Glucocorticoid signaling and stress-related limbic susceptibility pathway: about receptors, transcription machinery and microRNA

Mechanisms underlying stress effects on the brain: Basic concepts and clinical implications

Chronic stress impacts the brain through complex physiological, neurological, and immunological responses. The stress response involves the activation of the sympathetic-adrenal-medullary (SAM) system and the hypothalamic-pituitary-adrenal (HPA) axis, releasing stress hormones like norepinephrine and cortisol. While these responses are adaptive short-term, chronic stress disrupts homeostasis, increasing the risk of cardiovascular diseases, neurodegenerative disorders, and psychiatric conditions such as depression. This dysregulation is linked to persistent neuroinflammation, oxidative stress, and neurotransmitter imbalances involving dopamine and serotonin, impairing neuroplasticity and leading to structural changes in critical brain areas, such as the hippocampus and prefrontal cortex. Moreover, stress affects gene expression, particularly neuroinflammatory pathways, contributing to long-term cognitive function and emotional regulation alterations. Advancements in neuroimaging and molecular techniques, including MRI, PET, and SPECT, hold promise for identifying biomarkers and better understanding stress-induced brain changes. These insights are critical for developing targeted interventions to mitigate the adverse effects of chronic stress on brain health.

Caffeic acid differentially modulates behavior and neurochemicals in chronic unpredictable mild stress and dexamethasone induced models of depression

In the present study authors studied the effect of caffeic acid (CA) in chronic unpredictable mild stress (CUMS) and dexamethasone (DEXA) model of depression. CUMS (21 days) and DEXA (1.5 mg/kg × 21 days) was used for the induction of depression and anxiety related behavior. Locomotor activity was determined using actophotometer. Depression related behavior was determined using tail suspension test (TST) and forced swim test (FST) whereas for the determination of anxiety related behavior elevated plus maze (EPM) test was used. Following behavioral studies, mice were sacrificed by decapitation method. Hippocampus was dissected and was used for the neurochemical assays including 5-HT (serotonin), glutamate, nitrite and gamma-aminobutyric acid (GABA). The results obtained suggested that the CA (25-100 mg/kg, i.p.) did not affect the activity count in CUMS exposed and DEXA treated mice. CA (50 mg/kg) evoked anxiogenic reactions in CUMS model by increasing the hippocampal nitrite and glutamate level while CA (50 mg/kg) exerted anxiolysis in DEXA model by reducing the level of 5-HT. In CUMS model, CA exerted antidepressant like effect by increasing the hippocampal nitric oxide (NO) level, in DEXA model CA exerted antidepressant like effect by reducing the hippocampal glutamate level. CA failed to reverse DEXA mediated nNOS inhibition and therefore decreases hippocampal glutamate level to exert antidepressant like effect. Thus, CA modulate anxiety and depression related neurobehavioral alterations in both CUMS and DEXA models.

From Ligands to Behavioral Outcomes: Understanding the Role of Mineralocorticoid Receptors in Brain Function

Stress is a normal response to situational pressures or demands. Exposure to stress activates the hypothalamic-pituitary-adrenal (HPA) axis and leads to the release of corticosteroids, which act in the brain via two distinct receptors: mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Persistent HPA axis overactivation or dysregulation can disrupt an individual's homeostasis, thereby contributing to an increased risk for mental illness. On the other hand, successful coping with stressful events involves adaptive and cognitive processes in the brain that render individuals more resilient to similar stressors in the future. Here we review the role of the MR in these processes, starting with an overview of the physiological structure, ligand binding, and expression of MR, and further summarizing its role in the brain, its relevance to psychiatric disorders, and related rodent studies. Given the central role of MR in cognitive and emotional functioning, and its importance as a target for promoting resilience, future research should investigate how MR modulation can be used to alleviate disturbances in emotion and behavior, as well as cognitive impairment, in patients with stress-related psychiatric disorders.

Glucocorticoid Effect in Cancer Patients

The use of glucocorticoids is very varied in the context of cancer patients and includes the treatment of symptoms related to cancer, but also the management of the most common side effects of antitumor treatments or adverse events related to the immune system. There is a quantity of experimental evidence demonstrating that cancer cells are immunogenic. However, the effective activation of anticancer T cell responses closely depends on an efficient antigen presentation carried out by professional antigen-presenting cells such as dendritic cells (DCs). The classic strategies to improve the medical management of inflammation are aimed at exacerbating the host's immune response. Although successful in treating a number of diseases, these drugs have limited efficacy and variable responses can lead to unpredictable results. The ideal therapy should reduce inflammation without inducing immunosuppression and remains a challenge for healthcare personnel.

Heterogeneity in major depressive disorder: The need for biomarker-based personalized treatments

Major Depressive Disorder (MDD) or depression is a pathological mental condition affecting millions of people worldwide. Identification of objective biological markers of depression can provide for a better diagnostic and intervention criteria; ultimately aiding to reduce its socioeconomic health burden. This review provides a comprehensive insight into the major biomarker candidates that have been implicated in depression neurobiology. The key biomarker categories are covered across all the "omics" levels. At the epigenomic level, DNA-methylation, non-coding RNA and histone-modifications have been discussed in relation to depression. The proteomics system shows great promise with inflammatory markers as well as growth factors and neurobiological alterations within the endocannabinoid system. Characteristic lipids implicated in depression together with the endocrine system are reviewed under the metabolomics section. The chapter also examines the novel biomarkers for depression that have been proposed by studies in the microbiome. Depression affects individuals differentially and explicit biomarkers identified by robust research criteria may pave the way for better diagnosis, intervention, treatment, and prediction of treatment response.

Sex differences in the vulnerability of the hippocampus to prenatal stress

Distressing events during pregnancy that engage activity of the body's endocrine stress response have been linked with later life cognitive deficits in offspring and associated with developmental changes in cognitive-controlling neural regions. Interestingly, prenatal stress (PS)-induced alterations have shown some sex specificity. Here, we review the literature of animal studies examining sex-specific effect of physical PS on the function and structure of the hippocampus as hippocampal impairments likely underlie PS-associated deficits in learning and memory. Furthermore, the connectivity between the hypothalamic-pituitary-adrenal (HPA) axis and the hippocampus as well as the heavy presence of glucocorticoid receptors (GRs) in the hippocampus suggests this structure plays an important role in modulation of activity within stress circuitry in a sex-specific pattern. We hope that better understanding of sex-specific, PS-related hippocampal impairment will assist in uncovering the molecular mechanisms behind sex-based risk factors in PS populations across development, and perhaps contribute to greater precision in management of cognitive disturbances in this vulnerable population.

11β-Hydroxysteroid Dehydrogenase Type 1 as a Potential Treatment Target in Cardiovascular Diseases

Glucocorticoids (GCs) belong to the group of steroid hormones. Their representative in humans is cortisol. GCs are involved in most physiological processes of the body and play a significant role in important biological processes, including reproduction, growth, immune responses, metabolism, maintenance of water and electrolyte balance, functioning of the central nervous system and the cardiovascular system. The availability of cortisol to the glucocorticoid receptor is locally controlled by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Evidence of changes in intracellular GC metabolism in the pathogenesis of obesity, metabolic syndrome (MetS) and cardiovascular complications highlights the role of selective 11β-HSD1 inhibition in the pharmacotherapy of these diseases. This paper discusses the role of 11β-HSD1 in MetS and its cardiovascular complications and the importance of selective inhibition of 11β-HSD1.

Corticosterone as a Potential Confounding Factor in Delineating Mechanisms Underlying Ketamine's Rapid Antidepressant Actions

Recent research into the rapid antidepressant effect of subanesthetic doses of ketamine have identified a series of relevant protein cascades activated within hours of administration. Prior to, or concurrent with, these activation cascades, ketamine treatment generates dissociative and psychotomimetic side effects along with an increase in circulating glucocorticoids. In rats, we observed an over 3-fold increase in corticosterone levels in both serum and brain tissue, within an hour of administration of low dose ketamine (10 mg/kg), but not with (2R, 6R)-hydroxynorketamine (HNK) (10 mg/kg), a ketamine metabolite shown to produce antidepressant-like action in rodents without inducing immediate side-effects. Hippocampal tissue from ketamine, but not HNK, injected animals displayed a significant increase in the expression of sgk1, a downstream effector of glucocorticoid receptor signaling. To examine the role conscious sensation of ketamine's side effects plays in the release of corticosterone, we assessed serum corticosterone levels after ketamine administration while under isoflurane anesthesia. Under anesthesia, ketamine failed to increase circulating corticosterone levels relative to saline controls. Concurrent with its antidepressant effects, ketamine generates a release of glucocorticoids potentially linked to disturbing cognitive side effects and the activation of distinct molecular pathways which should be considered when attempting to delineate the molecular mechanisms of its antidepressant function.

Trans fat intake during pregnancy or lactation increases anxiety-like behavior and alters proinflammatory cytokines and glucocorticoid receptor levels in the hippocampus of adult offspring

Changes in dietary habits, including the increased consumption of processed foods, rich in trans fatty acids (TFA), have profound effects on offspring health in later life. Thus, this study aimed to assess the influence of maternal trans fat intake during pregnancy or lactation on anxiety behavior, as well as markers of inflammation, oxidative stress, and expression of glucocorticoid receptors (GR) of adult male offspring. Female Wistar rats were supplemented daily with soybean oil/fish oil (SO/FO) or hydrogenated vegetable fat (HVF) by oral gavage (3.0 g/kg body weight) during pregnancy or lactation. After weaning, male offspring received only standard diet. On the postnatal day 60, anxiety-like symptoms were assessed, the plasma was collected for the quantification of cytokines levels and the hippocampus removed for biochemical and molecular analysis. Our findings have evidenced that offspring from HVF-supplemented dams during pregnancy or lactation showed significantly greater levels of anxiety behavior. HVF supplementation increased plasma levels of proinflammatory cytokines and these levels were higher in the lactation period. In contrast, HVF supplementation decreased plasma levels of IL-10 in relation to SO/FO in both periods. Biochemical evaluations showed higher reactive species generation, protein carbonyl levels and catalase activity in offspring from HVF-supplemented dams during lactation. In addition, offspring from HVF-supplemented dams showed decreased GR expression in both supplemented periods. Together, these data indicate that consumption of TFA in different periods of development may increase anxiety-like behavior at least in part via alterations in proinflammatory and anti-inflammatory cytokine levels and GR expression in limbic brain regions.

Mild and Moderate Traumatic Brain Injury and Repeated Stress Affect Corticosterone in the Rat

Traumatic brain injury (TBI) survivors suffer from a range of morbidities, including post-traumatic endocrinopathies that can cause physical and mental changes in patients, greatly compromising quality of life. This study tested the hypothesis that mild and moderate diffuse TBI leads to chronic deficiencies in corticosterone (CORT) regulation following repeated exposure to restraint stress over time. Young adult male rats (n = 9–11/group) were subjected to mild or moderate TBI induced by midline fluid percussion injury (mFPI) or control sham surgery. At 6 and 24 h post-injury, both mild and moderate TBI resulted in elevated resting plasma CORT levels compared with uninjured shams. Independent of TBI severity, all rats had lower resting plasma CORT levels at 7, 14, 28, and 54 days post-injury compared with pre-surgery baseline CORT. Circulating levels of CORT were also evaluated under restraint stress and in response to dexamethasone (DEX), a synthetic glucocorticoid. Independent of TBI severity, restraint stress elevated CORT at 30, 60, and 90 min post-stressor initiation at all post-injury time-points. A blunted CORT response to restraint stress was observed with lower CORT levels after restraint at 28 and 54 days compared with 7 days post-injury (DPI), indicative of habituation to the stressor. A high dose of DEX lowered CORT levels at 90 min post-restraint stress initiation compared with low-dose DEX, independent of TBI severity. These results support TBI-induced CORT dysregulation at acute time-points, but additional studies that investigate the onset and progression of endocrinopathies, controlling for habituation to repeated restraint stress, are needed to inform the diagnosis and treatment of such morbidities in TBI survivors.

Stress & executive functioning: A review considering moderating factors

A multitude of studies investigating the effects of stress on cognition has produced an inconsistent picture on whether - and under which conditions - stress has advantageous or disadvantageous effects on executive functions (EF). This review provides a short introduction to the concept of stress and its neurobiology, before discussing the need to consider moderating factors in the association between stress and EF. Three core domains are described and discussed in relation to the interplay between stress and cognition: the influence of different paradigms on physiological stress reactivity, individual differences in demographic and biological factors, and task-related features of cognitive tasks. Although some moderating variables such as the endocrine stress response have frequently been considered in single studies, no attempt of a holistic overview has been made so far. Therefore, we propose a more nuanced and systematic framework to study the effects of stress on executive functioning, comprising a holistic overview from the induction of stress, via biological mechanisms and interactions with individual differences, to the influence of stress on cognitive performance.

The human stress response

The human stress response has evolved to maintain homeostasis under conditions of real or perceived stress. This objective is achieved through autoregulatory neural and hormonal systems in close association with central and peripheral clocks. The hypothalamic-pituitary-adrenal axis is a key regulatory pathway in the maintenance of these homeostatic processes. The end product of this pathway - cortisol - is secreted in a pulsatile pattern, with changes in pulse amplitude creating a circadian pattern. During acute stress, cortisol levels rise and pulsatility is maintained. Although the initial rise in cortisol follows a large surge in adrenocorticotropic hormone levels, if long-term inflammatory stress occurs, adrenocorticotropic hormone levels return to near basal levels while cortisol levels remain raised as a result of increased adrenal sensitivity. In chronic stress, hypothalamic activation of the pituitary changes from corticotropin-releasing hormone-dominant to arginine vasopressin-dominant, and cortisol levels remain raised due at least in part to decreased cortisol metabolism. Acute elevations in cortisol levels are beneficial to promoting survival of the fittest as part of the fight-or-flight response. However, chronic exposure to stress results in reversal of the beneficial effects, with long-term cortisol exposure becoming maladaptive, which can lead to a broad range of problems including the metabolic syndrome, obesity, cancer, mental health disorders, cardiovascular disease and increased susceptibility to infections. Neuroimmunoendocrine modulation in disease states and glucocorticoid-based therapeutics are also discussed.

Social defeat-induced Cingulate gyrus immediate-early gene expression and anxiolytic-like effect depend upon social rank

Social hierarchy is considered to impart an adaptive advantage to the species by reducing long-term conflict between conspecifics. While social stratification is frequently established via stress-inducing stimuli, the subsequent integration of individuals into the hierarchy may attenuate anxiety. Presently, we hypothesized that repeated reinforcement of murine social hierarchy in the dominant-submissive relationship (DSR) food-competition test would engender divergent neuroplastic changes mediating both social and anxiety-like behavior among selectively-bred Dominant (Dom) and Submissive (Sub) mice. Two weeks of repeated respective social victory or defeat reduced serum corticosterone levels of both Dom and Sub mice, whereas socially-defeated Sub mice demonstrated markedly greater exploration of the open arms of the elevated plus maze (EPM). At the same time, social victory led to markedly greater expression of the immediate-early genes (IEGs) c-Jun and EGR-1 in the lateral septal nucleus (LSN) among Dom mice, in contrast with defeated Sub counterparts which demonstrated four-fold greater IEG expression in the cingulate gyrus (Cg). These findings point towards involvement of the Cg in the anxiety-like effect among Sub mice after repeated social defeat, and suggest stabilization of the social hierarchy to attenuate the stress-inducing nature of social interaction, particularly for subordinates. Further study of the potentially anxiolytic-like effects of Cg activity should shed light upon the functional significance of the Cg in social interaction, social hierarchical sorting and anxiety.

Diurnal oscillations in human salivary microRNA and microbial transcription: Implications for human health and disease

The microbiome plays a vital role in human health and disease. Interaction between human hosts and the microbiome occurs through a number of mechanisms, including transcriptomic regulation by microRNA (miRNA). In animal models, circadian variations in miRNA and microbiome elements have been described, but patterns of co-expression and potential diurnal interaction in humans have not. We investigated daily oscillations in salivary miRNA and microbial RNA to explore relationships between these components of the gut-brain-axis and their implications in human health. Nine subjects provided 120 saliva samples at designated times, on repeated days. Samples were divided into three sets for exploration and cross-validation. Identification and quantification of host miRNA and microbial RNA was performed using next generation sequencing. Three stages of statistical analyses were used to identify circadian oscillators: 1) a two-way analysis of variance in the first two sample sets identified host miRNAs and microbial RNAs whose abundance varied with collection time (but not day); 2) multivariate modeling identified subsets of these miRNAs and microbial RNAs strongly-associated with collection time, and evaluated their predictive ability in an independent hold-out sample set; 3) regulation of circadian miRNAs and microbial RNAs was explored in data from autistic children with disordered sleep (n = 77), relative to autistic peers with typical sleep (n = 63). Eleven miRNAs and 11 microbial RNAs demonstrated consistent diurnal oscillation across sample sets and accurately predicted collection time in the hold-out set. Associations among five circadian miRNAs and four circadian microbial RNAs were observed. We termed the 11 miRNAs CircaMiRs. These CircaMiRs had 1,127 predicted gene targets, with enrichment for both circadian gene targets and metabolic signaling processes. Four CircaMiRs had "altered" expression patterns among children with disordered sleep. Thus, novel and correlated circadian oscillations in human miRNA and microbial RNA exist and may have distinct implications in human health and disease.

Social dominance predicts hippocampal glucocorticoid receptor recruitment and resilience to prenatal adversity

The developing fetus is highly sensitive to prenatal stress, which may alter Hypothalamic-Pituitary-Adrenal (HPA) axis programming and increase the risk of behavioral disorders. There is high variability among the human population, wherein many offspring of stressed pregnancies display resilience to adversity, while the remainder displays vulnerability. In order to identify biological substrates mediating between resilience or vulnerability to prenatal adversity, we exposed stress-resistant Dominant (Dom) and stress-sensitive Submissive (Sub) mice to mild prenatal restraint stress (PRS, 45 min on gestational days (GD) 15, 16 and 17). We hypothesized that PRS would differentially alter prenatal programming of limbic regions regulating the HPA axis and affect among Dom and Sub offspring. Indeed, PRS increased Sub offspring’s serum corticosterone, and exaggerated their anxiety- and depressive-like behavior, while Dom offspring remained resilient to the hormonal and behavioral consequences of PRS. Moreover, PRS exposure markedly facilitated glucocorticoid receptor (GR) recruitment to the hippocampus among Dom mice in response to restraint stress, which may be responsible for their resilience to stressful challenge. These findings suggest proclivity to adaptive or maladaptive prenatal programming of hippocampal GR recruitment to be inheritable and predictable by social dominance or submissiveness.

Maternal hormonal milieu influence on fetal brain development

An adverse maternal hormonal environment during pregnancy can be associated with abnormal brain growth. Subtle changes in fetal brain development have been observed even for maternal hormone levels within the currently accepted physiologic ranges. In this review, we provide an update of the research data on maternal hormonal impact on fetal neurodevelopment, giving particular emphasis to thyroid hormones and glucocorticoids. Thyroid hormones are required for normal brain development. Despite serum TSH appearing to be the most accurate indicator of thyroid function in pregnancy, maternal serum free T4 levels in the first trimester of pregnancy are the major determinant of postnatal psychomotor development. Even a transient period of maternal hypothyroxinemia at the beginning of neurogenesis can confer a higher risk of expressive language and nonverbal cognitive delays in offspring. Nevertheless, most recent clinical guidelines advocate for targeted high-risk case finding during first trimester of pregnancy despite universal thyroid function screening. Corticosteroids are determinant in suppressing cell proliferation and stimulating terminal differentiation, a fundamental switch for the maturation of fetal organs. Not surprisingly, intrauterine exposure to stress or high levels of glucocorticoids, endogenous or synthetic, has a molecular and structural impact on brain development and appears to impair cognition and increase anxiety and reactivity to stress. Limbic regions, such as hippocampus and amygdala, are particularly sensitive. Repeated doses of prenatal corticosteroids seem to have short-term benefits of less respiratory distress and fewer serious health problems in offspring. Nevertheless, neurodevelopmental growth in later childhood and adulthood needs further clarification. Future studies should address the relevance of monitoring the level of thyroid hormones and corticosteroids during pregnancy in the risk stratification for impaired postnatal neurodevelopment.

The role of microRNAs in glucocorticoid action

Glucocorticoids (GCs) are steroids with profound anti-inflammatory and immunomodulatory activities. Synthetic GCs are widely used for managing chronic inflammatory and autoimmune conditions, as immunosuppressants in transplantation, and as anti-tumor agents in certain hematological cancers. However, prolonged GC exposure can cause adverse effects. A detailed understanding of GCs' mechanisms of action may enable harnessing of their desirable actions while minimizing harmful effects. Here, we review the impact on the GC biology of microRNAs, small non-coding RNAs that post-transcriptionally regulate gene expression. Emerging evidence indicates that microRNAs modulate GC production by the adrenal glands and the cells' responses to GCs. Furthermore, GCs influence cell proliferation, survival, and function at least in part by regulating microRNA expression. We propose that the beneficial effects of GCs may be enhanced through combination with reagents targeting specific microRNAs.

The role of genetic variation in the glucocorticoid receptor (NR3C1) and mineralocorticoid receptor (NR3C2) in the association between cortisol response and cognition under acute stress

Although HPA - axis reactivity has repeatedly been related to cognitive functioning, ambiguity remains regarding the direction of the effect, i.e. whether it benefits or impairs functioning. Genetic factors that contribute to HPA - axis reactivity on the one hand and to cognitive functioning on the other could therefore help clarify the association between stress and cognition. We genotyped 10 single nucleotide polymorphisms (SNPs) on the NR3C1 gene (rs10482682, rs33389, rs10482633, rs10515522, rs2963156, rs4128428, rs9324918, rs41423247, rs6189, rs10052957) coding for the glucocorticoid receptor (GR) and 4 SNPs on the NR3C2 gene (rs6810951, rs4635799, rs11099695, rs2070950) coding for the mineralocorticoid receptor (MR) and required N=126 healthy males to perform tasks assessing attention and reasoning before and after experiencing an acute laboratory stressor (the Socially Evaluated Cold Pressor Test, SECPT). Haplotype analyses revealed significant effects of NR3C1 (p=0.011) and NR3C2 (p=0.034) on cortisol stress response. NR3C2 also influenced attentional performance via an interaction with stress-induced cortisol response (p<0.001). Neither NR3C1 haplotype nor NR3C2 haplotype was associated with reasoning abilities. Results suggest that the association between stress induced cortisol reactivity and cognition strongly depends on genetic variation. The idea of an optimal arousal level depending on stress reactivity and genetic disposition is discussed.

Nuclear deterrents: Intrinsic regulators of IL-1β-induced effects on hippocampal neurogenesis

Hippocampal neurogenesis, the process by which new neurons are born and develop into the host circuitry, begins during embryonic development and persists throughout adulthood. Over the last decade considerable insights have been made into the role of hippocampal neurogenesis in cognitive function and the cellular mechanisms behind this process. Additionally, an increasing amount of evidence exists on the impact of environmental factors, such as stress and neuroinflammation on hippocampal neurogenesis and subsequent impairments in cognition. Elevated expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus is established as a significant contributor to the neuronal demise evident in many neurological and psychiatric disorders and is now known to negatively regulate hippocampal neurogenesis. In order to prevent the deleterious effects of IL-1β on neurogenesis it is necessary to identify signalling pathways and regulators of neurogenesis within neural progenitor cells that can interact with IL-1β. Nuclear receptors are ligand regulated transcription factors that are involved in modulating a large number of cellular processes including neurogenesis. In this review we focus on the signalling mechanisms of specific nuclear receptors involved in regulating neurogenesis (glucocorticoid receptors, peroxisome proliferator activated receptors, estrogen receptors, and nuclear receptor subfamily 2 group E member 1 (NR2E1 or TLX)). We propose that these nuclear receptors could be targeted to inhibit neuroinflammatory signalling pathways associated with IL-1β. We discuss their potential to be therapeutic targets for neuroinflammatory disorders affecting hippocampal neurogenesis and associated cognitive function.

Genomic and epigenomic mechanisms of glucocorticoids in the brain

Following the discovery of glucocorticoid receptors in the hippocampus and other brain regions, research has focused on understanding the effects of glucocorticoids in the brain and their role in regulating emotion and cognition. Glucocorticoids are essential for adaptation to stressors (allostasis) and in maladaptation resulting from allostatic load and overload. Allostatic overload, which can occur during chronic stress, can reshape the hypothalamic-pituitary-adrenal axis through epigenetic modification of genes in the hippocampus, hypothalamus and other stress-responsive brain regions. Glucocorticoids exert their effects on the brain through genomic mechanisms that involve both glucocorticoid receptors and mineralocorticoid receptors directly binding to DNA, as well as by non-genomic mechanisms. Furthermore, glucocorticoids synergize both genomically and non-genomically with neurotransmitters, neurotrophic factors, sex hormones and other stress mediators to shape an organism's present and future responses to a stressful environment. Here, we discuss the mechanisms of glucocorticoid action in the brain and review how glucocorticoids interact with stress mediators in the context of allostasis, allostatic load and stress-induced neuroplasticity.

The effects of microRNAs on glucocorticoid responsiveness

PURPOSE

Glucocorticoids (GCs) are of wide usage in the clinical treatment of lymphoblastic malignancies such as acute lymphoblastic leukemia. However, individually distinctive responsiveness to the GC therapy may attenuate their clinical efficacy, and more reliable predictor for GC resistance is still eagerly needed. Recent studies indicate that microRNAs (miRNAs), which demonstrate regulatory functions targeting mRNAs during the post-transcription, involved in the regulation of GCs sensitivity through several mechanisms, especially adjusting the magnitude of GC receptors (GRs), which mediates the cellular effects of GCs and plays a pivotal role in GCs sensitivity, inspiring that special miRNAs pattern could serve as the biomarkers to predict GC sensitivity and bring forth potential strategies for overcoming drug resistance. In this review, we discuss related miRNAs and their diverse effects exerted on multifaceted complexity of GCs responsiveness for further exploiting the molecular mechanism of GC resistance and future construction of the molecular diagnostic method and reverse GC resistance.

METHODS

We have reviewed and searched for eligible literature relating to the effects of microRNAs on GC responsiveness from systematic PubMed searches.

RESULTS

GC response can be mediated by miRNAs through influence on GC signaling pathway, leading to diverse glucocorticoid responsiveness. Mutations in miRNA gene also influence GC response. As well, GCs regulate the function of several miRNAs, and suggesting a bidirectional influence among them.

CONCLUSIONS

It is possible and necessary that miRNAs serve as stable biomarkers and GC resistant patients would benefit from an effective and early screening test.

Cholinergic Signals from the CNS Regulate G-CSF-Mediated HSC Mobilization from Bone Marrow via a Glucocorticoid Signaling Relay

Hematopoietic stem cells (HSCs) are mobilized from niches in the bone marrow (BM) to the blood circulation by the cytokine granulocyte colony-stimulating factor (G-CSF) through complex mechanisms. Among these, signals from the sympathetic nervous system regulate HSC egress via its niche, but how the brain communicates with the BM remains largely unknown. Here we show that muscarinic receptor type-1 (Chrm1) signaling in the hypothalamus promotes G-CSF-elicited HSC mobilization via hormonal priming of the hypothalamic-pituitary-adrenal (HPA) axis. Blockade of Chrm1 in the CNS, but not the periphery, reduces HSC mobilization. Mobilization is impaired in Chrm1-∕- mice and rescued by parabiosis with wild-type mice, suggesting a relay by a blood-borne factor. We have identified the glucocorticoid (GC) hormones as critical for optimal mobilization. Physiological levels of corticosterone promote HSC migration via the GC receptor Nr3c1-dependent signaling and upregulation of actin-organizing molecules. These results uncover long-range regulation of HSC migration emerging from the brain.

Fluoxetine effects on molecular, cellular and behavioral endophenotypes of depression are driven by the living environment

Selective serotonin reuptake inhibitors (SSRIs) represent the most common treatment for major depression. However, their efficacy is variable and incomplete. In order to elucidate the cause of such incomplete efficacy, we explored the hypothesis positing that SSRIs may not affect mood per se but, by enhancing neural plasticity, render the individual more susceptible to the influence of the environment. Consequently, SSRI administration in a favorable environment promotes a reduction of symptoms, whereas in a stressful environment leads to a worse prognosis. To test such hypothesis, we exposed C57BL/6 mice to chronic stress in order to induce a depression-like phenotype and, subsequently, to fluoxetine treatment (21 days), while being exposed to either an enriched or a stressful condition. We measured the most commonly investigated molecular, cellular and behavioral endophenotypes of depression and SSRI outcome, including depression-like behavior, neurogenesis, brain-derived neurotrophic factor levels, hypothalamic-pituitary-adrenal axis activity and long-term potentiation. Results showed that, in line with our hypothesis, the endophenotypes investigated were affected by the treatment according to the quality of the living environment. In particular, mice treated with fluoxetine in an enriched condition overall improved their depression-like phenotype compared with controls, whereas those treated in a stressful condition showed a distinct worsening. Our findings suggest that the effects of SSRI on the depression- like phenotype is not determined by the drug per se but is induced by the drug and driven by the environment. These findings may be helpful to explain variable effects of SSRI found in clinical practice and to device strategies aimed at enhancing their efficacy by means of controlling environmental conditions.

Neonatal Proinflammatory Stress Induces Accumulation of Corticosterone and Interleukin-6 in the Hippocampus of Juvenile Rats: Potential Mechanism of Synaptic Plasticity Impairments

Infectious diseases in early postnatal ontogenesis can induce neuroinflammation, disrupt normal central nervous system development, and contribute to pathogenesis of cerebral pathologies in adults. To study long-term consequences of such early stress, we induced neonatal proinflammatory stress (NPS) by injecting bacterial lipopolysaccharide into rat pups on postnatal days 3 and 5 and then assessed the levels of corticosterone, proinflammatory cytokines and their mRNAs, and neurotrophins and their mRNAs in the hippocampus and neocortex of the one-month-old animals. Long-term potentiation (LTP) was studied in hippocampal slices as an index of synaptic plasticity. NPS-induced impairments of LTP were accompanied by the accumulation of corticosterone and IL-6 in the hippocampus. In the neocortex, a decrease in exon IV BDNF mRNA was detected. We suggest that excessive corticosterone delivery to hippocampal receptors and proinflammatory changes persisting during brain maturation are among the principal molecular mechanisms responsible for NPS-induced neuroplasticity impairments.

Late-Onset Cognitive Impairments after Early-Life Stress Are Shaped by Inherited Differences in Stress Reactivity

Early-life stress (ELS) has been associated with lasting cognitive impairments and with an increased risk for affective disorders. A dysregulation of the hypothalamus-pituitary-adrenal (HPA) axis, the body’s main stress response system, is critically involved in mediating these long-term consequences of adverse early-life experience. It remains unclear to what extent an inherited predisposition for HPA axis sensitivity or resilience influences the relationship between ELS and cognitive impairments, and which neuroendocrine and molecular mechanisms may be involved. To investigate this, we exposed animals of the stress reactivity mouse model, consisting of three independent lines selectively bred for high (HR), intermediate (IR), or low (LR) HPA axis reactivity to a stressor, to ELS and assessed their cognitive performance, neuroendocrine function and hippocampal gene expression in early and in late adulthood. Our results show that HR animals that were exposed to ELS exhibited an HPA axis hyper-reactivity in early and late adulthood, associated with cognitive impairments in hippocampus-dependent tasks, as well as molecular changes in transcript levels involved in the regulation of HPA axis activity (Crh) and in neurotrophic action (Bdnf). In contrast, LR animals showed intact cognitive function across adulthood, with no change in stress reactivity. Intriguingly, LR animals that were exposed to ELS even showed significant signs of enhanced cognitive performance in late adulthood, which may be related to late-onset changes observed in the expression of Crh and Crhr1 in the dorsal hippocampus of these animals. Collectively, our findings demonstrate that the lasting consequences of ELS at the level of cognition differ as a function of inherited predispositions and suggest that an innate tendency for low stress reactivity may be protective against late-onset cognitive impairments after ELS.

Transcription factor oscillations in neural stem cells: Implications for accurate control of gene expression

Naturally occurring oscillations in glucocorticoids induce a cyclic activation of the glucocorticoid receptor (GR), a well-characterized ligand-activated transcription factor. These cycles of GR activation/deactivation result in rapid GR exchange at genomic response elements and GR recycling through the chaperone machinery, ultimately generating pulses of GR-mediated transcriptional activity of target genes. In a recent article we have discussed the implications of circadian and high-frequency (ultradian) glucocorticoid oscillations for the dynamic control of gene expression in hippocampal neural stem/progenitor cells (NSPCs) (Fitzsimons et al., Front. Neuroendocrinol., 2016). Interestingly, this oscillatory transcriptional activity is common to other transcription factors, many of which regulate key biological functions in NSPCs, such as NF-kB, p53, Wnt and Notch. Here, we discuss the oscillatory behavior of these transcription factors, their role in a biologically accurate target regulation and the potential importance for a dynamic control of transcription activity and gene expression in NSPCs.

The impact of acute stress on cognitive functioning: a matter of cognitive demands?

INTRODUCTION

There is a controversy in the literature whether stress and related cortisol responses are beneficial or impairing for cognitive functioning. Conflicting results might be due to individual differences in stress reactivity and cognitive load of the applied tasks.

METHODS

N = 48 participants underwent the Socially Evaluated Cold Pressor Test and were confronted with the Frankfurter Aufmerksamkeits-Inventar-2 (FAIR-2) which is a low-load attention task and two subscales of the Intelligenz-Struktur-Test 2000 R (I-S-T 2000R) as a high-load reasoning task before and after the stressor. Participants were post hoc divided into high (stress induced cortisol increase of ≥1.5 nmol/l) vs. low-cortisol responders.

RESULTS

Cortisol responders showed an increased attentional performance in the post-stress condition (η² > .14). However, there were neither stress or responder main effects nor an interaction effect on reasoning abilities.

CONCLUSIONS

Results of the present study show that stress related changes in cognitive performance are due to individual differences in cortisol response and the cognitive load of the performed task. Future studies will show if these results are also valid for alternative cognitive tasks and if they can be replicated in female participants.

Isoform switching of steroid receptor co-activator-1 attenuates glucocorticoid-induced anxiogenic amygdala CRH expression

Maladaptive glucocorticoid effects contribute to stress-related psychopathology. The glucocorticoid receptor (GR) that mediates many of these effects uses multiple signaling pathways. We have tested the hypothesis that manipulation of downstream factors ('coregulators') can abrogate potentially maladaptive GR-mediated effects on fear-motivated behavior that are linked to corticotropin releasing hormone (CRH). For this purpose the expression ratio of two splice variants of steroid receptor coactivator-1 (SRC-1) was altered via antisense-mediated 'exon-skipping' in the central amygdala of the mouse brain. We observed that a change in splicing towards the repressive isoform SRC-1a strongly reduced glucocorticoid-induced responsiveness of Crh mRNA expression and increased methylation of the Crh promoter. The transcriptional GR target gene Fkbp5 remained responsive to glucocorticoids, indicating gene specificity of the effect. The shift of the SRC-1 splice variants altered glucocorticoid-dependent exploratory behavior and attenuated consolidation of contextual fear memory. In conclusion, our findings demonstrate that manipulation of GR signaling pathways related to the Crh gene can selectively diminish potentially maladaptive effects of glucocorticoids.

A users guide to HPA axis research

Glucocorticoid hormones (cortisol and corticosterone - CORT) are the effector hormones of the hypothalamic-pituitary-adrenal (HPA) axis neuroendocrine system. CORT is a systemic intercellular signal whose level predictably varies with time of day and dynamically increases with environmental and psychological stressors. This hormonal signal is utilized by virtually every cell and physiological system of the body to optimize performance according to circadian, environmental and physiological demands. Disturbances in normal HPA axis activity profiles are associated with a wide variety of physiological and mental health disorders. Despite numerous studies to date that have identified molecular, cellular and systems-level glucocorticoid actions, new glucocorticoid actions and clinical status associations continue to be revealed at a brisk pace in the scientific literature. However, the breadth of investigators working in this area poses distinct challenges in ensuring common practices across investigators, and a full appreciation for the complexity of a system that is often reduced to a single dependent measure. This Users Guide is intended to provide a fundamental overview of conceptual, technical and practical knowledge that will assist individuals who engage in and evaluate HPA axis research. We begin with examination of the anatomical and hormonal components of the HPA axis and their physiological range of operation. We then examine strategies and best practices for systematic manipulation and accurate measurement of HPA axis activity. We feature use of experimental methods that will assist with better understanding of CORT's physiological actions, especially as those actions impact subsequent brain function. This research approach is instrumental for determining the mechanisms by which alterations of HPA axis function may contribute to pathophysiology.

Acute stress alters individual risk taking in a time-dependent manner and leads to anti-social risk

Decision‐making processes can be modulated by stress, and the time elapsed from stress induction seems to be a crucial factor in determining the direction of the effects. Although current approaches consider the first post‐stress hour a uniform period, the dynamic pattern of activation of the physiological stress systems (i.e., the sympathetic nervous system and hypothalamic‐pituitary‐adrenal axis) suggests that its neurobehavioural impact might be heterogeneous. Here, we evaluate economic risk preferences on the gain domain (i.e., risk aversion) at three time points following exposure to psychosocial stress (immediately after, and 20 and 45 min from onset). Using lottery games, we examine decisions at both the individual and social levels. We find that risk aversion shows a time‐dependent change across the first post‐stress hour, evolving from less risk aversion shortly after stress to more risk averse behaviour at the last testing time. When risk implied an antisocial outcome to a third party, stressed individuals showed less regard for this person in their decisions. Participants’ cortisol levels explained their behaviour in the risk, but not the antisocial, game. Our findings reveal differential stress effects in self‐ and other‐regarding decision‐making and highlight the multidimensional nature of the immediate aftermath of stress for cognition.

Epigenetic Modifications of Major Depressive Disorder

Major depressive disorder (MDD) is a chronic disease whose neurological basis and pathophysiology remain poorly understood. Initially, it was proposed that genetic variations were responsible for the development of this disease. Nevertheless, several studies within the last decade have provided evidence suggesting that environmental factors play an important role in MDD pathophysiology. Alterations in epigenetics mechanism, such as DNA methylation, histone modification and microRNA expression could favor MDD advance in response to stressful experiences and environmental factors. The aim of this review is to describe genetic alterations, and particularly altered epigenetic mechanisms, that could be determinants for MDD progress, and how these alterations may arise as useful screening, diagnosis and treatment monitoring biomarkers of depressive disorders.

MicroRNA: Small RNA mediators of the brains genomic response to environmental stress

The developmental processes that establish the synaptic architecture of the brain while retaining capacity for activity-dependent remodeling, are complex and involve a combination of genetic and epigenetic influences. Dysregulation of these processes can lead to problems with neural circuitry which manifest in humans as a range of neurodevelopmental syndromes, such as schizophrenia, bipolar disorder and fragile X mental retardation. Recent studies suggest that prenatal, postnatal and intergenerational environmental factors play an important role in the aetiology of stress-related psychopathology. A number of these disorders have been shown to display epigenetic changes in the postmortem brain that reflect early life experience. These changes affect the regulation of gene expression though chromatin remodeling (transcriptional) and post-transcriptional influences, especially small noncoding microRNA (miRNA). These dynamic and influential molecules appear to play an important function in both brain development and its adaption to stress. In this review, we examine the role of miRNA in mediating the brain's response to both prenatal and postnatal environmental perturbations and explore how stress- induced alterations in miRNA expression can regulate the stress response via modulation of the immune system. Given the close relationship between environmental stress, miRNA, and brain development/function, we assert that miRNA hold a significant position at the molecular crossroads between neural development and adaptations to environmental stress. A greater understanding of the dynamics that mediate an individual's predisposition to stress-induced neuropathology has major human health benefits and is an important area of research.

Hypothalamic-Pituitary--Adrenal Axis-Feedback Control

The hypothalamo-pituitary-adrenal axis (HPA) is responsible for stimulation of adrenal corticosteroids in response to stress. Negative feedback control by corticosteroids limits pituitary secretion of corticotropin, ACTH, and hypothalamic secretion of corticotropin-releasing hormone, CRH, and vasopressin, AVP, resulting in regulation of both basal and stress-induced ACTH secretion. The negative feedback effect of corticosteroids occurs by action of corticosteroids at mineralocorticoid receptors (MR) and/or glucocorticoid receptors (GRs) located in multiple sites in the brain and in the pituitary. The mechanisms of negative feedback vary according to the receptor type and location within the brain-hypothalmo-pituitary axis. A very rapid nongenomic action has been demonstrated for GR action on CRH neurons in the hypothalamus, and somewhat slower nongenomic effects are observed in the pituitary or other brain sites mediated by GR and/or MR. Corticosteroids also have genomic actions, including repression of the pro-opiomelanocortin (POMC) gene in the pituitary and CRH and AVP genes in the hypothalamus. The rapid effect inhibits stimulated secretion, but requires a rapidly rising corticosteroid concentration. The more delayed inhibitory effect on stimulated secretion is dependent on the intensity of the stimulus and the magnitude of the corticosteroid feedback signal, but also the neuroanatomical pathways responsible for activating the HPA. The pathways for activation of some stressors may partially bypass hypothalamic feedback sites at the CRH neuron, whereas others may not involve forebrain sites; therefore, some physiological stressors may override or bypass negative feedback, and other psychological stressors may facilitate responses to subsequent stress.

Effects of histamine H1 receptor signaling on glucocorticoid receptor activity. Role of canonical and non-canonical pathways

Histamine H1 receptor (H1R) antagonists and glucocorticoid receptor (GR) agonists are used to treat inflammatory conditions such as allergic rhinitis, atopic dermatitis and asthma. Consistent with the high morbidity levels of such inflammatory conditions, these receptors are the targets of a vast number of approved drugs, and in many situations their ligands are co-administered. However, this drug association has no clear rationale and has arisen from clinical practice. We hypothesized that H1R signaling could affect GR-mediated activity, impacting on its transcriptional outcome. Indeed, our results show a dual regulation of GR activity by the H1R: a potentiation mediated by G-protein βγ subunits and a parallel inhibitory effect mediated by Gαq-PLC pathway. Activation of the H1R by its full agonists resulted in a composite potentiating effect. Intriguingly, inactivation of the Gαq-PLC pathway by H1R inverse agonists resulted also in a potentiation of GR activity. Moreover, histamine and clinically relevant antihistamines synergized with the GR agonist dexamethasone to induce gene transactivation and transrepression in a gene-specific manner. Our work provides a delineation of molecular mechanisms underlying the widespread clinical association of antihistamines and GR agonists, which may contribute to future dosage optimization and reduction of well-described side effects associated with glucocorticoid administration.

Temporal control of glucocorticoid neurodynamics and its relevance for brain homeostasis, neuropathology and glucocorticoid-based therapeutics

Glucocorticoids mediate plethora of actions throughout the human body. Within the brain, they modulate aspects of immune system and neuroinflammatory processes, interfere with cellular metabolism and viability, interact with systems of neurotransmission and regulate neural rhythms. The influence of glucocorticoids on memory and emotional behaviour is well known and there is increasing evidence for their involvement in many neuropsychiatric pathologies. These effects, which at times can be in opposing directions, depend not only on the concentration of glucocorticoids but also the duration of their presence, the temporal relationship between their fluctuations, the co-influence of other stimuli, and the overall state of brain activity. Moreover, they are region- and cell type-specific. The molecular basis of such diversity of effects lies on the orchestration of the spatiotemporal interplay between glucocorticoid- and mineralocorticoid receptors, and is achieved through complex dynamics, mainly mediated via the circadian and ultradian pattern of glucocorticoid secretion. More sophisticated methodologies are therefore required to better approach the study of these hormones and improve the effectiveness of glucocorticoid-based therapeutics.

Mechanisms of stress in the brain

The brain is the central organ involved in perceiving and adapting to social and physical stressors via multiple interacting mediators, from the cell surface to the cytoskeleton to epigenetic regulation and nongenomic mechanisms. A key result of stress is structural remodeling of neural architecture, which may be a sign of successful adaptation, whereas persistence of these changes when stress ends indicates failed resilience. Excitatory amino acids and glucocorticoids have key roles in these processes, along with a growing list of extra- and intracellular mediators that includes endocannabinoids and brain-derived neurotrophic factor (BDNF). The result is a continually changing pattern of gene expression mediated by epigenetic mechanisms involving histone modifications and CpG methylation and hydroxymethylation as well as by the activity of retrotransposons that may alter genomic stability. Elucidation of the underlying mechanisms of plasticity and vulnerability of the brain provides a basis for understanding the efficacy of interventions for anxiety and depressive disorders as well as age-related cognitive decline.

Early Life Stress, Nicotinic Acetylcholine Receptors and Alcohol Use Disorders

Stress is a major driving force in alcohol use disorders (AUDs). It influences how much one consumes, craving intensity and whether an abstinent individual will return to harmful alcohol consumption. We are most vulnerable to the effects of stress during early development, and exposure to multiple traumatic early life events dramatically increases the risk for AUDs. However, not everyone exposed to early life stress will develop an AUD. The mechanisms determining whether an individual’s brain adapts and becomes resilient to the effects of stress or succumbs and is unable to cope with stress remain elusive. Emerging evidence suggests that neuroplastic changes in the nucleus accumbens (NAc) following early life stress underlie the development of AUDs. This review discusses the impact of early life stress on NAc structure and function, how these changes affect cholinergic signaling within the mesolimbic reward pathway and the role nicotinic acetylcholine receptors (nAChRs) play in this process. Understanding the neural pathways and mechanism determining stress resilience or susceptibility will improve our ability to identify individuals susceptible to developing AUDs, formulate cognitive interventions to prevent AUDs in susceptible individuals and to elucidate and enhance potential therapeutic targets, such as the nAChRs, for those struggling to overcome an AUD.

Predictable enriched environment prevents development of hyper-emotionality in the VPA rat model of autism

Understanding the effects of environmental stimulation in autism can improve therapeutic interventions against debilitating sensory overload, social withdrawal, fear and anxiety. Here, we evaluate the role of environmental predictability on behavior and protein expression, and inter-individual differences, in the valproic acid (VPA) model of autism. Male rats embryonically exposed (E11.5) either to VPA, a known autism risk factor in humans, or to saline, were housed from weaning into adulthood in a standard laboratory environment, an unpredictably enriched environment, or a predictably enriched environment. Animals were tested for sociability, nociception, stereotypy, fear conditioning and anxiety, and for tissue content of glutamate signaling proteins in the primary somatosensory cortex, hippocampus and amygdala, and of corticosterone in plasma, amygdala and hippocampus. Standard group analyses on separate measures were complemented with a composite emotionality score, using Cronbach's Alpha analysis, and with multivariate profiling of individual animals, using Hierarchical Cluster Analysis. We found that predictable environmental enrichment prevented the development of hyper-emotionality in the VPA-exposed group, while unpredictable enrichment did not. Individual variation in the severity of the autistic-like symptoms (fear, anxiety, social withdrawal and sensory abnormalities) correlated with neurochemical profiles, and predicted their responsiveness to predictability in the environment. In controls, the association between socio-affective behaviors, neurochemical profiles and environmental predictability was negligible. This study suggests that rearing in a predictable environment prevents the development of hyper-emotional features in animals exposed to an autism risk factor, and demonstrates that unpredictable environments can lead to negative outcomes, even in the presence of environmental enrichment.

The symphonic structure of childhood stress reactivity: patterns of sympathetic, parasympathetic, and adrenocortical responses to psychological challenge

Despite widespread recognition that the physiological systems underlying stress reactivity are well coordinated at a neurobiological level, surprisingly little empirical attention has been given to delineating precisely how the systems actually interact with one another when confronted with stress. We examined cross-system response proclivities in anticipation of and following standardized laboratory challenges in 664 4- to 14-year-olds from four independent studies. In each study, measures of stress reactivity within both the locus coeruleus-norepinephrine system (i.e., the sympathetic and parasympathetic branches of the autonomic nervous system) and the corticotrophin releasing hormone system (i.e., the hypothalamic-pituitary-adrenal axis) were collected. Latent profile analyses revealed six distinctive patterns that recurred across the samples: moderate reactivity (average cross-system activation; 52%-80% of children across samples), parasympathetic-specific reactivity (2%-36%), anticipatory arousal (4%-9%), multisystem reactivity (7%-14%), hypothalamic-pituitary-adrenal axis specific reactivity (6%-7%), and underarousal (0%-2%). Groups meaningfully differed in socioeconomic status, family adversity, and age. Results highlight the sample-level reliability of children's neuroendocrine responses to stress and suggest important cross-system regularities that are linked to development and prior experiences and may have implications for subsequent physical and mental morbidity.

Stress, captivity, and reproduction in a wild bird species

In seasonal species, glucocorticoid concentrations are often highest during the breeding season. However, the role of increased hypothalamic-pituitary-adrenal (HPA) activity in the regulation of reproduction remains poorly understood. Our study is the first, to our knowledge, to document reproductive consequences of a non-pharmacological hindrance to seasonal HPA fluctuations. Using wild-caught male and female European starlings (Sturnus vulgaris) housed in an outdoor, semi-natural environment, we divided birds into two mixed-sex groups. One group remained in the outdoor aviary, where starlings breed at the appropriate time of year. The other group was transferred into an indoor flight aviary, where we predicted reproductive suppression to occur. We measured changes in corticosterone (CORT) at baseline and stress-induced concentrations prior to group separation and at the experiment's conclusion. After ten days, the birds showed remarkable differences in breeding behavior and HPA activity. Outdoor birds exhibited increases in baseline and stress-induced CORT and progressed into active breeding (pairing, nest building, egg laying, etc.). In contrast, indoor birds displayed no change in baseline or stress-induced CORT and few signs of active breeding. We found significant sex and treatment effects on expression of HPA and hypothalamic-pituitary-gonadal (HPG) axis elements, suggesting sex-specific regulatory mechanisms. Our data suggest a novel, facilitating role for the HPA axis in the transition between early breeding and active breeding in a wild, seasonal avian species. In addition, understanding how changes in housing condition affect seasonal HPA fluctuations may help alleviate barriers to breeding wild animals in captivity.

Depletion of FKBP51 in female mice shapes HPA axis activity

Psychiatric disorders such as depressive disorders and posttraumatic stress disorder are a major disease burden worldwide and have a higher incidence in women than in men. However, the underlying mechanism responsible for the sex-dependent differences is not fully understood. Besides environmental factors such as traumatic life events or chronic stress, genetic variants contribute to the development of such diseases. For instance, variations in the gene encoding the FK506 binding protein 51 (FKBP51) have been repeatedly associated with mood and anxiety. FKBP51 is a negative regulator of the glucocorticoid receptor and thereby of the hypothalamic–pituitary–adrenal axis that also interacts with other steroid hormone receptors such as the progesterone and androgen receptors. Thus, the predisposition of women to psychiatric disorders and the interaction of female hormones with FKBP51 and the glucocorticoid receptor implicate a possible difference in the regulation of the hypothalamic–pituitary–adrenal axis in female FKBP51 knockout (51KO) mice. Therefore, we investigated neuroendocrine, behavioural and physiological alterations relevant to mood disorders in female 51KO mice. Female 51KOs and wild type littermates were subjected to various behavioural tests, including the open field, elevated plus maze and forced swim test. The neuroendocrine profile was investigated under basal conditions and in response to an acute stressor. Furthermore, we analysed the mRNA expression levels of the glucocorticoid receptor and corticotrophin release hormone in different brain regions. Overall, female 51KO mice did not display any overt behavioural phenotype under basal conditions, but showed a reduced basal hypothalamic–pituitary–adrenal axis activity, a blunted response to, and an enhanced recovery from, acute stress. These characteristics strongly overlap with previous studies in male 51KO mice indicating that FKBP51 shapes the behavioural and neuroendocrine phenotype independent of the sex of the individual.

The Modulating Role of Stress in the Onset and Course of Tourette's Syndrome: A Review

Accumulating data indicate a common occurrence of tic exacerbations and periods of psychosocial stress. Patients with Tourette's syndrome (TS) also exhibit aberrant markers of hypothalamic-pituitary-adrenal (HPA) axis activation. Based on these findings, a functional relationship between stress and tic disorders has been suggested, but the underlying mechanism of how stress may affect tic pathology remains to be elucidated. We suggest that dopaminergic and noradrenergic neurotransmission as well as immunology play a crucial role in mediating this relationship. Two possibilities of causal direction might be assumed: (a) psychosocial stress might lead to an exacerbation of tics via activation of HPA axis and subsequent changes in neurotransmission or immunology and (b) TS-related abnormalities in neurotransmission or immunology result in a higher vulnerability of affected patients to respond to psychosocial stress with a strong activation of the HPA axis. It may also be the case that both assumptions hold true and interact with each other.