Greater Physiological and Behavioral Effects of Interrupted Stress Pattern Compared to Daily Restraint Stress in Rats

Repeated stress can trigger a range of psychiatric disorders, including anxiety. The propensity to develop abnormal behaviors after repeated stress is related to the severity, frequency and number of stressors. However, the pattern of stress exposure may contribute to the impact of stress. In addition, the anxiogenic nature of repeated stress exposure can be moderated by the degree of coping that occurs, and can be reflected in homotypic habituation to the repeated stress. However, expectations are not clear when a pattern of stress presentation is utilized that diminishes habituation. The purpose of these experiments is to test whether interrupted stress exposure decreases homotypic habituation and leads to greater effects on anxiety-like behavior in adult male rats. We found that repeated interrupted restraint stress resulted in less overall homotypic habituation compared to repeated daily restraint stress. This was demonstrated by greater production of fecal boli and greater corticosterone response to restraint. Furthermore, interrupted restraint stress resulted in a lower body weight and greater adrenal gland weight than daily restraint stress, and greater anxiety-like behavior in the elevated plus maze. Control experiments demonstrated that these effects of the interrupted pattern could not be explained by differences in the total number of stress exposures, differences in the total number of days that the stress periods encompased, nor could it be explained as a result of only the stress exposures after an interruption from stress. These experiments demonstrate that the pattern of stress exposure is a significant determinant of the effects of repeated stress, and that interrupted stress exposure that decreases habituation can have larger effects than a greater number of daily stress exposures. Differences in the pattern of stress exposure are therefore an important factor to consider when predicting the severity of the effects of repeated stress on psychiatric disorders.     

Photosynthetic Enzymes of the C4 Grass Setaria sphacelata Under Water Stress: A Comparison Between Rapidly and Slowly Imposed Water Deficit

Two stress imposing systems were used: a rapid stress developed by allowing excised leaves to loose water by transpiration, and a slow stress developed by withholding watering of potted plants. Carboxylating enzymes reacted differently on both types of stress. Rapid stress increased ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) activation, but both activities (initial and total) showed little variation with stress. Under slow stress the activation did not change, although both activities decreased much under stress. Phosphoenolpyruvate carboxylase (PEPC) showed a deep decrease of activity under rapid stress, nevertheless, a certain recovery was found under extreme stress. On the other hand, under slow stress the activity of PEPC showed a linear increase with decreasing relative water content. The ratio between physiological and maximal activity increased slightly under both types of stress. The activity of malic enzyme did not change under rapid stress, and decreased linearly under slow stress.     

逆境胁迫下作物基因表达更替的研究进展

本文综述了高等植物在厌氧、热激,盐分胁迫,养分胁迫,紫外辐射等各种逆境条件下,基因表达更替的一系列过程,提出基因表达变化对作物适应逆境条件的意义,并对今后的研究作了展望。     

Salt stress and hyperosmotic stress regulate the expression of different sets of genes in Synechocystis sp. PCC 6803.

Acclimation of microorganisms to environmental stress is closely related to the expression of various genes. We report here that salt stress and hyperosmotic stress have different effects on the cytoplasmic volume and gene expression in Synechocystis sp. PCC 6803. DNA microarray analysis indicated that salt stress strongly induced the genes for some ribosomal proteins. Hyperosmotic stress strongly induced the genes for 3-ketoacyl-acyl carrier protein reductase and rare lipoprotein A. Genes whose expression was induced both by salt stress and by hyperosmotic stress included those for heat-shock proteins and the enzymes for the synthesis of glucosylglycerol. We also found that each kind of stress induced a number of genes for proteins of unknown function. Our findings suggest that Synechocystis recognizes salt stress and hyperosmotic stress as different stimuli, although mechanisms common to the responses to each form of stress might also contribute to gene expression.     

Initial stress in biomechanical models of atherosclerotic plaques

Rupture of atherosclerotic plaques is the underlying cause for the majority of acute strokes and myocardial infarctions. Rupture of the plaque occurs when the stress in the plaque exceeds the strength of the material locally. Biomechanical stress analyses are commonly based on pressurized geometries, in most cases measured by in-vivo MRI. The geometry is therefore not stress-free. The aim of this study is to identify the effect of neglecting the initial stress state on the plaque stress distribution. Fifty 2D histological sections (7 patients, 9 diseased coronary artery segments), perfusion fixed at 100 mmHg, were segmented and finite element models were created. The Backward Incremental method was applied to determine the initial stress state and the zero-pressure state. Peak plaque and cap stresses were compared with and without initial stress. The effect of initial stress on the peak stress was related to the minimum cap thickness, maximum necrotic core thickness, and necrotic core angle. When accounting for initial stress, the general relations between geometrical features and peak cap stress remain intact. However, on a patient-specific basis, accounting for initial stress has a different effect on the absolute cap stress for each plaque. Incorporating initial stress may therefore improve the accuracy of future stress based rupture risk analyses for atherosclerotic plaques.     

Contributions of individual σB-dependent general stress genes to oxidative stress resistance of Bacillus subtilis

The general stress regulon of Bacillus subtilis comprises approximately 200 genes and is under the control of the alternative sigma factor σ(B). The activation of σ(B) occurs in response to multiple physical stress stimuli as well as energy starvation conditions. The expression of the general stress proteins provides growing and stationary nonsporulating vegetative cells with nonspecific and broad stress resistance. A previous comprehensive phenotype screening analysis of 94 general stress gene mutants in response to severe growth-inhibiting stress stimuli, including ethanol, NaCl, heat, and cold, indicated that secondary oxidative stress may be a common component of severe physical stress. Here we tested the individual contributions of the same set of 94 mutants to the development of resistance against exposure to the superoxide-generating agent paraquat and hydrogen peroxide (H(2)O(2)). In fact, 62 mutants displayed significantly decreased survival rates in response to paraquat and/or H(2)O(2) stress compared to the wild type at a confidence level of an α value of ≤ 0.01. Thus, we were able to assign 47 general stress genes to survival against superoxide, 6 genes to protection from H(2)O(2) stress, and 9 genes to the survival against both. Furthermore, we show that a considerable overlap exists between the phenotype clusters previously assumed to be involved in oxidative stress management and the actual group of oxidative-stress-sensitive mutants. Our data provide information that many general stress proteins with still unknown functions are implicated in oxidative stress resistance and further support the notion that different severe physical stress stimuli elicit a common secondary oxidative stress.     

Conserved features of chronic stress across phyla: the effects of long-term stress on behavior and the concentration of the neurohormone octopamine in the cricket, Gryllus texensis

Many of the deleterious effects of chronic stress in vertebrates are caused by the long-term elevation of stress hormones. These negative effects are thought to be unavoidable by-products of sustained activation of the stress response, but the details remain unclear. A comparative perspective may help in understanding chronic stress. We exposed crickets (Gryllus texensis) to a mock predator. A single exposure to a mock predator induced a transient increase in the hemolymph (blood) concentration of the insect stress neurohormone, octopamine. Repeated exposure to the mock predator increased basal levels of octopamine, similar to the effects of chronic stress on the basal levels of vertebrate stress hormones. This study is the first to report an increase in the basal levels of an invertebrate stress hormone in response to repeated flight-or-fight stress. Chronic stress reduced weight gain, and decreased feeding and enhanced weight loss after food deprivation in adult female crickets. However, chronic stress also increased the tendency of crickets to produce sustained flight. Therefore, this study supports the hypothesis that increasing basal levels of stress hormones may be a phylogenetically common response to chronically stressful conditions. It also demonstrates that chronic stress has both positive and negative effects in insects.     

Differential role of microenvironment in microencapsulation for improved cell tolerance to stress

The effect of the microenvironment in alginate–chitosan–alginate (ACA) microcapsules with liquid core (LCM) and solid core (SCM) on the physiology and stress tolerance of Sacchromyces cerevisiae was studied. The suspended cells were used as control. Cells cultured in liquid core microcapsules showed a nearly twofold increase in the intracellular glycerol content, trehalose content, and the superoxide dismutase (SOD) activity, which are stress tolerance substances, while SCM did not cause the significant physiological variation. In accordance with the physiological modification after being challenged with osmotic stress (NaCl), oxidative stress (H₂O₂), ethanol stress, and heat shock stress, the cell survival in LCM was increased. However, SCM can only protect the cells from damaging under ethanol stress. Cells released from LCM were more resistant to hyperosmotic stress, oxidative stress, and heat shock stress than cells liberated from SCM. Based on reasonable analysis, a method was established to estimate the effect of microenvironment of LCM and SCM on the protection of cells against stress factors. It was found that the resistance of LCM to hyperosmotic stress, oxidative stress, and heat shock stress mainly depend on the domestication effect of LCM’s microenvironment. The physical barrier of LCM constituted by alginate–chitosan membrane and liquid alginate matrix separated the cells from the damage of oxidative stress and ethanol stress. The significant tolerance against ethanol stress of SCM attributed to the physical barrier consists of solid alginate–calcium matrix and alginate–chitosan membrane.     

Intracellular distribution of heat-induced stress glycoproteins

Cellular heat stress results in elevated heat-shock protein (HSP) synthesis and in thermotolerance development. Recently, we demonstrated that protein glycosylation is also an integral part of the stress response with the identification of two major stress glycoproteins, GP50, associated with thermotolerance, and P-SG67, the “prompt” stress glycoprotein induced immediately during acute heat stress. In the present study, we characterized the subcellular location and redistribution of these proteins during the cellular injury and recovery phase. In unheated and heated CHO cells, both stress glycoproteins were present in each subcellular fraction isolated by differential centrifugation. However, the subcellular redistribution in the course of cellular recovery after heat stress was specific for each stress glycoprotein. GP50 was present in all subcellular fractions before heat stress, but showed relatively little redistribution after heat stress. By 24 h of recovery following stress, GP50 showed partial depletion from lysosomes and microsomes, and was mainly present in the mitochondria. Glycosylated P-SG67 was redistributed in a more complex fashion. It was seen predominantly in the lysosomes and microsomes immediately following heat-stress, but after 6 h of recovery following heat stress, it largely disappeared from the microsomes and was present mainly in the cytosol. By 24 h of recovery following heat stress, it was found predominantly in the nucleus-rich fraction and mitochondria. The localization of GP50 and P-SG67 by subcellular fractionation is consistent with immunolocalization studies and contrasts with the translocation of HSP70 after heat stress from cytosol to nuclei and nucleoli. These results reflect a characteristic distribution for each stress glycoprotein; their presence in virtually all subcellular fractions suggests multifunctional roles for the various stress glycoproteins in the cellular heat stress response. J. Cell. Biochem. 66:98–111, 1997. © 1997 Wiley-Liss, Inc.     

等渗Ca(NO3)2和NaCl胁迫对黄瓜幼苗生长及渗透调节物质含量的影响

采用营养液培养方法,以耐盐性较弱的‘津春2号’黄瓜品种为试材,研究了等渗Ca(NO3)2和NaCl胁迫对黄瓜幼苗生长、根系电解质渗透率、根系活力、Na+和K+含量及渗透调节物质含量的影响。结果显示:(1)在84mmol.L-1 NaCl和56mmol.L-1 Ca(NO3)2等渗胁迫下,黄瓜幼苗鲜重和干重均显著下降,且NaCl处理下降的幅度大于等渗Ca(NO3)2处理。(2)NaCl主要通过对黄瓜根系的伤害来抑制植株生长,表现为根系活力下降、根系质膜透性增大、Na+大量积累、K+含量显著下降、Na+/K+明显上升,最终导致根冠比下降;而Ca(NO3)2处理对根系质膜透性、K+含量、Na+/K+的影响均小于NaCl胁迫,且根系活力和根冠比上升,但Ca(NO3)2胁迫后叶片含水量和渗透调节能力均小于NaCl胁迫。(3)NaCl胁迫条件下,黄瓜幼苗内渗透调节物质以可溶性糖为主,而Ca(NO3)2胁迫以可溶性蛋白为主。研究表明,NaCl胁迫对黄瓜幼苗的伤害大于等渗Ca(NO3)2,NaCl主要通过破坏根系质膜结构影响植株生长,而Ca(NO3)2主要通过引起地上部生理干旱来影响植株生长。     

Heat-stress effects on reproduction and seed set in Linum usitatissimum L. (flax)

Heat stress can detrimentally affect the reproductive capacity of many plants. The effect of a 7 or 14 d heat stress on flowering, seed set, pollen viability and germinability of flax (Linum usistatissimum L.) was assessed under growth chamber conditions. An incremental (2 °C/h), cyclical (daytime high 40 °C and night‐time low 18 °C) heat stress was applied 12 d after the initiation of flowering. Although flower formation in flax was not affected by heat stress, boll formation and seed set were reduced with onset of the heat stress. On removal of heat stress the stressed plants showed a compensatory response, flowering and producing bolls at a greater rate than the control plants. Heat stress significantly prolonged flowering by 17 d. Boll weight and seed weight were reduced with heat stress and the number of malformed, sterile seed increased three‐fold after 14 d of heat stress. Pollen viability and appearance were negatively affected after 6 and 10 d of heat stress, respectively. Pollen germinability decreased by the sixth day of heat stress, with no pollen germinating by the tenth day. Effects of heat stress on pollen viability and germinability alone, which did not occur until after the sixth day of the stress, could not account for the decreased boll formation due to heat stress in flax. These observations suggest that a combined effect of heat stress on both pollen and ovules contributes to decreased boll formation and seed set in flax.     

Neural and cardiovascular responses to emotional stress in humans

Sympathetic neural responses to mental stress are well documented but controversial, whereas sympathetic neural responses to emotional stress are unknown. The purpose of this study was to investigate neural and cardiovascular responses to emotional stress evoked by negative pictures and reexamine the relationship between muscle sympathetic nerve activity (MSNA) and perceived stress. Mean arterial pressure (MAP), heart rate (HR), MSNA, and perceived stress levels were recorded in 18 men during three randomized trials: 1) neutral pictures, 2) negative pictures, and 3) mental stress. MAP and HR increased during mental stress (Delta14 +/- 2 mmHg and Delta15 +/- 2 beats/min, P < 0.001) but did not change during viewing of negative or neutral pictures. MSNA did not change during viewing of neutral (Delta1 +/- 1 burst/min, n = 16) or negative (Delta0 +/- 1 burst/min, n = 16) pictures or during mental stress (Delta1 +/- 2 burst/min, n = 13). Perceived stress levels were higher during mental stress (3 +/- 0 arbitrary units) than during viewing negative pictures (2 +/- 0 arbitrary units, P < 0.001). Perceived stress levels were not correlated to changes in MSNA during negative pictures (r = 0.10, P = 0.84) or mental stress (r = 0.36, P = 0.23). In conclusion, our results demonstrate robust increases in MAP and HR during mental stress, but not during emotional stress evoked by negative pictures. Although the influence of mental stress on MSNA remains unresolved, our findings challenge the concept that perceived stress levels modulate MSNA during mental stress.     

Psychophysiological characterization of persons with different resistance to stress

On the basis of behavioral characteristics while performing operator activity under the conditions of emotional stress, two types of subjects were identified with different neurophysiological reactions to emoional stress. In high stress resistant subjects, irrespective of the character of errors under stress, a decrease in the spectral power of theta-rhythm and an increase in the power in beta hand was observed. As compared to low stress resistant subjects, they were characterized by the predominance of activity of the right hemisphere. In low stress resistant subjects during the work under stress conditions the spectral power in beta-1 hand decreased. As compared to high stress resistant, they were characterized by the predominance of the left hemisphere.     

Amyotrophic lateral sclerosis-linked FUS/TLS alters stress granule assembly and dynamics

Background

Amyotrophic lateral sclerosis (ALS)-linked fused in sarcoma/translocated in liposarcoma (FUS/TLS or FUS) is concentrated within cytoplasmic stress granules under conditions of induced stress. Since only the mutants, but not the endogenous wild-type FUS, are associated with stress granules under most of the stress conditions reported to date, the relationship between FUS and stress granules represents a mutant-specific phenotype and thus may be of significance in mutant-induced pathogenesis. While the association of mutant-FUS with stress granules is well established, the effect of the mutant protein on stress granules has not been examined. Here we investigated the effect of mutant-FUS on stress granule formation and dynamics under conditions of oxidative stress.

Results

We found that expression of mutant-FUS delays the assembly of stress granules. However, once stress granules containing mutant-FUS are formed, they are more dynamic, larger and more abundant compared to stress granules lacking FUS. Once stress is removed, stress granules disassemble more rapidly in cells expressing mutant-FUS. These effects directly correlate with the degree of mutant-FUS cytoplasmic localization, which is induced by mutations in the nuclear localization signal of the protein. We also determine that the RGG domains within FUS play a key role in its association to stress granules. While there has been speculation that arginine methylation within these RGG domains modulates the incorporation of FUS into stress granules, our results demonstrate that this post-translational modification is not involved.

Conclusions

Our results indicate that mutant-FUS alters the dynamic properties of stress granules, which is consistent with a gain-of-toxic mechanism for mutant-FUS in stress granule assembly and cellular stress response.

     

Inter-individual variations in wall shear stress and mechanical stress distributions at the carotid artery bifurcation of healthy humans

Fluid shear stress and mechanical wall stress may play a role in the formation of early atherosclerotic lesions, but these quantities are difficult to measure in vivo. Our objective was to quantify these parameters in normal subjects in a clinical setting, and to define regions of low wall shear stress and high mechanical stress. The right carotid bifurcations of five healthy male volunteers were investigated using a novel non-invasive technique which integrates magnetic resonance angiography, ultrasonography, tonometry and state-of-the-art computational fluid dynamics and solid mechanics models. Significant inter-subject variations in patterns as well as magnitude of wall shear stress and mechanical stress were found. In spite of individual variabilities, this study revealed that some regions of the artery wall are exposed simultaneously to low wall shear stress and high mechanical stress and that these regions correspond to areas where atherosclerotic plaque develops. The coexistence of regions of low wall shear stress and high tensile stress may be an important determinant of the formation of atheroma in human arteries.     

干旱胁迫对降香黄檀幼苗光合生理特性的影响

采用温室盆栽方法,设置对照(CK)、轻度(LS)、中度(MS)和重度(HS)干旱胁迫4个水分条件,研究不同水分条件对降香黄檀幼苗光合和生理特性的影响。结果表明:(1)随着干旱胁迫程度增加,降香黄檀幼苗叶片叶绿素总含量总体呈现出下降趋势。(2)降香黄檀幼苗叶片净光合速率、气孔导度、胞间CO2浓度和蒸腾速率随着干旱胁迫强度增加均呈现出先增加后降低趋势,且MS和HS处理下的气孔导度和胞间CO2浓度同时降低,此时幼苗光合能力的下降主要受气孔因素限制。(3)随着干旱胁迫强度的增加,降香黄檀幼苗叶片细胞膜相对透性、丙二醛含量、游离脯氨酸含量和POD活性均呈现出增加趋势,而同期SOD和CAT活性呈现出先升高后降低趋势。可见,降香黄檀幼苗在轻度干旱胁迫下可通过增加叶片保护酶活性来清除活性氧对其组织造成的伤害,但胁迫超过一定程度后保护酶活性下降,表明降香黄檀幼苗的耐旱能力有限。