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PubMedDate not supplied

Chronic exposure to hypergravity affects thyrotropin-releasing hormone levels in rat brainstem and cerebellum.

In studies to determine the neurochemical mechanisms underlying adaptation to altered gravity we have investigated changes in neuropeptide levels in brainstem, cerebellum, hypothalamus, striatum, hippocampus, and cerebral cortex by radioimmunoassay. Fourteen days of hypergravity (hyperG) exposure resulted in significant increases in thyrotropin-releasing hormone (TRH) content of brainstem and cerebellum, but no changes in levels of other neuropeptides (beta-endorphin, cholecystokinin, met-enkephalin, somatostatin, and substance P) examined in these areas were found, nor were TRH levels significantly changed in any other brain regions investigated. The increase in TRH in brainstem and cerebellum was not seen in animals exposed only to the rotational component of centrifugation, suggesting that this increase was elicited by the alteration in the gravitational environment. The only other neuropeptide affected by chronic hyperG exposure was met-enkephalin, which was significantly decreased in the cerebral cortex. However, this alteration in met-enkephalin was found in both hyperG and rotation control animals and thus may be due to the rotational rather than the hyperG component of centrifugation. Thus it does not appear as if there is a generalized neuropeptide response to chronic hyperG following 2 weeks of exposure. Rather, there is an increase only of TRH and that occurs only in areas of the brain known to be heavily involved with vestibular inputs and motor control (both voluntary and autonomic). These results suggest that TRH may play a role in adaptation to altered gravity as it does in adaptation to altered vestibular input following labyrinthectomy, and in cerebellar and vestibular control of locomotion, as seen in studies of ataxia.

Adaptation, Physiological↗
PubMed2002

Gravity related research with fishes--perspectives in regard to the upcoming International Space Station, ISS.

During the entire evolution of life on Earth, the development of all organisms took place under constant gravity conditions, against which they achieved specific countermeasures for compensation and adaptation. On this background, it is still an open question to which extent altered gravity such as hypergravity (centrifuge) or microgravity (spaceflight) affects the normal individual development, either on the systemic level of the whole organism or on the level of individual organs or even single cells. The present review provides information on these questions, comprising gravistimulated effects on invertebrates and vertebrates (with the exception of mammals, since respective biomedically oriented reviews abound), focusing on developing fish as model systems, with special emphasis on the effect of altered gravity on the developing brain and vestibular system, comprising investigations on behaviour and plastic reactivities of the brain and inner ear. Clues and insights into the possible basic causes of space motion sickness-phenomena (SMS; a kinetosis) are provided as well as perspectives in regard to future work to be done including studies on the ISS concerning the analysis of gravistimulated effects on developmental issues (imprinting phase for graviperception?).

Adaptation, Physiological↗
PubMed2006

Cleavage and survival of Xenopus embryos exposed to 8 T static magnetic fields in a rotating clinostat.

In this study, we examined cleavage and survival of fertilized Xenopus embryos exposed to 8 T static magnetic fields (SMFs). We investigated fertilized Xenopus embryos exposed to magnetic field either in static chamber or in a rotating culture system. Our results showed that the exposure to the strong magnetic field of 8 T changed the third cleavage furrow from the usual horizontal one to a perpendicular one; however, when the direction of gravity was randomized by exposing embryos to magnetic field in a rotating culture system, the third cleavage furrow were formed horizontally, a finding which suggests that the observed distortion of the third cleavage furrow in magnetism-exposed embryos was accomplished by altering gravity effects which were elicited by diamagnetic force due to high gradient magnetic field. Our results also showed that the exposure to the strong magnetic field did not damage survival. These results demonstrate that SMF and altering gravity cause distortion of the third cleavage furrow and show that effects of exposing cleavage embryos to magnetic field were transient and did not affect the post-cleavage development. We also showed that strong magnetic field is not hazardous to the cleavage and blastula-gastrula transition of developing embryonic cells.

Animals↗
PubMed2004

Association between gravitational force and tissue metabolism in periparturient rats.

Recently, interest in mammalian reproduction and offspring survival in altered gravity has been growing. Because successful lactation is critical for mammalian neonate survival, we have been studying the effect of gravity metabolism. We have shown an exponential relationship between glucose metabolic rate in mammary tissue of periparturient rats and an increase in gravity load. In this study we showed that changes in mammary metabolic rate due to gravity force were accompanied by a decrease in glucose metabolism in adipose tissue and by a reduced size of adipocytes. We assume that these changes are likely due to changes in prolactin or leptin levels related to altered gravity load.

Adipocytes↗
PubMed1994

Parabolic flight experiments on physiological data acquisition and processing technologies using small jet aircraft (MU300).

The parabolic aircraft flight provides a short low gravity environment for approximately 20 seconds, which may not be sufficient for a research on the physiological phenomenon induced by actual weightlessness in space. However, the method is still useful to reveal essential and characteristic feature of physiological signs, and is available for testing hardware and also training of crew member during altered gravity. This paper reports the summary of parabolic flight experiments recently conducted as a NASDA program (1990-1992). The program is providing opportunities in low gravity research with small jet aircraft for researchers and agencies. The flight experiments in the life science area have been conducted mostly focused on a physiological changes and basic methodology which may be effective under the altered gravity condition. In this study, the following research team, NASDA, Research Institute of Environmental Medicine, Nagoya University, Toyohashi University of Technology, Tokyo Metropolitan Hospital, Torey Research Center and JSUP were involved and coordinated for the research.

Aircraft↗
PubMed1995

Calcium balance changes in tip growing plant cells under clinorotation.

Calcium is known to play an important role in the regulation of cellular processes as a secondary messenger in signal transduction to a specific response in all eucaryotic cells. Its messenger role is realized by transient changes in the Ca2+ cytosolic concentration induced by variety of external stimuli such as light, hormones and gravity. Recent findings claim the modifications in a calcium balance in plant cells in microgravity and under clinorotation reproducing partially the microgravity effect. Based on these data, the hypothesis is proposed that Ca2+ level changes can trigger the rearrangements in cell metabolism occurring in the conditions of altered gravity. However, the methods used in previous works permit only to determine the relative quantity of intracellular membrane-bound calcium and to observe the localization of free Ca2+. Therefore, it is of essential interest to measure the concentration of free calcium ions ([Ca2+]i) in plant cells under the influence of altered gravity. In this paper results from measurements of the [Ca2+]i in plant cells under clinorotation will be reviewed and discussed in an effort to examine their effectiveness, causes and consequences.

Calcium↗
PubMedDate not supplied

[Modeling of human movements under conditions of varying gravitational force].

The control of man's movements during adaptation to an altered gravity field was modelled by mathematical methods. Two types of movements were investigated: forearm displacements with various loads and repulsions from a support in zero-g and at high g's. It has been shown that movement coordination in altered gravity fields can be maintained due to a rearrangement of the control over muscle contraction which includes changes in the amplitude and pattern of joint momenta in harmony with the gravity changes.

Gravitation↗
PubMedDate not supplied

[The general principles of cellular gravisensing].

A review of the results of studies over many years into cellular mechanisms underlying gravireception in different cell types, which were carried out by the author in the laboratory during simulation of the effects of altered gravity using a clinostat and centrifuge and under the conditions of space flight. Comparative analyses of the obtained results with the published data has been performed. It was shown that besides specific features of adaptation of different cell types to altered gravity, including microgravity, there are common pathways of adaptation of the structural-functional organization of the cell to this factor. An integral molecular mechanism underlying cell gravisensing was revealed. A working hypothesis on general principles of cell gravisensing has been formulated.

Animals↗
PubMed2003

Effects of acute and repeated daily exposure to hypergravity on spatial learning in mice.

Studies in humans have revealed that exposure to altered gravity may lead to impairments in cognitive functions. The objective of this study was to test whether mice exposed to hypergravity using a centrifuge apparatus showed learning impairments in a spatial learning task. Mice rotating at 1G or at 2G acceleration gravity and non-rotating controls were tested for reactivity to a spatial change after either a single 1 h or five repeated 1 h daily rotations in the centrifuge. While no differences among groups were found in the performance after single exposure to altered gravity, 5 days of repeated exposures to 1G or 2G gravity conditions significantly affected mouse ability to discriminate a new spatial arrangement. Additionally, this effect was stronger in the animals repeatedly exposed to 2G rather than to 1G conditions.

Animals↗
PubMed2003

Cranial diameter pulsations measured by non-invasive ultrasound decrease with tilt.

INTRODUCTION: Intracranial pressure (ICP) may play a significant role in physiological responses to microgravity by contributing to the nausea associated with microgravity exposure. However, effects of altered gravity on ICP in astronauts have not been investigated, primarily due to the invasiveness of currently available techniques. We have developed an ultrasonic device that monitors changes in cranial diameter pulsation non-invasively so that we can evaluate ICP dynamics in astronauts during spaceflight. This study was designed to demonstrate the feasibility of our ultrasound technique under the physiological condition in which ICP dynamics are changed due to altered gravitational force. METHODS: Six healthy volunteers were placed at 60 degrees head-up, 30 degrees headup, supine, and 15 degrees head-down positions for 3 min at each angle. We measured arterial blood pressure (ABP) with a finger pressure cuff, and cranial diameter pulsation with a pulsed phase lock loop device (PPLL). RESULTS: Analysis of covariance demonstrated that amplitudes of cranial diameter pulsations were significantly altered with the angle of tilt (p < 0.001). The 95% confidence interval for linear regression coefficients of the cranial diameter pulsation amplitudes with tilt angle was 0.862 to 0.968. However, ABP amplitudes did not show this relationship. DISCUSSION: Our noninvasive ultrasonic technique reveals that the amplitude of cranial diameter pulsation decreases as a function of tilt angle, suggesting that ICP pulsation follows the same relationship. It is demonstrated that the PPLL device has a sufficient sensitivity to detect changes non-invasively in ICP pulsation caused by altered gravity.

Adult↗
PubMed2000

A model for studying the baroreflex in microgravity and hypergravity.

The study on development in altered gravity has been investigated in a wide range of animal species from a molecular level or cell culture to mammalian bodies. However development of the baroreflex has been studied in limited mammalian species even on the ground except the turtle to study diving reflex. The rat or mouse has been selectively used for studying the relationship between development of various functions and gravity especially microgravity, because of the limited body size for the loading space on the space ship, an experimental-animal most often used, and other biological characteristics. We have used the rat and rabbit for investigating the effect of microgravity on the development of the aortic baroflex. In the present paper a few results of our experiments using the rat will be shown and the appropriateness of the rat as a model system for studying the baroflex development in altered gravity will be discussed.

Age Factors↗
PubMed2003

Models of the mechanical sensitivity and growth of otoliths in fish.

It has been suggested that, in the fish, the change of otolith mass during development under altered gravity conditions and the growth of otoliths in normal conditions, are determined by feedback between otolith dynamics and the processes that regulate otolith growth. The hypothesis originates from an oscillator model of the otolith in which otolith mass is one of the parameters. However, the validity of this hypothesis is not obvious and has not been experimentally verified. We tested this hypothesis by comparing the oscillator model with a simplified spatially distributed model of the otolith. It was shown that in the case of a spatially distributed fixation of the otolith plate (otoconial layer) to the macular surface, the mechanical sensitivity of the otolith does not depend on the total otolith mass nor on its longitudinal size. It is determined by otolith thickness, the Young's modulus and viscosity of gel layer of the growing otolith. These parameters may change in order to maintain otolith sensitivity under conditions (such as growth or altered gravity) that change the dynamics of otolith movement.

Aging↗
PubMed1993

[Changes in the utricular otoconia of the chick embryo developed under 2G-gravity].

Whether or not vestibular adaptation occurs upon exposure to altered gravity is an important human problem. Studies have been performed to ascertain whether morphological changes in vestibular organs occur in animal models upon exposure to microgravity. On the other hand, the morphological changes which occur in vestibular organs under hypergravity have not yet been fully elucidated and morphological changes in the otoconia of the chick embryo exposed to hypergravity during the embryonic period remain to be thoroughly examined. The purpose of this paper is to clarify the effects of hypergravity on vestibular organs, especially its effects on otoconial formation in the developing chick embryo. Thus, we designed an apparatus which creates artificial gravity, creating approximately 2G gravity by means of centrifugation. The utricular macula was chosen for study because it can be prepared for examination with a minimum of dissection artifacts. The data presented show that morphological changes were confined to otoconial size alterations according to scanning electron microscopic observations. Giant otoconia were observed along the marginal zones of utricle .

Animals↗
PubMed1994

Teratogenic effects of gravitational changes.

In investigating the effect of gravitational changes on development, it is instructive to think of altered gravity (delta g) as a teratogen--that is, an environmental factor influencing development. Observed effects on skeletal development include: suppression of morphogenesis in centrifuged mouse limb buds; advanced fusion stages in centrifuged mouse palates; smaller crown rump lengths (CRL) and decreased number of pregnancies in centrifuged rats and mice; altered differentiation of growth plates in young growing rats in space; and decreased length of calcified long bone regions in fetal rats exposed to microgravity in utero. These studies show that delta g is able to alter development in vivo and in vitro and suggest that delta g operates, at least in part, at the cellular level.

Animals↗
PubMed1999

Culture in vector-averaged gravity environment in a clinostat results in detachment of osteoblastic ROS 17/2.8 cells.

Studies carried out in space flights and in altered gravitational environments have shown that exposure to altered gravity conditions results in alterations in cellular structure and function. In the present study, we used a clinostat to generate a vector-averaged gravity environment, and evaluated the responses of osteoblast-like ROS 17/2.8 cells subsequent to rotation at 50 r.p.m from 24 to 72 hr. We found that the cells started to detach during the first 24 hr of culture in clinostat, but not in stationary and horizontal rotation (the latter serving as a control for turbulence, shear forces and vibrations). At 24 hr, there was a significant decrease in the number of adherent cells under clino-rotation (2.75 +/- 0.5 x 10(5) in stationary culture versus 2.02 +/- 0.27 x 10(5) under clino-rotation), and 19.8% of adherent cells were trypan-blue positive when cultured in 2% fetal bovine serum. All the detached cells were trypan-blue positive. At 72 hr, the cells became confluent in all three groups. These results suggest that vector-averaged gravity could cause the death of osteoblasts during the first 24 hr of clino-rotation. We hypothesize that this cell death might play a role in the pathogenesis of osteoporotic bone loss as observed in actual space flight.

Animals↗
PubMed2003

Mass and mechanical sensitivity of otoliths.

It has been suggested that the changes of otolith mass during the otolith development in altered gravity conditions as well as the growth of otoliths in fishes in normal conditions are determined by the feedback between the otolith dynamics and the processes that regulate otolith growth. This hypothesis originates from the pendulum model of an otolith (de Vries, 1950), in which otolith mass is a parameters. The validity of this hypothesis is tested by comparing the pendulum model with a simplified spatially distributed model of an otolith. It was shown that when the otolith plate (otoconial layer) was spatially distributed and fixed to the macular surface, the mechanical sensitivity of the otolith does not depend on the total otolith mass and its longitudinal dimensions. It is determined by otolith thickness, Young's modulus, and the viscosity of the gel layer of the growing otolith. These parameters may change in order to secure otolith sensitivity under altered dynamic conditions (e.g., in microgravity). Possible hypotheses regarding the relationship between the otolith growth, otolith dynamics and animal growth are proposed and discussed here.

Acceleration↗
PubMed1979

Gravity as a biochemical determinant.

The existence of obvious morphological and physiological changes in living systems exposed to altered gravity immediately informs us that prior changes have taken place in the chemistry of exposed cells, tissues and organs. These changes include transients that return more or less promptly to the norm when the system is restored to the terrestrial g-field. For example, altered serum hormone and electrolyte levels in man, which appear to reflect successful adaptation to the conditions of orbital weightlessness, disappear shortly after return to Earth. Other changes--in mineral and protein constituents of the skeletal system in man, and cell wall composition in plants--are more persistent or even permanent. Hypogravitational departures from the norm include not only "weightlessness" as achieved in orbit, but also experimental modes of compensation, on the clinostat or by flotation. These techniques are useful in the study of hypogravity but cannot replace fully the weightless environment. Plant ethylene and peroxidase both increase under orbital, clinostat and/or flotation conditions whereas 3-phosphoglyceraldehyde-dehydrogenase increases under orbital but not clinostat conditions; cytochrome reductase and malic dehydrogenase levels are affected by the clinostat, but not by actual weightless conditions. How do the altered organismal biochemistries induced by the centrifuge and the clinostat relate to one another? Does gravity operate on living systems as a continuous variable from 0 to superterrestrial values, or do deviations from g(earth) generate non-uniform, discontinuous stress responses, irrespective of sign? In plants, measurements of wall lignin content and peroxidase activity yield opposite answers. Given the limited data so far available we will consider the meaning of these contradictions.

Adaptation, Physiological↗