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At least 523 records · Page 29Linked to original sources
PubMed1999

Importance of somatosensory input for spatial orientation in supine subjects: evaluated by pointing arm movements during linear acceleration.

Goal-directed movements are secured by sensory interactions among visual, vestibular and somatosensory information. Reliable inputs from the visual system have been known, and the contribution of otolithic information demonstrated most clearly by evidence that target-pointing arm movements shifted downward in astronauts with eyes closed under space microgravity (Watt 1997), whereas the direction of shift was the opposite in subjects under centrifuge hypergravity (Bock et al. 1996). Somatosensory contribution has been also supported by many reports. In the present study, we attempted to evaluate the otolithic contribution to spatial orientation by arm-pointing deviation in supine subjects exposed to Z-axis linear acceleration in darkness.

Acceleration↗
PubMed1999

Lipid peroxidation and polyamine metabolism in K562 cells subjected to altered gravity.

The mechanisms underlying cell sensitivity to the gravistimulus are still largely unknown. Recently, the oxidation of membrane lipids and the alteration of polyamine content have been shown to be involved in several cellular processes, from cell growth and differentiation, to aging and resistance to (a)biotic stress. Such an involvement was mediated by the modification of the activity and expression of lipoxygenase (LOX; E.C. 1.13.11.12) and diamine oxidase (DAO; E.C. 1.4.3.6), the enzymes which control membrane properties (LOX) and the catabolism of polyamines (DAO), respectively. In this study, the possible effects of altered gravity on membrane lipid peroxidation and polyamine metabolism were investigated, by subjecting human erythroleukemia K562 cell cultures to simulated hypogravity (by clinorotation) or hypergravity (by centrifugation).

Amine Oxidase (Copper-Containing)↗
PubMed1999

Influence of changes in gravity on the response of lung and vascular cells to ischemia/reperfusion in vitro.

Gravity and other physical forces (e.g., shear stress or mechanical stretch) will affect organ and cellular function, e.g., blood flow distribution, gas exchange, alveolar size and mechanical stresses within the lung. Microgravity produced marked alterations in lung blood flow and ventilation distribution while hypergravity exaggerated the regional differences in lung structure and function. Microgravity was found to decrease the metabolic activity in cardiac cells, WI-38 embryonic lung cells, and human lymphocytes. These studies show that changes in gravity will affect several aspects of organ and cellular function and produce major changes in blood flow and tissue/organ perfusion. However, these past studies have not addressed whether ischemia-reperfusion injury will be exacerbated or, ameliorated by changes in the gravity environment, e.g., space flight. Currently, nothing is known about how gravity will affect the susceptibility of different lung and vascular cells to this type of injury. Ischemia injury is the underlying cause of many clinical disorders with high morbidity and mortality. The subsequent reperfusion (reoxygenation) further compounds the initial ischemic stress. Understanding the possible exacerbation of transient ischemia under the stress of space flight or an increase in gravity is critical. We conducted studies that examined whether alterations in gravity affect the susceptibility of cells to ischemia-reperfusion injury, using an in vitro anoxia-reoxygenation model.

Animals↗
PubMed1999

Effects of hyper +Gz acceleration on brainstem and auditory cortical evoked potentials and cerebral blood flow in anesthetized rats.

Hypergravity acceleration along the long axis of the body (Gz) causes severe cardiovascular dysfunctions. Many studies have been conducted along this line. However, most previous studies used rather a short duration of hyper-Gz application, up to 30 sec, because application of large hyper-Gz brings animals into death. In order to elucidate effects of long duration of Gz application, we made experiments with Gz load for as long as 1000 sec. Cardiovascular dysfunctions and reduction of arterial blood pressure were usually accompanied by reduction of cerebral blood flow, leading subjects into loss of consciousness and into death. Recently, we studied the effects of +Gz load on evoked potentials. The present experiments shows effects of +Gz on brainstem auditory response and auditory evoked potentials.

Acceleration↗
PubMed1999

Evaluation of cerebral stresses under acceleration taking into account the lateral ventricles.

In certain flight configurations, fighter pilots are exposed to high Gz acceleration that may induce inflight loss of consciousness (LOC). That LOC is usually preceded by visual prodromes as greyout and blackout. The pathophysiological cause of these phenomena is used to be related to the effects of accelerations on the vascular system (Burton, 1988; Whinnery, 1990). However technological advances have created aircraft generating high accelerations with rapid onset rates (1-6 Gs-1). The symptomatology of inflight LOC has changed and prodromes no longer appear. Pilots also reported a lacunar amnesia of the LOC. In order to evaluate the potentially adverse effect of acceleration on the brain tissue, it was important to study its mechanical behavior under hypergravity. An approximation of the cerebral stresses was obtained by coupling an 'ex vivo' experiment (Guillaume et al., 1997) with a numerical simulation. Firstly, the calculations have been realized considering the brain as homogeneous. Secondly, the cerebral ventricles have been individualized. The results of these two approaches were compared.

Acceleration↗
PubMed2001

Ground simulation of the G-excess illusion.

Objective. To observe the subjects' perception of orientation following certain head movements or change of simulator cab attitude in hypergravity (HG), and assess the feasibility of simulating G-excess illusion on the ground by a centrifuge-like Spatial Disorientation (SD) simulator. Method. 1.6 G force field was generated by planetary rotation of the simulator. Perception of orientation of the cab were collected from twelve male pilots' report following their heads pitch movements in pitch plane or cab attitude changes in roll plane under 1.6 G. Result. While making a pitch-up head movement, the pilots experienced a 63.8 degrees +/- 48.3 degrees pitch-up attitude change of the cab in pitch plane, and when the cab was tilted left 20 degrees, pilots experienced a tilt-left perception of 48.6 degrees +/- 39.4 degrees in roll plane. Conclusion. Although there's strong Coriolis effects onboard the SD simulator under 1.6 G, most pilots experienced the G-excess illusion. It demonstrated that it was feasible to use the centrifuge-like device to generate this kind of illusion on the ground.

Adult↗
PubMed1977

Food and oxygen requirements for growing mice and turtles after hypergravitational development.

Although development of mice and turtles, both low-payload animals, can be influenced by ambient gravitational intensity, little is known regarding the influence of either their growth or their gravitational history upon life-support requirements. A 25-g male Box Turtle (Terrapene carolina, optimally growing at 30 degrees C and 1 G to double its size in 7 weeks) exhibits daily requirements of oxygen (100 ml) and food (200 mg, dry) which are only 3% of the requirement for a mouse (Swiss Webster, centrifuged at 22 degrees) of comparable size and growth rate. These requirements grow in proportion to the turtle's (body mass)0.9 and to the mouse's (body mass)0.5. After development at hypergravity g (of from 1.5 to 5 G expressed in multiples of the earth's gravity) there is a one-day delay for turtles but an immediate change for mice in these requirements upon return to 1 G. Although both show a decreased oxygen intake, the drop is greater for turtles (equalling g -0.4 of the baseline value, as corrected for body size, after return from 75 days exposure against g-0.08 for mice after 1-13 days exposure); the food intake drops for turtles (varies as g-1) while it rises for mice (varies as g0.6).

Animals↗
PubMed1977

Chronic acceleration in plants.

Since this subject was last reviewed (at the Symposium on Gravity and the Organism, 1967), relatively little new work on hypergravity effects on plants has appeared. Centrifugation has been used widely for separation of cellular components, but only occasionally as a primary environmental condition. With increasing magnitude of accelerative forces, the following effects have been reported by a number of authors working with many different plants. In the range 2-25 g, auxin transport and geotropic response in coleoptiles are increased and growth is stimulated. From 25 to 500 g, coleoptile growth is reduced and some morphological changes may be seen. At 1000-2500 g, root formation in willow cuttings increases. From 1000 g upward, cytoplasmic stratification occurs and seed germination decreases. Between 200 and 15000 g, chromosome damage has been observed. Algal cell polarity may be reversed at 5000 to 20000 g. Above 30000 g, the response of some cells to gibberellic acid is halted. Permanent morphologic changes in Escherichia coli are produced at 110000 g. Some plant cells have survived 176000 g for 20 hr.

Acceleration↗
PubMed2002

Fiber size, type, and myosin heavy chain content in rhesus hindlimb muscles after 2 weeks at 2 G.

BACKGROUND: Fiber atrophy and an increase in the percentage of fast fibers have been observed in Rhesus leg muscles after spaceflight. HYPOTHESIS: Hypergravity will result in muscle fiber hypertrophy and an increase in the percentage of slow fibers. METHODS: Open muscle biopsies were obtained from Rhesus soleus, medial gastrocnemius (MG), and tibialis anterior (TA) muscles before and after 14 d of centrifugation (2 G) and in time-matched controls. Cage activity levels were measured by telemetry. RESULTS: Based on monoclonal antibody binding for myosin heavy chains (MHC), the fastest region of soleus contained a higher proportion of type I+II (27 vs. 13%) and had a tendency for a lower proportion of type I (38 vs. 61%, p = 0.10) fibers after than before centrifugation. There was a higher proportion of type I+II fibers in post- vs. pre-2 G (10 vs. 0.6%) MG biopsies. Fiber type distribution and MHC composition were unaffected in the TA. Overall, mean fiber sizes were unaffected by centrifugation. Average cage activity levels were 36% lower during than before 2 G. CONCLUSIONS: Our hypothesis was rejected. The changes in the proportion of fibers expressing type I MHC are the reverse of that expected with chronic loading of extensors and, paradoxically, are similar to changes observed with chronic unloading, such as occurs during spaceflight, in this primate model. The data are consistent with the observed decrease in total daily activity levels.

Adaptation, Physiological↗
PubMed2001

Morphology changes in rat skeletal muscles after 19 day exposure to +2 G.

Effects of long duration hypergravity on m. soleus morphology characteristics are still unknown. Particularly, only one paper describes the size and myosin heavy chain profiles of rat hindlimb extensor muscle fibers after 2 weeks of +2 G exposure. Earlier it was shown that long term overloading induced changes in skeletal muscle fiber cross-sectional area (CSA), fiber composition, and imitochondrial content. The aim of our study was to evaluate quantitatively structural parameters of m. soleus contractile apparatus after 19 day exposure to +2 G overloading.

Animals↗
PubMed2001

Dystrophin in limb skeletal muscle fibers and creatinkinase leakage after acute +3 Gz acceleration in rhesus monkeys.

Intensive muscle tension induces significant blood accumulation of enzymes and structural proteins of the muscle origin. Altered macromolecular permeability of the sarcolemma is attributed to integrity of sarcolemmal cytoskeleton, mainly to dystrophin-sarcoglycan (DSG) complex. It is known that intensive tension of the antigravity extensor muscles is observed under conditions of gravitational overloading. We assumed that acute exposure to hypergravity would lead to serum accumulation of creatine phosphokinase (CK) associated with considerably altered integrity of the dystrophin layer in fibers of extensor muscles.

Acceleration↗
PubMed2001

Altered gravity effects on mothers and offspring: the importance of maternal behavior.

In this paper, I review and discuss recent studies of pregnant, parturient and lactating rat mothers and neonates exposed to hypo- and hypergravity. These studies are revealing new insights into how deviations form Earth-normal gravity may affect fundamental reproductive and ontogenetic processes in mammals. By way of background, I will first briefly summarize the spaceflights that have carried mammalian mothers and their offspring into space.

Animals↗
PubMed2000

Muscle derived serum enzyme accumulation after +Gz acceleration test in Rhesus monkeys exposed to bed rest.

It is known that several hours of intensive muscle tension result in accumulation of muscle derived enzymes and structural proteins (see review by Clarkson, 1997). We have assumed that, firstly, acute exposure to hypergravity may induce accumulation of serum creatine phosphokinase (CPK), and, secondly, level of that accumulation may be considerably altered after long term hypokinesia.

Animals↗
PubMed2000

Nociceptive responses and immunohistochemical changes in the rat brain under gravity stress.

It is well known that exposure to various stresses leads to pain suppression in animals. However, there is no report about the effects of gravitational alteration to serve as a kind of stress. The purpose of the present study is to clarify the effect of hypergravity (2 G) on the nociceptive responses and histochemical changes in rats. We examined the level of the threshold of withdrawal reflex against the noxious [correction of noxicious] stimulation in rats that were exposed to 2 G. Data show that the 2 G exposure elevates the nociceptive threshold. We have demonstrated for the first time that gravity change induces analgesic effects on rats in concomitant with c-fos induction in the arcuate, and paraventricular nuclei of rat hypothalamus. Gravity change acts as a kind of stress in rats.

Analgesia↗
PubMed2000

Mutation modulating activity in human serum factors induced after parabolic flight.

We have reported that human interferon, one of cytokines present in serum, can confer hypomutability on various human cells. On the contrary, we have also reported that serum factors from cancer patients can enhance cell mutability. Therefore, it seems likely that cell mutability is changed by cytokine-like serum factors in our body. It is one of important space problems whether the mutability of human cells is regulated in response to microgravity and hypergravity (gravitational stress). However, there is little information about cell mutability during such stress. In this study, we investigated whether the mutability is changed by exposing cells to human serum factors after gravitational stress.

Adult↗
PubMed2003

Acceleration effects on pupil size with control of mental and environmental factors.

BACKGROUND: Using still photography and cinematography, early studies reported that pupils dilate immediately on exposure to acceleration and the dilation persists during sustained +Gz. Due to the lack of control for mental and environmental factors and poor sampling rate in early techniques, we re-examined the effects of increased acceleration on pupil size in the human centrifuge. METHODS: Eight volunteers were dark adapted for 20 min by fixating on a 2.5 mm LED disk, 1 m away in otherwise complete darkness. Pupil diameters and horizontal and vertical eye movements were recorded binocularly in real time using an eye-tracking and pupillometry system. The recording sequence consisted of 1 min at +1 Gz, followed by transition to +3 Gz at 0.1 G x s(-1) 2 min at sustained +3 Gz, return to +1 Gz at 1 G x s(-1), and finally maintained at +1 Gz for another minute. During this sequence, the subject's heart rate was also monitored and the subject was instructed to subtract 2 from 1000 to maintain mental alertness. RESULTS: All subjects showed a significant decrease in pupil diameter (p < 0.05) and increase in heart rate (p = 0.02) during +3 Gz and regained the baseline level on sustained acceleration ranged from 0.6 to 3.3 mm. CONCLUSION: Our findings suggest that pupils constrict during hypergravity. It appears that the reflex regulation of pupil size is attributed to parasympathetic action through fibers originating in Edinger-Westphal's nucleus in the mesencephalon, which receives direct input from the otoliths.

Acceleration↗
PubMed2003

[High Gy induced vestibular disorders in guinea pigs and its countermeasure by preconditioning].

OBJECTIVE: To explore if high G exposure can cause vestibular disorder in guinea pig and the possibility of preventing it by preconditioning with exposure to a low hypergravity environment before high G stimulus. METHOD: A total of 86 guinea pigs were divided into 4 groups: 1) 28 were treated with a stimulus of +10 Gy for 5 min (+10 Gy group); 2) 28 were preconditioned by exposure to 2 G environment for 8 d before the +10 Gy stimulus (preconditioning group); 3) 20 were exposed to 2 G environment for 8 d, but without +10 Gy stimulus (2 G group); the rest 10 served as control. Their vestibular related behaviour, including vestibulo-spinal reflex (VSR) and vestibulo-ocular reflex (VOR) such as head tremble, head deviation, spontaneous nystagmus, eye deviation, body tilt or looping, were observed directly, the choline acetyltransferase (ChAT) activity in VNC (vestibular nucleon complex) in brain stem were investigated by immunohistochemistry technique, and the relative gamma in each group were analysed. RESULT: The incidence of behavioral abnormalities (BA) in 10 Gy group (79%) is significantly higher than that in preconditioning group (50%). The relative gamma of staining showed that the content of ChAT in VNC of the +10 Gy group and preconditioning group were significantly higher than that in control group, but no difference was found between them in +10 Gy and preconditioning groups. CONCLUSION: High G exposure of +10 Gy for 5 min could cause vestibular disorders in guinea pigs, and preconditioning with pre-exposure to 2 G environment could alleviate it. ChAT activity changes in VNC may contribute to its mechanisms.

Adaptation, Physiological↗