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PubMed2001

[Gravitational biology of integrative organisms and ecological system--the road map of space activities].

History of the International Space Station, ISS, and planning of its scientific use are described in this essay. Fundamental gravitational biology and its facility on the ISS have been identified to have the highest priority to conduct scientific experiments with variable G environment in orbit. The road map of space activities is clearly directing the efforts toward manned Mars exploration. The Centrifuge is a core element of the facilities dedicated to this endeavor. Several research subjects are discussed with the results obtained from the past space experiments. Direct effects of gravity on the biological system at the level of integrative organisms are major subjects of study that will be conducted on the large scaled centrifuge.

Biological Science Disciplines↗
PubMed2004

[Biology of size and gravity].

Gravity is a force that acts on mass. Biological effects of gravity and their magnitude depend on scale of mass and difference in density. One significant contribution of space biology is confirmation of direct action of gravity even at the cellular level. Since cell is the elementary unit of life, existence of primary effects of gravity on cells leads to establish the firm basis of gravitational biology. However, gravity is not limited to produce its biological effects on molecules and their reaction networks that compose living cells. Biological system has hierarchical structure with layers of organism, group, and ecological system, which emerge from the system one layer down. Influence of gravity is higher at larger mass. In addition to this, actions of gravity in each layer are caused by process and mechanism that is subjected and different in each layer of the hierarchy. Because of this feature, summing up gravitational action on cells does not explain gravity for biological system at upper layers. Gravity at ecological system or organismal level can not reduced to cellular mechanism. Size of cells and organisms is one of fundamental characters of them and a determinant in their design of form and function. Size closely relates to other physical quantities, such as mass, volume, and surface area. Gravity produces weight of mass. Organisms are required to equip components to support weight and to resist against force that arise at movement of body or a part of it. Volume and surface area associate with mass and heat transport process at body. Gravity dominates those processes by inducing natural convection around organisms. This review covers various elements and process, with which gravity make influence on living systems, chosen on the basis of biology of size. Cells and biochemical networks are under the control of organism to integrate a consolidated form. How cells adjust metabolic rate to meet to the size of the composed organism, whether is gravity responsible for this feature, are subject we discuss in this article. Three major topics in gravitational and space biology are; how living systems have been adapted to terrestrial gravity and evolved, how living systems respond to exotic gravitational environment, and whether living systems could respond and adapt to microgravity. Biology of size can contribute to find a way to answer these question, and answer why gravity is important in biology, at explaining why gravity has been a dominant factor through the evolutional history on the earth.

Adaptation, Physiological↗
PubMed1995

Optokinetic after-nystagmus under prolonged alteration in the direction of gravity.

Optokinetic nystagmus (OKN) and after-nystagmus (OKAN) show different responses depending on the direction of gravity with respect to the head and body. In 13 normal healthy persons (10 experimental and 3 control subjects), we studied the OKAN evoked by horizontal and vertical stimuli, in upright, side-lateral, and repeated upright positions along a time course of more than 6 h. The results showed continuous modifications of OKAN, the degree increasing with time. Lateral tilt produced different effects on the intrinsic vertical and horizontal optokinetic oculomotor systems.

Adolescent↗
PubMed1998

[Optokinetic nystagmus under prolonged alteration in the direction of gravity].

Optokinetic Nystagmus (OKN) exhibit different responses depending on the direction of gravity, with respect to head and body. In 13 normal healthy volunteers (10 experimental subjects and 3 controls), we studied the OKN evoked by horizontal and vertical stimuli, in upright, side-lateral, and repeated upright positions during a long time course of six test stages. Stage 1 was an upright sitting position. Stage 2 was a 90-degree recumbent lateral position immediately after Stage 1. Stage 3 was the same position as in Stage 2, but 2h later. Stage 4 was the same position, another 2h later (total of 4h). Stage 5 was a return to the upright position (the same as Stage 1) immediately after Stage 4. Stage 6 was a return to the same upright position, 2h after Stage 5. The results showed continuous modifications of OKN. A lateral tilt produced different effects on the horizontal and vertical optokinetic oculomotor systems. The gain in horizontal OKN (HOKN) decreased during Stages 2-4 with time, and returned to normal in Stages 5 and 6. As for vertical OKN (VOKN), the gain of upward (the direction by slow phase) OKN increased during Stages 2-4, and returned to normal in Stages 5 and 6. But the gain of downward OKN did not show any clear modulation. We showed that the change in gravity direction has a clear effect on OKN, and that it takes some time to reach the maximal and desirable level of modification. The difference in time-dependent modifications between HOKN and VOKN should be due to the difference in OKN-producing mechanisms and velocity storage systems.

Adolescent↗
PubMed2000

[Ocular counter-rolling after prolonged alteration in the direction of gravity].

To investigate the dynamics of otolith and oculomotor function, we subjected volunteers to a lateral body tilt for a period of two hours and analyzed ocular counter-rolling. Six healthy adult volunteers were roll-tilted along the naso-occipital axis at a speed of 0 degree/sec. from the 0 degree earth vertical position to the 90 degrees lateral tilt position. After two hours, the volunteers were returned to the 0 degree earth vertical position. Ocular counter-rolling was recorded using an infrared CCD camera. The video recordings were made in the dark while the volunteers had their eyes open. Recordings were obtained (1) as the volunteers was moved from the 0 degree earth vertical position to the 90 degrees lateral position, (2) 5 minutes after reaching the lateral position, (3) during the roll-back from the 90 degrees lateral position to the 0 degree upright position, two hours after the lateral tilt loading, and (4) 5 minutes after reaching the final upright position. The occurrence of ocular counter-rolling between the 0 degree upright position and the 30 degrees tilt position was confirmed during both roll movements from 0 degree to 90 degrees and from 90 degrees to 0 degree. The counter-rolling was most noticeable between the 0 degree and the 30 degrees positions. No differences in ocular counter-rolling during the roll-tilt and the roll-back situations were observed. These results indicate that the two-hour lateral tilt position did not produce any functional changes in the hair cells and/or the otolith-oculomotor system. All of the subjects exhibited ocular counter-counter-rolling during the initial stage of their roll-back to a normal upright position. This phenomenon might result from the additional bending of the hairs by inertia during the initiation of the backward roll motion.

Adult↗
PubMed1999

[The effect of overloading from intensive maneuvering on the function of the peripheral chromatic field of vision].

Data on the peripheral chromatic field of vision (PCFV) in pilots after centrifugation and missions with intensive maneuvering associated with accelerations (+Gz) higher than 6 g are presented. Depression of the PCFV area due to hypergravity was most expressed in the shortwave section of the visible spectrum and closely linked with the state of cranial hemodynamics. Changes in PCFV persisted for quite long period, i.e. initial values did not regain following 40 min since exposure to accelerations. Correlation between the degree of PCFV changes and pilot's tolerance to accelerations was established. According to the factual data analysis, the PCFV technique can be used to evaluate the dynamics of G-tolerance during intensive maneuvering aircraft.

Acceleration↗
PubMed1998

Cortical bone responses to 2G hypergravity in growing rats.

BACKGROUND: Rat cortical bone adaptation to chronic hypergravity (2G) was studied using young growing male Wistar rats (60 d). METHODS: Animals (10 rats) were subjected to chronic hypergravity (14 d) in order to understand the plastic nature of bone under a constant hypergravity stress using a special rodent habitat that was attached to a 12-ft. radius centrifuge. Also, an equal number of stationary controls were housed in a rodent vivarium containing identical cages that were used for centrifugation. After 14 d of centrifugation, femur bones were excised and prepared for morphological and biochemical measurements. RESULTS: Results showed that 2G had significantly shortened the femurs (3%) and reduced the cortical bone area (13%). In particular, hypergravity induced significant reductions in the thicknesses of cortical bone at the anterior (13%) and medial regions (15%) of the mid-diaphysis. However, femoral bone density, collagen and calcium concentrations were unaltered. The content of mature, stable bone collagen cross-links hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), were significantly greater in bones from centrifuged animals. CONCLUSION: Our findings suggest that short term exposure to 2G does not enhance bone formation or induce changes in cortical bone composition, or alter specific gravity. These data also suggest that bone maturation as reflected by collagen cross-linking is upregulated. However, it is undetermined at this time whether the enhanced content of mature bone collagen in the centrifuged rats is a result of either an increased rate of cross-linking or reduction in the degradation of "older collagen."

Adaptation, Physiological↗
PubMedDate not supplied

[Ultrastructure of the neuromuscular junctions in the rat soleus muscle under varying gravity conditions].

Changes in the ultrastructure of neuromuscular junctions have been considered as an index to adaptation of Wistar rats (whose pre- and postnatal ontogenesis proceeded on a centrifuge under constant rotation until the age of two months) to the hypergravity conditions (2G) and, then, to earth gravity (1G): on the 2nd and 15th days after centrifuge stoppage. The dynamic of synaptic vesicles was shown: their number increased at 2G and gradually decreased at 1G. Local damage of muscle fibers, partial separation of the motor axonal terminal from intrafusal fiber, and membrane twisting were noted at the increased gravity-dependent static load (2G). Neuromuscular junctions with signs of remodeling occurred more frequently in the experimental rats than in the control ones. It was proposed that adaptation of rats to 1G gravity after a prolonged sojourn under the hypergravity conditions (2G) was not completed within the studied period.

Animals↗
PubMedDate not supplied

[Brain ischemia induced by gravitational overload].

It is suggested that radial gravitational overloads in craniocaudal direction, during which the pressure in meningeal arteries drops to zero, can be used to model the ischemic state. The post-ischemic period is characterized by increasing content of lipid peroxidation products in the venous blood and by violation of the neurological state in rats. This ischemia model, requiring no anaesthesia for the experimental animals, can be used in the directed search for new neuroprotectors and their characterization.

Animals↗
PubMed2000

German acceleration research from the very beginning.

German airmen were experiencing G-induced physiological effects as early as WWI, although no research on acceleration physiology was conducted at that time in Germany. This changed in 1931 with the studies of Heinz von Diringshofen, who gained experience with prolonged acceleration in flight. The first German centrifuge was constructed by the von Diringshofen brothers and was in operation at the Air Ministry's Aeromedical Research Institute in Berlin from 1935-1945. After WWII, Otto Gauer and Heinz Haher authored the paper "Man under Gravity-Free Conditions," paving the way to manned space exploration and demonstrating the change of research interest from the effects of multiple G forces to those of zero G.

Acceleration↗
PubMed1992

Centrifuges: their development and use in gravitational biology.

The nature of centrifuges and their use in biological research are reviewed historically. Centrifuges are particularly important to research in gravitational biology because the inertial (centrifugal) forces developed by motion can be combined with gravitation to produce gravitational fields other than Earth gravity. In orbiting satellites centrifuges can provide an on-board 1 g environment. A similarity of results from the orbiting and ground-based 1 g controls will provide an essential assurance that the biological responses to the spacecraft environment are the result of changes in the gravitational field. The relationship of biological responses to gravitational fields greater or less than Earth gravity is considered. However, at present there is insufficient equivalent information to decide whether there is or is not a proportionality of response to fields stronger or weaker than Earth gravity.

Acceleration↗
PubMed1993

The cardiovascular response to the AGS.

An instrument, the AGS (artificial gravity simulator), has been built to produce artificial gravity. This paper reports preliminary results of experiments on human subjects conducted to study the cardiovascular response to various g-levels and exposure times.

Cardiovascular Deconditioning↗