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PubMed2000

Unique postural control of upside-down swimming catfish, Synodontis nigriventris, not affected by the change of gravity.

In general, most fishes maintain a swimming posture with the dorsal side towards the water surface under normal gravity condition. In contrast to normal fishes, a catfish Synodontis nigriventris, shows a unique postural control. The catfish keeps its posture with the ventral side towards the water surface and the dorsal side towards water bottom under normal gravity. This evidence leads one to assume that the upside-down posture of the catfish is controlled by gravity sensation in a manner different from that of other fishes. However, it has remained unclear to date whether the gravity sensation contributes to the unique postural control of this catfish. We examined its postural control in intact and labyrinth-removed catfish using a clinostat which generates a specific gravity environment (pseudo-microgravity) on earth. In addition, we examined its postural control under microgravity during parabolic flights.

Animals↗
PubMed2000

Rotation in clinostat results in apoptosis of osteoblastic ROS 17/2.8 cells.

Clinostat is an effective, ground-based tool which can be used to verify data from space flight, and to test hypotheses and experimental conditions for eventual space flights. Rotation in clinostat appears to mimic the microgravity environment by nulling the gravitational vector by continuous averaging. In the present study, we exposed osteoblast-like ROS 17/2.8 cells to a vector-averaged gravity environment in a clinostat and found that the cells undergo apoptotic death during the first 24 hr of clino-rotation. We suggest that apoptosis might be one of the mechanisms for reduced bone formation as observed in actual space flights.

Apoptosis↗
PubMed1994

Changes in serum 1,25-dihydroxyvitamin D3 and mRNAs for osteocalcin and alkaline phosphatase in femur unloaded by tail suspension in rats.

To elucidate the mechanism involved in the development of disuse atrophy of bone by skeletal unloading, changes in osteocalcin and alkaline phosphatase mRNAs, markers for bone formation, were studied in the hind limb bones of tail-suspended rats. Tail suspension for 8 and 14 days resulted in a significant decrease in osteocalcin mRNA in the femur when compared with age-matched non-suspended controls. Serum 1,25-dihydroxyvitamin D3 decreased to 60% of the control level after 8 days of skeletal unloading but regained almost normal levels over the next 7 days. Since it is known that vitamin D3 up regulates and glucocorticoid down regulates transcription of the osteocalcin gene, the endocrine response evoked by tail suspension may have aggravated the disuse atrophy caused by skeletal unloading in this study.

Alkaline Phosphatase↗
PubMed1995

Catecholamine response to stress: age related modifications in tail-suspended rats.

The catecholamine response to acute stress has been shown to change with age. However, alterations under chronic stress conditions have not been established. This study attempted to determine whether aging modifies the catecholamine response to chronic stress load in rats subjected to tail suspension. Urinary excretions of epinephrine (E) and norepinephrine (NE) were monitored before and during the tail suspension experiments in rats at two different ages: 5 weeks old (young) and 18 months old (aged). Basal excretions of E and NE before the suspension were higher in the aged rats, indicating that sympathetic-adrenal medullary activities increase with age under resting conditions. The chronic stress load elicited E responses in the aged rats similar to those in the young rats. The NE responses, however, were completely different in that tail suspension caused a greater increase in NE excretion in the young rats than in the aged rats. This finding suggests that the sympathetic response to chronic stress load changes with age.

Adrenal Glands↗
PubMed2003

[Effects of 21 d -6 degrees head down bed-rest on pulmonary gas distribution and little airway function].

OBJECTIVE: To probe the effect of 21 d -6 degrees head down bed-rest (HDBR) on pulmonary gas distribution and little airway function. METHOD: The indices of the pulmonary gas distribution and little airway function (delta N2, CV, CV/VC%, LCI) were measured in 16 healthy male subjects before, during and after 21 d -6 degrees HD-BR. RESULT: Comparing with before and early days of HDBR, recovery supine delta N2 increased significantly. CV increased significantly only on the first day of HDBR, and changes of CV/VC% were same as CV. The changes of LCI were not significant. CONCLUSION: The indices of pulmonary gas distribution were affected by 21 d -6 degrees HDBR. Pulmonary gas distribution was more uneven during and after 21 d -6 degrees HDBR.

Adolescent↗
PubMed2003

[Preventive effects of exercise training on bone loss during 21 d -6 degrees head down bed-rest].

OBJECTIVE: To observe the protective effects of exercise training during 21 d -6 degrees head down bed rest (HDBR) on bone loss. METHOD: Ten healthy young men were randomly divided into HDBR group and HD-BR exercise group, with 5 in each group. Both groups were exposed to -6 degrees head down bed rest for 21 d. The subjects in the exercise group performed exercise with a bicycle ergometer in supine position 1 h/d during bed rest. Femur bone mineral density (BMD), serum bone gla protein (BGP) as well as hydroxyproline/creatinine (HOP/Cr) were determined before and during 20 d HDBR. RESULT: As compared with the before HDBR values, average femur BMD decreased by 5.8% and 0.9% for HDBR group and HDBR and exercise group respectively. HOP/Cr significantly increased in the HDBR group and was significantly higher than the HDBR exercise group. BGP decreased in both groups with no significant difference. CONCLUSION: Exercise during 21 d -6 degrees HDBR is beneficial in preventing bone loss.

Adolescent↗
PubMed2002

Effects of chronic hindlimb suspension on landing performance in response to head-down drop in rats.

Effects of hindlimb unloading and reloading on the patterns of landing and posture adjustment in response to head-down drop from a height of approximately 30 cm were investigated in rats. Seven weeks old male Wistar rats were hindlimb-unloaded by tail suspension for 9 consecutive weeks. Motor tests were performed immediately after the termination of suspension and recovery patterns were checked during 8 weeks of ambulation recovery. Although all of the control rats were able to land smoothly by using the four limbs as the shock absorber, the unloaded rats landed by hitting their abdomen. The hindlimb-unloaded, but not control, rats dorsi-flexed their trunk during fall. The mean angle of abdominal side was approximately 145 degrees in control and approximately 215 degrees in unloaded rats. Even though such phenomena were maintained for approximately 12 hours, the response of the trunk angle recovered significantly 2 days later. However, it was not normalized completely even after 8 weeks. Hyper-extension of ankle joints and eversion of hindlimbs at landing were also noted in the unloaded rats. These phenomena were not recovered at all. It was generally suggested that severe detrimental effects on the landing performance of rats are induced following 9-weeks of suspension. And some of the responses are irreversible.

Abdominal Muscles↗
PubMed2003

Cranial diameter pulsations measured by non-invasive ultrasound decrease with tilt.

INTRODUCTION: Intracranial pressure (ICP) may play a significant role in physiological responses to microgravity by contributing to the nausea associated with microgravity exposure. However, effects of altered gravity on ICP in astronauts have not been investigated, primarily due to the invasiveness of currently available techniques. We have developed an ultrasonic device that monitors changes in cranial diameter pulsation non-invasively so that we can evaluate ICP dynamics in astronauts during spaceflight. This study was designed to demonstrate the feasibility of our ultrasound technique under the physiological condition in which ICP dynamics are changed due to altered gravitational force. METHODS: Six healthy volunteers were placed at 60 degrees head-up, 30 degrees headup, supine, and 15 degrees head-down positions for 3 min at each angle. We measured arterial blood pressure (ABP) with a finger pressure cuff, and cranial diameter pulsation with a pulsed phase lock loop device (PPLL). RESULTS: Analysis of covariance demonstrated that amplitudes of cranial diameter pulsations were significantly altered with the angle of tilt (p < 0.001). The 95% confidence interval for linear regression coefficients of the cranial diameter pulsation amplitudes with tilt angle was 0.862 to 0.968. However, ABP amplitudes did not show this relationship. DISCUSSION: Our noninvasive ultrasonic technique reveals that the amplitude of cranial diameter pulsation decreases as a function of tilt angle, suggesting that ICP pulsation follows the same relationship. It is demonstrated that the PPLL device has a sufficient sensitivity to detect changes non-invasively in ICP pulsation caused by altered gravity.

Adult↗
PubMed2003

The impact of skeletal unloading on bone formation.

Skeletal unloading leads to decreased bone formation and decreased bone mass. Bone resorption is uncoupled from bone formation, contributing to the bone loss. During space flight bone is lost principally from the bones most loaded in the 1 g environment. Determining the mechanism(s) by which loading of bone is sensed and translated into a signal(s) controlling bone formation remains the holy grail in this field. It seems likely that matrix/cell interactions will underlie much of the mechanocoupling. Integrins are a prime mediator of such interactions. The role for systemic hormones such as PTH, GH and 1,25(OH)2D compared to locally produced factors such as IGF-I, PTHrP, BMPs and TGF beta in modulating the cellular response to load remains unclear. Our studies demonstrate that skeletal unloading leads to resistance to the anabolic actions of IGF-I on bone as a result of failure of IGF-I to activate its own signaling pathways. This is associated with a reduction in integrin expression, suggesting crosstalk between these two pathways. As the mechanism(s) by which bone responds to changes in mechanical load with changes in bone formation is further elucidated, applications of this knowledge to other etiologies of osteoporosis are likely to develop. Skeletal unloading provides a perturbation in bone mineral homeostasis that can be used to understand the mechanisms by which bone mineral homeostasis is maintained, and that such understanding will lead to effective treatment for disuse osteoporosis in addition to preventive measures for the bone loss that accompanies space travel.

Aerospace Medicine↗
PubMed2003

[Mechanisms of impairment of precise movements during long-term hypokinesia].

Antiorthostaic hypokinesia (AOHK) was found to entail a considerable diminishing of the control system's precision abilities. In the first 14-30 days of the AOHK (the 1st stage), variability of interimpike intervals (ISI) was sharply increased as well as the degree of synchronisation of the motor units' (MU) activity; starting from the 30th day (the 2nd stage), a regular diminishing of the ISI occurred and the MU synchronisation disappeared. The data obtained suggest the different nature of the precision disorders during the 1st and the 2nd stages of the AOHK: a reflex responses to support unloading and the atrophic processes in the muscles, respectively.

Aerospace Medicine↗
PubMed2003

[Effect of deafferentation on the size and myosin phenotype of muscle fibers during stretching of rat m. soleus and gravitational unloading].

The study was purposed to evaluate the contribution of the reflectory and local components during the chronic stretch of the postural muscle to the attenuation of the unloading-induced fiber size reduction and changes in the myosin heavy chain (MHC) profile. The surgical unilateral deafferentation (dorsal rhizotomy) was used. It was shown that unilateral deafferentation didn't influence on the amelioration of unloading-induced fiber size reduction in chronically stretched soleus muscle. Thus, the results obtained in the present study don't confirm the hypothesis, supposing the predominant contribution of the muscle afferent activation to the attenuation of unloading-induced fiber atrophy. Deafferentation of unloaded as well as control rats leads to the increase of the percentage of fibers expressing slow MYC isoforms.

Animals↗
PubMed2003

[The water-salt balance and renal function in space flights and in model experiments].

Study of a condition of mineral and water-electrolyte metabolism, function of kidneys, and their hormonal regulation during model experiments (hypokinesia, bed rest, immersion etc.), and also in space flights and in readaptation period, has shown a major role of water-electrolyte homeostasis during general adaptation of humans and animals to new conditions of life and to conditions of weightlessness in particular. The change in regulation of volumes of fluid milieu in an initial period of weightlessness was shown to be the consequence of redistribution of blood and hemodynamics of the shifts resulting in change of production of volume-regulation hormones, formation of negative water balance, and redistribution of fluid in the organism among various fluid compartments. At later stages of flight or long-term hypokinesia, a change of water-electrolyte homeostasis occurs with a decrease in the kidneys excretion of sodium, and diuresis, but with an increased excretion of calcium and production of ADH and RAAS hormones. Following returning to earth gravitation, the majority of astronauts have adaptive reactions, compensating for the loss extracellular fluid and mineral substances and formation of "earth" water-electrolyte homeostasis. For estimation of water-electrolyte homeostasis and the functions of kidneys in astronauts, various functional loading tests have been developed. The developed system of preventive maintenance is successfully used for abolition of adverse changes at various stages of space flight and in readaptation period.

Astronauts↗
PubMed2003

[Changes of dentin, dental pulp and periodontium tissue in tail-suspended rats].

OBJECTIVE: To investigate the metabolic changes of calcium and phosphorus in dentin, dental pulp and periodontium in tail-suspended rats, and the functions of TGF-beta 1, c-fos, collagen-I and collagen IV in dentin, dental pulp and periodontium. METHOD: Relative percentage contents of Ca, P in dentin, dental pulp and periodontium were measured with scanning electron microscope and energy spectrum analytical system in 3 groups of rats. The expression of TGF-beta 1, c-fos, collagen-I and collagen IV were also observed. RESULT: In the suspension group, the relative percentage content of Ca declined significantly, while P increased slightly. There were no significant differences of Ca, P in alveolar bone. The expressions of TGF-beta 1, c-fos and collagen-I declined, but the expression of collagen-IV in pulp vessel increased. There were no significant changes of expressions of TGF-beta 1, c-fos, collagen-I and collagen-IV in the vicinity of PDL. After adopting artificial countermeasures, the above expressions restored partly. CONCLUSION: Weightlessness might cause abnormal mineralization in dentin, and 1.5 G artificial countermeasures could eliminate the above changes of mineral metabolism. The poor mineralization of dentin might be associated with the reduced secretion of TGF-beta 1, c-fos and collagen-I in tail-suspended rats.

Animals↗
PubMed2003

[Effects of exercise training during 21 d -6 degrees head down bed rest on dynamic posture equilibrium and motor coordination].

OBJECTIVE: To study the effects of 21 d -6 degrees head down bed rest (HDBR) with exercise training on dynamic posture equilibrium and motor coordination. METHOD: Ten healthy young men were randomly divided into HDBR control groups and HDBR exercise groups, with 5 in each group. The subjects in the exercise group performed exercise with a bicycle ergometer in the supine position 1 h/d during bed rest. Dynamic posture equilibrium as well as isokinetic concentric muscular strength were determined before and after 21 d HD-BR. RESULT: After HDBR, average dynamic proprioception score and dynamic motor coordination decreased significantly, relative peak torque (peak torque /body weights PT/BW) also decreased significantly and accompanied with increase of the peak torque ratio between hamstrings and quadriceps (H/Q) in HDBR control groups. Average dynamic proprioception score and dynamic motor coordination in the HDBR exercise groups remained above the HDBR control groups, but the H/Q ratio showed no significant change. CONCLUSION: The results showed that exercise training during 21 d -6 degrees head-down tilt bed-rest do have beneficial effects on retaining the dynamic posture equilibrium and dynamic motor coordination of the subjects after bed rest.

Adolescent↗
PubMed2003

[Changes of endocrine hormones during -6 degrees head down bed rest in human].

OBJECTIVE: To investigate changes of endocrine hormones during 7 d head down bed rest (HDBR). METHOD: Six healthy male volunteers served as the subjects and experienced 7 d -6 degrees HDBR. Urine was collected from 6:00-22:00 and from 22:00-6:00. Serum was collected 48 h before HDBR, 48 h and 120 h during HDBR. Then the endocrine indices in urine and serum were determined. RESULT: 1) The levels of serum CORT and ALD increased at 48 h during HDBR, while serum T3, T4, TP, UN decreased but they all recovered to normal at 120 h during HDBR. 2) The level of urine CORT, ALD and NE reached its peak in 24-48 h, and then gradually decreased to normal level. CONCLUSION: The endocrine indices in serum and urine changed in the early period but returned to normal level gradually with the proceeding of HDBR.

Adaptation, Physiological↗
PubMed2002

Effects of nine weeks of unloading on neuromuscular activities in adult rats.

Effects of 9-week hindlimb suspension and 8-week recovery on locomotor performance and electromyogram (EMG) activities of soleus (Sol), plantaris (Pl), lateral gastrocnemius (LG), and tibialis anterior (TA), were studied in adult rats. Hyperextension of knee and ankle joints, noted after nine weeks of suspension, did not recover during 8-week ambulation. Growth of Sol was fully inhibited by suspension and did not recover completely within 8 weeks of ambulation. The EMG levels in Sol, Pl, and LG 1 day after suspension were 52-76% less than the pre-suspension level (resting on the floor). These activities were recovered to or near the pre-suspension level around 1 week, but decreased again to 10-29% of controls from 7 to 9 weeks. The integrated EMG of TA was elevated during the first week of suspension but then gradually declined to control levels within four weeks. At the end of suspension, the Sol and Pl, not the LG, EMGs remained reduced and the TA EMG remained hyperactive. Co-activation of dorsi- and plantar- flexors occurred often during quadripedal walking following suspension. Such a phenomenon was not observed in the control rats. These phenomena were recovered within 1 week. It is suggested that the unloading-related alterations of neuromuscular activities and/or locomotion, but not the hyperextension of knee and ankle joints, in rats are reversible.

Animals↗