Experimental models of stress

The cycle of stress: A systematic review of the impact of chronic psychological stress models on the rodent estrous cycle

Stress is known to impair reproduction through interactions between the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. However, while it is well accepted that stress can alter estrous cycle regularity, a key indicator of female's HPG axis function, effects of different types of psychological stress have been inconsistent. This systematic review evaluated the impact of rodent models of psychological stress on estrous cyclicity, while reporting biological parameters pertaining to HPA or HPG axis function assessed within these studies. We performed a systematic database search and included articles that implemented a psychological stress model in rodents and reported estrous cyclicity for at least two cycles after initiation of stress. Of the 32 studies included, 62.5% reported post-stress alterations to estrous cyclicity, with Chronic Mild Stress (CMS) models showing the most conclusive effects. Twenty-five studies measured HPG or HPA axis markers, with cycle disruptions being commonly observed in parallel with altered estradiol and increased corticosterone levels. Our review highlights gaps in reporting estrous cyclicity assessments and makes recommendations to improve comparability between studies.

Prolonged stress response induced by chronic stress and corticosterone exposure causes adult neurogenesis inhibition and astrocyte loss in mouse hippocampus

Chronic stress is a pervasive and complex issue that contributes significantly to various mental and physical health disorders. Using the previously established chronic unpredictable stress (CUS) model, which simulates human stress situations, it has been shown that chronic stress induces major depressive disorder (MDD) and memory deficiency. However, this established model is associated with several drawbacks, such as limited research reproducibility and the inability to sustain stress response. To resolve these issues, we developed a new CUS model (CUS+C) that included exogenous corticosterone exposure to induce continuous stress response. Thereafter, we evaluated the effect of this new model on brain health. Thus, we observed that the use of the CUS+C model decreased body and brain weight gain and induced an uncontrolled coat state as well as depressive-like behavior in adult mice. It also impaired learning memory function and cognitive abilities, reduced adult hippocampal neurogenesis as well as the number of hippocampal astrocytes, and downregulated glial fibrillary acidic protein expression in the brains of adult mice. These findings can promote the utilization and validity of the animal stress model and provide new information for the treatment of chronic stress-induced depressive and memory disorders.

Deciphering the Metabolome under Stress: Insights from Rodent Models

Despite intensive research efforts to understand the molecular underpinnings of psychological stress and stress responses, the underlying molecular mechanisms remain largely elusive. Towards this direction, a plethora of stress rodent models have been established to investigate the effects of exposure to different stressors. To decipher affected molecular pathways in a holistic manner in these models, metabolomics approaches addressing altered, small molecule signatures upon stress exposure in a high-throughput, quantitative manner provide insightful information on stress-induced systemic changes in the brain. In this review, we discuss stress models in mice and rats, followed by mass spectrometry (MS) and nuclear magnetic resonance (NMR) metabolomics studies. We particularly focus on acute, chronic and early life stress paradigms, highlight how stress is assessed at the behavioral and molecular levels and focus on metabolomic outcomes in the brain and peripheral material such as plasma and serum. We then comment on common metabolomics patterns across different stress models and underline the need for unbiased -omics methodologies and follow-up studies of metabolomics outcomes to disentangle the complex pathobiology of stress and pertinent psychopathologies.

The Counter Effect of Exercise on Cisplatin-Induced Cognitive and Proliferation Impairments

Background Cisplatin, a widely used chemotherapeutic agent, offers therapeutic benefits for cancer treatment but often leads to adverse effects on neurogenesis and oxidative stress, causing cognitive impairment. Concurrent physical activity has been proposed as a potential strategy to counteract these side effects. This study aimed to investigate the impact of physical exercise on cisplatin-induced cognitive impairment in a mouse model. Methods Adult male mice (n=45) were divided into three groups: control, cisplatin-treated (2.3 mg/kg), and exercise/cisplatin. Cisplatin was administered intraperitoneally over one month, while the exercise/cisplatin group underwent moderate-intensity exercise alongside cisplatin treatment. Spatial memory was evaluated using the novel object recognition (NOR) task, and hippocampal proliferation and oxidative stress were examined using Ki-67 and glutathione peroxidase (GPx) immunohistochemistry (IHC) staining, respectively. Statistical analyses were performed using the GraphPad Prism 4.0 software (GraphPad Software, San Diego, CA). Results The cisplatin-treated mice exhibited significantly lower preference index (PI) scores in the NOR task compared to the control (p<0.001) and exercise/cisplatin (p<0.001) groups. IHC staining revealed impaired hippocampal proliferation and increased oxidative stress in the cisplatin-treated group relative to the control and exercise/cisplatin groups. The introduction of a moderate-intensity exercise protocol appeared to mitigate the decline in hippocampal proliferation and oxidative damage induced by cisplatin. Additionally, cisplatin-treated mice experienced weight loss, while exercise attenuated this effect. Conclusion Cisplatin treatment resulted in decreased memory, hippocampal proliferation, and weight loss in mice. Concurrent moderate-intensity exercise seemed to alleviate these effects, suggesting a potential role for physical activity in ameliorating cisplatin-induced cognitive decline. This study underscores the importance of incorporating exercise as a complementary strategy to enhance cognitive outcomes in cancer patients undergoing cisplatin treatment.

Prefrontal allopregnanolone mediates the adverse effects of acute stress in a mouse model of tic pathophysiology

Ample evidence suggests that acute stress can worsen symptom severity in Tourette syndrome (TS); however, the neurobiological underpinnings of this phenomenon remain poorly understood. We previously showed that acute stress exacerbates tic-like and other TS-associated responses via the neurosteroid allopregnanolone (AP) in an animal model of repetitive behavioral pathology. To verify the relevance of this mechanism to tic pathophysiology, here we tested the effects of AP in a mouse model recapitulating the partial depletion of dorsolateral cholinergic interneurons (CINs) seen in post-mortem studies of TS. Mice underwent targeted depletion of striatal CINs during adolescence and were tested in young adulthood. Compared with controls, partially CIN-depleted male mice exhibited several TS-relevant abnormalities, including deficient prepulse inhibition (PPI) and increased grooming stereotypies after a 30-min session of spatial confinement - a mild acute stressor that increases AP levels in the prefrontal cortex (PFC). These effects were not seen in females. Systemic and intra-PFC AP administration dose-dependently worsened grooming stereotypies and PPI deficits in partially CIN-depleted males. Conversely, both AP synthesis inhibition and pharmacological antagonism reduced the effects of stress. These results further suggest that AP in the PFC mediates the adverse effects of stress on the severity of tics and other TS-related manifestations. Future studies will be necessary to confirm these mechanisms in patients and define the circuitry responsible for the effects of AP on tics.

Effect of sound-induced repeated stress on the development of pain and inflammation in the temporomandibular joint of female and male rats

Temporomandibular disorder (TMD) is a common painful condition of the temporomandibular joint (TMJ) and associated structures. Stress is a significant risk factor for developing this painful condition that predominantly affects women. This study aimed to test the hypothesis that stress increases the risk of developing TMJ pain by facilitating inflammatory mechanisms in female and male rats. To test this hypothesis, we evaluated TMJ carrageenan-induced expression of pro-inflammatory cytokines and migration of inflammatory cells and TMJ formalin-induced nociception in female and male rats submitted to a repeated stress protocol induced by sound. We found that sound-induced repeated stress facilitates TMJ inflammation and contributes to TMJ nociception development equally in females and males. We conclude that stress is a risk factor for developing painful TMJ conditions in males and females, at least in part, by favoring the inflammatory process similarly in both sexes.

Effects of ultrasound-induced stress on gut microbiota of mice

Background and Aim

Prolonged stress causes deleterious effects on both the organism and its microbiota. In this study, we examined the effects of exposure to variable frequency ultrasound (US) on the gut microbiota-liver-brain axis of mice.

Materials and Methods

This study was conducted on 20 mature clinically healthy sexually naive C57BL/6J male mice (42-45 days old). Group 1 (Normal) consisted of healthy intact mice (n = 10). Group 2 (Stress) consisted of mice subjected to US-induced stress (n = 10) for 20 days with alternating frequencies (20-45 kHz). Stool samples were collected on days 0, 10, and 20, and the corresponding DNA was later subjected to 16SrRNA sequencing. After mice were sacrificed on day 21, the leukocyte count, blood serum biochemical parameters, and liver and brain antioxidant status were measured. Behavioral testing was performed on days 17, 18, and 19.

Results

Ultrasound lead to higher stress and anxiety levels; increase in creatinine by 8.29% and gamma-glutamyltransferase activity by 5 times, a decrease in alkaline phosphatase activity by 38.23%, increase of de Ritis coefficient by 21.34%; increased liver and brain superoxide dismutase level by 20.8% and 21.5%, respectively; the stress-related changes in the gut microbiota composition - Bacteroidaceae and Firmicutes.

Conclusion

Subjecting mice to 20 days of US-induced stress leads to systemic disorders due to oxidative stress and a decrease in the diversity of the gut microbiota.

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

Ethical Implications in Making Use of Human Cerebral Organoids for Investigating Stress-Related Mechanisms and Disorders

The generation of three-dimensional cerebral organoids from human-induced pluripotent stem cells (hPSC) has facilitated the investigation of mechanisms underlying several neuropsychiatric disorders, including stress-related disorders, namely major depressive disorder and post-traumatic stress disorder. Generating hPSC-derived neurons, cerebral organoids, and even assembloids (or multi-organoid complexes) can facilitate research into biomarkers for stress susceptibility or resilience and may even bring about advances in personalized medicine and biomarker research for stress-related psychiatric disorders. Nevertheless, cerebral organoid research does not come without its own set of ethical considerations. With increased complexity and resemblance to in vivo conditions, discussions of increased moral status for these models are ongoing, including questions about sentience, consciousness, moral status, donor protection, and chimeras. There are, however, unique ethical considerations that arise and are worth looking into in the context of research into stress and stress-related disorders using cerebral organoids. This paper provides stress research-specific ethical considerations in the context of cerebral organoid generation and use for research purposes. The use of stress research as a case study here can help inform other practices of in vitro studies using brain models with high ethical considerations.

The impact of stress and anesthesia on animal models of infectious disease

Stress and general anesthesia have an impact on the functional response of the organism due to the detrimental effects on cardiovascular, immunological, and metabolic function, which could limit the organism's response to an infectious event. Animal studies have formed an essential step in understanding and mitigating infectious diseases, as the complexities of physiology and immunity cannot yet be replicated in vivo. Using animals in research continues to come under increasing societal scrutiny, and it is therefore crucial that the welfare of animals used in disease research is optimized to meet both societal expectations and improve scientific outcomes. Everyday management and procedures in animal studies are known to cause stress, which can not only cause poorer welfare outcomes, but also introduces variables in disease studies. Whilst general anesthesia is necessary at times to reduce stress and enhance animal welfare in disease research, evidence of physiological and immunological disruption caused by general anesthesia is increasing. To better understand and quantify the effects of stress and anesthesia on disease study and welfare outcomes, utilizing the most appropriate animal monitoring strategies is imperative. This article aims to analyze recent scientific evidence about the impact of stress and anesthesia as uncontrolled variables, as well as reviewing monitoring strategies and technologies in animal models during infectious diseases.

Stress Evaluation of Mouse Husbandry Environments for Improving Laboratory Animal Welfare

Animal welfare is recognized as essential for the coexistence of humans and animals. Considering the increased demand and interest in animal welfare, many methods for improving animal welfare are being devised, but which method reduces animal stress has not been scientifically verified. Therefore, reducing animal stress by providing a proper breeding environment and environmental enrichment can be the basis for animal study. In this study, stress levels were assessed based on the mouse-breeding environment. We considered that the higher the body weight and the lower the corticosterone concentration, the lower the stress. According to the results, animals in the individual ventilation cages were determined to have lower serum cortisol concentrations, while the body weight of the animals was increased when in individual ventilation cages compared with individual isolated cages and when providing environmental enrichment compared with group breeding or not providing environmental enrichment. The results provide appropriate guidelines for improving laboratory animal welfare.

Pre-clinical Investigations of Therapeutic Markers Associated with Acute and Chronic Restraint Stress: A Nuclear Magnetic Resonance Based Contrast Metabolic Approach

Stress can be defined by two parameters, first the psychological sensing of pressure and second is the body's response. However, the exposure time to stress depicts the biological response produced against it. The effect of acute and chronic restraint stress on anxiety and the production of systemic metabolites were investigated in male Sprague-Dawley (SD) rats. Behavioural test was performed on elevated plus maze (EPM) in conjunction with the statistical analysis that exhibited the habituation during long term exposure to stress when compared with the short-term stress. These behaviour-based changes resulted in interpolated concentration of some serum metabolites like carbohydrates, amino acids and lipids as analysed by NMR. Metabolic analysis along with the multivariate analysis demonstrated that the expression of concentration of metabolites including glutamate, proline, succinate, citrate, and tyrosine is higher in the acute stress than the chronic stress, while glucose and lipids i.e., LDL and VLDL changed in the opposite trends. Thus, the aforesaid study provides an analytical strategy for the characterization of perturbed metabolites induced due to the behavioural modifications in an organism. It may further aid in developing potential therapeutic markers at the metabolic levels which may broaden the treatment options for stress and anxiety related disorders.

miR-218: A Stress-Responsive Epigenetic Modifier

Understanding the epigenetic role of microRNAs (miRNAs) has been a critical development in the field of neuropsychiatry and in understanding their underlying pathophysiology. Abnormalities in miRNA expression are often seen as key to the pathogenesis of many stress-associated mental disorders, including major depressive disorder (MDD). Recent advances in omics biology have further contributed to this understanding and expanded the role of miRNAs in networking a diverse array of molecular pathways, which are essentially related to the stress adaptivity of a healthy brain. Studies have highlighted the role of many such miRNAs in causing maladaptive changes in the brain's stress axis. One such miRNA is miR-218, which is debated as a critical candidate for increased stress susceptibility. miR-218 is expressed throughout the brain, notably in the hippocampus and prefrontal cortex (PFC). It is expressed at various levels through life stages, as seen by adolescent and adult animal models. Until now, a minimal number of studies have been conducted on human subjects to understand its role in stress-related abnormalities in brain circuits. However, several studies, including animal and cell-culture models, have been used to understand the impact of miR-218 on stress response and hypothalamic-pituitary-adrenal (HPA) axis function. So far, expression changes in this miRNA have been found to regulate signaling pathways such as glucocorticoid signaling, serotonergic signaling, and glutamatergic signaling. Recently, the developmental role of miR-218 has generated interest, given its increasing expression from adolescence to adulthood and targeting the Netrin-1/DCC signaling pathway. Since miR-218 expression affects neuronal development and plasticity, it is expected that a change in miR-218 expression levels over the course of development may negatively impact the process and make individuals stress-susceptible in adulthood. In this review, we describe the role of miR-218 in stress-induced neuropsychiatric conditions with an emphasis on stress-related disorders.

Critical Problems for Research in Animal Sheltering, a Conceptual Analysis

Animal shelter research has seen significant increases in participation over the past several decades from academic organizations, private organizations, public entities, and even corporations that aims to improve shelter programs, processes, operations, and outcomes for the various stakeholders/participants involved in a shelter system (animals, humans, the community, wildlife, and the environment). These efforts are scattered through a huge variety of different research areas that are challenging to define and scope for organizations seeking to start new lines of research inquiry. This work aims to enumerate some of the most critical outstanding problems for research in animal sheltering in a conceptual framework that is intended to help direct research conversations toward the research topics of highest impact (with the highest quality outcomes possible). To this end, we define seven (7) key areas for research: animal behavior, adoptions and special needs populations, medical conditions, disease transmission, community, ecology, and wellness (one health), operations, and public-private-academic-corporate collaboration. Within each of these areas, we review specific problems and highlight examples of successes in each area in the past several decades. We close with a discussion of some of the topics that were not detailed in this manuscript but, nonetheless, deserve some mention. Through this enumeration, we hope to spur conversation around innovative methodologies, technologies, and concepts in both research and practice in animal sheltering.

Central Adiponectin Signaling – A Metabolic Regulator in Support of Brain Plasticity

Brain plasticity and metabolism are tightly connected by a constant influx of peripheral glucose to the central nervous system in order to meet the high metabolic demands imposed by neuronal activity. Metabolic disturbances highly affect neuronal plasticity, which underlies the prevalent comorbidity between metabolic disorders, cognitive impairment, and mood dysfunction. Effective pro-cognitive and neuropsychiatric interventions, therefore, should consider the metabolic aspect of brain plasticity to achieve high effectiveness. The adipocyte-secreted hormone, adiponectin, is a metabolic regulator that crosses the blood-brain barrier and modulates neuronal activity in several brain regions, where it exerts neurotrophic and neuroprotective properties. Moreover, adiponectin has been shown to improve neuronal metabolism in different animal models, including obesity, diabetes, and Alzheimer’s disease. Here, we aim at linking the adiponectin’s neurotrophic and neuroprotective properties with its main role as a metabolic regulator and to summarize the possible mechanisms of action on improving brain plasticity via its role in regulating the intracellular energetic activity. Such properties suggest adiponectin signaling as a potential target to counteract the central metabolic disturbances and impaired neuronal plasticity underlying many neuropsychiatric disorders.

Effect of Hibiscus syriacus Linnaeus extract and its active constituent, saponarin, in animal models of stress-induced sleep disturbances and pentobarbital-induced sleep

Treatment of sleep disorders promotes the long-term use of commercially available sleep inducers that have several adverse effects, including addiction, systemic fatigue, weakness, loss of concentration, headache, and digestive problems. Therefore, we aimed to limit these adverse effects by investigating a natural product, the extract of the Hibiscus syriacus Linnaeus flower (HSF), as an alternative treatment. In the electric footshock model, we measured anxiety and assessed the degree of sleep improvement after administering HSF extract. In the restraint model, we studied the sleep rate using PiezoSleep, a noninvasive assessment system. In the pentobarbital model, we measured sleep improvement and changes in sleep-related factors. Our first model confirmed the desirable effects of HSF extract and its active constituent, saponarin, on anxiolysis and Wake times. HSF extract also increased REM sleep time. Furthermore, HSF extract and saponarin increased the expression of cortical GABAA receptor α1 (GABAAR α1) and c-Fos in the ventrolateral preoptic nucleus (VLPO). In the second model, HSF extract and saponarin restored the sleep rate and the sleep bout duration. In the third model, HSF extract and saponarin increased sleep maintenance time. Moreover, HSF extract and saponarin increased cortical cholecystokinin (CCK) mRNA levels and the expression of VLPO c-Fos. HSF extract also increased GABAAR α1 mRNA level. Our results suggest that HSF extract and saponarin are effective in maintaining sleep and may be used as a novel treatment for sleep disorder. Eventually, we hope to introduce HSF and saponarin as a clinical treatment for sleep disorders in humans.

Regulation of stress response on the hypothalamic-pituitary-gonadal axis via gonadotropin-inhibitory hormone

Under stressful condition, reproductive function is impaired due to the activation of various components of the hypothalamic-pituitaryadrenal (HPA) axis, which can suppress the activity of the hypothalamic-pituitary-gonadal (HPG) axis at multiple levels. A hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH) is a key negative regulator of reproduction that governs the HPG axis. Converging lines of evidence have suggested that different stress types and their duration, such as physical or psychological, and acute or chronic, can modulate the GnIH system. To clarify the sensitivity and reactivity of the GnIH system in response to stress, we summarize and critically review the available studies that investigated the effects of various stressors, such as restraint, nutritional/metabolic and social stress, on GnIH expression and/or its neuronal activity leading to altered HPG action. In this review, we focus on GnIH as the potential novel mediator responsible for stress-induced reproductive dysfunction.

Deciphering the RNA universe in sperm in its role as a vertical information carrier

The inheritance of neurophysiologic and neuropsychologic complex diseases can only partly be explained by the Mendelian concept of genetic inheritance. Previous research showed that both psychological disorders like post-traumatic stress disorder and metabolic diseases are more prevalent in the progeny of affected parents. This could suggest an epigenetic mode of transmission. Human studies give first insight into the scope of intergenerational influence of stressors but are limited in exploring the underlying mechanisms. Animal models have elucidated the mechanistic underpinnings of epigenetic transmission. In this review, we summarize progress on the mechanisms of paternal intergenerational transmission by means of sperm RNA in mouse models. We discuss relevant details for the modelling of RNA-mediated transmission, point towards currently unanswered questions and propose experimental considerations for tackling these questions.

Sympathetic Neural Control in Humans with Anxiety-Related Disorders

Numerous conceptual models are used to describe the dynamic responsiveness of physiological systems to environmental pressures, originating with Claude Bernard's milieu intérieur and extending to more recent models such as allostasis. The impact of stress and anxiety upon these regulatory processes has both basic science and clinical relevance, extending from the pioneering work of Hans Selye who advanced the concept that stress can significantly impact physiological health and function. Of particular interest within the current article, anxiety is independently associated with cardiovascular risk, yet mechanisms underlying these associations remain equivocal. This link between anxiety and cardiovascular risk is relevant given the high prevalence of anxiety in the general population, as well as its early age of onset. Chronically anxious populations, such as those with anxiety disorders (i.e., generalized anxiety disorder, panic disorder, specific phobias, etc.) offer a human model that interrogates the deleterious effects that chronic stress and allostatic load can have on the nervous system and cardiovascular function. Further, while many of these disorders do not appear to exhibit baseline alterations in sympathetic neural activity, reactivity to mental stress offers insights into applicable, real-world scenarios in which heightened sympathetic reactivity may predispose those individuals to elevated cardiovascular risk. This article also assesses behavioral and lifestyle modifications that have been shown to concurrently improve anxiety symptoms, as well as sympathetic control. Lastly, future directions of research will be discussed, with a focus on better integration of psychological factors within physiological studies examining anxiety and neural cardiovascular health. © 2022 American Physiological Society. Compr Physiol 12:1-33, 2022.

Understanding how stress responses and stress-related behaviors have evolved in zebrafish and mammals

Stress response is essential for the organism to quickly restore physiological homeostasis disturbed by various environmental insults. In addition to well-established physiological cascades, stress also evokes various brain and behavioral responses. Aquatic animal models, including the zebrafish (Danio rerio), have been extensively used to probe pathobiological mechanisms of stress and stress-related brain disorders. Here, we critically discuss the use of zebrafish models for studying mechanisms of stress and modeling its disorders experimentally, with a particular cross-taxon focus on the potential evolution of stress responses from zebrafish to rodents and humans, as well as its translational implications.

Microglial-glucocorticoid receptor depletion alters the response of hippocampal microglia and neurons in a chronic unpredictable mild stress paradigm in female mice

Chronic psychological stress is one of the most important triggers and environmental risk factors for neuropsychiatric disorders. Chronic stress can influence all organs via the secretion of stress hormones, including glucocorticoids by the adrenal glands, which coordinate the stress response across the body. In the brain, glucocorticoid receptors (GR) are expressed by various cell types including microglia, which are its resident immune cells regulating stress-induced inflammatory processes. To study the roles of microglial GR under normal homeostatic conditions and following chronic stress, we generated a mouse model in which the GR gene is depleted in microglia specifically at adulthood to prevent developmental confounds. We first confirmed that microglia were depleted in GR in our model in males and females among the cingulate cortex and the hippocampus, both stress-sensitive brain regions. Then, cohorts of microglial-GR depleted and wild-type (WT) adult female mice were housed for 3 weeks in a standard or stressful condition, using a chronic unpredictable mild stress (CUMS) paradigm. CUMS induced stress-related behavior in both microglial-GR depleted and WT animals as demonstrated by a decrease of both saccharine preference and progressive ratio breakpoint. Nevertheless, the hippocampal microglial and neural mechanisms underlying the adaptation to stress occurred differently between the two genotypes. Upon CUMS exposure, microglial morphology was altered in the WT controls, without any apparent effect in microglial-GR depleted mice. Furthermore, in the standard environment condition, GR depleted-microglia showed increased expression of pro-inflammatory genes, and genes involved in microglial homeostatic functions (such as Trem2, Cx3cr1 and Mertk). On the contrary, in CUMS condition, GR depleted-microglia showed reduced expression levels of pro-inflammatory genes and increased neuroprotective as well as anti-inflammatory genes compared to WT-microglia. Moreover, in microglial-GR depleted mice, but not in WT mice, CUMS led to a significant reduction of CA1 long-term potentiation and paired-pulse ratio. Lastly, differences in adult hippocampal neurogenesis were observed between the genotypes during normal homeostatic conditions, with microglial-GR deficiency increasing the formation of newborn neurons in the dentate gyrus subgranular zone independently from stress exposure. Together, these findings indicate that, although the deletion of microglial GR did not prevent the animal's ability to respond to stress, it contributed to modulating hippocampal functions in both standard and stressful conditions, notably by shaping the microglial response to chronic stress.

Therapeutic effects of saffron extract on different memory types, anxiety, and hippocampal BDNF and TNF-α gene expressions in sub-chronically stressed rats

Objective: While stress reportedly impairs memory, saffron enhances it. This study investigated the therapeutic effects of saffron extract on different memory types, anxiety-like behavior, and expressions of BDNF and TNF-α genes in sub-chronically stressed rats.Methods: Rats were randomly assigned to control, restraint stress (6 h/day/7 days), two 7-days saffron treatments with 30 and 60 mg/kg, and two stress-saffron groups (30 and 60 mg/kg/7 post-stress days). Serum cortisol level and hippocampal BDNF and TNF-α gene expressions were measured. Open field, passive avoidance, novel object recognition, and object location tests were performed to assess anxiety-like behavior and avoidance as well as cognitive and spatial memories, respectively.Results: The low saffron dose in the sub-chronic stressed group led to a significant increase in passive avoidance latency from day 3 onward whereas this effect was observed after 7 days under the high-dose treatment that simultaneously led to a significant decline in serum cortisol level. While the low saffron dose led to a sharp drop in hippocampal TNF-α gene expression, the high dose significantly increased the hippocampal BDNF gene expression in the sub-chronic stress group. Finally, both saffron doses reduced anxiety in the stressed groups.Conclusion: Compared to the low saffron dose, the high dose had a latent but long-lasting impact. Cognitive and spatial memories remained unaffected by either stress or saffron treatment. In addition, only the high saffron dose reversed anxiety in the sub-chronically stressed group. These findings suggest that various doses of saffron act differently on different brain functions under sub-chronic stress conditions.Abbreviations: Brain derived neurotrophic factor (BDNF), tumor necrosis factor-α (TNF-α), hypothalamic-pituitary-adrenal axis (HPA), novel object recognition task (NORT), novel object location task (NOLT), open field test (OFT), passive avoidance (PA).

High-throughput rat immunoglobulin G N-glycosylation profiling revealed subclass-specific changes associated with chronic stress

Immunoglobulin G (IgG) glycosylation corresponds well with immune system changes, so it can potentially be used as a biomarker for the consequences of chronic stress such as low-grade inflammation and enhanced immunosenescence in older animals. Here we present a high-throughput glycoproteomic workflow, including IgG enrichment, HILIC glycopeptide purification, and nano-LC-MS analysis of tryptic glycopeptides applied for the analysis of rat IgG. A cohort of 80 animals was exposed to seven stressors in a customized chronic stress protocol with blood and tissue sampling in three timepoints. Young female rats experienced an increase in agalactosylated glycoforms on IgG2a and IgG2c accompanied by a decrease in monogalactosylation. Among old females, increased galactosylation was observed in the IgG2b subclass, pointing to an anti-inflammatory activity of IgG. Additionally, IgG Fc N-glycosylation patterns in Sprague Dawley rats were analyzed, quantified, and reported for the first time. Our findings emphasize age-, sex- and subclass-dependent differences in IgG glycosylation related to chronic stress exposure, confirming the relevance of newly developed methods for further research in glycobiology of rodent immune response. SIGNIFICANCE: In this study, we showed that a high-throughput streamlined methodology based on protein L 96-well monolithic plates for efficient rat IgG immunoaffinity enrichment from blood plasma, paired with appropriate tryptic glycopeptide preparation, HILIC-SPE enrichment, and nano-LC-MS methods was suitable for quick processing of large sample sets. We report a subclass-specific profiling and changes in rat IgG Fc galactosylation and adrenal gland immunohistochemistry of male and female animals exposed to a customized chronic stress protocol.

Effect of chronic unpredictable stress on the progression of experimental apical periodontitis in rats

AIM

To establish an experimental model combining chronic stress and apical periodontitis by assessing the development of periapical lesions in rats in three different time points.

METHODOLOGY

Forty-eight male Wistar rats were randomly assigned into two equal groups: Apical periodontitis (AP) and AP + Stress (AP + S). The animals of the AP group were not exposed to stressful conditions whereas the AP + S group were exposed to a variety of stressors on a daily basis until the end of the experiment. After three weeks of chronic unpredictable stress, apical periodontitis was induced in both groups by exposing the pulpal tissue of the mandibular first molar to the oral environment. Each group was further subdivided into three subgroups according to the euthanasia period: 14, 21 and 28 days after pulp exposure. The animals were weighed, and the blood was collected for corticosterone serum dosage by radioimmunoassay. The mandibles were removed and submitted to histopathological and microtomography analyses to assess the inflammatory response and the progression of periapical lesions. Comparisons between the AP and AP + S groups were performed using Student's t-test and Mann-Whitney U-test for parametric and nonparametric data, respectively. The one-way anova test followed by Tukey's test (parametric data) and Kruskal-Wallis followed by Dunn's test (nonparametric data) were used for comparisons between the three time points within the same group (P < 0.05).

RESULTS

The AP + S group had a significantly lower average percentage of weight gain at 14 days and 21 days after AP induction (P < 0.05). Significantly higher levels of corticosterone were found in the AP + S group at 21 days (P < 0.05). The AP + S group had a significantly greater intensity and extension of inflammatory infiltrate with larger areas of bone loss compared to the AP groups at 21 days (P < 0.05). The volume of the periapical lesions in the AP + S group was significantly larger than that of the AP group 21 days following pulp exposure (P < 0.05).

CONCLUSIONS

The chronic unpredictable stress model applied for 6 weeks exacerbated the inflammatory response and increased bone loss associated with AP, especially 21 days after its induction. This model appears to be suitable for investigating the bidirectional relationship between apical periodontitis and chronic stress.

SGK1 knockdown in the medial prefrontal cortex reduces resistance to stress-induced memory impairment

Down-regulation of serum and glucocorticoid-regulated kinase1 (SGK1) expression has been reported in the postmortem prefrontal cortex (PFC) of subjects with post-traumatic stress disorder. Furthermore, experimental treatments that reduce SGK1 function in the medial prefrontal cortex (mPFC) cause depressive-like behaviors and synaptic dysfunction. Therefore, we examined the effect of SGK1 down-regulation in the mPFC on resistance to stress-induced cognitive impairment. Rats with viral-mediated knockdown of SGK1 in the mPFC were subjected to either a brief 20-min restraint plus 20 intermittent tail shocks or a prolonged 60-min restraint plus 60 intermittent tail shocks, after which their performance in an object recognition task was assessed. Recognition memory remained intact in control rats following the brief stress, but was impaired in rats with SGK1 knockdown in the mPFC. Prolonged stress impaired recognition memory in both control rats and rats with SGK1 knockdown. Our findings indicate that altered mPFC SGK1 signaling is a potential mechanism for resistance to stress-induced cognitive impairment.

Detecting the effects of predator-induced stress on the global metabolism of an ungulate prey using fecal metabolomic fingerprinting

Few field tests have assessed the effects of predator-induced stress on prey fitness, particularly in large carnivore-ungulate systems. Because traditional measures of stress present limitations when applied to free-ranging animals, new strategies and systemic methodologies are needed. Recent studies have shown that stress and anxiety related behaviors can influence the metabolic activity of the gut microbiome in mammal hosts, and these metabolic alterations may aid in identification of stress. In this study, we used NMR-based fecal metabolomic fingerprinting to compare the fecal metabolome, a functional readout of the gut microbiome, of cattle herds grazing in low vs. high wolf-impacted areas within three wolf pack territories. Additionally, we evaluated if other factors (e.g., cattle nutritional state, climate, landscape) besides wolf presence were related to the variation in cattle metabolism. By collecting longitudinal fecal samples from GPS-collared cattle, we found relevant metabolic differences between cattle herds in areas where the probability of wolf pack interaction was higher. Moreover, cattle distance to GPS-collared wolves was the factor most correlated with this difference in cattle metabolism, potentially reflecting the variation in wolf predation risk. We further validated our results through a regression model that reconstructed cattle distances to GPS-collared wolves based on the metabolic difference between cattle herds. Although further research is needed to explore if similar patterns also hold at a finer scale, our results suggests that fecal metabolomic fingerprinting is a promising tool for assessing the physiological responses of prey to predation risk. This novel approach will help improve our knowledge of the consequences of predators beyond the direct effect of predation.

Applications of the SR4G Transgenic Zebrafish Line for Biomonitoring of Stress-Disrupting Compounds: A Proof-of-Concept Study

Transgenic zebrafish models have been successfully used in biomonitoring and risk assessment studies of environmental pollutants, including xenoestrogens, pesticides, and heavy metals. We employed zebrafish larva (transgenic SR4G line) with a cortisol-inducible green fluorescence protein reporter (eGFP) as a model to detect stress responses upon exposure to compounds with environmental impact, including bisphenol A (BPA), vinclozolin (VIN), and fluoxetine (FLX). Cortisol, fluorescence signal, and mRNA levels of eGFP and 11 targeted genes were measured in a homogenized pool of zebrafish larvae, with six experimental replicates for each endpoint. Eleven targeted genes were selected according to their association with stress-axis and immediate early response class of genes. Hydrocortisone (CORT)and dexamethasone (DEX) were used as positive and negative controls, respectively. All measurements were done in two unstressed and stressed condition using standardized net handling as the stressor. A significant positive linear correlation between cortisol levels and eGFP mRNA levels was observed (r> 0.9). Based on eGFP mRNA levels in unstressed and stressed larvae two predictive models were trained (Random Forest and Logistic Regression). Both these models could correctly predict the blunted stress response upon exposure to BPA, VIN, FLX and the negative control, DEX. The negative predictive value (NPV) of these models were 100%. Similar NPV was observed when the predictive models trained based on the mRNA levels of the eleven assessed genes. Measurement of whole-body fluorescence intensity signal was not significant to detect blunted stress response. Our findings support the use of SR4G transgenic larvae as an in vivo biomonitoring model to screen chemicals for their stress-disrupting potentials. This is important because there is increasing evidence that brief exposures to environmental pollutants modify the stress response and critical coping behaviors for several generations.

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

A Potential Role for Stress-Induced Microbial Alterations in IgA-Associated Irritable Bowel Syndrome with Diarrhea

Stress is a known trigger for flares of inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS); however, this process is not well understood. Here, we find that restraint stress in mice leads to signs of diarrhea, fecal dysbiosis, and a barrier defect via the opening of goblet-cell associated passages. Notably, stress increases host immunity to gut bacteria as assessed by immunoglobulin A (IgA)-bound gut bacteria. Stress-induced microbial changes are necessary and sufficient to elicit these effects. Moreover, similar to mice, many diarrhea-predominant IBS (IBS-D) patients from two cohorts display increased antibacterial immunity as assessed by IgA-bound fecal bacteria. This antibacterial IgA response in IBS-D correlates with somatic symptom severity and was distinct from healthy controls or IBD patients. These findings suggest that stress may play an important role in patients with IgA-associated IBS-D by disrupting the intestinal microbial community that alters gastrointestinal function and host immunity to commensal bacteria.

Stress in mice causes diarrhea, dysbiosis, barrier defect, increased antibacterial IgA

Stress-induced microbial changes are sufficient to elicit the above effects

IBS-D patients from two cohorts display increased and unique antibacterial IgA

Antibacterial IgA in IBS-D correlates with patient symptom severity

Salivary Alpha-Amylase in Experimentally-Induced Muscle Pain

Salivary alpha-amylase (sAA) is a marker of psychological stress and might also be a potential marker for pain-associated stress due its non-invasive, cost-effective, and stress-free collection. The current study aimed to investigate whether the levels of sAA are influenced by experimentally induced muscle pain. In this study, 26 healthy, pain-free and age-matched participants (23.8 ± 2.6 years) were included, 13 women and 13 men. Prior to the experiment, questionnaires assessing health and anxiety were completed. Muscle pain was then induced through intramuscular injection of 0.4 mL hypertonic saline (56.5 mg/mL) into the masseter muscle and unstimulated whole saliva samples were collected at baseline before injection, 2 min, and 15 min after injection. A commercially available colorimetric assay was used to analyze the sAA. Perceived pain and stress were assessed using a 0–100 Numeric Rating Scale for each sample. There were no significant differences in sAA levels prior and after injection of hypertonic saline (p > 0.05) although sAA levels showed a slight decrease during experimentally-induced muscle pain. However, a strong correlation was observed between self-reported pain and perceived level of stress during experimentally-induced muscle pain (r₂ = 0.744; p < 0.0001). Furthermore, there was a moderate correlation between the levels of sAA at baseline and during experimental pain (r₂ = 0.687; p < 0.0001). In conclusion, this study could not show any association between the levels of sAA and perceived pain and or/stress. However, since a significant strong correlation could be observed between perceived stress and pain intensity, this study indicates that experimentally-induced muscle pain could be used as a stress model.

Chronic stress and endothelial dysfunction: mechanisms, experimental challenges, and the way ahead

Although chronic stress is an important risk factor for cardiovascular diseases (CVD) onset, the underlying mechanisms driving such pathophysiological complications remain relatively unknown. Here, dysregulation of innate stress response systems and the effects of downstream mediators are strongly implicated, with the vascular endothelium emerging as a primary target of excessive glucocorticoid and catecholamine action. Therefore, this review article explores the development of stress-related endothelial dysfunction by focusing on the following: 1) assessing the phenomenon of stress and complexities surrounding this notion, 2) discussing mechanistic links between chronic stress and endothelial dysfunction, and 3) evaluating the utility of various preclinical models currently employed to study mechanisms underlying the onset of stress-mediated complications such as endothelial dysfunction. The data reveal that preclinical models play an important role in our efforts to gain an increased understanding of mechanisms underlying stress-mediated endothelial dysfunction. It is our understanding that this provides a good foundation going forward, and we propose that further efforts should be made to 1) more clearly define the concept of stress and 2) standardize protocols of animal models with specific guidelines to better indicate the mental complications that are simulated.

Regulation of natural killer cell activity by glucocorticoids, serotonin, dopamine, and epinephrine

The immune system and the nervous system are highly complex organs composed of various different cells that must interact with each other for proper function of the system. This communication can be mediated by soluble factors. The factors released by the nervous system (neurotransmitters) differ from those released by the immune system (cytokines). Nevertheless, the nervous and immune systems can influence each other’s activity because immune cells express neurotransmitter receptors, and neurons express cytokine receptors. Moreover, immune cells can synthesize and release neurotransmitters themselves, thus using neurotransmitter-mediated pathways via autocrine and paracrine mechanisms. Natural killer (NK) cells are innate lymphocytes that are important for early and effective immune reactions against infections and cancer. Many studies have shown the strong influence of stress and the nervous system on NK cell activity. This phenomenon may be one reason why chronic stress leads to a higher incidence of infections and cancer. Here, we review the effects of neuroendocrine factors on the different activities of NK cells. Understanding the effects of neuroendocrine factors on NK cell activities during physiological and pathophysiological conditions may result in novel therapeutic strategies to enhance NK cell functions against tumors.

The Effect of Electroacupuncture on Plasma Fibrinogen Levels in Restraint Stress Wistar Rats

Objective: Blood is a suspended cellular element that dissolves in plasma. Blood transports oxygen and nutrients to all body cells and carries metabolic waste from the whole body. The nature of blood flowing through vessels is a factor that plays an important role in oxygen delivery and tissue perfusion. In acute stress conditions, various reactions can occur and affect the blood flow in blood vessels. Electroacupuncture (EA) is an additional therapy with minimal side-effects that can improve the quality of blood flow. This study investigated the effect of EA bilaterally at ST 36 (Zusanli) on plasma fibrinogen. Materials and Methods: Eighteen male Wistar rats were divided randomly into 3 groups: (1) a control group (n = 6); (2) a restraint-stress group (n = 6); and (3) a restraint-stress-and-EA group (n = 6). EA was performed in group 3 after the rats were subjected to 3 hours of restraint stress. Results: There were significant mean differences in plasma fibrinogen levels (P = 0.048; 95% confidence interval: 0.5-109.5) between the restraint stress groups and the control group. Conclusion: This study showed that the EA on ST 36 lowered levels of plasma fibrinogen of Wistar rats in restraint stress model.

Fecal Metabolomics as a Novel Noninvasive Method for Short-Term Stress Monitoring in Beef Cattle

Traditional measures of short-term stress response such as fecal glucocorticoid metabolites (FGM) are widely used in controlled settings to quantify the intensity of stimulation to which cattle are exposed. However, FGMs present several methodological and interpretation pitfalls when applied on animals in free-ranging conditions. In this study, we proposed an NMR-based fecal metabolomics strategy for noninvasive stress detection in beef cattle. Using a longitudinal sample collection, we monitored the changes in the fecal metabolome and FGM concentrations before and after an acute stressful event. Our results showed that while the fecal metabolome changed as a function of stress (p < 0.001), the mean concentrations of FGM did not change (Levene's test: F-ratio: 0.87, p-value: 0.44). Furthermore, we showed that the interanimal variability observed in the stress response was correlated with the individual fecal microbiota. This result was in line with recent findings, indicating the gut microbiome as a crucial mediator of stress response. We conclude that NMR-based fecal metabolomics proved to be a reliable methodology to assess stress response and that its future applicability to studies for stress monitoring in range animals may be more appropriate than FGM analysis.

Chronic treatment with five vascular risk factors causes cerebral amyloid angiopathy but no Alzheimer pathology in C57BL6 mice

Alzheimer's disease (AD) is a progressive neurodegenerative brain disorder and the most common form of dementia coming along with cerebral amyloid angiopathy (CAA) in more than 70% of all cases. However, CAA occurs also in pure form without AD pathology. Vascular life style risk factors such as obesity, hypertension, hypercholesterolemia, diabetes, stress or an old age play an important role in the progression of CAA. So far, no animal model for sporadic CAA has been reported, thus the aim of the present study was to create and characterize a new mouse model for sporadic CAA by treatment with different vascular risk factors. Healthy C57BL6 mice were treated with lifestyle vascular risk factors for 35 or 56 weeks: lipopolysaccharide, social stress, streptozotozin, high cholesterol diet and copper in the drinking water. Four behavioral tests (black-white box, classical maze, cheeseboard maze and plus-maze discriminative avoidance task) showed impaired learning, memory and executive functions as well as anxiety with increased age. The treated animals exhibited increased plasma levels of cortisol, insulin, interleukin-1ß, glucose and cholesterol, confirming the effectiveness of the treatment. Confocal microscopy analysis displayed severe vessel damage already after 35 weeks of treatment. IgG positive staining points to a severe blood-brain barrier (BBB) disruption and furthermore, cerebral bleedings were observed in a much higher amount in the treatment group. Importantly, inclusions of beta-amyloid in the vessels indicated the development of CAA, but no deposition of beta-amyloid plaques and tau pathology in the brains were seen. Taken together, we characterized a novel sporadic CAA mouse model, which offers a strategy to study the progression of the disease and therapeutic and diagnostic interventions.

Lateral hypothalamic neurotensin neurons promote arousal and hyperthermia

Sleep and wakefulness are greatly influenced by various physiological and psychological factors, but the neuronal elements responsible for organizing sleep-wake behavior in response to these factors are largely unknown. In this study, we report that a subset of neurons in the lateral hypothalamic area (LH) expressing the neuropeptide neurotensin (Nts) is critical for orchestrating sleep-wake responses to acute psychological and physiological challenges or stressors. We show that selective activation of Nts^LH neurons with chemogenetic or optogenetic methods elicits rapid transitions from non-rapid eye movement (NREM) sleep to wakefulness and produces sustained arousal, higher locomotor activity (LMA), and hyperthermia, which are commonly observed after acute stress exposure. On the other hand, selective chemogenetic inhibition of Nts^LH neurons attenuates the arousal, LMA, and body temperature (Tb) responses to a psychological stress (a novel environment) and augments the responses to a physiological stress (fasting).

A neurotensin-producing subset of neurons in the lateral hypothalamus promote arousal and thermogenesis; these neurons are necessary for appropriate sleep-wake and body temperature responses to various stressors.

Adjusting sleep-wake behavior in response to environmental and physiological challenges may not only be of protective value, but can also be vital for the survival of the organism. For example, while it is crucial to increase wake to explore a novel environment to search for potential threats and food sources, it is also necessary to decrease wake and reduce energy expenditure during prolonged absence of food. In this study, we report that a subset of neurons in the lateral hypothalamic area (LH) expressing the neuropeptide neurotensin (Nts) is critical for orchestrating sleep-wake responses to such challenges. We show that brief activation of Nts^LH neurons in mice evokes immediate arousals from sleep, while their sustained activation increases wake, locomotor activity, and body temperature for several hours. In contrast, when Nts^LH neurons are inhibited, mice are neither able to sustain wake in a novel environment nor able to reduce wake during food deprivation. These data suggest that Nts^LH neurons may be necessary for generating appropriate sleep-wake responses to a wide variety of environmental and physiological challenges.

Common and differential transcriptional responses to different models of traumatic stress exposure in rats

The effect of six different traumatic stress protocols on the transcriptome of the rat adrenal gland was examined using RNA sequencing. These protocols included chronic variable stress, chronic shock, social defeat and social isolation. The response of the transcriptome to stress suggested that there are genes that respond in a universal or stress modality-independent manner, as well as genes that respond in a stress modality-specific manner. Using a small number of the genes selected from the modality-independent set of stress-sensitive genes, a sensitive and robust measure of chronic stress exposure was developed. This stress-sensitive gene expression (SSGE) index could detect chronic traumatic stress exposure in a wide range of different stress models in a manner that was relatively independent of the modality of stress exposure and that paralleled the intensity of stress exposure in a dose-dependent manner. This measure could reliably distinguish control and stressed individuals in the case of animals exposed to the most intense stress protocols. The response of a subset of the modality-specific genes could also distinguish some types of stress exposure, based solely on changes in the pattern of gene expression. The results suggest that it is possible to develop diagnostic measures of traumatic stress exposure based solely on changes in the level of expression of a relatively small number of genes.

Assessment of the role of intracranial hypertension and stress on hippocampal cell apoptosis and hypothalamic-pituitary dysfunction after TBI

In recent years, hypopituitarism caused by traumatic brain injury (TBI) has been explored in many clinical studies; however, few studies have focused on intracranial hypertension and stress caused by TBI. In this study, an intracranial hypertension model, with epidural hematoma as the cause, was used to explore the physiopathological and neuroendocrine changes in the hypothalamic-pituitary axis and hippocampus. The results demonstrated that intracranial hypertension increased the apoptosis rate, caspase-3 levels and proliferating cell nuclear antigen (PCNA) in the hippocampus, hypothalamus, pituitary gland and showed a consistent rate of apoptosis within each group. The apoptosis rates of hippocampus, hypothalamus and pituitary gland were further increased when intracranial pressure (ICP) at 24 hour (h) were still increased. The change rates of apoptosis in hypothalamus and pituitary gland were significantly higher than hippocampus. Moreover, the stress caused by surgery may be a crucial factor in apoptosis. To confirm stress leads to apoptosis in the hypothalamus and pituitary gland, we used rabbits to establish a standard stress model. The results confirmed that stress leads to apoptosis of neuroendocrine cells in the hypothalamus and pituitary gland, moreover, the higher the stress intensity, the higher the apoptosis rate in the hypothalamus and pituitary gland.

Effect of different stressors on voluntary ethanol intake in ethanol-dependent and nondependent C57BL/6J mice

Several animal models have evaluated the effect of stress on voluntary ethanol intake with mixed results. The experiments reported here examined the effects of different stressors on voluntary ethanol consumption in dependent and nondependent adult male C57BL/6J mice. In Experiment 1, restraint, forced swim, and social defeat stress procedures all tended to reduce ethanol intake in nondependent mice regardless of whether the stress experience occurred 1 h or 4 h prior to ethanol access. The reduction in ethanol consumption was most robust following restraint stress. Experiment 2 examined the effects of forced swim stress and social defeat stress on drinking in a dependence model that involved repeated cycles of chronic intermittent ethanol (CIE) exposure. Repeated exposure to forced swim stress prior to intervening test drinking periods that followed repeated cycles of CIE exposure further increased ethanol consumption in CIE-exposed mice while not altering intake in nondependent mice. In contrast, repeated exposure to the social defeat stressor in a similar manner reduced ethanol consumption in CIE-exposed mice while not altering drinking in nondependent mice. Results from Experiment 3 confirmed this selective effect of forced swim stress increasing ethanol consumption in mice with a history of CIE exposure, and also demonstrated that enhanced drinking is only observed when the forced swim stressor is administered during each test drinking week, but not if it is applied only during the final test week. Collectively, these studies point to a unique interaction between repeated stress experience and CIE exposure, and also suggest that such an effect depends on the nature of the stressor. Future studies will need to further explore the generalizability of these results, as well as mechanisms underlying the ability of forced swim stress to selectively further enhance ethanol consumption in dependent (CIE-exposed) mice but not alter intake in nondependent animals.

Effects of acute restraint stress, prolonged captivity stress and transdermal corticosterone application on immunocompetence and plasma levels of corticosterone on the cururu Toad (Rhinella icterica)

Glucocorticoid steroids modulate immunocompetence in complex ways with both immunoenhancing and immunosuppressive effects in vertebrates exposed to different stressors. Such bimodal effects have been associated with variation in duration and intensity of the stress response. Given that natural populations have been exposed to a multitude of stressors, a better understanding of the functional association between duration and intensity of the stress response, the resulting changes in glucocorticoid plasma levels and their impact on different aspects of immunocompetence emerges as a cornerstone for vertebrate conservation strategies. We investigated the effects of a restraint challenge (with and without movement restriction), long-term captivity, and transdermal corticosterone application on plasma levels of corticosterone (hereinafter referred to as CORT) and different parameters of innate immunocompetence in the male cururu toads (Rhinella icterica). We show that for R. icterica restraint for 24h proved to be a stressful condition, increasing CORT by 3-fold without consistent immunological changes. However, the application of a more intense stressor (restraint with movement restriction), for the same period, potentiated this response resulting in a 9-fold increase in CORT, associated with increase Neutrophil/Lymphocyte ratio (N:L) and a lower bacterial killing ability (BKA). Transdermal application of corticosterone efficiently mimics repeated acute stress response events, without changing the immune parameters even after 13 days of treatment. Interestingly, long-term captivity did not mitigate the stress response, since the toads maintained 3-fold increased CORT even after 3 months under these conditions. Moreover, long-term captivity in the same condition increased total leukocyte count (TLC) and generated an even greater decrease in BKA, suggesting that consequences of the stress response can be aggravated by time in captivity.

Depressive rumination alters cortisol decline in Major Depressive Disorder

Depressive rumination - a central characteristic of Major Depressive Disorder (MDD) - is a maladaptive emotion regulation strategy that prolongs sad mood and depressive episodes. Considerable research demonstrates the emotional and behavioral consequences of depressive rumination, yet few studies investigate its effect on neuroendocrine functioning. The current study examined the effect of an emotion regulation manipulation on the trajectory of cortisol concentrations among individuals with MDD and healthy controls (CTL). Sadness was induced via forced failure. Participants then were randomly assigned to a depressive rumination or distraction emotion regulation induction. MDDs in the rumination condition exhibited less cortisol decline compared to MDDs in the distraction condition and compared to CTLs in either condition. Findings suggest that depressive rumination alters the trajectory of cortisol secretion in MDD and may prolong cortisol production. Results thereby provide important insights into the interaction of biological and psychological factors through which distress contributes to MDD.

Day and night: diurnal phase influences the response to chronic mild stress

Chronic mild stress (CMS) protocols are widely used to create animal models of depression. Despite this, the inconsistencies in the reported effects may be indicative of crucial differences in methodology. Here, we considered the time of the diurnal cycle in which stressors are applied as a possible relevant temporal variable underlying the association between stress and behavior. Most laboratories test behavior during the light phase of the diurnal cycle, which corresponds to the animal's resting period. Here, rats stressed either in their resting (light phase) or active (dark phase) periods were behaviorally characterized in the light phase. When exposure to CMS occurred during the light phase of the day cycle, rats displayed signs of depressive and anxiety-related behaviors. This phenotype was not observed when CMS was applied during the dark (active) period. Interestingly, although no differences in spatial and reference memory were detected (Morris water maze) in animals in either stress period, those stressed in the light phase showed marked impairments in the probe test. These animals also showed significant dendritic atrophy in the hippocampal dentate granule neurons, with a decrease in the number of spines. Taken together, the observations reported demonstrate that the time in which stress is applied has differential effects on behavioral and neurostructural phenotypes.

A consensus endocrine profile for chronically stressed wild animals does not exist

Given the connection between chronic stress and health, there has been a growing emphasis on identifying chronically stressed wild animals, especially in relation to anthropogenic disturbances. There is considerable confusion, however, in how to identify chronically stressed wild animals, but the most common assumption is that measures of glucocorticoid (GC) function will increase. In an attempt to determine an "endocrine profile" of a chronically stressed wild animal, this review collected papers from the literature that measured baseline GC, stress-induced GC, measures of integrated GC, negative feedback, hypothalamic-pituitary-adrenal axis sensitivity, and/or body weight in chronically stressed animals. The collected studies encompassed laboratory and field studies, numerous diverse species, and multiple techniques for inducing chronic stress. Each paper was ranked according to its relevance to wild animals and scored as to whether the measured response increased, decreased, or stayed the same after exposure to chronic stress. The analyses uncovered so much variation between studies that the literature does not support a generalized endocrine profile in how wild animals respond to chronic stress. The common predictions appear to be based almost entirely on theoretical models rather than empirical data. The three most important variables affecting GC responses were the stressors used to induce chronic stress, the potential for those stressors to induce habituation, and the taxon of the focal species. The best approach for identifying a chronically stressed population appears to be documentation of changes at multiple levels of GC regulation, but the direction of the change (increase or decrease) may be relatively unimportant compared to the fact that the response changes at all. The conclusion is that a consistent, predictable, endocrine response to chronic stress, regardless of the protocol used to induce chronic stress and the species under study, does not exist.

Melissa officinalis and Passiflora caerulea infusion as physiological stress decreaser

The objective of this study was to determine the effect of a Melissa officinalis and Passiflora caerulea infusion on the severity of physiological chronic stress induced by movement restriction in CF-1 mice. 40 CF-1 male mice, six weeks of age, were divided into 4 groups (n = 10 for each group): (1) Group RS/MP received two treatments, induced stress through movement restriction and a infusion of Melissa officinalis and Passiflora caerulea in a dose of 200 mg/kg, (2) RS group with induced stress using movement restriction, (3) MP group, which received only a infusion, and (4) a CONTROL group that received no treatment. The severity of the stress was obtained by analysis of the physical parameters of body weight, thymus and spleen, and associated biomarkers with stress, corticosterone, and glucose. Animals that consumed Melissa officinalis and Passiflora caerulea infusion had lower plasma corticosterone levels (Student's t test, Welch, p = 0.05), which is the most important biomarker associated with physiological stress, demonstrating a phytotherapy effect.

Brain Physiology and Pathophysiology in Mental Stress

Exposure to various forms of stress is a common daily occurrence in the lives of most individuals, with both positive and negative effects on brain function. The impact of stress is strongly influenced by the type and duration of the stressor. In its acute form, stress may be a necessary adaptive mechanism for survival and with only transient changes within the brain. However, severe and/or prolonged stress causes overactivation and dysregulation of the hypothalamic pituitary adrenal (HPA) axis thus inflicting detrimental changes in the brain structure and function. Therefore, chronic stress is often considered a negative modulator of the cognitive functions including the learning and memory processes. Exposure to long-lasting stress diminishes health and increases vulnerability to mental disorders. In addition, stress exacerbates functional changes associated with various brain disorders including Alzheimer’s disease and Parkinson’s disease. The primary purpose of this paper is to provide an overview for neuroscientists who are seeking a concise account of the effects of stress on learning and memory and associated signal transduction mechanisms. This review discusses chronic mental stress and its detrimental effects on various aspects of brain functions including learning and memory, synaptic plasticity, and cognition-related signaling enabled via key signal transduction molecules.