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At least 91 records · Page 5

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NASA NTRS1983

Hypergravic fields and parallel controllers for thermoregulation

To test the proposal that mammals have parallel neurocontrollers for temperature regulation, Long-Evans hooded male rats were exposed to cold while in a 3-G field. When exposed to cold, these rats consumed 35 percent less oxygen/min at 3 G than they did when exposed to cold at 1 G. However, rats acclimated for 6 wk to 5 C consumed oxygen at the same rate during cold exposure at 3 G as at 1 G. Because cold-acclimated rats generate heat primarily by nonshivering thermogenesis while rats acclimated to room temperature rely to a greater extent on shivering, the 35 percent decrease in oxygen consumption of cold-exposed room-temperature rats in 3-G fields may reflect an inactivation of shivering. These oxygen consumption measurements, together with measurements of core and tail temperatures of rats in 3-G fields, are consistent with the proposal that neurocontrollers for thermoregulation are arranged in parallel and can be uncoupled by hypergravic fields.

Monson, C. B.↗

NASA NTRS1983

Rat body size, composition and growth at hypo- and hypergravity

The effects of hypergravity (centrifugation) on body composition were investigated. Hypogravitational and hypergravitational aspects were reflected in the research effort. A list of publications is provided.

Pitts, G. C.↗

NASA NTRS1984

Hypergravity effects on litter size, nursing activity, prolactin, TSH, T3, and T4 in the rat

In a recent study of the effects of hypergravity (HG) on the reproductive system of the rat, it was found that the estrous cycle is perturbed in a pseudopregnancy-like pattern upon first exposure of animals to HG. This can be prevented by previous exposure to HG or by administration of bromergo cryptin. Adapted rats can mate and deliver in HG. However, little is known of the condition of the individual pregnant rat, fetuses, and newborn pups in this environment. There are also questions regarding the effects of HG on the number of fetuses, the mortality rate in different HG levels, and the effects on production and secretion of PRL and TSH. The present investigation is concerned with such questions, taking into account possible approaches to avoid or minimize the lethal effects of HG. The obtained results suggest that peripartum plasma PRL levels and thyroid hormone levels are critical for the survival of the litter.

Megory, E.↗

NASA NTRS1985

Hypergravity induced prolactin surge in female rats

Acute initial exposure to hypergravity (HG) was previously found to induce prolonged diestrous in rats, which was followed by return to normal estrous cycling upon more prolonged exposure to continuous HG. Bromergocryptine was found to prevent this prolonged diestrous. In this study it is found that in female rats 20 h of 3.14 G exposure (D-1 1200 h until D-2 0800 h) can induce prolactin surge at D-2 1600 h. Shorter exposure time (8 h), or exposure during a different part of the estrous cycle (19 h: from D-1 0700 h until D-2 0200 h) could not elicit this prolactin surge. Similar exposure of male rats of HG did not alter significantly their prolactin levels. It is possible that the hypothalamus of male and female rats responds differently to stimulation by HG.

Megory, E.↗

NASA NTRS1988

Ocular torsion in upright and tilted positions during hypo- and hypergravity of parabolic flight

Four subjects considered resistant to motion sickness were tested in KC-135 parabolic flight to examine ocular torsion at hypo-gravity and hypergravity. Three of these subjects showed no significant torsion at zero G in either the upright position or when tilted 30 deg to right or left. At 1.8 G in the tilted positions, they showed greater ocular counterrolling than at 1 G. None of these three subjects became motion sick. The fourth subject showed eye torsion toward his left in all positions at zero G. This leftward bias could also be seen at 1.8 G when tilted left ear down, the side that induces rightward counterrolling. There he had less eye torsion than at 1 G. This subject became motion sick. These results support the hypothesis that asymmetry of the utricular system may be well compensated in the normal 1 G environment, but unmasked in unaccustomed gravitational situations, suggesting a possible predictive test for space adaptation syndrome.

Diamond, Shirley G.↗

NASA NTRS1994

Development of life sciences equipment for microgravity and hypergravity simulation

The mission of the Life Science Division at the NASA Ames Research Center is to investigate the effects of gravity on living systems in the spectrum from cells to humans. The range of these investigations is from microgravity, as experienced in space, to Earth's gravity, and hypergravity. Exposure to microgravity causes many physiological changes in humans and other mammals including a headward shift of body fluids, atrophy of muscles - especially the large muscles of the legs - and changes in bone and mineral metabolism. The high cost and limited opportunity for research experiments in space create a need to perform ground based simulation experiments on Earth. Models that simulate microgravity are used to help identify and quantify these changes, to investigate the mechanisms causing these changes and, in some cases, to develop countermeasures.

Mulenburg, G. M.↗

NASA NTRS1999

Hypergravity Facilities: Extending Knowledge Over the Continuum of Gravity

Historical perspectives, reasons for gravitational research, key questions regarding centrifuges, particular centrifuge discussions, vestibular research facilities, the hypergravity facility for cell culture, the human research facility, as well as the center for bioinformatics are all topics discussed in viewgraph form.

Souza, Kenneth A.↗

NASA NTRS2000

Effects of Hypergravity and Adrenalectomy on Total Body Bone Mineral Content in Male Rats

Girten, Beverly↗

NASA NTRS2001

Hypergravity Effects on the Mother-Offspring System in Mammals

In 1995, ten pregnant female rats were launched on the Space Shuttle (STS-70) on Gestational day (G) 11 of their 22-day pregnancy as part of the NASA/NIH.Rodent (R)2 Experiment. Following landing on G20, fetuses were harvested from half of the dams, 0 g while the remaining five dams underwent birth. Spaceflight did not interrupt pregnancy, alter litter sizes, or affect body weights or gender ratios of the fetuses or neonates. Analyses of rats exposed to Hypergravity (HG) at 2.0-g, HG 1.75-g, HG 1.5-g were also conducted. Dams were exposed to continuous centrifugation from G I I through G20, with brief daily stops for animal health checks and maintenance. For both the G20 and Birth dams, comparable litter sizes and litter gender ratios were observed across gravity conditions. However, centrifugation-exposed (HG and RC) fetuses and neonates showed significantly lower body masses (p less than 0.05) relative to SC offspring. FIG 2.0-g offspring weighed significantly less than those in all other gravity conditions (p less than 0.05). Changes in the mothers care of the young will be discussed.

Ronca, April E.↗

NASA NTRS2001

The Effects of Hypergravity and Adrenalectomy on Bone Mineral Content, Urine Calcium and Body Mass in Rats

The effects of 14 days of increased gravitational load, and the absence of adrenal stress hormones on total body bone mineral content (BMC) were examined in male Sprague-Dawley rats. Centrifugation at 2 Gs (2G) was used to increase the gravitational load, and bilateral adrenalectomy (ADX) was used to eliminate the production of adrenal stress hormones. Stationary groups at 1 G (1G) and sham operated (SHAM) animals served as controls. Thirty rats (n=6 or 8) made up the four experimental groups (1G SHAM, 1G ADX, 2G SHAM and 2G ADX). BMC was assessed by dual energy x-ray absorptiometry (DXA) which was performed to determine the total body bone mineral content, and also through bone ashing of the left femur and the left humerus. Activity was determined through biotelemetry, also body mass and food intake were measured. Multi-factorial analysis of variance (MANCOVA) and Newman Keuls post hoc tests were used to analyze significant effects (p is less than 0.05) for the primary variables. Results from both DXA and the ashed femur indicated that BMC decreased significantly with increased G for both the SHAM and ADX groups. The BMC determined by DXA for the 1G ADX group was also significantly lower than the 1G SHAM group, however the 2G SHAM and 2G ADX groups were not significantly different. However, the bone ashing results showed the femur differed significantly only between the rates of centrifugation and not between the ADX and SHAM. The humerus showed no significant difference between any of the groups. There was a significant decrease in body mass with increased G and there was no ADX effect on body mass. When DXA BMC was normalized for body mass changes, there were no significant group differences. However, with bone ashing, the femur BMC/BW still showed significant difference between rates of centrifugation, with the 2G group being lower. Activity level decreased with body mass, and food intake data showed there was significant hypophagia during the first few days of centrifugation. Urine calcium was measured and was found decrease at the start of centrifugation for the 2G groups and rise to a level higher than that of the stationary groups. Finally, the correlation between BW and BMC was determined to be highly correlated (r = .71). These results suggest that the decrease in total body BMC seen with hypergravity may be based to a large extent on the differences in body mass induced by the 2G load.

Lau, A.↗

NASA NTRS2001

Hypergravity Loading the Cultured Osteoblasts: Modeling and Experimental Analysis of Cellular Morphology and the Cytoskeleton

Bone forming cells, osteoblasts, respond to various mechanical forces, including mechanical strain and fluid-induced shear stress. This study examined whether osteoblasts detect changes in gravity as a mechanical force, as assessed by cellular morphology and dimensions of the cytoskeletal network. We used modeling to evaluate how gravity influences cell morphology given theoretical differences in densities between the surrounding medium, cytoplasm, and nucleus. A mechanical model was built based on analysis of axisymmetric shell structures (Fast4 software) to study the effects of 10 times gravity (10G) on cell height. The model indicated 0.02% decrease in overall cell height when the medium was 10% denser than the nucleus or cytoplasm, 5.9 x 10(exp-5)% decrease when the nucleus was 10% denser than the cytoplasm or medium, and 1.3 x 10(exp-5)% decrease when the cell cytoplasm was 10% denser than the nucleus or medium. To experimentally evaluate the influence of gravity, cultured primary fetal rat osteoblasts were grown to near confluence and centrifuged at 10G for 3 hours. Actin, microtubules, and nuclei were fluorescently labeled and analyzed by confocal microscopy to determine overall microtubule and actin network height. Centrifugation led to an apparent reduction in height of both the microtubule (-16%) and the actin (-20%) networks relative to stationary controls. Thus, both modeling and experiments indicate that hypergravity reduces the height of the osteoblast cell layer and their microtubule and actin networks. This combination of modeling and experimental analyses will help us to better understand the mechanical loading of osteoblasts.

Searby, N. D.↗

NASA NTRS1994

Tolerance of Snakes to Hypergravity

Sensitivity of carotid blood flow to +Gz (head-to-tail) acceleration was studied in six species of snakes hypothesized to show varied adaptive cardiovascular responses to gravity. Blood flow in the proximal carotid artery was measured in 15 snakes before, during and following stepwise increments of +0.25Gz force produced on a 2.4 m diameter centrifuge. During centrifugation each snake was confined to a straight position within an individually- fitted acrylic tube with the head facing the center of rotation. We measured the centrifugal force at the tail of the snake in order to quantify the maximum intensity of force gradient promoting antero-posterior pooling of blood. Tolerance to increased gravity was quantified as the acceleration force at which carotid blood flow ceased. This parameter varied according to the gravitational adaptation of species defined by their ecology and behavior. At the extremes, carotid blood flow decreased in response to increasing gravity and approached zero near +1Gz in aquatic and ground-dwelling species, whereas in climbing species carotid flow was maintained at forces in excess of +2Gz. Surprisingly, tolerant (arboreal) species withstood hypergravic forces of +2 to +3 G. for periods up to 1 h without cessation of carotid blood flow or apparent loss of consciousness. Data suggest that relatively tight skin of the tolerant species provides a natural antigravity suit which is of prime importance in counteracting Gz stress on blood circulation.

Lillywhite, H. B.↗

NASA NTRS1995

Elevator Illusion and Gaze Direction in Hypergravity

A luminous visual target in a dark hypergravity (Gz greater than 1) environment appears to be elevated above its true physical position. This "elevator illusion" has been attributed to changes in oculomotor control caused by increased stimulation of the otolith organs. Data relating the magnitude of the illusion to the magnitude of the changes in oculomotor control have been lacking. The present study provides such data.

Cohen, Malcolm M.↗

NASA NTRS2002

Effects of Hypergravity Exposure On Plasma Oxytocin Concentrations In Pregnant and Lactating Rat Dams

Rat dams and offspring were exposed to 1.5-g, 1.75-g or 2.0-g hypergravity (hg) from Gestational day (G) 11 until Postnatal day (P) 10. To ascertain the role of maternal factors in reduced postnatal body weights of offspring developed in hg, the dams' lactational hormones were measured. Oxytocin (OT), the major hormone responsible for milk ejection, was reduced in hg dams whereas prolactin (Prl), involved in milk production, was unchanged. Video analyses of nursing behavior revealed that hg dams spent more time nursing relative to 1-g controls. We hypothesized impaired milk transfer from dam to pup, however pup body weight gains following a discrete suckling episode were comparable across conditions. Changes in lactational hormones and nursing behavior by dams exposed to hg do not account for reduced body masses of their offspring.

Baer, Lisa A.↗

NASA NTRS2002

Neither Milk Production, Milk Transfer Nor Pup Growth Hormone Account for Reduced Body Weights of Rat Pups Reared In Hypergravity

Studies spanning the gravity continuum from 0 to 2-g are revealing new insights into how mammalian reproduction and development may proceed in the microgravity of space. Rat pups reared from either conception or midgestation in hypergravity (hg) weigh 6-15% less than 1-g controls. In the present study we analyzed maternal and pup factors that may account for reduced body weight of hg reared pups. Beginning on Gestational day (G)11 of the rats' 22 day pregnancy, rat dams and their litters were continuously exposed to either 1.5-g, 1.75-g or 2.0-g. Prolaction (Prl) and oxytocin (OT) were measured in hg-exposed dams during either pregnancy (G20) or lactation (Postnatal day [P] 10). Gravity related differences in Prl were not observed whereas OT was depressed during lactation in hg dams relative to controls (p less than 0.05). Milk transfer measured during a discrete suckling episode was actually increased in hg-reared litters and comparable numbers of milk-letdowns were observed in the two conditions. Recent reports using dwarfing phenotypes in mouse mutants have provided evidence for postnatal dependence on growth hormone (GH) and insulin-like growth factors (IGFs). Plasma GH measured in P10 pups using enzyme immunoassay (EIA) was significantly elevated in hg pups relative to 1-g controls (mean +/- sd., ng/ml: 2.0-g, 10.6 [3.0], 1.5-g 8.9 [4.0], 1.0-g, 7.95 [3.1]). Together, these findings suggest that neither milk production, milk transfer nor pup GH play significant roles in reduced body weights of hg-reared pups. Studies underway are focused on insulin-like growth factors.

Bear, L. A.↗

NASA NTRS2003

Hypergravity-Induced Changes in Hematological and Lymphocyte Function Parameters in a Mouse Model

The purpose of this study was to quantify hypergravity-induced changes in hematological and lymphocyte characteristics. Mice were subjected to 1, 2, and 3G and euthanized on days 1 , 4, 7, 10, and 21. The data show that increased gravitational force resulted in persistent hypothermia. Red blood cell (RBC) counts, hematocrit, and hemoglobin were reduced by day 21, whereas hemoglobin and RBC volume were low at most times of measurement. A transient increase was noted in platelet numbers in the 3G group. Fluctuations in spontaneous blastogenesis of lymphocytes were dependent upon centrifugation time and not gravity. Changes in splenocyte responses to T and B cell mitogens due to gravity were also noted. Cytokine production was primarily affected during the first week; IL-2, IL-4 and TNF-alpha were increased, whereas IFN-gamma was decreased. These findings indicate that altered gravity can influence both hematological and functional variables that may translate into serious health consequences.

Gridley, Daila S.↗

NASA NTRS1995

Effect of microgravity and hypergravity on embryo axis alignment during postencystment embryogenesis in Artemia franciscana (Anostraca)

Cysts of brine shrimp attached with a liquid adhesive to 12-mm diameter glass coverslips in a syringe-type fluid processing apparatus were flown aboard the NASA space shuttle Discovery, flight STS-60, from 3-11 February 1994, and were allowed to undergo postencystment embryogenesis and to hatch in microgravity. The shuttle flight and the ground-based control coverslips with attached cysts were parallel to the earth's surface during incubation in salt water. Based on the position of the cyst shell crack in the attached cyst population, the ground-control nauplii emerged mostly upward. On the shuttle in microgravity, although our method of detection of orientation would not reveal emergence toward the coverslip, the ratio of the position of the cyst shell crack in the population after hatching best fit the predicted values of a random direction for nauplii emergence. Centrifugation on earth was then used to create hypergravity forces of up to 73 g during postencystment embryogenesis and hatching. The upward orientation of emerging nauplii showed a high degree of correlation (r(2) =98.8%) with a linear relationship to the log of g, with 78.2% of the total hatching upward at 1 g and 91.0% hatching upward at 73 g.

NASA Program NSCORT↗

NASA NTRS1998

Chronic exposure to hypergravity affects thyrotropin-releasing hormone levels in rat brainstem and cerebellum

In studies to determine the neurochemical mechanisms underlying adaptation to altered gravity we have investigated changes in neuropeptide levels in brainstem, cerebellum, hypothalamus, striatum, hippocampus, and cerebral cortex by radioimmunoassay. Fourteen days of hypergravity (hyperG) exposure resulted in significant increases in thyrotropin-releasing hormone (TRH) content of brainstem and cerebellum, but no changes in levels of other neuropeptides (beta-endorphin, cholecystokinin, met-enkephalin, somatostatin, and substance P) examined in these areas were found, nor were TRH levels significantly changed in any other brain regions investigated. The increase in TRH in brainstem and cerebellum was not seen in animals exposed only to the rotational component of centrifugation, suggesting that this increase was elicited by the alteration in the gravitational environment. The only other neuropeptide affected by chronic hyperG exposure was met-enkephalin, which was significantly decreased in the cerebral cortex. However, this alteration in met-enkephalin was found in both hyperG and rotation control animals and thus may be due to the rotational rather than the hyperG component of centrifugation. Thus it does not appear as if there is a generalized neuropeptide response to chronic hyperG following 2 weeks of exposure. Rather, there is an increase only of TRH and that occurs only in areas of the brain known to be heavily involved with vestibular inputs and motor control (both voluntary and autonomic). These results suggest that TRH may play a role in adaptation to altered gravity as it does in adaptation to altered vestibular input following labyrinthectomy, and in cerebellar and vestibular control of locomotion, as seen in studies of ataxia.

NASA Discipline Neuroscience↗