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.     

Tensile Tissue Stress Affects the Orientation of Cortical Microtubules in the Epidermis of Sunflower Hypocotyl

Abstract In turgid multicellular organs, it is convenient to differentiate between the two kinds of tensile forces acting in cell walls as a result of turgor pressure. The primary forces occur both in situ and in cells isolated from the organ, whereas the secondary forces occur only in situ. The latter are an unavoidable physical consequence of the variation in mechanical parameters of tissues forming layers or strands. The most rigid tissue is under maximal tensile force, whereas the least rigid is under maximal compressive force. These forces cause tissue stresses (that is, certain tissues are under tensile stress, whereas others are under compressive stress in the organ). The primary and secondary forces result in primary and secondary stress in cell walls, respectively. The anisotropy of the primary stress is a function of cell shape. For instance, in cylindric cells the anisotropy expressed as the ratio of longitudinal to transverse stresses is 0.5. The anisotropy of the secondary stress is a function of the compound structure of the organ. For example, in the epidermis of sunflower hypocotyl, the longitudinal secondary stress is much higher than the transverse stress. The primary and secondary stresses are superimposed, and, as a consequence, the stress anisotropy in the outer thick walls of epidermal cells is greater than 1. These outer epidermal walls transmit most of the tissue stress. When the epidermis is peeled but remains turgid, only primary stress remains, but loading of the peel can reestablish the original stress anisotropy. We studied the effect of stress anisotropy changes on the orientation of cortical microtubules (CMTs) in the sunflower hypocotyl epidermis. We showed that changes in stress anisotropy cause the CMT orientation to change in the direction of maximal wall stress. In situ, the relatively high tensile tissue stress in the epidermis causes maximal stress in the longitudinal direction and relatively steep CMT orientation. When the tissue stress is removed from the epidermis by peeling, the CMTs tend to reorient toward the transverse direction, which is the direction of maximal stress in the primary component. On application of external longitudinal stress, to substitute for tissue stress, CMTs tend to reorient in the longitudinal direction. However, a relatively high rate of plastic strain is caused by the stress applied to the peel in an acid medium. This produces a less steep orientation of CMTs. It appears that the change in stress anisotropy orients the CMT in the direction in which the stress is maximal after the change, but there is also some effect of the growth rate on the orientation. Received 4 January 2000; accepted 10 February, 2000     

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.     

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.

     

A transgenic mouse model for monitoring endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is caused by the accumulation of unfolded proteins in the ER lumen, and is associated with vascular and neurodegenerative diseases. Although the connection between ER stress and some disease-related proteins has been studied using animal models of these diseases, no in vivo data concerning ER stress are available. Here we report a new method for monitoring ER stress in vivo, based on XBP-1 mRNA splicing by inositol requiring-1 (IRE-1) during ER stress. The stress indicator was constructed by fusing XBP-1 and venus, a variant of green fluorescent protein. During stress, the spliced indicator mRNA is translated into an XBP-1-venus fusion protein, which can be detected by its fluorescence. We used transgenic animals expressing the ER stress indicator to show that it can be used to monitor physiological and pathological ER stress in vivo.     

Stress granules: RNP-containing cytoplasmic bodies arising in stress: Structure and mechanism of organization

The review considers recent data on stress granules, which are dense RNP-containing cytoplasmic bodies that arise under stress conditions, e.g., in heat shock, UV irradiation, energy depletion, and oxidative stress. There is evidence that stress granules accumulate incomplete initiation complexes containing mRNA associated with proteins, small ribosomal subunits, and some translation initiation factors, and that stress granules are formed when cells are depleted of the ternary complex (eIF2-tRNA^Met-GTP), in particular, upon eIF2A phosphorylation or a decrease in GTP. Large ribosomal subunits and the ternary complex are absent from stress granules. The structural basis of stress granules is known. It is probable, however, that RNA-binding protein TIA-1, which normally occurs in the nucleus, forms prion-like aggregates that serve as scaffolds for other components of stress granules. The cytoskeleton facilitates the accumulation of stress granule components in local cytoplasmic sites. Studies of the formation and composition of stress granules are important for a better understanding of the regulation of translation initiation in vivo and the mechanisms of the cell response to stress factors.     

Antitoxin MqsA helps mediate the bacterial general stress response

Although it is well recognized that bacteria respond to environmental stress through global networks, the mechanism by which stress is relayed to the interior of the cell is poorly understood. Here we show that enigmatic toxin-antitoxin systems are vital in mediating the environmental stress response. Specifically, the antitoxin MqsA represses rpoS, which encodes the master regulator of stress. Repression of rpoS by MqsA reduces the concentration of the internal messenger 3,5-cyclic diguanylic acid, leading to increased motility and decreased biofilm formation. Furthermore, the repression of rpoS by MqsA decreases oxidative stress resistance via catalase activity. Upon oxidative stress, MqsA is rapidly degraded by Lon protease, resulting in induction of rpoS. Hence, we show that external stress alters gene regulation controlled by toxin-antitoxin systems, such that the degradation of antitoxins during stress leads to a switch from the planktonic state (high motility) to the biofilm state (low motility).     

Dynamic changes in small nuclear ribonucleoproteins of heat-stressed and thermotolerant HeLa cells

Living organisms when subjected to various forms of environmental stress mount a physiological response to survive the long- and short-term ill-effects of the stress. The stress response may involve selective shut down of non-essential metabolic activities and the repair of macromolecular damage resulting from the stress. Messenger RNA splicing in cultured HeLa cells is one of the processes inhibited by heat stress. Splicing is protected from such inhibition in stress-preconditioned cells that have acquired a tolerant state characterised by increased cell survival and resistance to other environmental stresses. Stress tolerant cells have heat shock proteins (HSPs) that had been induced by the preconditioning process. To examine the biochemical changes induced by stress in the splicing apparatus, we analysed the small nuclear ribonucleoprotein (snRNP) particles associated with spliceosomes in normal, stressed, and stress tolerant cells. We show that (a) the spliceosomal component U4/U5/U6 snRNP particle is disassembled by heat stress into intermediates of splicing assembly, (b) prior induction of stress tolerance protects the structural and functional integrity of snRNPs if cells are subsequently exposed to a severe stress and (c) a novel 65 kDa protein is associated with small nuclear ribonucleoprotein particles in stress tolerant cells.     

沙冬青逆境胁迫分子生物学研究进展

逆境胁迫是影响植物生长发育的重要因素,植物的抗逆机理是分子生物学研究的重要领域。随着分子生物学技术的发展,有关植物抗逆方面的研究已取得了很大的进展,初步揭示了植物应对逆境胁迫适应性的分子机理。沙冬青是我国温带荒漠地区惟一的常绿灌木,具有很强的抗逆性,是开展植物逆境胁迫研究和抗逆基因筛选的理想材料。本文综合论述了抗逆植物沙冬青的抗逆机理及逆境胁迫相关基因的分子生物学研究进展,为植物抗逆基因工程发掘更多的基因资源和抗旱植物的抗逆性研究提供思路。     

Autophagy and the integrated stress response

Autophagy is a tightly regulated pathway involving the lysosomal degradation of cytoplasmic organelles or cytosolic components. This pathway can be stimulated by multiple forms of cellular stress, including nutrient or growth factor deprivation, hypoxia, reactive oxygen species, DNA damage, protein aggregates, damaged organelles, or intracellular pathogens. Both specific, stimulus-dependent and more general, stimulus-independent signaling pathways are activated to coordinate different phases of autophagy. Autophagy can be integrated with other cellular stress responses through parallel stimulation of autophagy and other stress responses by specific stress stimuli, through dual regulation of autophagy and other stress responses by multifunctional stress signaling molecules, and/or through mutual control of autophagy and other stress responses. Thus, autophagy is a cell biological process that is a central component of the integrated stress response.     

Chlorophyll Fluorescence as a Tool in Cereal Crop Research

Chlorophyll (Chl) fluorescence is a subtle reflection of primary reactions of photosynthesis. Intricate relationships between fluorescence kinetics and photosynthesis help our understanding of photosynthetic biophysical processes. Chl fluorescence technique is useful as a non-invasive tool in eco-physiological studies, and has extensively been used in assessing plant responses to environmental stress. The review gives a summary of some Chl fluorescence parameters currently used in studies of stress physiology of selected cereal crops, namely water stress, heat stress, salt stress, and chilling stress.     

Stress activation of Bacillus subtilis sigma B can occur in the absence of the sigma B negative regulator RsbX.

Environmental stress activates sigma B, the general stress response sigma factor of Bacillus subtilis, by a pathway that is negatively controlled by the RsbX protein. To determine whether stress activation of sigma B occurs by a direct effect of stress on RsbX, we constructed B. subtilis strains which synthesized various amounts of RsbX or lacked RsbX entirely and subjected these strains to ethanol stress. Based on the induction of a sigma B-dependent promoter, stress activation of sigma B can occur in the absence of RsbX. Higher levels of RsbX failed to detectably influence stress induction, but reduced levels of RsbX resulted in greater and longer-lived sigma B activation. The data suggest that RsbX is not a direct participant in the sigma B stress induction process but rather serves as a device to limit the magnitude of the stress response.     

Femoral head apparent density distribution predicted from bone stresses

A new theory relating bone morphology to applied stress is used to predict the apparent density distribution in the femoral head and neck. Cancellous bone is modeled as a self-optimizing material and cortical bone as a saturated (maximum possible bone density) response to stress in the bone tissue. Three different approaches are implemented relating bone apparent density to: (1) the von Mises stress, (2) the strain energy density in the mineralized tissue and (3) a defined closed effective stress (spherical stress). An iterative nonlinear three-dimensional finite element model is used to predict the apparent density distribution in the femoral head and neck for each of the three approaches. It is shown that the von Mises stress (an open effective stress) cannot accurately predict bone apparent density. It is shown that strain energy density and the defined closed effective stress can predict apparent density and that they give predictions consistent with the observed density pattern in the femoral head and neck.     

Salinity Stress in Wheat: Effects,Mechanisms and Management Strategies

Salinity stress is a major threat to global food production and its intensity is continuously increasing because of anthropogenic activities. Wheat is a staple food and a source of carbohydrates and calories for the majority of people across the globe. However, wheat productivity is adversely affected by salt stress, which is associated with a reduction in germination, growth, altered reproductive behavior and enzymatic activity, disrupted photosynthesis, hormonal imbalance, oxidative stress, and yield reductions. Thus, a better understanding of wheat (plant) behavior to salinity stress has essential implications to devise counter and alleviation measures to cope with salt stress. Different approaches including the selection of suitable cultivars, conventional breeding, and molecular techniques can be used for facing salt stress tolerance. However, these techniques are tedious, costly, and labor-intensive. Management practices are still helpful to improve the wheat performance under salinity stress. Use of arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria, and exogenous application of phytohormones, seed priming, and nutrient management are important tools to improve wheat performance under salinity stress. In this paper, we discussed the effect of salinity stress on the wheat crop, possible mechanisms to deal with salinity stress, and management options to improve wheat performance under salinity conditions.