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PubMed1998

Effects of gravity on early development.

The development of embryonic and larval stages of the South African Toad Xenopus laevis D, was investigated in hyper-g up to 5 g (centrifuge), in simulated 0 g (fast-rotating clinostat), in alternating low g, hyper-g (parabolic flights) and in microgravity (Spacelab missions D1, D-2). The selected developmental stages are assumed to be very sensitive to environmental stimuli. The results showed that the developmental reaction processes run normal also in environments different to 1 g and that aberrations in behavior and morphology normalize after return to 1 g. Development, differentiation, and morphology of the gravity perceiving parts of the vestibular system (macula-organs) had not been affected by exposure to different g-levels.

Adaptation, Physiological↗
PubMed1998

Metabolic adaptation to long term changes in gravity environment.

Biochemical analyses of the brain of Cichlid fish larvae, exposed during their very early development for 7 days to an increased acceleration of 3g (hyper-gravity), revealed a decrease in brain nucleoside diphosphate kinase (NDPK) as well as creatine kinase (BB-CK) activity. Using high performance liquid chromatography (HPLC) the concentrations of adenine nucleotides (AMP, ADP, ATP), phospliocreatine (CP), as well as of nicotineamide adenine dinucleotides (NAD, NADP) were analyzed in the brain of hyper-g exposed larvae vs. 1g controls. A slight reduction in the total adenine nucleotides (TAN) as well as the adenylate energy charge (AEC) was found. In parallel a significant increase in the NAD concentration and a corresponding decrease in NADP concentration occurred in larva's hyper-g brains vs. 1 g controls. These results give further evidence for an Influence of gravity on cellular level and furthermore contribute to a clarification of the cellular signal-response chain for gravity perception.

Adenine Nucleotides↗
PubMed1998

On inappropriately used neuronal circuits as a possible basis of the "loop-swimming" behaviour of fish under reduced gravity: a theoretical study.

One hypothesis for the explanation of the so-called "loop-swimming" behaviour in fish when being subjected to reduced gravity assumes that the activities of the differently weighted otoliths of the two labyrinths are well compensated on ground but that a functional asymmetry is induced in weightlessness, resulting in a tonus asymmetry of the body and by this generating the "loop-swimming" behaviour. The basis of this abnormal behaviour has to be searched for in the central nervous system (cns), where the signal-transduction from the inner ear- related signal internalisation to the signal response takes place. Circuits within the CNS of fish, that could possibly generate the "loop-swimming", might be as follows: An asymmetric activation of vestibulospinal circuits would directly result in a tonus asymmetry of the body. An asymmetric activation of the oculomotor nucleus would generate an asymmetrical rotation of the eyes. This would cause in its turn asymmetric images on the two retinas, which were forwarded to the diencephalic accessory optic system (AOS). It is the task of the AOS to stabilize retinal images, thereby involving the cerebellum, which is the main integration center for sensory and motor modalities. With this, the cerebellar output would generate a tonus asymmetry of the body in order to make the body of the fish follow its eyes. Such movements (especially when assuming an open loop control) would end up in the aforementioned "loop-swimming" behaviour.

Animals↗
PubMed1998

Influence of long-term hyper-gravity on the reactivity of succinic acid dehydrogenase and NADPH-diaphorase in the central nervous system of fish: a histochemical study.

In the course of a densitometric evaluation, the histochemically demonstrated reactivity of succinic acid dehydrogenase (SDH) and of NADPH-diaphorase (NADPHD) was determined in different brain nuclei of two teleost fish (cichlid fish Oreochromis mossambicus, swordtail fish Xiphophorus helleri), which had been kept under 3g hyper-gravity for 8 days. SDH was chosen since it is a rate limiting enzyme of the Krebs cycle and therefore it is regarded as a marker for metabolic and neuronal activity. NADPHD reactivity reflects the activity of nitric oxide synthase. Nitric oxide (NO) is a gaseous intercellular messenger that has been suggested to play a major role in several different in vivo models of neuronal plasticity including learning. Within particular vestibulum-connected brain centers, significant effects of hyper-gravity were obtained, e.g., in the magnocellular nucleus, a primary vestibular relay ganglion of the brain stem octavolateralis area, in the superior rectus subdivision of the oculomotoric nucleus and within cerebellar eurydendroid cells, which in teleosts possibly resemble the deep cerebellar nucleus of higher vertebrates. Non-vestibulum related nuclei did not respond to hyper-gravity in a significant way. The effect of hyper-gravity found was much less distinct in adult animals as compared to the circumstances seen in larval fish (Anken et al., Adv. Space Res. 17, 1996), possibly due to a development correlated loss of neuronal plasticity.

Afferent Pathways↗
PubMed2000

Gravitational neurobiology of fish.

In vertebrates (including man), altered gravitational environments such as weightlessness can induce malfunctions of the inner ears, based on irregular movements of the semicircular cristae or on dislocations of the inner ear otoliths from the corresponding sensory epithelia. This will lead to illusionary tilts, since the vestibular inputs are not confirmed by the other sensory organs, which results in an intersensory conflict. Vertebrates in orbit therefore face severe orientation problems. In humans, the intersensory conflict may additionally lead to a malaise, commonly referred to as space motion sickness (SMS), a kinetosis. During the first days at weightlessness, the orientation problems (and SMS) disappear, since the brain develops a new compensatory interpretation of the available sensory data. The present review reports on the neurobiological responses--particularly of fish--observed at altered gravitational states, concerning behaviour and neuroplastic reactivities. Recent investigations employing microgravity (spaceflight, parabolic aircraft flights, clinostat) and hyper-gravity (laboratory centrifuges as ground based research tools) yielded clues and insights into the understanding of the respective basic phenomena.

Animals↗
PubMed2000

Emesis and space motion sickness in amphibians.

Amphibians possess the ability to vomit in response to a variety of stimuli that provoke emesis in mammals. Pharmacological studies have establish that the ejection of gastric contents and the basic mechanism for vomiting have been phylogenetically conserved among these tetrapods. As part of on-going comparative studies on emesis in vertebrates, we previously documented that some postmetamorphic anurans and salamander larvae experience motion-induced emesis when exposed to the provocative stimulus of parabolic aircraft flight. However, more recent experiments suggest that there are strict conditions for inducing emesis in amphibians exposed to parabolic flight and that amphibians are not as sensitive to this stimulus as mammals. Further studies on emesis in lower vertebrates may help us understand the processes that cause emesis in abnormal gravitational regimes.

Amphibians↗
PubMed2001

Response of renal sympathetic nerve activity to parabolic flight-induced gravitational change in conscious rats.

The renal sympathetic nerve activity (RNA) response to gravitational changes induced by parabolic flight was examined in chronically instrumented conscious rats. Two types of RNA responses were found. In six out of 12 rats, the RNA did not respond during the 2 G period, but immediately fell to background levels on entry into microgravity (microG), then recovered to the 1 G control level during continued microG (shutdown obvious group). In the other six rats, the RNA increased to 158+/-13% at the end of the 2 G period, increased further to 195+/-22% on entry into microG, then gradually recovered to that seen at 1 G (shutdown obscure group). The mean arterial pressure in the shutdown obvious group was significantly higher and the heart rate tended to be higher than in the shutdown obscure group, suggesting that the baseline sympathetic tone in the shutdown obvious group was higher than in the shutdown obscure group. These results suggest that the RNA response to parabolic flight might be affected by the baseline sympathetic tone.

Animals↗
PubMedDate not supplied

Plasma membrane NADH oxidase is gravi-responsive.

NADH oxidase activities measured with intact tissue sections and with isolated plasma membrane vesicles from etiolated hypocotyls of soybean (Glycine max) respond to gravity and imposed centrifugal forces. The response is one of inhibition of activity with tissue sections lying flat for 20 min or less at 1 x g and one of stimulation with times of lying flat of 30 min or longer at 1 x g. Turning the tissue sections upside down resulted in stimulation of the activity with a lag of about 30 min. Returning the sections to the normal upright position resulted in a return to initial rates with a lag of less than 20 min. Both the stimulated and non-stimulated activities oscillate with a period of 24 min, precluding a more precise analyses of lag times. The activity was stimulated reversibly to a maximum of about 2-fold both in tissue sections and in isolated plasma membrane vesicles when subjected to centrifugal forces of 10 to 400 x g for 0.5 to 4 min duration. The findings are the first description of a gravi-responsive enzymatic activity related to the growth response in plants.

Cell Membrane↗
PubMed2001

Plasma membrane NADH oxidase of maize roots responds to gravity and imposed centrifugal forces.

NADH oxidase activities measured with excised roots of dark-grown maize (Zea mays) seedlings and with isolated plasma membrane vesicles from roots of dark-grown maize oscillated with a regular period length of 24 min and were inhibited by the synthetic auxin 2,4-dichlorophenoxyacetic [correction of dichorophenoxyacetic] acid. The activities also responded to orientation with respect to gravity and to imposed centrifugal forces. Turning the roots upside down resulted in stimulation of the activity with a lag of about 10 min. Returning the sections to the normal upright position resulted in a return to initial rates. The activity was stimulated reversibly to a maximum of about 2-fold with isolated plasma membrane vesicles, when subjected to centrifugal forces of 25 to 250 x g for 1 to 4 min duration. These findings are the first report of a gravity-responsive enzymatic activity of plant roots inhibited by auxin and potentially related to the gravity-induced growth response.

2,4-Dichlorophenoxyacetic Acid↗
PubMed2003

Bdelloid rotifers as model system to study developmental biology in space.

Bdelloid rotifers are suitable model systems for space experiments. Due to their developmental pattern they appear adequate to investigate the role of the cytoskeleton during oogenesis and during early developmental stages, and to reflect the effects of disturbances in the spatial arrangement of cytoskeletal components. The effect of weightlessness on the developmental pattern of a bdelloid rotifer will be studied in the International Space Station: in preparation for it we are performing ground-based experiments on the development of rotifer embryos under either increased or decreased gravity. The model studied is Macrotrachela quadricornifera, a species of rotifers belonging to the Bdelloidea class. Samples exposed to gravity disturbance were analyzed for morphology and fitness-related parameters. Rotifers were exposed over several days to altered gravity conditions and the morphology of eggs laid during this period were investigated using a confocal laser microscope. A subset of eggs was allowed to hatch to determine newborn developmental time and age at maturity. High (up to 20 g) gravity was obtained in a slow centrifuge suitable for animal cultivation over several days. To produce low (simulated 0.0001 g) gravity a Random Positioning Machine equipped with a 'rotifer bioreactor' was used. Under all conditions the rotifer retained normal life-history traits, and did not show permanent changes in embryo morphology, regardless to the stresses to which it was exposed. Only some modification of the shape of early embryos, experiencing 20 g, has been noted, but later developmental stages appeared unaffected, and normal juveniles hatched. Whether this result indicates any capacity to repair damage during embryogenesis of these Spiralia experiencing 20 g is an open question. The significance of the result as well as the use of instruments to simulate gravity perturbations are discussed.

Animals↗
PubMed2006

Proteomic analysis of Saccharomyces cerevisiae under high gravity fermentation conditions.

Saccharomyces cerevisiae KAY446 was utilized for ethanol production, with glucose concentrations ranging from 120 g/L (normal) to 300 g/L (high). Although grown in a high glucose environment, S. cerevisiae still retained the ability to produce ethanol with a high degree of glucose utilization. iTRAQ-mediated shotgun proteomics was applied to identify relative expression change of proteins under the different glucose conditions. A total of 413 proteins were identified from three replicate, independent LC-MS/MS runs. Unsurprisingly, many proteins in the glycolysis/gluconeogenesis pathway showed significant changes in expression level. Twenty five proteins involved in amino acid metabolism decreased their expression, while the expressions of 12 heat-shock related proteins were also identified. Under high glucose conditions, ethanol was produced as a major product. However, the assimilation of glucose as well as a number of byproducts was also enhanced. Therefore, to optimize the ethanol production under very high gravity conditions, a number of pathways will need to be deactivated, while still maintaining the correct cellular redox or osmotic state. Proteomics is demonstrated here as a tool to aid in this forward metabolic engineering.

Ethanol↗
PubMed2003

Structure and function of the thymus during adaptation of rats to hypergravitation.

Five-day exposure to hypergravitation (2g) induced structural and functional changes in the thymus: intensification of cell destruction and inhibition of mitotic activity of lymphocytes in all functional components of the organ. This leads to a significant (2-fold) decrease in thymus weight, area of the thymus cortex on histological section, blurring of the corticomedullary interface because of lymphocyte depletion of the cortical matter. The size and number of thymic bodies decrease 3.4 times compared to the control. This indicates that by day 5 of continuous hypergravitation (2g) exposure the lymphoid tissue does not completely adapt to hypergravitation.

Animals↗
PubMed2003

Improvement of the ethanol productivity in a high gravity brewing at pilot plant scale.

A 23 full factorial design was used to study the influence of different experimental variables, namely wort gravity, fermentation temperature and nutrient supplementation, on ethanol productivity from high gravity wort fermentation by Saccharomyces cerevisiae (lager strain), under pilot plant conditions. The highest ethanol productivity (0.69 g l(-1) h(-1)) was obtained at 20 degrees P [degrees P is the weight of extract (sugar) equivalent to the weight of sucrose in a 100 g solution at 20 degrees C], 15 degrees C, with the addition of 0.8% (w/v) yeast extract, 24 mg l(-1) ergosterol and 0.24% (v/v) Tween 80.

Biomass↗
PubMed1999

Simulated weightlessness and hyper-g results in opposite effects on the regeneration of the cortical microtubule array in protoplasts from Brassica napus hypocotyls.

Enzymatic digestion of the cell wall of Brassica napus hypocotyls gave a heterogeneous suspension of protoplasts with the cortical microtubules (CMTs) randomly organised or CMTs organised in parallel. The effect of variable g-influences has been tested on CMT organisation. In contrast to the 1 g-protoplasts, which reorganised the CMTs into parallel arrays during the 96 h test period, the frequency of randomly-oriented CMTs in the protoplasts exposed to simulated weightlessness (0 g) on a 2-D clinostat increased significantly during the same period. The opposite effect was obtained when the protoplasts were exposed to hyper-g (7 or 10 g), where the reorganisation of the CMTs into parallel arrays was accelerated compared to the 1 and 0 g-protoplasts. These results indicate that a unidirectional gravity force is a necessity for the reorganisation of CMTs in protoplasts to parallel arrays and that CMTs act as responding elements that are able to sense different levels of gravity. Besides the inability of the protoplasts to reorganise the CMTs into parallel arrays, the quantity of CMTs in the individual protoplast decreased during 4 days of simulated weightlessness, both compared to the CMTs quantity in the protoplasts immediately after isolation and compared to the 1 g- and hyper-g-protoplasts after 24 and 48 h of g-exposure. The size of the protoplasts was also affected by the g-exposure. Protoplasts exposed to simulated 0 g increased significantly after 24 and 48 h, whereas the 1 g- and 10 g-protoplasts maintained the same size during the 48 h test period.

Brassica↗
PubMed2003

Hyper-gravity effects on the Arabidopsis transcriptome.

Callus cultures of Arabidopsis thaliana (cv. Columbia) in Petri dishes were exposed to altered g-forces by centrifugation (1-10 g). Using semi-quantitative RT-PCR transcripts of genes coding for metabolic key enzymes (ADP-glucose pyrophosphorylase, ADPG-PP; beta-amylase, fructose-1,6-bisphosphatase, FBPase; glyceraldehyde-P dehydrogenase, GAPDH; hydroxymethylglutaryl-CoA reductase, HMG; phenylalanine-ammonium-lyase, PAL; PEP carboxylase, PEPC) were used to monitor threshold conditions for g-number (all) and time of exposure (beta-amylase) which led to altered amounts of the gene product. Exposure to approximately 5 g and higher for 1 h resulted in altered transcript levels: transcripts of beta-amylase, PAL, and PEPC were increased, those of ADPG-PP decreased, while those of FBPase, GAPDH, and HMG were not affected. This probably indicates a shift from starch synthesis to starch degradation and increased rates of anaplerosis (PEPC: supply of ketoacids for amino acid synthesis). In order to get more information about g-related effects on gene expression, we used a 1-h exposure to 7 g for a microarray analysis, using a commercial A. thaliana chip with 4105 unique annotated clusters/genes (IncyteGenomics). Transcripts of more than 200 genes were significantly increased in amount (ratio 7 g/1 g control; 2(1.6) and larger). They fall into several categories. Transcripts coding for enzymes of major pathways form the largest group (25%), followed by gene products involved in cellular organization and cell wall formation/rearrangement (17%), signalling, phosphorylation/dephosphorylation (12%), proteolysis and transport (10% each), hormone synthesis plus related events (8%), defense (4%), stress-response (2%), and gravi-sensing (2%). Many of the alterations are part of a general stress response, but some changes related to the synthesis/rearrangement of cell wall components could be more hyper-g-specific. We only found few gene products, which were decreased in relation to 1 g controls, and these were less significant (ratio < 2(1.6)). We thus assume that g-forces above a threshold of about 5 g for 1 h are sensed by plant cells in general, causing distinct metabolic responses, which obviously in part, are regulated by gene expression.

Arabidopsis↗