Irreversible morphological changes in leg bone following chronic gravitational unloading of growing rats

Effects of gravitational unloading or loading on the growth and development of hindlimb bones were studied in rats. Male Wistar rats were hindlimb-unloaded or loaded at 2-G from the postnatal day 4 to month 3. The morphology and mineral content of tibia and fibula, as well as the mobility of ankle joints, were measured at the end of 3-month suspension or loading, and 1, 2, and 3 months after ambulation recovery. Growth-related increases of bone weight and mineral density were inhibited by unloading. But they were gradually recovered toward the control levels, even though they were still less than those in the age-matched controls after 3 months. None of the parameters were influenced by 2-G loading. However, here we report that chronic unloading causes abnormal morphological development in hindlimb bone of growing rats. Irreversible external bend of the shaft and rotation of the distal end of tibia, which limit the dorsiflexion of ankle joints, were induced following chronic gravitational unloading during developing period. It is also suggested that such phenomena are caused by the abnormal mechanical forces imposed by muscle utilization with altered patterns. The activity of ankle dorsiflexor was increased and that of plantarflexor was inhibited during unloading.     

Phloem unloading in tobacco sink leaves: insensitivity to anoxia indicates a symplastic pathway

Phloem unloading in transition sink leaves of tobacco (Nicotiana tabacum L.) was analyzed by quantitative autoradiography. Detectable levels of labeled photoassimilates entered sink leaves approx. 1 h after source leaves were provided with ¹⁴CO₂. Samples of tissue were removed from sink leaves when label was first detected and further samples were taken at the end of an experimental phloem-unloading period. The amount of label in veins and in surrounding cells was determined by microdensitometry of autoradiographs using a microspectrophotometer. Photoassimilate unloaded from first-, second-and third-order veins but not from smaller veins. Import termination in individual veins was gradual. Import by the sink leaf was completely inhibited by exposing the sink leaf to anaerobic conditions, by placing the entire plant in the cold, or by steam-girdling the sink-leaf petiole. Phloem unloading was completely inhibited by cold; however, phloem unloading continued when the sink-leaf petiole was steam girdled or when the sink leaf was exposed to a N₂ atmosphere. Compartmental efflux-analysis indicated that only a small percentage of labeled nutrients was present in the free space after unloading from sink-leaf veins in a N₂ atmosphere. The results are consistent with passive symplastic transfer of photoassimilates from phloem to surrounding cells.Symbol VI radio of ¹⁴C in veins and interveinal tissue     

改良的大鼠模拟失重模型制备方法*

目的: 介绍一种改良的尾部悬吊使后肢去负荷的制备大鼠模拟失重模型的方法。方法: 90只成年雄性SD大鼠随机分为对照组,经典尾吊组和改良尾吊组(每组30只)。经典尾吊组利用医用胶带和纱布制作大鼠尾套后悬吊大鼠尾部。改良尾吊组在上述操作基础之上,在尾套内增加聚乙烯发泡棉隔层,以缓冲纱布对尾部的挤压,保证远端血液循环。对照组尾部不做特殊处理。尾吊4周后观察尾部损伤和尾套脱落等并发症,测量大鼠体质量及右侧比目鱼肌湿重。结果: 与对照组相比,经典尾吊组的比目鱼肌湿重/体质量比值显著减少,但体质量无显著差异,大鼠尾部远端出现缺血坏死损伤的发生率为40.0%,尾套脱落的发生率为26.7%,模型成功率为33.3%;与经典尾吊组相比,改良尾吊组的尾部损伤程度明显降低,远端缺血坏死率为13.3%, 尾套脱落率为3.3%,模型成功率为83.3% (P均＜0.05)。结论: 采用改良尾吊法建立大鼠模拟失重模型能够显著减少鼠尾坏死和尾套脱落发生率,简单易行,提高了模型制备的成功率。     

A brief review

This article serves as a brief history and review of EBM—how EBM developed, its strengths and limitations, and the need for constant improvements. Hopefully, this review will have enhanced your understanding of EBM and its importance and stimulated you to apply EBM to your own practice. As more data and therapies become available, and as clinical guidelines continue to evolve based on EBM, we should expect patient outcomes to improve.     

植物体内光合同化物韧皮部装载和卸出研究进展

近年来研究表明,植物体内光合同化物的韧皮部装载和卸出均有其本途径和质外体途径,装载转运的糖类主要有：（２）棉子糖及其人类似物（以共质体方式装载）;（２）蔗糖（以质外体方式装载）。同化物的共质体卸出可通过扩散和集中作用实现,而质外体卸出则根据蔗糖在质外体是否水解而分为两种类型。卸出和装载的途径、机理因植物种类及库源关系而不同,也会受生长发育阶段及环境的变化而调整。深入研究韧皮部装载和帛出调控机制,对     

Mechanical and electrical adaptation of skeletal muscle to gravitational unloading

The physiological and biochemical properties of limb skeletal muscle have been shown to adapt to variety of experimental conditions. Among these is the microgravity encountered with spaceflight. It is adaptations accompanying skeletal muscle disuse atrophy. Foremost among these changes is a reduction in the force-generating capacity, which is presumably a direct result of decrease in fiber number and diameter. These changes suggest a spaceflight-induced reduction in muscle work capacity. The interesting finding that the reduction of the mechanical tension is not proportional to the reduction of muscle weight, fiber diameter, and concentration of contractile protein suggested that changes of electrical activity might contribute to the reduction of the contraction force in disused muscle. The purpose of our study was to assess the effects of a 7-d "dry" immersion on the contractile properties of the triceps surae muscle.     

Modeled gravitational unloading triggers differentiation and apoptosis in preosteoclastic cells

Gravity acts permanently on organisms as either static or dynamic stimulation. Understanding the influence of gravitational and mechanical stimuli on biological systems is an intriguing scientific problem. More than two decades of life science studies in low g, either real or modeled by clinostats, as well as experimentation with devices simulating different types of controlled mechanical stimuli, have shown that important biological functions are altered at the single cell level. Here, we show that the human leukemic line FLG 29.1, characterized as an osteoclastic precursor model, is directly sensitive to gravitational unloading, modeled by a random positioning machine (RPM). The phenotypic expression of cytoskeletal proteins, osteoclastic markers, and factors regulating apoptosis was investigated using histochemical and immunohistochemical methods, while the expression of the corresponding genes was analyzed using RT-PCR. A quantitative bone resorption assay was performed. Autofluorescence spectroscopy and imaging were applied to gain information on cell metabolism. The results show that modeled hypogravity may trigger both differentiation and apoptosis in FLG 29.1 cells. Indeed, when comparing RPM versus 1 x g cultures, in the former we found cytoskeletal alterations and a marked increase in apoptosis, but the surviving cells showed an osteoclastic-like morphology, overexpression of osteoclastic markers and the ability to resorb bone. In particular, the overexpression of both RANK and its ligand RANKL, maintained even after return to 1 x g conditions, is consistent with the firing of a differentiation process via a paracrine/autocrine mechanism.     

A brief review of holopelagic annelids

Annelids are one of the most successful major animal lineagesin terms of number of species and of habitats occupied. Despiteannelids being common in terrestrial, aquatic, and marine environments,only a limited number of lineages have evolved a holopelagicexistence. Most of these holopelagic lineages belong to Phyllodocida(nereidids, syllids, scale worms, and jawed worms) and moreparticularly often within the family Phyllodocidae. These wormsgenerally appear to retain many characteristics of adult annelids.Moreover, we provide molecular evidence showing that the well-knownalciopids are derived from within Phyllodocidae. In contrast,at least two lineages, Poeobius meseres/Flota flabelligera andprobably Chaetopterus pugaporcinus, are derived through paedomorphicprocesses acting on larvae from lineages that have sedentaryadult forms. Herein, we will briefly review the known diversityof holopelagic annelids with discussion of their evolutionaryorigins.     

A brief review of Chinese synapsids

In this short note are reviewed all the synapsid discoveries made in China between 1935 and 1980; their stratigraphical and geological distributions are discussed. A few systematic corrections are included.     

Mild hypothermic cross adaptation resists hypoxic injury in hearts: a brief review

Severe cardiac hypoxia is responsible for significant morbidity and mortality in an emergency setting. Most cardiac hypoxia relates to ischemia and surgical events. Although the ischemic mortality rate and the risks of cardiac surgery have significantly decreased in past decades, myocardial protection still plays a major role in survival of hypoxic injury. Cross adaptation as a physiological regulation for homeostasis can resist injury caused by harmful environmental effects and diseases, including hypothermic adaptation. Treatment with hypothermia has been used for fifty years as a protective mechanism to avoid hypoxic injury. Since cold temperatures can cause damage, it is important to gather physiological data to distinguish protective from injurious temperatures. Although results of temperature trials in clinical practice vary, a critical temperature to resist hypoxic/ischemic injury in heart was found to be around 30 degrees C, suggesting a hypothermia protective threshold. Pretreatment with mild hypothermia can resist subsequent hypoxia/ischemia, implying involvement of cross adaptation in protection. Safeguard hypothermia can directly reduce the build up of harmful metabolites and energy demand in hypoxic tissues, as well as preserve mitochondrial membrane specific proteins beta subunit of F1-ATPase and adenine nucleotide translocase isoform 1. Mechanisms of preservation include inactivation of the p53 related pathways, representing anti-apoptosis, and modification of the mRNA level of succinodehydrogenease, indicating a beneficial effect on the aerobic pathway. Stress proteins are also induced. Resultant cellular adaptations serve to maintain myocardial integrity and improve functional recovery during reoxygenation or reperfusion.     

研究报告: 模拟航天失重病理特征的小鼠模型的制备

目的 航天员返回地球后常常出现共济失调、步态紊乱,是航天医学难题。急需制备一种符合航天失重导致运动失调病理特征的小鼠,为药物筛选提供新模型。方法 将雄性C57BL/6J小鼠随机分成：a.对照组,野生健康成年小鼠;b.标准模型组-后肢悬吊组（hindlimb unloading,HU）,按照常规方法建立后肢悬吊法模型;c.假手术组（顶核注射磷酸缓冲液组）;d.模拟病理特征模型组（顶核注射甲醛组）,该组利用立体定位向健康成年雄性小鼠的小脑顶核内微量注射病理浓度的甲醛（尾吊组脑部测得的浓度）。造模结束后用转棒、平衡木、步态分析来评估小鼠的运动能力、小脑切片尼氏染色检测顶核神经元死亡、试剂盒及荧光组化检测甲醛生成酶——氨基脲敏感胺氧化酶（semicarbazide-sensitive amine oxidase,SSAO）活性及表达。用甲醛荧光探针检测小脑顶核的甲醛浓度。结果 后肢悬吊组相较对于对照组的小鼠运动平衡能力下降、步态紊乱,并伴随小脑内SSAO活性及表达增强、内源甲醛显著上升、顶核神经元死亡。其次,模拟病理特征组小鼠的顶核注射病理浓度甲醛注射后,也出现尾吊标准模型类似的生化及行为变化...     

A brief review of microbial arsenate respiration

In this review, we summarize the important recent findings relating to arsenate respi‐ration by bacteria. A brief discussion of freshwater arsenic cycling is provided, with attention placed on the microbial contributions to this cycle. The basic evidence for microbial growth on arsenate is presented for studies with both consortia and isolates, followed by a summary of the physiology and phytogeny of four arsenate‐respiring bac‐teria: Chrysiogenes arsenatis strain BAL‐1^T, Desulfotomaculum auripigmentum strain OREX‐4, Sulfurospirillum arsenophilus strain MIT‐13, and S. barnesii strain SES‐3. Drawing on biochemical studies of the arsenate reductasefrom S. barnesii strain SES‐3, a preliminary model for growth on arsenate is proposed. We conclude with a discussion of the importance of microbial arsenate reduction in the environment.     

Investigation of the regulation of bone mass by mechanical loading: from quantitative cytochemistry to gene array

From the 1860s to the early 1980s, the process that fitted bone architecture and mass to function had been investigated and characterized. It was known that increases in exercise were associated with increased bone mass, and that disuse caused osteopaenia, but the mechanisms by which those processes were regulated was not understood. The idea that osteocytes, the cells embedded in bone, were sensitive to the effects of mechanical loading was attractive, yet there was almost no experimental support for it, at least in part because the cells were considered inaccessible for study. In 1984, the techniques devised by Chayen and his co-workers were focused on this area. By analysis of the activity of the enzyme glucose 6-phosphate dehydrogenase in osteocytes in sections of avian bone that had been subjected to brief periods of applied mechanical loading, we showed for the first time that osteocytes could respond within a few minutes to mechanical stimulation. The lack of elevation of activity of other glycolytic enzymes led to the conclusion that this elevation was due to increased activity of the pentose shunt pathway, which was likely to be associated with increased production of reducing equivalents for biosynthesis, and ribose sugars for RNA synthesis. This was the first demonstration of an ability of osteocytes to respond to an external mechanical event and in effect provided a mechanistic link for the fundamental principle of what is known as Wolff's law of bone remodelling. These studies were dependent on several technical advances brought together in the Chayen Cellular Biology Laboratory at the Kennedy Institute. The ability to make cryosections of undecalcified bone, to perform cytochemical analysis of (soluble) enzyme activities by use of colloid stabilizers in the reaction medium, and finally to measure accurately the coloured reaction products by microdensitometry (which avoided optical heterogeneity errors) combined to provide a powerful way to explore bone cell function in situ. In the intervening years since then, similar studies have become routine, and the impact of molecular biological advances in hard tissues have remained dependent on techniques pioneered in the Chayen laboratory. During such studies, other advances have spun off, so that osteocyte gene expression has been analysed in samples taken from sections where the precise tissue characteristics were known, leading to advances in understanding of intercellular signalling mechanisms in bone by differential display, and the role of apoptosis in osteocytes in regulation of osteoclastic resorption. Still more recently, materials extracted from undecalcified sections have been used in gene array studies to discover new candidate genes with a role in the adaptive mechanism. Without Joe Chayen's involvement in this area, which now impacts on almost all bone biological science either directly or indirectly, our understanding of the pathophysiology of osteoporosis would have been very different.     

Lymphocyte reduction induced by hindlimb unloading： distinct mechanisms in the spleen and thymus

Hindlimb unloading (HU) in rodent is a well-accepted ground-based model used to simulate some of the condi-tions of space flight and reproduce its deleterious effects on the musculoskeletal, cardiovascular and immune systems. In this study, the effects of HU on lymphocyte homeostasis in the spleen and thymus of mice were examined. HU was found to drastically deplete various cell populations in the spleen and thymus. These changes are likely to be mediated by apoptosis, since DNA strand breaks indicative of apoptosis were detected by terminal deoxynucleotidyl transferase-mediated nick end-labeling in both splenocytes and thymocytes. Surprisingly, administration of opioid antagonists or interference with the Fas-FasL interaction was able to block HU-induced reductions of splenocytes, but not thymocytes. On the other hand, steroid receptor antagonists blocked the reduction of lymphocyte numbers in both spleen and thymus. Therefore, the effects of HU on the homeostasis of splenocytes and thymocytes must be exerted through distinct mechanisms.     

Age‐related differences in synaptic plasticity following muscle unloading

The objective of the present investigation was to determine the effects of muscle unloading—a form of subtotal disuse— on the morphology of the neuromuscular junction (NMJ) in younger and aged animals. Sixteen aged (22 months) and 16 young adult (8 months) male Fischer 344 rats were assigned to control and hindlimb suspension (HS) conditions (n = 8/group). At the conclusion of the 4 week experimental period, soleus muscles were collected, and immunofluorescent procedures were used to visualize acetylcholine (ACh) vesicles and receptors, nerve terminal branching, as well as NCAM and NT‐4 expression. Quantitative analyses revealed that aged controls displayed significant (p < 0.05) reductions in area and perimeter length of ACh vesicle and receptor regions, without affecting nerve terminal branch number or length. In contrast to younger NMJs, which were resilient to the effects of unloading, NMJs of aged HS rats demonstrated significant expansion of ACh vesicle and receptor dimensions compared to aged controls. Qualitative analyses of NCAM staining indicated that aging alone somewhat increased this molecule's expression (aged controls > young controls). Among the four groups, however, the greatest amount of NCAM content was detected among aged HS muscles, matching the degree of synaptic plasticity exhibited in those muscles. Unlike NCAM, the expression of NT‐4 did not appear to differ among the treatment groups. These data suggest that although young adult muscle maintains normal NMJ structure during prolonged exposure to unloading, aged NMJs experience significant adaptation to that stimulus. © 2003 Wiley Periodicals, Inc. J Neurobiol 57: 246–256, 2003     

Phloem loading and unloading of sugars and amino acids

In terrestrial higher plants, phloem transport delivers most nutrients required for growth and storage processes. Some 90% of plant biomass, transported as sugars and amino nitrogen (N) compounds in a bulk flow of solution, is propelled though the phloem by osmotically generated hydrostatic pressure differences between source (net nutrient export) and sink (net nutrient import) ends of phloem paths. Source loading and sink unloading of sugars, amino N compounds and potassium largely account for phloem sap osmotic concentrations and hence pressure differences. A symplasmic component is characteristic of most loading and unloading pathways which, in some circumstances, may be interrupted by an apoplasmic step. Raffinose series sugars appear to be loaded symplasmically. However, sucrose, and probably certain amino acids, are loaded into minor veins from source leaf apoplasms by proton symporters localized to plasma membranes of their sieve element/companion cell (se/cc) complexes. Sucrose transporters, with complementary kinetic properties, are conceived to function as membrane transporter complexes that respond to alterations in source/sink balance. In contrast, symplasmic unloading is common for many sink types. Intervention of an apoplasmic step, distal from importing phloem, is reserved for special situations. Effluxers that release sucrose and amino acids to the surrounding apoplasm in phloem loading and unloading are yet to be cloned. The physiological behaviour of effluxers is consistent with facilitated membrane transport that can be energy coupled. Roles of sucrose and amino acid transporters in phloem unloading remain to be discovered along with mechanisms regulating symplasmic transport. The latter is hypothesized to exert significant control over phloem unloading and, in some circumstances, phloem loading.     

A generic 3-dimensional system to mimic trabecular bone surface adaptation

The paper presents the structure optimizing system based on surface remodelling. The grounds for algorithm formulation are given by the bone remodelling phenomenon leading to optimization of trabecular network in the bone. The assumptions, algorithms and limitations of the own mesh generator Cosmoprojector are described. Unlike other approaches, the system is able to mimic real bone evolution including tissue consolidation and separation. The article presents a closed system consisting of finite element mesh generation, decision criteria for structure adaptation and finite element analysis in parallel environment. It also provides some computation results obtained by using specially designed software.