Combined effects of radiation and simulated microgravity on intestinal tumorigenesis in C3B6F1 ApcMin/+ mice

Explorations of the Moon and Mars are planned as future manned space missions, during which humans will be exposed to both radiation and microgravity. We do not, however, know the health effects for such combined exposures. In a ground-based experiment, we evaluated the combined effects of radiation and simulated microgravity on tumorigenesis by performing X-irradiation and tail suspension in C3B6F1 ApcMin/+ mice, a well-established model for intestinal tumorigenesis. Mice were irradiated at 2 weeks of age and underwent tail suspension for 3 or 11 weeks using a special device that avoids damage to the tail. The tail suspension treatment significantly reduced the thymus weight after 3 weeks but not 11 weeks, suggesting a transient stress response. The combination of irradiation and tail suspension significantly increased the number of small intestinal tumors less than 2 mm in diameter as compared with either treatment alone. The combined treatment also increased the fraction of malignant tumors among all small intestinal tumors as compared with the radiation-only treatment. Thus, the C3B6F1 ApcMin/+ mouse is a useful model for assessing cancer risk in a simulated space environment, in which simulated microgravity accelerates tumor progression when combined with radiation exposure.

New curcumin-loaded nanocapsules as a therapeutic alternative in an amnesia model

This study aimed to investigate the action of two different formulations of curcumin (Cur)-loaded nanocapsules (Nc) (Eudragit [EUD] and poly (ɛ-caprolactone) [PCL]) in an amnesia mice model. We also investigated the formulations' effects on scopolamine-induced (SCO) depressive- and anxiety-like comorbidities, the cholinergic system, oxidative parameters, and inflammatory markers. Male Swiss mice were randomly divided into five groups (n = 8): group I (control), group II (Cur PCL Nc 10 mg/kg), group III (Cur EUD Nc 10 mg/kg), group IV (free Cur 10 mg/kg), and group V (SCO). Treatments with Nc or Cur (free) were performed daily or on alternate days. After 30 min of treatment, the animals received the SCO and were subjected to behavioral tests 30 min later (Barnes maze, open-field, object recognition, elevated plus maze, tail suspension tests, and step-down inhibitory avoidance tasks). The animals were then euthanized and tissue was removed for biochemical assays. Our results demonstrated that Cur treatment (Nc or free) protected against SCO-induced amnesia and depressive-like behavior. The ex vivo assays revealed lower acetylcholinesterase (AChE) and catalase (CAT) activity, reduced thiobarbituric species (TBARS), reactive species (RS), and non-protein thiols (NSPH) levels, and reduced interleukin-6 (IL-6) and tumor necrosis factor (TNF) expression. The treatments did not change hepatic markers in the plasma of mice. After treatments on alternate days, Cur Nc had a more significant effect than the free Cur protocol, implying that Cur may have prolonged action in Nc. This finding supports the concept that it is possible to achieve beneficial effects in nanoformulations, and treatment on alternate days differs from the free Cur protocol regarding anti-amnesic effects in mice.

Eldecalcitol prevents muscle loss and osteoporosis in disuse muscle atrophy via NF-κB signaling in mice

We investigated the effect of eldecalcitol on disuse muscle atrophy. C57BL/6J male mice aged 6 weeks were randomly assigned to control, tail suspension (TS), and TS-eldecalcitol-treated groups and were injected intraperitoneally twice a week with either vehicle (control and TS) or eldecalcitol at 3.5 or 5 ng for 3 weeks. Grip strength and muscle weights of the gastrocnemius (GAS), tibialis anterior (TA), and soleus (SOL) were determined. Oxidative stress was evaluated by malondialdehyde, superoxide dismutase, glutathione peroxidase, and catalase. Bone microarchitecture was analyzed using microcomputed tomography. The effect of eldecalcitol on C2C12 myoblasts was analyzed by measuring myofibrillar protein MHC and the atrophy markers Atrogin-1 and MuRF-1 using immunofluorescence. The influence of eldecalcitol on NF-κB signaling pathway and vitamin D receptor (VDR) was assessed through immunofluorescence, (co)-immunoprecipitation, and VDR knockdown studies. Eldecalcitol increased grip strength (P < 0.01) and restored muscle loss in GAS, TA, and SOL (P < 0.05 to P < 0.001) induced by TS. An improvement was noted in bone mineral density and bone architecture in the eldecalcitol group. The impaired oxidative defense system was restored by eldecalcitol (P < 0.05 to P < 0.01 vs. TS). Eldecalcitol (10 nM) significantly inhibited the expression of MuRF-1 (P < 0.001) and Atrogin-1 (P < 0.01), increased the diameter of myotubes (P < 0.05), inhibited the expression of P65 and P52 components of NF-κB and P65 nuclear location, thereby inhibiting NF-κB signaling. Eldecalcitol promoted VDR binding to P65 and P52. VDR signaling is required for eldecalcitol-mediated anti-atrophy effects. In conclusion, eldecalcitol exerted its beneficial effects on disuse-induced muscle atrophy via NF-κB inhibition.

Murine Models of Tenotomy-Induced Mechanical Overloading and Tail-Suspension-Induced Mechanical Unloading

Skeletal muscle is a highly plastic tissue that can alter its mass and strength in response to mechanical stimulation, such as overloading and unloading, which lead to muscle hypertrophy and atrophy, respectively. Mechanical loading in the muscle influences muscle stem cell dynamics, including activation, proliferation, and differentiation. Although experimental models of mechanical overloading and unloading have been widely used for the investigation of the molecular mechanisms regulating muscle plasticity and stem cell function, few studies have described the methods in detail. Here, we describe the appropriate procedures for tenotomy-induced mechanical overloading and tail-suspension-induced mechanical unloading, which are the most common and simple methods to induce muscle hypertrophy and atrophy in mouse models.

Myricitrin exhibits antidepressant-like effects and reduces IL-6 hippocampal levels in the chronic mild stress model

The flavonoid myricitrin showed an antidepressant-like effect in the tail suspension test and increased hippocampal neurogenesis, as well as demonstrating anti-inflammatory effects. Interestingly, inflammation has been linked to depression, and anti-inflammatory drugs showed promising results as antidepressant-like drugs. Thus, the present study evaluated the effects of myricitrin in the chronic mild stress (CMS) model, a translational and valid animal model of depression, using the mini-experiment design to improve the reproducibility of the findings. The sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST) were the readouts of depressive-like phenotypes induced by CMS. Relative adrenal weight was employed as an index of the hypothalamus-pituitary-adrenal (HPA) axis activation. Interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha levels were measured in the hippocampus. Myricitrin (10 mg/kg, intraperitoneally, for 14 days) reversed depressive-like behaviors induced by CMS (increased immobility in the FST, the TST and anhedonia), as well as decreased adrenal hypertrophy and hippocampal levels of IL-6 in stressed mice. Similar results were observed by imipramine (20 mg/kg, intraperitoneally, for 14 days), a serotonin and norepinephrine reuptake inhibitor (positive control). A significant correlation was observed between immobility time in the TST, and hippocampal IL-6 levels. Hippocampal TNF-α levels were not affected by CMS or drug treatment. In conclusion, myricitrin exhibited an antidepressant-like profile in CMS, and this effect may be associated with its anti-inflammatory activity.

Structural characteristics of the bone surrounding dental implants placed into the tail-suspended mice

BACKGROUND

There are many unclear points regarding local structural characteristics of the bone surrounding the implant reflecting the mechanical environment.

PURPOSE

The purpose of this study is to quantitatively evaluate bone quality surrounding implants placed into the femurs of mice in an unloading model, and to determine the influence of the mechanical environment on bone quality.

METHODS

Twenty 12-week-old male C57BL6/NcL mice (n = 5/group) were used as experimental animals. The mice were divided into two groups: the experimental group (n = 10) which were reared by tail suspension, and the control group (n = 10) which were reared normally. An implant was placed into the femur of a tail-suspended mouse, and after the healing period, they were sacrificed and the femur was removed. After micro-CT imaging, Villanueva osteochrome bone stain was performed. It was embedded in unsaturated polyester resin. The polymerized block was sliced passing through the center of the implant body. Next, 100-μm-thick polished specimens were prepared with water-resistant abrasive paper. In addition to histological observation, morphometric evaluation of cancellous bone was performed, and the anisotropy of collagen fibers and biological apatite (BAp) crystals was analyzed.

RESULTS

As a result, the femoral cortical bone thickness and new peri-implant bone mass showed low values in the tail suspension group. The uniaxial preferential orientation of BAp c-axis in the femoral long axis direction in the non-implant groups, but biaxial preferential orientation of BAp c-axis along the long axis of implant and femoral long axis direction were confirmed in new bone reconstructed by implant placement. Collagen fiber running anisotropy and orientation of BAp c-axis in the bone surrounding the implant were not significantly different due to tail suspension.

CONCLUSIONS

From the above results, it was clarified that bone formation occurs surrounding the implant even under extremely low load conditions, and bone microstructure and bone quality adapted to the new mechanical environment are acquired.

Blood lipid profile changes in type 2 diabetic rats after tail suspension and reloading

Purpose

The effects of the tail suspension and reloading on the protein and lipid metabolism in muscle and blood in type 2 diabetes mellitus (T2DM) are unclear. This study evaluated the hypothesis that skeletal muscle catabolism is greater in T2DM than in non-diabetes mellitus (non-DM) rats and that the activity-dependent changes in the intramuscular lipid accumulation and blood lipid profile are poorer in T2DM than in non-DM rats.

Methods

T2DM and non-DM rats were suspended for two weeks followed by reloading for two weeks. The muscle and blood were then examined.

Results

In contrast to our hypothesis, there was no marked difference between the T2DM and non-DM groups in terms of the skeletal muscle catabolism and activity-dependent changes in intramuscular lipid accumulation. However, the blood lipid profile increased in the T2DM group compared to the non-DM group. One interesting finding in this study was the decrease in non-high-density lipoprotein (non-HDL) cholesterol levels after one week of reloading followed by a significant increase in the non-HDL cholesterol levels after two weeks of reloading in the T2DM group.

Conclusion

These results suggest that a dramatic increase in activity after a period of inactivity may rapidly improve the blood lipid profile in T2DM rats.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01511-y.

Combined HIV-1 Tat and oxycodone activate the hypothalamic-pituitary-adrenal and -gonadal axes and promote psychomotor, affective, and cognitive dysfunction in female mice

The majority of HIV⁺ patients present with neuroendocrine dysfunction and ~50% experience co-morbid neurological symptoms including motor, affective, and cognitive dysfunction, collectively termed neuroHIV. In preclinical models, the neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat), promotes neuroHIV pathology that can be exacerbated by opioids. We and others find gonadal steroids, estradiol (E₂) or progesterone (P₄), to rescue Tat-mediated pathology. However, the combined effects of Tat and opioids on neuroendocrine function and the subsequent ameliorative capacity of gonadal steroids are unknown. We found that conditional HIV-1 Tat expression in naturally-cycling transgenic mice dose-dependently potentiated oxycodone-mediated psychomotor behavior. Tat increased depression-like behavior in a tail-suspension test among proestrous mice, but decreased it among diestrous mice (who already demonstrated greater depression-like behavior); oxycodone reversed these effects. Combined Tat and oxycodone produced apparent behavioral disinhibition of anxiety-like responding which was greater on diestrus than on proestrus. These mice made more central entries in an open field, but spent less time there and demonstrated greater circulating corticosterone. Tat increased the E₂:P₄ ratio of circulating steroids on diestrus and acute oxycodone attenuated this effect, but repeated oxycodone exacerbated it. Corticotropin-releasing factor was increased by Tat expression, acute oxycodone exposure, and was greater on diestrus compared to proestrus. In human neuroblastoma cells, Tat exerted neurotoxicity that was ameliorated by E₂ (1 or 10 nM) or P₄ (100, but not 10 nM) independent of oxycodone. Oxycodone decreased gene expression of estrogen and κ-opioid receptors. Thus, neuroendocrine function may be an important target for HIV-1 Tat/opioid interactions.

Evaluation and comparison of the antidepressant-like activity of Artemisia dracunculus and Stachys lavandulifolia ethanolic extracts: an in vivo study

Several studies have supported the preventive and therapeutic values of phenolic compounds including chlorogenic acid, syringic acid, vanillic acid, ferulic acid, caffeic acid, luteolin, rutin, catechin, kaempferol, and quercetin in mental disorders. Since these secondary metabolites are reported as the phenolic compounds of Artemisia dracunculus (A. dracunculus) and Stachys lavandulifolia (S. lavandulifolia), the main aim of this study was the evaluation and comparison of the phenolic contents, flavonoids, and antidepressant-like activity of Artemisia dracunculus with Stachys lavandulifolia. Antidepressant-like activity of the extracts was evaluated in the forced swimming test (FST) and the tail suspension test (TST). Moreover, the open field test was conducted to evaluate the general locomotor activity of mice following treatment with the extracts. Since phenolic compounds and flavonoids play main roles in pharmacological effects, the phenolic and flavonoid contents of the extracts were measured. Though significant difference between the phenolic contents of the extracts was not observed, but S. lavandulifolia exhibited higher flavonoid contents. Animal treatment with extracts decreased the immobility times in both FST and TST compared to the vehicle group without any significant effect on the locomotor activity of animals. Also, S. lavandulifolia at 400 mg/kg showed higher potency in both tests compared to A. dracunculus. Our results provided promising evidence on the antidepressant-like activity of both extracts which could be related to flavonoids as the main components of the extracts, but more studies need to be conducted to specify the main compounds and the mechanisms involved in the observed effects.

Effect of hindlimb unloading and reloading on the soleus and plantaris muscles in diabetic rats

[Purpose] This study aimed to induce disuse muscle atrophy in Goto-Kakizaki rats, a type 2 diabetes model, to investigate the effects of reloading on the soleus and plantaris muscles. [Materials and Methods] Wistar and Goto-Kakizaki (GK) rats were divided into 6 groups: Wistar Control (WC), GK Control (GC), Wistar Tail suspension (WS), GK Tail suspension (GS), and Wistar Reload (WR), GK Reload (GR). [Results] Investigation of myofiber cross-sectional area in Goto-Kakizaki rat soleus muscles indicated that the GS group showed significantly lower values than the GC and GR groups. No significant differences were observed between the GC and GR groups. However, investigation of plantaris muscles in Goto-Kakizaki rats indicated that the GS and GR groups showed a significant decrease compared to the GC group. No significant differences were found between the GS and GR groups. [Conclusion] Investigation of muscle weight/body weight ratios and myofiber cross-sectional area in tail suspension groups confirmed the induction of muscular atrophy. The differences in the degree of atrophy and recovery in terms of myofiber cross-sectional area observed in Goto-Kakizaki rat plantaris muscles may be influenced by the myofiber type and diabetes.

An extract of Synedrella nodiflora (L) Gaertn exhibits antidepressant properties through monoaminergic mechanisms

Synedrella nodiflora (SNE) has been used traditionally for many neurological conditions and some of these neuroactive effects have been scientifically substantiated. The usefulness of SNE in depression has however not been investigated despite the availability of data in other disease models indicating it may be useful. The present study therefore examined the effect of SNE in acute murine models of depression and the possible mechanisms mediating its activities in these models. Preliminary qualitative phytochemical and high performance liquid chromatography (HPLC) screening were conducted on SNE. The behavioural effects of SNE (100, 300 and 1000 mg/kg) pre-treated mice were examined in the forced swimming (FST) and tail suspension (TST) tests. Behavioural events such as mobility (swimming, climbing, curling and climbing), and immobility, were scored. The possible involvement of monoamines in the effects of SNE was assessed in the TST by pre-treating mice with α-methyldopa, reserpine and para-chlorophenylalanine (pCPA) in separate experiments. Flavonoids, tannins, saponins, alkaloids, cardiac glycosides, coumarins, triterpenes, sterols, anthraquinones and phenolic compounds were present in SNE. HPLC analysis revealed the presence of two major constituents observed at retention times 42.56 and 46.51 min, with percentage composition of 45.72% and 36.88% respectively. SNE significantly reduced immobility scores in both FST and TST, suggesting antidepressant effects. The antidepressant properties of SNE were reversed by the pre-treatment of α-methyldopa, reserpine and pCPA, suggesting a possible involvement of monoamines (noradrenaline and serotonin) in its mechanism(s) of actions. SNE exhibits antidepressant effects, possibly mediated through an interplay of enhancement of noradrenergic and serotoninergic mechanisms.

CKIP-1 knockout offsets osteoporosis induced by simulated microgravity

Casein kinase 2-interacting protein 1 (CKIP-1) is a negative regulator for bone formation. CKIP-1 knockout (KO) mice are very important for research on countermeasures to bone loss induced by space microgravity. Under simulated microgravity, the bone metabolism of CKIP-1 KO mice was different than that of wild-type (WT) mice. Many experiments all showed that the KO mice had significantly enhanced ossification in the tail suspension conditions, and the differences were closely related to the time the mice were exposed to the microgravity environment. Our results reveal the effect of CKIP-1 on the regulation of bone metabolism and osteogenesis in vivo and the ability of this gene to offset osteoporosis, and they suggest an approach to the treatment of osteoporosis induced by microgravity in space.

Elcatonin prevents bone loss caused by skeletal unloading by inhibiting preosteoclast fusion through the unloading-induced high expression of calcitonin receptors in bone marrow cells

This study aimed to clarify whether elcatonin (EL) has a preventive action on bone dynamics in skeletal unloading. Seven-week-old male C57BL/6J mice with either ground control (GC) or tail suspension (TS) were administered EL 20U/kg or a vehicle (veh) three times per week and assigned to one of the following four groups: GCEL, GCveh, TSEL, and TSveh. Blood samples and bilateral femurs and tibias of the mice were obtained for analysis. After 7days of unloading, the trabecular bone mineral density in the distal femur obtained via peripheral quantitative computed tomography and the trabecular bone volume were significantly higher in the TSEL group than in the TSveh group. The bone resorption histomorphometric parameters, such as the osteoclast surface and osteoclast number, were significantly suppressed in the TSEL mice, whereas the number of preosteoclasts was significantly increased. The plasma level of tartrate-resistant acid phosphatase-5b (TRACP-5b) was significantly lower in the TSEL group than in all other groups. In the bone marrow cell culture, the number of TRACP-positive (TRACP(+)) multinucleated cells was significantly lower in the TSEL mice than in the TSveh mice, whereas the number of TRACP(+) mononucleated cells was higher in the TSEL mice. On day 4, the expression of nuclear factor of activated T-cells, cytoplasmic, calcineurin-dependent 1 (NFATc1), cathepsin K and d2 isoform of vacuolar ATPase V0 domain (ATP6V0D2) mRNA in the bone marrow cells in the TSEL mice was suppressed, and the expression of calcitonin receptor (Calcr) mRNA on day 1 and Calcr antigen on day 4 were significantly higher in the TSveh mice than in the GCveh mice. EL prevented the unloading-induced bone loss associated with the high expression of Calcr in the bone marrow cells of mouse hindlimbs after tail suspension, and it suppressed osteoclast development from preosteoclasts to mature osteoclasts through bone-resorbing activity. This study of EL-treated unloaded mice provides the first in vivo evidence of a physiological role of EL in the inhibition of the differentiation process from preosteoclasts to osteoclasts.

The antidepressant-like effect of bacopaside I: possible involvement of the oxidative stress system and the noradrenergic system

In the present study, the antidepressant-like effect of bacopaside I, a saponin compound present in the Bacopa monniera plant, was evaluated by behavioral and neurochemical methods. Bacopaside I (50, 15 and 5 mg/kg) was given to mice via oral gavage for 7 successive days. The treatment significantly decreased the immobility time in mouse models of despair tests, but it did not influence locomotor activity. Neurochemical assays suggested that treatment by bacopaside I (50, 15 and 5 mg/kg) improved brain antioxidant activity to varying degrees after the behavioral despair test. Bacopaside I (15 and 5 mg/kg) significantly reversed reserpine-induced depressive-like behaviors, including low temperature and ptosis. Conversely, bacopaside I did not affect either brain MAO-A or MAO-B activity after the behavioral despair test in mice. Additionally, 5-hydroxytryptophan (a precursor of 5-serotonin) was not involved in the antidepressant-like effect of bacopaside I. These findings indicated that the antidepressant-like effect of bacopaside I might be related to both antioxidant activation and noradrenergic activation, although the exact mechanism remains to be further elucidated.

Jump exercise during hindlimb unloading protect against the deterioration of trabecular bone microarchitecture in growing young rats

Three-dimensional femoral trabecular architecture was investigated in tail-suspended young growing rats and the effects of jump exercise during the period of tail-suspension were also examined. Eight-week-old male Wistar rats (n = 24) were randomly assigned to three body weight-matched groups: a tail suspended group (SUS, n = 8); a sedentary control group (CON, n = 8) and rats primed with jump exercise during the period of tail suspension (JUM, n = 8). The jump exercise protocol consisted of 30 jumps/day, five days/week with a 40 cm jump height. After 3 weeks of jump exercise, bone mineral density (BMD) of the entire right femur was measured using dual energy X-ray absorptiometry. Three-dimensional trabecular bone architecture at the distal femoral metaphysis was evaluated using microcomputed tomography (micro-CT). Tail suspension caused a decrease in femoral BMD (-5%, p < 0.001) and trabecular bone architectural deterioration. Deterioration in the trabecular network during hindlimb unloading was mostly attributed to the reduction of trabecular number (-32%, p < 0.001) in the distal femoral metaphysis. Jump exercise during the tail suspension period increased trabecular thickness (14%, p < 0.001) and the reduction of trabecular number was suppressed. The present data indicate that jump exercise applied during hindlimb unloading could be able to inhibit bone loss and trabecular bone architectural deterioration caused by tail suspension.

Study of Antidepressant and Sedative-Hypnotic Activity of Hydroalcoholic Extract of Asperugo procumbens L. Aerial Parts in Mice

Asperugo procumbents L. has been used in Iranian traditional medicine for the refreshing, tranquillizing and mood elevating activities. The present study was undertaken to evaluate the antidepressant and sedative-hypnotic potential of acute administration of the hydroalcoholic extract of this plant in mice. Additionally, the effects of flumazenil on the hypnotic activity of the extracts were evaluated. None of the doses of the extract could significantly reduce immobility time in comparison with control group in antidepressant tests. In hypnotic test, 250 and 400 mg/kg dose ssign ificantly increased pentobarbital-induced sleeping time compared to vehicle. All of the doses of the extract significantly reduced the latency to sleep in comparison to the vehicle. Flumazenil reversed the augmented effects of extracts in pentobarbital-induced hypnotic test. The results of the present study indicate the low antidepressant and good sedative-hypnotic effects of the hydroalcoholic extract of Asperugo procumbens aerial parts in mice and that the central benzodiazepine receptors are involved in the sedative-hypnotic effects of this plant.

Effect of simulated weightlessness on the healing of experimental gastric ulcer in rats

AIM: To investigate the effect of simulated weightlessness on the healing of acetic acid-induced experimental gastric ulcer in rats and to explore the potential mechanisms involved.

METHODS: Thirty-two SD rats were randomly and equally divided into four groups: 7 d tail suspension group, 7 d control group,14 d tail suspension, and 14 d control group. Gastric ulcer was induced in rats with acetic acid. Tail suspension was used to simulate the weightlessness condition 3 days after ulcer induction. The gastric ulcer area was measured with a vernier caliper. The ultrastructure of regenerative mucosa was observed by electronic microscopy. Epidermal growth factor (EGF) level in gastric juice was determined by radioimmunoassay (RIA). The staging of ulcer healing was performed.

RESULTS: Compared to the 7 d control group, the ulcer area significantly increased (6.0 mm² ± 1.7 mm² vs 2.2 mm² ± 0.7 mm², t = 5.661, P < 0.01) and the stage of ulcer significantly decreased (χ² = 12.771, P < 0.01) in the 7d suspension group. Compared to the 14 d control group, the ulcer area and EGF level increased (3.0 mm² ± 1.2 mm² vs 1.1 mm² ± 0.4 mm², t = 4.233, P < 0.01; 0.155 ng/mL ± 0.052 ng/mL vs 0.103 ng/mL ± 0.019 ng/mL, t = 2.635, P < 0.05) in the 14 d suspension group. Compared to the 7 d suspension group, the ulcer area, EGF level and stage of ulcer significantly decreased (3.0 mm² ± 1.2 mm² vs 6.0 mm² ± 1.7 mm², t = 3.805, P < 0.01; 0.155 ng/mL ± 0.052 ng/mL vs 0.434 ng/mL ± 0.137 ng/mL, t = 5.657, P < 0.01; χ² = 12.953, P < 0.01) in the 14 d suspension group. The ultrastructural restoration and histological maturity of healed ulcer in the 7 d and 14 d suspension groups were inferior to those in the 7 d and 14 d control groups.

CONCLUSION: Simulated weightlessness may depress the structure of regenerative gastric mucosa, delay the healing of ulcer, and increase EGF level in gastric juice.