Behavioral and neuroendocrine effects of the exposure to chronic restraint or variable stress in early adolescent rats

Adolescent restraint stress enhances adult nicotine reinforcement in male and female rats

Adolescent stress is a risk factor for the initiation of nicotine use, but whether adolescent stress can enhance nicotine reinforcement when it is initiated later in adulthood is unknown, and it is unclear whether males and females are equally impacted. Therefore, this study assessed physiological responses (body weight and blood serum corticosterone - CORT) to restraint stress (RS) during adolescence (P28-55) or during adulthood (P70-96) in male and female Sprague-Dawley rats. When all subjects reached adulthood (P69 or 110; 2 weeks after termination of stress exposure), they were tested on sucrose preference and intravenous single-dose nicotine (0.03 mg/kg/infusion) self-administration. It was found that all rats displayed a significant CORT response to RS. Importantly, stress during adolescence, but not during adulthood, enhanced subsequent acquisition of nicotine intake tested in adulthood. Although this effect was observed in both sexes, only males displayed reduced body weight gain and adult sucrose preference. Moreover, regardless of stress exposure, females were more stimulated by nicotine, consumed more nicotine overall, and displayed enhanced nicotine seeking. These results suggest that adolescence is a period of heightened sensitivity to the enhancing effect of repeated stress on the susceptibility to develop nicotine dependence later in life in both sexes.

Protective Effects of Kefir Against Unpredictable Chronic Stress Alterations in Mice Central Nervous System, Heart, and Kidney

Kefir is a probiotic mixture with anxiolytic and antioxidant properties. Chronic stress can lead to anxiety disorders and increase oxidative damage in organs such as the heart and kidney. In this study, we examined whether kefir ameliorates the anxiety-like behavior of mice submitted to chronic unpredictable stress (CUS) by modulating brain-derived neurotrophic factor (BDNF) and corticosterone levels and whether kefir modifies the oxidative parameters in the heart and kidney of mice. Male Swiss mice received kefir (0.3 mL/100 g/day) or milk for 30 days (gavage). On the 10th day, the mice were submitted to CUS. Behavioral analysis was performed using the elevated plus maze and forced swimming tests. BDNF levels were analyzed in brain tissues. Heart and kidney superoxide dismutase (SOD), catalase, glutathione (GSH), thiobarbituric acid reactive substances (TBARS), 3-nitrotyrosine, metalloproteinase-2 (MMP-2), and plasma corticosterone were evaluated. Kefir reverted the CUS-induced decrease in the time spent in the open arms, the increase in grooming frequency, and decrease in the head dipping frequency, but not the reduced immobility time. CUS decreased the cerebellum BDNF levels and increased corticosterone levels, which were restored by Kefir. Neither catalase and SOD activities nor GSH, TBARS, 3-nitrotyrosine, and MMP-2 were modified by CUS in the heart. In the kidney, CUS increased 3-nitrotyrosine and MMP-2. Kefir increased the antioxidant defense in the heart and kidney of control and CUS mice. These results suggest that kefir ameliorated CUS-induced anxiety-like behavior by modulating brain BDNF and corticosterone levels. Kefir also increased the antioxidant defense of mice heart and kidney.

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.

Effect of chronic stress on cardiovascular and ventilatory responses activated by both chemoreflex and baroreflex in rats

Chronic stress results in physiological and somatic changes. It has been recognized as a risk factor for several types of cardiovascular dysfunction and changes in autonomic mechanisms, such as baroreflex and chemoreflex activity. However, the effects of different types of chronic stress on these mechanisms are still poorly understood. Therefore, in the present study, we investigated, in adult male rats, the effect of repeated restraint stress (RRS) or chronic variable stress (CVS) on baroreflex, chemoreflex and heart rate variability in a protocol of 14 days of stress sessions. Exposure to RRS and CVS indicated no changes in the basal level of either arterial pressure or heart rate. However, RRS and CVS were able to attenuate sympathovagal modulation and spontaneous baroreflex gain. Additionally, only RRS was able to increase the power of the low-frequency band of the systolic blood pressure spectrum, as well as the slope of linear regression of baroreflex bradycardic and tachycardic responses induced by vasoactive compounds. Additionally, our study is one of the first to show that exposure to RRS and CVS decreases the magnitude of the pressor response and potentiates respiratory responses to chemoreflex activation, which can trigger cardiovascular and respiratory pathologies. Furthermore, the basal respiratory parameters, such as minute ventilation and tidal volume, were significantly decreased by both protocols of chronic stress. However, only CVS increased the basal respiratory frequency. In this way, the findings of the present study demonstrate the impact of chronic stress in terms of not only depressive-like behavior but also alterations of the autonomic baroreflex responses and cardiocirculatory variability (systolic blood pressure and pulse interval).Our results provide evidence that chronic stress promotes autonomic dysregulation, and impairment of baroreflex, chemoreflex and heart rate variability.

Stressor during Early Adolescence in Hyperreactive Female Wistar Kyoto Rats Induces a 'Double Hit' Manifested by Variation in Neurobehaviors and Brain Monoamines

Stress is an additive factor in the development of depressive-like profiles that mainly onsets during adolescence. However, effects of early post-weaning stress on developing brain neurochemical pathways in inducing anxiety- and depressive-like profiles in vulnerable females have not been extensively studied. The Wistar Kyoto (WKY) rat, a putative model of adolescent depression and stress-sensitivity could elucidate the pathophysiology of stress-related depression in vulnerability. Through such an approach, links between inherent risk for predisposition to depression and homotypic stress, as in a 'double hit' would unravel endocrine regulation, interference in developing neural pathways and neurobehaviors. Here, early adolescent WKY female rats were subjected to 1-h physical restraint over 7 days followed by neurobehavioral testing in the elevated plus maze (EPM) and forced swim test (FST). The stressor's effectiveness was assayed by plasma corticosterone (CORT) and altered functioning in depression-implicated brain areas by assaying monoamines/metabolites. Homotypic stress induced an anxiolytic-like response in the EPM with learned helplessness and reduced struggling behavior in FST. Significant elevation in CORT levels (p < 0.05) indicated an upregulated HPA axis. Medial prefrontal cortex, a still maturing brain area, exhibited increased serotonin (5-HT) metabolite (p < 0.01) and turnover rates (p < 0.01) indicative of altered/maladaptive serotonergic functioning. Nucleus accumbens (p < 0.05) and dorsal striatum (p < 0.01) also depicted increased 5-HT metabolite, with the latter also demonstrating reduced Dopamine turnover (p < 0.01) as a result of homotypic stress. Hence, female WKY rats could constitute a diathesis-stress model to study underlying mechanisms of stress-related depression.

The AT1 Receptor Antagonist Losartan Does Not Affect Depressive-Like State and Memory Impairment Evoked by Chronic Stressors in Rats

The present study investigated the effect of the treatment with the angiotensin II type 1 receptor (AT₁) antagonist losartan in the depressive-like state and memory impairment evoked by exposure to either homotypic (i.e., repeated exposure to the same type of stressor) or heterotypic (i.e., exposure to different aversive stimuli) chronic stressors in rats. For this, male Wistar rats were subjected to a 10 days regimen of repeated restraint stress (RRS, homotypic stressor) or chronic variable stress (CVS, heterotypic stressor) while being concurrently treated daily with losartan (30 mg/kg/day, p.o.). Depressive-like state was evaluated by analysis of the alterations considered as markers of depression (decreased sucrose preference and body weight and coat state deterioration), whereas cognitive non-emotional performance was tested using the novel object recognition (NOR) test. Locomotor activity was also evaluated in the open field test. Both RRS and CVS impaired sucrose preference and caused coat state deterioration, whereas only CVS impaired body weight gain. Besides, RRS impaired short-term memory (but not long-term memory) in the NOR test. Neither depressive-like state nor memory impairment evoked by the chronic stressors was affected by the treatment with losartan. Nevertheless, CVS increased the locomotion, which was inhibited by losartan. Taken together, these results provide evidence that the chronic treatment with losartan does not affect the depressive-like state and memory impairment evoked by either homotypic or heterotypic chronic stress regimens in rats.

Alcohol, psychomotor-stimulants and behaviour: methodological considerations in preclinical models of early-life stress

BACKGROUND

In order to assess the risk associated with early-life stress, there has been an increase in the amount of preclinical studies investigating early-life stress. There are many challenges associated with investigating early-life stress in animal models and ensuring that such models are appropriate and clinically relevant.

OBJECTIVES

The purpose of this review is to highlight the methodological considerations in the design of preclinical studies investigating the effects of early-life stress on alcohol and psychomotor-stimulant intake and behaviour.

METHODS

The protocols employed for exploring early-life stress were investigated and summarised. Experimental variables include animals, stress models, and endpoints employed.

RESULTS

The findings in this paper suggest that there is little consistency among these studies and so the interpretation of these results may not be as clinically relevant as previously thought.

CONCLUSION

The standardisation of these simple stress procedures means that results will be more comparable between studies and that results generated will give us a more robust understanding of what can and may be happening in the human and veterinary clinic.

The Anti-Stress Effect of Mentha arvensis in Immobilized Rats

Stress can lead to inflammation, accelerated aging, and some chronic diseases condition. Mentha arvensis (MA) is a traditional medicine having antioxidant and anti-inflammatory activities. The present study investigated the anti-stress role of MA and fermented MA (FMA) extract in immobilized rats. We studied the lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 cells and rats were immobilized for 2 h per day for 14 days using a restraining cage. MA (100 mg/kg) and FMA (100 mg/kg) were orally administered to rats 1 h prior to immobilization. Using high-performance liquid chromatography (HPLC) analysis, we determined the rosmarinic acid content of MA and FMA. The generation of malondialdehyde (MDA) and nitric oxide (NO) in RAW 246.7 cells were suppressed by both MA and FMA. In rats, MA and FMA notably improved the body weight, daily food intake, and duodenum histology. MDA and NO level were gradually decreased by MA and FMA treatment. MA and FMA significantly controlled the stress-related hormones by decreasing corticosterone and β-endorphin and increasing serotonin level. Moreover, protein expression levels of mitogen activated protein kinases (MAPK) and cyclooxygenase-2 (COX-2) were markedly downregulated by MA and FMA. Taken together, MA and FMA could ameliorate immobilized-stress by reducing oxidative stress, regulating stress-related hormones, and MAPK/COX-2 signaling pathways in rats. Particularly, FMA has shown greater anti-stress activities than MA.

Microbial lysate upregulates host oxytocin

Neuropeptide hormone oxytocin has roles in social bonding, energy metabolism, and wound healing contributing to good physical, mental and social health. It was previously shown that feeding of a human commensal microbe Lactobacillus reuteri (L. reuteri) is sufficient to up-regulate endogenous oxytocin levels and improve wound healing capacity in mice. Here we show that oral L. reuteri-induced skin wound repair benefits extend to human subjects. Further, dietary supplementation with a sterile lysate of this microbe alone is sufficient to boost systemic oxytocin levels and improve wound repair capacity. Oxytocin-producing cells were found to be increased in the caudal paraventricular nucleus [PVN] of the hypothalamus after feeding of a sterile lysed preparation of L. reuteri, coincident with lowered blood levels of stress hormone corticosterone and more rapid epidermal closure, in mouse models. We conclude that microbe viability is not essential for regulating host oxytocin levels. The results suggest that a peptide or metabolite produced by bacteria may modulate host oxytocin secretion for potential public or personalized health goals.

Translational relevance of rodent models of hypothalamic-pituitary-adrenal function and stressors in adolescence

Elevations in glucocorticoids that result from environmental stressors can have programming effects on brain structure and function when the exposure occurs during sensitive periods that involve heightened neural development. In recent years, adolescence has gained increasing attention as another sensitive period of development, a period in which pubertal transitions may increase the vulnerability to stressors. There are similarities in physical and behavioural development between humans and rats, and rats have been used effectively as an animal model of adolescence and the unique plasticity of this period of ontogeny. This review focuses on benefits and challenges of rats as a model for translational research on hypothalamic-pituitary-adrenal (HPA) function and stressors in adolescence, highlighting important parallels and contrasts between adolescent rats and humans, and we review the main stress procedures that are used in investigating HPA stress responses and their consequences in adolescence in rats. We conclude that a greater focus on timing of puberty as a factor in research in adolescent rats may increase the translational relevance of the findings.

Immediate and delayed anxiety- and depression-like profiles in the adolescent Wistar-Kyoto rat model of endogenous depression following postweaning social isolation

In order to understand links that exist between inherited risk or predisposition, brain and behavioural development, endocrine regulation and social/environmental stimuli, animal models are crucial. The Wistar-Kyoto (WKY) rat has been shown to have validity as a model of adult and adolescent depression. While sex- and age-specific differences in some of the face, predictive and construct validities of the model such as depression-like behaviours have been established, anhedonia and anxiety using other induced anxiety paradigms such as elevated plus maze remain equivocal. First, post-weaning social isolation effects on inherent and induced anxiety behaviours were tested during two critical time periods, early- and mid-adolescence. Isolation induced immediate effects on novel environment-induced hyperactivity and anxiety-related behaviours. Adolescent WKYs demonstrated reduced 50-kHz ultrasonic vocalizations suggesting agoraphobia-like behaviours. Second, isolated rats, despite being subsequently social-/group-housed demonstrated longer lasting effects on social interaction measures and anhedonia. This establishes that the depression-like profile observed during early- and mid-adolescence persists into late adolescence and early adulthood in WKY. Further, that interventions at a later stage during adolescence may not be able to reverse early adolescent effects in the context of pre-disposition, thus highlighting the irreversibility of being double-hit during critical time periods of brain and behavioural development and maturation.

Exposure to early adversity: Points of cross-species translation that can lead to improved understanding of depression

The relationship between developmental exposure to adversity and affective disorders is reviewed. Adversity discussed herein includes physical and sexual abuse, neglect, or loss of a caregiver in humans. While these stressors can occur at any point during development, the unique temporal relationship to specific depressive symptoms was the focus of discussion. Further influences of stress exposure during sensitive periods can vary by gender and duration of abuse as well. Data from animal studies are presented to provide greater translational and causal understanding of how sensitive periods, different types of psychosocial stressors, and sex interact to produce depressive-like behaviors. Findings from maternal separation, isolation rearing, chronic variable stress, and peer-peer rearing paradigms clarify interpretation about how various depressive behaviors are influenced by age of exposure. Depressive behaviors are broken down into the following categories: mood and affect, anhedonia, energy, working memory, sleep-wake, appetite changes, suicide, and general malaise. Cross-species evidence from humans, nonhuman primates, rats, and mice within each of these categories is discussed. In conclusion, sensitive periods for affective-related behaviors (anxiety, mood, and controllability) occur earlier in life, while other aspects of depression are associated with adversity later during adolescence.

Psychological stress-induced catecholamines accelerates cutaneous aging in mice

Psychological stress may be an important extrinsic factor which influences aging process. However, neither study demonstrated the mechanism by which chronic stress participates in skin aging. Aim of this study was to investigate the effects of chronic psychological stress on mice skin. Mice were daily submitted to rotational stress, for 28 days, until euthanasia. After 28 days, mice were killed and normal skin was analyzed. Macroscopically, dorsum skin of chronically stressed mice presented more wrinkled when compared to that of nonstressed mice. In mice skin, chronic stress increased lipid peroxidation, carbonyl protein content, nitrotyrosine levels, neutrophil infiltration, neutrophil elastase, tissue inhibitor of metalloproteinase-1 and metalloproteinase-8 levels. Nevertheless, chronic stress reduced dermis thickness, collagen type I, fibrilin-1 and elastin protein levels in mice skin. In in vitro assays, murine skin fibroblasts were exposed to elevated epinephrine levels plus inhibitors of reactive oxygen species (ROS) and reactive nitrogen species (RNS), fibroblast activity was evaluated in a short time. In skin fibroblast culture, treatment with inhibitors of ROS and RNS synthesis abolished the increase in carbonyl protein content and lipid peroxide accumulation induced by epinephrine. In conclusion, chronic psychological stress may be an important extrinsic factor, which contributes to skin aging in mice.

Exogenous Tryptophan Promotes Cutaneous Wound Healing of Chronically Stressed Mice through Inhibition of TNF-α and IDO Activation

Stress prolongs the inflammatory response compromising the dermal reconstruction and wound closure. Acute stress-induced inflammation increases indoleamine 2, 3-dioxygenase-stimulated tryptophan catabolism. To investigate the role of indoleamine 2, 3-dioxygenase expression and tryptophan administration in adverse effects of stress on cutaneous wound healing, mice were submitted to chronic restraint stress and treated with tryptophan daily until euthanasia. Excisional lesions were created on each mouse and 5 or 7 days later, the lesions were analyzed. In addition, murine skin fibroblasts were exposed to elevated epinephrine levels plus tryptophan, and fibroblast activity was evaluated. Tryptophan administration reversed the reduction of the plasma tryptophan levels and the increase in the plasma normetanephrine levels induced by stress 5 and 7 days after wounding. Five days after wounding, stress-induced increase in the protein levels of tumor necrosis factor-α and indoleamine 2, 3-dioxygenase, and this was inhibited by tryptophan. Stress-induced increase in the lipid peroxidation and the amount of the neutrophils, macrophages and T cells number was reversed by tryptophan 5 days after wounding. Tryptophan administration inhibited the reduction of myofibroblast density, collagen deposition, re-epithelialization and wound contraction induced by stress 5 days after wounding. In dermal fibroblast culture, the tryptophan administration increased the cell migration and AKT phosphorylation in cells treated with high epinephrine levels. In conclusion, tryptophan-induced reduction of inflammatory response and indoleamine 2, 3-dioxygenase expression may have accelerated cutaneous wound healing of chronically stressed mice.

Inoculation stress hypothesis of environmental enrichment

One hallmark of psychiatric conditions is the vast continuum of individual differences in susceptibility vs. resilience resulting from the interaction of genetic and environmental factors. The environmental enrichment paradigm is an animal model that is useful for studying a range of psychiatric conditions, including protective phenotypes in addiction and depression models. The major question is how environmental enrichment, a non-drug and non-surgical manipulation, can produce such robust individual differences in such a wide range of behaviors. This paper draws from a variety of published sources to outline a coherent hypothesis of inoculation stress as a factor producing the protective enrichment phenotypes. The basic tenet suggests that chronic mild stress from living in a complex environment and interacting non-aggressively with conspecifics can inoculate enriched rats against subsequent stressors and/or drugs of abuse. This paper reviews the enrichment phenotypes, mulls the fundamental nature of environmental enrichment vs. isolation, discusses the most appropriate control for environmental enrichment, and challenges the idea that cortisol/corticosterone equals stress. The intent of the inoculation stress hypothesis of environmental enrichment is to provide a scaffold with which to build testable hypotheses for the elucidation of the molecular mechanisms underlying these protective phenotypes and thus provide new therapeutic targets to treat psychiatric/neurological conditions.

Stress vulnerability during adolescence: comparison of chronic stressors in adolescent and adult rats

OBJECTIVE

This study investigated the physiological and somatic changes evoked by daily exposure to the same type of stressor (homotypic) or different aversive stressor stimuli (heterotypic) in adolescent and adult rats, with a focus on cardiovascular function. The long-term effects of stress exposure during adolescence were also investigated longitudinally.

METHODS

Male Wistar rats were exposed to repeated restraint stress (RRS, homotypic) or chronic variable stress (CVS, heterotypic).

RESULTS

Adrenal hypertrophy, thymus involution, and elevated plasma glucocorticoid were observed only in adolescent animals, whereas reduction in body weight was caused by both stress regimens in adults. CVS increased mean arterial pressure (adolescent: p = .001; adult: p = .005) and heart rate (HR; adolescent: p = .020; adult: p = .011) regardless of the age, whereas RRS increased blood pressure selectively in adults (p = .001). Rest tachycardia evoked by CVS was associated with increased cardiac sympathetic activity in adults, whereas a decreased cardiac parasympathetic activity was observed in adolescent animals. Changes in cardiovascular function and cardiac autonomic activity evoked by both CVS and RRS were followed by alterations in baroreflex activity and vascular reactivity to vasoconstrictor and vasodilator agents in adolescent adult animals. Except for the circulating glucocorticoid change, all alterations observed during adolescence were reversed in adulthood.

CONCLUSIONS

These findings suggest a stress vulnerability of adolescents to somatic and neuroendocrine effects regardless of stress regimen. Our results indicated an age-stress type-specific influence in stress-evoked cardiovascular/autonomic changes. Data suggest minimal consequences in adulthood of stress during adolescence.

Immediate and long-term effects of psychological stress during adolescence in cardiovascular function: comparison of homotypic vs heterotypic stress regimens

Adolescence has been proposed as an ontogenic period of vulnerability to stress. Nevertheless, the impact of stressful events during adolescence in cardiovascular activity is poorly understood. Therefore, the purpose of this study was to investigate the immediate and long-lasting effects of exposure to stressful events during adolescence in cardiovascular function of rats. To this end, we compared the impact of 10-days exposure to two chronic stress protocols: the repeated restraint stress (RRS, homotypic) and chronic variable stress (CVS, heterotypic). Independent groups of animals were tested 24h (immediate) or three weeks (long-lasting) following completion of stress period. Exposure to CVS, but not RRS, during adolescence increased basal HR values without affecting arterial pressure, which was followed by augmented power of oscillatory component at low frequency (sympathetic-related) of the pulse interval (PI). RRS enhanced variance of the PI with an increase in the power of both low and high (parasympathetic-related) frequency components. RRS also increased the baroreflex gain. Neither RRS nor CVS affected systolic arterial pressure variability. The RRS-evoked changes in PI variability were long-lasting and persisted into adulthood while all alterations evoked by the CVS were reversed in adulthood. These findings indicate a stress type-specific influence in immediate and long-term effects of stress during adolescence in cardiovascular function. While immediate changes in cardiovascular function were mainly observed following CVS, long-lasting autonomic consequences in adulthood were observed only in animals exposed to RRS during adolescence.

Influence of a probiotic lactobacillus strain on the intestinal ecosystem in a stress model mouse

Daily exposure to stressful situations affects the health of humans and animals. It has been shown that psychological stress affects the immune system and can exacerbate diseases. Probiotics can act as biological immunomodulators in healthy people, increasing both intestinal and systemic immune responses. The use of probiotics in stress situations may aid in reinforcing the immune system. The aim of this study was to evaluate the effect of a probiotic bacterium on the gut immune system of mice that were exposed to an experimental model of stress induced by food and mobility restriction. The current study focused on immune cells associated with the lamina propria of the intestine, including CD4+ and CD8+ T lymphocytes, CD11b+ macrophages, CD11c+ dendritic cells, and IgA+ B lymphocytes, as well as the concentrations of secretory IgA (S-IgA) and cytokine interferon gamma (INF-γ in intestinal fluid. We also evaluated the probiotic's influence on the gut microbiota. Probiotic administration increased IgA producing cells, CD4+ cells in the lamina propria of the small intestine, and S-IgA in the lumen; it also reduced the levels of IFN-γ that had increased during stress and improved the intestinal microbiota as measured by an increase in the lactobacilli population. The results obtained from administration of the probiotic to stressed mice suggest that the use of food containing these microorganisms may work as a palliative to reinforce the immune system.

Sensitization of restraint-induced corticosterone secretion after chronic restraint in rats: involvement of 5-HT₇ receptors

Serotonin (5-HT) modulates the hypothalamic-pituitary-adrenal (HPA) axis response to stress. We examined the effect of chronic restraint stress (CRS; 20 min/day) as compared to control (CTRL) conditions for 14 days, on: 1) restraint-induced ACTH and corticosterone (CORT) secretion in rats pretreated with vehicle or SB-656104 (a 5-HT₇ receptor antagonist); 2) 5-HT₇ receptor-like immunoreactivity (5-HT₇-LI) and protein in the hypothalamic paraventricular nucleus (PVN) and adrenal glands (AG); 3) baseline levels of 5-HT and 5-hydroxyindolacetic acid (5-HIAA), and 5-HIAA/5-HT ratio in PVN and AG; and 4) 5-HT-like immunoreactivity (5-HT-LI) in AG and tryptophan hydroxylase (TPH) protein in PVN and AG. On day 15, animals were subdivided into Treatment and No treatment groups. Treatment animals received an i.p. injection of vehicle or SB-656104; No Treatment animals received no injection. Sixty min later, Treatment animals were either decapitated with no further stress (0 min) or submitted to acute restraint (10, 30, 60 or 120 min); hormone serum levels were measured. No Treatment animals were employed for the rest of measurements. CRS decreased body weight gain and increased adrenal weight. In CTRL animals, acute restraint increased ACTH and CORT secretion in a time of restraint-dependent manner; both responses were inhibited by SB-656104. Exposure to CRS abolished ACTH but magnified CORT responses to restraint as compared to CTRL conditions; SB-656104 had no effect on ACTH levels but significantly inhibited sensitized CORT responses. In CTRL animals, 5-HT₇-LI was detected in magnocellular and parvocellular subdivisions of PVN and sparsely in adrenal cortex. Exposure to CRS decreased 5-HT₇-LI and protein in the PVN, but increased 5-HT₇-LI in the adrenal cortex and protein in whole AG. Higher 5-HT and 5-HIAA levels were detected in PVN and AG from CRS animals but 5-HIAA/5-HT ratio increased in AG only. Finally, whereas 5-HT-LI was sparsely observed in the adrenal cortex of CTRL animals, it strongly increased in the adrenal cortex of CRS animals. No TPH protein was detected in AG from both animal groups. Results suggest that CRS promotes endocrine disruption involving decreased ACTH and sensitized CORT responses to acute restraint. This phenomenon may be associated with increased function and expression of 5-HT₇ receptors as well as 5-HT turnover in AG.

Effects of lactational and/or in utero exposure to environmental contaminants on the glucocorticoid stress-response and DNA methylation of the glucocorticoid receptor promoter in male rats

Perinatal events can reprogram the hypothalamo-pituitary-adrenal axis for the entire lifespan leading to abnormal glucocorticoid stress-response (GSR) in adulthood: a phenomenon reported to be mediated by changes in DNA methylation of the glucocorticoid receptor (GR) gene promoter. We examined whether in utero and/or lactational exposure to mixtures of environmental contaminants can also induce abnormal GSR during adulthood. The experiment included nine treatment groups. From gestation day (GD) 0 until postnatal day (PND) 20, dams were fed daily with a cookie laced with corn oil (control) or a chemical mixture (M) [polychlorinated biphenyls (PCBs), organochlorine pesticides, and methylmercury] at 0.5 or 1.0mg/kg/day (0.5M, and M). At birth, some control (C) and M litters were cross-fostered to create four groups with the following in utero/postnatal exposure: C/C, M/C, C/M, M/M. Other dams received 1.8ng/kg/day of a mixture of aryl hydrocarbon receptor (AhR) agonists (non-ortho PCBs, PC-dibenzodioxins and PC-dibenzofurans) without or with 0.5M (0.5MAhR). In adult male offspring the abundance of GR in treated groups was not different from the control, but the AhR and M groups were significantly different from each other with opposite effects in the hippocampus and liver. There was no change in DNA methylation of the GR promoter (exon-17 and -110). Abnormal GSRs were detected in the AhR, 0.5MAhR, CM, and MM groups. The literature associates abnormal GSR with metabolic and mental health impairments, thus these results support further investigation of the influence of developmental exposure to environmental contaminants and predisposition to stress-induced diseases.

Psychological stress in adolescent and adult mice increases neuroinflammation and attenuates the response to LPS challenge

Background

There is ample evidence that psychological stress adversely affects many diseases. Recent evidence has shown that intense stressors can increase inflammation within the brain, a known mediator of many diseases. However, long-term outcomes of chronic psychological stressors that elicit a neuroinflammatory response remain unknown.

Methods

To address this, we have modified previously described models of rat/mouse predatory stress (PS) to increase the intensity of the interaction. We postulated that these modifications would enhance the predator-prey experience and increase neuroinflammation and behavioral dysfunction in prey animals. In addition, another group of mice were subjected to a modified version of chronic unpredictable stress (CUS), an often-used model of chronic stress that utilizes a combination of stressors that include physical, psychological, chemical, and other. The CUS model has been shown to exacerbate a number of inflammatory-related diseases via an unknown mechanism. Using these two models we sought to determine: 1) whether chronic PS or CUS modulated the inflammatory response as a proposed mechanism by which behavioral deficits might be mediated, and 2) whether chronic exposure to a pure psychological stressor (PS) leads to deficits similar to those produced by a CUS model containing psychological and physical stressors. Finally, to determine whether acute PS has neuroinflammatory consequences, adult mice were examined at various time-points after PS for changes in inflammation.

Results

Adolescent mice subjected to chronic PS had increased basal expression of inflammation within the midbrain. CUS and chronic PS mice also had an impaired inflammatory response to a subsequent lipopolysaccharide challenge and PS mice displayed increased anxiety- and depressive-like behaviors following chronic stress. Finally, adult mice subjected to acute predatory stress had increased gene expression of inflammatory factors.

Conclusion

Our results demonstrate that predatory stress, an ethologically relevant stressor, can elicit changes in neuroinflammation and behavior. The predatory stress model may be useful in elucidating mechanisms by which psychological stress modulates diseases with an inflammatory component.