Timing matters: the interval between acute stressors within chronic mild stress modifies behavioral and physiologic stress responses in male rats

Testicular histopathology in rats co-exposed to heat and psychological stressors

Objectives

The present study aimed to investigate the effect of co-exposure to heat and psychological stressors on testicular tissue as one of the major male reproductive organs in rats.

Methods

Forty adult male Wistar rats were divided into four groups of 10 animals each. The first group was exposed to heat stress (Temperature Humidity Index: 57.75 ± 3), the second group was exposed to three psychological stressors including strobe light ultrasonic sound, and tilting cage, and the third group was co-exposed to both heat and psychological stress daily. The order of exposure to various psychological stressors was randomized. Following the last day of the 40 -day exposure, the rats were euthanized and their testicular tissues were fixed in Bouin's solution. Moreover, a tissue processor, a microtome as well as hematoxylin, and eosin staining were used for tissue preparation.

Results

The co-exposure to psychological and heat stress can cause negative testis histopathological changes including spermatid retention, degeneration of round spermatids and spermatocytes, degeneration and depletion of elongated Spermatid, Sertoli cell status, tubular degeneration/atrophy, Leydig cell atrophy, tubular dilatation, re-tubular dilation, and sclerosis status in a number of rats. Moreover, the histopathological changes were higher in the group exposed to heat stress compared with those exposed to psychological stress.

Conclusions

Although exposure to either stressor alone can affect testicular tissue as part of the reproductive system, co-exposure to both stressors may result in an increased risk of adverse effects on testicular tissue.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Persistent muscle hyperalgesia after adolescent stress is exacerbated by a mild-nociceptive input in adulthood and is associated with microglia activation

Non-specific low back pain (LBP) is a major global disease burden and childhood adversity predisposes to its development. The mechanisms are largely unknown. Here, we investigated if adversity in young rats augments mechanical hyperalgesia and how spinal cord microglia contribute to this. Adolescent rats underwent restraint stress, control animals were handled. In adulthood, all rats received two intramuscular injections of NGF/saline or both into the lumbar multifidus muscle. Stress induced in rats at adolescence lowered low back pressure pain threshold (PPT; p = 0.0001) and paw withdrawal threshold (PWT; p = 0.0007). The lowered muscle PPT persisted throughout adulthood (p = 0.012). A subsequent NGF in adulthood lowered only PPT (d = 0.87). Immunohistochemistry revealed changes in microglia morphology: stress followed by NGF induced a significant increase in ameboid state (p < 0.05). Repeated NGF injections without stress showed significantly increased cell size in surveilling and bushy states (p < 0.05). Thus, stress in adolescence induced persistent muscle hyperalgesia that can be enhanced by a mild-nociceptive input. The accompanying morphological changes in microglia differ between priming by adolescent stress and by nociceptive inputs. This novel rodent model shows that adolescent stress is a risk factor for the development of LBP in adulthood and that morphological changes in microglia are signs of spinal mechanisms involved.

Effect of chronic restraint stress and western-diet feeding on colonic regulatory gene expression in mice

BACKGROUND

Diet-induced obesity (DIO) and psychological stress are significant independent regulators of gastrointestinal physiology; however, our understanding of how these two disorders influence the host-microbe interface is still poorly characterized. The aim of this study was to assess the combined influences of diet-induced obesity and psychological stress on microbiome composition and colonic gene expression.

METHODS

C57BL/6J mice (n = 48) were subject to a combination of 22 weeks of Western diet (WD) feeding and a chronic restraint stressor (CRS) for the last 4 weeks of feeding. At the end of the combined intervention, microbiome composition was determined from cecal contents, and colonic tissue gene expression was assessed by multiplex analysis using NanoString nCounter System and real-time qPCR.

RESULTS

WD feeding induced a DIO phenotype with increased body weight, worsened metabolic markers, and alterations to microbiome composition. CRS reduced body weight in both dietary groups while having differential effects on glucose metabolism. CRS improved the Firmicutes/Bacteroidetes ratio in WD-fed animals while expanding the Proteobacteria phyla. Significantly lower expression of colonic Tlr4 (p = 0.008), Ocln (p = 0.004), and Cldn3 (p = 0.004) were noted in WD-fed animals compared to controls with no synergistic effects observed when combined with CRS. No changes to colonic expression of downstream inflammatory mediators were observed. Interestingly, higher levels of expression of Cldn2 (p = 0.04) and bile acid receptor Nr1h4 (p = 0.02) were seen in mice exposed to CRS.

CONCLUSION

Differential but not synergistic effects of WD and CRS were noted at the host-microbe interface suggesting multifactorial responses that require further investigation.

Stress-induced body weight loss and improvements in cardiometabolic risk factors do not translate to improved myocardial ischemic tolerance in western diet-fed mice

Although both diet-induced obesity and psychological stress are recognized as significant independent contributors to cardiometabolic and behavioral disorders, our understanding of how these two disorders interact and influence cardiometabolic risk and myocardial ischemic tolerance is limited. The aim of this study was to assess the combined effects of an obesogenic diet and psychological stress on cardiometabolic risk factors (body weight, dyslipidemia, insulin sensitivity) and postischemic cardiovascular outcomes. C57Bl/6J mice (n = 48) were subject to a combination of 22 weeks of western diet (WD) feeding and chronic restraint stress (CRS) for the last 4 weeks. Metabolic and behavioral changes were assessed using glucose tolerance tests and open field tests (OFTs), respectively. After 22 weeks, cardiac function and ischemic tolerance were assessed in Langendorff perfused hearts. WD feeding increased body weight and worsened blood lipids and insulin sensitivity. WD-fed mice also exhibited reduced exploratory behavior within the OFT. CRS reduced body weight and increased locomotion in both dietary groups and had differential effects on fasting glucose metabolism in the two dietary groups while not impacting non-fasting insulin. Although the WD only marginally reduced reperfusion left ventricular developed pressure recovery, CRS worsened reperfusion diastolic dysfunction in both dietary groups. Interestingly, despite WD+CRS animals exhibiting improved cardiometabolic parameters compared to the WD group, these changes did not translate to marked improvements to postischemic cardiac outcomes. In conclusion, in this study, combined WD feeding and CRS did not act synergistically to worsen cardiometabolic risk factors but instead improved them. Despite these cardiometabolic improvements, WD+CRS increased reperfusion end diastolic pressure which may be indicative of worsened ischemia/reperfusion injury.

Effect of Co-exposure to Heat and Psychological Stressors on Sperm DNA and Semen Parameters

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Co-exposure to heat and psychological stressors on semen quality have been studied.

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Combined exposure group had significantly lower semen quality compared with those of others.

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Heat exposure group had a higher percentage of sperm DNA damage compared to others.

The present study aims to investigate the effects of co-exposure to heat and psychological stress on sperm DNA and semen parameters among male rats. The study was conducted on 40 healthy adult male Wistar rats. The rats were randomly categorized into four groups of same size consisting of a control group, a heat stress, psychological and co-exposure groups. The heat stress group was exposed to a temperature of 36 °C at 20% relative humidity. The psychological stress exposure group was subjected to three stressors including exposure to strobe light, noise and tilting cage. According the results,the co-exposure group had lower mean sperm parameters including sperm count (17.22 ± 4.22 10⁶/ml), motility (42.63 ± 12.95 %), viability (48.50 ± 23.25 %), normal morphology (56 ± 7.5%), progressive motility (11.61 ± 7.81%), non-progressive motility (31.18 ± 7.77%), curvilinear velocity (24.11 ± 3.81 μm/s) and straight-line velocity (3.2 ± 1.4 μm/s) when compared with those of the other groups (P = 0.001). Mean sperm immobility (57.36 ± 12.95%) and non-progressive motility (37.93 ± 11.15%) in the co-exposure group was higher compared to the other groups (P = 0.001 and P = 0.333, respectively). Assessment of damage to sperm DNA revealed that the heat exposure group had a higher percentage of sperm DNA damage (9.44 ± 6.80 %) compared to others (P = 0.185). In case of all of exposure scenario, the chance that the semen quality decreased compared to the control group has been increased. In general the combined stress had a greater significant effect on sperm parameters compared to other exposure groups, except for DNA damage.

New Insights into Depressive Disorder with Respect to Low-Grade Inflammation and Fish Oil Intake

Unipolar depression has been recognized as one of the major diseases by the World Health Organization in the 21st century. The etiology of depression is complicated and includes genetic factors, stress, aging, and special physical status (pregnancy, metabolic syndrome, and trauma). Numerous animal and human studies have demonstrated that n-3 polyunsaturated fatty acids (n-3 PUFAs) are highly correlated to cognition and depression. These nutritional antidepressants, including EPA and DHA, have a range of neurobiological activities contributing to their potential antidepressant effects. Our preclinical and clinical studies have indicated that n-3 PUFA supplementation in addition to standard antidepressant medications may provide synergistic neuroprotective and antioxidant/inflammatory effects. To translate our preliminary findings into clinical application, this paper reviews the existing evidence on the antidepressant effects of n-3 PUFAs and the potential underlying mechanisms, which include modulation of chronic lowgrade inflammation and the corresponding changes in peripheral blood immune biomarkers.

Antidepressant-like effect of Ganoderma lucidum spore polysaccharide-peptide mediated by upregulation of prefrontal cortex brain-derived neurotrophic factor

A 28-kDa polysaccharide-peptide (PGL) with antidepressant-like activities was isolated from spores of the mushroom Ganoderma lucidum. It was unadsorbed on DEAE-cellulose. Its internal amino acid sequences manifested pronounced similarity with proteins from the mushrooms Lentinula edodes and Agaricus bisporus. The monosaccharides present in 28-kDa PGL comprised predominantly of glucose (over 90%) and much fewer galactose, mannose residues, and other residues. PGL manifested antidepressant-like activities as follows. It enhanced viability and DNA content in corticosterone-injured PC12 cells(a cell line derived from a pheochromocytoma of the rat adrenal medulla with an embryonic origin from the neural crest containing a mixture of neuroblastic cells and eosinophilic cells) and reduced LDH release. A single acute PGL treatment shortened the duration of immobility of mice in both tail suspension and forced swimming tests. PGL treatment enhanced sucrose preference and shortened the duration of immobility in mice exposed to chronic unpredictable mild stress (CUMS). Chronic PGL treatment reversed the decline in mouse brain serotonin and norepinephrine levels but did not affect dopamine levels. PGL decreased serum corticosterone levels and increased BDNF mRNA and protein levels and increased synapsin I and PSD95 levels in the prefrontal cortex. This effect was completely blocked by pretreatment with the BDNF antagonist K252a, indicating that PGL increased synaptic proteins in a BDNF-dependent manner.Key points• An antidepressive polysaccharide-peptide PGL was isolated from G. lucidum spores.• PGL protected PC12 nerve cells from the toxicity of corticosterone.• PGL upregulated BDNF expression and influenced key factors in the prefrontal cortex.

Anxiety, depression, and asthma: New perspectives and approaches for psychoneuroimmunology research

The field of psychoneuroimmunology has advanced the understanding of the relationship between immunology and mental health. More work can be done to advance the field by investigating the connection between internalizing disorders and persistent airway inflammation from asthma and air pollution exposure. Asthma is a prominent airway condition that affects about 10% of developing youth and 7.7% of adults in the United States. People who develop with asthma are at three times increased risk to develop internalizing disorders, namely anxiety and depression, compared to people who do not have asthma while developing. Interestingly, sex differences also exist in asthma prevalence and internalizing disorder development that differ based on age. Exposure to air pollution also is associated with increased asthma and internalizing disorder diagnoses. New perspectives of how chronic inflammation affects the brain could provide more understanding into internalizing disorder development. This review on how asthma and air pollution cause chronic airway inflammation details recent preclinical and clinical research that begins to highlight potential mechanisms that drive comorbidity with internalizing disorder symptoms. These findings provide a foundation for future studies to identify therapies that can simultaneously treat asthma and internalizing disorders, thus potentially decreasing mental health diagnoses in asthma patients.

Effects of Achillea tenuifolia Lam. hydro-alcoholic extract on anxiety-like behavior and reproductive parameters in rat model of chronic restraint stress

INTRODUCTION

Achillea tenuifolia Lam (AT) has several biological activities and medicinal properties. In this study, we elucidated the impact of the AT on anxiety-related behaviors, reproductive parameters, antioxidant capacity in male rats subjected to chronic restraint stress (CRS).

METHODS

35 Wistar rats were divided into five groups: control, CRS-control (received normal saline) and three CRS-treated groups received AT extract (100, 150, and 200 mg/kg body weight) for 21 consequences days. To induce CRS rats, the rats were immobilized for 21 days and received the extract orally. On the last day of treatment, anxiety-related behaviors were assessed through the sucrose preference test (SPT) as well as elevated plus maze (EPM) tests. Corticosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH), testosterone levels were evaluated to determine reproductive capacity. Sperm parameters including the total count, motility, and viability were also analyzed. Weight of body, testis and seminal vesicles was measured as well.

RESULTS

The findings revealed that 100, 150, and 200 mg/kg of AT extract had anxiolytic effects in CRS rats, as confirmed by the EPM test and SPT. In addition, AT extract could improve fertile capacity and sperm quality to varying degrees. The level of corticosterone had decreased, whereas the level of LH, FSH and testosterone had increased in CRS-treated rats. Moreover, the reduced level of MDA coincided with an increased rate of antioxidant capacity. Our findings suggest that AT extract could alleviate stress-induced dysfunctions.

CONCLUSION

Overall, these observations would infer that AT extract could improve fertility capacity and behavioral impairment in the stress conditions.

GRAPHICAL ABSTRACT

Assumption pathway describing the probability underlying mechanism of CRS-induced anxiety and reproductive toxicity and protective effect of AT.

Priorities in stress research: a view from the U.S. National Institute of Mental Health

The mission of the National Institute of Mental Health is to transform the understanding and treatment of mental illnesses through basic and clinical research, paving the way for prevention, recovery, and cure. In consultation with a broad range of experts, the NIMH has identified a set of priorities for stress biology research aimed squarely at creating the basic and clinical knowledge bases for reducing and alleviating mental health burden across the lifespan. Here, we discuss these priority areas in stress biology research, which include: understanding the heterogeneity of stressors and outcomes; refining and expanding the experimental systems used to study stress and its effects; embracing and exploiting the complexity of the stress response; and prioritizing translational studies that seek to test mechanistic hypotheses in human beings. We emphasize the challenge of establishing mechanistic links across levels of analysis to explain how and when specific and diverse stressors lead to enduring changes in neural systems and produce lasting functional deficits in mental health relevant behaviors. An improved understanding of mechanisms underlying stress responses and the functional consequences of stress can and will speed translation from basic research to predictive markers of risk and to improved, personalized interventions for mental illness.

Peri-adolescent asthma: Acute impacts on innate immune response, corticosterone, and microglia in mice

Asthma is highly comorbid with anxiety in youth. We investigated the hypothalamic-pituitary-adrenal (HPA) axis and microglia as mechanisms underlying asthma and anxiety comorbidity. We induced asthma symptoms in developing BALB/cJ mice with house dust mite (HDM) for airway inflammation and methacholine (MCH) for bronchoconstriction. On the last day of exposure, we analyzed samples at six timepoints. Lung IL-5 and IL-1β expression peaked 4 h after final HDM exposure. Circulating corticosterone was blunted in a sex- and treatment-specific temporal pattern. Hippocampal IL-1β expression and microglial area were marginally increased 24 h after MCH exposure. These results provide a foundation for further work investigating asthma-anxiety mechanisms.

Individual Variation in Glucocorticoid Plasticity: Considerations and Future Directions

The hypothalamic–pituitary–adrenal (HPA) axis regulates the secretion of glucocorticoids, hormones with diverse roles ranging from regulating daily metabolic demand to coping with sudden perturbations. As a result, glucocorticoids are thought to help vertebrates track their changing environments and coordinate plasticity in diverse phenotypes. While this endocrine system is highly plastic—where one individual can produce multiple phenotypes across varying environmental conditions—little is understood about the degree to which individuals, populations, or species differ in circulating glucocorticoid plasticity. Empirical research quantifying individual variation in glucocorticoid plasticity has increased in recent years, though the multiple complex roles of the HPA-axis make it challenging to generalize the extent to which individual variation in plasticity exists. I provide an overview of current findings on variation in glucocorticoids plasticity, and outline multiple types of glucocorticoid plasticity researchers should consider in future work to advance our understanding of the causes and consequences of individual variation in glucocorticoid plasticity.

Expression alteration of microRNAs in Nucleus Accumbens is associated with chronic stress and antidepressant treatment in rats

BACKGROUND

Nucleus Accumbens (NAc) is a vital brain region for the process of reward and stress, whereas microRNA plays a crucial role in depression pathology. However, the abnormality of NAc miRNA expression during the stress-induced depression and antidepressant treatment, as well as its biological significance, are still unknown.

METHODS

We performed the small RNA-sequencing in NAc of rats from three groups: control, chronic unpredictable mild stress (CUMS), and CUMS with an antidepressant, Escitalopram. We applied an integrative pipeline for analyzing the miRNA expression alternation in different model groups, including differential expression analysis, co-expression analysis, as well as a subsequent pathway/network analysis to discover both miRNA alteration pattern and its biological significance.

RESULT

A total of 423 miRNAs were included in analysis.18/8 differential expressing (DE) miRNA (adjusted p < 0.05, |log2FC| > 1) were observed in controls Vs. depression/depression Vs. treatment, 2 of which are overlapping. 78% (14/18) of these miRNAs showed opposite trends of alteration in stress and treatment. Two micro RNA, miR-10b-5p and miR-214-3p, appeared to be hubs in the regulation networks and also among the top findings in both differential analyses. Using co-expression analysis, we found a functional module that strongly correlated with stress (R = 0.96, P = 0.003), and another functional module with a moderate correlation with anhedonia (R = 0.89, P = 0.02). We also found that predicted targets of these miRNAs were significantly enriched in the Ras signaling pathway, which is associated with both depression, anhedonia, and antidepressant treatment.

CONCLUSION

Escitalopram treatment can significantly reverse NAc miRNA abnormality induced by chronic stress. However, the novel miRNA alteration that is absent in stress pathology also emerges, which means that antidepressant treatment is unlikely to bring miRNA expression back to the same level as the controls. Also, the Ras-signaling pathway may be involved in explaining the depression disease etiology, the clinical symptom, and treatment response of stress-induced depression.

Fish Oil, but Not Olive Oil, Ameliorates Depressive-Like Behavior and Gut Microbiota Dysbiosis in Rats under Chronic Mild Stress

Background: This study investigated the effects of fish oil and olive oil in improving dysbiosis and depressive-like symptoms. Methods and results: Male rats were fed normal, fish oil-rich or olive oil-rich diets for 14 weeks. Chronic mild stress (CMS) was administered from week 2. The sucrose preference test (SPT) and forced swimming test (FST) were used to determine depressive-like behavior. The SPT results revealed that the CMS, CMS with imipramine (CMS+P) treatment, and CMS with olive oil diet (CMS+O) groups exhibited significantly reduced sucrose intake from week 8, whereas the fish oil diet (CMS+F) group exhibited significantly reduced sucrose intake from week 10. The FST results showed that the immobile time of the CMS+F group was significantly less than that of the CMS-only group. Next generation sequencing (NGS) results showed CMS significantly reduced the abundance of Lactobacillus and increased that of Marvinbryantia and Ruminiclostridium_6. However, the CMS+F group showed an increase in the abundance of Eisenbergiella, Ruminococcaceae_UCG_009, and Holdemania, whereas the CMS+O group showed an increase in the abundance of Akkermansia. Conclusions: CMS stimuli altered the gut microbiome in depressed rats. Fish oil and olive oil exerted part of a prebiotic-like effect to ameliorate dysbiosis induced by CMS. However, only fish oil ameliorated depressive-like symptoms.

Variability in PolyIC induced immune response: Implications for preclinical maternal immune activation models

Maternal infection during pregnancy may increase the risk of offspring neurodevelopmental disorders. The preclinical Polyinosinic-polycytidylic acid (PolyIC) model has become one of the most widely used approaches in maternal immune activation (MIA) research. However, variability in molecular weight may impact the immune activating potential of PolyIC. Nulliparous rats injected with high molecular weight PolyIC exhibit pronounced cytokine response and sickness behavior that was not observed in rats injected low molecular weight PolyIC. Although an essential next step is to extend these studies to pregnant animals, the preliminary results suggest that PolyIC molecular weight is an important experimental design consideration.