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At least 127 records · Page 7Linked to original sources
PubMed1994

GRAVIRESPONSES IN PARAMECIUM CAUDATUM AND DIDINIUM NASUTUM EXAMINED UNDER VARIED HYPERGRAVITY CONDITIONS

The swimming behaviours of two species of ciliates characterized by different mechanosensory and ciliary motor properties were investigated under hypergravity up to 5.4 g. The experiments were designed to examine large numbers of cells using video recording, digital data processing and statistics for the documentation of the rates and orientations of swimming. The gravikinetic responses (change in active swimming rates) were calculated from (1) the velocities of vertical swimming in the gravity field, (2) sedimentation of Ni2+-immobilized cells and (3) the intrinsic rate of propulsion, independent of gravity. Propulsion was determined from the intersection of regression lines of the gravity-dependent upward and downward swimming velocities. The rates of swimming and sedimentation, and consequently the gravikineses, were linear functions of gravitational acceleration. Comparisons of cell populations from different cultures suggest that there is an age-dependent change in gravikinesis. In starved Paramecium caudatum (7-day cultures), the kinetic responses antagonizing sedimentation (negative gravikinesis) increased with acceleration. In Didinium nasutum, negative gravikinesis was documented at 1 g in downward-swimming specimens only, which agrees with the mechanosensory organization of this cell. Hypergravity induced the gravikinesis of Didinium to change sign. In both species, and at all accelerations tested, a neutral gravitaxis was documented. Such behaviour incorporates distinct acceleration-dependent orientational and velocity responses, keeping populations of cells stationary in the gravity field (taxis coefficients close to zero).

Journal Article↗
PubMed2000

Effects of hypergravity on morphology and osteopontin expression in the rat otolith organs.

Recovery from balance disorders after spaceflight is supposed to reflect the process of readaptation to normal gravitational environment (1G) from microgravity. Linear acceleration including gravity is perceived by otolith pathways, therefore, it could be assumed that possible plastic changes in any part of otolithic pathways from the level of the vestibular periphery to the central vestibular system might be responsible for adaptive mechanisms to an altered gravitational environment. In the present study, to elucidate a role of otoconia in adaptation to altered gravity, we examined the effects of hypergravity (2G) on morphology and synthesis of saccular and utricular otoconia in young adult rats. Morphology of otoconia was examined by scanning electron microscopy. Otoconial synthesis was assessed by mRNA expression of osteopontin, a matrix protein of otoconia, in otolithic maculae as a marker of otoconial genesis determined by a real-time quantitative PCR method. The present results showed that neither otoconial morphology nor otoconial synthesis was affected by up to one week exposure to hypergravity. These findings suggest that changes in neurotransmission at the synapses of the peripheral and/or central vestibular system rather than the changes in otoconial morphology and synthesis may be involved in adaptive mechanisms to an altered gravitational environment.

Animals↗
PubMed1989

Pilot performance is increased after alternating hypo- and hypergravity states.

An increase of performance of six experienced pilots in a complex in-flight aerobatics test repeated after a period of alternating zero-hypergravity conditions, lasting for 30 minutes, was observed, if compared with the same test before such exposition. There was no difference in the increase of the pilot performance, if the in-flight test was repeated after a period of rest of the same duration. We conclude that in experienced pilots adaptation to a complex in-flight test remains uninfluenced by alternating zero-hypergravity conditions, realized in a light transport plane. Perhaps adaptation to alternating gravity conditions is implemented better than to full weightlessness in experienced subjects. This is to be proved in real space flights.

Adaptation, Physiological↗
PubMed1984

The immune system: effects of hypergravity and hypogravity.

The force of gravity has been inescapable until only the last few decades. Space programs conducted by several nations now make possible the study of hypergravity and hypogravity in a variety of scientific areas. Although much work has focused on the physiological aspects of gravity, its effects on the immune system are only beginning to be appreciated. An understanding of these effects is not only of theoretical interest, but important in predicting the health of astronauts exposed to hypergravity and hypogravity. These studies may also help to answer the larger question of how stress affects the immune response.

Animals↗
PubMed1978

Studies on the erythron and the ferrokinetic responses in beagles adapted to hypergravity.

Red cell survival, ferrokinetics, and hematologic parameters were investigated in Beagle dogs exposed to chronic hypergravity (2.6 Gx). Ineffective erythropoiesis, red cell mass, plasma volume, and 51 Cr elution were significantly increased; maximum 59Fe incorporation was decreased; and there was no change in the mean erythrocyte life span following autologous injection of 51Cr-labeled red cells and 59Fe-labeled transferrin. Red cell count, Fcells, total body hemoglobin (Hb), susceptability to osmotic lysis, and differential reticulocyte count were increased. White blood cell count, venous blood %Hb, mean cell volume, mean cell Hb, mean cell Hb concentration, and serum iron were decreased. No changes were observed for body mass, mg Fe per g Hb, iron binding capacity, percent saturation of iron carrying capacity, or the electrophoretic mobility of purified Hb. This study indicated that chronic exposure to hypergravity induced changes in red cell size, volume, total mass, and membrane permeability.

Adaptation, Physiological↗
PubMed1993

[Effects of hypergravity on Paramecium tetraurelia].

Previous space experiments carried out in Paramecium tetraurelia have shown that exposure to microgravity results in an enhancement of cell multiplication. An opposite effect occurs when paramecia are exposed to hypergravity. Changes in cell growth rate observed in hypergravity cannot be ascribed to the bacteria present in the culture medium, the same effect being observed when paramecia grow in sterile medium.

Animals↗
PubMed1998

Hypergravity exposure decreases gamma-aminobutyric acid immunoreactivity in axon terminals contacting pyramidal cells in the rat somatosensory cortex: a quantitative immunocytochemical image analysis.

Quantitative evaluation of gamma-aminobutyric acid immunoreactivity (GABA-IR) in the hindlimb representation of the rat somatosensory cortex after 14 days of exposure to hypergravity (hyper-G) was conducted by using computer-assisted image processing. The area of GABA-IR axosomatic terminals apposed to pyramidal cells of cortical layer V was reduced in rats exposed to hyper-G compared with control rats, which were exposed either to rotation alone or to vivarium conditions. Based on previous immunocytochemical and behavioral studies, we suggest that this reduction is due to changes in sensory feedback information from muscle receptors. Consequently, priorities for muscle recruitment are altered at the cortical level, and a new pattern of muscle activity is thus generated. It is proposed that the reduction observed in GABA-IR of the terminal area around pyramidal neurons is the immunocytochemical expression of changes in the activity of GABAergic cells that participate in reprogramming motor outputs to achieve effective movement control in response to alterations in the afferent information.

Animals↗
PubMed1998

Hypergravity can reduce but not enhance the gravitropic response of Chara globularis protonemata.

The relationship between the position of the statoliths and the direction and rate of tip growth in negatively gravitropic protonemata of Chara globularis was studied with a centrifuge video microscope. Cells placed perpendicularly to the acceleration vector (stimulation angle 90 degrees) showed a gradual reduction of the gravitropic curvature with increasing accelerations from 1 g to 8 g despite complete sedimentation of all statoliths on the centrifugal cell flank. It is argued that the increased weight of the statoliths in hypergravity impairs their acropetal transport which is induced when the cell axis deviates from the normal upright orientation. When the statoliths were centrifuged deep into the apical dome at 6 g and a stimulation angle of 170 degrees the gravitropic curvature after 1 h was identical to that determined for the same cells at 1 g and the same stimulation angle. This indicates that gravitropism in Chara protonemata is either independent of the pressure exerted by the statoliths on an underlying structure or is already saturated at 1 g. When the statoliths were moved along the apical cell wall at 8 g and the stimulation angle was gradually increased from 170 degrees to 220 degrees the gravitropic curvature reverted sharply when the cluster of statoliths passed over the cell pole. This experiment supports the hypothesis that in Chara protonemata asymmetrically distributed statoliths inside the apical dome displace the Spitzenkorper and thus the centre of growth, resulting in gravitropic bending. In contrast to the positively gravitropic Chara rhizoids, no modifications either in the transport of statoliths during basipetal acceleration (6 g, stimulation angle 0 degree, 5 h) or in the subsequent gravitropic response could be detected in the protonemata. The different effects of centrifugation on the positioning of statoliths in Chara protonemata and rhizoids indicate subtle differences in the function of the cytoskeleton in both types of cells.

Centrifugation↗
PubMed1988

Effects of microgravity and hypergravity on the cell: investigations on Paramecium tetraurelia.

Previous space CYTOS experiments have shown that space flights resulted in an increase in growth of Paramecia cultures. Microgravity is the major factor responsible of this response: indeed the stimulatory effect disappeared in inflight cultures placed on a 1 g centrifuge aboard the Spacelab. On the other hand, exposure to different levels of hypergravity on Earth resulted in an opposite response, i.e. to a reduced cell growth rate. A possible mechanism of microgravity on paramecia is discussed.

Animals↗
PubMed1993

Effects of unilateral selective hypergravity stimulation on gait.

The purpose of this work is to analyse the neural mechanisms of human motor perturbations induced by dynamic changes in gravity. A unilateral selective hypergravity stimulation (USHS) was produced by stretching an elastic band between the right shoulder and foot. The consequences of the extensor muscle tone change due to the positioning (increased muscular loading) and to its removal (decreased muscular loading) by the elastic band were observed on motor gait skill. Gait spatio-temporal parameters (horizontal displacement of both feet) and lower limb functional length variations (efficiency of flexion and extension movements of the lower limbs) were measured. The latter measure was performed using a device specially designed for that purpose. The main results were: (1) during and after USHS, gait perturbations appeared on the left--the body side not directly stimulated, (2) just after the end of USHS, perturbations were present on the right (homolateral) side evidencing a post treatment effect which caused a decrease in functional shortening of the lower limb during extension and an increase of functional shortening of the lower limb during stance (opposite in sense to the modification observed during swing). Such results afford evidence that, in addition to vestibular receptors, the mechanoreceptors of extensor muscles are involved in determining the changes in motor skills observed at the beginning and at the end of space flights.

Adaptation, Physiological↗
PubMed1996

A hypergravity related sensitive period during the development of the roll induced vestibuloocular reflex in an amphibian (Xenopus laevis).

In tadpoles of Xenopus laevis, the effects of an exposure to hypergravity on the development of the roll-induced static vestibuloocular reflex (rVOR) were investigated. Special attention was given to the onset of the 9 or 12 days lasting 3 g period during early life. Recordings of rVOR characteristics for complete 360 degrees rolls of the tadpoles started 24 h after the end of the 3 g period. The rVOR peak-to-peak amplitudes from the 3 g samples recorded at the 2nd and 3rd day after termination of the 3 g exposure agreed with that recorded from the 1 g reared tadpoles for the youngest group, but were reduced by 30% in the older tadpoles. During further development under 1 g condition, the rVOR amplitude of tadpoles with 3 g experience did not change if the 3 g exposure started before the first appearance of the rVOR, but increased if it had started thereafter, albeit on a lower level than that of the 1 g reared siblings. The results support the existence of a sensitive period for the rVOR development, and additionally demonstrate that the period during which the rVOR appeared for the first time is an important milestone for the development of adaptive properties of the underlying neuronal network.

Animals↗
PubMed1988

Core temperature is regulated, although at a lower temperature, in rats exposed to hypergravic fields.

1. In rats acclimated to 23 degrees C (RT rats) or 5 degrees C (CA rats), core temperature (Tc), tail temperature (Tt) and oxygen consumption (VO2) were measured during exposure to a hypergravic field. 2. Rats were exposed for 5.5 h to a 3 g field while ambient temperature (Ta) was varied. For the first 2 h, Ta was 25 degrees C; then Ta was raised to 34 degrees C for 1.5 h. During this period of warm exposure, Tc increased 4 degrees C in both RT and CA rats. Finally, Ta was returned to 25 degrees C for 2 h, and Tc decreased toward the levels measured prior to warm exposure. 3. In a second experiment at 3 g, RT and CA rats were exposed to cold (12 degrees C) after two hours at 25 degrees C. During the one hour cold exposure, Tc fell 1.5 degrees C in RT and 0.5 degree C in CA rats. After cold exposure, when ambient temperature was again 25 degrees C, Tc of RT and CA rats returned toward the levels measured prior to the thermal disturbance. 4. Rats appear to regulate their temperature, albeit at a lower level, in a 3 g field.

Acclimatization↗
PubMed1997

Effects of perfusion on the mechanical behavior of the brain-exposed to hypergravity.

In certain flight configurations, fighter pilots are exposed to high Gz acceleration which may induce inflight loss of consciousness (G-LOC). In order to study the mechanical effects induced by these accelerations on the cerebral structures, an experimental model has been developed in vitro. Fresh bovine brains were excised and placed in a transparent mold modeling the inside of the skull. Half of these brains were perfused during the experiment. This assembly was placed into the gondola of a centrifuge, in front of a camera lens. Displacements and deformations of the brains were filmed and recorded at different onset rates. Measurements were made after off-line digitalization of images. Experimental data were incorporated into a finite element calculation code whose mesh represented the brain. The applied behavior law was elastic, the structure being considered as homogeneous and isotropic. The first results concerned the elastic properties of the brains under hypergravity. The mean value of the Young's modulus of the nonperfused brain was 46.8 kPa, which corresponded to the values published in reference literature. For the perfused brains, the mean value of the Young's modulus was higher. The mean value of the equivalent Poisson's ratio was 0.35. In fact, contrary to impacts, the mechanical stimulation is long enough to allow fluid displacements. The mean value of the equivalent Poisson's ratio calculated in the present study should probably be increased since this study was performed post mortem.

Aerospace Medicine↗
PubMed1999

HSP70 induction may explain the long-lasting resistance to heat of Drosophila melanogaster having lived in hypergravity.

In this study, we showed that in flies kept for 2 weeks at 1 (terrestrial gravity), 3 or 5 x g (hypergravity, HG) before transfer to 1 x g, resistance to heat remained higher in HG flies for several weeks after the transfer. The measurement of heat shock protein 70 (hsp70) indicated no induction of the protein in HG, but the study revealed that flies living in HG expressed more hsp70 only after being submitted to severe stress. The higher induction of hsp70 may explain the higher thermotolerance of these HG-treated young flies. Finally, an unknown protein was observed only in females. This protein may belong to a class of higher molecular weight hsp (hsp110), which have not previously been observed in Drosophila.

Age Factors↗
PubMed1999

Resistance to stress as a function of age in Drosophila melanogaster living in hypergravity.

Male and female fruitflies (Drosophila melanogaster) living at different gravity levels [1g: terrestrial gravity; 3 and 5g: hypergravity (HG)] were used to investigate the age-specific (young: 7 days; middle-aged: 28 days; and old: 49 days) resistance to various stresses (starvation, desiccation, and cold). The experiment showed that the resistance of the flies to the studied stresses decreased with age, except in the case of females submitted to starvation which was increased. These variations were explained by the amount of lipid. Variation in desiccation resistance was not explained by the amount of water. As a function of gravity, no or slight differences were observed for the studied stresses. The resistance to heat of young flies increased with the gravity level. This resistance was not explained by a decreased locomotor activity of HG-living flies during heat stress, nor by the water and lipid contents.

Aging↗
PubMedDate not supplied

An age-dependent sensitivity of the roll-induced vestibuloocular reflex to hypergravity exposure of several days in an amphibian (Xenopus laevis).

In tadpoles of the Southern Clawed Toad (Xenopus laevis), the effects of an exposure to hypergravity of several days duration on the development of the roll-induced static vestibuloocular reflex (rVOR) were investigated. Special attention was given to the onset of the 9 or 12 days lasting 3G-period during early life. First recordings of the rVOR characteristics for complete 360 degrees rolls of the tadpoles were performed 24 hrs after the end of the 3G-period. The rVOR peak-to-peak amplitudes as well as the VOR-gain for a roll angle of 15 degrees from 3G-and 1G-samples recorded at the 2nd and 3rd day after 3G-termination agreed for the youngest group, but were reduced by approx. 30% in the older tadpoles. Long-term observations lasting up to 8 weeks after termination of the 3G-period, demonstrated (i) an early retardation of the development, and (ii) a developmental acceleration in all groups so that after 2 weeks in the stage 6/9- and 33/36-samples and after 8 weeks in the stage 45-tadpoles, the rVOR-amplitude as well as the rVOR-gain for a 15 degrees roll were at the same level in both the 3G- and the 1G-samples. The results support the existence of a sensitive period for the rVOR development, and additionally demonstrate the importance of the period of the first appearance of the rVOR for the development of adaptive properties of the underlying neuronal network. They also demonstrate the dominant efficiency of genetic programs in the functional development of the vestibular system. Methodological approaches are discussed which will be useful in the further description of the critical period. They include studies on the neuronogenesis and synaptic maturation within the vestibular pathways as well as on the fundamentals of buoyancy control during swimming. A modular but closed mini-system for experimental use is described which allows survival periods lasting many weeks and multiple types of treatments of developing aquatic animals in orbit, controlled automatically.

Adaptation, Physiological↗
PubMed1999

The asymmetrical growth of otoliths in fish is affected by hypergravity.

Size and asymmetry (size difference between the left and the right side) of inner ear otoliths of larval cichlid fish were determined after a long-term stay at moderate hypergravity conditions (3g; centrifuge), in the course of which the animals completed their ontogenetic development from hatch to freely swimming. Both the normal morphogenetic development as well as the timely onset and gain of performance of the swimming behaviour was not impaired by the experimental conditions. However, both utricular and saccular otoliths (lapilli and sagittae, respectively) were significantly smaller after hyper-g exposure as compared to parallely raised 1g control specimens. The asymmetry of sagittae was significantly increased in the experimental animals, whereas the respective asymmetry con-cerning lapilli was pronouncedly decreased in comparison to the 1g controls. These findings suggest, that the growth and the development of bilateral asymmetry of otoliths is guided by the environmental gravity vector.

Animals↗
PubMed2003

Differential impact of hypergravity on maturating innervation in vestibular epithelia during rat development.

Over the past decades, the new opportunity of space flights has revealed the importance of gravity as a mechanical constraint for terrestrial organisms as well as its influence on the somatosensory system. The lack of gravitational reference in orbital flight induces changes in equilibrium, with major modifications involving neuromorphological and physiological adaptations. However, few data have illustrated the putative effect of gravity on sensory vestibular epithelial development. We asked if gravity, the primary stimulus of utricles could act as an epigenetic factor. As sensorial deprivation linked to weightlessness is technically difficult, we used a ground-based centrifuge to increase the gravitational vector, in order to hyperstimulate the vestibule. In this study, 3 days after mating, pregnant females were submitted to hypergravity, 2 g (HG). Their embryos were raised, born and postnatally developed under HG. The establishment of connections between primary vestibular afferent neurons and hair cells in the utricle of these young rats was followed from birth to postnatal day 6 (PN6) and compared to embryos developed in normogravity (NG): Immunocytochemistry for neurofilaments and microvesicles revealed the differential effects of gravity on the late neuritogenic and synaptogenic processes in utricles. Taking type I hair cell innervation as a criterion of maturation, we found that primary afferent fibres reached the vestibular epithelium and enveloped hair cells in the same way, both under NG and HG. Thus, this phenomenon of leading growth cones to their epithelial target appears to be dependent on intrinsic genetic properties and not on an external stimulus. In contrast, the maturation of connection processes between type 1 hair cells and the afferent calyx, concerning specifically the microvesicles at their apex, was delayed under HG. Therefore, gravity appears to be an epigenetic factor influencing the late maturation of utricles. These differential effects of altered gravity on the development of the vestibular epithelium are discussed.

Animals↗