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PubMed1975

Physiologic characteristics of vestibular first-order canal neurons in the cat. I. Response plane determination and resting discharge characteristics.

The response plane and resting rate characteristics of first-order, vestibular, semicircular canal neurons were studied in 67 cats under sodium pentobarbital anesthesia using single-unit recording techniques in the eighth nerve. Five hundred fifty-nine units were classified as to the canal they were associated with by employing an identification technique based on physiologic response patterns to brief, high-level (up to 250 degrees/S2) angular accelerations delivered in various head positions. All horizontal canal neurons had increased firing rates to ampullopetal and all vertical canal units to ampullofugal endolymph flow. The average observed roll and pitch null points for each canal were used to determine the average sensitivity vectors for the right horizontal, anterior, and posterior canals. These sensitivity vectors were at a variance of 4.6-10.2 degrees from those predicted by anatomical measurements (3). The mean resting discharge characteristics of 318 first-order neurons was 36.0 spikes/s (range 0.50-114 spikes/s). No significant difference was noted between horizontal and anterior canal neurons on horizontal and anterior canal neurons on the basis of resting rate. The resting rate of the posterior canal neuron population was significantly lower. The regularity of the resting discharge varied in all three canals and the average coefficient of variation was 0.238 for the population, with a range of 0.298-1.030. The population distribution of all resting-rate statistical parameters appeared to be unimodal, indicating that first-order canal neurons may not be broken into discrete populations on the basis of resting-rate characteristics. Of 47 adequately examined first-order canal neurons, 25 demonstrated a repeatable and predictable alteration in their resting discharge as their position to gravity was reoriented. This alteration was usually nonadapting and varied in magnitude according to the degree of tilt and original starting position. Of 25 canal gravity units, 4 had nearby units from the same canal which were unresponsive to gravity, suggesting the effect was due to a limited distortion of the crista or cupula rather than an overall displacement of the cupula.

Acceleration↗
PubMed2001

Changes in root cap pH are required for the gravity response of the Arabidopsis root.

Although the columella cells of the root cap have been identified as the site of gravity perception, the cellular events that mediate gravity signaling remain poorly understood. To determine if cytoplasmic and/or wall pH mediates the initial stages of root gravitropism, we combined a novel cell wall pH sensor (a cellulose binding domain peptide-Oregon green conjugate) and a cytoplasmic pH sensor (plants expressing pH-sensitive green fluorescent protein) to monitor pH dynamics throughout the graviresponding Arabidopsis root. The root cap apoplast acidified from pH 5.5 to 4.5 within 2 min of gravistimulation. Concomitantly, cytoplasmic pH increased in columella cells from 7.2 to 7.6 but was unchanged elsewhere in the root. These changes in cap pH preceded detectable tropic growth or growth-related pH changes in the elongation zone cell wall by 10 min. Altering the gravity-related columella cytoplasmic pH shift with caged protons delayed the gravitropic response. Together, these results suggest that alterations in root cap pH likely are involved in the initial events that mediate root gravity perception or signal transduction.

Arabidopsis↗
PubMed1994

Influence of gravity on the circadian timing system.

The circadian timing system (CTS) is responsible for daily temporal coordination of physiological and behavioral functions both internally and with the external environment. Experiments in altered gravitational environments have revealed changes in circadian rhythms of species ranging from fungi to primates. The altered gravitational environments examined included both the microgravity environment of spaceflight and hyperdynamic environments produced by centrifugation. Acute exposure to altered gravitational environments changed homeostatic parameters such as body temperature. These changes were time of day dependent. Exposure to gravitational alterations of relatively short duration produced changes in both the homeostatic level and the amplitude of circadian rhythms. Chronic exposure to a non-earth level of gravity resulted in changes in the period of the expressed rhythms as well as in the phase relationships between the rhythms and between the rhythms and the external environment. In addition, alterations in gravity appeared to act as a time cue for the CTS. Altered gravity also affected the sensitivity of the pacemaker to other aspects of the environment (i.e., light) and to shifts of time cues. Taken together, these studies lead to the conclusion that the CTS is indeed sensitive to gravity and its alterations. This finding has implications for both basic biology and space medicine.

Adaptation, Physiological↗
PubMed2001

Enhanced Hoffman-reflex in human soleus muscle during exposure to microgravity environment.

Responses of Hoffman-reflex in the soleus muscle to changes of gravity levels created by parabolic flight of a jet airplane were investigated in four healthy male subjects. The subjects maintained a sitting position with seat belts fastened, keeping the anterior ankle and posterior knee angles at approximately 135 degrees. The gravity levels were altered from 1- to 2-G, and then microgravity was created for approximately 20 s. The levels were recovered from 1.5- to 1-G during the descending phase. The time interval between the stimulation and either M- or H-wave was not influenced by the changes in gravity levels. The amplitude of the M-wave during hyper- and microgravity was identical to that obtained at 1-G. However, the H-wave amplitude was increased when the subjects were exposed to microgravity (approximately four times vs. 1-G level). The H/M ratio was also elevated during microgravity. Further, such a phenomenon was maintained throughout the 20 s of microgravity exposure. Hypergravity at 1.5- or 2-G had no effect on the H-wave amplitude. It is suggested that an acute exposure to microgravity increases the excitability of the soleus motor pool and the increased excitability is restored immediately when the gravity level is elevated.

Adult↗
PubMed1999

[The use of microfluorimetric analysis for the studies of the influence of changed gravity on isolated lymphocytes in the spleen of the mouse].

Effects of simulated changed gravity on isolated splenetic lymphocytes of mouse were evaluated with the microfluorimetic technique enabling observation of probe fluorescence in individual cells. It was stated that 5 and 60 min of clinostatting stimulated fluorochrome accumulation in cells whereas centrifugation, particularly for 60-minutes, decreased the ability of cells to accumulate fluorescein. Also, alteration of the gravity force had the opposite effect on the ability of cells to retain fluorescein. The most significant drain of the dye immediately after short hypogravity may be indicative of the functional lability of cells during clinostatting. However, as judged by slight changes in intracellular pH, metabolic and regulatory functions were not affected. Hypergravity for 15 min decreased intracellular pH. The increased period of centrifugation stabilized the parameter. Absence of changes in the proliferative activity in all the test exposures also backs up the conclusion that short-term changes in gravity do not produce any substantial shifts in the morphofunctional state of cells in vitro.

Animals↗
PubMed2004

Evidence for macular gravity receptor modulation of hypothalamic, limbic and autonomic nuclei.

Mice lacking normal vestibular gravity reception show altered homeostatic, circadian and autonomic responses to hypergravity (+G) exposure. Using c-Fos as a marker of neuronal activation, the current study identifies CNS nuclei that may be critical for initiating and integrating such responses to changes in vestibular signaling. This experiment utilized the mutant C57BL/6JEi-het mouse (het), which lacks macular otoconia and thus gravity receptor function. Following 2 h of 2G (2x Earth's gravity) exposure (via centrifugation) the neuronal responses of the het mice were compared with wildtype mice similarly exposed to 2G, as well as het and wildtype 1G controls. Wildtype mice exposed to 2G demonstrated robust c-Fos expression in multiple autonomic, hypothalamic and limbic nuclei, including: the lateral septum, bed nucleus of the stria terminalis, amygdala, paraventricular hypothalamus, dorsomedial hypothalamus, arcuate, suprachiasmatic hypothalamus, intergeniculate leaflet, dorsal raphe, parabrachial and locus coeruleus. The het mice exposed to 2G demonstrated little to null c-Fos expression in these nuclei with a few exceptions and, in general, a similar pattern of c-Fos to 1G controls. Data from this study further support the existence of a complex and extensive influence of the neurovestibular system on homeostatic, circadian and possibly autonomic regulatory systems.

Animals↗
PubMed1983

Research on the adaptation of skeletal muscle to hypogravity: past and future directions.

Our current understanding of hypogravity-induced atrophy of skeletal muscles is based primarily on studies comparing pre- and post-flight properties of muscles. Interpretations are necessarily qualified by the assumption that the stress of reentry and readjustment to terrestrial gravity do not alter the parameters being analyzed. The neuromuscular system is highly responsive to changes in functional demands and capable of rapid adaptation, making this assumption questionable. A reexamination of the changes in the connective tissue and synaptic terminals of soleus muscles from rats orbited in biosatellites and sampled postflight indicates that these structural alterations represent adaptative responses of the atrophic muscles to the increased workload of returning to 1 G, rather than hypogravity per se. The atrophy of weightlessness is postulated to result because muscles are both underloaded and used less often. Proper testing of this hypothesis requires quantitation of muscle function by monitoring electromyography, force output and length changes during the flight. Experiments conducted in space laboratories, like those being developed for the Space Shuttle, will avoid the complications of reentry before tissue sampling and allow time course atudies of the rate of development of adaptive changes to zero gravity. Another area of great importance for future studies of muscle atrophy is inflight measurement of plasma levels of hormones and tissue receptor levels. Glucocorticoids, thyroid hormone and insulin exert dramatic regulatory influences on muscle structure. Prevention of neuromuscular atrophy becomes increasingly more important as spaceflights increase in duration. Definition of the atrophic mechanism is essential to developing means of preventing neuromuscular atrophy.

Adaptation, Physiological↗
PubMed1987

Blood-brain barrier leakage and brain edema in stroke-prone spontaneously hypertensive rats. Effect of chronic sympathectomy and low protein/high salt diet.

Brain edema associated with severe chronic hypertension was studied in stroke-prone spontaneously hypertensive rats (SHRSP), 5 to 9 months of age. Blood-brain barrier (BBB) leakage sites and intracerebral spreading pathways for plasma proteins were delineated by an intravenously (i.v.) injected exogenous dye tracer (Evans blue), known to form a complex with albumin in blood, and by immunohistochemical visualization of extravasated endogenous plasma proteins. The tissue content of edema fluid was estimated by measuring the specific gravity of selected brain regions, stained or unstained by the tracer dye, on a bromobenzene-kerosene gradient column. Multifocal BBB leakage sites were macroscopically detected within the cerebral cortex and the deep gray matter after i.v. circulation of Evans blue-albumin for 30 min. After 24 h of i.v. circulation the dye tracer had spread not only locally in the gray matter but also into the adjacent white matter, where it was widely distributed. Immunohistochemically visualized plasma proteins showed similar distribution. Unilateral superior cervical ganglionectomy performed at 4 weeks of age neither increased the incidence of major BBB opening to Evans blue-albumin nor altered the specific gravity of the ipsilateral cerebral hemisphere in grown-up SHRSP, furthermore, the blood pressure remained unchanged. The lack of significant effect on BBB function may possibly be attributed to the extensive reinnervation of the cerebral arteries, verified in the grown-up SHRSP using the Falck-Hillarp fluorescence method for visualization of catecholaminergic nerve fibers. In SHRSP raised on a low-protein and high-salt diet the mean arterial blood pressure was 212 mm Hg compared to 195 mm Hg in controls (P less than 0.05) and the incidence of BBB opening was 72% compared to 25% in controls (P less than 0.05). After 24 h of i.v. circulation of Evans blue-albumin, brain regions stained by the dye tracer showed significantly reduced specific gravity (P less than 0.001), while unstained regions had normal values. Thus the brain edema fluid spread, as revealed by specific gravity measurements, corresponded to the intracerebral distribution of extravasated plasma proteins.

Animals↗
PubMed1988

Chromal focus of acquired chromatic discrimination loss and solvent exposure among printshop workers.

Acquired dyschromatopsia has been associated with exposure to organic solvents. However, the chromal focus of the loss may be indicative of its gravity. According to Kollner's rule, blue-yellow loss reflects changes in external retinal layers, while red-green loss appears to be indicative of internal retinal or optic nerve damage. The objective of the present study was to examine chromatic discrimination capacity of 30 printshop workers exposed to organic solvent mixtures, and of a non-exposed reference group. Colour vision was assessed with a colour arrangement test designed to detect acquired dyschromatopsia, the Lanthony D-15 desaturated panel. Quantitative analysis, using Bowman's colour confusion index, revealed significantly higher scores indicative of colour vision loss among the exposed workers as compared to the non-exposed. Analysis of covariance, with age as co-variate, showed colour confusion index to be significantly associated with job category. Similarly, qualitative analysis showed that the exposed workers presented a significantly higher prevalence of acquired dyschromatopsia as compared to the non-exposed group. However, analysis of the type of chromatic discrimination loss showed that among the nonexposed persons, dyschromatopsia was localized only in the blue-yellow range, while for 35% of the dyschromatopic-exposed persons, red-green loss as well as blue-yellow loss were present. Three-dimensional chi 2-analysis showed that the complex pattern of dyschromatopsia was not related to age, but to job category. These findings suggest that the type of dyschromatopsia, reflecting the gravity of neural alterations, may be a function of exposure level and/or the ophthalmotoxic properties of the particular solvents used.

Adult↗
PubMed1999

Agravitropic mutant for the study of hydrotropism in seedling roots.

Roots have been shown to respond to a moisture gradient by positive hydrotropism. Agravitropic mutant plants are useful for the study of the hydrotropism in roots because on Earth hydrotropism is obviously altered by the gravity response in the roots of normally gravitropic plants. The roots are able to sense water potential gradient as small as 0.5 MPa mm(-1). The root cap includes the sensing apparatus that causes a differential growth at the elongation region of roots. A gradient in apoplastic calcium and calcium influx through plasmamembrane in the root cap is somehow involved in the signal transduction mechanism in hydrotropism, which may cause a differential change in cell wall extensibility at the elongation region. We have isolated an endoxy loglucan transferase (EXGT) gene that is strongly expressed in pea roots and appears to be involved in the differential growth in hydrotropically responding roots. Thus, it is now possible to study hydrotropism in roots by comparing with or separate from gravitropism. These results also imply that microgravity conditions in space are useful for the study of hydrotropism and its interaction with gravitropism.

Calcium Channels↗
PubMed2002

Effect of clinorotation on in vitro cultured explants of Mentha piperita L.

An in vitro culture system was used to study the influence of gravity on axillary shoot formation and adventitious root regeneration in Mentha piperita L. The direction of the gravity vector was altered by displacing stem node explants in different orientations. Also, microgravity conditions were simulated by rotating the explants on a horizontal clinostat so that the main axis of nodes was either parallel (Cpa) or perpendicular to the clinostat axis (Ccp and Ccf, centripetally and centrifugally oriented, respectively). Mint nodes were cultured on solidified Linsmaier and Skoog's medium [Physiol. Plant. 18 (1965) 100] adding a filter-sterilized aqueous solution of 2 mg/l benzyladenine (BA) in half of the cultures. The proliferation of axillary shoots as well as adventitious root formation were not affected by altering upright explant orientation. On the contrary clinorotation was able to modify plantlet development. In absence of BA, leaf width was hindered by Cpa treatment and penultimate internode length was enhanced by Ccp. Furthermore, a negative effect of Cpa treatment was observed in root length parameter, while Ccp increased the root number both in absence and in presence of BA. An effect strictly connected to clinorotation in presence of BA was the occurrence of hyperhydricity. Moreover, explants under clinorotation treatments switched their gravitropic response modifying shoot curvature.

Adenine↗
PubMed1972

Lysosomal localization of -fructofuranosidase-containing liposomes injected into rats.

Yeast beta-fructofuranosidase (invertase) or (131)I-labelled albumin were entrapped into liposomes composed of phosphatidylcholine, cholesterol and phosphatidic acid. Of the beta-fructofuranosidase activity in the liposomal preparations 96-100% was latent. The following observations were made in experiments with rats injected with protein-containing liposomes. 1. After injection of beta-fructofuranosidase-containing liposomes (220 units or 1.5mg of beta-fructofuranosidase and 17.5mg of lipid), beta-fructofuranosidase activity in blood retained its latency but the activity declined to 50% of the injected dose in 1h. Within 6h much of this activity was recovered in the liver and spleen (respectively 45% and 10% of that injected). For up to 21h after injection, the mitochondrial-lysosomal fraction was the principal location of the hepatic beta-fructofuranosidase activity. 2. Lysosomal localization of liposomal protein was supported by the observed increase in the trichloroacetic acid-soluble radioactivity during incubation of the lysosome-rich fraction of the liver of rats injected with liposomes containing (131)I-labelled albumin. 3. Association of liposomal protein with lysosomes was demonstrated on subfractionation of the mitochondrial-lysosomal fraction of the liver of rats injected with beta-fructofuranosidase-containing liposomes in a Ficoll-mannitol gradient. beta-Fructofuranosidase, lysosomal and mitochondrial enzyme marker activities were found to exhibit similar distribution patterns along the gradient. However, in similar experiments with rats previously injected with Triton WR-1339 or dextran (known to alter the specific gravity of lysosomes), only beta-fructofuranosidase and lysosomal marker moved along the gradient, in strikingly similar patterns. 4. The lysosomal localization of injected liposome-entrapped material can probably be utilized in the treatment of certain disorders in man.

Albumins↗
PubMed1999

Flotation method for extracting insects from poultry manure samples.

We examined the efficacy of a sucrose-based flotation method for extracting 3 prevalent insect species from poultry house manure: 3rd-instar Musca domestica L. (Diptera: Muscidae), Carcinops pumilio (Erichson) (Coleoptera: Histeridae) adults, and Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae) adults. A 0.6 M sucrose solution in distilled water altered the specific gravity to 1.2 and caused the 3 species to float to the water surface for easy separation. An analysis of variance (ANOVA) showed significant effects of the solution volume to sample mass ratio on recovery rates (F = 35.96, P < 0.0001), but no differences in species-specific recovery rates (F = 0.97, P = 0.3824). Among samples agitated in a ratio of at least 3.2 ml solution per gram of sample mass, we observed neither significant ratio effects (F = 1.37, P = 0.2442) nor significant differences in species-specific recovery rates (F = 2.05, P = 0.1353); overall, we recovered 97.49 +/- 0.20% of all individuals of the 3 species. Our analyses demonstrated that sucrose-based flotation was a statistically valid method of collecting these species from poultry manure samples.

Animals↗
PubMed1995

Effects of microgravity on the structure of leaves cells involved in water transport.

The oppression of plant cells growth and accelerated of their aging and cell structure changes take place during growth of plants at conditions of long time space flight or clinorotation. Such changes reflect the alterations of gravity-sensitive links in plant cell metabolism, of plant polarity and possible of water balance of plants at weightlessness. Because the study of plant cells ultrastructure changes that took part in water transport under microgravity influence was the aim of our investigation.

Biological Transport↗
PubMed2002

Eye movements to yaw, pitch, and roll about vertical and horizontal axes: adaptation and motion sickness.

BACKGROUND: In the search for parameters to predict motion sickness that can be measured in the laboratory, we performed a longitudinal investigation in aviators. Since the vestibular system is involved in the generation of motion sickness as well as eye movements, vestibulo-ocular reflex (VOR) parameters seemed relevant. We investigated three topics: 1) the effect of axis orientation and its orientation to gravity on the VOR; 2) changes in VOR parameters depending on flight experience; and 3) differences in VOR parameters in aircrew with high and low susceptibility to motion sickness. HYPOTHESIS: Nystagmus decay after angular velocity steps would be faster for non-susceptible and trained aviators. METHODS: We recorded eye movements evoked by angular on-axis velocity steps (+/- 90 degrees x S(-2), to and from 90 degrees x S(-1)) in yaw, pitch, and roll, about both the Earth vertical and Earth horizontal axes in 14 subjects with a low susceptibility to motion sickness. These data were compared with those of 10 subjects with a high susceptibility. RESULTS: Horizontal axis rotations are nauseogenic. We found that during (per) and post-condition, left- and rightward rotation responses were equal, and the orientation with respect to gravity did not alter the basic nystagmus decay, apart from a sinusoidal modulation. Moreover, pitch and roll rotations show equal nystagmus decays, significantly faster than for yaw; yaw and pitch peak velocities were equal and were larger than for roll. With regard to changes in VOR parameters depending on flight experience, we found that repeated vestibular stimulation reduced nystagmus decay as well as the otolith modulation. With respect to the changes in VOR parameters and motion sickness susceptibility, we found that subjects highly susceptible to motion sickness showed a slower decay of nystagmus with a larger peak velocity than less susceptible subjects. CONCLUSIONS: Group averages indicate a difference in eye movement parameters, only in yaw, depending on flight experience; and between subjects with low and high susceptibility to motion sickness. The involvement of the velocity storage mechanism as realized by an internal model is given as a plausible explanation.

Adaptation, Physiological↗
PubMed1991

[The immunological indices in different types of gouty nephropathy and the degree of renal structure involvement].

Patients with different types of podagric nephropathy were examined for 21 indicators of the functional activity of T and B lymphocytes and neutrophils. The data obtained were compared to the degree of impairment of the basic renal structures. Among the study immunologic indicators to estimate the gravity of morphological alterations in the glomeruli, the decrease of the titers of antibodies to DNA is of definite specificity, whereas the fall of the concentration of circulating immune complexes is of definite specificity in the assessment of alteration in the stroma.

Antibodies↗