the triceps surae muscle in healthy males during 120-days head-down tilt (HDT) and countermeasures.

To reveal mechanisms responsible for changes in muscle contractility during microgravity, it seems expedient to perform similar studies under microgravity or conditions simulating microgravity. Among standard methods for simulating microgravity, hypokinesia modelling support unloading (or rather its redistribution), and hypodynamia are employed. Absence of weight loading, decreased muscular effort characteristic of the Earth conditions due to counteracting gravity, results in a general muscle underloading and therefore in lowered activity of the proprioceptive input. This may be one of the reasons not only for a resetting of motor coordination and control, but also for a gradual development of a persistent change in the motor control system. The basis of countermeasures against negative consequences of microgravity (hypokinesia) is the correct choice of countermeasures. In this connection of specific interest is a study of the magnitude of change in skeletal muscle contractility in humans after a variety of countermeasures when functional activity is lowered by a long-term 120-days HDT which is an adequate simulation of physiological microgravity-induced effects.

Adult↗
PubMed1998

Altered gravity modulates 5-lipoxygenase in human erythroleukemia K562 cells.

Mammalian lipoxygenases catalyse the first committed step in the so-called "arachidonate cascade", leading to the production of potent bioactive molecules, such as leukotrienes, lipoxins and hepoxilins. Leukotrienes interact with G protein-couple receptors involved in neuronal plasticity and T lymphocyte activation, lipoxins activate leukocytes, hepoxilines control the insulin release and stimulate the phospholipase C. Lipoxygenase (linoleate:oxygen oxidoreductase; E.C. 1.13.11.34; 5-LOX) are responsible for lymphocyte maturation and programmed death (apoptosis) of neuronal cells. Therefore, 5-LOX might be Space relevant, because among the most striking effects of Space enviroment are indeed those on T lymphocyte activation, neuronal cell growth and suspectedly apoptosis. In this study, the possible effects of the force of gravity on the activity and expression of 5-LOX have been investigated by subjecting human erythroleukemia K562 cells to simulated hypogravity or hypergravity.

Arachidonate 5-Lipoxygenase↗