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At least 307 records · Page 17Linked to original sources
PubMed2001

The vestibulo-ocular reflex of hypergravity rats.

The vertebrate vestibular system detects linear (otolith organs) and angular (semicircular canals) acceleration. The function of the otolith system is twofold, 1: perception of linear acceleration of the head, and 2: assessment of the spatial orientation of the head relative to the vector of gravity. Because of the latter function, a change of gravity will affect the vestibular input which, in turn, may have a wide range of serious physiological effects, for instance on ocular reflexes. The function of the vestibulo-ocular reflex (VOR) is to stabilize the visual image on the retina. Measurement of this VOR provides a method to investigate the (processing within the) vestibular system. Discrimination between gravity and linear acceleration, caused by movement of the head, is not possible. Therefore, information from the otolith system must be constantly compared with additional information from other sensory systems in order to solve the inherent ambiguity between tilt and translation. In this processing, cues from the semicircular canals also play a role. During parabolic flight, experiments can be performed at altered gravity levels for brief periods of time. On earth, the only effective possibility to manipulate gravity for longer periods of time is a centrifuge. Together with experiments in weightlessness during orbital flight, these methods form useful tools to investigate the influence of gravity on physiology. In our laboratory, rats have been kept inside a centrifuge at 2.5 g during their entire life-span (i.e. including gestation).

Acceleration↗
PubMed2000

A model for studying the baroreflex in microgravity and hypergravity.

The study on development in altered gravity has been investigated in a wide range of animal species from a molecular level or cell culture to mammalian bodies. However development of the baroreflex has been studied in limited mammalian species even on the ground except the turtle to study diving reflex. The rat or mouse has been selectively used for studying the relationship between development of various functions and gravity especially microgravity, because of the limited body size for the loading space on the space ship, an experimental-animal most often used, and other biological characteristics. We have used the rat and rabbit for investigating the effect of microgravity on the development of the aortic baroflex. In the present paper a few results of our experiments using the rat will be shown and the appropriateness of the rat as a model system for studying the baroflex development in altered gravity will be discussed.

Age Factors↗
PubMed2003

[Measurement of cerebral blood oxygen saturation with near infrared spectroscopy and its application in hypergravity].

OBJECTIVE: To measure the oxygen saturation of blood in rat's brain non-invasively after acceleration with near infrared spectroscopy technique. METHOD: A serious of model about different ischemia and hypoxia of head, measured oxygen saturation by phlebotomize were made, and the difference with normal group was obtained. Its absorption intensity was measured and a curve showing the difference between the normal value was drawn. According to the curve, cerebral blood oxygen saturation after acceleration was calculated with the measured absorption intensity after high or push-pull maneuver by near infrared spectroscopy. RESULT: Compared high +Gz and push pull effect group with 0 Gz group, the content of ox hemoglobin reduced, in opposition the deox hemoglobin increased, the greater the difference, the lower the content of oxygen saturation of blood. CONCLUSION: Oxygen saturation of blood in the rat's brain can be obtained non-invasively with near infrared spectroscopy.

Acceleration↗
PubMed2004

Human corticospinal excitability in microgravity and hypergravity during parabolic flight.

INTRODUCTION: Spontaneous electromyographic (EMG) activity in the soleus muscle of the rat varies with the changing gravitational force in parabolic flight, presumably in an appropriate way to resist the load. We investigated how decreased and increased gravitational force affects EMG in human back and arm muscles and to what extent the motor cortex is responsible for any modulation seen. METHODS: Three healthy subjects stood during 10 parabolas consisting of periods (duration 20-25 s) of 1.8 G, then 0 G, and then 1.8 G. EMG recordings were made from right deltoid and left and right erector spinae (ES) muscles and transcranial magnetic stimulation (TMS) was applied to the motor cortex to produce motor evoked potentials (MEPs) in target muscles. RESULTS: In one exemplary subject, EMG levels and MEP areas increased in the left ES and right ES during periods of 0 G, which was less pronounced with the arm abducted. No significant changes were seen in EMG levels or MEP areas during periods of 1.8 G. Pooled data from the three subjects showed a similar pattern, revealing a facilitation of MEP responses in left and right ES muscles in periods of 0 G. DISCUSSION: EMG levels and MEP areas in ES muscles increased during periods of 0 G, suggesting that back muscle activity is "turned on" to stabilize the axial skeleton when the vertical compression forces present on Earth are removed. Further analysis suggested that microgravity produced activation of ES muscles through an increase in corticospinal excitability.

Acceleration↗
PubMed2004

Role of gravity in mammalian development: effects of hypergravity and/or microgravity on the development of skeletal muscles.

Effects of hindlimb suspension or exposure to 2-G between postnatal day 4 and month 3 and of 3-month recovery at 1-G environment on the characteristics of rat hindlimb muscles were studied. Pronounced growth inhibition was induced by unloading, but not by 2-G loading. It is suggested that the development and/or differentiation of soleus muscle fibers are closely associated with gravitational loading. The data indicated that gravitational unloading during postnatal development inhibits the myonuclear accretion in accordance with subnormal numbers of both mitotic active and quiescent satellite cells. Even though the fiber formation and longitudinal fiber growth were not influenced, cross-sectional growth of muscle fibers was also inhibited in association with lesser myonuclear domain and DNA content per unit volume of myonucleus. Unloading-related inhibition was generally normalized following the recovery.

Animals↗
PubMed2004

Effects of 2 G hypergravity exposure on Bobwhite (Colinus virginianus) and Japanese quail (Coturnix coturnix japonica).

We compared reproductive fitness and early postnatal growth of Bobwhite (Colinus virginianus) and Japanese (Coturnix coturnix japonica) quail incubated and hatched during 2 G centrifugation. Fertilized Bobwhite and Japanese quail eggs were placed in portable incubators on the 8-ft International Space Station Test Bed (ISSTB) Centrifuge at NASA Ames Research Center. The quail eggs were incubated throughout hatching and reared until Postnatal day (P)4 at either 1.0, 1.2 or 2.0 G. Two days before hatching, candling revealed significantly greater numbers of viable Bobwhite than Japanese quail eggs at all g-loads. Bobwhite quail exhibited significantly better hatching success at all g-loads than did Japanese quail. Bobwhite hatchlings were sensitive to gravitational loading as evidenced by reduced postnatal body mass and length of 2 G hatchlings relative to 1 G control hatchlings. In contrast, mass and length of Japanese quail hatchlings were unaffected by 1.2 or 2 G exposure. Together, our findings provide evidence for superior viability and hatching success in Bobwhite quail relative to Japanese quail, coupled with greater sensitivity of postnatal body growth and development to 2 G loading. Bobwhite quail may be better suited than Japanese quail for scientific studies on space biology platforms.

Animals↗
PubMed1995

[Morphological studies of endocrine cells of the pancreas in rats after exposure to micro- and hypergravity].

Effects of changed gravity on the function of insulin-producing beta-cells and glucagon-producing alpha-cells in pancreas of rats after the 14-day missions of Cosmos-1887, -2044, and those pre- and postnatal development of which till day 60 proceeded at 2 G in a permanently rotating ground centrifuge were studied with the use of morphological techniques. The comparison of beta- and alpha-cells from pancreas of rats flown in space and subjected to relatively reduced gravity after transition from 2 G to 1 G in the laboratory experiment allow to deduce that the postflight reduced production of insulin by beta-cells and glucagon by alpha-cells has been caused by microgravity, whereas the hindered secretion of hormones is associated with the gravity stress within the first hours after recovery.

Animals↗
PubMed1996

Performance of a simple aiming task in hypergravity: I. overall accuracy.

BACKGROUND: Visuo-motor performance is known to be affected by exposure to hyper-gravity (hyper-G), but the underlying mechanisms remain to be determined; the present study investigated the role of target mislocalization. METHOD: Subjects pointed before, during and after exposure to hyper-G at targets without seeing their hand. Target positions were displayed: a) throughout each pointing response; b) before response onset; or c) in normal gravity prior to a set of movements. RESULTS AND CONCLUSIONS: For all display conditions, subjects pointed higher in hyper-G than in normal gravity from the first movement on. We attribute the discrepancy between this finding and previous results (8, 12) to different movement strategies. The effects of hyper-G on pointing performance were small, but sustained when targets were displayed before or throughout each movement, but they were large and transient when targets were memorized in normal-G. We conclude that too-high pointing in hyper-G cannot be simply explained by the "elevator illusion," and propose a tentative interpretation based on known perceptual deficits.

Adult↗