Decreased plasma levels of nitric oxide metabolites, angiotensin II, and aldosterone in spontaneously hypertensive rats exposed to 5 mT static magnetic field

Previously, we found that whole body exposure to static magnetic fields (SMF) at 10 mT (B(max)) and 25 mT (B(max)) for 2-9 weeks suppressed and delayed blood pressure (BP) elevation in young, stroke resistant, spontaneously hypertensive rats (SHR). In this study, we investigated the interrelated antipressor effects of lower field strengths and nitric oxide (NO) metabolites (NO(x) = NO(2)(-) + NO(3)(-)) in SHR. Seven-week-old male rats were exposed to two different ranges of SMF intensity, 0.3-1.0 mT or 1.5-5.0 mT, for 12 weeks. Three experimental groups of 20 animals each were examined: (1) no exposure with intraperitoneal (ip) saline injection (sham-exposed control); (2) 1 mT SMF exposure with ip saline injection (1 mT); (3) 5 mT SMF exposure with ip saline injection (5 mT). Arterial BP, heart rate (HR), skin blood flow (SBF), plasma NO metabolites (NO(x)), and plasma catecholamine levels were monitored. SMF at 5 mT, but not 1 mT, significantly suppressed and retarded the early stage development of hypertension for several weeks, compared with the age matched, unexposed (sham exposed) control. Exposure to 5 mT resulted in reduced plasma NO(x) concentrations together with lower levels of angiotensin II and aldosterone in SHR. These results suggest that SMF may suppress and delay BP elevation via the NO pathways and hormonal regulatory systems.     

WHO health risk assessment process for static fields

The World Health Organization (WHO) has a commitment to helping Member States achieve safe, sustainable and health-enhancing human environments, protected from biological, chemical and physical agents. The latter includes advising on the health impact of electromagnetic fields (EMFs) and radiation.

The results of the WHO/ICNIRP/NRPB workshop on static magnetic fields, published in this volume, provide a valuable and much needed contribution to the health risk assessment of exposure to static electric and magnetic fields, which is currently being coordinated by the WHO's International EMF Project. This WHO health risk assessment will be published as an environmental health criteria (EHC) monograph in early 2005.

This paper briefly gives an overview of the process of developing the WHO static fields EHC monograph, the criteria applied to studies that could contribute to the EHC, along with the ‘weight-of-evidence’ approach to health risk assessment. In addition, there is an increasing awareness of the need to account for uncertainty in the science database. This is traditionally addressed by further research, and the EMF project addresses these needs through the development of a ‘research agenda’. However, research programmes may take several years to complete, and the long latency associated with diseases such as cancer in people may also preclude a rapid outcome in some studies. The issue of current uncertainty is being addressed by the WHO EMF project through the development of a ‘precautionary framework’ in which precautionary measures will be applied to policy recommendations.     

Short-term invasibility patterns in burnt and unburnt experimental Mediterranean grassland communities of varying diversities

This paper reports the findings of a short-term natural invasibility field study in constructed Mediterranean herbaceous communities of varying diversities, under a fire treatment. Three components of invasibility, i.e. species richness, density and biomass of invaders, have been monitored in burnt and unburnt experimental plots with resident diversity ranging from monocultures to 18-species mixtures. In general, species richness, density and biomass of invaders decreased significantly with the increase of resident species richness. Furthermore, the density and biomass of invading species were significantly influenced by the species composition of resident communities. Although aboveground biomass, leaf area index, canopy height and percent bare ground of the resident communities explained a significant part of the variation in the success of invading species, these covariates did not fully explain the effects of resident species richness. Fire mainly influenced invasibility via soil nutrient levels. The effect of fire on observed invasibility patterns seems to be less important than the effects of resident species richness. Our results demonstrate the importance of species richness and composition in controlling the initial stages of plant invasions in Mediterranean grasslands but that there was a lack of interaction with the effects of fire disturbance.     

Dependence of Visual Cell Properties on Intracortical Synapses Among Hypercolumns: Analysis by a Computer Model

The role of intracortical synapses in affecting the property of visual cells is investigated by means of an original mathematical model of cortical circuitry in V1. The model represents a compromise between computational simplicity and physiological reliability. The model incorporates four different inputs into a cortical cell: thalamic input from the lateral geniculate nucleus, according to an even Gabor function; short-range inhibition confined within the hypercolumn; a long-range excitation, which emphasizes the properties of the input; and a long-range inhibition. In the model we assume that all cells receive a similar thalamic input, which differs simply according to its position in the retina and orientation preference. Simulations were performed, with different parameter values, to assess the main characteristics of cell response (i.e., the width and locations of subregions in the receptive field (RF), orientation tuning curve, and response to drifting and counterphase gratings) as a function of the strength and extension of intracortical excitatory synapses. Results suggest that, if intracortical excitation is confined within the hypercolumn, the cells exhibit the same properties as simple cells, both with regards to the width and shape of the RF, orientation tuning curve, and response to drifting and counterphase gratings. By contrast, if excitatory synapses extend beyond the hypercolumn with sufficient strength, the cells exhibit the typical characteristics of complex cells. A progressive shift from complex to simple cells can be realized with a monotonic variation in parameters. Simulations are also performed with a hierarchical model, to suggest possible experiments able to discriminate the present recurrent mechanism from the classical hierarchical one. Results support the assumptions of previous simpler models (Chance et al., 1999) and may help to understand and assess the role of intracortical synapses in rigorous quantitative terms.     

Effects of extremely low frequency electromagnetic fields on membrane-associated enzymes

The effects of extremely low frequency electromagnetic fields of 75 Hz were studied on different membrane-associated enzymes. Only the activities of three enzymes out of seven exposed to the field decreased approximately of about 54-61% with field amplitudes above a threshold of 73-151 microT depending on the enzyme. The same field had no effect on the activities of either integral membrane enzymes such as Ca,ATPase, Na/K,ATPase, and succinic dehydrogenase or peripheral membrane enzymes such as photoreceptor PDE. The decrease in enzymatic activity of the field-sensitive enzymes was independent of the time of permanence in the field and was completely reversible. When these enzymes were solubilized with Triton, no effect of the field was obtained on the enzymatic activity, suggesting the crucial role of the membrane in determining the conditions for enzyme inactivation. The role of the particular linkage of the field-sensitive enzymes to the membranes is also discussed.     

Cellular recruitment and the development of the myocardium

The vertebrate embryo experiences very rapid growth following fertilization. This necessitates the establishment of blood circulation, which is initiated during the early somite stages of development when the embryo begins to exhibit three-dimensional tissue organization. Accordingly, the contractile heart is the first functional organ that develops in both the bird and mammalian embryo. The vertebrate heart is quickly assembled as a simple two-layer tube consisting of an outer myocardium and inner endocardium. During embryogenesis, the heart undergoes substantial growth and remodeling to meet the increased circulatory requirements of an adult organism. Until recently, it was thought that all the cells that comprise the muscle of the mature heart could trace their roots back to two bilaterally distributed mesodermal fields within the early gastrula. It is now known that the cellular components that give rise to the myocardium have multiple ancestries and that de novo addition of cardiac myocytes to the developing heart occurs at various points during embryogenesis. In this article, we review what is presently known about the source of the cells that contribute to the myocardium and explore reasons why multiple myocardial cell sources exist.     

表皮生长因子和降钙素基因相关肽在高频电磁场 治疗急性胃损伤中作用研究

目的：探讨高频电磁场（high-frequency electromagnetic fields,HEMFs）曝露治疗急性胃损伤的作用机制。方法：选用健康SD大鼠,以Indomethacin灌胃法复制胃粘膜急性损伤模型,观察40．68MHz HEMFs（波长为7．3m）曝露（微热量,30—50mA,15min,1／d）治疗1或6次后,大鼠胃粘膜损伤程度（胃损伤指数和病理损伤积分）、胃粘膜血流量、血浆表皮生长因子（epidermal growth factor,EGF）和降钙素基因相关肽（calcitonin gene—related peptide,CGRP）水平。结果：HEMFs曝露1次后,胃粘膜血流量较对照组明显升高（P〈0．05）,大鼠胃粘膜损伤程度、血浆EGF和CGRP水平较对照组均无显著性差异（P均〉0．05）;HEMFs曝露6次后,胃粘膜损伤程度较对照组明显改善（P均〈0．05）,胃粘膜血流量显著升高（P〈0．05）,血浆EGF和CGRP水平较对照组无显著性差异（P均〉0.05）。结论：HEMFs曝露治疗大鼠胃粘膜急性损伤可能与其增加胃粘膜血流量有关,与血EGF和CGRP无关。     

水稻砷污染及其对砷的吸收和代谢机制

水稻是当今世界大部分地区(尤其是东南亚)的主要的粮食作物之一,同时也是砷(As)进入食物链的主要途径之一。日益严重的水稻田As污染,不但影响了稻米的产量和品质,而且通过食物链威胁着人体健康。如何减少水稻地上部(尤其是米粒)As的含量和降低其毒性,及提高水稻As耐性是亟需解决的世界食品安全问题。深入了解水稻对As的吸收、积累和代谢的生理及分子生物学机制是解决水稻As污染的关键途径。综述国内外研究,对今后深入研究提出建议。     

基于Cytb基因的动物检材种属鉴定在非传统领域的部分运用

传统意义上的种属鉴定主要用于法医学研究方面,然而随着科技的进步及社会发展的需要,种属鉴定在其他领域也有广泛的应用。主要以线粒体Cytb基因为切入点,简要介绍了线粒体DNA及Cytb基因的结构和特点,总结和归纳了基于Cytb基因进行种属鉴定的相关技术方法在打击动物走私、濒危物种保护、食品及动物产品或制品等的检验检疫方面的运用情况,并对存在的问题及发展趋势做一阐述。     

不同抗性品种稻田捕食性节肢动物的群落结构

对3个类型稻田早、晚稻捕食性节肢动物群落调查,结果表明:共有捕食性节肢动物67种,丰富度以蜘蛛高于捕食性昆虫类;早稻高于晚稻;中抗品种高于抗虫和感虫品种。早稻以皿蛛科Linyphiidae的食虫沟瘤蛛UlmmeliatainsecticepesBoes.etStr.占优势,晚稻则以狼蛛科Lycosidae的相对丰盛度最高。早稻捕食性天敌数量动态以中抗品种峰期最长;感性样田中天敌平均密度与中抗样田差异不显著,与抗虫品种差异显著;捕食性节肢动物多样性随着品种抗性的增强呈降低趋势,优势度随着品种抗性的增强而增强。晚稻3个品种样田中天敌的平均密度差异不显著;各品种样田的多样性明显高于早稻,且波动幅度小于早稻,品种之间多样性差异较小,晚稻群落可能具有较高的稳定性。