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The dissipative Kerr soliton combs based on microresonators have attracted wide attention due to their high coherence and on-chip integration. Meanwhile, the soliton microcombs have shown broad applications in coherent communication, on-chip low-noise microwave synthesizer, optical clock, etc. However, the performance of these applications is typically limited by their bandwidth as the precise tuning of the soliton microcombs usually relies on the thermoelectric cooler, which is slow and may increase the system’s complexity. Here, we demonstrate the observation of dissipative solitons based on the magnesium fluoride resonator with an ultrahigh-quality (Q) factor of about 927 million. The ‘power-kicking’ scheme is employed to lock and stabilize the solitons actively. Also, tuning the acousto-optical modulator allows changing the bandwidth and recoil of the solitons. This approach enables more direct and concise feedback and reduces the system’s complexity.

Flaxseed meal extracted by cold pressing was degummed and defatted by enzyme to obtain flaxseed protein. The application of flaxseed protein in ice cream was studied. The factors influencing flax protein ice cream were flax protein, cream, skim milk powder and sucrose. The formula of flax protein ice cream was optimized by single factor and orthogonal experiments with sensory evaluation as index. The optimum formula was determined as follows: flax protein content 3%, skimmed milk powder content 13%,cream content 15%, and sucrose content 16%. The sensory score of flax protein ice cream was 95.32 ± 0.41,the expansion rate was 69.67% ± 0.91%, and the melting resistance was 5.28% ± 0.98%.

The dissipative Kerr soliton combs based on microresonators have attracted wide attention due to their high coherence and on-chip integration. Meanwhile, the soliton microcombs have shown broad applications in coherent communication, on-chip low-noise microwave synthesizer, optical clock, etc. However, the performance of these applications is typically limited by their bandwidth as the precise tuning of the soliton microcombs usually relies on the thermoelectric cooler, which is slow and may increase the system's complexity. Here, we demonstrate the observation of dissipative solitons based on the magnesium fluoride resonator with an ultrahigh-quality (Q) factor of about 927 million. The 'power-kicking' scheme is employed to lock and stabilize the solitons actively. Also, tuning the acousto-optical modulator allows changing the bandwidth and recoil of the solitons. This approach enables more direct and concise feedback and reduces the system's complexity. [ABSTRACT FROM AUTHOR]

The aim of this study was to, from the point of neurogenic inflammation, explore the pathogenesis of colitis and to provide direct evidence for the neurogenic colitis hypothesis. Male Sprague-Dawley rats (180-220 g) anesthetized with chloral hydrate were intrathecally (ith) implanted with polyethylene-10 (PE-10) catheter to reach the spinal cord T₁₂-L₅ level. Substance P (SP) was ith injected once a day for 14 d. The disease active index (DAI) score was calculated by rat body weight and stool. The macroscopic and HE staining-microscopic pathologies of colon/spinal tissue were evaluated. By immunofluorescence staining, the protein expression of a pro-inflammatory cytokine, migration inhibitory factor (MIF), in colon tissue was detected and was semi-quantitatively analyzed. The results showed that in the colon tissue, inflammation was dose-dependently aggravated by ith SP 10 μ and 20 μ, whereas in the spinal tissue, only slight edema and congestion were seen in SP 20 μ group. The MIF protein of colon tissue was increased in ith SP 10 μ and 20 μ groups (P<0.05, P<0.01 as compared to normal saline group respectively), but in the spinal tissue, there was no obvious MIF protein expression either in SP groups or in normal saline group. Pretreatment with neurokinin-1 (NK₁) receptor antagonist ([D-Pro2, D-Trp7, 9] -SP, 22.4 μ, ith, 10 min before ith SP) prolonged the latency of DAI rising and reduced the DAI amplitude, as well as prevented the high MIF expression induced by ith SP. These results suggest that rat colitis can be induced by direct SP stimulation in lumbar spine via activating central NK₁ receptor; and that colonic MIF is possibly one of the inflammatory factors involved in this pathogenesis. These data provide a reasonable support to the hypothesis of colitis being a neurogenic inflammation. In addition, a potential clinical significance for the finding that higher concentration of spinal SP can induce colitis via NK₁ receptor is discussed.

In recent years, there has emerged academic tendency towards the neurogenic mechanism of ulcerative colitis (UC). As one of the supports to the hypothesis of UC being a neurogenic inflammation, we have built a colitis model by intrathecal (ith) injection of a haptten 2,4-dinitrochlorobenzene (DNCB) to DNCB-sensitized rats. In order to explore further the neuroimmunal mechanism of this colitis model, we here focused on a pro-inflammatory cytokine, migration inhibitory factor (MIF), to observe its expression in rat colon nervous tissue and spinal cord in the colitis induced by ith injection of DNCB. At the same time we also observed the effect of MIF antibody pretreatment on the disease active index (DAI) score and the colon pathology by HE staining in the colitis rats. The results obtained showed that the immunofluorescence intensity of double staining of MIF protein in colon nervous tissue and spinal cord was increased in 0.8% and 1.6% DNCB-induced colitis groups than that in the control (60% ethanol) group. Both the colon pathology and the DAI score were significantly reduced by MIF antibody ith pretreatment. Ith injection of 0.8% DNCB after MIF antibody (1:10, 1:5) pretreatment could only induce lower DAI score (P<0.01 as compared, respectively, to the IgG pretreatment group). The colon pathological changes in ith 0.8% DNCB rats were mild, even little after MIF antibody (1:10, 1:5) pretreatment. These results suggest that MIF in spinal cord and enteric nervous system is possibly involved in the rat colitis induced by ith injection of DNCB, which reflects a neuroimmunal mechanism underlying this kind of colitis. MIF is possibly one of the important neurochemical factors in this experimental colitis, even in the UC.

High sustained positive Gz (+Gz) exposures have been shown to have a pathophysiological impact on the brain in rats. However, the consequence for brain function such as learning and memory remains elusive. In the present study, we investigated locomotor activity, learning ability and memory in rats over 6 days (d) following +6 Gz/3 min and +10 Gz/3 min exposures. In an open field test, rats treated with +10 Gz showed a significant increase in the time spent in the center square immediately and 2d after exposure compared with control rats. In contrast, the number of grid crosses and number of rears of rats decreased significantly immediately after +6 Gz and +10 Gz exposures. In addition, a Y-maze test revealed that +Gz exposures reduced the number of correct responses and increased total reaction time in rats, and the number of correct responses was negatively correlated with the total reaction time in all groups throughout the period of study. Moreover, the passive avoidance test exhibited that the latency increased significantly on 0 d and decreased significantly on 6 d after +Gz exposures compared with control. Thus, +6 Gz/3 min and +10 Gz/3 min exposures may transiently decrease locomotor activity, impair learning, and induce a deficit in memory retention in rats.

Increased venous compliance in lower limbs may be contributed to postflight orthostatic intolerance; however, direct animal studies to address the changes of venous compliance to microgravity have been rare. The purpose of this study was to determine compliance changes in femoral veins of rabbits after 21 days of head-down rest. Head-down rest -20 dgrees rabbit model was used to simulate weightlessness. 24 healthy male New Zealand Rabbits were randomly divided into 21 days of head-down rest group (HDR), horizontal immobilization group (HIG) and Ctrl group (Ctrl), with 8 in each. We constructed pressure-volume relationships from femoral veins in vivo for all groups after simulation by changing the venous internal volume and measuring the corresponding pressure. Microstructure of femoral vein wall in 3 groups was observed. Compared among the groups, the corresponding intravenous pressure of Ctrl was the highest when intravenous volume was expanded and HDR was the lowest. The parameter 3 , and P 2 in quadratic equations of femoral venous P-V relationship of HDR group were significantly higher than these values of HIG group and Ctrl group. The structure of femoral vein wall of HDR rabbits changed significantly, outlines of some endothelium cells (EC) became short and columnar or cubic, some of EC fell off and smooth muscle layer became thinner. These results indicate that, the femoral venous compliance increased after weightlessness simulation. This may partially underlie the mechanism of orthostatic hypotension seen in astronauts during an orthostatic stress after exposure to microgravity.

Objective: To investigate effects of 3 weeks simulated weightlessness on biomechanical parameters, alkaline phosphatase (ALP), acid phosphatase (ACP) and collagen I of hind-limb bones in tail-suspended rats., Method: Fourteen male SD rats were divided equally into control group (CON) and experimental group; tail-suspended (TS) was used to simulate weightlessness. After 3 weeks tail-suspension, biomechanical parameters of femur were measured; ALP, ACP and collagen I of tibia were observed., Result: Elastic load, maximum load, and bending rigidity coefficient decreased significantly (P<0.01), while the maximum deformation and bending toughness coefficient increased markedly (P<0.01 or P<0.05). Morphological results showed that ALP declines significantly in TS group, ACP and type I collagen increased significantly in TS group., Conclusion: After tail-suspension for 3 weeks, growth of rat's weight bearing bones are suppressed, biomechanical capability declines, and collagen I metabolism becomes disordered.

Objective: To investigate changes of learning ability and somatostatin (SS) changes after positive acceleration (+Gz) exposures., Method: Eighty male SD rats were randomly divided into 3 groups: control group (Con), +6 Gz/3 min group (+6 Gz), and +10 Gz/3 min group (+10 Gz), 8 rats in each group. Changes of learning ability in rats were observed at 0 d, 2 d, 4 d and 6 d after +Gz exposure. SS in hippocampus was measured by RIA at 0 d, 2 d and 4 d after +Gz exposures (there were 8 rats every time, in each group)., Result: In Y-maze test, number of correct response decreased significantly (P<0.01), and total reaction time increased significantly (P<0.01) in +6 Gz and +10 Gz groups as compared with control group; number of correct response and total reaction time in +10 Gz group changed significantly at 0 d (P<0.01 or P<0.05) as compared with +6 Gz group. RIA showed that, content of SS in hippocampus declined at 0 d and 2 d (P<0.05 or P<0.01) in +6 Gz and +10 Gz groups as compared with control group., Conclusion: +Gz exposure could impair learning ability of rats, and inhibit expression of SS in hippocampus.

Objective: To study the protective effects of low gravity preconditioning against learning and memory function impairment induced by high gravity exposure in rats., Method: Twenty-four male SD rats were randomized equally into control group, high gravity exposure group (+10 Gz/3 min) and low gravity preconditioning group (LGP group, preconditioned by a daily exposure to +4 Gz/3 min for 3 days before +10 Gz/3 min exposure). Both the learning and memory abilities of the rats in the 3 groups were examined after +10 Gz/3 min exposure., Results: In open field test, the rats exposed to +10 Gz/3 min, in comparison with the control rats, exhibited significantly declined total square-crossing and rearing (SCR) on days 0 and 2 (P<0.05), with also significantly prolonged stay in the central square at 0 d(P<0.01). In the low gravity preconditioned rats, SCR declined and length of stay in the central square increased significantly on day 0 (P<0.01). Compared with the rats in +10 Gz/3 min group, the rats in the LGP group showed decreased length of stay in the central square on day 2, and such changes was statistically significant on day 6 (P<0.05), but there was no difference in SCR at all time points. In Y-maze test, the number of times of right reaction (RR) decreased and the reaction time (RT) increased significantly in +10 Gz/3min group compared with those of the control group (P<0.01), whereas no significant differences were found between the control group and LGP group. Compared with +10 Gz/3 min group, the RR was increased (P<0.01) and RT shortened significantly (P<0.01) in LGP group. In the step-through test, the latent time (LT) increased (P<0.05) on day 0 but was then shortened significantly on day 6 in + 10 Gz/3min group (P<0.01), and no difference was found between LGP group and the control group. LT on day 6 increased significantly (P<0.01) in LGP group as compared with the +10 Gz/3 min group., Conclusion: High gravity exposure-induced rat learning and memory impairment can be markedly improved by lower gravity preconditioning.

Introduction: The development of orthostatic hypotension (OH) is complex and multi-factorial. Previous simulation work indicates that myocardial contractility depression (MCD) may increase OH when there is a total blood volume decrease. This paper hypothesized that MCD increased OH in both humans with and without decrease in blood volume., Methods: A model, which was previously used to reproduce cardiovascular response to lower body negative pressure (LBNP), hypovolemia, and MCD, was modified by incorporating the physiologic mechanism of plasma filtration into the interstitium during LBNP. The model was evaluated by human experimental results. Using the model, HR and BP response to LBNP were simulated at conditions of 10%, 20%, and 30% MCD. Additionally, HR and BP response to LBNP were simulated at conditions of 10% and 20% MCD with a 12% decrease in blood volume., Results: Simulation results indicate that the increments of HR and decrements of systolic BP (SBP) and mean arterial pressure (MAP) rise with the increases of MCD. Specifically, simulation results indicate that about 30% MCD would cause OH (HR: 117 bpm; SBP: 92 mmHg; MAP: 78 mmHg). It also indicates that about 20% MCD would cause OH (HR: 134 bpm, SBP: 84 mmHg, MAP: 73 mmHg) with a 12% decrease in total blood volume., Conclusion: It is suggested that MCD increases OH whether or not there is a total blood decrease, and further suggested that MCD induced by both spaceflight and heart disease may increase OH.

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.

Objective: To study the effect of combined stress of noise and + Gz on learning and memory in rats., Method: Thirty-two male SD rats were randomly divided into 4 groups: control group, +10 Gz/3 min group, 90 dB(A)/30 min noise group, combined stress group (+10 Gz/3 min and 90 dB(A)/30 min), 8 rats in each group. Changes of learning and memory after stresses were measured by means of Y-maze test, open field test and step-through test., Result: As compared with control group and noise group, the number of correct reactions decreased significantly (P<0.01) and the reaction time increased significantly (P<0.01) in combined stress group at all time after stress; time stay in center grille (TSCG) increased significantly immediately after stress (P<0.01). When compared with control group, total time (TT) and number of error (NE) increased significantly (P<0.01) while latent time (LT) decreased significantly immediately and 6 d after stress (P<0.01). As compared with +10 Gz group, number of correct reactions in combined stress group decreased significantly (P<0.05) and reaction time increased significantly (P<0.01) immediately after stress., Conclusion: It is suggested that combined stress of noise and +Gz may impair learning and memory of rats, and +Gz seems to contribute more to the combined effects.

To assess the potential value of intermittent artificial gravity as an efficient countermeasure, our previous studies have showed that daily 4-h standing (STD) is sufficient in counteracting muscle atrophy but not bone atrophy induced by simulated microgravity. The aim of the present study was to determine whether intermittent gravitational loading by daily 2-h or 4-h, +45 degrees head-up tilt (HUT) is more effective than STD in counteracting muscle and, particularly, bone atrophy due to simulated microgravity. Sprague-Dawley male rats weighing 290-300 g were subjected to a 28-d tail-suspension to simulate microgravity deconditioning. Daily HUT for 2, or 4 h was used to provide intermittent gravitational loading in foot-ward and tail-ward directions. The results showed that 4 h/d HUT was sufficient, and 2 h/d was less effective, in preventing adverse changes in muscle weights, fiber types, and cross-sectional areas (CSA) of muscles due to a 28-d simulated microgravity. The % protections by 4 h/d HUT in maintaining the CSAs of type I fibers in soleus, medial and lateral gastrocnemius and extensor digitorum longus muscles were 103%, 82%, 102%, and 83%, respectively. However, according to changes in physical and mechanical properties of femur, daily 4-h HUT was ineffective in attenuating the adverse changes in bone due to a 28-d simulated microgravity. Reductions in wet, dry, and ash weights and decreases in mechanical strength of femur did not show significant improvement by daily 2-h or 4-h HUT. Taken together, the findings indicate that the countermeasure effectiveness of daily 2-h or 4-h HUT for muscles is comparable with that by daily STD with the same durations. Daily 4-h HUT, as 4-h STD, is also ineffective in attenuating adverse changes in bone mass, but seems partially effective in preventing declines in mechanical properties due to simulated microgravity.

Aim: To provide proof for Evidence-based Medicine as well quality control, our laboratory detected the thrombin activity on various body position., Methods: By autogenous contrast and cross matched survey, 105 volunteers divided into 3 season patches of winter, spring and summer, blood samples were drawn from the same part in both standing and lying position. Both samples and the quality control were detected to investigate the effect of the body position to thrombin activity's changing. The data were analyzed by SPSS 10.0., Results: Taking the lying's data as baseline, the average changing on all those the "5" index was 7.07% and the highest changing reached 9.33%. This kind changing had great significant differences (P < 0.01). According to the t value, sequences ranged: FIB > TT > PT > INR > APTT. FIB, TT and APTT's values slowly raised, adversely PT and INR slowly went down. While sitting for 15 min after lying, these indices returned to 95.2% of the original value in sitting position in addition. Season, age and device had no relationship with body position., Conclusion: Changing body position can result in obvious physiological variation of thrombin activity.

Objective: To investigate changes of bone morphogenesis proteins (BMP), transforming growth [correction of grouth] factors-beta (TGF-beta) in tibia and the growing of femur in tail-suspended rats after 21 d simulated weightlessness., Method: Fourteen male SD rats were randomly divided into control group (CON) and tall-suspension group (TS). After 21 d tail-suspension, basic physical parameters of the femur were measured; changes of BMP, TGF-beta in tibia were assayed by immunohistochemical method., Result: During 21 d tail-suspension, all rats grew well without apparent stress reaction. After 21 d weightlessness simulation, wet weight, dried weight, ash, diameter and density of femur in TS group declined significantly (P<0.01). Immunohistochemical results of tibia showed that both BMP and TGF-beta declined in tissues from all regions of the tibia., Conclusion: After 21 d tall-suspension, the growth of rat's weight bearing bones were suppressed, production and secretion of BMP and TGF-beta was holdback.

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.

Skeleton system may adapt to multiform mechanical stimulus including gravity so as to modulate the balance between bone formation and absorption. Osteopenia under microgravity is mainly due to decrease of bone formation which relates closely to the low level of osteoblast activity. The proliferation and adhesive ability of osteoblast are reduced. The cells also express less messenger and protein of the differentiation and maturation-related substances, such as alkaline phosphatase, osteocalcin and type I collagen. The secretion of many growth factors is decreased and osteoblast responses less to them. It still remains unknown why the osteoblast is disfunctioned under microgravity. A hypothesis suggests the cellular shape changes may be the answer.

Weightlessness is inavoidable during spaceflight. It brings profound physiological effects on human body. Vascular remodeling is one of the important changes of cardiovascular system caused by weightlessness or simulated weightlessness. The paper summarized the studies on the effects of weightlessness or weightlessness simulation on vascular remodeling in recent years. The emergence and development of the concept of vascular remodeling were briefly reviewed. The advances of study on vascular remodeling in recent years was briefly discussed with the points focused on the effects of weightlessness or weightlessness simulation on cardiovascular remodeling and its mechanism. It is proposed that cardiovascular remodeling might be important in studying the causes of orthostatic intolerance after spaceflight.

Objective: To investigate the effects of rotating clinostat simulated weightlessness on the differentiation-related gene expression of ROS17/2.8 (rat osteosarcoma) cells., Method: Cultured ROS17/2.8 cells were exposed to rotating clinostat simulated weightlessness for 24, 48 and 72 h with control group in 1 G condition. Total RNA in cells was isolated and reverse transcription PCR analysis was made. Gene expression of type I collagen alpha 1 chain and alkaline phosphatase were examined by their ratios to beta-actin., Result: The expression of type I collagen alpha I chain and alkaline phosphatase (ALP) gene was significantly lower after 72 h exposure to clinostat simulated weightlessness than that of the control group (P<0.01)., Conclusion: Differentiation of rat osteosarcoma cells was reduced after exposure to rotating clinostat simulated weightlessness for 72 h.

Objective. To observe the changes of pressure-volume relationships of rabbit femoral veins and their structural changes caused by simulated weightlessness. Method. Head-Down Tilt (HDT) -20 degrees rabbit model was used to simulate weightlessness. Twenty four healthy male New Zealand Rabbits were randomly divided into 21 d HDT group,10 d HDT group and control group, (8 in each group). Pressure-volume (P-V) relationship of rabbits femoral veins was measured and the microstructure of the veins was observed. Result. The femoral vein P-V relationship curves of HDT groups showed a larger volume change ratio than that of control group. This change was that 21 d HDT group was even more obvious than that of HDT-10 d group. B1 and B2 in quadratic equations of 21 d HDT group were significantly higher than the values of both 10 d HDT group and control group during expansion (inflow) and collapse (outflow) (P<0.01). The result of histological examination showed that the contents and structure of femoral vein wall of HDT-rabbits changed significantly. Endothelial cells of femoral vein became short and columnar or cubic, some of which fell off. Smooth muscle layer became thinner. Conclusion. Femoral venous compliance increased after weightlessness-simulation and the femoral venous compliance in 21 d-HDT rabbits increased more obviously than that in 10 d-HDT rabbits. The structure of femoral vein wall had changed obviously.

Objective. To investigate the rule of intensity and duration of HSP70 expression in rat brain and its relationship with brain injury after repeated +Gz exposures. Method. SD male rats were arranged into control group, +2 Gz, +4 Gz, +6 Gz, and +10 Gz exposure groups. Rat brains were taken 6 h, 10 h, 1 d, 2 d, 4 d or 6 d after +Gz exposure for histopathologic and immunohistochemic or in situ hybridization studies. The expression of HSP70 and HSP70 mRNA or morphology of neurons were observed. Result. The intensity and duration of HSP70 expression were weak and brief at +2 Gz exposure, but was relatively extensive. There was a middling reaction of HSP70 only in hippocampal area after +10 Gz exposure. The duration, extension and intensity of HSP70 expression were wide, long and strong after +4 Gz and +6 Gz exposures. After 1 or 3-5 times exposures, the HSP70 expression reached its peak on the first day after +4 Gz exposures, and dropped obviously on the second day. However the expression of HSP70 maintained a high level after 2 d and was still higher than normal on the 6 d after 3-5 times repeated +4 Gz exposures. The distribution of HSP70 mRNA expression was as same as that of the HSP70 expression but the peak appeared much earlier (10 h) and its duration was shorter. After +10 Gz/5 min exposure, degenerated neurons were found in cortex, hippocampus and thalamus regions while the number of degenerated neurons were obviously decreased in such areas in pre-exposure groups with repeated +4 Gz/3 min for 3-5 times. Conclusion. The intensity and duration of HSP70 and HSP70 mRNA expression after +4 Gz and +6 Gz exposure were stronger and longer than +2 Gz and +10 Gz exposure. The degree of neuron damage after +10 Gz/5 min exposure in pre-exposure groups with repeated +4 Gz/3 min 3-5 times was obviously slight comparing with that of single +10 Gz exposure group.

Objective. To explore the influence of repeated lower +Gz exposures on high +Gz exposure induced brain injury in rats. Method. Forty SD male rats were randomly divided into control group (5 rats), +10 Gz/5 min group (5 rats) +4 Gz exposure one time, three times and five times group (10 rats each group). After 1 d or 6 d of +4 Gz exposure each group were exposed to +10 Gz again. Three days after +10 Gz exposure the neuron damage was observed by light microscope in HE stained section. Result. There was no brain damage after repeated +4 Gz/3 min exposure 5 times so it was reasonable to use this exposure intensity as ischemia stimulation. +10 Gz/5 min exposure could result in irreversible neuron damage such as neuron degeneration and coagulation necrosis. The experiment results suggested that after +10 Gz/5 min exposure there were degenerated neurons in cortex, hippocampus and thalamus. The number of degenerated neurons were obviously decreased in cortex, hippocampus and thalamus when exposed to +10 Gz/5 min again after repeated +4 Gz/3 min 3-5 times. Conclusion. The degree of neuron damage was obviously slight at the time of exposure to +10 Gz/5 min again after repeated +4 Gz/3 min 3-5 times. The ischemia tolerance at the time of exposure to +Gz was similar to other brain ischemia.

Studies on effect of simulated microgravity on cardiovascular function and counter effect of lower body negative pressure (LBNP) in recent years were summarized. The mechanism of simulated microgravity induced orthostatic intolerance may involve the reduction of cardiovascular function and cerebral blood flow, and endocrine changes. The significance of mathematical model in the study of mechanism of microgravity induced orthostatic intolerance was also discussed. The counter effect of LBNP was emphasized.