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Histological and histomorphological examinations of tibiae taken from young (body mass = 27 g) and adult (body mass = 73 g) male Mongolian gerbils Meriones unguiculatus was fulfilled. Tibial bones of Mongolian gerbils have a hockey-stick form and are extremely thin. Morphologically the gerbil's tibial bone is very similar to that of rat. The cartilaginous growth plate in the epiphysis is divided into the areas of dominance, proliferation, and hypertrophy/calcification. In young gerbils, height of the cartilaginous growth plate is thrice as large as in adult animals. Immediately under the growth plate there is an area of primary spongiosis consisting of tightly packed thin bone trabeculae with a cartilage in the center. In adult gerbils, trabeculae in the primary spongiosis are less numerous as compared with young animals; they are thicker and more apart. In young gerbils, primary spongiosis is higher than in adult animals. The primary spongiosis region grades into ill-defined secondary spongiosis. Not numerous trabeculae of the secondary spongiosis are thicker comparing with trabeculae of the primary spongiosis, more separated from one another and fully ossified. In adult gerbils, secondary spongiosis is a bit larger than in young animals, mostly due to thickening of the bone trabeculae.

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Survey histological study of the heart, lung, liver, kidney, pancreas, adrenals, thymus, spleen, testicles of the Mongolian gerbil Meriones unguiculatus with a body mass of about 27 g showed their macro- and microscopic similarity with the organs of laboratory rats and mice notwithstanding some slight differences. For instance, the ascending knee of Hengle's loop in the gerbil kidney is much better developed and forms in whole a kind of a singular cortical fiber bordering the medulla. It is the well-developed parts of Hengle's ascending loop in gerbil that ensures a more complete water reabsorption decrease the quantity of urine and sharply reduce the amount of exogenous fluid vitally important for animals in arid areas. The Mongolian gerbil is distinguished by large adrenals and small corticosteroid-sensitive thymus and spleen suggesting high sensitivity of this animal to stresses. Spleen abundance of both mature and immature megacariosities--thrombogoniums--explains the rapid coagulability as compared with rats and mice.

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Experiments with rats deprived of support loading on hind limbs by tail-suspension showed that injection of hormones participating in bone metabolism impeded the development of tibial spongy osteopenia; also, normalization of longitudinal bone growth was observed in several cases. Investigations were aimed to evaluate the effectiveness of growth hormone, sex hormones, thyreoid hormones, calcitonin, CNS stimulating ephedrine and strychnine, and graded support loads. The best results were obtained after injection of calcitonin combined with sinestrol (synthetic analog of estradiol) and graded support loads which acted as initiators and amplifiers of hormonal effects. The combination of calcitonin, sinestrol and support loads prevented osteopenia and provided the normal bone growth in length during rat's suspension.

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Experiments with tail-suspended female rats demonstrated that injection of sinestrol (synthesized estradiol) and myocalcic (sermon calcitonin) on a background of graded weight bearing (suspension interruption for 2 hrs. a day) prevented osteopenia in the spongy metaphyses of the shin-bone deprived of loading.

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The qualitative histomorphometric techniques were used to study the dynamics of tibia structural recovery from osteopenia in 30 female rats previously suspended by tail for 30 days. The suspension was found to have caused osteopenia in the tibial proximal metaphysis that was fully gone only after 60 day; in other words, readaptation took twice as much time as the osteopenia development. This fact should be taken into consideration by designers of rehabilitative methods.

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Summarized are the results of comparative analysis of morphological changes in rat's skeletal muscles after microgravity and its simulation. On completion of space flight, hindlimb muscles of rats exhibited atrophy developed in space microgravity in consequence of the lack of weight-bearing loads and changes solely in the slow anti-g muscles due to the hemodynamic disorders appearing after space flight. Immobilization combined with clinostatting cannot be a veridical laboratory model of microgravity, as horizontally positioned animals still possess weight and, besides, experience severe chronic stress of immobilization. Tail suspension with the head-end permanently down and the hind limbs out of use appeared the most demonstrative model of the space microgravity effects. With this model, the hindlimb muscles underwent changes identical to what had been observed in space flown animals. Data of the simulation studies suggest stabilization of muscle atrophy at a certain level and an earlier and stronger reaction to the hindlimb unloading in young rats as compared to old animals. Skeletal muscles in females and males responded to suspension similarly in spite of difference in the hormonal status.

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Histomorphometry of the iliac bone in Macaca mulatta males was performed in experiments with 30-d head-down tilting (HDT, n = 6) and 8-10-d "dry" immersion (DI, n = 6). The iliac crest was sampled two weeks before DI or a month prior to HDT, and immediately after completion of the experiments. HDT was shown to provoke osteopenia in the bone spongy manifested by losses in the volume of spongiosa, number of trabeculae, and growth of the space in-between. Osteoids were noted to gain volume and thickness, whereas the osteoclast resorption surface was not altered The iliac spongiosa deviations following DI were qualitatively similar to those after HDT but more marked as evidenced by reduction in such integral parameter as the spongy volume. Analysis of the data and their comparison with iliac bones taken from the space-flown primates suggest that DI can be viewed as another, besides HDT, ground-based model of microgravity effects on the spongy bone. Exposure in DI was less durable and yet caused qualitatively same atrophy of the iliac spongiosa as HDT though a bit more significant.

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Histomorphometric and immunocytochemical methods were employed in comparative morphofunctional analysis of the endocrine glands of female and male rats deprived of support loads on the hind limbs by tail suspension. It was shown that pituitary somatotrophs, pancreatic insulocytes and thyroid calcitonin-producing cells in females and males react to deficiency of support loading equally by reducing the functional activity. Blood testosterone decreases in the tail-suspended rats and concurrent hyperplasia of Leydig's cells in testicles are suggestive of an abnormal testosterone synthesis/secretion by these cells in consequence of resticle displacement toward the abdomen. Activation of adenohypophysial gonadotrophs producing the luteinizing hormone that controls the Leydig's cells proliferation appears to be a feedback reaction of gonadotrophs to the low testosterone level in blood.

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In a 30-d experiment with tail-suspension of male and female rats histomorphometric studies were performed to compare impacts of deficient weight loading on the tibial spongy tissue. The 30-d suspension was found to slow down the body and adrenal mass gain irrespective of sex; however, this effect was more pronounced in male rats suggesting a greater stress to males as compared to females. Also, suspension caused tibial osteopenia in either of sexes. Decreases in the tibial spongy mass in suspended male and female rats were similar to control. At the same time, inhibition of the longitudinal bone growth attested by diminished height of the cartilaginous growth plate was more noticeable in males as compared with females. We attribute this observation to the reduction in testosterone production and a more violent stress reaction.

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Histological and histomorphometric effects of ibandronate on the metaphyseal spongiosis in tibia were studied in tail-suspended rats and their controls in a 30-d experiment. Ten- to twenty-day course of ibandronate at a dose of 6 micrograms/kg of the body mass per diem altered the architectonics of metaphyseal spongiosis and increased materially the total spongiosis volume no matter whether those were suspended rats or controls. Spongiosis growth was a result of a sharp deterioration of resorption and spongy bone remodelling due to ibandronate. The substance also exhibited a strong durable action inferring that it might be used for prevention of osteopenia for lack of loading on the musculoskeletal system.

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Morphofunctional changes in somatotrophs and gonadotrophs of the adenohypophysis and Leydig's cells in the testicles were investigated histologically and hystomorphometrically in male rats following microgravity or tail-suspension. Deficient loading of the musculoskeletal system in microgravity was shown to suppress the functional activity of somatotrophs, gonadotrophs and, seemingly, Leydig's cells. As a consequence, blood levels of the growth hormone and testosterone reduced in the space-flown rats. Reduction of the production of the main anabolic hormones is one of the causes for growth inhibition, prevalence of catabolism and consequent muscular atrophy and osteopenia. Simulation of the lack of weight loading inherent to the zero-g environment by suspension also leads to suppression of the somatotrophs activity, whereas the concentration and functional activity of gonadotrophs make a sharp rise. Proliferation of Leydig's cells in the testicles was noted to be very high despite desolation of the seminal canals and disintegration of the testicle epithelium. These findings drive to the conclusion that suspension affects deeply the spermiogenous and androgenous functions of the testicle which is not observed in animals exposed to microgravity. These differences evidence that genesis of the musculoskeletal atrophy in the suspended and space-flown rats was dissimilar.

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Healing of peroneal bone fracture was studied histologically and histomorphologically in rats exposed to a 30-d tail-suspension. To fracture bones, anesthetized rats were operated on day 15 of suspension. Hind limb deprivation of the support loading for a period of 30 days minimizes healing processes in fractured peroneal bones as was evidenced by undersized callus and lowered strength of bone consolidation. Mass-metric and histomorphometric investigations showed that, as compared with the control, on day 15 of regeneration the callous mass and volume in the suspended rats were by 34% and 35% less, respectively; the newly formed spongy bone, the fibrous-cartilaginous tissue and the cartilage were by 44%, 70% and 86% smaller in size, respectively. Nonetheless, healing dynamics in the suspended rats was not disturbed and the calluses were on the same phase of development as in the control, which is attested by similarity of the histological picture. Based on the comparative retrospective analysis of fracture healing in rats in 15- and 30-d experiments, the extended (30-d) suspension did not further impede the post-traumatic bone regeneration. It is suggested that minimization of bone fracture healing during the 15-d suspension was conditioned not only by inhibition of the growth hormone production but also by an acute stress reaction in the early period of adaptation.

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Experiment with rats the hind limbs of which were deprived of support loads (tail suspension) for two weeks following operational fracture of fibular bones evidenced inhibited callus formation and lowered strength of bone fragments consolidation. Injection of anabolic steroid retabolite to the traumatized animals together with limited support loading was favorable to the bone callus formation and consolidation of fragments. This measure also distinctly increased the functional activity of adenohypophysial somatotrophs (growth hormone producers) and thyroid C-cells (calcitonine producers). The direct dependence of bone fracture healing on the somatotropic function of the adenohypophysis suggests that the favorable effect of retabolite combined with the support loading is at least partly achieved through the somatorophic function of the adenohypophysis.

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The article includes excerpts from The Bioethic Rules of Research With Humans and Animals that have established on analysis of national and international bioethic guidelines for biomedical research with the use of humans and animals and are a part of the ISS human use guidelines.

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Presented are literary and authors' data on functioning of the endocrine glands involved in the control of calcium turnover in microgravity. On analysis of research findings the conclusion has been made that exposure to microgravity stimulates functional activity of the parathyroid and suppresses thyroid C-cells producing the parathyroid hormone and calcitonin, respectively. Shifts in the calcium-controlling endocrine systems are considered to be adaptive and play an important role in pathogenesis of disorders in calcium turnover in microgravity.

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Progress of osteopenia in 40-, 100-, and 220-d old rats who had been suspended by tails to release support loading on their hind limbs for 30 days was compared. Deficient support loading was shown to inhibit the longitudinal growth of tibia and produce osteopenia of the proximal metaphysis spongiosis in all groups of rats. Humerus of the rats whose front limbs were still partially loaded, suffered same changes as tibia though much less pronounced. Inhibition of bone growth in length and osteopenia in bone spongiosis reached maximum dimensions in 220-d old rats as a result of summation of kindred changes due to the load deprivation, and aging. Established was a correlation between suppression of the functional activity of STH-cells in adenohypophysis and progress of bone atrophy during suspension. Functional activity of thyroid calcitonin-producing cells was also reduced with the maximum decline in the 40-d old rats.

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The authors present a historical sketch on the ethics of use of animals in life sciences experiments. Experiments with animals are necessary to expand knowledge in the field of life sciences including the space ones, and health service. It is emphasized that these experiments must be performed with observance of certain moral rules and utilize minimum animals suffice to obtain statistically significant data. The first draft of SRC-IBMP Guidelines on the use of laboratory animals has been published.

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In a 3-wk experiment with tail-suspended rats histological and histomorphometric methods were used to determine the effects of graded gravitational loading (GGL) and anabolic steroid retabolil (nortestosterone decanoate) on the course of atrophy in soleus m. (SM), gastrocnemius m. (GM), tibia and humerus, and functioning of somatotrophic hormones (STH) of the pituitary and thyrocytes of the thyroid. Suspension was found to produce atrophy in SM and, to a less degree, in GM, partial transformation of SM slow fibers into the fast ones, suppression of the tibial longitudinal growth, demineralization of the tibial and humeral spongious metaphyses; besides, functional activities of STH-cells and thyrocytes were inhibited. Graded gravitational loading of rats by intermittence of suspension for 2 hrs slowed down atrophy in both muscles and osteopenia in tibia, stimulated the synthetic and secretory functions of STH-cells without any marked effect on thyrocytes or humeral osteopenia. GGL failed to influence the slow-to-fast transformation of SM fibers. Two injections of retabolil at the total dose of 3 mg/kg of the body mass somewhat interfered with the SM atrophy and humoral osteopenia, and were favorable to the synthetic but not secretory activity of STH-cells. Neither SM and tibial atrophies nor thyroid activity of the gland were improved. The prophylactic action of GGL upon the SM and humeral atrophies was significantly higher when combined with retabolil, whereas GM and tibia were not noticeably cured by retabolil. Inhibition of the SM atrophy and humeral osteopenia in rats treated with GGL and retabolil concurred with elevated activities of STH-cells and thyrocytes indirectly suggesting their more intensive production of the growth hormone and thyroid hormones, respectively.

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The histomorphometric method there was used to study effects of ephedrine, strychnine, and support loads on the atrophy of m. soleus and m. gastrocnemius in rats with load-deprived lower extremities (14-day tail-suspension). Deficiency of support loads on the lower extremities led to atrophy of the muscles, especially the slow m. soleus. Injections of ephedrine (0.06 mg/kg), strychnine (0.015 mg/kg) as well as ephedrine and strychnine at one and the same time did not affect the development of atrophy. On the contrary, daily 2-hr support loading of the rear extremities had a favourable effect on the muscle atrophy as it was slowed down. Particularly effective were injections of ephedrine on the background of support loads following which the mass of m. soleus in the suspended rats was close to vivarium control. It is suggested that the preventive effect of ephedrine is associated with stimulating the CNS controllers of the somatotropic function of the pituitary body and eventual enhancement of the somatotropic hormone production.

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