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At least 163 records · Page 9Linked to original sources

PubMed2001

Functional regeneration of a gravity sensory system during development in an insect (Gryllus bimaculatus).

The efficiency of the regenerated cercal gravity sensory system was investigated in adult crickets (Gryllus bimaculatus). Regeneration was induced by amputations of cerci during different periods of development. Numbers of gravity-sensitive (clavate) sensilla on regenerated and intact cerci were identical if amputations were performed up to four times before the 6th instar. If older instars were included, regenerated cerci had fewer clavate sensilla than intact cerci. Compensatory head responses induced by stimulation of either regenerated or intact gravity sense organs were identical if cerci were amputated up to three times. However, four or more amputations caused weaker responses in the regenerated than in the intact sense organs. These experiments make the existence of a sensitive period during development of the cercal gravity sensory system unlikely. They support the postulation that functional regeneration is influenced by neuroplastic processes and proprioceptive gravity sensitive systems.

Aging↗

PubMed1987

An electric current associated with gravity sensing in maize roots.

The study of gravisensing would be greatly enhanced if physiological events associated with gravity sensing could be detected separately from subsequent growth processes. This report presents a means to discriminate sensing from the growth processes. By using a vibrating probe, we have found an electric current generated by the gravity sensing region of the root cap of maize (Zea mays cv Merit) in response to gravistimulation. On the upper surface of the root cap, the change from the endogenous current has a density of 0.55 microampere per square centimeter away from gravity. The onset of the current shift has a characteristic of lag of three to four minutes after gravistimulation, which corresponds to the presentation time for gravity sensing in this tissue. A description of the current provides some information about the sensing mechanism, as well as being a valuable means to detect gravity sensing independently of differential growth.

Electric Conductivity↗

PubMed1988

Indomethacin and dexamethasone treatment in experimental neoplastic spinal cord compression: Part 1. Effect on water content and specific gravity.

Water content and specific gravity were measured in the cervical, high thoracic, thoracic, and lumbar segments in an experimental model of neoplastic epidural spinal cord compression in rats harboring a thoracolumbar tumor. Increased content of water was observed only in the compressed lumbar cord segments of paralyzed rats (P less than 0.04). A progressive increase in specific gravity values of the compressed segments accompanied the increasing severity of neurological dysfunction (P less than 0.003 in paraplegic rats). Electron microscopy of the compressed cord revealed enlarged interstitial spaces, myelin breakdown, and extravasated blood cellular elements. Treatment with dexamethasone (10 mg/kg q 12 hr x 3) failed to reduce the increased content of water, but corrected specific gravity changes. Treatment with indomethacin (10 mg/kg q 12 hr x 3) reduced both elevated water content and specific gravity values back to normal levels. In untreated animals, the interval between the first neurological sign (limp tail) and paraplegia was 2.8 +/- 0.34 days (mean +/- SE). Treatment with dexamethasone lengthened this period by 28.6% (P less than 0.05); treatment with indomethacin lengthened it by 66.4% (P less than 0.005). We conclude that, because the specific gravity measurements in this model reflect complex pathophysiological processes, their translation into water content values is not advisable. Pharmacological intervention with indomethacin compares favorably with dexamethasone in reduction of spinal cord edema and in delaying the onset of paraplegia.

Animals↗

PubMed1989

Influence of specific gravity and food on movement of granules in the gastrointestinal tract of rats.

The suitability of rats as an animal model for estimating the bioavailability of controlled-release granules in humans was investigated. Non-disintegrating granules (diameter of 0.8 mm; specific gravity of 0.9-1.85) were used as a model preparation. Twenty granules were administered to fed rats, fasted rats and rats given soft food, and the number of granules remaining in the gastrointestinal tract was counted at suitable intervals. Granules with a specific gravity of 1.25 administered to fasted rats were rapidly emptied from the stomach with a 50% gastric emptying time of 1 h as compared with granules with a specific gravity of less than 1.0 or with a high specific gravity such as 1.85. The presence of food in the stomach reduced the emptying rate of granules. The mean transit time of granules through the small intestinal tract was not influenced by the specific gravity or the presence of food. The mean transit time was about 3 h. It was found that the transit profile of granules through the gastrointestinal tract in rats was similar to that of granules in humans. Accordingly, it is possible to use rats at the preformulation stage for estimating the bioavailability of controlled-release granules in humans.

Animals↗

PubMed1996

Development of centrifugal phytotron to study the gravity effect on vegetable plant growth.

The present Spacetron is used to cultivate plants over a long term by controlling environment condition. The cultivation drum was rotated in perpendicular direction creating fluctuation in gravity. Centrifugal force plus 1 G ground gravity, are distributed unevenly over the cultivation drum. This fluctuation effect on plant growth was not clear. In the modified Spacetron the cultivation drum rotates horizontally whereas the plant stage rotated in the perpendicular direction. To find the basic information for design of centrifugal phytotron the two axes Spacetron Junior (clinostat) was developed to formulate the micro and hypergravity environment. It would be used to study the effect on a plant growth process of different gravity conditions. In order to produce the different values of gravity, the clinostat's axis was rotated with a stepping motor at different angular velocity. The axis rotated at 5.2 revolutions per minute (rpm) to create a centrifugal force equivalent to 0.01 G and the plant stage was rotated at 5.2 rpm. The chlorophyll value is higher in the plants under microgravity condition of 0.01 G whereas the fresh weight and dry weight are higher in the plants under control condition of 1 G earth gravity. The result of this study showed that the plant growth was affected by microgravity along with other known factors such as vibration and unknown factors.

Biomass↗

PubMed2003

[Gravity resistance, another graviresponse in plants--function of anti-gravitational polysaccharides].

The involvement of anti-gravitational polysaccharides in gravity resistance, one of two major gravity responses in plants, was discussed. In dicotyledons, xyloglucans are the only cell wall polysaccharides, whose level, molecular size, and metabolic turnover were modified under both hypergravity and microgravity conditions, suggesting that xyloglucans act as anti-gravitational polysaccharides. In monocotyledonous Poaceae, (1-->3),(1-->4)-beta glucans, instead of xyloglucans, were shown to play a role as anti-gravitational polysaccharides. These polysaccharides are also involved in plant responses to other environmental factors, such as light and temperature, and to some phytohormones, such as auxin and ethylene. Thus, the type of anti-gravitational polysaccharides is different between dicotyledons and Poaceae, but such polysaccharides are universally involved in plant responses to environmental and hormonal signals. In gravity resistance, the gravity signal may be received by the plasma membrane mechanoreceptors, transformed and transduced within each cell, and then may modify the processes of synthesis and secretion of the anti-gravitational polysaccharides and the cell wall enzymes responsible for their degradation, as well as the apoplastic pH, leading to the cell wall reinforcement. A series of events inducing gravity resistance are quite independent of those leading to gravitropism.

Cell Wall↗

PubMed2001

Estimation of the probability for exceeding thresholds of urine specific gravity and plasma concentration of furosemide at various intervals after intravenous administration of furosemide in horses.

OBJECTIVE: To estimate the probability of concurrently exceeding thresholds for plasma concentration of furosemide and urine specific gravity after IV administration of furosemide in horses. ANIMALS: 12 mature healthy Thoroughbred (n = 6) or Quarter Horse (6) mares. PROCEDURE: Venous blood was collected from each horse prior to and 0.25, 0.5, 0.75, 1, 2, 3, 4, 4.5, 5, and 6 hours after IV administration of 250 mg (first experiment) or 500 mg (second experiment) of furosemide. Urine was collected hourly between 1 and 6 hours after administration of furosemide at both doses. Concentrations of furosemide were determined by use of an ELISA. Concentration of furosemide and urine specific gravity was modeled as a function of time, accounting for inter- and intrahorse variabilities. On the basis of pharmacokinetic and specific gravity data, the probability of exceeding a concentration of 100 ng of furosemide/ml as a function of time was determined, using a semiparametric smooth functional averaging method. A bootstrap approach was used to assess the inherent variation in this estimated probability. RESULTS: The estimated probability of exceeding the threshold of 100 ng of furosemide/ml and urine specific gravity < 1.012 was approximately 0% between 4.0 and 5.5 hours after IV administration of 250 mg of furosemide/horse, and ranged from 0 to 1% between 4 and 5.5 hours after IV administration of 500 mg of furosemide/horse. The probability of a horse being falsely identified as in violation of regulatory concentrations was inversely associated with time. CONCLUSIONS AND CLINICAL RELEVANCE: Coupling plasma furosemide concentration with urine specific gravity testing will greatly reduce the chance that some horses are misclassified as being in violation of regulatory concentrations.

Animals↗

PubMed1998

Plant cells in vitro under altered gravity.

Establishing the role of gravity in plant requires information about how gravity regulates the metabolism of individual cells. Plant cells and tissues in vitro are valuable models for such purpose. Disrupted intercellular relations in such models have allowed to elucidate both the gravity role in non-specialised to gravity plant cells and the correlative relation role of an intact plant organism. The data obtained from non-numerous space and clinostat experiments with plant cells in vitro have demonstrated that their metabolism is sensitive to g-environment. The most experiments have shown a decrease in the biomass production and cell proliferation of spaceflight samples compared with ground controls, although there is study reporting of increased biomass production in an anise suspension culture and D. carota crown gall tissue culture. At the same time, results of experiments with single carrot cells and tomato callus culture demonstrated similarities in differentiation process in microgravity and in ground controls. Noted ultrastructural arrangement in cells, especially mitochondria and plastids, have been related to altered energy load and functions of organelles in microgravity, as well as changes in the lipid peroxidation and the content of malonic dyaldehyde in a haplopappus tissue culture under altered gravity supposed with modification of membrane structural-functional state. This article focuses on growth aspects of the cultured cells in microgravity and under clinostat conditions and considers those aspects that require further analysis.

Asteraceae↗

PubMed2002

Plants and gravity. Special issue.

This issue of the Journal of Plant Growth Regulation explores the effects of gravity on plant growth and development from several perspectives. Most of the review papers consider plants and gravity from the viewpoint of ground-based laboratory research, and several papers consider gravitropism, the directed growth in response to gravity, in some detail. However, another approach to study the effects of gravity on plant is to effectively remove the force due to gravity. A very dramatic way to accomplish this goal is through the free-fall conditions achieved by spacecraft in low Earth orbit, so some of the authors have reviewed recent advances in spaceflight research with plant systems.

Gravitation↗

PubMedDate not supplied

Sensorimotor aspects of high-speed artificial gravity: II. The effect of head position on illusory self motion.

The effects of cross-coupled stimuli on the semicircular canals are shown to be influenced by the position of the subject's head with respect to gravity and the axis of rotation, but not by the subject's head position relative to the trunk. Seventeen healthy subjects made head yaw movements out of the horizontal plane while lying on a horizontal platform (MIT short radius centrifuge) rotating at 23 rpm about an earth-vertical axis. The subjects reported the magnitude and duration of the illusory pitch or roll sensations elicited by the cross-coupled rotational stimuli acting on the semicircular canals. The results suggest an influence of head position relative to gravity. The magnitude estimation is higher and the sensation decays more slowly when the head's final position is toward nose-up (gravity in the subject's head x-z-plane) compared to when the head is turned toward the side (gravity in the subject's head y-z-plane). The results are discussed with respect to artificial gravity in space and the possible role of pre-adaptation to cross-coupled angular accelerations on earth.

Adolescent↗

PubMed1982

Determination of the specific gravity of certain helminth eggs using sucrose density gradient centrifugation.

The specific gravities of ten species of helminth eggs were determined using sucrose density gradient centrifugation. Fecal or egg concentrate was layered over a 3 to 54% sucrose density gradient. The gradient was then centrifuged at 800 g for 20 min, allowing 5 min for acceleration and 5 for deceleration. Bands formed were identified and measured. Refractive index was measured at the middle of narrow bands, or at the level at which the concentration of eggs was highest, in the case of wide bands or when no band was formed. The specific gravity corresponding to this refractive index was taken as the specific gravity of the eggs. The ten species of helminth eggs studied and specific gravities measured on three or four gradients were: Toxascaris leonina, 1.0559; Ancylostoma caninum, 1.0559; Toxocara canis, 1.0900; Parascaris equorum, 1.0969; Toxocara cati (embryonated), 1.1005; Ascaris suum, 1.1299; Trichuris suis, 1.1299; Trichuris vulpis, 1.1453; Taenia sp., 1.2251; and Physaloptera sp., 1.2376. These determinations agree with or approximate those of previous workers. The specific gravities of P. equorum, T. suis, Taenia sp., and Physaloptera sp., are reported for the first time.

Animals↗

PubMed2000

Effect of different gravity environments on DNA fragmentation and cell death in Kalanchoe leaves.

Different gravity environments have been shown to significantly affect leaf-plantlet formation and asexual reproduction in Kalanchoë daigremontiana Ham. and Perr. In the present work, we investigated the effect of gravity at tissue and cell levels. Leaves and leaf-plantlets were cultured for different periods of time (min to 15 d) in different levels of gravity stimulation: simulated hypogravity (1 rpm clinostats; 2 x 10(-4) g), 1 g (control) and hypergravity (centrifugation; 20 and 150 g). Both simulated hypogravity and hypergravity affected cell death (apoptosis) in this species, and variations in the number of cells showing DNA fragmentation directly correlated with nitric oxide (NO) formation. Apoptosis in leaves was more common as gravity increased. Apoptotic cells were localized in the epidermis, mainly guard cells, in leaf parenchyma, and in tracheary elements undergoing terminal differentiation. Exposures to acute hypergravity (up to 60 min) showed that chloroplast DNA fragmentation occurred prior to nuclear DNA fragmentation, marginalization of chromatin, nuclear condensation, and nuclear blebbing. Addition of sodium nitroprusside (NO donor) mimicked centrifugation. NO and DNA fragmentation decreased with N(G)-monomethyl-L-arginine (NO-synthase inhibitor). The variations in NO levels, nucleoid DNA fragmentation, and cell death show how chloroplasts, cells and leaves may respond (and adapt) to gravity changes.

Apoptosis↗

PubMed1999

The Dependence of the Apparent Contact Angles on Gravity.

We have studied theoretically the effect of gravity on the rough solid-liquid interface and have shown that its tension is enhanced by gravity when gas is adsorbed at it. As a result, the apparent contact angle on rough surfaces, which has been considered not to be influenced by gravity so far, can be raised by gravity. The calculated dependence of contact angles on gravity under the ordinary conditions of the sessile drop method is large enough to detect by experiment. The observed asymmetrical deviations from Wenzel's contact angle caused by the gas adsorption at the solid-liquid interface and by the liquid adsorption at the solid-gas interface are explained in terms of this gravitational effect. Copyright 1999 Academic Press.

Journal Article↗

PubMed1996

Grip-force responses to unanticipated object loading: load direction reveals body- and gravity-referenced intrinsic task variables.

Humans preserve grasp stability by automatically regulating the grip forces when loads are applied tangentially to the grip surfaces of a manipulandum held in a precision grip. The effects of the direction of the load force in relation to the palm, trunk, and gravity were investigated in blindfolded subjects. Controlled, tangential load-forces were delivered in an unpredictable manner to the grip surface in contact with the index finger either in the distal and proximal directions (away from and toward the palm) or in the ulnar and radial directions (transverse to the palm). The hand was oriented in: (1) a standard position, with the forearm extended horizontally and anteriorly in intermediate pronosupination; (2) an inverted position, reversing the direction of radial and ulnar loads in relation to gravity; and (3) a horizontally rotated position, in which distal loads were directed toward the trunk. The amplitude of the grip-force responses (perpendicular to the grip surface) varied with the direction of load in a manner reflecting frictional anisotropies at the digit-object interface; that is, the subjects automatically scaled the grip responses to provide similar safety margins against frictional slips. For all hand positions, the time from onset of load increase to start of the grip-force increase was shorter for distal loads, which tended to pull the object out of the hand, than for proximal loads. Furthermore, this latency was shorter for loads in the direction of gravity, regardless of hand position. Thus, shorter latencies were observed when frictional forces alone opposed the load, while longer latencies occurred when gravity also opposed the load or when the more proximal parts of the digits and palm were positioned in the path of the load. These latency effects were due to different processing delays in the central nervous system and may reflect the preparation of a default response in certain critical directions. The response to loads in other directions would incur delays required to implement a new frictional scaling and a different muscle activation pattern to counteract the load forces. We conclude that load direction, referenced to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp on objects subjected to unpredictable load forces. In contrast, the grip-force safety margin against frictional slips did not vary systematically with respect to these task variables. Instead, the magnitude of the grip-force responses varied across load direction and hand orientation according to frictional differences providing similar safety margins supporting grasp stability.

Adult↗

PubMed1995

Detection of gravity-induced polarity of cytoplasmic streaming in Chara.

Gravity induces a polarity of cytoplasmic streaming in vertically-oriented internodal cells of characean algae. The motive force that powers cytoplasmic streaming is generated at the ectoplasmic/endoplasmic interface. The velocity of streaming, which is about 100 micrometers/s at this interface, decreases with distance from the interface on either side of the cell to 0 micrometers/s near the middle. Therefore, when discussing streaming velocity it is necessary to specify the tangential plane through the cell in which streaming is being measured. This is easily done with a moderate resolution light microscope (which has a lateral resolution of 0.6 micrometers and a depth of field of 1.4 micrometers), but is obscured when using any low resolution technique, such as low magnification light microscopy or laser Doppler spectroscopy. In addition, the effect of gravity on the polarity of cytoplasmic streaming declines with increasing physiological age of isolated cells. Using a classical mechanical analysis, we show that the effect of gravity on the polarity of cytoplasmic streaming cannot result from the effect of gravity acting directly on individual cytoplasmic particles. We suggest that gravity may best be perceived by the entire cell at the plasma membrane-extracellular matrix junction.

Cell Polarity↗

PubMed2005

A quantitative computed tomography assessment of brain weight, volume, and specific gravity in severe head trauma.

BACKGROUND: Computed tomography DICOM images analysis allows a quantitative measurement of organ weight, volume and specific gravity in humans. METHODS: The brain weight, volume and specific gravity of 15 traumatic brain-injury patients (3+/-2 days after trauma) were computed using a specially designed software (BrainView). Data were compared with those obtained from 15 healthy subjects paired for age and overall intracranial volume. RESULTS: Hemisphere weight were 91 g higher in patients than in controls (1167+/-101 vs 1076+/-112 g; p<0.05). Specific gravity of hemispheres (1.0367+/-0.0017 vs 1.0335+/-0.0012 g/ml; p<0.001), brainstem (1.0302+/-0.0016 vs 1.0277+/-0.0015 g/ml; p<0.001) and cerebellum (1.0396+/-0.0020 vs 1.0375+/-0.0015 g/ml; p<0.05) was significantly higher in traumatic brain injury (TBI) patients than in controls (all p<0.0001 without interaction). This increase in specific gravity was evenly distributed between the hemispheres, the brainstem and the cerebellum, and the grey and white matter. It was more pronounced in the rostral than in the caudal areas of the hemispheres. It was independent of the volume of brain contusion, of the mechanism of head injury, of natremia and of initial Glasgow coma score. CONCLUSION: Human TBI patients present a diffuse increase in specific gravity. This observation is in sharp opposition with the data derived from the experimental literature.

Adolescent↗

PubMed2000

Gravity-directed calcium current in germinating spores of Ceratopteris richardii.

Gravity directs the early polar development in single cells of Ceratopteris richardii Brogn. It acts over a limited period of time during which it irreversibly determines the axis of the spore cell's development. A self-referencing calcium selective electrode was utilized to record the net movement of calcium across the cell membrane at different positions around the periphery of the spore during the period in which gravity orients the polarity of the spore. A movement of calcium into the cell along the bottom and out of the cell along the top was detected. This movement was specific, polarized, and strongest in a direction that opposed the vector of gravity. Treatment with nifedipine, a calcium-channel blocker, diminished the calcium current and caused the cell to lose its responsiveness to the orienting influence of gravity. Results shown suggest that calcium plays a crucial role in the ability of a single cell to respond to gravity and in the subsequent establishment of its polarity.

Calcium↗

PubMed2000

Gravity-induced absorbance changes in Phycomyces: a novel method for detecting primary responses of gravitropism.

The negative gravitropism of the sporangiophores of Phycomyeces blakesleeanus Burgeff is elicited by different sensory inputs, which include flexure of the growing zone, buoyance of lipid globules and sedimentation of paracrystalline proteins, so-called octahedral crystals (C. Schimek et al., 1999a, Planta 210: 132-142). Gravity-induced absorbance changes (GIACs), which are associated with primary events of gravity sensing, were detected in the growing zones of sporangiophores. After placing sporangiophores horizontally, GIACs were detected after a latency of about 5 min, i.e. 15-25 min prior to gravitropic bending. The spectroscopic properties of the GIACs indicate that gravitropic stimulation could imply the reduction of cytochromes. The GIACs were spectrally distinct from light-induced absorbance changes (LIACs), showing that the primary responses of the light and gravity transduction chains are different. A dual stimulation with gravity and light generated GIAC-LIACs which were distinct from the absorbance changes occurring after the single stimuli and which indicate that light and gravity interact early in the respective transduction chains.

Cytochromes↗