Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness

Narrative Review of the Complex Interaction between Pain and Trauma in Children: A Focus on Biological Memory, Preclinical Data, and Epigenetic Processes

The incidence and collective impact of early adverse experiences, trauma, and pain continue to increase. This underscores the urgent need for translational efforts between clinical and preclinical research to better understand the underlying mechanisms and develop effective therapeutic approaches. As our understanding of these issues improves from studies in children and adolescents, we can create more precise preclinical models and ultimately translate our findings back to clinical practice. A multidisciplinary approach is essential for addressing the complex and wide-ranging effects of these experiences on individuals and society. This narrative review aims to (1) define pain and trauma experiences in childhood and adolescents, (2) discuss the relationship between pain and trauma, (3) consider the role of biological memory, (4) decipher the relationship between pain and trauma using preclinical data, and (5) examine the role of the environment by introducing the importance of epigenetic processes. The ultimate scope is to better understand the wide-ranging effects of trauma, abuse, and chronic pain on children and adolescents, how they occur, and how to prevent or mitigate their effects and develop effective treatment strategies that address both the underlying causes and the associated physiological and psychological effects.

Stress-induced Changes in Autonomic Reactivity Vary with Adolescent Violence Exposure and Resting-state Functional Connectivity

Exposure to violence during childhood can lead to functional changes in brain regions that are important for emotion expression and regulation, which may increase susceptibility to internalizing disorders in adulthood. Specifically, childhood violence exposure can disrupt the functional connectivity among brain regions that include the prefrontal cortex (PFC), hippocampus, and amygdala. Together, these regions are important for modulating autonomic responses to stress. However, it is unclear to what extent changes in brain connectivity relate to autonomic stress reactivity and how the relationship between brain connectivity and autonomic responses to stress varies with childhood violence exposure. Thus, the present study examined whether stress-induced changes in autonomic responses (e.g., heart rate, skin conductance level (SCL)) varied with amygdala-, hippocampus-, and ventromedial prefrontal cortex (vmPFC)-whole brain resting-state functional connectivity (rsFC) as a function of violence exposure. Two hundred and ninety-seven participants completed two resting-state functional magnetic resonance imaging scans prior to (pre-stress) and after (post-stress) a psychosocial stress task. Heart rate and SCL were recorded during each scan. Post-stress heart rate varied negatively with post-stress amygdala-inferior parietal lobule rsFC and positively with post-stress hippocampus-anterior cingulate cortex rsFC among those exposed to high, but not low, levels of violence. Results from the present study suggest that post-stress fronto-limbic and parieto-limbic rsFC modulates heart rate and may underlie differences in the stress response among those exposed to high levels of violence.

Neural response to stress differs by sex in young adulthood

Increase in stress-related disorders in women begins post-puberty and persists throughout the lifespan. To characterize sex differences in stress response in early adulthood, we used functional magnetic resonance imaging while participants underwent a stress task in conjunction with serum cortisol levels and questionnaires assessing anxiety and mood. Forty-two healthy subjects aged 18-25 years participated (21M, 21F). Interaction of stress and sex in brain activation and connectivity were examined. Results demonstrated significant sex differences in brain activity with women exhibiting increased activation in regions that inhibit arousal compared to men during the stress paradigm. Women had increased connectivity among stress circuitry regions and default mode network, whereas men had increased connectivity between stress and cognitive control regions. In a subset of subjects (13F, 17M), we obtained gamma-aminobutyric acid (GABA) magnetic resonance spectroscopy in rostral anterior cingulate cortex (rostral ACC) and dorsolateral prefrotal cortex (dlPFC) and conducted exploratory analyses to relate GABA measurements with sex differences in brain activation and connectivity. Prefrontal GABA levels were negatively associated with inferior temporal gyrus activation in men and women and with ventromedial prefrontal cortex activation in men. Despite sex differences in neural response, we found similar subjective ratings of anxiety and mood, cortisol levels, and GABA levels between sexes, suggesting sex differences in brain activity result in similar behavioral responses among the sexes. These results help establish sex differences in healthy brain activity from which we can better understand sex differences underlying stress-associated illnesses.

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.

Restraint or immobilization: a comparison of methodologies for restricting free movement in rodents and their potential impact on physiology and behavior

Restriction of free movement has historically been used as a model for inducing acute and chronic stress in laboratory animals. This paradigm is one of the most widely employed experimental procedures for basic research studies of stress-related disorders. It is easy to implement, and it rarely involves any physical harm to the animal. Many different restraint methods have been developed with variations in the apparatuses used and the degree of limitation of movement. Unfortunately, very few studies directly compare the differential impact of the distinct protocols. Additionally, restraint and immobilization terms are not differentiated and are sometimes used interchangeably in the literature. This review offers evidence of great physiological differences in the impact of distinct restraint procedures in rats and mice and emphasizes the need for a standardized language on this topic. Moreover, it illustrates the necessity of additional systematic studies that compare the effects of the distinct restraint methodologies, which would help to decide better which procedure should be used depending on the objectives of each particular study.

Distinct populations of corticotropin-releasing factor (CRF) neurons mediate divergent yet complementary defensive behaviors in response to a threat

Defensive behaviors in response to a threat are shared across the animal kingdom. Active (fleeing, sheltering) or passive (freezing, avoiding) defensive responses are adaptive and facilitate survival. Selecting appropriate defensive strategy depends on intensity, proximity, temporal threat threshold, and past experiences. Hypothalamic corticotropin-releasing factor (CRF) is a major driver of an acute stress response, whereas extrahypothalamic CRF mediates stress-related affective behaviors. In this review, we shift the focus from a monolithic role of CRF as an anxiogenic peptide to comprehensively dissecting contributions of distinct populations of CRF neurons in mediating defensive behaviors. Direct interrogation of CRF neurons of the central amygdala (CeA) or the bed nucleus of the stria terminalis (BNST) show they drive unconditioned defensive responses, such as vigilance and avoidance of open spaces. Although both populations also contribute to learned fear responses in familiar, threatening contexts, CeA-CRF neurons are particularly attuned to the ever-changing environment. Depending on threat intensities, they facilitate discrimination of salient stimuli predicting manageable threats, and prevent their generalization. Finally, hypothalamic CRF neurons mediate initial threat assessment and active defense such as escape to shelter. Overall, these three major populations of CRF neurons demonstrate divergent, yet complementary contributions to the versatile defense system: heightened vigilance, discriminating salient threats, and active escape, representing three legs of the defense tripod. Despite the 'CRF exhaustion' in the field of affective neuroscience, understanding contributions of specific CRF neurons during adaptive defensive behaviors is needed in order to understand the implications of their dysregulation in fear- and anxiety-related psychiatric disorders. This article is part of the Special Issue on "Fear, Anxiety and PTSD".

Continuous Monochromatic Blue Light Exacerbates High-Fat Diet-Induced Kidney Injury via Corticosterone-Mediated Oxidative Stress

Excessive illumination is one of the most severe environmental factors that impacts the organism. There is growing evidence that obesity significantly contributes to the onset of chronic kidney disease. However, the effect of continuous light on the kidney and which color can produce an apparent phenomenon remains elusive. In this study, C57BL/6 mice given either a normal diet (LD-WN) or a high-fat diet (LD-WF) were subjected to a light cycle of 12 h of illumination followed by 12 h of darkness for 12 weeks. Meanwhile, 48 high-fat diet mice were given a 24 h monochromatic light exposure of varying colors (white, LL-WF; blue, LL-BF; green, LL-GF) for 12 weeks. As expected, the LD-WF mice showed significant obesity, kidney injury, and renal dysfunction compared with the LD-WN group. LL-BF mice had worse kidney injury than LD-WF mice, including higher Kim-1 and Lcn2. The kidney of the LL-BF group showed marked glomerular and tubular injury, with decreased levels of Nephrin, Podocin, Cd2ap, and α-Actinin-4 compared to LD-WF. LL-BF also reduced the antioxidant capacity, including GSH-Px, CAT, and T-AOC, increased the production of MDA, and inhibited the activation of the NRF2/HO-1 signaling pathway. Furthermore, LL-BF upregulated the mRNA levels of the pro-inflammatory factors Tnf-α, Il-6, and Mcp-1, decreasing the inhibitory inflammatory Il-4 expression. We observed increased plasma corticosterone (CORT), renal glucocorticoid receptors (GR) expression, Hsp90, Hsp70, and P23 mRNA levels. These findings suggested that LL-BF increased CORT secretion and affected glucocorticoid receptors (GR) in comparison to the LD-WF group. Moreover, in vitro research demonstrated that CORT treatment increased oxidative stress and inflammation, which was counteracted by adding a GR inhibitor. Thus, the sustained blue light worsened kidney damage, possibly by inducing elevated CORT and increasing oxidative stress and inflammation via GR.

Chronic social defeat alters behaviors and neuronal activation in the brain of female Mongolian gerbils

Chronic social defeat has been found to be stressful and to affect many aspects of the brain and behaviors in males. However, relatively little is known about its effects on females. In the present study, we examined the effects of repeated social defeat on social approach and anxiety-like behaviors as well as the neuronal activation in the brain of sexually naïve female Mongolian gerbils (Meriones unguiculatus). Our data indicate that repeated social defeats for 20 days reduced social approach and social investigation, but increased risk assessment or vigilance to an unfamiliar conspecific. Such social defeat experience also increased anxiety-like behavior and reduced locomotor activity. Using ΔFosB-immunoreactive (ΔFosB-ir) staining as a marker of neuronal activation in the brain, we found significant elevations by social defeat experience in the density of ΔFosB-ir stained neurons in several brain regions, including the prelimbic (PL) and infralimbic (IL) subnuclei of the prefrontal cortex (PFC), CA1 subfields (CA1) of the hippocampus, central subnuclei of the amygdala (CeA), the paraventricular nucleus (PVN), dorsomedial nucleus (DMH), and ventrolateral subdivision of the ventromedial nucleus (VMHvl) of the hypothalamus. As these brain regions have been implicated in social behaviors and stress responses, our data suggest that the specific patterns of neuronal activation in the brain may relate to the altered social and anxiety-like behaviors following chronic social defeat in female Mongolian gerbils.

Appropriate Image Selection With Virtual Reality in Vestibular Rehabilitation: Cross-sectional Study

BACKGROUND

While vestibular rehabilitation with virtual reality (VR) is becoming more popular every day, the disadvantages of this method are not yet clear.

OBJECTIVE

The aim of this study is to examine the effect of the image to be used in vestibular rehabilitation with VR on the systems that provide body posture.

METHODS

The study was carried out with 36 participants (18 women and 18 men) aged 18 to 30 years. To assess balance control components separately, a sensory organization test was administered to the participants in the presence of stressful and relaxing environment images with VR technology. The State-Trait Anxiety Inventory survey was also used to measure the stress values in the created environments.

RESULTS

The State-Trait Anxiety Inventory survey revealed that while stressful videos significantly increased stress, relaxing videos reduced stress. Among measurements obtained in the presence of VR, significant decreases were observed mostly in the visual system data. A significant increase in vestibular system data (P=.01) was observed with a decrease in visual system data (P<.001) when the relaxing image was presented. Additionally, there was a significant difference in the somatosensory (P=.001), composite (P=.002), and visual system (P<.001) data in the presence of stressful videos.

CONCLUSIONS

Although the use of a VR system for vestibular rehabilitation is relatively new, no extant studies have examined how the image type used in VR can affect the integration of visual system data. Therefore, this study is unique in terms of showing the effects of the stress created by the change in the type of the image used in VR. When VR technology is used for therapeutic vestibular rehabilitation for patients whose balance disorder is due to the vestibular system, stress-free videos should be used. However, the use of stressful videos in VR technology will be beneficial in the rehabilitation of those with balance disorders due to the somatosensory system.

Do diurnal salivary cortisol curves carry meaningful information about the regulatory biology of the HPA axis in healthy humans?

Salivary cortisol stress biomarkers have been extensively used in epidemiological work to document links between stress and ill health. There has been little effort to ground field friendly cortisol measures in the hypothalamic-pituitary-adrenal (HPA) axis regulatory biology that is likely relevant to delineating mechanistic pathways leading from stress exposure to detrimental health outcomes. Here, we utilized a healthy convenience sample (n = 140) to examine normal linkages between extensively collected salivary cortisol measures and available laboratory probes of HPA axis regulatory biology. Participants provided 9 saliva samples per day over 6 days within a month, while engaging in usual activities, and also participated in 5 regulatory tests (adrenocorticoptripin stimulation, dexamethasone/corticotropin-releasing-hormone stimulation, metyrapone, dexamethasone suppression, and Trier Social Stress Test). Logistical regression was used to test specific predictions linking cortisol curve components to regulatory variables and to explore widely for non-predicted associations. We found support for 2 of 3 original hypotheses, showing associations (1) between cortisol diurnal decline and feedback sensitivity as measured by dexamethasone suppression, and (2) between morning cortisol levels and adrenal sensitivity. We did not find links between central drive (metyrapone test) and end of day salivary levels. We confirmed an a priori expectation of limited linkage between regulatory biology and diurnal salivary cortisol measures, beyond those predicted. These data support an emerging focus on measures related to diurnal decline in epidemiological stress work. They raise questions about the biological meaning of other curve components, including morning cortisol levels, and perhaps CAR (Cortisol Awakening Response). If morning cortisol dynamics are linked to stress, more work on adrenal sensitivity in stress adaptation and stress-health links may be warranted.

Vulnerability and resilience to cardiovascular and neuroendocrine effects of stress in adult rats with historical of chronic stress during adolescence

AIMS

This study investigated the influence of exposure to stress during adolescence in autonomic, cardiovascular, neuroendocrine and somatic changes evoked by chronic stress in adult rats.

MAIN METHODS

Animals were subjected to a 10-days protocol of repeated restraint stress (RRS, habituating) or chronic variable stress (CVS, non-habituating) during adolescence, adulthood, or repeated exposure to either RRS or CVS in adolescence and adulthood (adolescence+adulthood group). The trials to measure autonomic, cardiovascular, neuroendocrine and somatic changes in all experimental groups were performed in adulthood.

KEY FINDINGS

CVS increased basal circulating corticosterone levels and caused adrenal hypertrophy in the adolescence+adulthood group, an effect not identified in animals subjected to this stressor only in adulthood or adolescence. CVS also caused a sympathetically-mediated resting tachycardia in the adulthood group. This effect of CVS was not identified in the adolescence+adulthood group once the increased cardiac sympathetic activity was buffered by a decrease in intrinsic heart rate in these animals. Moreover, the impairment in baroreflex function observed in the adulthood group subjected to CVS was shifted to an improvement in animals subjected to repeated exposure to this stressor during adolescence and adulthood. The RRS in the adolescence+adulthood group caused a sympathetically-mediated resting tachycardia, which was not observed in the adulthood group.

SIGNIFICANCE

Our findings suggest that enduring effects of adverse events during adolescence included a vulnerability to neuroendocrine changes and a resilience to autonomic and cardiovascular dysfunctions caused by the CVS. Furthermore, results of RRS indicated a vulnerability to cardiovascular and autonomic changes evoked by homotypic stressors.

Windows into stress: a glimpse at emerging roles for CRHPVN neurons

The corticotropin-releasing hormone cells in the paraventricular nucleus of the hypothalamus (CRH^PVN) control the slow endocrine response to stress. The synapses on these cells are exquisitely sensitive to acute stress, leveraging local signals to leave a lasting imprint on this system. Additionally, recent work indicates that these cells also play key roles in the control of distinct stress and survival behaviors. Here we review these observations and provide a perspective on the role of CRH^PVN neurons as integrative and malleable hubs for behavioral, physiological, and endocrine responses to stress.

Stress-induced symptom exacerbation: Stress increases voiding frequency, somatic sensitivity, and urinary bladder NGF and BDNF expression in mice with subthreshold cyclophosphamide (CYP)

Symptom exacerbation due to stress is prevalent in many disease states, including functional disorders of the urinary bladder (e.g., overactive bladder (OAB), interstitial cystitis/bladder pain syndrome (IC/BPS)); however, the mechanisms underlying the effects of stress on micturition reflex function are unclear. In this study we designed and evaluated a stress-induced symptom exacerbation (SISE) mouse model that demonstrates increased urinary frequency and somatic (pelvic and hindpaw) sensitivity. Cyclophosphamide (CYP) (35 mg/kg; i.p., every 48 hours for a total of 4 doses) or 7 days of repeated variate stress (RVS) did not alter urinary bladder function or somatic sensitivity; however, both CYP alone and RVS alone significantly (p ≤ 0.01) decreased weight gain and increased serum corticosterone. CYP treatment when combined with RVS for 7 days (CYP+RVS) significantly (p ≤ 0.01) increased serum corticosterone, urinary frequency and somatic sensitivity and decreased weight gain. CYP+RVS exposure in mice significantly (p ≤ 0.01) increased (2.6-fold) voiding frequency as we determined using conscious, open-outlet cystometry. CYP+RVS significantly (p ≤ 0.05) increased baseline, threshold, and peak micturition pressures. We also evaluated the expression of NGF, BDNF, CXC chemokines and IL-6 in urinary bladder in CYP alone, RVS alone and CYP+RVS mouse cohorts. Although all treatments or exposures increased urinary bladder NGF, BDNF, CXC and IL-6 content, CYP+RVS produced the largest increase in all inflammatory mediators examined. These results demonstrated that CYP alone or RVS alone creates a change in the inflammatory environment of the urinary bladder but does not result in a change in bladder function or somatic sensitivity until CYP is combined with RVS (CYP+RVS). The SISE model of CYP+RVS will be useful to develop testable hypotheses addressing underlying mechanisms where psychological stress exacerbates symptoms in functional bladder disorders leading to identification of targets and potential treatments.

Do categorically distinct stressors alter the attention to visual food cues?

Stressor exposure affects food intake as well as the preference for high or low palatability foods, but little is known about how stressor types impact the visual attention to food images. We used eye tracking methodology in humans to determine if activation of the hypothalamus-pituitary-adrenal (HPA) axis and sympathetic nervous system is associated with changes in attention to food images as determined by measuring changes in oculomotor activity. Specifically, we tested two questions: 1) Do categorically distinct stressors alter aspects of visual attention to food images as determined by oculomotor activity (i.e., saccade latency, gaze duration, and saccade bouts)? 2) Do categorically distinct stressors differentially affect visual attention to food images of high or low palatability? A total of sixty participants were randomly divided into one of three test groups: controls, an anticipatory stressor group, or a reactive stressor group. We measured salivary cortisol and salivary alpha-amylase (sAA) before and after stressor exposure to confirm activation of the HPA axis and sympathetic nervous system, respectively. Following stressor exposure participants performed an eye-tracking test using a standardized food picture database (Food-pics). We analyzed saccade latency, gaze duration, and saccade bouts in balanced pairs of food and non-food images. Salivary cortisol was elevated by both stressors, although the elevation in salivary cortisol to the reactive stressor was driven by women only. sAA was elevated only by the anticipatory stressor. There were main effects of image type for all three eye-tracking variables, with initial saccades of shorter latency to food images and longer gaze duration and more saccade bouts with food images. Participants exposed to the reactive stressor reduced gaze duration on food images relative to controls, and this affect was not linked to palatability or salivary cortisol levels. We conclude that the reactive stressor decreased time spent looking at food, but not non-food, images. These data are partly consistent with the idea that reactive stressors reduce attention to non-critical visual signals.

Bed nucleus of the stria terminalis CB1 receptors and the FAAH enzyme modulate anxiety behavior depending on previous stress exposure

The endocannabinoid (eCB) anandamide (AEA) is synthesized on-demand in the post-synaptic terminal and can act on presynaptic cannabinoid type 1 (CB1) receptors, decreasing the release of neurotransmitters, including glutamate. AEA action is ended through enzymatic hydrolysis via FAAH (fatty acid amid hydrolase) in the post-synaptic neuron. eCB system molecules are widely expressed in brain areas involved in the modulation of fear and anxiety responses, including the Bed Nucleus of the Stria Terminalis (BNST), which is involved in the integration of autonomic, neuroendocrine, and behavioral regulation. The presence of the CB1 and FAAH was described in the BNST; however, their role in the modulation of defensive reactions is not fully comprehended. In the present work we aimed at investigating the role of AEA and CB1 receptors in the BNST in modulating anxiety-related behaviors. Adult male Wistar rats received local BNST injections of the CB1 receptor antagonist AM251 (0.1-0.6 nmol) and/or the FAAH inhibitor (URB597; 0.001-0.1 nmol) and were evaluated in the elevated plus maze (EPM) test, with or without previous acute restraint stress (2 h) exposure, or in the contextual fear conditioning. We observed that although AM251 and URB597 had no effects on the EPM, they increased and decreased, respectively, the conditioned fear response. Supporting a possible influence of stress in these differences, URB597 was able to prevent the restraint stress-induced anxiogenic effect in the EPM. The present data, therefore, suggest that eCB signaling in the BNST is recruited during more aversive situations to counteract the stress effect.

Physical Activity and Cortisol Regulation: A Meta-Analysis

Physical activity participation is associated with effective stress coping, indicated by decreases in both physiological stress reactivity and perceived stress. Quantifying the effect of physical activity on the diurnal regulation of one key physiological stress indicator, the stress hormone, cortisol, across studies may demonstrate the extent to which physical activity participation is associated with diurnal HPA axis regulation. We meta-analyzed studies examining relations between physical activity participation and indices of HPA axis regulation: the diurnal cortisol slope and the cortisol awakening response. We also examined moderators of the relation. The analysis revealed a small, non-zero negative averaged correlation between physical activity and the diurnal cortisol slope (r = -0.043, 95% CI [-0.080, -0.004]). Examination of sample sociodemographic differences, study design characteristics, cortisol measurement methods, and physical activity variables as moderators revealed few effects on the relation between physical activity and diurnal cortisol slope. We did not observe lower levels of variability in the mean cortisol awakening response at higher levels of physical activity participation, and moderator analyses showed little evidence of reductions in heterogeneity for this effect. We found some evidence of systematic publication bias. Findings suggest higher physical activity is associated with a steeper diurnal cortisol slope. However, the cortisol awakening response did not differ by physical activity level. Future studies testing the physical activity and cortisol regulation association should use standardized physical activity measures, follow guidelines for better quality cortisol sampling collection and analysis, and test relations in large-scale empirical studies to confirm the direction and causality of the effect.

Effects of Group Size on Behavior, Reproduction, and mRNA Expression in Brains of Brandt's Voles

For social animals, a moderate group size is greatly important to maintain their reproductive success. However, the underlying neurobiological mechanism of group size on behavior and reproduction has rarely been investigated. In this study, we examined the effects of group size (1, 2, 4 pairs of adult male and female voles raised per cage) on behavior and reproduction. Meanwhile, the mRNA expression of stress and reproduction response-related genes in male brains was detected. We found that Brandt's voles (Lasiopodomys brandtii) in the large-sized group fight more severely than those in the small-sized group. Meanwhile, male voles were more anxious than females. The average number of embryos and litters per female in the medium-sized group was significantly higher than that of large-sized group. In male voles, stress- or reproduction-response mRNA expressions were more related to final group size or final density due to death caused by fighting. Our results indicated that a moderate group size was beneficial to the reproductive output of Brandt's voles. Our study highlights the combined effects of stress- or reproduction-related gene expression or behavior in regulating the fitness of voles with different group sizes.

Stress and the hypothalamic-pituitary-adrenal axis: How can the COVID-19 pandemic inform our understanding and treatment of acute insomnia?

Stress and sleep are very closely linked, and stressful life events can trigger acute insomnia. The ongoing COVID-19 pandemic is highly likely to represent one such stressful life event. Indeed, a wide range of cross-sectional studies demonstrate that the pandemic is associated with poor sleep and sleep disturbances. Given the high economic and health burden of insomnia disorder, strategies that can prevent and treat acute insomnia, and also prevent the transition from acute insomnia to insomnia disorder, are necessary. This narrative review outlines why the COVID-19 pandemic is a stressful life event, and why activation of the hypothalamic-pituitary-adrenal axis, as a biological marker of psychological stress, is likely to result in acute insomnia. Further, this review outlines how sleep disturbances might arise as a result of the COVID-19 pandemic, and why simultaneous hypothalamic-pituitary-adrenal axis measurement can inform the pathogenesis of acute insomnia. In particular, we focus on the cortisol awakening response as a marker of hypothalamic-pituitary-adrenal axis function, as cortisol is the end-product of the hypothalamic-pituitary-adrenal axis. From a research perspective, future opportunities include identifying individuals, or particular occupational or societal groups (e.g. frontline health staff), who are at high risk of developing acute insomnia, and intervening. From an acute insomnia treatment perspective, priorities include testing large-scale online behavioural interventions; examining if reducing the impact of stress is effective and, finally, assessing whether "sleep vaccination" can maintain good sleep health by preventing the occurrence of acute insomnia, by preventing the transition from acute insomnia to insomnia disorder.

The Endogenous Cannabinoid and the Nitricoxidergic Systems in the Modulation of Stress Responses

The effects on stress-induced analgesia (SIA) from endogenous cannabinoid system (ECS) and nitric oxide (NO) interaction after 1 h of restraint stress were evaluated in male Wistar rats. The animals were subjected to 1 h of restraint and then injected with different combinations of cannabinoid receptor type 1 agonist anandamide (AEA) or antagonist AM251 along with an NO donor, NO precursor, or inhibitor of NO synthase. Nociception was evaluated using paw pressure (PP) or hot plate (HP) tests. AEA was administered immediately after the end of restraint-SIA (r-SIA). Administration of NO precursor reversed the pronociceptive effect of the CB1 agonist on r-SIA. Both the CB1 antagonist and the NOS inhibitor neutralized the pro-analgesic effect of L-arginine (L-arg). Administration of an NO donor, instead, increased r-SIA. Our experiments confirmed that the endogenous cannabinoid and the NO-ergic systems interact in the modulation of r-SIA. This interaction probably implies NO as a second messenger of the ECS.

Expression Profile of miRNA from High, Middle, and Low Stress-Responding Sheep during Bacterial Endotoxin Challenge

Animals respond to stress by activating a wide array of physiological and behavioral responses that are collectively referred to as the stress response. MicroRNAs (miRNAs) are small, noncoding RNAs that play key roles in the regulation of homeostasis. There are many reports demonstrating examples of stress-induced miRNA expression profiles. The aim of this study was to determine the circulatory miRNA profile of variable stress-responding lambs (n = 112) categorized based on their cortisol levels as high (HSR, 336.2 ± 27.9 nmol/L), middle (MSR, 147.3 ±9.5 nmol/L), and low (LSR, 32.1 ± 10.4 nmol/L) stress responders post-LPS challenge (400 ng/kg iv). Blood was collected from the jugular vein at 0 (T0) and 4 h (T4) post-LPS challenge, and miRNAs were isolated from four animals from each group. An array of 84 miRNAs and 6 individual miRNAs were evaluated using qPCR. Among 90 miRNAs, there were 48 differentially expressed (DE) miRNAs (log fold change (FC) > 2 < log FC) in the HSR group, 46 in the MSR group, and 49 in the LSR group compared with T0 (control) samples. In the HSR group, three miRNAs, miR-485-5p, miR-1193-5p, and miR-3957-5p were significantly (p < 0.05) upregulated, while seven miRNAs, miR-376b-3p, miR-376c-3p, miR-411b-5p, miR-376a-3p, miR-376b-3p, miR-376c-3p, and miR-381-3p, were downregulated (p < 0.05) as compared to the LSR and MSR groups. Functional analysis of DE miRNAs revealed their roles in Ras and MAPK signaling, cytokine signaling, the adaptive immune system, and transcription pathways in the HSR phenotype, implicating a hyper-induced acute-phase response. In contrast, in the LSR group, enriched pathways included glucagon signaling metabolic regulation, the transportation of amino acids and ions, and the integration of energy metabolism. Taken together, these results indicate variation in the acute-phase response to an immune stress challenge, and these miRNAs are implicated in regulating responses within cortisol-based phenotypes.

Sodium Intake and Disease: Another Relationship to Consider

Sodium (Na+) is crucial for numerous homeostatic processes in the body and, consequentially, its levels are tightly regulated by multiple organ systems. Sodium is acquired from the diet, commonly in the form of NaCl (table salt), and substances that contain sodium taste salty and are innately palatable at concentrations that are advantageous to physiological homeostasis. The importance of sodium homeostasis is reflected by sodium appetite, an "all-hands-on-deck" response involving the brain, multiple peripheral organ systems, and endocrine factors, to increase sodium intake and replenish sodium levels in times of depletion. Visceral sensory information and endocrine signals are integrated by the brain to regulate sodium intake. Dysregulation of the systems involved can lead to sodium overconsumption, which numerous studies have considered causal for the development of diseases, such as hypertension. The purpose here is to consider the inverse-how disease impacts sodium intake, with a focus on stress-related and cardiometabolic diseases. Our proposition is that such diseases contribute to an increase in sodium intake, potentially eliciting a vicious cycle toward disease exacerbation. First, we describe the mechanism(s) that regulate each of these processes independently. Then, we highlight the points of overlap and integration of these processes. We propose that the analogous neural circuitry involved in regulating sodium intake and blood pressure, at least in part, underlies the reciprocal relationship between neural control of these functions. Finally, we conclude with a discussion on how stress-related and cardiometabolic diseases influence these circuitries to alter the consumption of sodium.

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.

Understanding the Role of Oxidative Stress, Neuroinflammation and Abnormal Myelination in Excessive Aggression Associated with Depression: Recent Input from Mechanistic Studies

Aggression and deficient cognitive control problems are widespread in psychiatric disorders, including major depressive disorder (MDD). These abnormalities are known to contribute significantly to the accompanying functional impairment and the global burden of disease. Progress in the development of targeted treatments of excessive aggression and accompanying symptoms has been limited, and there exists a major unmet need to develop more efficacious treatments for depressed patients. Due to the complex nature and the clinical heterogeneity of MDD and the lack of precise knowledge regarding its pathophysiology, effective management is challenging. Nonetheless, the aetiology and pathophysiology of MDD has been the subject of extensive research and there is a vast body of the latest literature that points to new mechanisms for this disorder. Here, we overview the key mechanisms, which include neuroinflammation, oxidative stress, insulin receptor signalling and abnormal myelination. We discuss the hypotheses that have been proposed to unify these processes, as many of these pathways are integrated for the neurobiology of MDD. We also describe the current translational approaches in modelling depression, including the recent advances in stress models of MDD, and emerging novel therapies, including novel approaches to management of excessive aggression, such as anti-diabetic drugs, antioxidant treatment and herbal compositions.

Rapid volumetric brain changes after acute psychosocial stress

Stress is an important trigger for brain plasticity: Acute stress can rapidly affect brain activity and functional connectivity, and chronic or pathological stress has been associated with structural brain changes. Measures of structural magnetic resonance imaging (MRI) can be modified by short-term motor learning or visual stimulation, suggesting that they also capture rapid brain changes. Here, we investigated volumetric brain changes (together with changes in T1 relaxation rate and cerebral blood flow) after acute stress in humans as well as their relation to psychophysiological stress measures. Sixty-seven healthy men (25.8±2.7 years) completed a standardized psychosocial laboratory stressor (Trier Social Stress Test) or a control version while blood, saliva, heart rate, and psychometrics were sampled. Structural MRI (T1 mapping / MP2RAGE sequence) at 3T was acquired 45 min before and 90 min after intervention onset. Grey matter volume (GMV) changes were analysed using voxel-based morphometry. Associations with endocrine, autonomic, and subjective stress measures were tested with linear models. We found significant group-by-time interactions in several brain clusters including anterior/mid-cingulate cortices and bilateral insula: GMV was increased in the stress group relative to the control group, in which several clusters showed a GMV decrease. We found a significant group-by-time interaction for cerebral blood flow, and a main effect of time for T1 values (longitudinal relaxation time). In addition, GMV changes were significantly associated with state anxiety and heart rate variability changes. Such rapid GMV changes assessed with VBM may be induced by local tissue adaptations to changes in energy demand following neural activity. Our findings suggest that endogenous brain changes are counteracted by acute psychosocial stress, which emphasizes the importance of considering homeodynamic processes and generally highlights the influence of stress on the brain.

Dexmedetomidine improves the acute stress reactivity of male rat through interventions of serum- and glucocorticoid-inducible kinase 1 and nNOS in the bed nucleus of the stria terminalis

Moderate acute stress responses are beneficial for adaptation and maintenance of homeostasis. Exposure of male rat to stress induces effects in the bed nucleus of the stria terminalis (BNST), for it can be activated by the same stimuli that induce activation of the hypothalamic-pituitary-adrenal axis. However, the underlying mechanism of the BNST on male stress reactivity remains unclear. In this study, we explored whether systematic administration of dexmedetomidine (DEXM) altered the acute stress reactivity through its effect on the BNST. Male Sprague-Dawley rats in the stress (STRE) group, DEXM group, and the DEXM + GSK-650394 (GSK, an antagonist of serum- and glucocorticoid-inducible kinase 1 (SGK1)) group, except those in the vehicle (VEH) group, underwent 1-h restraint plus water-immersion (RPWI) exposure. All the rats proceeded the open field test (OFT) 24 h before RPWI and 1 h after RPWI. After the second OFT, the rats received VEH, DEXM (75 μg/kg i.p.), or were pretreated with GSK (2 μM i.p.) 0.5 h ahead of DEXM respectively. The third OFT was conducted 6 h after drug administration and then the rats were sacrificed. The rats that experienced RPWI showed dramatically elevated serum corticosterone (CORT), multiplied neuronal nitric oxide synthase (nNOS) and SGK1 in the BNST, and terrible OFT behavior. We discovered when the nNOS and SGK1 were decreased in the rat BNST through DEXM treatment, the serum CORT was reduced and the OFT manifestation was ameliorated, whereas these were restrained by GSK application. Our results reveal that modest interventions to SGK1 and nNOS in the BNST improve the male rat reactivity to acute stress, and DEXM was one modulator of these effects.

Thomas F, Battaglia F. High-frequency rTMS modulates emotional behaviors and structural plasticity in layers II/III and V of the mPFC

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique, and it has been increasingly used as a nonpharmacological intervention for the treatment of various neurological and neuropsychiatric diseases, including depression. In humans, rTMS over the prefrontal cortex is used to induce modulation of the neural circuitry that regulates emotions, cognition, and depressive symptoms. However, the underlying mechanisms are still unknown. In this study, we investigated the effects of a short (5-day) treatment with high-frequency (HF) rTMS (15 Hz) on emotional behavior and prefrontal cortex morphological plasticity in mice. Mice that had undergone HF-rTMS showed an anti-depressant-like activity as evidenced by decreased immobility time in both the Tail Suspension Test and the Forced Swim Test along with increased spine density in both layer II/III and layer V apical and basal dendrites. Furthermore, dendritic complexity assessed by Sholl analysis revealed increased arborization in the apical portions of both layers, but no modifications in the basal dendrites branching. Overall, these results indicate that the antidepressant-like activity of HF-rTMS is paralleled by structural remodeling in the medial prefrontal cortex.

Clinical characteristics of patients with unexplainable hypothalamic disorder diagnosed by the corticotropin-releasing hormone challenge test: a retrospective study

BACKGROUND

The corticotropin-releasing hormone (CRH) challenge test can distinguish the disorders of the hypothalamus from those of the pituitary. However, the pathophysiology of hypothalamic disorder (HD) has not been fully understood. This study aimed to elucidate the clinical characteristics of patients with unexplainable HD, diagnosed by the CRH challenge test.

METHODS

We retrospectively reviewed patients who underwent the CRH challenge test. Patients were categorized into four groups as follows: patients with peak serum cortisol ≥18 μg/dL were assigned to the normal response (NR) group (n = 18), among patients with peak serum cortisol < 18 μg/dL and peak adrenocorticotropic hormone (ACTH) increase ≥two-fold, patients without obvious background pathology were assigned to the unexplainable-HD group (n = 18), whereas patients with obvious background pathology were assigned to the explainable-HD group (n = 38), and patients with peak serum cortisol < 18 μg/dL and peak ACTH increase <two-fold were assigned to the pituitary disorder (PD) group (n = 15). Inter-group comparisons were performed based on clinical characteristics.

RESULTS

In the CRH challenge test, the peak plasma ACTH levels were significantly lower in the unexplainable-HD group than in the NR group, despite more than two-fold increase compared to basal levels. The increase in serum cortisol was significantly higher in the unexplainable-HD group than in the explainable-HD and PD groups. Although patients in the unexplainable-HD group showed a clear ACTH response in the insulin tolerance test, some patients had peak serum cortisol levels of < 18 μg/dL. Furthermore, attenuated diurnal variations and low normal levels of urinary free cortisol were observed. Most patients in the unexplainable-HD group were young women with chronic fatigue. However, supplementation with oral hydrocortisone at physiological doses reduced fatigue only in some patients.

CONCLUSIONS

Patients with unexplainable HD diagnosed by the CRH challenge test had hypothalamic-pituitary-adrenal (HPA) axis dysfunction and some patients had mild central adrenal insufficiency. Hydrocortisone supplementation reduced fatigue only in some patients, suggesting that HPA axis dysfunction may be a physiological adaptation. Further investigation of these patients may help elucidate the pathophysiology of myalgic encephalitis/chronic fatigue syndrome.

Differential responses toward conditioned and unconditioned stimuli, but decreased hypothalamic-pituitary-adrenal axis responsiveness in neonatal hippocampal lesioned monkeys

The hippocampus is important for long-term memory storage, but also plays a role in regulating the hypothalamic-pituitary-adrenal (HPA) axis and emotional behaviors. We previously reported that early hippocampal damage in monkeys result in increased anxious expression and blunted HPA responses to an acute stressor. Here, we further probe their responses toward aversive stimuli (conditioned and unconditioned) and evaluate HPA axis dysfunction. Responses toward social, innate, and learned aversive stimuli, fear potentiated acoustic startle, and pituitary-adrenal function were investigated in 13 adult rhesus monkeys with neonatal hippocampal lesions (Neo-Hibo=6) and controls (Neo-C=7). Neo-Hibo monkeys' responses depend on the type of unconditioned stimulus, with increased anxiety behaviors toward social and learned, but decreased reactivity toward innate stimuli. Neo-C and Neo-Hibo monkeys exhibited similar performance learning conditioned cues and safety signals. Neo-Hibo monkeys were less sensitive to HPA axis stimulation, potentially suggesting adrenal fatigue. Current findings suggest that the hippocampus plays a large role in regulating not only anxiety behaviors, but also the HPA-axis, a neural system crucial to regulate how we respond to the world around us. These data have important clinical significance considering that many developmental neuropsychiatric disorders exhibit altered hippocampal structure and function, emotional and HPA axis dysregulation.

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

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

The Central Nervous Mechanism of Stress-Promoting Cancer Progression

Evidence shows that stress can promote the occurrence and development of tumors. In recent years, many studies have shown that stress-related hormones or peripheral neurotransmitters can promote the proliferation, survival, and angiogenesis of tumor cells and impair the body’s immune response, causing tumor cells to escape the “surveillance” of the immune system. However, the perception of stress occurs in the central nervous system (CNS) and the role of the central nervous system in tumor progression is still unclear, as are the underlying mechanisms. This review summarizes what is known of stress-related CNS-network activation during the stress response and the influence of the CNS on tumors and discusses available adjuvant treatment methods for cancer patients with negative emotional states, such as anxiety and depression.

Targeting the cannabinoid system to counteract the deleterious effects of stress in Alzheimer’s disease

Alzheimer’s disease is a progressive neurodegenerative disorder characterized histologically in postmortem human brains by the presence of dense protein accumulations known as amyloid plaques and tau tangles. Plaques and tangles develop over decades of aberrant protein processing, post-translational modification, and misfolding throughout an individual’s lifetime. We present a foundation of evidence from the literature that suggests chronic stress is associated with increased disease severity in Alzheimer’s patient populations. Taken together with preclinical evidence that chronic stress signaling can precipitate cellular distress, we argue that chronic psychological stress renders select circuits more vulnerable to amyloid- and tau- related abnormalities. We discuss the ongoing investigation of systemic and cellular processes that maintain the integrity of protein homeostasis in health and in degenerative conditions such as Alzheimer’s disease that have revealed multiple potential therapeutic avenues. For example, the endogenous cannabinoid system traverses the central and peripheral neural systems while simultaneously exerting anti-inflammatory influence over the immune response in the brain and throughout the body. Moreover, the cannabinoid system converges on several stress-integrative neuronal circuits and critical regions of the hypothalamic-pituitary-adrenal axis, with the capacity to dampen responses to psychological and cellular stress. Targeting the cannabinoid system by influencing endogenous processes or exogenously stimulating cannabinoid receptors with natural or synthetic cannabis compounds has been identified as a promising route for Alzheimer’s Disease intervention. We build on our foundational framework focusing on the significance of chronic psychological and cellular stress on the development of Alzheimer’s neuropathology by integrating literature on cannabinoid function and dysfunction within Alzheimer’s Disease and conclude with remarks on optimal strategies for treatment potential.

Functional brain-wide network mapping during acute stress exposure in rats: Interaction between the lateral habenula and cortical, amygdalar, hypothalamic and monoaminergic regions

Upon stress exposure, a broad network of structures comes into play in order to provide adequate responses and restore homeostasis. It has been known for decades that the main structures engaged during the stress response are the medial prefrontal cortex, the amygdala, the hippocampus, the hypothalamus, the monoaminergic systems (noradrenaline, dopamine and serotonin) and the periaqueductal gray. The lateral habenula (LHb) is an epithalamic structure directly connected to prefrontal cortical areas and to the amygdala, whereas it functionally interacts with the hippocampus. Also, it is a main modulator of monoaminergic systems. The LHb is activated upon exposure to basically all types of stressors, suggesting it is also involved in the stress response. However, it remains unknown if and how the LHb functionally interacts with the broad stress response network. In the current study we performed in rats a restraint stress procedure followed by immunohistochemical staining of the c-Fos protein throughout the brain. Using graph theory-based functional connectivity analyses, we confirm the principal hubs of the stress network (e.g., prefrontal cortex, amygdala and periventricular hypothalamus) and show that the LHb is engaged during stress exposure in close interaction with the medial prefrontal cortex, the lateral septum and the medial habenula. In addition, we performed DREADD-induced LHb inactivation during the same restraint paradigm in order to explore its consequences on the stress response network. This last experiment gave contrasting results as the DREADD ligand alone, clozapine-N-oxide, was able to modify the network.

Stressed and wired: The effects of stress on the VTA circuits underlying motivated behavior

Stress affects many brain regions, including the ventral tegmental area (VTA), which is critically involved in reward processing. Excessive stress can reduce reward-seeking behaviors but also exacerbate substance use disorders, two seemingly contradictory outcomes. Recent research has revealed that the VTA is a heterogenous structure with diverse populations of efferents and afferents serving different functions. Stress has correspondingly diverse effects on VTA neuron activity, tending to decrease lateral VTA dopamine (DA) neuron activity, while increasing medial VTA DA and GABA neuron activity. Here we review the differential effects of stress on the activity of these distinct VTA neuron populations and how they contribute to decreases in reward-seeking behavior or increases in drug self-administration.

Increased Hippocampal Glucocorticoid Receptor Expression and Reduced Anxiety-Like Behavior Following Tuina in a Rat Model With Allergic Airway Inflammation

OBJECTIVE

This study aimed to explore the influence mechanism of Tuina on anxiety-like behavior in immature rats with allergic airway inflammation (AAI).

METHODS

A total of 27 Sprague-Dawley male rats (aged ∼5 weeks) were divided randomly into control, AAI, and AAI with Tuina groups (9 rats per group). The anxiety-like behavior was assessed by an open field test and elevated plus-maze test. Allergic airway inflammation was assessed based on the pathological score of the lung, plasma ovalbumin-specific immunoglobulin E, interleukin 4, interleukin 5, and tumor necrosis factor-alpha levels. Glucocorticoid receptor (GR) messenger RNA and protein expression in the hippocampus and lung were detected by polymerase chain reaction and immunohistochemistry, respectively. Meanwhile, corticotropin-releasing hormone (CRH) messenger RNA in the hypothalamus, the plasma levels of adrenocorticotropic hormone and corticosterone were also determined respectively by polymerase chain reaction and enzyme-linked immunosorbent assay for hypothalamic-pituitary-adrenal axis (HPA) function.

RESULTS

The AAI group had obvious anxiety-like behavior and hyperactive HPA axis, along with decreased GR expression in the hippocampus and lung. Following Tuina, AAI and the anxiety-like behavior were efficiently reduced, and the hyperactivity of HPA axis was efficiently inhibited, along with enhanced GR expression in the hippocampus and lung.

CONCLUSION

Glucocorticoid receptor expression in the hippocampus and lung was enhanced, and anxiety-like behavior was reduced following Tuina in rats with AAI.

The growing field of immunometabolism and exercise: Key findings in the last 5 years

This perspective review highlights the impact of physical exercise on immunometabolic responses in the past 5 years. Understanding immunometabolism as a part of immunological research is essential. Furthermore, the roles of both acute and chronic effects of physical exercise on health, aging, and chronic diseases in immunometabolic changes should be elaborated. In immune cells, β2 adrenergic signaling stimulates the preferential mobilization of inflammatory phenotypes, such as CD16⁺ monocytes and CD8⁺ T cells, into the bloodstream after a physical exercise session. The mobilization of immune cells is closely related to the availability of energetic substrates for the cell and mechanisms associated with the uptake and oxidation of fatty acids and glucose. These cells, especially senescent T cells, are mobilized to the peripheral tissues and undergo apoptotic signaling, stimulating the creation of a "vacant space" where new cells will be matured and replaced in the circulation. This results in the upregulation of the expression and secretion of anti-inflammatory cytokines (IL-10 and IL-1ra), leading to increased regulatory immune cells that provide immunoregulatory properties. Thus, we suggest that a significant nutrient available to the cell will favor oxidative metabolism, augment ATP production, and consequently maintain the immune cells in their quiescent state, as well as promote rapid activation function. Therefore, based on the studies discussed in this perspective review, we highlight the importance of performing moderate-intensity continuous and high-intensity intermittent aerobic exercises, due to a higher magnitude of energetic demand and release of anti-inflammatory cytokines (IL-6 and IL-10).

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.

Chronic Stress in Bipolar Disorders Across the Different Clinical States: Roles of HPA Axis and Personality

INTRODUCTION

Chronic stress has been linked to the pathophysiology of bipolar disorder (BD); however, the underlying mechanism remains unclear. In BD patients, hypothalamic-pituitary-adrenal (HPA) axis activity is associated with stress. This study aimed to examine the relationship between HPA axis activity and BD symptoms in various clinical states, as well as how personality influences the process.

METHODS

This study investigated the differences in HPA axis activity among four BD states. We enrolled 813 BD patients in an 8-week longitudinal study to examine the relationship between HPA axis activity and symptom trajectories using dynamic temporal warping (DTW) analysis and an unsupervised machine learning technique. Furthermore, using mediation analyses, the relationship between the HPA axis, personality, and BD symptoms was investigated.

RESULTS

Analysis of variance (ANOVA) analysis showed that glucocorticoid cortisol (CORT) and adrenocorticotropin (ACTH) did not differ significantly among the four clinical states of BD. The DTW integrating clustering analysis revealed that the two clusters were optimal, with cluster 1 characterized by severe manic symptoms, which then improved, and cluster 2, characterized by milder manic severity, which also improved. The two clusters showed different ACTH levels (t = 2.289, p = 0.022), and logistic regression analysis revealed a slight positive association between ACTH levels and cluster 1. Furthermore, the mediation analysis indicated that ACTH influences curative efficacy via conscientiousness (βc =0.103, p=0.001).

DISCUSSION

In conclusion, we found that a higher level of ACTH is associated with severe manic symptoms, indicating a chronic stress response in BD patients. Additionally, the ACTH levels affect short-term BD curative efficacy via the mediation of conscientiousness, providing a psychotherapeutic strategy direction for BD.

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

Child maltreatment and hypothalamic-pituitary-adrenal axis functioning: A systematic review and meta-analysis

Alterations in hypothalamic-pituitary-adrenal (HPA) axis and its effector hormone cortisol have been proposed as one possible mechanism linking child maltreatment experiences to health disparities. In this series of meta-analyses, we aimed to quantify the existing evidence on the effect of child maltreatment on various measures of HPA axis activity. The systematic literature search yielded 1,858 records, of which 87 studies (k = 132) were included. Using random-effects models, we found evidence for blunted cortisol stress reactivity in individuals exposed to child maltreatment. In contrast, no overall differences were found in any of the other HPA axis activity measures (including measures of daily activity, cortisol assessed in the context of pharmacological challenges and cumulative measures of cortisol secretion). The impact of several moderators (e.g., sex, psychopathology, study quality), the role of methodological shortcomings of existing studies, as well as potential directions for future research are discussed.

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.

Sleep fragmentation engages stress-responsive circuitry, enhances inflammation and compromises hippocampal function following traumatic brain injury

Traumatic brain injury (TBI) impairs the ability to restore homeostasis in response to stress, indicating hypothalamic-pituitary-adrenal (HPA)-axis dysfunction. Many stressors result in sleep disturbances, thus mechanical sleep fragmentation (SF) provides a physiologically relevant approach to study the effects of stress after injury. We hypothesize SF stress engages the dysregulated HPA-axis after TBI to exacerbate post-injury neuroinflammation and compromise recovery. To test this, male and female mice were given moderate lateral fluid percussion TBI or sham-injury and left undisturbed or exposed to daily, transient SF for 7- or 30-days post-injury (DPI). Post-TBI SF increases cortical expression of interferon- and stress-associated genes characterized by inhibition of the upstream regulator NR3C1 that encodes glucocorticoid receptor (GR). Moreover, post-TBI SF increases neuronal activity in the hippocampus, a key intersection of the stress-immune axes. By 30 DPI, TBI SF enhances cortical microgliosis and increases expression of pro-inflammatory glial signaling genes characterized by persistent inhibition of the NR3C1 upstream regulator. Within the hippocampus, post-TBI SF exaggerates microgliosis and decreases CA1 neuronal activity. Downstream of the hippocampus, post-injury SF suppresses neuronal activity in the hypothalamic paraventricular nucleus indicating decreased HPA-axis reactivity. Direct application of GR agonist, dexamethasone, to the CA1 at 30 DPI increases GR activity in TBI animals, but not sham animals, indicating differential GR-mediated hippocampal action. Electrophysiological assessment revealed TBI and SF induces deficits in Schaffer collateral long-term potentiation associated with impaired acquisition of trace fear conditioning, reflecting dorsal hippocampal-dependent cognitive deficits. Together these data demonstrate that post-injury SF engages the dysfunctional post-injury HPA-axis, enhances inflammation, and compromises hippocampal function. Therefore, external stressors that disrupt sleep have an integral role in mediating outcome after brain injury.

Stress-induced HPA activation in virtual navigation and spatial attention performance

Background

Previous research has shown that spatial performance (e.g. navigation, visuospatial memory, attention) can be influenced by acute stress; however, studies have produced mixed findings sometimes showing an improvement after stress, other times showing impairment or no overall effect. Some of these discrepancies may be related to: the type of stress system activated by the stressor (sympathetic adrenal medulla [SAM] or hypothalamic-pituitary-adrenocortical [HPA]); whether cortisol responders vs. nonresponders are analyzed subsequent to main effects; and sex differences in stress responses. In the present study, we examine the influence of HPA activation from an acute laboratory stressor (Socially Evaluated Cold Pressor test [SECPT]) on performance during two spatial tasks: Useful Field of View (UFOV; a measure of spatial attention) and virtual reality (VR) navigation. We assigned 31 males and 30 females to either the SECPT or a Non-Stress condition prior to the two spatial tasks. Cardiovascular measures including heart rate and blood pressure, and salivary cortisol biosamples were obtained at specific time points.

Results

Participants in the Stress condition showed increases in heart rate, systolic and diastolic blood pressure indicating sympathetic adrenal medulla (SAM) axis activation. Stress also led to increases in salivary cortisol, suggesting hypothalamic-pituitary-adrenocortical (HPA) activation. Stress did not influence overall performance in the spatial attention UFOV or the VR navigation task. However, a sex difference in spatial attention was detected when participants were divided into Stress-cortisol responders and non-responders in the UFOV task. Male Stress-cortisol responders (n = 9) showed better UFOV accuracy than female Stress-cortisol responders (n = 6); no sex differences were found among the Non-Stress control group. Furthermore, for females in the stress condition (n = 14), higher cortisol responses were associated with lower spatial attention performance.

Conclusions

Socially Evaluated Cold Pressor stress resulted in no change in speed or accuracy in a VR navigation task. For the spatial attention task, the SECPT led to a sex difference among Stress-cortisol responders with males showing improved accuracy over females. The relationship between HPA activation and prefrontal cortex activity may be necessary to understand sex differences in spatial attention performance.

Hippocampus-Anterior Hypothalamic Circuit Modulates Stress-Induced Endocrine and Behavioral Response

Hippocampal input to the hypothalamus is known to be critically involved in mediating the negative feedback inhibition of stress response. However, the underlying neural circuitry has not been fully elucidated. Using a combination of rabies tracing, pathway-specific optogenetic inhibition, and cell-type specific synaptic silencing, the present study examined the role of hippocampal input to the hypothalamus in modulating neuroendocrine and behavioral responses to stress in mice. Transsynaptic rabies tracing revealed that the ventral hippocampus (vHPC) is monosynaptically connected to inhibitory cells in the anterior hypothalamic nucleus (AHN-GABA cells). Optogenetic inhibition of the vHPC→AHN pathway during a restraint stress resulted in a prolonged and exaggerated release of corticosterone, accompanied by an increase in stress-induced anxiety behaviors. Consistently, tetanus toxin-mediated synaptic inhibition in AHN-GABA cells produced a remarkably similar effect on the corticosterone release profile, corroborating the role of HPC→AHN pathway in mediating the hippocampal control of stress responses. Lastly, we found that chronic inhibition of AHN-GABA cells leads to cognitive impairments in both object and social recognition memory. Together, our data present a novel hypothalamic circuit for the modulation of adaptive stress responses, the dysfunction of which has been implicated in various affective disorders.

The Influence of Adverse Childhood Experiences in Pain Management: Mechanisms, Processes, and Trauma-Informed Care

Adverse childhood experiences (ACEs) increase the likelihood of reduced physical and psychological health in adulthood. Though understanding and psychological management of traumatic experiences is growing, the empirical exploration of ACEs and physical clinical outcomes remains under-represented and under-explored. This topical review aimed to highlight the role of ACEs in the experience of chronic pain, pain management services and clinical decision making by: (1) providing an overview of the relationship between ACEs and chronic pain; (2) identifying biopsychosocial mechanisms through which ACEs may increase risk of persistent pain; (3) highlighting the impact of ACEs on patient adherence and completion of pain management treatment; and (4) providing practical clinical implications for pain management. Review findings demonstrated that in chronic pain, ACEs are associated with increased pain complications, pain catastrophizing and depression and the combination of these factors further heightens the risk of early treatment attrition. The pervasive detrimental impacts of the COVID-19 pandemic on ACEs and their cyclical effects on pain are discussed in the context of psychological decline during long treatment waitlists. The review highlights how people with pain can be further supported in pain services by maintaining trauma-informed practices and acknowledging the impact of ACEs on chronic pain and detrimental health outcomes. Clinicians who are ACE-informed have the potential to minimize the negative influence of ACEs on treatment outcomes, ultimately optimizing the impact of pain management services.

Rutland C. Equine Stress: Neuroendocrine Physiology and Pathophysiology

This review presents new aspects to understanding the neuroendocrine regulation of equine stress responses, and their influences on the physiological, pathophysiological, and behavioral processes. Horse management, in essence, is more frequently confirmed by external and internal stress factors, than in other domestic animals. Regardless of the nature of the stimulus, the equine stress response is an effective and highly conservative set of interconnected relationships designed to maintain physiological integrity even in the most challenging circumstances (e.g., orthopedic injuries, abdominal pain, transport, competitions, weaning, surgery, and inflammation). The equine stress response is commonly a complementary homeostatic mechanism that provides protection (not an adaptation) when the body is disturbed or threatened. It activates numerous neural and hormonal networks to optimize metabolic, cardiovascular, musculoskeletal, and immunological functions. This review looks into the various mechanisms involved in stress responses, stress-related diseases, and assessment, prevention or control, and management of these diseases and stress. Stress-related diseases can not only be identified and assessed better, given the latest research and techniques but also prevented or controlled.

Corticotropin-releasing factor receptor 1 in infralimbic cortex modulates social stress-altered decision-making

Chronic stress could lead to a bias in behavioral strategies toward habits. However, it remains unclear which neuronal system modulates stress-induced behavioral abnormality during decision making. The corticotropin-releasing factor (CRF) system in the medial prefrontal cortex (mPFC), which has been implicated in governing strategy choice, is involved in the response to stress. The present study aimed to clarify whether altered function in cortical CRF receptors is linked to abnormal behaviors after chronic stress. In results, mice subjected to a 10-day social defeat preferred to use a habitual strategy. The infralimbic cortex (IL), but not the prelimbic cortex (PL) or anterior cingulate cortex (ACC), showed higher cFos expression in stress-subjected mice than in control mice, which may be associated with habitual behavior choice. Furthermore, CRF receptor 1 (CRFR1) agonist and antagonist infusion in IL during behavioral training mimicked and rescued stress-caused behavioral change in the decision-making assessment, respectively. An electrophysiological approach showed that the frequencies of both spontaneous IPSC and spontaneous EPSC, but not their amplitude, increased after stress and were modulated by CRFR1 agents. Further recordings revealed that an increased ratio of excitation to inhibition (E/I ratio) of IL by stress was rescued under conditions with CRFR1 antagonist. Collectively, these data indicate that CRFR1 plays a critical role in stress-permitted or enhanced glutamatergic and GABAergic presynaptic transmission in direct or indirect ways, as well as the modulation for E/I ratio in the IL. Thus, CRFR1 in the mPFC may be a proper target for treating cases of chronic stress-altered behavior.

Occlusal Disharmony-A Potential Factor Promoting Depression in a Rat Model

Objectives: Patients with occlusal disharmony (OD) may be susceptible to depression. The hypothalamus−pituitary−adrenal axis, 5-HT and 5HT2AR in the prefrontal cortex (PFC), amygdala, and hippocampus are involved in the modulation of emotion and depression. This study investigated whether OD affects the HPA axis and 5-HT system and, subsequently, produces depression-like behaviors in rats. Materials and methods: OD was produced by removing 0.5 and 0.25 mm of hard tissue from the cusps of the maxillary molars in randomly selected sides of Sprague−Dawley rats. CUS involved exposure to 2 different stressors per day for 35 days. OD-, CUS-, and OD + CUS-treated groups and an untreated control group were compared in terms of behavior, endocrine status and brain histology. Results: There were significant differences among the four groups in the behavior tests (p < 0.05), especially in the sucrose preference test, where there was a significant decrease in the OD group compared to the control group. ACTH and CORT concentrations were significantly higher in the OD + CUS group than the control group (p < 0.05). Expression of GR and 5-HT2AR in the PFC, amygdala and hippocampal CA1 was significantly higher in the OD, CUS and OD + CUS groups than the control group (p < 0.05). Conclusion: OD promotes depression-like behaviors through peripheral and central pathways via the HPA axis, GR and 5-HT system.