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PubMed1981

Changes in the microstructure of the vestibular apparatus of tadpoles (Rana temporaria) developed in simulated weightlessness.

The vestibular apparatus of tadpoles (Rana temporaria) exposed to simulated weightlessness was examined by electron microscopy. Extended exposure to simulated weightlessness is followed by significant alterations in the sensory epithelia and also in the otolith membrane. Large vacuoles, filled with necrobiotic mitochondria and fragments of endoplasmic reticulum, were concentrated in the region where an otolith membrane covers the hair cells but were mostly absent in zones of the epithelia with undifferentiated cells. The number of otoconia in the otolith membrane was diminished. The results were compared with data from space flight experiments and some concordance was noted. The possible connection between some unusual behavior of the tadpoles after weightlessness simulation and the structural alterations in the gravitational sensors was discussed.

Animals↗
PubMed2003

[Changes of reactivity of rabbit femoral venous rings after 21 d simulated weightlessness].

OBJECTIVE: To study the effects of simulated weightlessness on reactivity of leg veins. METHOD: Vascular bathing technique was used to measure the contractile responses of rabbit femoral venous rings to Ht, PE and KCl, and the dilatory responses to ACh and SNP after horizontal confinement or head-down tilt confinement for 21 d. RESULT: After simulated weightlessness for 21 d, the contractile response of rabbit femoral venous rings to higher concentrations of PE and KCl decreased significantly (P<0.05); the contractile response to Ht also decreased, but not significantly (P>0.05); the dilatory responses to ACh and SNP did not change significantly in both groups. CONCLUSION: Contractile response of rabbit femoral vein decreased after simulated weightlessness for 21 d, which might partly explain the occurrence of orthostatic intolerance in men after space flight.

Acetylcholine↗
PubMed2001

[Counter-effect of intermittent +Gz exposures on vasoreactivity in decline in hind body arteries of rats under simulated weightlessness].

Objective. To investigate the counter-effect of intermittent artificial gravity, the present study examined vasoreactivity changes of femoral and mesenteric arteries in rats subjected to simulated weightlessness plus standing or centrifugation. Method. Forty male Sprague-Dawley rats were divided into simultaneous control (CON), simulated weightlessness (SUS), simulated weightlessness plus 1 h standing (STD1), simulated weightlessness plus 1.5 G centrifugation (1.5 G), and simulated weightlessness plus 2.6 G centrifugation (2.6 G) groups. Responses of arteries to vasoconstrictor were examined in vitro using isolated femoral and mesenteric arterial rings. Result. The contractile responsiveness to KCl or PE of femoral and mesenteric arterial rings isolated from SUS significantly decreased as compared with CON. And those of STD1 and the two centrifuged groups significantly enhanced as compared with that of SUS. Whereas there was no difference among STD1, 1.5 G, 2.6 G and CON. Conclusion. Simulated weightlessness may result in decreased contractile responses to KCl and PE of rat femoral and mesenteric arteries. Both STD1, 1.5 G, and 2.6 G prevented the decrease of contractile response to KCl and PE of femoral arteries.

Animals↗
PubMed1999

[Counteracting effect of hypoxia and Qigong on cardiac rhythm during orthostatic test post simulated weightlessness].

OBJECTIVE: To try to find a new method for countermeasuring the effect of simulated weightlessness. METHODS: The study was carried out in fifteen male healthy subjects, 19-22 years, -6 degrees head-down bed rest (-6 degrees HDBR) for 21 d was used as a weightlessness simulation model. The subjects were divided into three groups: control group (-6 degrees HDBR), hypoxia group (-6 degrees HDBR + inhalation of hypoxic gas mixture two times a day, 20 min each time) and Qigong group (-6 degrees HDBR + Qigong, three times per day, 45 min each time). Orthostatic test (+75 degrees 20 min) was conducted on each subject pre- and post-HDBR. RESULTS: Cardiac rhythm during the orthostatic test was normal pre-HDBR but sinus cardiac arrhythmias were observed in two subjects of the control group and nodal cardiac arrhythmias were observed in two subjects in Qigong group after HDBR. No cardiac arrhythmia was found in hypoxia group. CONCLUSION: Hypoxia is more effective in countermeasuring orthostatic intolerance after weightlessness than Qigong.

Adult↗
PubMed1998

[Changes of brain potentials related to selective mental arithmetic during simulated weightlessness].

To study the effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) during a selective mental arithmetic task were compared between head down tilt (HDT) and head up tilt (HUT) in 15 normal subjects. The results were: target (T) flash signals induced significant slow positive potentials and they decreased significantly in amplitude especially during HDT as compared with that during HUT. The data provide new evidence indicating that the ability of brain response declined during simulated weightlessness.

Adult↗
PubMed2004

[Ultrastructural changes in cerebral cortex and cerebellar cortex of rats under simulated weightlessness].

OBJECTIVE: To study the ultrastructural changes in the cerebral cortex and cerebellar cortex of rats under simulated weightlessness and the possible mechanism. METHOD: The tail-suspended rats model (-30 degrees head down tilt) was adopted to simulate weightlessness in the experiment. The rats were suspended for 7 d, 14 d, 21 d, and 28 d, and then were perfused through the hearts. The specimens were drawn from the rats' cerebral cortex and cerebellar cortex for electron microscopy. RESULT: The results showed that under simulated weightlessness, the main changes in the neuron can be described as follows: swelling of mitochondria, endoplasmic reticulum and Golgi complex, even formation of big empty vesicles; reduction of number of synaptic vesicles in IV layer; increase corrugation of capillary lumen and thickening of basement membrane. Degranulation of rough endoplasmic reticulum in Purkinje's cells of the cerebellar cortex occurred obviously. On the 14th and the 21st day of suspension, the changes were most significant and tended to return to normal on the 28th day. CONCLUSION: The experimental results demonstrated that simulated weightlessness led to ultrastructural changes in the cerebral cortex and cerebella cortex of rats. The ultrastructure changed with the course of simulated weightlessness and tended to return to normal. It showed an adaption to the simulated weightlessness.

Adaptation, Physiological↗
PubMed1999

[Echocardiographic assessment of left ventricular structure and function after simulated weightlessness in rats].

Objective. To investigate whether the changes in rat after simulated weightlessness are similar to those in astronaut after flight. Methods. The effects of 4 wk tail-suspension on left ventricular structure and function in rats were examined by echocardiography. Results. After 4 wk of simulated weightlessness, the thickness of both the anterior and posterior wall in left ventricle (LV) showed a general trend of decrease, but these changes were not statistically significant; the end-systolic and end-diastolic internal dimensions (ESD and EDD respectively) of LV decreased significantly; and the end-systolic volume, end-diastolic volume and stroke volume (ESV, EDV and SV respectively) were all reduced; so did the relevant indices of them. There were no significant differences in ejection fraction (EF) and fractional shortening (FS) between the tail-suspended and control groups. The left ventricular mass (LVM) and its index (LVMI) were decreased. The peak velocities of blood flow of aorta, pulmonary artery and mitral valve didn't show any significant change after simulated weightlessness. Conclusion. Medium-term simulated weightlessness may lead to a significant decrease in left ventricular internal dimension, ventricular volume, and mass, and a trend of decrease in mean left ventricular wall thickness. These changes in rats are similar to those observed in astronauts postflight.

Animals↗
PubMed1996

[Changes of brain potentials related to visual attention during simulated weightlessness].

To study the possible effect of simulated weightlessness on brain function state, the brain event-related potentials (ERPs) during a simple visual selective response task were compared between head down tilt (HDT) and head up tilt (HUT) in 9 normal subjects. The results were: both the target (T) and non-target (NT) flash signals induced significant slow positive potentials which were supposed to be related to the attention activity; the amplitude of the positive potentials in the frontal regions decreased significantly especially for NT-ERPs during HDT as compared with that during HUT. The data provide new evidence indicating that the ability of brain response declined during simulated weightlessness and more attention should be paid to the study of brain function during space flight.

Attention↗
PubMed1998

Alteration of vasoreactivity of mesenteric arteries in rats after two-week simulated weightlessness.

To investigate the effects of simulated weightlessness on vasoreactivity of mesenteric arteries, rats were tail-suspended for two weeks, and vasoreactivity were studied in vitro using isolated mesenteric arterial ring. The results showed that maximal contractile responses to KCl (10-80 mmol/L) and phenylephrine (PE, 10(-10)-10(-4) mol/L) were attenuated in arterial rings isolated from tail-suspended rats. After constriction caused by 10(-7) mol/L PE, maximal dilatory responses induced by sodium nitroprusside (SNP, 10(-10)-10(-4) mol/L) were not different between tail-suspended and control groups. These data indicated that contractile ability of mesenteric artery was diminished by tail-suspension, whereas the dilatory capacity of arterial smooth muscle was not altered.

Animals↗
PubMed2002

[Effects of simulated weightlessness on ultrastructure of soleus muscle spindle in rats].

OBJECTIVE: To study changes in ultrastructure of soleus muscle spindle induced by simulated weightlessness in rats. METHOD: Weightlessness was simulated by tail suspension in female rats. The ultrastructure of isolated soleus muscle spindle were observed in 4 d, 7 d, 14 d tail-suspended and 14 d recovered rats. RESULT: Chaotic myofibril, hyperplasia of mitochondria, and enlargement of terminal cisterna were found in the ultrastructure of isolated soleus muscle spindle in 4 d tail-suspended rats. The ultrastructure of isolated soleus muscle spindle in 7 d tail-suspended rats showed more distinct changes, while that in 14 d tail-suspended rats showed obvious retrograde changes. The ultrastructure of isolated muscle spindle in 14 d recovered rats after 14 d tail-suspension were similar to that of control group. CONCLUSION: Simulated weightlessness could induce time-related and reversible changes in ultrastructure of soleus muscle spindle in rats.

Animals↗
PubMed2000

Changes in myocardial contractility and contractile proteins after four weeks of simulated [correction of simulate] weightlessness in rats.

The interaction between the gravitational field, the position of the body, and the functional characteristics of the blood vessels determines the distribution of intravascular volume. In turn, this distribution determines cardiac pump function. One of the most profound circulatory changes that occurs in man during exposure to weightlessness is a cephalad redistribution of fluid caused by the lack of hydrostatic pressure in this microgravitative environment. The cephalad redistribution of fluid results in a loss of blood volume and then induces a decrease in preload. Recently, a decrease in sensitivity of arteriole to catecholamine has reported in rats of simulated weightlessness. This change in arteriole may reduce afterload. As a result, cardiovascular system may be shifted to a hypokinetic state during weightlessness condition for long-term. Echocardiographic data from astronauts during space flight showed an increase in heart rate, a 12 % decrease in stroke volume, and a 16 % decrease in left end diastolic volume. Electron-microscopic studies have shown changes in cardiac morphology in rats after exposure to microgravity for 7-12.5 days. After the COSMOS 2044 flight for 14 days, the light-microscopic studies have shown an atrophy of papillary muscles in rats left cardiac ventricle. It is not clear whether the function of atrophic myocardium is impaired. The data in three aspects as mentioned above suggest that weightlessness or simulated weightlessness may decrease the myocardial function. However, definite changes in cardiac performance have been hard to prove due to many limits. This studies were to answer two questions: Is the myocardial contractility depressed in rats subjected to simulated weightlessness for four weeks? What are the underlying mechanisms of the changing contractility?

Animals↗
PubMed2004

[Effects of BMP-2 on the gene expression of rat osteosarcoma cells under simulated weightlessness].

OBJECTIVE: To investigate the effect of BMP-2 on (the) gene expression of rat osteosarcoma cells (ROS17/2.8) under rotating clinostat simulated weightlessness. METHOD: ROS17/2.8 cells were cultivated in 1 G control and rotating clinostat simulated weightlessness with 500 ng/ml BMP-2 in the culture medium. Total RNA in cells was isolated after 24, 48 and 72 h. Reverse transcription PCR analysis was made to examine the gene expression of alpha 1 chain of type I collagen (collagen I alpha 1) and alkaline phosphatase (ALP). RESULT: The expression of COL-I alpha 1 mRNA induced by BMP-2 was much more than that without BMP-2 in 24 h and 48 h group (P<0.01). The level of ALP mRNA induced by BMP-2 was significantly high in 48 h or 72 h group (respectively P<0.01, P<0.05). The level of BMP-2 induced expression of COL-I alpha 1 mRNA was significantly lower under 48 h of simulated weightlessness than in 1 G condition (P<0.01). The level of ALP mRNA was significantly lower under simulated weightlessness for 48 h or 72 h (P<0.01). CONCLUSION: BMP-2 can stimulate the differentiation of ROS17/2.8 cells in 1 G condition and this process is reduced under simulated weightlessness.

Alkaline Phosphatase↗
PubMed1977

Dynamics of sleep patterns during prolonged simulated weightlessness.

Subjects immersed for 6 days in water, simulating weightlessness, exhibited marked changes in the total time spent in sleep and in the percentage of that time spent in each sleep stage. The length of time spent in Stage 4 deep sleep and in REM sleep decreased in the first half of the 6-day immersion period. During the latter half of the immersion period, a clear adaptive response was observed in the sleep patterns: the sequential appearance of the different stages of sleep and the percentage of time spent in the six stages of sleep showed a clear approach to the pre-immersion data. During the 3-day post-immersion period, the patterns approached the normal pre-immersion levels, although there was some overshoot or a negative phase period characterizing this approach. By the sixth day of immersion, the percentage of time spent in each stage of sleep had returned to near normal pre-immersion values, but the total time spent in sleep was still somewhat less than normal. This fact suggests that, once adapted to a condition of weightlessness, the sleep requirement may be less than during normal ambulatory life. During the post-immersion period, the pattern of Stage 4 sleep at early evening, midnight and dawn showed no special reactive characteristics, but rather a clear recovery towards the original pattern. On the other hand, at the duration of REM sleep, it overshot the pre-immersion values at the beginning of the post-immersion period, and then returned to the original pattern. These experiments suggest that some of the changes in sleep patterns which are observed under conditions simulating weightlessness may be adaptive.

Adaptation, Physiological↗
PubMed1999

[Vasoconstrictor responsiveness of rat basilar artery enhanced by simulated weightlessness].

OBJECTIVE: To investigate the effects of simulated weightlessness on contractile responsiveness of the basilar artery. METHODS: Rats were subjected to tail-suspension for 4-wk to simulate the effect of weightlessness, responses of perfused isolated basilar arterial rings to various vasoactive compounds were examined. RESULTS: Maximal isometric contractile responses to KCl [ (10~100) mmol/L], arginine vasopressin [AVP, (10(-15)~10(-7) mol/L], or 5-hydroxytryptamine [5-HT, (10(-12) ~ 10(-4) mol/ L] were significantly enhanced in arterial rings isolated from 4-wk tail-suspended as compared with that from simultaneous control rats. CONCLUSION: These results indicate that medium-term simulated weightlessness may result in an enhanced contractile responsiveness in rat basilar artery, and strongly support the hypothesis of cerebrovascular syncope-initiating mechanism.

Aerospace Medicine↗
PubMed2003

[Influence of simulated weightlessness on the morphology of nerve endings of muscle spindle in rat soleus muscle].

OBJECTIVE: To study changes in structure and innervation of soleus muscle spindle in rats induced by simulated weightlessness. METHOD: Weightlessness was simulated by tail suspension in female rats. The technique of Fawosky's Staining was used to detect the morphology of nerve endings of soleus muscle spindle in 7 d, 14 d, 21 d tail-suspended and control rats. RESULT: The intrafusal muscle fibers were regular and nerve endings were intact and clear in the soleus spindles of control rats. No obvious change was observed in muscle spindles of 7 d tail-suspended rats. Intrafusal muscle fibers became irregular, with rough and vague nerve endings in 14 d tail-suspended rats. The distinct retrograde change of muscle spindles and nerve endings were observed in 21 d tail-suspended rats. Degeneration and rupture were found in nerve endings, which made it unclear and pale in staining. CONCLUSION: Simulated weightlessness could induce time-related changes in structure and innervation of soleus muscle spindle in rats.

Animals↗
PubMed1998

[Study on mechanisms of T lymphocyte function changes in mice under simulated weightlessness in terms of IL-2 and Bcl-2 gene transcription].

To understand the mechanisms of T lymphocyte function changes under simulated weightlessness T lymphocyte proliferation (MTT assay), IL-2 production (biological assay), IL-2 gene (dot blot) and Bcl-2 oncogene (RT-PCR) transcription of splenic cell were observed in mice. The results showed that on the 7 th and 14 th day of simulated weightlessness T lymphocyte proliferation and IL-2 production decreased and significant on the 14 th day; on the 7 th and 14 th day of simulated weightlessness IL-2 and Bcl-2 gene transcription decreased, significant on the 14 day. It demonstrated that simulated weightlessness inhibits IL-2 production by decreasing IL-2 gene transcrition. IL-2 and Bcl-2 gene may be regulators of lymphocyte function under simulated weightlessness.

Animals↗
PubMed2001

Simulated weightlessness alters the nycthemeral distribution of energy expenditure in rats.

The energy metabolism adaptations to simulated weightlessness in rats by hindlimb tail suspension are unknown. 12 male rats were assigned to 7 days of isolation, 7 days of habituation to the suspension device, 10 days of simulated weightlessness, and 3 days of recovery. The 24-hour energy expenditure was measured by continuous indirect calorimetry. We calculated the 12-hour energy expenditure during the active (night) and inactive (day) periods, the minimal observed metabolic rates with the day values taken as an index of the basal metabolic rate, and the non-basal energy expenditure representing the cost of physical activity plus the diet-induced thermogenesis. Suspension did not change the mean 24-hour energy expenditure (360.8+/-15.3 J min(-1) kg(-0.67)), but reduced the night/day difference by 64 % (P<0.05) through a concomitant drop in night-energy expenditure and increase in day values. The difference between night and day minimal metabolic rates was reduced by 81 % (P<0.05), and the transient rise in day values suggests an early and moderate basal metabolic rate increase (9 %). An overall 19 % reduction in non-basal energy expenditure was observed during simulated weightlessness (P<0.05), which was mainly attributable to a reduction in the cost of physical activity. 3 days of recovery restored the night/day differences but increased the 24-hour energy expenditure by 10 % (P<0.05). In conclusion, hindlimb tail suspension in rats did not alter the 24-hour energy expenditure, but it transiently increased the basal metabolic rate, and altered both the energy expended on physical activity and the nycthemeral distribution of motor activity. These data suggest that the circadian rhythms of energy expenditure are affected during simulated weightlessness.

Animals↗
PubMed2002

The effect of simulated weightlessness on hypobaric decompression sickness.

BACKGROUND: A discrepancy exists between the incidence of ground-based decompression sickness (DCS) during simulated extravehicular activity (EVA) at hypobaric space suit pressure (20-40%) and crewmember reports during actual EVA (zero reports). This could be due to the effect of gravity during ground-based DCS studies. HYPOTHESIS: At EVA suit pressures of 29.6 kPa (4.3 psia), there is no difference in the incidence of hypobaric DCS between a control group and group exposed to simulated weightlessness (supine body position). METHODS: Male subjects were exposed to a hypobaric pressure of 29.6 kPa (4.3 psi) for up to 4 h. The control group (n = 26) pre-oxygenated for 60 min (first 10 min exercising) before hypobaric exposure and walking around in the altitude chamber. The test group (n = 39) remained supine for a 3 h prior to and during the 60-min pre-oxygenation (also including exercise) and at hypobaric pressure. DCS symptoms and venous gas emboli (VGE) at hypobaric pressure were registered. RESULTS: DCS occurred in 42% in the control and in 44% in simulated weightlessness group (n.s.). The mean time for DCS to develop was 112 min (SD +/- 61) and 123 min (+/- 67), respectively. VGE occurred in 81% of the control group subjects and in 51% of the simulated weightlessness subjects (p = 0.02), while severe VGE occurred in 58% and 33%, respectively (p = 0.08). VGE started after 113 min (+/- 43) in the control and after 76 min (+/- 64) in the simulated weightlessness group. CONCLUSIONS: No difference in incidence of DCS was shown between control and simulated weightlessness conditions. VGE occurred more frequently during the control condition with bubble-releasing arm and leg movements.

Adolescent↗