Effects Of Chronic Mild Stress Research Articles

Effects of Chronic Stress on Prefrontal Cortex Transcriptome in Mice Displaying Different Genetic Backgrounds

There is increasing evidence that depression derives from the impact of environmental pressure on genetically susceptible individuals. We analyzed the effects of chronic mild stress (CMS) on prefrontal cortex transcriptome of two strains of mice bred for high (HA)and low (LA) swim stress-induced analgesia that differ in basal transcriptomic profiles and depression-like behaviors. We found that CMS affected 96 and 92 genes in HA and LA mice, respectively. Among genes with the same expression pattern in both strains after CMS, we observed robust upregulation of Ttr gene coding transthyretin involved in amyloidosis, seizures, stroke-like episodes, or dementia. Strain-specific HA transcriptome affected by CMS was associated with deregulation of genes involved in insulin secretion (Acvr1c, Nnat, and Pfkm), neuropeptide hormone activity (Nts and Trh), and dopamine receptor mediated signaling pathway (Clic6, Drd1a, and Ppp1r1b). LA transcriptome affected by CMS was associated with genes involved in behavioral response to stimulus (Fcer1g, Rasd2, S100a8, S100a9, Crhr1, Grm5, and Prkcc), immune effector processes (Fcer1g, Mpo, and Igh-VJ558), diacylglycerol binding (Rasgrp1, Dgke, Dgkg, and Prkcc), and long-term depression (Crhr1, Grm5, and Prkcc) and/or coding elements of dendrites (Crmp1, Cntnap4, and Prkcc) and myelin proteins (Gpm6a, Mal, and Mog). The results indicate significant contribution of genetic background to differences in stress response gene expression in the mouse prefrontal cortex.Electronic supplementary materialThe online version of this article (doi:10.1007/s12031-012-9850-1) contains supplementary material, which is available to authorized users.

The impact of prefertilization chronic mild stress on postnatal morphometric development

Objective. The aim of the present study was to examine the effects of chronic mild stress (CMS) induced before the fertilization on gestational maternal weight, length of gestation, and postnatal morphometric development.Material and method. Study is carried out on 18 Wistar albino rats; six females in the stress group, six females in the control group, and six males to be used for mating. CMS was induced in rats of the stress group for 4 weeks, followed by a post-CMS waiting period of 5-weeks. Rats were left for mating at the end of the post-CMS period. Weight gain in pregnant rats was monitored and length of gestation and litter size were recorded in the stress and control groups. Growth parameters of pups pertaining to the body, cranium, thorax, and limbs were measured until week 11.Findings. Weight gained by pregnant rats in the stress group was less than the control group. Increases in mean morphometric parameters from day 0 to week 11 in the stress group were less than the control group (p < 0.05). Furthermore, when developmental parameters at weeks 7, 9, and 11 were compared between genders, females in the stress group were found more affected than males (p < 0.05).Conclusion. CMS sustained before fertilization has a negative effect on gestational maternal weight and postnatal morphometric development of pups, more prominently in females.

Effect of chronic mild stress on serotonergic markers in the skin and brain of the NC/Nga atopic-like mouse strain

Atopic eczema is often worsened by stress. While acute stress is associated with increased turnover of serotonin (5-hydroxytryptamine; 5-HT), chronic stress causes a decrease. In chronic stress, there is a decrease of the 5-HT1A receptor (R)- and an increase in the 5-HT2AR-responsiveness to 5-HT. In the present study, the impact of chronic mild stress on the expression of 5-HT1A and 5-HT2A receptors and serotonin transporter protein (SERT) was investigated in eczematous skin and brain of atopic-like NC/Nga mice. Twenty-four NC/Nga mice were subjected to chronic mild stress for 12weeks, and eczema was induced by applying a mite antigen (Dermatophagoides pteronyssinus) on the ears for the last 4weeks. The mice were divided into three groups, eight per group, stressed eczematous (SE), non-stressed eczematous (NSE) and stressed control (SC). The biopsies were analysed by immunohistochemistry, using a streptavidin-biotin technique. There was an increased number of 5-HT containing dermal mast cell-like mononuclear cells in the skin of mice with eczema (SE and NSE, respectively) compared with the SC, and a tendency to more 5-HT-positive cells in the SE compared with the NSE group. Increased 5-HT1AR immunoreactivity (IR) in the skin and hippocampus of the eczematous groups compared to the control group was seen, but no difference between the SE and NSE groups. The epidermal immunoreactivity for 5-HT2AR was highest in the SE and NSE compared to the SC group, and was also higher in the SE compared to NSE. 5-HT2AR expression was also seen on nerve bundles, the number and intensity of such bundles being decreased in the SE compared to the NSE group. In the CA1 area of the hippocampus, there was an increase in the quantity of cells immunoreactive for 5-HT2AR in the SE versus the NSE group and also in the SE versus the SC group. SERT-IR was found also on nerve bundles with a decreased number in the SE compared to the NSE and SC group. There is a modulation of the expression of serotonergic markers in the eczematous skin and brain of the atopic-like mouse during chronic mild stress.

Satellite Meeting at ESDR 2011: Abstracts from Neurobiology of the Skin Symposium

Atopic eczema is often worsened by stress. We have studied the effect of chronic mild stress in the atopic-like NC/Nga mouse strain. The mice were subjected to chronic mild stress for 12 weeks and eczema was induced by applying a mite antigen (Dermatophagoides pteronyssinus) on the ears for the last 4 weeks. The mice were divided into stressed eczematous, non-stressed eczematousand stressed control groups. Serum corticosterone levels were determined at the endpoint of the experiment. The biopsies from skin and brain have been analyzed using immunohistochemistry and RT-PCR. The diameter of the ears was larger in the stressed eczematous group compared to the other groups. Moreover, the corticosterone levels were significantly lower in the stressedeczematous group. The neuromediators being studied are serotonin, its transporter protein, as well as its receptors, and the tachykinin substance P and its receptor neurokinin-1.

Octreotide ameliorates gastric lesions in chronically mild stressed rats

To evaluate the effect of chronic mild stress (CMS) on the emergence of gastric ulcers and possible modulation by octreotide, a synthetic somatostatin analogue. Adult male Wistar rats were subjected to nine different unpredictable random stress procedures for 21 d, a multifactorial interactional animal model for CMS. Octreotide was administered daily for 21 d at two dose levels (50 and 90 μg/kg) before exposure to stress procedure. Macro- and microscopical assessments were made, in addition to quantification of plasma corticosterone and gastric mucosal inflammatory, oxidative stress, and apoptotic biomarkers. Exposure to CMS elevated plasma corticosterone (28.3 ± 0.6 μg/dL, P = 0.002), an event that was accompanied by gastric lesions (6.4 ± 0.16 mm, P = 0.01) and confirmed histopathologically. Moreover, the insult elevated gastric mucosal lipid peroxides (13 ± 0.5 nmol/g tissue, P = 0.001), tumor necrosis factor-α (3008.6 ± 78.18 pg/g tissue, P < 0.001), prostaglandin E2 (117.1 ± 4.31 pg/g tissue, P = 0.002), and caspase-3 activity (2.4 ± 0.14 OD/mg protein, P = 0.002). Conversely, CMS mitigated interleukin-10 (627.9 ± 12.82 pg/g tissue, P = 0.001). Furthermore, in animals exposed to CMS, octreotide restored plasma corticosterone (61% and 71% from CMS, P = 0.002) at both dose levels. These beneficial effects were associated with a remarkable suppression of gastric lesions (38% and 9% from CMS, P = 0.01) and reversal of derangements in gastric mucosa. The current investigation provides evidence that exposure to CMS induces gastric ulceration, which was alleviated by administration of octreotide possibly possessing antioxidant, anti-inflammatory, and anti-apoptotic actions.

Effect of chronic mild stress on hippocampal transcriptome in mice selected for high and low stress-induced analgesia and displaying different emotional behaviors

There is increasing evidence that mood disorders may derive from the impact of environmental pressure on genetically susceptible individuals. Stress-induced hippocampal plasticity has been implicated in depression. We studied hippocampal transcriptomes in strains of mice that display high (HA) and low (LA) swim stress-induced analgesia and that differ in emotional behaviors and responses to different classes of antidepressants. Chronic mild stress (CMS) affected expression of a number of genes common for both strains. CMS also produced strain specific changes in expression suggesting that hippocampal responses to stress depend on genotype. Considerably larger number of genes, biological processes, molecular functions, biochemical pathways, and gene networks were affected by CMS in LA than in HA mice. The results suggest that potential drug targets against detrimental effects of stress include glutamate transporters, and cholinergic, cholecystokinin (CCK), glucocorticoids, and thyroid hormones receptors. Furthermore, some biological processes evoked by stress and different between the strains, such as apoptosis, neurogenesis and chromatin modifications, may be responsible for the long-term, irreversible effects of stress and suggest a role for epigenetic regulation of mood related stress responses.

Possible involvement of stress hormones and hyperglycaemia in chronic mild stress-induced impairment of immune functions in diabetic mice

Stress, an important aspect of modern life, has long been associated with an altered homeostatic state. Little is known about the effect of the life stress on the outcome of diabetes mellitus, especially related to the higher risk of infections. Here, we evaluate the effects of chronic mild stress (CMS) exposure on the evolution of type I diabetes induced by streptozotocin administration in BALB/c mice. Exposure of diabetic mice to CMS resulted in a significant reduction of survival and a sustained increase in blood glucose values. Concerning the immune response, chronic stress had a differential effect in mice with diabetes with respect to controls, showing a marked decrease in both T- and B-cell proliferation. No correlation was found between splenic catecholamine or circulating corticosterone levels and the proliferative response. However, a significant negative correlation was found between glucose levels and concanavalin A- and lipopolysaccharide-stimulated proliferative responses of T and B cells. A positive correlation between blood glucose and splenic catecholamine concentrations was found in diabetic mice but not in controls subjected to CMS. Hence, the present report shows that diabetic mice show a worse performance in immune function after stress exposure, pointing to the importance of considering life stress as a risk factor for patients with diabetes.

Sustained stress-induced changes in mice as a model for chronic depression

Major depression is a chronic disabling disorder, often preceded by stress. Despite emerging clinical interest in mechanisms perpetuating episodes of depression and/or establishing increased vulnerability for relapse, little attention has been paid to address these aspects in experimental models. Here, we studied the long-term neuroadaptive effects of chronic mild stress (CMS) as well as the effectiveness of a course of an antidepressant treatment. CMS was applied for 6 weeks, and paroxetine was administered from the third week and continued for 2 weeks thereafter. In order to validate our CMS procedure, we first studied short-term (24 h after CMS) hippocampal cell proliferation and neurogenesis, along with anhedonic-like behaviour. Subsequently, we examined the long-term (one month after CMS) anhedonia, hippocampal neurogenesis, the regulation of c-Fos immunoreactivity and neurotransmitter levels in different areas as well as cortical spine density and hippocampal expression of synaptic proteins. CMS induced a decrease in short-term neurogenesis that was fully recovered in the long term. In addition, CMS-induced lasting anhedonia and region-specific changes in neuronal activity (c-Fos immunoreactivity) and neurotransmitter (glutamate and GABA) levels. Repeated paroxetine reverted these effects with the exception of decreased neuronal activity in the dentate gyrus (DG) and GABA levels in the ventral hippocampus. Moreover, CMS downregulated the GAD65 and VGLUT1 expressions. This study shows region-specific long-term neurobiological adaptations induced by CMS and residual hippocampal signs after paroxetine treatment. We propose the use of this model to study molecular mechanisms involved in chronic depression and vulnerability for relapse.

Effect of chronic mild stress and imipramine on the proteome of the rat dentate gyrus

The present study uses a proteomic approach to examine possible alterations of protein expression in the hippocampus of rats that are subjected to chronic mild stress (CMS). These rats serve as an animal model that was developed to mimic anhedonia, which is one of the core symptoms of depression. As antidepressant treatment is effective after a few weeks of administration, we also aimed to identify changes that were linked to chronic (once daily for 4 weeks) and 'pulse' (once a week) administration of imipramine. Fifteen differential proteins were identified with 2D electrophoresis followed by mass spectrometry. Although both methods of imipramine administration restored normal sucrose consumption in rats that were subjected to CMS, the molecular mechanisms of these two therapies were different. CMS-induced changes in the levels of dynactin 2, Ash 2, non-neuronal SNAP25 and alpha-enolase were reversed by chronic imipramine, but 'pulse' treatment was not that effective.

Opposite effects of alcohol in regulating stress-induced changes in body weight between the two mouse lines with enhanced or low opioid system activity

Considering the involvement of the opioid system in alcoholism, depression and metabolism - known risk factors in human obesity, we studied the effects of chronic mild stress (CMS) and alcohol intake on body weight in two mouse lines selected for high (HA-high analgesia) or low (LA-low analgesia) swim stress-induced analgesia. In comparison to LA mice, HA mice exhibit an upregulation of opioid receptor system function, different depression-like behavior and reduced energy expenditure in stress. LA animals showed enhanced basal and CMS-induced alcohol drinking versus HA. Now we report different effects of alcohol under no stress (control) and CMS conditions on food intake and body weight between the lines. CMS in animals with no access to alcohol increased body weight in both HA and LA mice, with no effect of CMS on food intake in either line and without differences between the lines. In LA mice alcohol reduced body weight under both conditions although significantly more under the control than CMS conditions. In contrast, in HA mice alcohol increased body weight more under the CMS than under control conditions. The results suggest that opioid system may modulate effects of alcohol on stress -induced changes in body weight.

Alcohol reverses depressive and pronociceptive effects of chronic stress in mice with enhanced activity of the opioid system.

The role of the opioid system in mediating effects of alcoholism and stress in depression is far from clear. We studied, therefore, the effects of chronic mild stress (CMS) and alcohol drinking on depression-like behavior and nociception in lines of mice selected for high (HA) or low (LA) swim stress-induced analgesia. Compared to the LA mice, the HA animals display up-regulation of opioid receptor system function and depression-like behavior in tail suspension test (TST). We report now that alcohol reverses depressive and pronociceptive effect of CMS in HA mice. In contrast, in LA mice CMS does not affect nociception or behavior in TST and the animals are not susceptible to alcohol under CMS. The results suggest that opioid system activity may determine the effects of alcohol on behavior under stress and, therefore, link predispositions to depression and to alcoholism.

Stress induced cognitive deficit is differentially modulated in BALB/c and C57Bl/6 mice: Correlation with Th1/Th2 balance after stress exposure

This work shows a comparative study on the effects of chronic mild stress upon learning and memory and immunity, in BALB/c and C57BL/6 mice. Stressed BALB/c, but not C57Bl/6 mice, showed a poor learning performance, morphological alterations in the hippocampus with an increase in oxidative stress. A correlation between poor memory performance and the increase of the Th2/Th1 balance was found. Our results suggest that vulnerability to cognitive deficit associated with stress exposition could be related to a differential regulation of Th1/Th2 cytokine balance, suggesting a better learning performance for individuals that produce Th1 type cytokine after stress exposition.

The effect of chronic mild stress on tumor-bearing rats’ behavior and its mechanism

Object: Much evidence has demonstrated that stress and tumor interact, but the mechanisms are poorly understood. The purpose of this study is to discuss the effect of unpredictable chronic mild stress (CMS) upon the behavior of Walker 256 tumor-bearing rats and its mechanism. Methods: Observe the effects of CMS on the sucrose consumption, activities, body weight and levels of serums TNF-α and IL-6 of both tumor-bearing rats and non-tumor-bearing rats, and on the levels of Bcl-2 and the phosphor-ERK1/2 in their hippocampus. Results: CMS can reduce the average sucrose consumption, behavioral scores, body weight gain, expression of Bcl-2 and p-ERK1/2 protein in hippocampus, and increase serums TNF-α and IL-6 of both tumor-bearing rats and non-tumor-bearing rats. The stressed tumor-bearing rats had less sucrose consumption, body weight gain and lower behavioral scores, but higher level of serum TNF-α than stressed non-tumor-bearing rats. A negative correlation was found between the levels of serum TNF-α and sucrose consumption, while a positive correlation between the expression of Bcl-2 protein in hippocampus proper and sucrose consumption. Conclusion: CMS can reduce the protein levels of Bcl-2 and p-ERK1/2 in the rats’ hippocampus, which contributes to the changes in the rats’ behavior caused by CMS. Tumor-bearing rats are prone to behave depressively after the exposure to CMS. Our findings have suggested that the tumor, by increasing the inflammatory reaction, can be taken as a stressor, affecting the hippocampus and consequently causing depression by decreasing the expression of Bcl-2 and p-ERK1/2 in hippocampus.

Effects of Chronic Mild Stress on the Development of Atherosclerosis and Expression of Toll‐Like Receptor 4 Signaling Pathway in Adolescent Apolipoprotein E Knockout Mice

Here, we investigated the effect of chronic mild stress (CMS) on the development of atherosclerosis as well as the expression of Toll-like receptors (TLRs) signaling pathway in adolescent apolipoprotein E knockout (apoE-/-) mice. Mice were subjected to daily CMS for 0, 4, and 12 weeks, respectively. To identify the expression of Toll-like receptor 4 signaling pathway in adolescent apolipoprotein E knockout mice subjected to CMS, we compared gene expression in aortas of stressed and unstressed mice using TLRs signaling pathway real-time PCR microarrays consisting of 87 genes. We found that atherosclerosis lesions both in aortic tress and sinuses of CMS mice were significantly increased linearly in response to duration of CMS exposure. Among 87 genes analyzed, 15 genes were upregulated in stressed mice, especially TLR4, myeloid differentiation factor 88 (MyD88), and IL-1β, and 28 genes were downregulated compared with nonstressed mice. CMS mice demonstrated markedly increased aortic atherosclerosis that were associated with significant increases in levels of expression of TLR4, MyD88, nuclear factor κB (NF-κB), MCP-1, IL-1β, TNF-α, and sICAM-1. Taken together, our results suggest an important role for TLR4 signaling pathway in atherosclerosis in a CMS mouse model.

Differences in ethanol drinking between mice selected for high and low swim stress-induced analgesia

Alcoholism is a complex disorder, still not fully understood, in which environmental and inherited risk factors play essential roles. Of particular importance may be chronic exposure to stress thought to increase preference for ethanol in genetically susceptible individuals. Animal and human data suggest that the opioid system may be involved in the development of alcohol dependence. We studied the effects of chronic mild stress (CMS) on the voluntary intake of 8% ethanol in the mouse lines displaying high (HA) or low (LA) swim stress-induced analgesia. These lines differ in the activity of the endogenous opioid system. Normally, 8% ethanol is aversive to rodents. We found that LA mice with the low opioid system activity exposed to CMS manifested greater ethanol intake than under no stress conditions. No such effect of CMS on ethanol consumption was observed in HA mice that display the enhanced opioid system activity. We conclude that CMS imposed on individuals with a genetically determined low opioid activity may favor the development of ethanol abuse.

Chronic stress increases the production of volatile sulphur compounds in rats

In the great majority of cases, halitosis is originated in the mouth itself and psychological symptoms have been pointed out as one of halitosis‐inducing factor. The aim of this study was to evaluate, in laboratory animals, the effect of chronic mild stress (CMS) on the production of volatile sulfur compounds (VSC), the main component of bad breath. VSC measurements were made using a portable industrial monitor (Halimeter) once a week, during seven weeks, in control and stressed adult males Wistar rats. CMS group was submitted to the stress protocol on weeks 3, 4 and 5 (Student t test; p&lt;0.05). Rats submitted to CMS presented an increase in the production of oral VSC, in comparison to the control group, on week 3 (22±1 vs. 18±1 ppb), week 4 (25±1 vs. 16±1 ppb), week 5 (24±1 vs. 17±1 ppb) and week 6 (26±2 vs.19±1 ppb), with no difference on week 7 (16±1 vs. 16 ± 0.6 ppb). Our data confirm the influence of stress on the production of oral VSC and demonstrate that this effect is still observed one week after the cessation of stress stimulus. Financial Support: FAPESP, CNPq

P.2.b.007 Effects of chronic mild stress on depression-like behavior and antioxidant status in mice.

P.2.b.007 Effects of chronic mild stress on depression-like behavior and antioxidant status in mice.

Behavioral and physiological effects of chronic mild stress in female rats

Anhedonia, a core symptom of clinical depression, refers to the loss of interest in normally rewarding stimuli; the chronic mild stress paradigm, an animal model of depression, was designed with this as an underlying feature. The procedure consists of the administration of a variety of ecologically relevant stressors over long durations. Its effects have been thoroughly investigated in male but not female rats. This study examines the appropriateness of stressors designed to evaluate the development and progression of depression in two strains of female rats, the effectiveness of two measures of anhedonia, and the relationship between stress reactivity and the estrous cycle. Changes in hedonic status were indexed for three weeks following a three week baseline period using two standard behavioral measures of anhedonia: sucrose intake and preference and thresholds for brain stimulation reward. Decreases in 24 h sucrose intake were observed in both strains during the first week of stress manipulations, and continued to decline thereafter for the remainder of the stress phase; in contrast, sucrose preference was unaffected by the stressors, indicating an overall reduction in fluid intake. No changes in the thresholds for brain stimulation reward were observed. The cyclical pattern of estrous was altered in both strains with a significant reduction in the number of regular cycles as a consequence of both the stressors and brain stimulation reward. Furthermore, cyclicity was not reinstated in many animals even six weeks after stress manipulations and behavioral tests had ceased. While the physiological measures suggest that the mild stressors are disruptive to female rats, the results of the behavioral tests are not consistent with the notion that the stressors induce an anhedonic state.

Protein kinase C-dependent NF-kappaB activation is altered in T cells by chronic stress.

Chronic stress has been associated with impaired immune function. In this work we studied the effect of chronic mild stress (CMS) exposure on the early intracellular pathways involved in T cells after stimulation with mitogen. We found that mitogen stimulation of T lymphocytes from CMS-exposed mice resulted in a reduction of the intracellular [Ca2+] rise, an impairment of growth-promoting protein kinase C (PKC) activation, a lower NF-kappaB activation and an increase in the inhibitory cAMP-protein kinase A (PKA) pathway activity with respect to those found in control lymphocytes. However, T cell activation with the direct PKC activator phorbol 12-myristate 13-acetate plus calcium ionophore led to a similar proliferative response in both CMS and control lymphocytes, indicating that signals downstream of PKC would not be affected by stress. In summary, our results show that chronic stress induced an alteration in T cell early transduction signals that result in an impairment of the proliferative response.

Effects of chronic mild stress on sexual behavior, locomotor activity and consumption of sucrose and saccharine solutions

Many symptoms of human depressive disorders are also observed in animals after exposure to unpredictable stressors. The chronic mild stress (CMS) paradigm was developed in order to better model the human situation by using chronic mild stressors over a longer period. It is claimed that the model induces anhedonia in the animals, a core symptom of depression in humans. Despite the fact that the CMS model has a high degree of face validity, there are a number of laboratories in which the establishment of the model is less reliably observed. We have examined behavior (sexual activity and open field activity) together with hedonic measures (sucrose and saccharine intake) after exposure to CMS. CMS decreased male sexual activity (e.g. reduced capability to ejaculate) and increased activity in an open field test. The hedonic measures showed diverging results after CMS in our laboratory. Sucrose consumption was reduced, while saccharine consumption did not show a comparable change. It is concluded that CMS induces comparable alterations to some depression-like symptoms in humans. Saccharine consumption is not a reliable indicator of the hedonic responsiveness to CMS.