Onset Of Microgravity Research Articles

Transient cerebral blood flow responses during microgravity

PurposeA number of studies has well described central cardiovascular changes caused by changing gravity levels as they occur e.g. during parabolic flight. limited data exists describing the effect of microgravity on the cerebrovascular system and brain perfusion. MethodsIn this study middle cerebral artery velocity (MCAv) of 16 participants was continuously monitored on a second-by-second basis during 15 consecutive parabolas (1G, 1,8G, 0G, 1,8G) using doppler ultrasound. Simultaneously central cardiovascular parameters (heart rate, mean arterial blood pressure, cardiac output) were assessed. ResultsResults revealed an immediate reaction of central cardiovascular parameters to changed gravity levels. In contrast, changes in MCAv only initially were in accordance with a normal cerebral autoregulation. Whereas all of the measured central cardiovascular parameters seemed to have reached a steady state after approximately 8 s of microgravity, MCAv, after an initial decrease with the onset of microgravity, increased again during the second half of the microgravity phase. ConclusionIt is concluded that this increase in MCAv during the second half of the microgravity period reflects a decrease of cerebrovascular resistance caused by a pressure driven increased venous outflow and/or a contraction of precapillary sphincters in order to avoid hyperperfusion of the brain.

Microgravity and Hypergravity Observations of Equiaxed Solidification of Al-Cu Alloys Using <i>In Situ</i> X-Radiography Recorded in Real-Time on Board a Parabolic Flight

During solidification of metallic alloys, thermosolutal natural convection plays a significant role in grain nucleation, subsequent growth and morphology, as well as the formation of casting defects. In this work, an Al-5wt%Ti-1wt%B inoculated Al-20wt%Cu alloy was solidified, near-isothermally, using a Bridgman-type gradient furnace, while being monitored in real-time via in-situ X-radiography as part of a parabolic flight microgravity campaign. Each parabola consisted of a transition through 24 seconds of hypergravity (1.8 g), followed by 22 seconds of microgravity, and a then a further 24 seconds of hypergravity. Solidification was controlled such that nucleation occurred coincident with the onset of microgravity. This allowed for the effects of microgravity on equiaxed nucleation and initial growth, followed by continuing solidification in hypergravity, to be observed, as well as the effect on the semi-coherent grain structure when transitioning between the two.

Gender-related sensitivity of development and growth to real microgravity inXenopus laevis

Exposure of organisms to microgravity can induce morphological, physiological, and behavioral modifications which normalize after re-entry in 1g-condition within hours to few weeks. Development of Xenopus laevis tadpoles, their metamorphosis, and adults' growth were monitored for 3 years after their flight on the 12-day Soyuz mission TMA13 to the International Space Station. At onset of microgravity, tadpoles had just developed the hind limb (stage 47) or forelimb bud (stage 50). Recordings during the first 4 days after landing revealed no differences of developmental progresses and growth between flight and ground tadpoles. Further development and growth were strongly retarded in all animals; nevertheless, significant differences appeared between flight and ground groups during this postflight period. They include (1) acceleration of development in stage 47 but not stage 50 flight tadpoles; (2) earlier metamorphosis of stage 47 flight tadpoles compared to their 1g-ground controls while stage 50 flight tadpoles metamorphosed later than their ground controls; (3) maintenance of a tail during the juvenile stage exclusively in some stage 47 flight animals, and (4) accelerated growth of stage 47 male flight toads but retarded growth of stage 50 flight males compared to the respective 1g-ground control males. No difference of growth was detected between flight and ground females after metamorphosis. All differences between flight and ground animals disappeared 1 year after landing. We conclude (1) that limited spatial and nutritional conditions during the mission period caused developmental retardation, and (2) that the thyroid gland of Xenopus is susceptible to spatial environment, in particular, during the period of beginning activation.

Cytosolic calcium, hydrogen peroxide and related gene expression and protein modulation in Arabidopsis thaliana cell cultures respond immediately to altered gravitation: parabolic flight data

Callus cell cultures of Arabidopsis thaliana (cv. Columbia) were exposed to parabolic flights in order to assess molecular, short-term responses to altered gravity fields. Using transgenic cell lines, hydrogen peroxide (H2 O2 ) and cytosolic Ca(2+) were continuously monitored. In parallel, the metabolism of samples was chemically quenched (RNAlater, Ambion for RNA; acid/base for NADPH, NADP) at typical stages of a parabola [1g before pull up; end of pull up (1.8g), end of microgravity (20s) and end of pull out (1.8g)]. Cells exhibited an increase in both Ca(2+) and H2 O2 with the onset of microgravity, and a decline thereafter. This behaviour was accompanied by a decrease of the NADPH/NADP redox ratio, indicating Ca(2+) -dependent activation of a NADPH oxidase. Microarray analyses revealed concomitant expression profiles. At the end of the microgravity phase, 396 transcripts were specifically up-, while 485 were down-regulated. Up-regulation was dominated by Ca(2+) - and ROS-related gene products. The same material was also used for analysis of phosphopeptides with 2-D SDS PAGE. Relevant spots were identified by liquid chromatography-MS. With the exception of a chaperone (HSP 70-3), hypergravity (1.8g) and microgravity modified different sets of proteins. These are partly involved in primary metabolism (glycolysis, gluconeogenesis, citrate cycle) and detoxification of ROS. Taken together, these data show that both gene expression and protein modulation jointly respond within seconds to alterations in the gravity field, with a focus on metabolic adaptation, signalling and control of ROS.

Signal transduction in primary human T lymphocytes in altered gravity – results of the MASER-12 suborbital space flight mission

We investigated the influence of altered gravity on key proteins of T cell activation during the MASER-12 ballistic suborbital rocket mission of the European Space Agency (ESA) and the Swedish Space Cooperation (SSC) at ESRANGE Space Center (Kiruna, Sweden). We quantified components of the T cell receptor, the membrane proximal signaling, MAPK-signaling, IL-2R, histone modifications and the cytoskeleton in non-activated and in ConA/CD28-activated primary human T lymphocytes. The hypergravity phase during the launch resulted in a downregulation of the IL-2 and CD3 receptor and reduction of tyrosine phosphorylation, p44/42-MAPK phosphorylation and histone H3 acetylation, whereas LAT phosphorylation was increased. Compared to the baseline situation at the point of entry into the microgravity phase, CD3 and IL-2 receptor expression at the surface of non-activated T cells were reduced after 6 min microgravity. Importantly, p44/42-MAPK-phosphorylation was also reduced after 6 min microgravity compared to the 1g ground controls, but also in direct comparison between the in-flight μg and the 1g group. In activated T cells, the reduced CD3 and IL-2 receptor expression at the baseline situation recovered significantly during in-flight 1g conditions, but not during microgravity conditions. Beta-tubulin increased significantly after onset of microgravity until the end of the microgravity phase, but not in the in-flight 1g condition. This study suggests that key proteins of T cell signal modules are not severely disturbed in microgravity. Instead, it can be supposed that the strong T cell inhibiting signal occurs downstream from membrane proximal signaling, such as at the transcriptional level as described recently. However, the MASER-12 experiment could identify signal molecules, which are sensitive to altered gravity, and indicates that gravity is obviously not only a requirement for transcriptional processes as described before, but also for specific phosphorylation / dephosphorylation of signal molecules and surface receptor dynamics.

Beta-adrenoceptor pathway enhances mitochondrial function in human neural stem cells via rotary cell culture system

The structure and function of the human nervous system are altered in space when compared with their state on earth. To investigate directly the influence of simulated microgravity conditions which may be beneficial for cultivation and proliferation of human neural stem cells (hNSCs), the rotary cell culture system (RCCS) developed at the National Aeronautics and Space Administration (NASA) was used. RCCS allows the creation of a unique microgravity environment of low shear force, high-mass transfer and enables three-dimensional (3D) cell culture of dissimilar cell types. The results show that simulated microgravity using an RCCS would induce β-adrenoceptor, upregulate cAMP formation and activate both PKA and CREB (cAMP response element binding protein) pathways. The expression of intracellular mitochondrial genes, including PGC1α (PPAR coactivator 1α), nuclear respiratory factors 1 and 2 (NRF1 and NRF2) and mitochondrial transcription factor A (Tfam), regulated by CREB, were all significantly increased at 72h after the onset of microgravity. Accordingly and importantly, the ATP level and amount of mitochondrial mass were also increased. These results suggest that exposure to simulated microgravity using an RCCS would induce cellular proliferation in hNSCs via an increased mitochondrial function. In addition, the RCCS bioreactor would support hNSCs growth, which may have the potential for cell replacement therapy in neurological disorders.

Parabolic maneuvers of the Swiss Air Force fighter jet F-5E as a research platform for cell culture experiments in microgravity

Long-term sensitivity of human cells to reduced gravity has been supposed since the first Apollo missions and was demonstrated during several space missions in the past. However, little information is available on primary and rapid gravi-responsive elements in mammalian cells. In search of rapid-responsive molecular alterations in mammalian cells, short-term microgravity provided by parabolic flight maneuvers is an ideal way to elucidate such initial and primary effects. Modern biomedical research at the cellular and molecular level requires frequent repetition of experiments that are usually performed in sequences of experiments and analyses. Therefore, a research platform on Earth providing frequent, easy and repeated access to real microgravity for cell culture experiments is strongly desired. For this reason, we developed a research platform onboard the military fighter jet aircraft Northrop F-5E “Tiger II”. The experimental system consists of a programmable and automatically operated system composed of six individual experiment modules, placed in the front compartment, which work completely independent of the aircraft systems. Signal transduction pathways in cultured human cells can be investigated after the addition of an activator solution at the onset of microgravity and a fixative or lysis buffer after termination of microgravity. Before the beginning of a regular military training flight, a parabolic maneuver was executed. After a 1 g control phase, the parabolic maneuver starts at 13,000 ft and at Mach 0.99 airspeed, where a 22 s climb with an acceleration of 2.5 g is initiated, following a free-fall ballistic Keplerian trajectory lasting 45 s with an apogee of 27,000 ft at Mach 0.4 airspeed. Temperature, pressure and acceleration are monitored constantly during the entire flight. Cells and activator solutions are kept at 37 °C during the entire experiment until the fixative has been added. The parabolic flight profile provides up to 45 s of microgravity at a quality of 0.05 g in all axes. Access time is 30 min before take-off; retrieval time is 30 min after landing. We conclude that using military fighter jets for microgravity research is a valuable tool for frequent and repeated cell culture experiments and therefore for state-of-the art method of biomedical research.

Morphometric investigations of sensory vestibular structures in tadpoles (Xenopus laevis) after a spaceflight: implications for microgravity-induced alterations of the vestibuloocular reflex

In lower vertebrates, gravity deprivation by orbital flights modifies the vestibuloocular reflex. Using the amphibian Xenopus laevis, the experiments should clarify to which extent macular structures of the labyrinth are responsible for these modifications. In particular, the shape of otoconia and number and size of sensory macular cells expressing CalBindin were considered. CalBindin is common in mature sensory cells including vestibular hair cells and is probably involved in otoconia formation. Two developmental stages were used for this study: stage 26/27 embryos, which were unable to perform the roll-induced vestibuloocular reflex (rVOR) at onset of microgravity, and stage 45 tadpoles, which had already developed the reflex. The main observations were that the developmental progress of the animals was not affected by microgravity; that in the young tadpole group with normal body shape the rVOR was not modified by microgravity, while in the older group with microgravity experience, the rVOR was augmented; and that significant effects on the shape of otoconia and on the number and size of CalBindin-expressing cells of the labyrinthine maculae cells were absent. In addition, behavioural data were never significantly correlated with morphological features of macular structures such as size and number of CalBindin-expressing cells. It is postulated that mechanisms of vestibular adaptation to microgravity during early development are probably based on mechanisms located in central structures of the vestibular system.

Microgravity-induced modifications of the vestibuloocular reflex inXenopus laevistadpoles are related to development and the occurrence of tail lordosis

During space flights, tadpoles of the clawed toad Xenopus laevis occasionally develop upward bended tails (tail lordosis). The tail lordosis disappears after re-entry to 1g within a couple of days. The mechanisms responsible for the induction of the tail lordosis are unknown; physical conditions such as weight de-loading or physiological factors such as decreased vestibular activity in microgravity might contribute. Microgravity (microg) also exerts significant effects on the roll-induced vestibuloocular reflex (rVOR). The rVOR was used to clarify whether tail lordosis is caused by physiological factors, by correlating the occurrence of microg-induced tail lordosis with the extent of microg-induced rVOR modifications. Post-flight recordings from three space flights (D-2 Spacelab mission, STS-55 in 1993; Shuttle-to-Mir mission SMM-06, STS-84 in 1997; French Soyuz taxi flight Andromède to ISS in 2001) were analyzed in these experiments. At onset of microgravity, tadpoles were at stages 25-28, 33-36 or 45. Parameters tested were rVOR gain (ratio between the angular eye movement and the lateral 30 degrees roll) and rVOR amplitude (maximal angular postural change of the eyes during a 360 degrees lateral roll). A ratio of 22-84% of tadpoles developed lordotic tails, depending on the space flight. The overall observation was that the rVOR of tadpoles with normal tails was either not affected by microgravity, or it was enhanced. In contrast, the rVOR of lordotic animals always revealed a depression. In particular, during post-flight days 1-11, tadpoles with lordotic tails from all three groups (25-28, 33-36 and 45) showed a lower rVOR gain and amplitude than the 1g-controls. The rVOR gain and amplitude of tadpoles from the groups 25-28 and 33-36 that developed normal tails was not affected by microgravity while the rVOR of microg-tadpoles from the stage-45 group with normal tails revealed a significant rVOR augmentation. (1) the vestibular system of tadpoles with lordotic tails is developmentally retarded by microgravity; (2) after a critical status of vestibular maturation obtained during the appearance of first swimming, microgravity activates an adaptation mechanism that causes a sensitization of the vestibular system.

Influence of microgravity on mitogen binding and cytoskeleton in Jurkat cells

The effects of microgravity on Jurkat cells — a T-lymphoid cell line — was studied on a sounding rocket flight. An automated pre-programmed instrument permitted the injection of fluorescent labelled concanavalin A (Con A), culture medium and/or fixative at given times. An in-flight 1 g centrifuge allowed the comparison of the data obtained in microgravity with a 1 g control having the same history related to launch and re-entry. After flight, the cells fixed either at the onset of microgravity or after a 12 minute incubation time with fluorescent concanavalin A were labelled for vimentin and actin and analysed by fluorescence microscopy. Binding of Con A to Jurkat cells is not influenced by microgravity, whereas patching of the Con A receptors is significantly lower. A significant higher number of cells show changes in the structure of vimentin in microgravity. Most evident is the appearance of large bundles, significantly increased in the microgravity samples. No changes are found in the structure of actin and in the colocalisation of actin on the inner side of the cell membrane with the Con A receptors after binding of the mitogen.

Cerebral blood flow velocity in humans exposed to 24 h of head-down tilt.

This study investigates cerebral blood flow (CBF) velocity in humans before, during, and after 24 h of 6 degree head-down tilt (HDT), which is a currently accepted experimental model to simulate microgravity. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery of eight healthy male subjects. Mean CBF velocity increased from the pre-HDT upright seated baseline value of 55.5 +/- 3.7 (SE) cm/s to 61.5 +/- 3.3 cm/s at 0.5 h of HDT (P < 0.05), reached a peak value of 63.2 +/- 4.1 cm/s at 3 h of HDT, and remained significantly above the pre-HDT baseline for > or = 6 h of HDT. During upright seated recovery (1-5 h post-HDT), mean CBF velocity decreased to 87% of the pre-HDT baseline value (P < 0.05). Mean CBF velocity correlated well with calculated intracranial arterial pressure (IAP) (r = 0.54, P < 0.001). As analyzed by linear regression, mean CBF velocity = 29.6 + 0.32IAP. These results suggest that HDT increases CBF velocity by increasing IAP during several hours after the onset of microgravity. Importantly, the decrease in CBF velocity after HDT may be responsible, in part, for the increased risk of syncope observed in subjects after prolonged bed rest and also in astronauts returning to Earth.