Hysteresis in coral reefs under macroalgal toxicity and overfishing

Macroalgae and corals compete for the available space in coral reef ecosystems.While herbivorous reef fish play a beneficial role in decreasing the growth of macroalgae, macroalgal toxicity and overfishing of herbivores leads to proliferation of macroalgae. The abundance of macroalgae changes the community structure towards a macroalgae-dominated reef ecosystem. We investigate coral-macroalgal phase shifts by means of a continuous time model in a food chain. Conditions for local asymptotic stability of steady states are derived. It is observed that in the presence of macroalgal toxicity and overfishing, the system exhibits hysteresis through saddle-node bifurcation and transcritical bifurcation. We examine the effects of time lags in the liberation of toxins by macroalgae and the recovery of algal turf in response to grazing of herbivores on macroalgae by performing equilibrium and stability analyses of delay-differential forms of the ODE model. Computer simulations have been carried out to illustrate the different analytical results.

Electronic Supplementary Material

The online version of this article (doi:10.1007/s10867-014-9371-y) contains supplementary material, which is available to authorized users.     

基于奥马哈理论的护理模式 对慢性阻塞性肺疾病患者肺功能及细菌感染率的影响

目的探讨基于奥马哈理论的护理模式对慢性阻塞性肺疾病(COPD)患者肺功能、症状控制、细菌感染率及生活质量的影响。方法选取2018年1月至2019年1月我院收治的134例COPD患者,采用随机数字表法将研究对象分为观察组(n=69)与对照组(n=65),对两组患者住院期间肺功能、症状控制情况、细菌感染率、睡眠情况以及生活质量进行评估和分析。结果观察组患者肺功能情况优于入院时(P0.05)。两组患者泌尿系统感染发生率最高,其次为褥疮创面感染和口腔感染。观察组患者泌尿系感染的发生率低于对照组(P0.05)。两组患者干预后PSQI量表评分和CAT评分均低于入院前,且观察组患者总分低于对照组(均P0.05)。干预后观察组患者SF-36评分均高于对照组(均P0.05)。结论在基于奥马哈理论的护理模式下,COPD患者的肺功能得到加强,继发感染的发生减少,生活质量得到提高。     

The Glycine-Alanine Dipeptide Repeat from C9orf72 Hexanucleotide Expansions Forms Toxic Amyloids Possessing Cell-to-Cell Transmission Properties

Hexanucleotide expansions, GGGGCC, in the non-coding regions of the C9orf72 gene were found in major frontotemporal lobar dementia and amyotrophic lateral sclerosis patients (C9FTD/ALS). In addition to possible RNA toxicity, several dipeptide repeats (DPRs) are translated through repeat-associated non-ATG-initiated translation. The DPRs, including poly(GA), poly(GR), poly(GP), poly(PR), and poly(PA), were found in the brains and spinal cords of C9FTD/ALS patients. Among the DPRs, poly(GA) is highly susceptible to form cytoplasmic inclusions, which is a characteristic of C9FTD/ALS. To elucidate DPR aggregation, we used synthetic (GA)₁₅ DPR as a model system to examine the aggregation and structural properties in vitro. We found that (GA)₁₅ with 15 repeats fibrillates rapidly and ultimately forms flat, ribbon-type fibrils evidenced by transmission electron microscopy and atomic force microscopy. The fibrils are capable of amyloid dye binding and contain a characteristic cross-β sheet structure, as revealed by x-ray scattering. Furthermore, using neuroblastoma cells, we demonstrated the neurotoxicity and cell-to-cell transmission property of (GA)₁₅ DPR. Overall, our results show the structural and toxicity properties of GA DPR to facilitate future DPR-related therapeutic development.     

An Improved Method for Rapid Intubation of the Trachea in Mice

Despite some anatomical and physiological differences, mouse models continue to be an essential tool for studying human lung disease. Bleomycin toxicity is a commonly used model to study both acute lung injury and fibrosis, and multiple methods have been developed for administering bleomycin (and other toxic agents) into the lungs. However, many of these approaches, such as transtracheal instillation, have inherent drawbacks, including the need for strong anesthetics and survival surgery. This paper reports a quick, reproducible method of intratracheal intubation that involves mild inhaled anesthesia, visualization of the trachea, and the use of a surrogate spirometer to confirm exposure. As a proof of concept, 8-12 week old C57BL/6 mice were administered either 2.0 U/kg of bleomycin or an equivalent volume of PBS, and both damage and fibrotic endpoints were measured post-exposure. This procedure allows researchers to treat a large cohort of mice in a relatively short period with little expense and minimal post-procedure care.     

Antifeedant and toxic activity of Trichilia americana extract against the larvae of Spodoptera litura

The biological activity of a crude methanolic extract of Trichilia americana (Sesse and Mocino) Pennington (Meliaceae) was assessed using the Asian armyworm, Spodoptera litura (Fabr.) (Lepidoptera: Noctuidae). The extract exhibited strong antifeedant activity in a choice leaf disc bioassay with 0.18 g cm^–2 extract deterring feeding by 50%. In nutritional assays, the crude extract reduced growth, consumption and the utilisation of ingested and digested food in a dose-dependent manner when fed to larvae, suggesting both antifeedant and toxic activities. When relative growth rates were plotted against relative consumption rates, the growth efficiency of the S. litura fed on diet containing T. americana crude extract was significantly less than that of control larvae. This result further indicates that the extract acts as both an antifeedant and chronic toxin. Toxicity is only seen following ingestion and was not observed following topical application or injection into the hemocoel. Larvae reared initially on extract-containing diet then transferred to control diet showed nutritional indices comparable to those of larvae fed continuously on control diet. This suggests that the extract is not permanently damaging the insect's digestive tract. The mode-of-action of the extract as a chronic toxin remains unknown.     

阿米洛利抑制NHE-1减轻低氧性肺动脉平滑肌细胞增殖

目的：研究Na^＋／H^＋交换抑制剂阿米洛利对低氧刺激的大鼠肺动脉平滑肌细胞（PASMCs）增殖的影响,以及Na^＋／H^＋交挟体-l（NHE-1）活性和表达的变化.方法：常氧（21％O2）或低氧（2％O2）条件下培养PASMCs,并分别给予浓度为1．653、3．125、6．25、12．5、25和50μmol／L．等不同浓度的阿米洛利,培养24h,采用MTT比色实验和免疫组化检测PCNA阳性细胞率的方法反映细胞增殖情况,同时采用激光共聚焦检测细胞内pH以反映Na^＋／H^＋交换体-1活性,RT—PCR法检测Na^＋／H^＋交换体-1mRNA的表达量.结果：低氧培养的PASMCs细胞内pH升高,NHE—1mRNA的表达增多,而阿米洛利可以降低细胞内pH,减少NHE—1mRNA的表达量。同时低氧较常氧培养MTT光吸收值较常氧培养明显升高。PCNA阳性细胞率明显增高,而给予阿米洛利时上述两个指标随药物浓度增加而逐渐下降。结论：低氧可以激活PASMCs细胞膜上的E—1,增加其mRNA水平表达量,使细胞内碱化,促进细胞增殖,而Na^＋／H^＋交换抑制剂阿米洛利可以抑制其活性,减少mRNA水平的表达,导致细胞内酸化,从而抑制细胞增殖,并且此抑制作用在3．125～50μmol／L．浓度范围内呈现明显的浓度依赖性。     

Toxicity versus avoidance response of golden shiner, Notemigonus crysoleucas, to five metals

Avoidance thresholds and 96-h LC50 values were determined for golden shiners, Noiemigonus crysoleucas , for five individual elements: chromium, Cr; copper, Cu; cadmium, Cd; arsenic, As; selenium, Se. The avoidance concentrations were 73, 26 and 28 μgl^-1 for Cr-VI, Cu and As-III, respectively. Cadmium and Se were not avoided at experimental concentrations up to 68 and 3489 μg1^-1, respectively. Acute flow-through 96-h LC50 values were Cr-VI 55·0, Cu 84·6, and As-III 12·5 mg 1^-1, which were more than two orders of magnitude above avoidance concentrations. The acute flow-through 96-h LC50 values for Cd and Se were 2·8 and 11·2 mg 1^-1, respectively. These concentrations are 31 and 2·2 times the highest concentration employed in the avoidance tests, neither of which were avoided by the test organisms. Thus, simple toxicity tests do not identify the environmental hazard of some elements, and the most toxic elements may not elicit a behavioural response. When used in concert with tests of organism function, more realistic indicators of environmental hazard or safety may be determined.     

Hexavalent chromium reduction in <Emphasis Type="Italic">Desulfovibrio vulgaris</Emphasis> Hildenborough causes transitory inhibition of sulfate reduction and cell growth

Desulfovibrio vulgaris Hildenborough is a well-studied sulfate reducer that can reduce heavy metals and radionuclides [e.g., Cr(VI) and U(VI)]. Cultures grown in a defined medium had a lag period of approximately 30 h when exposed to 0.05 mM Cr(VI). Substrate analyses revealed that although Cr(VI) was reduced within the first 5 h, growth was not observed for an additional 20 h. The growth lag could be explained by a decline in cell viability; however, during this time small amounts of lactate were still utilized without sulfate reduction or acetate formation. Approximately 40 h after Cr exposure (0.05 mM), sulfate reduction occurred concurrently with the accumulation of acetate. Similar amounts of hydrogen were produced by Cr-exposed cells compared to control cells, and lactate was not converted to glycogen during non-growth conditions. D. vulgaris cells treated with a reducing agent and then exposed to Cr(VI) still experienced a growth lag, but the addition of ascorbate at the time of Cr(VI) addition prevented the lag period. In addition, cells grown on pyruvate displayed more tolerance to Cr(VI) compared to lactate-grown cells. These results indicated that D. vulgaris utilized lactate during Cr(VI) exposure without the reduction of sulfate or production of acetate, and that ascorbate and pyruvate could protect D. vulgaris cells from Cr(VI)/Cr(III) toxicity. J.D. Wall and M.W. Fields are both affiliated to the Virtual Institute of Microbial Stress and Survival (). M.E. Clark and S.B. Thieman contributed equally to this work.     

八种植物提取物对蔬菜害虫的室内毒力研究

研究了巴豆 (Croton tiglium L.)等八种植物的提取物对几种常见蔬菜害虫的非选择性拒食和毒杀作用。研究结果表明 :巴豆、青蒿、米仔兰等三种植物提取物在 0 .5 %浓度时对菜粉蝶 5龄幼虫的拒食率分别达到96 .36 %、82 .4 2 %和 86 .30 % ,对菜粉蝶 3龄幼虫的毒杀死亡率分别为 5 9.38%、2 8.1 3%和 4 3.75 % ;对黄曲条跳甲成虫的毒杀死亡率为 77.5 0 %、5 6 .2 5 %和 4 8.75 % ;对美洲斑潜蝇幼虫的毒杀死亡率分别为 83.33%、5 6 .6 7%和 73.33%。     

原油和消油剂对鱼类毒性的研究进展

原油对鱼类的毒性主要来自其水溶性成分,可导致鱼卵死亡或发育畸形,并造成鱼类麻痹、发炎、粘膜受损和死亡。消油剂的使用在分散了油膜的同时也带来二次污染,其活性剂对鱼类产生新的毒性影响。消油剂将原油分散为乳化颗粒并能进入鱼体内,加大了原油的毒性并延长其作用时间。综述了原油和消油剂对鱼类毒性的研究进展,展望了鱼类在相关毒性试验领域的应用及发展方向。