Neural Regulation of the Stress Response: The Many Faces of Feedback

Exploring Electrical Neuromodulation as an Alternative Therapeutic Approach in Inflammatory Bowel Diseases

Background and Objectives: This review systematically evaluates the potential of electrical neuromodulation techniques-vagus nerve stimulation (VNS), sacral nerve stimulation (SNS), and tibial nerve stimulation (TNS)-as alternative treatments for inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's Disease (CD). It aims to synthesize current evidence on the efficacy and safety of these modalities, addressing the significant burden of IBD on patient quality of life and the limitations of existing pharmacological therapies. Materials and Methods: We conducted a comprehensive analysis of studies from PubMed, focusing on research published between 1978 and 2024. The review included animal models and clinical trials investigating the mechanisms, effectiveness, and safety of VNS, SNS, and TNS in IBD management. Special attention was given to the modulation of inflammatory responses and its impact on gastrointestinal motility and functional gastrointestinal disorders associated with IBD. Results: Preliminary findings suggest that VNS, SNS, and TNS can significantly reduce inflammatory markers and improve symptoms in IBD patients. These techniques also show potential in treating related gastrointestinal disorders during IBD remission phases. However, the specific mechanisms underlying these benefits remain to be fully elucidated, and there is considerable variability in treatment parameters. Conclusions: Electrical neuromodulation holds promise as a novel therapeutic avenue for IBD, offering an alternative to patients who do not respond to traditional treatments or experience adverse effects. The review highlights the need for further rigorous studies to optimize stimulation parameters, understand long-term outcomes, and integrate neuromodulation effectively into IBD treatment protocols.

Effects of cortisol administration on heart rate variability and functional connectivity across women with different depression histories

Abnormalities within the hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system have been implicated in depression. Studies have reported glucocorticoid insensitivity and reduced heart rate variability (HRV) in depressive disorders. However, little is known about the effects of cortisol on HRV and resting-state functional connectivity (rsFC) of the central autonomic network (CAN) in depression. We collected resting-state fMRI and cardiac data for women with different depression histories (n = 61) after administration of cortisol and placebo using a double-blind crossover design. We computed rsFC for R-amygdala and L-amygdala seeds and assessed the change in HRV after cortisol (cortisol-placebo). Analyses examined the effects of acute cortisol administration on HRV and rsFC of the R-amygdala and L-amygdala. There was a significant interaction between HRV and treatment for rsFC between the amygdala and CAN regions. We found lower rsFC between the L-amygdala and putamen for those with a greater decrease in HRV after cortisol. There was also reduced rsFC between the R-amygdala and dorsomedial prefrontal cortex, putamen, middle cingulate cortex, insula, and cerebellum in those with lower HRV after cortisol. These results remained significant after adjusting for depression symptoms, age, and race. Our findings suggest that the effect of cortisol on CAN connectivity is related to its effects on HRV. Overall, these results could inform transdiagnostic interventions targeting HRV and the stress response systems across clinical and non-clinical populations.

Nuclei-specific hypothalamus networks predict a dimensional marker of stress in humans

The hypothalamus is part of the hypothalamic-pituitary-adrenal axis which activates stress responses through release of cortisol. It is a small but heterogeneous structure comprising multiple nuclei. In vivo human neuroimaging has rarely succeeded in recording signals from individual hypothalamus nuclei. Here we use human resting-state fMRI (n = 498) with high spatial resolution to examine relationships between the functional connectivity of specific hypothalamic nuclei and a dimensional marker of prolonged stress. First, we demonstrate that we can parcellate the human hypothalamus into seven nuclei in vivo. Using the functional connectivity between these nuclei and other subcortical structures including the amygdala, we significantly predict stress scores out-of-sample. Predictions use 0.0015% of all possible brain edges, are specific to stress, and improve when using nucleus-specific compared to whole-hypothalamus connectivity. Thus, stress relates to connectivity changes in precise and functionally meaningful subcortical networks, which may be exploited in future studies using interventions in stress disorders.

Inter- and transgenerational heritability of preconception chronic stress or alcohol exposure: Translational outcomes in brain and behavior

Chronic stress and alcohol (ethanol) use are highly interrelated and can change an individual's behavior through molecular adaptations that do not change the DNA sequence, but instead change gene expression. A recent wealth of research has found that these nongenomic changes can be transmitted across generations, which could partially account for the "missing heritability" observed in genome-wide association studies of alcohol use disorder and other stress-related neuropsychiatric disorders. In this review, we summarize the molecular and behavioral outcomes of nongenomic inheritance of chronic stress and ethanol exposure and the germline mechanisms that could give rise to this heritability. In doing so, we outline the need for further research to: (1) Investigate individual germline mechanisms of paternal, maternal, and biparental nongenomic chronic stress- and ethanol-related inheritance; (2) Synthesize and dissect cross-generational chronic stress and ethanol exposure; (3) Determine cross-generational molecular outcomes of preconception ethanol exposure that contribute to alcohol-related disease risk, using cancer as an example. A detailed understanding of the cross-generational nongenomic effects of stress and/or ethanol will yield novel insight into the impact of ancestral perturbations on disease risk across generations and uncover actionable targets to improve human health.

The Role of Cortisol in Chronic Stress, Neurodegenerative Diseases, and Psychological Disorders

Cortisol, a critical glucocorticoid hormone produced by the adrenal glands, plays a pivotal role in various physiological processes. Its release is finely orchestrated by the suprachiasmatic nucleus, governing the circadian rhythm and activating the intricate hypothalamic-pituitary-adrenal (HPA) axis, a vital neuroendocrine system responsible for stress response and maintaining homeostasis. Disruptions in cortisol regulation due to chronic stress, disease, and aging have profound implications for multiple bodily systems. Animal models have been instrumental in elucidating these complex cortisol dynamics during stress, shedding light on the interplay between physiological, neuroendocrine, and immune factors in the stress response. These models have also revealed the impact of various stressors, including social hierarchies, highlighting the role of social factors in cortisol regulation. Moreover, chronic stress is closely linked to the progression of neurodegenerative diseases, like Alzheimer's and Parkinson's, driven by excessive cortisol production and HPA axis dysregulation, along with neuroinflammation in the central nervous system. The relationship between cortisol dysregulation and major depressive disorder is complex, characterized by HPA axis hyperactivity and chronic inflammation. Lastly, chronic pain is associated with abnormal cortisol patterns that heighten pain sensitivity and susceptibility. Understanding these multifaceted mechanisms and their effects is essential, as they offer insights into potential interventions to mitigate the detrimental consequences of chronic stress and cortisol dysregulation in these conditions.

The Neuroendocrine Impact of Acute Stress on Synaptic Plasticity

Stress induces changes in nervous system function on different signaling levels, from molecular signaling to synaptic transmission to neural circuits to behavior-and on different time scales, from rapid onset and transient to delayed and long-lasting. The principal effectors of stress plasticity are glucocorticoids, steroid hormones that act with a broad range of signaling competency due to the expression of multiple nuclear and membrane receptor subtypes in virtually every tissue of the organism. Glucocorticoid and mineralocorticoid receptors are localized to each of the cellular compartments of the receptor-expressing cells-the membrane, cytosol, and nucleus. In this review, we cover the neuroendocrine effects of stress, focusing mainly on the rapid actions of acute stress-induced glucocorticoids that effect changes in synaptic transmission and neuronal excitability by modulating synaptic and intrinsic neuronal properties via activation of presumed membrane glucocorticoid and mineralocorticoid receptors. We describe the synaptic plasticity that occurs in 4 stress-associated brain structures, the hypothalamus, hippocampus, amygdala, and prefrontal cortex, in response to single or short-term stress exposure. The rapid transformative impact of glucocorticoids makes this stress signal a particularly potent effector of acute neuronal plasticity.

Stress, a Brief Update

Stress is fundamental for health and adaptation; it is an evolutionarily conserved response that involves several systems in the organism. The study of the stress response could be traced back to the end of the nineteenth century with George Beard's or Claude Bernard's work and, from that moment on, several studies that have allowed the elucidation of its neurobiology and the consequences of suffering from it were consolidated. In this theoretical review, we discuss the most relevant researches to our knowledge on the study of stress response, from the concept of stress, its neurobiology, the hormonal response during stress, as well as its regulation, the effects of acute and chronic stress, stress from cognition, the different stress responses during life, as well as its relationship with different psychiatric disorders. Taken together, the reviewed research updates the classic perspective on stress, increasing the factors that should be considered in research to explore the effects of stress on health.

Effects of neuromodulation on cognitive and emotional responses to psychosocial stressors in healthy humans

Physiological and psychological stressors can exert wide-ranging effects on the human brain and behavior. Research has improved understanding of how the sympatho-adreno-medullary (SAM) and hypothalamic-pituitary-adrenocortical (HPA) axes respond to stressors and the differential responses that occur depending on stressor type. Although the physiological function of SAM and HPA responses is to promote survival and safety, exaggerated psychobiological reactivity can occur in psychiatric disorders. Exaggerated reactivity may occur more for certain types of stressors, specifically, psychosocial stressors. Understanding stressor effects and how the body regulates these responses can provide insight into ways that psychobiological reactivity can be modulated. Non-invasive neuromodulation is one way that responding to stressors may be altered; research into these interventions may provide further insights into the brain circuits that modulate stress reactivity. This review focuses on the effects of acute psychosocial stressors and how neuromodulation might be effective in altering stress reactivity. Although considerable research into stress interventions focuses on treating pathology, it is imperative to first understand these mechanisms in non-clinical populations; therefore, this review will emphasize populations with no known pathology and consider how these results may translate to those with psychiatric pathologies.

Early Chronic Stress Induced Changes within the Locus Coeruleus in Sporadic Alzheimer's Disease

Chronic exposure to stress throughout the lifespan has been the focus of many studies on Alzheimer's disease (AD) because of the similarities between the biological mechanisms involved in chronic stress and the pathophysiology of AD. In fact, the earliest abnormality associated with the disease is the presence of phosphorylated tau protein in locus coeruleus neurons, a brain structure highly responsive to stress and perceived threat. Here, we introduce allostatic load as a useful concept for understanding many of the complex, interacting neuropathological changes involved in the AD degenerative process. In response to chronic stress, aberrant tau proteins that begin to accumulate within the locus coeruleus decades prior to symptom onset appear to represent a primary pathological event in the AD cascade, triggering a wide range of interacting brain changes involving neuronal excitotoxicity, endocrine alterations, inflammation, oxidative stress, and amyloid plaque exacerbation. While it is acknowledged that stress will not necessarily be the major precipitating factor in all cases, early tau-induced changes within the locus coeruleus-norepinephrine pathway suggests that a therapeutic window might exist for preventative measures aimed at managing stress and restoring balance within the HPA axis.

Juvenile social isolation affects the structure of the tanycyte-vascular interface in the hypophyseal portal system of the adult mice

Accumulating evidence indicates that social stress in the juvenile period affects hypothalamic-pituitary-adrenal (HPA) axis activity in adulthood. The biological mechanisms underlying this phenomenon remain unclear. We aimed to elucidate them by comparing adult mice that had experienced social isolation from postnatal day 21-35 (juvenile social isolation (JSI) group) with those reared normally (control group). JSI group mice showed an attenuated HPA response to acute swim stress, while the control group had a normal response to this stress. Activity levels of the paraventricular nucleus in both groups were comparable, as shown by c-Fos immunoreactivities and mRNA expression of c-Fos, Corticotropin-releasing factor (CRF), Glucocorticoid receptor, and Mineralocorticoid receptor. We found greater vascular coverage by tanycytic endfeet in the median eminence of the JSI group mice than in that of the control group mice under basal condition and after acute swim stress. Moreover, CRF content after acute swim stress was greater in the median eminence of the JSI group mice than in that of the control group mice. The attenuated HPA response to acute swim stress was specific to JSI group mice, but not to control group mice. Although a direct link awaits further experiments, tanycyte morphological changes in the median eminence could be related to the HPA response.

The impact of early-life environment on absence epilepsy and neuropsychiatric comorbidities

This review discusses the long-term effects of early-life environment on epileptogenesis, epilepsy, and neuropsychiatric comorbidities with an emphasis on the absence epilepsy. The WAG/Rij rat strain is a well-validated genetic model of absence epilepsy with mild depression-like (dysthymia) comorbidity. Although pathologic phenotype in WAG/Rij rats is genetically determined, convincing evidence presented in this review suggests that the absence epilepsy and depression-like comorbidity in WAG/Rij rats may be governed by early-life events, such as prenatal drug exposure, early-life stress, neonatal maternal separation, neonatal handling, maternal care, environmental enrichment, neonatal sensory impairments, neonatal tactile stimulation, and maternal diet. The data, as presented here, indicate that some early environmental events can promote and accelerate the development of absence seizures and their neuropsychiatric comorbidities, while others may exert anti-epileptogenic and disease-modifying effects. The early environment can lead to phenotypic alterations in offspring due to epigenetic modifications of gene expression, which may have maladaptive consequences or represent a therapeutic value. Targeting DNA methylation with a maternal methyl-enriched diet during the perinatal period appears to be a new preventive epigenetic anti-absence therapy. A number of caveats related to the maternal methyl-enriched diet and prospects for future research are discussed.

A subpopulation of agouti-related peptide neurons exciting corticotropin-releasing hormone axon terminals in median eminence led to hypothalamic-pituitary-adrenal axis activation in response to food restriction

The excitatory action of gamma-aminobutyric-acid (GABA) in the median-eminence (ME) led to the steady-state release of corticotropin-releasing hormone (CRH) from CRH axon terminals, which modulates the hypothalamic-pituitary-adrenal (HPA) axis. However, in ME, the source of excitatory GABAergic input is unknown. We examined agouti-related peptide (AgRP) expressing neurons in the arcuate nucleus as a possible source for excitatory GABAergic input. Here, we show that a subpopulation of activated AgRP neurons directly project to the CRH axon terminals in ME elevates serum corticosterone levels in 60% food-restricted mice. This increase in serum corticosterone is not dependent on activation of CRH neuronal soma in the paraventricular nucleus. Furthermore, conditional deletion of Na⁺-K⁺-2Cl^– cotransporter-1 (NKCC1), which promotes depolarizing GABA action, from the CRH axon terminals results in significantly lower corticosterone levels in response to food restriction. These findings highlight the important role of a subset of AgRP neurons in HPA axis modulation via NKCC1-dependent GABAergic excitation in ME.

Sex differences in autonomic responses to stress: implications for cardiometabolic physiology

Chronic stress is a significant risk factor for negative health outcomes. Furthermore, imbalance of autonomic nervous system control leads to dysregulation of physiological responses to stress and contributes to the pathogenesis of cardiometabolic and psychiatric disorders. However, research on autonomic stress responses has historically focused on males, despite evidence that females are disproportionality affected by stress-related disorders. Accordingly, this mini-review focuses on the influence of biological sex on autonomic responses to stress in humans and rodent models. The reviewed literature points to sex differences in the consequences of chronic stress, including cardiovascular and metabolic disease. We also explore basic rodent studies of sex-specific autonomic responses to stress with a focus on sex hormones and hypothalamic-pituitary-adrenal axis regulation of cardiovascular and metabolic physiology. Ultimately, emerging evidence of sex differences in autonomic-endocrine integration highlights the importance of sex-specific studies to understand and treat cardiometabolic dysfunction.

What the hippocampus tells the HPA axis: Hippocampal output attenuates acute stress responses via disynaptic inhibition of CRF+ PVN neurons

The hippocampus exerts inhibitory feedback on the release of glucocorticoids. Because the major hippocampal efferent projections are excitatory, it has been hypothesized that this inhibition is mediated by populations of inhibitory neurons in the hypothalamus or elsewhere. These regions would be excited by hippocampal efferents and project to corticotropin-releasing factor (CRF) cells in the paraventricular nucleus of the hypothalamus (PVN). A direct demonstration of the synaptic responses elicited by hippocampal outputs in PVN cells or upstream GABAergic interneurons has not been provided previously. Here, we used viral vectors to express channelrhodopsin (ChR) and enhanced yellow fluorescent protein (EYFP) in pyramidal cells in the ventral hippocampus (vHip) in mice expressing tdTomato in GABA- or CRF-expressing neurons. We observed dense innervation of the bed nucleus of the stria terminalis (BNST) by labeled vHip axons and sparse labeling within the PVN. Using whole-cell voltage-clamp recording in parasagittal brain slices containing the BNST and PVN, photostimulation of vHip terminals elicited rapid excitatory postsynaptic currents (EPSCs) and longer-latency inhibitory postsynaptic currents (IPSCs) in both CRF+ and GAD + cells. The ratio of synaptic excitation and inhibition was maintained in CRF + cells during 20 Hz stimulus trains. Photostimulation of hippocampal afferents to the BNST and PVN in vivo inhibited the rise in blood glucocorticoid levels produced by acute restraint stress. We thus provide functional evidence suggesting that hippocampal output to the BNST contributes to a net inhibition of the hypothalamic-pituitary axis, providing further mechanistic insights into this process using methods with enhanced spatial and temporal resolution.

Non-Targeted Metabolomic Analysis of Chicken Kidneys in Response to Coronavirus IBV Infection Under Stress Induced by Dexamethasone

Stress in poultry can lead to changes in body metabolism and immunity, which can increase susceptibility to infectious diseases. However, knowledge regarding chicken responses to viral infection under stress is limited. Dexamethasone (Dex) is a synthetic glucocorticoid similar to that secreted by animals under stress conditions, and has been widely used to induce stress in chickens. Herein, we established a stress model in 7-day-old chickens injected with Dex to elucidate the effects of stress on IBV replication in the kidneys. The metabolic changes, immune status and growth of the chickens under stress conditions were comprehensively evaluated. Furthermore, the metabolic profile, weight gain, viral load, serum cholesterol levels, cytokines and peripheral blood lymphocyte ratio were compared in chickens treated with Dex and infected with IBV. An LC-MS/MS-based metabolomics method was used to examine differentially enriched metabolites in the kidneys. A total of 113 metabolites whose abundance was altered after Dex treatment were identified, most of which were lipids and lipid-like molecules. The principal metabolic alterations in chicken kidneys caused by IBV infection included fatty acid, valine, leucine and isoleucine metabolism. Dex treatment before and after IBV infection mainly affected the host’s tryptophan, phenylalanine, amino sugar and nucleotide sugar metabolism. In addition, Dex led to up-regulation of serum cholesterol levels and renal viral load in chickens, and to the inhibition of weight gain, peripheral blood lymphocytes and IL-6 production. We also confirmed that the exogenous cholesterol in DF-1 cells promoted the replication of IBV. However, whether the increase in viral load in kidney tissue is associated with the up-regulation of cholesterol levels induced by Dex must be demonstrated in future experiments. In conclusion, chick growth and immune function were significantly inhibited by Dex. Host cholesterol metabolism and the response to IBV infection are regulated by Dex. This study provides valuable insights into the molecular regulatory mechanisms in poultry stress, and should support further research on the intrinsic link between cholesterol metabolism and IBV replication under stress conditions.

Hypothalamic Neurochemical Changes in Long-Term Recovered Bilateral Subdiaphragmatic Vagotomized Rats

Background

Vagus nerve is one of the crucial routes in communication between the immune and central nervous systems. The impaired vagal nerve function may intensify peripheral inflammatory processes. This effect subsides along with prolonged recovery after permanent nerve injury. One of the results of such compensation is a normalized plasma concentration of stress hormone corticosterone – a marker of hypothalamic-pituitary-adrenal (HPA) axis activity. In this work, we strive to explain this corticosterone normalization by studying the mechanisms responsible for compensation-related neurochemical alterations in the hypothalamus.

Materials and Methods

Using microarrays and high performance liquid chromatography (HPLC), we measured genome-wide gene expression and major amino acid neurotransmitters content in the hypothalamus of bilaterally vagotomized rats, 1 month after surgery.

Results

Our results show that, in the long term, vagotomy affects hypothalamic amino acids concentration but not mRNA expression of tested genes.

Discussion

We propose an alternative pathway of immune to CNS communication after vagotomy, leading to activation of the HPA axis, by influencing central amino acids and subsequent monoaminergic neurotransmission.

Social sleepers: The effects of social status on sleep in terrestrial mammals

Social status among group-living mammals can impact access to resources, such as water, food, social support, and mating opportunities, and this differential access to resources can have fitness consequences. Here, we propose that an animal's social status impacts their access to sleep opportunities, as social status may predict when an animal sleeps, where they sleep, who they sleep with, and how well they sleep. Our review of terrestrial mammals examines how sleep architecture and intensity may be impacted by (1) sleeping conditions and (2) the social experience during wakefulness. Sleeping positions vary in thermoregulatory properties, protection from predators, and exposure to parasites. Thus, if dominant individuals have priority of access to sleeping positions, they may benefit from higher quality sleeping conditions and, in turn, better sleep. With respect to waking experiences, we discuss the impacts of stress on sleep, as it has been established that specific social statuses can be characterized by stress-related physiological profiles. While much research has focused on how dominance hierarchies impact access to resources like food and mating opportunities, differential access to sleep opportunities among mammals has been largely ignored despite its potential fitness consequences.

Sciatic nerve injury rebalances the hypothalamic-pituitary-adrenal axis in rats with persistent changes to their social behaviours

Increased glucocorticoids characterise acute pain responses, but not the chronic pain state, suggesting specific modifications to the hypothalamic-pituitary-adrenal (HPA)-axis preventing the persistent nature of chronic pain from elevating basal glucocorticoid levels. Individuals with chronic pain mount normal HPA-axis responses to acute stressors, indicating a rebalancing of the circuits underpinning these responses. Preclinical models of chronic neuropathic pain generally recapitulate these clinical observations, but few studies have considered that the underlying neuroendocrine circuitry may be altered. Additionally, individual differences in the behavioural outcomes of these pain models, which are strikingly similar to the range of behavioural subpopulations that manifest in response to stress, threat and motivational cues, may also be reflected in divergent patterns of HPA-axis activity, which characterises these other behavioural subpopulations. We investigated the effects of sciatic nerve chronic constriction injury (CCI) on adrenocortical and hypothalamic markers of HPA-axis activity in the subpopulation of rats showing persistent changes in social interactions after CCI (Persistent Effect) and compared them with rats that do not show these changes (No Effect). Basal plasma corticosterone did not change after CCI and did not differ between groups. However, adrenocortical sensitivity to adrenocorticotropic hormone (ACTH) diverged between these groups. No Effect rats showed large increases in basal plasma ACTH with no change in adrenocortical melanocortin 2 receptor (MC₂ R) expression, whereas Persistent Effect rats showed modest decreases in plasma ACTH and large increases in MC₂ R expression. In the paraventricular nucleus of the hypothalamus of Persistent Effect rats, single labelling revealed significantly increased numbers of corticotropin releasing factor (CRF) +ve and glucocorticoid receptor (GR) +ve neurons. Double-labelling revealed fewer GR +ve CRF +ve neurons, suggesting a decreased hypothalamic sensitivity of CRF neurons to circulating corticosterone in Persistent Effect rats. We suggest that in addition to rebalancing the HPA-axis, the increased CRF expression in Persistent Effect rats contributes to changes in complex behaviours, and in particular social interactions.

Autonomic Neural Circuit and Intervention for Comorbidity Anxiety and Cardiovascular Disease

Anxiety disorder is a prevalent psychiatric disease and imposes a significant influence on cardiovascular disease (CVD). Numerous evidence support that anxiety contributes to the onset and progression of various CVDs through different physiological and behavioral mechanisms. However, the exact role of nuclei and the association between the neural circuit and anxiety disorder in CVD remains unknown. Several anxiety-related nuclei, including that of the amygdala, hippocampus, bed nucleus of stria terminalis, and medial prefrontal cortex, along with the relevant neural circuit are crucial in CVD. A strong connection between these nuclei and the autonomic nervous system has been proven. Therefore, anxiety may influence CVD through these autonomic neural circuits consisting of anxiety-related nuclei and the autonomic nervous system. Neuromodulation, which can offer targeted intervention on these nuclei, may promote the development of treatment for comorbidities of CVD and anxiety disorders. The present review focuses on the association between anxiety-relevant nuclei and CVD, as well as discusses several non-invasive neuromodulations which may treat anxiety and CVD.

Circulating hormones and dominance status predict female behavior during courtship in a lekking species

Female competitive behaviors during courtship can have substantial fitness consequences yet we know little about the physiological and social mechanisms underlying these behaviors - particularly for females of polygynous lek mating species. We explored the hormonal and social drivers of female intersexual and intrasexual behavior during courtship by males in a captive population of Indian peafowl. We investigated whether (1) female non-stress induced circulating estradiol (E2) and corticosterone (CORT) levels or (2) female dominance status in a dyad predict female solicitation behavior. We also tested whether female circulating E2 and CORT predict dominant females' aggressive behaviors toward subordinate females in the courtship context. Our findings demonstrate that females with higher levels of circulating E2 as well as higher levels of circulating CORT solicit more courtships from males. Dominant females also solicit more courtships from males than subordinate females. Female intrasexual aggressive behaviors during courtship, however, were not associated with circulating levels of E2 or CORT. Overall, we conclude that circulating steroid hormones in conjunction with social dominance might play a role in mediating female behaviors associated with competition for mates. Experimental manipulation and measures of hormonal flexibility throughout the breeding season in relation to competitive and sexual behaviors will be necessary to further examine the link between hormonal mechanisms and female behavior in polygynous lekking systems.

The Paraventricular Nucleus of the Hypothalamus in Control of Blood Pressure and Blood Pressure Variability

The paraventricular nucleus (PVN) is a highly organized structure of the hypothalamus that has a key role in regulating cardiovascular and osmotic homeostasis. Functionally, the PVN is divided into autonomic and neuroendocrine (neurosecretory) compartments, both equally important for maintaining blood pressure (BP) and body fluids in the physiological range. Neurosecretory magnocellular neurons (MCNs) of the PVN are the main source of the hormones vasopressin (VP), responsible for water conservation and hydromineral balance, and oxytocin (OT), involved in parturition and milk ejection during lactation. Further, neurosecretory parvocellular neurons (PCNs) take part in modulation of the hypothalamic–pituitary–adrenal axis and stress responses. Additionally, the PVN takes central place in autonomic adjustment of BP to environmental challenges and contributes to its variability (BPV), underpinning the PVN as an autonomic master controller of cardiovascular function. Autonomic PCNs of the PVN modulate sympathetic outflow toward heart, blood vessels and kidneys. These pre-autonomic neurons send projections to the vasomotor nucleus of rostral ventrolateral medulla and to intermediolateral column of the spinal cord, where postganglionic fibers toward target organs arise. Also, PVN PCNs synapse with NTS neurons which are the end-point of baroreceptor primary afferents, thus, enabling the PVN to modify the function of baroreflex. Neuroendocrine and autonomic parts of the PVN are segregated morphologically but they work in concert when the organism is exposed to environmental challenges via somatodendritically released VP and OT by MCNs. The purpose of this overview is to address both neuroendocrine and autonomic PVN roles in BP and BPV regulation.

The neuroendocrinology of stress: Glucocorticoid signaling mechanisms

Glucocorticoid signaling plays major roles in energy homeostasis and adaptation to adversity, and dysregulation of this process is linked to systemic and psychological pathology. Over the last several decades, new work has challenged many of the long-standing assumptions regarding regulation of glucocorticoid secretion and glucocorticoid signaling mechanisms, revealing an exquisite complexity that accompanies the important and perhaps global role of these hormones in physiological and psychological regulation. New findings have included discovery of membrane signaling, direct neural control of the adrenal, a role for pulsatile glucocorticoid release in glucocorticoid receptor signaling, marked sex differences in brain glucocorticoid biology, and salutary as well as deleterious roles for glucocorticoids in long- and short-term adaptations to stress. This review covers some of the major lessons learned in the area of mechanisms of glucocorticoid signaling, and discusses how these may inform the field moving forward.

Cortical–Hypothalamic Integration of Autonomic and Endocrine Stress Responses

The prevalence and severity of cardiovascular disease (CVD) are exacerbated by chronic stress exposure. While stress-induced sympathetic activity and elevated glucocorticoid secretion impair cardiovascular health, the mechanisms by which stress-responsive brain regions integrate autonomic and endocrine stress responses remain unclear. This review covers emerging literature on how specific cortical and hypothalamic nuclei regulate cardiovascular and neuroendocrine stress responses. We will also discuss the current understanding of the cellular and circuit mechanisms mediating physiological stress responses. Altogether, the reviewed literature highlights the current state of stress integration research, as well unanswered questions about the brain basis of CVD risk.

Effects of Acute Stress on the Oscillatory Activity of the Hippocampus-Amygdala-Prefrontal Cortex Network

Displaying a stress response to threatening stimuli is essential for survival. These reactions must be adjusted to be adaptive. Otherwise, even mental illnesses may develop. Describing the physiological stress response may contribute to distinguishing the abnormal responses that accompany the pathology, which may help to improve the development of both diagnoses and treatments. Recent advances have elucidated many of the processes and structures involved in stress response management; however, there is still much to unravel regarding this phenomenon. The main aim of the present research is to characterize the response of three brain areas deeply involved in the stress response (i.e., to an acute stressful experience). Specifically, the electrophysiological activity of the infralimbic division of the medial prefrontal cortex (IL), the basolateral nucleus of the amygdala (BLA), and the dorsal hippocampus (dHPC) was recorded after the infusion of 0.5 µl of corticosterone-releasing factor into the dorsal raphe nucleus (DRN), a procedure which has been validated as a paradigm to cause acute stress. This procedure induced a delayed reduction in slow waves in the three structures, and an increase in faster oscillations, such as those in theta, beta, and gamma bands. The mutual information at low theta frequencies between the BLA and the IL increased, and the delta and slow wave mutual information decreased. The low theta-mid gamma phase-amplitude coupling increased within BLA, as well as between BLA and IL. This electrical pattern may facilitate the activation of these structures, in response to the stressor, and memory consolidation.

Amygdala substructure volumes in Major Depressive Disorder

The role of the amygdala in the experience of emotional states and stress is well established. Connections from the amygdala to the hypothalamus activate the hypothalamic-pituitaryadrenal (HPA) axis and the cortisol response. Previous studies have failed to find consistent whole amygdala volume changes in Major Depressive Disorder (MDD), but differences may exist at the smaller substructural level of the amygdala nuclei. High-resolution T1 and T2-weighted-fluid-attenuated inversion recovery MRIs were compared between 80 patients with MDD and 83 healthy controls (HC) using the automated amygdala substructure module in FreeSurfer 6.0. Volumetric assessments were performed for individual nuclei and three anatomico-functional composite groups of nuclei. Salivary cortisol awakening response (CAR), as a measure of HPA responsivity, was measured in a subset of patients. The right medial nucleus volume was larger in MDD compared to HC (p = 0.002). Increased right-left volume ratios were found in MDD for the whole amygdala (p = 0.004), the laterobasal composite (p = 0.009) and in the central (p = 0.003) and medial (p = 0.014) nuclei. The CAR was not significantly different between MDD and HC. Within the MDD group the left corticoamygdaloid transition area was inversely correlated with the CAR, as measured by area under the curve (AUCg) (p ≤ 0.0001). In conclusion, our study found larger right medial nuclei volumes in MDD compared to HC and relatively increased right compared to left whole and substructure volume ratios in MDD. The results suggest that amygdala substructure volumes may be involved in the pathophysiology of depression.

Effect of dexamethasone on gene expression of cannabinoid receptor type 1 and adenosine monophosphate-activated protein kinase in the hypothalamus of broilers (Gallus domesticus)

Hypothalamic neural circuits play a critical role in integrating peripheral signals and conveying information about energy and nutrient status. We detected cannabinoid receptor type 1 (CB1) distribution in the hypothalamus, liver, duodenum, jejunum, and ileum among 7- and 35-day-old broilers. The effects of dexamethasone (DEX) on CB1 gene expression were evaluated by in vitro and in vivo experiments on glucocorticoid receptor (GR) and adenosine monophosphate-activated protein kinase (AMPK) in the hypothalamus of broilers. In vitro, hypothalamic cells from 17-day-old broiler embryos were incubated with either 0.1% dimethyl sulfoxide or DEX (100 nmol/mL) for 1 h. In the in vivo study, 28-day-old broilers were injected with DEX for 24 h or 72 h. Results showed that CB1 was mainly expressed in the hypothalamus, and 72 h DEX treatment increased the expression. One-day treatment of broilers with DEX did not change the hypothalamic CB1 gene expression. Moreover, DEX treatment for 24 h and 72 h increased the mRNA level of hypothalamic AMPKα2 and GR. However, no differences were observed on the gene expression of CB1, GR, and AMPKα2 in hypothalamic cells with DEX-treated for 1 h. In conclusion, CB1 is mainly expressed in the hypothalamus of broilers; 72-h DEX exposure can regulate the CB1 system and AMPK signaling pathway of the broiler hypothalamus.

The expression of mimecan in adrenal tissue plays a role in an organism's responses to stress

Mimecan encodes a secretory protein that is secreted into the human serum as two mature proteins with molecular masses of 25 and 12 kDa. We found 12-kDa mimecan to be a novel satiety hormone mediated by the upregulation of the expression of interleukin (IL)-1β and IL-6 in the hypothalamus. Mimecan was found to be expressed in human pituitary corticotroph cells and was up-regulated by glucocorticoids, while the secretion of adrenocorticotropic hormone (ACTH) in pituitary corticotroph AtT-20 cells was induced by mimecan. However, the effects of mimecan in adrenal tissue on the hypothalamic–pituitary–adrenal (HPA) axis functions remain unknown. We demonstrated that the expression of mimecan in adrenal tissues is significantly downregulated by hypoglycemia and scalded stress. It was down-regulated by ACTH, but upregulated by glucocorticoids through in vivo and in vitro studies. We further found that 12-kDa mimecan fused protein increased the corticosterone secretion of adrenal cells in vivo and in vitro. Interestingly, compared to litter-mate mice, the diurnal rhythm of corticosterone secretion was disrupted under basal conditions, and the response to restraint stress was stronger in mimecan knockout mice. These findings suggest that mimecan stimulates corticosterone secretion in the adrenal tissues under basal conditions; however, the down-regulated expression of mimecan by increased ACTH secretion after stress in adrenal tissues might play a role in maintaining the homeostasis of an organism’s responses to stress.

Psychobiological mechanisms underlying the mood benefits of meditation: A narrative review

Psychological stressors can lead to distress and result in autonomic arousal and activation of a stress response. Ongoing or persistent stress can disrupt the stress response feedback mechanisms and result in elevated cortisol and pro-inflammatory cytokines which can cause damage to brain regions involved in the regulation of mood and emotion. We propose that the magnitude of the stress response experienced in response to psychological stressors depends on a number of modifiable psychological processes including an individual’s level of self-compassion, dispositional mindfulness, tendency to ruminate and attentional bias. We further propose that the stress response elected by psychological stressors can be meditated by influencing these modifiable psychological processes, and that meditation practices can decrease stress and improve mood by decreasing stress reactivity on a psychological, physiological and neurobiological level. We explore this in a narrative review.

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Meditation decreases blood pressure, heart rate, cortisol and cytokine levels.

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Meditation increases self-compassion, dispositional mindfulness and meta-cognition.

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Meditation improves attention and memory.

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Meditation results in brain changes in regions related to emotion regulation.

Longitudinal changes in amygdala, hippocampus and cortisol development following early caregiving adversity

Although decades of research have shown associations between early caregiving adversity, stress physiology and limbic brain volume (e.g., amygdala, hippocampus), the developmental trajectories of these phenotypes are not well characterized. In the current study, we used an accelerated longitudinal design to assess the development of stress physiology, amygdala, and hippocampal volume following early institutional care. Previously Institutionalized (PI; N = 93) and comparison (COMP; N = 161) youth (ages 4–20 years old) completed 1–3 waves of data collection, each spaced approximately 2 years apart, for diurnal cortisol (N = 239) and structural MRI (N = 156). We observed a developmental shift in morning cortisol in the PI group, with blunted levels in childhood and heightened levels in late adolescence. PI history was associated with reduced hippocampal volume and reduced growth rate of the amygdala, resulting in smaller volumes by adolescence. Amygdala and hippocampal volumes were also prospectively associated with future morning cortisol in both groups. These results indicate that adversity-related physiological and neural phenotypes are not stationary during development but instead exhibit dynamic and interdependent changes from early childhood to early adulthood.

Hurricane Irma induces divergent behavioral and hormonal impacts on an urban and forest population of invasive Anolis lizards: evidence for an urban resilience hypothesis

Hurricanes can have both profound short-term effects on animal populations and serve as long-term drivers of evolutionary change. Animals inhabiting varying habitats may differ in their response to hurricane impacts. Increasing evidence suggests that animals from urban areas exhibit different behavioral and physiological traits compared to rural counterparts, including attenuated hormonal stress responses and a lowered propensity for flight behavior. A unique opportunity was presented when Hurricane Irma hit Florida on 10 September 2017 and interrupted a study of invasive brown anoles (Anolis sagrei) at an urban and a forest. Using data collected before and after Hurricane Irma, we documented that forest anoles exhibited a greater avoidance of people and more male territorial behavior for a longer period of time following the hurricane. Post-hurricane both populations increased corticosterone concentrations post-capture stress, but urban anoles recovered 2 weeks faster than forest conspecifics. A dexamethasone suppression experiment suggested that these population differences were the result of forest anoles having a less effective negative feedback regulating corticosterone secretion. In the brain, forest anoles had higher corticosterone concentrations within the amygdala and parts of the cortex associated with stress than urban lizards. One explanation may be Hurricane Irma brought flooding and debris that altered the landscape leading to behavioral instability, and urban lizards already exhibited ecological adjustments that permitted a more rapid recovery (i.e. the ‘urban resilience’ hypothesis). Testing if urban animals are more resilient to natural disasters can inform conservationists interested in understanding their role in facilitating invasive species expansion and what their increasing presence may indicate for animal populations.

NCK1 Regulates Amygdala Activity to Control Context-dependent Stress Responses and Anxiety in Male Mice

Anxiety disorder (AD) is characterized by the development of maladaptive neuronal circuits and changes to the excitatory/inhibitory (E/I) balance of the central nervous system. Although AD is considered to be heritable, specific genetic markers remain elusive. Recent genome-wide association studies (GWAS) studies have identified non-catalytic region of tyrosine kinase adaptor protein 1 (NCK1), a gene that codes for an intracellular adaptor protein involved in actin dynamics, as an important gene in the regulation of mood. Using a murine model in which NCK1 is inactivated, we show that male, but not female, mice display increased levels of context-dependent anxiety-like behaviors along with an increase in circulating serum corticosterone relative to control. Treatment of male NCK1 mutant mice with a positive allosteric modulator of the GABA_A receptor rescued the anxiety-like behaviors implicating NCK1 in regulating neuronal excitability. These defects are not attributable to apparent defects in gross brain structure or in axon guidance. However, when challenged in an approach-avoidance conflict paradigm, male NCK1-deficient mice have decreased neuronal activation in the prefrontal cortex (PFC), as well as decreased activation of inhibitory interneurons in the basolateral amygdala (BLA). Finally, NCK1 deficiency results in loss of dendritic spine density in principal neurons of the BLA. Taken together, these data implicate NCK1 in the control of E/I balance in BLA. Our work identifies a novel role for NCK1 in the regulation of sex-specific neuronal circuitry necessary for controlling anxiety-like behaviors. Further, our work points to this animal model as a useful preclinical tool for the study of novel anxiolytics and its significance towards understanding sex differences in anxiolytic function.

Brain mechanisms of HPA axis regulation: neurocircuitry and feedback in context Richard Kvetnansky lecture

Regulation of stress reactivity is a fundamental priority of all organisms. Stress responses are critical for survival, yet can also cause physical and psychological damage. This review provides a synopsis of brain mechanisms designed to control physiological responses to stress, focusing primarily on glucocorticoid secretion via the hypothalamo-pituitary-adrenocortical (HPA) axis. The literature provides strong support for multi-faceted control of HPA axis responses, involving both direct and indirect actions at paraventricular nucleus (PVN) corticotropin releasing hormone neurons driving the secretory cascade. The PVN is directly excited by afferents from brainstem and hypothalamic circuits, likely relaying information on homeostatic challenge. Amygdala subnuclei drive HPA axis responses indirectly via disinhibition, mediated by GABAergic relays onto PVN-projecting neurons in the hypothalamus and bed nucleus of the stria terminalis (BST). Inhibition of stressor-evoked HPA axis responses is mediated by an elaborate network of glucocorticoid receptor (GR)-containing circuits, providing a distributed negative feedback signal that inhibits PVN neurons. Prefrontal and hippocampal neurons play a major role in HPA axis inhibition, again mediated by hypothalamic and BST GABAergic relays to the PVN. The complexity of the regulatory process suggests that information on stressors is integrated across functional disparate brain circuits prior to accessing the PVN, with regions such as the BST in prime position to relay contextual information provided by these sources into appropriate HPA activation. Dysregulation of the HPA in disease is likely a product of inappropriate checks and balances between excitatory and inhibitory inputs ultimately impacting PVN output.

Effects of long-lasting social isolation and re-socialization on cognitive performance and brain activity: a longitudinal study in Octodon degus

Social isolation is considered a stressful situation that results in increased physiological reactivity to novel stimuli, altered behaviour, and impaired brain function. Here, we investigated the effects of long-term social isolation on working memory, spatial learning/memory, hippocampal synaptic transmission, and synaptic proteins in the brain of adult female and male Octodon degus. The strong similarity between degus and humans in social, metabolic, biochemical, and cognitive aspects, makes it a unique animal model that can be highly applicable for further social, emotional, cognitive, and aging studies. These animals were socially isolated from post-natal and post-weaning until adulthood. We also evaluated if re-socialization would be able to compensate for reactive stress responses in chronically stressed animals. We showed that long-term social isolation impaired the HPA axis negative feedback loop, which can be related to cognitive deficits observed in chronically stressed animals. Notably, re-socialization restored it. In addition, we measured physiological aspects of synaptic transmission, where chronically stressed males showed more efficient transmission but deficient plasticity, as the reverse was true on females. Finally, we analysed synaptic and canonical Wnt signalling proteins in the hypothalamus, hippocampus, and prefrontal cortex, finding both sex- and brain structure-dependent modulation, including transient and permanent changes dependent on stress treatment.

Anti-Stress Properties of Atypical Antipsychotics

Stress exposure represents a major environmental risk factor for schizophrenia and other psychiatric disorders, as it plays a pivotal role in the etiology as well as in the manifestation of disease symptomatology. It may be inferred that pharmacological treatments must be able to modulate the behavioral, functional, and molecular alterations produced by stress exposure to achieve significant clinical outcomes. This review aims at examining existing clinical and preclinical evidence that supports the ability of atypical antipsychotic drugs (AAPDs) to modulate stress-related alterations. Indeed, while the pharmacodynamic differences between AAPDs have been extensively characterized, less is known on their ability to regulate downstream mechanisms that are critical for functional recovery and patient stabilization. We will discuss stress-related mechanisms, spanning from neuroendocrine function to inflammation and neuronal plasticity, which are relevant for the manifestation of schizophrenic symptomatology, and we will discuss if and how AAPDs may interfere with such mechanisms. Considering the impact of stress in everyday life, we believe that a better understanding of the potential effects of AAPDs on stress-related mechanisms may provide novel and important insights for improving therapeutic strategies aimed at promoting coping mechanisms and enhancing the quality of life of patients affected by psychiatric disorders.

The stress of Arctic warming on polar bears

Arctic ecosystems are changing rapidly in response to climate warming. While Arctic mammals are highly evolved to these extreme environments, particularly with respect to their stress axis, some species may have limited capacity to adapt to this change. We examined changes in key components of the stress axis (cortisol and its carrier protein-corticosteroid binding globulin [CBG]) in polar bears (Ursus maritimus) from western Hudson Bay (N = 300) over a 33 year period (1983-2015) during which time the ice-free period was increasing. Changing sea ice phenology limits spring hunting opportunities and extends the period of onshore fasting. We assessed the response of polar bears to a standardized stressor (helicopter pursuit, darting, and immobilization) during their onshore fasting period (late summer-autumn) and quantified the serum levels of the maximum corticosteroid binding capacity (MCBC) of CBG, the serum protein that binds cortisol strongly, and free cortisol (FC). We quantified bear condition (age, sex, female with cubs or not, fat condition), sea ice (breakup in spring-summer, 1 year lagged freeze-up in autumn), and duration of fasting until sample collection as well as cumulative impacts of the latter environmental traits from the previous year. Data were separated into "good" years (1983-1990) when conditions were thought to be optimal and "poor" years (1991-2015) when sea ice conditions deteriorated and fasting on land was extended. MCBC explained 39.4% of the variation in the good years, but only 28.1% in the poor ones, using both biological and environmental variables. MCBC levels decreased with age. Changes in FC were complex, but more poorly explained. Counterintuitively, MCBC levels increased with increased time onshore, 1 year lag effects, and in poor ice years. We conclude that MCBC is a biomarker of stress in polar bears and that the changes we document are a consequence of climate warming.

Associations of Food-Chewing Discomfort with Health Behaviors and Cognitive and Physical Health Using Pooled Data from the Korean Health Panel (2010-2013)

Using 4 years of pooled data from the Korean Health Panel (2010-2013), the prevalence of food-chewing discomfort in adults over the age of 19 was investigated and the cross-sectional relationship between food-chewing discomfort and health behaviors and cognitive and physical health was identified. The prevalence of food-chewing discomfort was 31%: young adults (<40 years), 17.9%; middle-aged adults (40-64 years), 28.9%; and older adults (≥65 years), 57.1% (p < 0.0001). When food-chewing discomfort was sometimes, often, or always rather than never, odds ratios (ORs) were analyzed after controlling for sociodemographic characteristics. Significant OR results of target variables were smoking (OR 1.15, 1.37, 1.50), drinking (1.08, 0.87, 0.73), problem drinking (1.87, 1.67, 1.34), abstinence from drinking (1.23, 1.34, 1.42), nonphysical activity (OR 0.87 only significant, 0.94 nonsignificant, 1.10 nonsignificant), memory decline (2.07, 2.56, 3.31), decision-making difficulty (1.76, 2.78, 4.37), limitation of daily life due to illness (2.29, 3.60, 3.92), and the presence of a chronic disease (1.28, 1.62, 1.73), respectively. In conclusion, there were associations of food-chewing discomfort with increased smoking and decreased alcohol consumption, with increased difficulty in decision-making and memory decline, limitations in daily life due to disease, and the presence of chronic diseases. Therefore, it is necessary to investigate the causal relationship between chewing and health behaviors and cognitive and physical health through longitudinal studies.

Gut microbiota modulates stress-induced hypertension through the HPA axis

Stress is associated with an increased risk of hypertension, and the incidence of stress-related hypertension has risen rapidly in recent years; however, the underlying mechanisms remain elusive. Gut dysbiosis has been demonstrated to contribute to hypertension and hyperactivation of the hypothalamus-pituitary-adrenal (HPA) axis. Based on our previous findings showing the altered gut microbiota in the rats of stress-induced hypertension (SIH), the present study aims to investigate whether the stress-induced alteration in gut microbiota can lead to the dysfunction of the HPA axis which contributes to the development of SIH. SIH was developed in rats subjected to electric foot-shock combined with buzzer noise stressors. The gut microbiota of rats were deleted by administering an antibiotic cocktail containing ampicillin (1 g/L), vancomycin (500 mg/L), neomycin (1 g/L), and metronidazole (1 g/L) in drinking water. The serum levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were tested using enzyme-linked immunosorbent assay (ELISA). The mRNA expression of glucocorticoid receptor (GR) and corticotropin-releasing factor (CRF), CRFR1 and CRFR2 was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The cellular protein expressions of corticotropin-releasing hormone (CRH), c-fos, and GR were examined by immunohistochemical staining. In the present study, SIH rats showed a hyperactive HPA axis as indicated by the increased CRH expression in the paraventricular nucleus (PVN) of the hypothalamus, the elevated serum ACTH or CORT concentrations, and increased adrenal gland index. The decreased GR expression and increased CRFR1 in the hypothalamus might underlie the hyperactivation of the HPA axis. The microbial deletion by antibiotics mitigated the hyperactivation of the HPA axis and attenuated the stress-induced elevation of blood pressure, indicating that the causal link of gut microbiota to SIH is mediated, at least in part, by the HPA axis activity. Our findings shed new light on the mechanisms underlying SIH.

Environmental enrichment prevents chronic stress-induced brain-gut axis dysfunction through a GR-mediated mechanism in the central nucleus of the amygdala

BACKGROUND

Cognitive behavioral therapy (CBT) improves quality of life of patients with irritable bowel syndrome (IBS), a disorder characterized by chronic visceral pain and abnormal bowel habits. Whether CBT can actually improve visceral pain in IBS patients is still unknown. The aim of this study is to evaluate whether environment enrichment (EE), the animal analog of CBT, can prevent stress-induced viscero-somatic hypersensitivity through changes in glucocorticoid receptor (GR) signaling within the central nucleus of the amygdala (CeA).

METHODS

Rats were housed in either standard housing (SH) or EE for 7 days before and during daily water avoidance stress (WAS) exposure (1-h/d for 7 days). In the first cohort, visceral and somatic sensitivity were assessed via visceromotor response to colorectal distention and von Frey Anesthesiometer 24 hous and 21 days after WAS. In another cohort, the CeA was isolated for GR mRNA quantification.

KEY RESULTS

Environment enrichment for 7 days before and during the 7 days of WAS persistently attenuated visceral and somatic hypersensitivity when compared to rats placed in SH. Environment enrichment exposure also prevented the WAS-induced decrease in GR expression in the CeA.

CONCLUSION & INFERENCES

Pre-exposure to short-term EE prevents the stress-induced downregulation of GR, and inhibits visceral and somatic hypersensitivity induced by chronic stress. These results suggest that a positive environment can ameliorate stress-induced pathology and provide a non-pharmacological therapeutic option for disorders such as IBS.

Nervous mechanisms of restraint water-immersion stress-induced gastric mucosal lesion

Stress-induced gastric mucosal lesion (SGML) is one of the most common visceral complications after trauma. Exploring the nervous mechanisms of SGML has become a research hotspot. Restraint water-immersion stress (RWIS) can induce GML and has been widely used to elucidate the nervous mechanisms of SGML. It is believed that RWIS-induced GML is mainly caused by the enhanced activity of vagal parasympathetic nerves. Many central nuclei, such as the dorsal motor nucleus of the vagus, nucleus of the solitary tract, supraoptic nucleus and paraventricular nucleus of the hypothalamus, mediodorsal nucleus of the thalamus, central nucleus of the amygdala and medial prefrontal cortex, are involved in the formation of SGML in varying degrees. Neurotransmitters/neuromodulators, such as nitric oxide, hydrogen sulfide, vasoactive intestinal peptide, calcitonin gene-related peptide, substance P, enkephalin, 5-hydroxytryptamine, acetylcholine, catecholamine, glutamate, γ-aminobutyric acid, oxytocin and arginine vasopressin, can participate in the regulation of stress. However, inconsistent and even contradictory results have been obtained regarding the actual roles of each nucleus in the nervous mechanism of RWIS-induced GML, such as the involvement of different nuclei with the time of RWIS, the different levels of involvement of the sub-regions of the same nucleus, and the diverse signalling molecules, remain to be further elucidated.

Lasting Impact of Chronic Adolescent Stress and Glucocorticoid Receptor Selective Modulation in Male and Female Rats

Adolescent animals are vulnerable to the effects of stress on brain development. We hypothesized that long-term effects of adolescent chronic stress are mediated by glucocorticoid receptor (GR) signaling. We used a specific GR modulator (CORT108297) to pharmacologically disrupt GR signaling in adolescent rats during exposure to chronic variable stress (CVS). Male and female rats received 30 mg/kg of drug during a 2-week CVS protocol starting at PND46. Emotional reactivity (open field) and coping behaviors (forced swim test (FST)) were then tested in adulthood, 5 weeks after the end of the CVS protocol. Blood samples were collected two days before FST and serial samples after the onset of the swim test to determine baseline and stress response levels of HPA hormones respectively. Our results support differential behavioral, physiological and stress circuit reactivity to adolescent chronic stress exposure in males and females, with variable involvement of GR signaling. In response to adolescent stress, males had heightened reactivity to novelty and exhibited marked reduction in neuronal excitation following swim stress in adulthood, whereas females developed a passive coping strategy in the FST and enhanced HPA axis stress reactivity. Only the latter effect was attenuated by treatment with the GR modulator C108297. In summary, our data suggest that adolescent stress differentially affects emotional behavior and circuit development in males and females, and that GR manipulation during stress can reverse at least some of these effects.

Acute and Chronic Insomnia: What Has Time and/or Hyperarousal Got to Do with It?

Nearly one-third of the population reports new onset or acute insomnia in a given year. Similarly, it is estimated that approximately 10% of the population endorses sleep initiation and maintenance problems consistent with diagnostic criteria for chronic insomnia. For decades, acute and chronic insomnia have been considered variations of the same condition or disorder, only really differentiated in terms of chronicity of symptoms (days/weeks versus months). Whether or not acute and chronic insomnia are part of the same phenomena is an important question, one that has yet to be empirically evaluated. The goal of the present theoretical review was to summarize the definitions of acute and chronic insomnia and discuss the role that hyperarousal may have in explaining how the pathophysiology of acute and chronic insomnia is likely different (i.e., what biopsychological factors precipitate and/or perpetuate acute insomnia, chronic insomnia, or both?).

Chronic Stress, Inflammation, and Colon Cancer: A CRH System-Driven Molecular Crosstalk

Chronic stress is thought to be involved in the occurrence and progression of multiple diseases, via mechanisms that still remain largely unknown. Interestingly, key regulators of the stress response, such as members of the corticotropin-releasing-hormone (CRH) family of neuropeptides and receptors, are now known to be implicated in the regulation of chronic inflammation, one of the predisposing factors for oncogenesis and disease progression. However, an interrelationship between stress, inflammation, and malignancy, at least at the molecular level, still remains unclear. Here, we attempt to summarize the current knowledge that supports the inseparable link between chronic stress, inflammation, and colorectal cancer (CRC), by modulation of a cascade of molecular signaling pathways, which are under the regulation of CRH-family members expressed in the brain and periphery. The understanding of the molecular basis of the link among these processes may provide a step forward towards personalized medicine in terms of CRC diagnosis, prognosis and therapeutic targeting.

Glucocorticoid receptor expression in the stress-limbic circuitry is differentially affected by prenatal alcohol exposure and adolescent stress

The dense expression of glucocorticoid receptors (GR) within the amygdala, medial prefrontal cortex (mPFC) and paraventricular nucleus of hypothalamus (PVN) mediates many aspects of emotional and stress regulation. Importantly, both prenatal alcohol exposure (PAE) and adolescent stress are known to induce emotional and stress dysregulation. Little is known, however, about how PAE and/or adolescent stress may alter the expression of GR in the amygdala, mPFC, and PVN. To fill this gap, we exposed PAE and control adolescent male and female rats to chronic mild stress (CMS) and assessed GR mRNA expression in the amygdala, mPFC, and PVN immediately following stress or in adulthood. We found that the effects of PAE on GR expression were more prevalent in the amygdala, while effects of adolescent stress on GR expression were more prevalent in the mPFC. Moreover, PAE effects in the amygdala were more pronounced during adolescence and adolescent stress effects in the mPFC were more pronounced in adulthood. GR expression in the PVN was affected by both PAE and adolescent stress. Finally, PAE and/or adolescent stress effects were distinct between males and females. Together, these results suggest that PAE and adolescent CMS induce dynamic alterations in GR expression in the amygdala, mPFC, and PVN, which manifest differently depending on the brain area, age, and sex of the animal. Additionally, these data indicate that PAE-induced hyperresponsiveness to stress and increased vulnerability to mental health problems may be mediated by different neural mechanisms depending on the sex and age of the animal.

Coping Style of Pigs Is Associated With Different Behavioral, Neurobiological and Immune Responses to Stressful Challenges

Based on the animal’s reaction to environmental challenges, consistent but different coping styles can be identified, which in turn may have consequences for health and welfare. Therefore, profound knowledge of the complex interrelationships between individual behavioral response patterns, underlying neurobiological mechanisms and immunological effects is required. The aim of this study was to examine whether pigs with different coping styles exhibit distinct behavioral, neurobiological and immune responses to stressful situations. Therefore, pigs (n = 40) were classified as proactive, reactive or intermediate animals according to a repeatedly-performed backtest, and behavioral, neuroendocrine and immune alterations were analyzed without any stress before weaning on day 28 and after a stress treatment on day 32. Our results show that the behavioral responses in an open-field/novel-object test characterized proactive pigs as more active. There were no significant differences in adrenocorticotropic hormone and cortisol concentrations between pigs with different coping characteristics. However, we found that proactive pigs displayed significantly increased plasma noradrenaline levels in response to stress, which may reflect a higher sympathetic reactivity of these animals. Furthermore, the present study revealed coping style differences in mRNA expression of mineralocorticoid, glucocorticoid, oxytocin and arginine vasopressin receptors and the immediate early gene c-fos in stress-related brain regions. While proactive pigs responded to stress with higher mRNA expression of arginine vasopressin, mineralocorticoid and glucocorticoid receptors, reactive pigs displayed higher oxytocin receptor and c-fos mRNA expression, indicating different neurobiological mechanisms of distinct coping styles in response to stressful challenges. Moreover, we also found humoral immune differences between proactive, intermediate and reactive animals. Proactive pigs had a higher total serum IgA concentration before and after stress treatment, with a significant increase in response to stress compared to reactive and intermediate pigs. In contrast, stress-induced IgM concentrations only increased in reactive and intermediate animals, suggesting that the effects of coping style on humoral immunity may differ depending on the specific function of the immunoglobulin classes. In conclusion, this multidisciplinary study expands the concept of coping style in farm animals, particularly in terms of individual stress reactivity and disease susceptibility, and thus contributes to the understanding of the biology of animal welfare.

Genetic Factors Mediate the Impact of Chronic Stress and Subsequent Response to Novel Acute Stress

Individual differences in physiological and biobehavioral adaptation to chronic stress are important predictors of health and fitness; genetic differences play an important role in this adaptation. To identify these differences we measured the biometric, neuroendocrine, and transcriptional response to stress among inbred mouse strains with varying degrees of genetic similarity, C57BL/6J (B), C57BL/6NJ (N), and DBA/2J (D). The B and D strains are highly genetically diverse whereas the B and N substrains are highly similar. Strain differences in hypothalamic-pituitary-adrenal (HPA) axis cross-sensitization were determined by plasma corticosterone (CORT) levels and hippocampal gene expression following 7-weeks of chronic mild stress (CMS) or normal housing (NH) and subsequent exposure to novel acute restraint. Fecal CORT metabolites and body and organ weights were also measured. All strains exposed to CMS had reduced heart weights, whereas body weight gain was attenuated only in B and N strains. Acute stress alone produced larger plasma CORT responses in the D and N strains compared to the B strain. CMS paired with acute stress produced cross-sensitization of the CORT response in the N strain. The N strain also had the largest number of hippocampal transcripts with up-regulated expression in response to stress. In contrast, the D strain had the largest number of transcripts with down-regulated expression following CMS and acute stress. In summary, we observed differential responses to CMS at both the physiological and molecular level among genetically diverse strains, indicating that genetic factors drive individual differences in experience-dependent regulation of the stress response.