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PubMedDate not supplied

[Alterations of nucleolar DNA localization caused by simulated microgravity].

The functions of the nucleolus responsible for the biosynthesis of ribosomes in altered gravity are still unclear. The location of nucleolar DNA both in control and simulated microgravity has been investigated using fluorescent and immunogold cytochemistry. We have determined the redistribution of rDNA in the nucleolar components accompanied by their ultrastructure changes. According to this the lowering of rDNA transcription level under simulated microgravity was supposed.

Cell Nucleolus↗
PubMedDate not supplied

[Structural changes of chloroplasts and galactolipid contents in Chlorella cells during clinorotation].

Research of chloroplast ultrastructure in Chlorella cells grown during long-term period under clinorotation has been carried out. Different changes of the chloroplast structure, concerning both the amount of starch grains and stroma electron density as well as membrane system have been revealed. Occurrence of more significant bends of the thylakoids compared to the control and more loose arrangement of the thylakoids in a bunch were noted. The most significant changes were observed in a membrane system, in particular, appearance of the non-uniform expansions of the inter- and intrathylakoid spaces in Chlorella chloroplasts. Taking into account the role of galactolipids as important components of the photosynthetic membranes, the content of general galactolipids, monogalactosyldiacylglycerol and digalactosyldiacylglicerol in Chlorella cells was determined. It was assumed that statistically significant increase of the galactolipid content, especially of MDG, can probably be one of the reasons of membrane system reorganizations in Chlorella cells under altered gravity.

Chlorella↗
PubMedDate not supplied

[Status of the lipid peroxidation system in the tissues of rats following a 7-day flight on the Kosmos-1667 biosatellite].

Rats flown for 7 days on Cosmos-1667 were for the first time used to measure antioxidative enzymes (superoxide dismutase, glutathione peroxidase, glutathione reductase, catalase), lipid peroxidation products (diene conjugates, malonic dialdehyde, Schiff bases) and tocopherol. Enhanced lipid peroxidation in the heart was completely compensated by activation of antioxidative enzymes. The content of all lipid peroxidation products measured in the liver increased; this was accompanied by a decrease of glutathione peroxidase and an increase of superoxide dismutase activities. It is suggested that lipid peroxidation was activated in response to altered gravity.

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

A spaceflight study of synaptic plasticity in adult rat vestibular maculas.

Behavioral signs of vestibular perturbation in altered gravity have not been well correlated with structural modifications in neurovestibular centers. This ultrastructural research investigated synaptic plasticity in hair cells of adult rat utricular maculas exposed to microgravity for nine days on a space shuttle. The hypothesis was that synaptic plasticity would be more evident in type II hair cells because they are part of a distributed modifying macular circuitry. All rats were shared with other investigators and were subjected to treatments unrelated to this experiment. Maculas were obtained from flight and control rats after shuttle return (R + 0) and nine days post-flight (R + 9). R + 9 rats had chromodacryorrhea, a sign of acute stress. Tissues were prepared for ultrastructural study by conventional methods. Ribbon synapses were counted in fifty serial sections from medial utricular macular regions of three rats of each flight and control group. Counts in fifty additional consecutive sections from one sample in each group established method reliability. All synapses were photographed and located to specific cells on mosaics of entire sections. Pooled data were analyzed statistically. Flown rats showed abnormal posture and movement at R + 0. They had statistically significant increases in total ribbon synapses and in sphere-like ribbons in both kinds of hair cells; in type II cells, pairs of synapses nearly doubled and clusters of 3 to 6 synapses increased twelve-fold. At R + 9, behavioral signs were normal. However, synapse counts remained high in both kinds of hair cells of flight maculas and were elevated in control type II cells. Only counts in type I cells showed statistically significant differences at R + 9. High synaptic counts at R + 9 may have resulted from stress due to experimental treatments. The results nevertheless demonstrate that adult maculas retain the potential for synaptic plasticity. Type II cells exhibited more synaptic plasticity, but space flight induced synaptic plasticity in type I cells.

Acoustic Maculae↗
PubMed1980

Effects of radiographic contrast media on results of urinalysis, with emphasis on alteration in specific gravity.

The effect of radiographic contrast medium on the urine specific gravity of ten clinically normal dogs was evaluated. Urinary excretion of different dosages of intravenously administered triiodinated contrast medium caused significant alterations of urine specific gravity. The magnitude of change was related primarily to preinjection urine specific gravity values rather than dosage of contrast medium. In general, preinjection urine specific gravities < 1.040 were increased 15 minutes after injection of contrast material, whereas preinjection urine specific gravities > 1.040 were decreased 15 minutes after injection of contrast medium. A linear relationship was identified between the concentration of radiographic contrast medium in either distilled water or urine and the specific gravity of these mixtures. This simulated the effects of radiologic contrast medium on urine specific gravity when used for retrograde urethrocystography. Results of the investigation indicated that urinary excretion of radiographic contrast media significantly alters urine specific gravity values in normal dogs and renders postinjection urine samples unsuitable for diagnostic evaluation of renal tubular concentrating capacity. In addition, previously reported errors in urine protein, glucose, and sediment evaluations attributed to radiographic contrast media were reviewed.

Animals↗
PubMed1999

ARG1 (altered response to gravity) encodes a DnaJ-like protein that potentially interacts with the cytoskeleton.

Gravitropism allows plant organs to direct their growth at a specific angle from the gravity vector, promoting upward growth for shoots and downward growth for roots. Little is known about the mechanisms underlying gravitropic signal transduction. We found that mutations in the ARG1 locus of Arabidopsis thaliana alter root and hypocotyl gravitropism without affecting phototropism, root growth responses to phytohormones or inhibitors of auxin transport, or starch accumulation. The positional cloning of ARG1 revealed a DnaJ-like protein containing a coiled-coil region homologous to coiled coils found in cytoskeleton-interacting proteins. These data suggest that ARG1 participates in a gravity-signaling process involving the cytoskeleton. A combination of Northern blot studies and analysis of ARG1-GUS fusion-reporter expression in transgenic plants demonstrated that ARG1 is expressed in all organs. Ubiquitous ARG1 expression in Arabidopsis and the identification of an ortholog in Caenorhabditis elegans suggest that ARG1 is involved in other essential processes.

Amino Acid Sequence↗
PubMed2001

Genetic and chemical reductions in protein phosphatase activity alter auxin transport, gravity response, and lateral root growth.

Auxin transport is required for important growth and developmental processes in plants, including gravity response and lateral root growth. Several lines of evidence suggest that reversible protein phosphorylation regulates auxin transport. Arabidopsis rcn1 mutant seedlings exhibit reduced protein phosphatase 2A activity and defects in differential cell elongation. Here we report that reduced phosphatase activity alters auxin transport and dependent physiological processes in the seedling root. Root basipetal transport was increased in rcn1 or phosphatase inhibitor-treated seedlings but showed normal sensitivity to the auxin transport inhibitor naphthylphthalamic acid (NPA). Phosphatase inhibition reduced root gravity response and delayed the establishment of differential auxin-induced gene expression across a gravity-stimulated root tip. An NPA treatment that reduced basipetal transport in rcn1 and cantharidin-treated wild-type plants also restored a normal gravity response and asymmetric auxin-induced gene expression, indicating that increased basipetal auxin transport impedes gravitropism. Increased auxin transport in rcn1 or phosphatase inhibitor-treated seedlings did not require the AGR1/EIR1/PIN2/WAV6 or AUX1 gene products. In contrast to basipetal transport, root acropetal transport was normal in phosphatase-inhibited seedlings in the absence of NPA, although it showed reduced NPA sensitivity. Lateral root growth also exhibited reduced NPA sensitivity in rcn1 seedlings, consistent with acropetal transport controlling lateral root growth. These results support the role of protein phosphorylation in regulating auxin transport and suggest that the acropetal and basipetal auxin transport streams are differentially regulated.

Arabidopsis↗
PubMed1997

Monitoring acute whole-body fluid redistribution by changes in leg and neck volumes.

BACKGROUND: Acute fluid shifts initiate chronic cardiovascular acclimation to altered posture or gravity. HYPOTHESIS: We hypothesized that neck volume increases with acute tilt from vertical to horizontal and head-down positions, and that neck volume correlates negatively with leg volume during tilting. METHODS: Strain gauges measured changes in calf and neck volumes in 9 subjects during the following tilt table protocol: 90 degrees (upright control), 54 degrees, 30 degrees, 12 degrees, 0 degree (horizontal supine), -6 degrees (head-down tilt), -12 degrees, -6 degrees, 0 degree, 12 degrees, 30 degrees, 54 degrees, and 90 degrees. Each position was held for 30 s. RESULTS: Tilting from 90 degrees upright to 0 degree supine increased neck volume 3.09 +/- 0.37% (mean +/- SE); neck volume increased further above upright control to 4.26 +/- 0.39% at -12 degrees head-down tilt. In the calf, tilting produced significant volume decrements of 1.66 +/- 0.36% below 90 degrees control at 0 degree supine, and 2.03 +/- 0.50% below control at -12 degrees tilt. Neck volume elevation consistently exceeded the absolute magnitude of calf volume reduction at a given tilt angle by a factor of about 1.5, and the two were linearly correlated (r2 = 0.60). CONCLUSIONS: Responses of body segment volumes to tilt were practically instantaneous, indicating that venous blood volume translocation accounted for the changes. We conclude that leg and neck volume changes provide a convenient, non-invasive, and sensitive means of assessing acute regional fluid shifts in humans.

Adult↗
PubMed1991

Positional nystagmus due to alteration of the specific gravity in the labyrinth.

Horizontal positional nystagmus having characteristics similar to ice water caloric nystagmus was induced by injecting heavy water into the rabbit middle ear cavity or facial nerve through the stylomastoid foramen. Furthermore, with general administration of glycerol to normal subjects, horizontal positional nystagmus as with general administration of heavy water to experimental animals was observed. It is possible that alteration of the specific gravity arising from infiltration of heavy water or glycerol into the labyrinth accounts for the manifestation of positional nystagmus. These studies on positional nystagmus may be one of the means to elucidate the mechanism of caloric nystagmus and to examine the function of the human blood-labyrinth-barrier.

Adolescent↗
PubMed1986

Amphibian egg cytoplasm response to altered g-forces and gravity orientation.

Elucidation of dorsal/ventral polarity and primary embryonic axis development in amphibian embryos requires an understanding of cytoplasmic rearrangements in fertile eggs at the biophysical, physiological, and biochemical levels. Evidence is presented that amphibian egg cytoplasmic components are compartmentalized. The effects of altered orientation to the gravitational vector (i.e., egg inversion) and alterations in gravity force ranging from hypergravity (centrifugation) to simulated microgravity (i.e., horizontal clinostat rotation) on cytoplasmic compartment rearrangements are reviewed. The behavior of yolk compartments as well as a newly defined (with monoclonal antibody) non-yolk cytoplasmic compartment, in inverted eggs and in eggs rotated on horizontal clinostats at their buoyant density, is discussed.

Animals↗
PubMed2002

The effect of gravity on coral morphology.

Coral morphological variability reflects either genetic differences or environmentally induced phenotypic plasticity. We present two coral species that sense gravity and accordingly alter their morphology, as characterized by their slenderness (height to diameter) ratio (SR). We experimentally altered the direction (and intensity) of the gravitational resultant force acting along or perpendicular to the main body axis of coral polyps. We also manipulated light direction, in order to uncouple gravity and light effects on coral development. In the experiments, vertically growing polyps had significantly higher SR than their horizontal siblings even when grown in a centrifuge (experiencing different resultant gravitational forces in proximal and distal positions). Lowest SR was in horizontal side-illuminated polyps, and highest in vertical top-illuminated polyps. Adult colonies in situ showed the same pattern. Gravitational intensity also affected polyp growth form. However, polyp volume, dry skeleton weight and density in the various centrifuge positions, and in aquaria experiments, did not differ significantly. This reflects the coral's ability to sense altered gravity direction and intensity, and to react by changing the development pattern of their body morphology, but not the amount of skeleton deposited.

Animals↗
PubMed1999

G-factor as a tool in basic research: mechanisms of orthostatic tolerance.

The inability to tolerate upright standing posture due to development of orthostatic hypotension is a clinical problem experienced by more than 500,000 people in the United States. In addition, orthostatic intolerance is an operational problem since as many as 25 to 64 percent of the crew members from U.S. space shuttle flights have been reported to experience presyncopal incidents during postflight stand tests. Last year alone, more than 10,000 cases of unexplained syncope were reported in active duty personnel in all U.S. military services. Many clinical investigations have focused on measurements of physiological functions in patients with orthostatic instability in an effort to identify possible mechanisms that underlie the problem. Although this approach has provided important insight into mechanisms associated with syncope, identification of causal relationships are limited by pre-existing pathologic conditions. Causal relationships can be better defined when physiological mechanisms that underlie blood pressure regulation are altered in healthy subjects by increasing or decreasing their gravity environment (so-called "G-factor" approach) and subsequent changes in orthostatic tolerance are induced. The purpose of this paper is to review data on physiological functions measured from healthy human subjects who have undergone exposure to various levels of low or high gravity in an effort to assess our understanding about mechanisms of orthostatic tolerance. Specifically, results from human subjects exposed to bedrest, spaceflight, and high sustained acceleration will be used to provide insight into the plasticity of mechanisms underlying adaptations of blood pressure regulation orthostatic performance.

Baroreflex↗
PubMed1979

Computed tomography in pulmonary sarcoidosis.

A group of 34 proven cases of pulmonary sarcoidosis was investigated by computed tomography (CT) to determine whether CT provided any information beyond that obtained from conventional chest films. Computed tomography disclosed a surprisingly high prevalence of minor pleural changes in sarcoidosis, including two patients with small pleural effusions. Unsuspected bullae and isolated "granulomatous" nodules were additionally demonstrated. Increases in lung density and alterations in gravity dependent vascular perfusion were assessed; these may reflect alterations in the vascular bed, and the increased density is possibly due to diffuse invasion of the lung not recognizable by conventional chest X-ray films. Tracheal compression was noted in one case and vertebral densities in three. Prominence of "small air spaces" was recorded in four patients; the nature of the pathology responsible for this finding is at present speculative. While not replacing conventional chest radiography, CT does make a definite contribution to the assessment of pulmonary sarcoidosis.

Adolescent↗
PubMed1990

Method for preservation of water content during prolonged storage of cerebral tissue.

We set out to determine whether prolonged freezing of samples of cerebral tissue would alter specific gravity measurements. Our goal was to devise a method to prevent tissue water evaporation during transportation and storage of human cerebral samples in order to allow accurate measurements of specific gravity and water content at a delayed time. Control cerebral samples from healthy and water-intoxicated anaesthetized adult mice were immediately immersed in a gravimetric column for fresh specific gravity measurements. Cerebral samples from the same animals were also preserved by rapid freezing in liquid nitrogen, followed by deep-freeze storage at -80 degrees C for up to 7 days. The mean specific gravity and standard error of 65 non-oedematous and 18 oedematous fresh cerebral samples was 1,0483 +/- 2 x 10(-4) and 1,0433 +/- 5 x 10(-4), respectively. Freezing for 1 h to 7 days resulted in no significant alteration of specific gravity for 109 non-oedematous and 27 oedematous samples (P greater than 0.05). We describe a rapid freezing technique that is practical for transportation and storage of experimental or surgical cerebral specimens. Our findings indicate that storage of cerebral samples in liquid nitrogen, with or without subsequent deep-freezing, preserves water content of normal and oedematous cerebral tissue, thereby allowing accurate measurements at a later time.

Body Water↗
PubMed2000

Gravity and thermoregulation: metabolic changes and circadian rhythms.

Gravity appears to alter thermoregulation through changes in both the regulated level of body temperature and the rhythmic organization of temperature regulation. Gravity has been hypothesized to have an associated metabolic cost. Increased resting energy expenditure and dietary intake have been observed in animals during centrifuge experiments at hypergravity. Thus far, only animals have shown a corresponding reduction in metabolism in microgravity. Altered heat loss has been proposed as a response to altered gravitational environments, but remains documented only as changes in skin temperature. Changes in circadian timing, including the body temperature rhythm, have been shown in both hypergravity and microgravity, and probably contribute to alterations in sleep and performance. Changes in body temperature regulation may result from circadian disturbance, from the direct or indirect actions of gravity on the regulated temperature, or from changes in thermoregulatory effectors (heat production and heat loss) due to altered gravitational load and convective changes. To date, however, we have little data on the underlying thermoregulatory changes in altered gravity, and thus the precise mechanisms by which gravity alters temperature regulation remain largely unknown.

Animals↗