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At least 397 records · Page 22Linked to original sources
PubMed2004

Morphometric changes in vagal nerves of fourth generation mice passage-bred in a 2-G environment.

INTRODUCTION: Previous studies have shown that microgravity induces both functional and structural adaptations in the autonomic nerves. Functional adaptation to hypergravity has also been reported, but structural change has not yet been isolated. The purpose of this study was to evaluate structural adaptation to hypergravity in the parasympathetic nerve. METHOD: We selected fourth generation mice which were passage-bred in a 2-G environment by cycles of coupling, delivery, and growth. Complete left cervical vagal nerves of these mice were studied in transverse sections by electron microscopy. The number of small (diameter < 5 microm, thin and light-stained myelin sheath) and large (diameter > 5 microm, thick and dark-stained myelin sheath) myelinated fibers was counted. RESULTS: The total number of all myelinated fibers (2 G: 795 +/- 103, 1 G: 644 +/- 60) and the number of small myelinated fibers (2 G: 657 +/- 95, 1 G: 522 +/- 66) were significantly greater in the 2-G mice than those in the 1-G mice (p < 0.05). The number of large myelinated fibers in the 2-G mice was greater than that in the 1-G mice, although it was not statistically significant (2 G: 138 +/- 15, 1-G: 122 +/- 16; p = 0.091). DISCUSSION: The results show that the autonomic nerves can adapt structurally to hypergravity. We contend that the present results are due to the fact that the mice were passage-bred. As far as we know, this is the first report to show an increase in myelinated fibers in autonomic nerves under prolonged exposure to an increased G environment.

Adaptation, Physiological↗
PubMed2003

Antibody binding in altered gravity: implications for immunosorbent assay during space flight.

A single antibody-incubation step of an indirect, enzyme-linked immunosorbent assay (ELISA) was performed during microgravity, Martian gravity (0.38 G) and hypergravity (1.8 G) phases of parabolic flight, onboard the NASA KC-135 aircraft. Antibody-antigen binding occurred within 15 seconds; the level of binding did not differ between microgravity, Martian gravity and 1 G (Earth's gravity) conditions. During hypergravity and 1 G, antibody binding was directly proportional to the fluid volume (per microtiter well) used for incubation; this pattern was not observed during microgravity. These effects in microgravity may be due to "fluid spread" within the chamber (observed during microgravity with digital photography), leading to greater fluid-surface contact and subsequently antibody-antigen contact. In summary, these results demonstrate that: i) ELISA antibody-incubation and washing steps can be successfully performed by human operators during microgravity, Martian gravity and hypergravity; ii) there is no significant difference in antibody binding between microgravity, Martian gravity and 1 G conditions; and iii) a smaller fluid volume/well (and therefore less antibody) was required for a given level of binding during microgravity. These conclusions indicate that reduced gravity would not present a barrier to successful operation of immunosorbent assays during spaceflight.

Antigen-Antibody Reactions↗
PubMed2006

Changes in gravitational force cause changes in gene expression in the lens of developing zebrafish.

Gravity has been a constant physical factor during the evolution and development of life on Earth. We have been studying effects of simulated microgravity on gene expression in transgenic zebrafish embryos expressing gfp under the influence of gene-specific promoters. In this study, we assessed the effect of microgravity on the expression of the heat shock protein 70 (hsp70) gene in lens during development using transgenic zebrafish embryos expressing gfp under the control of hsp70 promoter/enhancer. Hsp70:gfp expression was up-regulated (45%) compared with controls during the developmental period that included the lens differentiation stage. This increase was lens specific, because the entire embryo showed only a 4% increase in gfp expression. Northern blot and in situ hybridization analysis indicated that the hsp70:gfp expression recapitulated endogenous hsp70 mRNA expression. Hypergravity exposure also increased hsp70 expression during the same period. In situ hybridization analysis for two lens-specific crystallin genes revealed that neither micro- nor hypergravity affected the expression level of betaB1-crystallin, a non-hsp gene used as a marker for lens differentiation. However, hypergravity changed the expression level of alphaA-crystallin, a member of the small hsp gene family. Terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) assay analysis showed that altered-gravity (Deltag) decreased apoptosis in lens during the same period and the decrease correlated with the up-regulation of hsp70 expression, suggesting that elimination of nuclei from differentiating lens fiber cells was suppressed probably through hsp70 up-regulation. These results support the idea that Deltag influences hsp70 expression and differentiation in lens-specific and developmental period specific manners and that hsp family genes play a specific role in the response to Deltag.

Animals↗
PubMed1992

Human ocular torsion during parabolic flights: an analysis with scleral search coil.

Rotation of the eyes about the visual axis is known as ocular torsion. A lateral inclination (a "roll") of the head induces ocular torsion in the opposite direction, a response known as ocular counterrolling. For six subjects, we recorded the static (head still) and dynamic (head in oscillatory roll motion) ocular torsion in normal 1 g condition and also during the microgravity and hypergravity periods of parabolic flight, using the electromagnetic scleral search coil technique. With the head still, the direction and magnitude of torsion that occurred in response to microgravity and hypergravity differed substantially from one individual to another, but there was a significant difference in torsional magnitude between the microgravity and hypergravity periods, for all static head positions including the upright position. Under normal 1 g conditions, counterrolling compensated for about 16% of (voluntary) static head roll, while dynamic counterroll was much larger, up to 36% of head roll at 0.55 Hz. With increasing frequency of head oscillation between 0.33 Hz and 0.55 Hz, the gain of counterrolling increased and there was no change in the phase relationship. The gain of dynamic counterroll (in response to voluntary head rolling) was not significantly less in hypogravity, suggesting that on the ground at these frequencies the contribution of gravity and gravity receptors to this reflex is redundant: this reflex is probably driven by the semicircular canals. In some subjects, the torsional displacement in microgravity is accompanied by micro-torsional oscillatory motion.

Adult↗
PubMed1978

Effect of chronic centrifugation on bone density of the dog.

Sixteen male Beagle dogs, 293 to 509 days old, were exposed almost continuously for 3 months to 2.0 G on a 7.9m radius centrifuge. The dogs were maintained on the centrifuge by means of a specially designed, automated waste disposal and life support system. Bone density was measured by a 125I Profile Scanner in the anterior, medial posterior and lateral cortex of the femoral mid-shaft. As compared to mean density in the femora of normal gravity controls, centrifuged dogs showed a 0.8% (P less than 0.05) lower mean linear absorption in their femora. However, the regression of density on the square-root of cross-sectional area/pi differs very significantly in the animals living at earth gravity and those living at hypergravity. Thin hypergravic bones are denser, thick hypergravic ones are less dense than the corresponding ones of normal gravity controls.

Animals↗
PubMed1984

The influence of extra load on the mechanical behavior of skeletal muscle.

Eleven international jumpers and throwers engaged in year round training were divided into experimental (n = 6) and control (n = 5) groups. The experimental group was tested before and after a 3 weeks simulated hypergravity period, and again 4 weeks after the hypergravity period. The high gravity condition was created by wearing a vest weighing about 13% of the subjects body weight. The vest was worn from morning to evening including the training sessions, and only removed during sleep. The daily training of all subjects consisted of classical weight training and jumping drills. No changes in the ordinary training program were allowed in the experimental group, except for the use of the vest. Vertical jumps, drop jumps and a 15 s continuous jumping test were used to measure the explosive power characteristics of the subjects. After the hypergravity period the experimental subjects demonstrated significant (5-10%, P less than 0.05-0.01) improvements in most of the variables studied: however, 4 weeks after cessation of the high gravity period they tended to return towards the starting values. No changes were observed in the results of the control group. The improvement observed in the experimental subjects was explained as fast adaptation to the simulated high gravity field. It is suggested that adaptation had occurred both in neuromuscular functions and in metabolic processes.

Adult↗
PubMed2000

Moving weightless objects. Grip force control during microgravity.

When we move grasped objects, our grip force precisely anticipates gravitational and inertial loads. We analysed the control of grip forces during very substantial load changes induced by parabolic flights. During these flight manoeuvres, the gravity varies between hypergravity associated with a doubling of normal terrestrial gravity and a 20-s period of microgravity. Accordingly, the contribution of the object's weight to the load changed from being twice the normal value to being absent. Two subjects continuously performed vertical and horizontal movements of an object equipped with grip force and acceleration sensors. Whereas, during vertical movements performed under normal and hypergravity, a load force maximum occurred at the lower turning point and a minimum at the upper turning point, the load force pattern was completely changed under microgravity. In particular, the upper turning point was also associated with a load force maximum. Analysis of the grip forces produced by the two subjects revealed that the grip forces underwent the same characteristic changes as the load forces. Thus, subjects were able to adjust grip forces in anticipation of arm movement-induced fluctuations in load force under different and novel load conditions. Adaptation to changing levels of gravity was also obvious when the vertical and horizontal movements were compared: grip forces depended heavily on movement direction during normal and hypergravity but not during microgravity. The predictive coupling of grip force and load force was observed even during transitions between gravity levels, indicating rapid adaptation to changing load conditions. To account for the striking preservation of the normal characteristics of grip force control, we suggest that a highly automatized, extremely flexible sensorimotor mechanism firmly implemented within the central nervous system can cope with even massive changes in the environmental conditions.

Adaptation, Physiological↗
PubMed1999

Effects of centrifuging at 2g on rat long bone metaphyses.

Hypergravity may be considered as a means of counteracting the deleterious effects of microgravity on bone tissue. The effects of exposure to 4 days of hypergravity provided by centrifuging, on bone tissue were studied using histomorphometry. Young 53-day-old male Sprague Dawley rats were randomly divided into a centrifuged group (2g, n = 10), a rotated group (ROTATE, n = 6) of rats exposed to 1.03 g placed in cages near the centre of rotation of the centrifuge and a stationary control group (CONTROL, n = 10). The body mass of the 2g rats was decreased by this experience by 16% compared to CONTROL. The width of the tibial growth plate of 2g was decreased. In two out of ten 2g rats, the hypertrophic zone was injured. In both the tibial and humeral primary (1 degrees ) spongiosae, a reduced 1 degrees spongiosa width (-35% and -24%, ROTATE versus CONTROL respectively; -37% and -41%, 2g versus CONTROL respectively) associated with bone gain (+27% for tibia and humerus ROTATE versus CONTROL; + 16% and +20%, 2g versus CONTROL respectively) was observed in both ROTATE and 2g. In the tibial secondary (2 degrees) spongiosa, bone mass was increased in the 2g (+13% 2g versus CONTROL) rats due to thicker trabeculae, but was decreased in ROTATE rats (-12% versus CONTROL) due to thinner trabeculae. The parameters of formation and resorption activities were stimulated in the 2g and ROTATE groups, the formation activity being more enhanced in 2g. No structural changes were observed in the humeral 2 degrees spongiosa in any of the groups. Numeral bone formation parameters were decreased in 2g and ROTATE but resorption activity was increased in 2g and decreased in ROTATE compared to CONTROL. In conclusion, as early as the 4th day, 2g hypergravity induced reduced endochondral bone formation and increased cancellous bone mass. Rotation led to mixed results including reduced endochondral bone formation, increased bone volume in the 1 degrees spongiosa and bone loss in the 2 degrees spongiosa.

Animals↗
PubMed2003

Changes in gravitational forces induce modifications of gene expression in A. thaliana seedlings.

By comparing the expression patterns of selected genes from Arabidopsis thaliana (L.) Heynh. grown either at 1 g or on a clinostat (horizontally or vertically inverted, 1 rpm), and either used directly or after hypergravity stimulation, we have shown that the pattern of expression did not proceed in a stereotypical manner. Rather, the selected genes fell into different classes. These classes include (i) those insensitive to the gravitational conditions, (ii) those that are regulated in an opposite manner by hypergravity and clinostat conditions, (iii) those that are desensitised to hypergravity by long-term culture on a clinostat, and (iv) those enhanced by such a treatment. Our data suggest that rapid reorientation of gene expression is likely to occur in response to changes in the gravitational conditions.

Arabidopsis↗
PubMed2003

The development of gravity sensory systems during periods of altered gravity dependent sensory input.

Gravity related behavior and the underlying neuronal networks are the most suitable model systems to study basic effects of altered gravitational input on the development of neuronal systems. A feature of sensory and motor systems is their susceptibility to modifications of their adequate physical and/or chemical stimuli during development. This discovery led to the formulation about critical periods, which defines the period of susceptibility during post-embryonal development. Critical periods can be determined by long-lasting modifications of the stimulus input for the gravity sensory system (GSS). Techniques include: (1) destruction of the gravity sense organ so that the gravity cannot be detected any longer and the central neuronal network of the GSS is deprived of gravity related information, (2) loading or deloading of parts of the body by weights or counterweights, respectively, which compensates for the gravitational pull, and (3) absence or augmentation of the gravitational environment per se by the exposure of organisms to microgravity during spaceflights or to hypergravity by centrifugation. Most data came from studies on compensatory eye or head movements in the clawed toad Xenopus laevis, the cichlid fish Oreochromis mossambicus, and crickets (Acheta domesticus, Gryllus bimaculatus). The responses are induced by a roll or pitch stimulation of the gravity sense organs, but are also affected by sensory inputs from proprioreceptors and eyes. The development of these compensatory eye and head responses reveals species-specific time courses. Based on experiments using spaceflights, centrifugation, lesion and loading or deloading, all species revealed a significant susceptibility to modifications of the gravity sensory input during development. Behavioral responses were depressed (Xenopus) or augmented (Xenopus, Oreochronis) by microgravity, and depressed by hypergravity except in crickets. In Acheta, however, the sensitivity of its position sensitive neuron PSI was reduced by microgravity. After termination of the period of modified gravity sensory input, all behavioral and physiological modifications disappeared, in some preparations such as the PSI of Acheta or the eye response in Xenopus, however, delayed after exposure to hypergravity. Irreversible modifications were rare; one example were malformations of the body of Xenopus tadpoles caused by lesion induced deprivation. Several periods of life such as the period of hatching or first appearance of gravity related reflexes revealed a specific sensitivity to altered gravity. Although all studies gave clear evidences for a basic sensitivity of developing GSSs to long-lasting modifications of the gravity sensory input, clear arguments for the existence of a critical period in the development of the sense of gravity are still missing. It has to take into consideration that during long-term exposures, adaptation processes take place which are guided by central physiological and genetically determined set points. The International Space Station (ISS) is the necessary platform of excellence if biological research is focussed on the analysis of long-term space effects on organisms.

Animals↗
PubMed1979

Thermoregulation in unrestrained rats during and after exposure to 1.5--4 G.

Unrestrained rats were exposed to cold for 1 h during and immediately after exposure to hypergravic fields (1.5--4 G) to determine if they recover their ability to thermoregulate on reentry to 1-G conditions. In contrast to the decreased body temperatures observed when cold exposure occurred concurrently with acceleration, hypothalamic, carotid, and brown fat temperatures did not fall when rats were exposed to cold immediately after return to 1 G. These results support the hypothesis that the thermoregulatory alterations seen under hypergravic conditions are manifestations of an effect of ongoing exposure to hypergravity and can be reversed on termination of acceleration. The reversibility of the thermoregulatory impairment is apparently unaffected by the magnitude of the acceleration field over a range of 1.5--4 G.

Adaptation, Physiological↗
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↗
PubMed1992

Altered gravity conditions affect early EGF-induced signal transduction in human epidermal A431 cells.

Epidermal growth factor (EGF) activates a well-characterized signal transduction cascade in human A431 epidermal carcinoma cells. Among the early responses evoked by EGF are receptor clustering, cell rounding, and early gene expression. These processes have been studied under various gravity conditions. In addition, we have investigated signalling pathways as induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), forskolin, and A23187 that bypass the EGF receptor, but mimic the partial activation of signal transduction pathways. Hypergravity, simulated microgravity, and real microgravity have been obtained by means of centrifuge, fast-rotating clinostat, and sounding rocket, respectively. EGF-induced c-fos gene expression is suppressed in simulated microgravity (clinostatting) and even more so in real microgravity, while hypergravity increases early gene expression. This indicates that gravity inhibits early EGF-induced signal transduction. However, neither microgravity nor clinostatting affect EGF-induced EGF receptor clustering, suggesting that inhibition of EGF-induced signal transduction by microgravity and clinostatting is independent of EGF receptor clustering. EGF-induced cell rounding is enhanced under clinostatting, while hypergravity does not significantly influence this process. Furthermore, both under clinostatting and real microgravity, EGF- and TPA-induced c-fos expression is decreased, while forskolin and A23187-induced c-fos expression remains unaltered. These observations demonstrate that gravity affects specific components in the EGF-induced signal transduction circuitry, in particular the protein kinase C pathway which is common to EGF and TPA activated intracellular signalling.

Calcimycin↗
PubMed1997

The development of vestibular connections in rat embryos in microgravity.

Existing experimental embryological data suggests that the vestibular system initially develops in a very rigid and genetically controlled manner. Nevertheless, gravity appears to be a critical factor in the normal development of the vestibular system that monitors position with respect to gravity (saccule and utricle). In fact several studies have shown that prenatal exposure to microgravity causes temporary deficits in gravity-dependent righting behaviors, and prolonged exposure to hypergravity from conception to weaning causes permanent deficits in gravity-dependent righting behaviors. Data on hypergravity and microgravity exposure suggest some changes in the otolith formation during development, in particular the size although these changes may actually vary with the species involved. In adults exposed to microgravity there is a change in the synaptic density in the optic sensory epithelia suggesting that some adaptation may occur there. However, effects have also been reported in the brainstem. Several studies have shown synaptic changes in the lateral vestibular nucleus and in the nodulus of the cerebellum after neonatal exposure to hypergravity. We report here that synaptogenesis in the medial vestibular nucleus is retarded in developing rat embryos that were exposed to microgravity from gestation days 9 to 19.

Animals↗
PubMed1988

The effects of gravitational forces on reproduction and development.

It is clear that increased gravitational forces can affect biologic reproduction and development, although exact mechanisms of action have not been established. Except for three studies of male pilot and astronaut fertility, human reproduction and development studies of chronic or acute exposure to micro- or hypergravity environments have not been carried out. Only two reproduction and development studies (both Soviet) have been done under chronic or acute exposure to microgravity. It is unlikely that chronic human exposure to hypergravity will occur except when planets much larger than Earth are colonized. Colonies dependent on reproduction for continued existence probably could not be established on planets with masses significantly dissimilar to Earth because hypergravity or hypogravity are likely to affect reproduction adversely and cause abnormal growth and development. Acute exposures to gravitational changes in the later stages of development appear to be less detrimental, but much remains to be discovered about how gravity affects reproduction and development of mammals, humans in particular. Earth's gravitational force has helped to shape human reproduction and development. Only when the limits of mammalian biology on both sides of 1 g are explored will we be able to determine the extent to which gravity determines biologic structure and function.

Animals↗
PubMed1994

Gravitational neuromorphology.

This review shows that morphological studies of the central, peripheral and autonomic nervous system of animals exposed to altered gravity yield data which are extremely significant for our understanding of the mechanisms of adaptation of the nervous system, and of the mammalian organism as a whole, to increased and decreased loading. Neuromorphological studies, correlating structure and function, indicate a decreased activity in weightlessness for spinal ganglia neurons and motoneurons of the spinal cord, as well as the neurons of the hypothalamic nuclei producing arginine vasopressin and growth hormone releasing factor. Structural changes of the somatosensory cortex and spinal ganglia suggest a decreased afferent flow to the somatosensory cortex in microgravity. The results characterize the mechanisms of structural adaptation to a decreased afferent flow in microgravity by the neurons in the hemisphere cortex and brain stem nuclei. There is also morphological evidence for an increased sensitivity of the otolith apparatus and for the development of a hyponoradrenergic syndrome in weightlessness. These studies have shown that both microgravity and the simulation of microgravity effects by tail suspension-induced structural changes in the large neurons of lumbar spinal ganglia and motoneurons of the lumbar spinal cord, which occur under conditions of nerve cell hypoactivity. The structural changes, and consequently the development of neuron hypoactivity, are expressed more extensively after microgravity than after tail suspension for the same length of time. The influence of microgravity and hypergravity on animals is expressed by opposing changes in nervous tissue structure in the spinal ganglia, spinal cord, and nodulus of cerebellar vermis. These changes indicate neuron hypoactivity under microgravity and neuron hyperactivity under 2 G. Morphological assessment of the functional state of other structures of the brain under hypergravity will require further study. Can all structural changes which occur in nerve tissue under microgravity or under hypergravity be explained on the basis of increased or decreased activity of its structural elements? The presently available data regarding the correlation of structure and functional state of cells in brain and spinal cord suggest an affirmative answer. Ultrastructural studies of the nodular cortex of the cerebellum in rats after different duration spaceflights provide what appears to be a convincing example. However, it should be pointed out that the criteria for the morphological assessment of the functional state of single nerve cells will certainly be different from those for groups of neurons connected in a nerve cell network.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Human gaze instability during brief exposure to reduced gravity.

The stability of gaze in three dimensions (horizontal, vertical and torsional) was investigated with the electromagnetic scleral search-coil technique during the microgravity phase of parabolic flights under two visual fixation conditions: fixation on a real target and on an imagined target. Subjects were secured upright with the head immobilized by a dental bite. There were torsional eye movements in response to the imposition of reduced gravitoinertial forces under both visual fixation conditions. The pattern of these movements was consistent with our previous findings on six other subjects. No significant horizontal eye movements were observed in either fixation condition. Under the condition of fixation on an imagined target, direction-specific vertical nystagmus was observed with slow phase directed upwards during transition from hypergravity to microgravity. The slow phase was directed downwards during transition from microgravity to hypergravity, although the nystagmus was of lower frequency and the magnitude of the slow phase velocity appeared to be smaller than during transition from hypergravity to microgravity. The vertical eye movements could be attributed to a change of otolithic stimulation along the subject's z axis since the rate of pitch rotation of the aircraft during parabolic flight was too slow to produce an effective canal input. These kinds of reflex eye movements could degrade vision during manoeuvres or turbulence in flight.

Adult↗
PubMed1989

The biological clock of Neurospora in a microgravity environment.

The circadian rhythm of conidiation in Neurospora crassa is thought to be an endogenously derived circadian oscillation; however, several investigators have suggested that circadian rhythms may, instead, be driven by some geophysical time cue(s). An experiment was conducted on space shuttle flight STS-9 in order to test this hypothesis; during the first 7-8 cycles in space, there were several minor alterations observed in the conidiation rhythm, including an increase in the period of the oscillation, an increase in the variability of the growth rate and a diminished rhythm amplitude, which eventually damped out in 25% of the flight tubes. On day seven of flight, the tubes were exposed to light while their growth fronts were marked. Some aspect of the marking process reinstated a robust rhythm in all the tubes which continued throughout the remainder of the flight. These results from the last 86 hours of flight demonstrated that the rhythm can persist in space. Since the aberrant rhythmicity occurred prior to the marking procedure, but not after, it was hypothesized that the damping on STS-9 may have resulted from the hypergravity pulse of launch. To test this hypothesis, we conducted investigations into the effects of altered gravitational forces on conidiation. Exposure to hypergravity (via centrifugation), simulated microgravity (via the use of a clinostat) and altered orientations (via alterations in the vector of a 1 g force) were used to examine the effects of gravity upon the circadian rhythm of conidiation.

Biological Clocks↗