Neurobiology of Stress

All in vivo studies using laboratory animals should be guided by the Three Rs: Replacement, Reduction and Refinement. The concept of Reduction is important in sample size estimation; the sample size used should allow the detection of a biologically meaningful effect size using appropriate statistical tests, but not at the expense of animal suffering. Because studies using chronic variable stress (CVS) procedures deliberately impose suffering, we reasoned that Three Rs principles would be a strong consideration in experimental design. To explore this, we conducted a systematic review of CVS studies to ask whether a biologically meaningful effect size was used to determine the sample size. Only one article in our sample of 385 reported doing this. Accordingly, it is questionable whether most of these studies align strongly with the principle of Reduction. While determining a biologically meaningful effect size is not always straightforward, we believe it is central to making biologically informed decisions about study design and interpretation, and we discuss possible ways forward.

Exposure to stress can cause long-lasting enhancement of fear and other defensive responses that extend beyond the cues or contexts associated with the original traumatic event. These nonassociative consequences of stress, referred to as fear sensitization, are thought to underlie some symptoms of trauma-related disorders. Fear sensitization has been predominately studied using the Stress-Enhanced Fear Learning (SEFL) paradigm, which models the stress-induced amplification of fear learning. Less is known about the mechanisms through which unlearned fear responses are sensitized by stress. Here, we investigated the neural mechanisms for sensitization of unlearned fear responses using a paradigm we termed Stress-Enhanced Fear Responding (SEFR). In this model, mice exposed to a single session of footshock stress exhibit enhanced freezing to a novel tone stimulus. To investigate brain regions that might mediate SEFR, we first used c-Fos mapping to identify neural activity changes associated with stress-induced enhancement of unlearned fear. Our c-Fos screen identified the posterior paraventricular thalamus (pPVT) as a region that was persistently hyperactive after footshock stress and whose activity correlated with behavioral expression of SEFR. Using fiber photometry, we observed that SEFR, but not SEFL, was associated with increased activity in the pPVT. Next, we found that chemogenetic inhibition of the pPVT blocked both the induction of SEFR during stress and its later expression, while artificial stimulation of pPVT in stress-naive mice was sufficient to recapitulate SEFR. Interestingly, pPVT inhibition or stimulation did not affect acquisition or expression of SEFL. In conclusion, our results indicate that sensitization of fear learning (SEFL) and sensitization of unlearned fear (SEFR) have distinct neural mechanisms. Our results identify pPVT hyperactivity as a mechanism for stress-induced sensitization of unlearned fear and highlight pPVT as a potential target for treating arousal and reactivity symptoms of trauma- and stressor-related disorders.

Exposure to early life stress (ELS) can exert long-lasting impacts on emotional regulation. The corticolimbic system including the basolateral amygdala (BLA), ventral hippocampus (vHIP), and the medial prefrontal cortex (mPFC) plays a key role in fear learning. Using the limited bedding paradigm (LB), we examined the functional consequences of ELS on excitatory and inhibitory tone in the prelimbic (PL) mPFC after fear conditioning in rats. In adults, LB exposure enhanced in vivo glutamate release in the PL mPFC during fear conditioning in male, but not female offspring. In contrast, the glutamate response to fear conditioning was diminished in LB-exposed pre-adolescent males, but not females. We investigated whether reduced glutamatergic inputs and/or elevated inhibitory tone might contribute to the diminished glutamate response in the mPFC following LB in pre-adolescent male rats. Indeed, we found that LB exposure specifically increased the activation of PV, but not SST interneurons in layer V, but not layer II/III of the PL mPFC in fear-exposed pre-adolescent males. Presynaptic glutamate release probability was reduced by LB exposure in layer V, but increased in layer II/III of the PL mPFC. These functional changes might be related to the LB-induced alterations in the bilaminar distribution of BLA and vHIP projections to the PL mPFC we observed in pre-adolescent males. Overall, our findings suggest that ELS modifies glutamate release and PL mPFC function during fear conditioning in a sex- and age-dependent fashion, likely through layer-specific shifts in excitation/inhibition balance. Significance StatementEarly life stress (ELS) increases the risk of developing affective disorders and long-term emotional dysregulation might arise from disruptions in the development of the fear circuitry. This study examines how ELS modifies fear-induced activity of long-range excitatory projections and local inhibitory microcircuits in the developing prefrontal cortex. We tested whether ELS-induced alterations in prefrontal cortex function are sex- and age-dependent, leading to the well-documented sex differences in emotional behavioral outcome. Studying how ELS differentially modifies regional excitatory inputs and cell type specific activation in the prefrontal cortex during a critical period of brain development will enhance our understanding of the neurobiological mechanisms underlying the pathogenesis of emotional dysregulation and inspire more targeted intervention after exposure to early adversity.

Early life stress can have significant effects on the developing brain and lead to changes in the structure and function of brain regions involved in stress regulation, emotion and cognitive control. Here, we used the social instability stress (SIS) protocol to understand the impact of social stress during mild (PND30) and late (PND45) adolescence. Our results revealed that SIS can compromise the dominance-subordination coping strategy but does not affect social recognition and motivation in rats. Moreover, SIS can lead to subtle modifications at the molecular level that hamper normal development of the prefrontal cortex in a sex- and age-dependent manner. Understanding the impact of early life stress on brain organization is crucial for developing effective prevention and intervention strategies. By identifying those who are most vulnerable to the effects of stress and providing targeted support and resources, it may be possible to mitigate the negative consequences of early adversity and promote healthy brain development.

Social stress is a risk factor for psychiatric disorders and also influences immune function. While it is known that acute social stress impacts the number of immune cells in circulation, the temporal dynamics of stress induced immune-related transcriptional changes in human blood remain unclear. To investigate changes in gene expression, we exposed 26 adults to the Trier Social Stress Test (TSST), and collected blood at baseline, as well as 5, 30, 60 and 90 min after stress. Whole-blood gene expression was profiled using a 5 targeted RNA-sequencing method (STRT). Differential expression was analyzed using linear and cubic models. We observed a total of 54 differentially expressed genes following stress. Fast responses, with a transient peak immediately following stress, were enriched for cytotoxic T cell, NK cell and dendritic cell functions (e.g., GZMB, GNLY, CCL4 and GZMA) and paralleled lymphocyte count changes. In contrast, gradual, linear responses without any evident peak were enriched for neutrophil related genes (e.g., FPR2, PLAUR, CXCR2, AQP9, and QPCT) and did not mirror neutrophil counts, indicating cell intrinsic transcriptional changes. From pathway and transcription factor enrichment analyses, IL-12 family mediated signaling is inferred as a central mechanism linking stress to immune gene regulation. Our results show that acute psychosocial stress induces both fast and slower changes in gene expression in different immune cell populations. The involvement of the IL-12-STAT4 axis and genes such as PLAUR and FPR2 suggests molecular mechanisms through which stress-related immune activation may contribute to vulnerability for anxiety and depressive disorders.

The lateral habenula (LHb) inhibits midbrain monoaminergic neurons, thereby regulating emotion/cognition. Abnormally high activity in the LHb causes behavioral disorders, but how stressful experiences affect neuronal circuits underlying emotion remains poorly understood. Here, we report the effects of chronic stress on the LHb in postnatal day (P)1-9, P10-20, and P36-45 mice in the pre-, early, and late stages of LHb maturation. At P60, only mice exposed during P10-20 exhibited LHb-specific changes: abnormally high-stress reactivity shown by the expression of the immediate-early gene product (Zif268/Egr1) with insufficient number of parvalbumin (PV) neurons containing GABA. Furthermore, these mice showed anxiety/depression-like behaviors in the light-dark box test/forced swim test. Thus, experiences in early-life are essential for the maturation of neuronal circuits underlying emotion. Early-life stress is thought to have caused anxiety/depression in adulthood by disrupting the maturation of inhibitory PV neurons in the LHb in a period-specific manner.

The amygdala is a key brain region that processes stress-related inputs to reshape future behaviors. The lateral amygdala (LA), basolateral amygdala (BLA), and central amygdala (CeA) are important subregions that mediate different aspects of stress experiences from receiving sensory input to memory formation and behavioral responding. The principal neurons in these regions are glutamatergic pyramidal neurons, which are genetically separable into two subpopulations, protein phosphatase 1 regulatory subunit 1B-positive (Ppp1r1b, also known as DARPP-32) parvocellular neurons and R-spondin2-positive (Rspo2) magnocellular neurons. Recent studies show that these two subpopulations of amygdala neurons differentially regulate appetitive versus aversive behaviors. The research goal of this study is to explore whether amygdala Ppp1r1b and Rspo2 neurons are transcriptionally activated by moderate stress experience, such that persistent cellular changes are made to influence future functional output of these two subtypes of neurons. To test transcriptional activation, we focused on c-Fos, one of the early genes that are transiently expressed in response to cellular stimulations to regulate downstream gene transcription. Moderate stress was introduced through brief footshocks, with mice without footshock as controls. Between shocked and control mice, we observed similar numbers of Ppp1r1b or Rspo2 neurons per unit area that expressed c-Fos, which was consistent across LA-BLA and CeA. Moreover, in LA-BLA, Ppp1r1b/c-Fos cells consistently outnumber Rspo2/c-Fos cells across treatment conditions, and the reverse is true in CeA. These results suggest that moderate stress experience is not sufficient to induce robust transcriptional alterations in the two key subpopulations of amygdala neurons, and Ppp1r1b versus Rspo2 neuron activities, as measured by c-Fos expression levels, show differential dominance in amygdala subregions.

The ability of the medial prefrontal cortex (mPFC) to exert top-down control of behavior is affected by stress. The molecular response of mPFC to stress is incompletely understood, however, in part because of the regions cellular heterogeneity. Here we used single nucleus RNA sequencing (snRNAseq) to map specific molecular cell types within the mPFC and to detect cell-type specific transcriptional changes to foot-shock stress. We identified Ptgs2, encoding cyclo-oxygenase 2, as an important candidate that is upregulated in layer II/III excitatory neurons after stress. Specifically, Ptgs2 was transiently upregulated with shock-induced fear learning and fear expression, along with Bdnf, Nptx2, and Lingo1, in a layer II/III neuronal population marked by the neuronal excitatory gene Slc17a7 and cell-type specific neuropeptide Penk. These dynamic cell-type specific expression patterns identified with snRNAseq were validated with quantitative fluorescent in situ hybridization. Using a pharmacological approach, we found that systemic lumiracoxib, a selective Ptgs2-inhibitor, led to a significant reduction in fear expression. Furthermore, genetic ablation of Ptgs2 in excitatory Camk2a-expressing neurons led to reduced stress-induced anxiety-like behaviors. Together these findings suggest that Ptgs2 is expressed in a dynamic, cell-type specific way in Layer II/III Penk+ neurons in mPFC, and that its role in prostaglandin and /or endocannabinoid regulation within these neurons may be an important mediator of stress-related behavior.

The impact of stress on gene expression in different cell types of the brain remains poorly characterized. Three pioneering studies have recently used translating ribosome affinity purification followed by RNA sequencing (TRAP-seq) to assess the response to stress in CA3 pyramidal neurons of the hippocampus. The results suggest that acute stress alters the translation of thousands of genes in CA3 pyramidal neurons, and that this response is strongly modulated by factors such as sex, genotype and a history of early life stress. However, our reanalysis of these datasets leads to different conclusions. We confirm that acute stress induces robust translational changes in a small set of genes. However, we found no evidence that either early life stress or sex have an effect on gene translation induced by acute stress. Our findings highlight the need for additional studies with adequate sample sizes and proper methods of analysis to assess the impact of stress across cell types in the brain.

Developmental stress is a well-established risk factor for mental health disorders, yet the neural mechanisms underlying these outcomes remain incompletely understood. Inhibitory brain networks, particularly within the amygdala, are disrupted by stress and implicated in stress-related psychopathologies. Using a rodent model, the current study investigated the isolated and combined effects of prenatal and adolescent stress on adult social interactions and GABAergic neurons surrounded by perineuronal nets (PNNs) in the basolateral amygdala (BLA). Male and female rats were exposed to chronic variable stressors (CVS) prenatally (PS), during adolescence (AS), or during both prenatal and adolescent periods (PS+AS). In adulthood, all animals were tested for social behavior with same-sex weight-matched partners, and brains were collected for identification of BLA inhibitory neurons (GAD67 staining) and PNNs (Wisteria Floribunda Agglutinin staining). For social behavior, AS alone robustly increased social investigation in adulthood relative to non-stressed (NS) controls and animals exposed to combined PS+AS. PS+AS subjects did not significantly differ from NS controls, suggesting that prenatal stress exposure prevented adolescent stress-induced increases in adult social investigation. An analogous data pattern was observed in the BLA. AS alone decreased the number GAD67+ neurons surrounded by PNNs (co-labeled) relative to NS controls and subjects exposed to combined PS+AS. When the percentage of total GAD67+ neurons co-labeled with PNNs was assessed, both PS alone and AS alone reduced the proportion of GAD67+ neurons surrounded by PNNs, whereas combined PS+AS had no effect. Overall, these data suggest that prenatal stress exposure prevents adolescent stress-induced disruptions to perineuronal nets surrounding inhibitory neurons in the BLA, potentially conferring resilience to adolescent stress-induced changes in inhibitory function and social behavior. HighlightsO_LIAdolescent stress exposure increased social investigation in adulthood. C_LIO_LIAdolescent stress decreased the number of BLA cells co-labeled with GAD67 and WFA. C_LIO_LIPrenatal or adolescent stress decreased the proportion of inhibitory neurons with PNNs. C_LIO_LIWhen preceded by prenatal stress, effects of adolescent stress were not observed. C_LI

Early life stress (ELS) adversely affects physiological and behavioral outcomes, increasing the vulnerability to stress-related disorders, such as post-traumatic stress disorder (PTSD). PTSD prevalence is significantly higher in women and is partially mediated by genetic risk variants. Understanding how sex influences the interaction of PTSD risk genes, such as FKBP5, with trauma-related behaviors is crucial for uncovering PTSDs neurobiological pathways. The development of in-depth behavioral analysis tools using unsupervised behavioral classification is thereby a crucial tool to increase the understanding of the behavioral outcomes related to stress-induced fear memory formation. The current study investigates the sex-specific effects of ELS exposure by using the limited bedding and nesting (LBN) paradigm. The LBN exposure disrupted different facets of the hypothalamic-pituitary-adrenal (HPA) axis in a sex-specific manner directly after stress and at adult age. Moreover, freezing was altered by LBN exposure in both the acquisition and the retrieval of fear in a sex-dependent manner. Unsupervised behavioral analysis revealed a higher active fear response after LBN exposure during fear acquisition in females, but not in males. The regulation of the HPA axis is closely intertwined with cellular metabolism and core regulatory cascades. To investigate the impact of LBN exposure on tissue-specific metabolism, a metabolomic pathway analysis in the basolateral amygdala revealed a specific sex- and stress-dependent effect on purine, pyrimidine, and glutamate metabolism. The present study highlights the intricate interplay between metabolic pathways and the neurobiological substrates implicated in fear memory formation and stress regulation. Overall, these findings highlight the importance of considering sex-specific metabolic alterations in understanding the neurobiological mechanisms underlying stress-related disorders and offer potential avenues for targeted interventions.

Post-Traumatic Stress Disorder (PTSD) is a debilitating condition in which a traumatic experience triggers symptoms related to re-experiencing, avoidance, arousal, and mood dysregulation. PTSD negatively impacts 6% of people during their lifetime, with women being disproportionally affected and exhibiting different, more severe symptoms than men. Despite this widespread impact, the molecular mechanisms underlying PTSD and its sex differences remain poorly understood. Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) is a neuropeptide which participates in fine-tuning circuitry throughout the brain and has been associated with PTSD in humans, especially in women. Here, we use Single Prolonged Stress (SPS), an animal model of PTSD, to explore the roles of PACAP and sex in PTSD-like behaviors. Specifically, a PACAP agonist or antagonist was infused into the infralimbic (IL) prefrontal cortex, a region key to regulating fear- and anxiety-related behaviors, prior to SPS in male and female rats. One week later, rats were tested in open field/novel object, elevated plus maze, and social interaction. Utilizing a behavioral indexing method, we were able to uncover SPS effects in PTSD-related behavioral domains that were differentially impacted by PACAP manipulations in males and females. While both sexes exhibited increased threat avoidance and decreased threat assessment following SPS, females increased sociability while males decreased sociability. Males also appeared to be protected by IL PACAP antagonism while female SPS phenotypes were exacerbated by IL PACAP agonism. Furthermore, RNAscope revealed that PACAP in the prefrontal cortex responds differently to SPS in males and females. Together, these findings suggest complex relationships between SPS, sex, and IL PACAP which may have important implications for treating PTSD in men and women. HIGHLIGHTSO_LISPS induces different PTSD-like phenotypes in male and female rats C_LIO_LISPS increases threat avoidance and decreases threat appraisal in both sexes C_LIO_LISociability is decreased in males but increased in females following SPS C_LIO_LIIL PACAP manipulation exerts diverging SPS behavioral effects in males and females C_LIO_LIPrefrontal PACAP signaling plays a sex-specific role in SPS molecular mechanisms C_LI

Fear extinction is an adaptive behavioral process critical for organisms survival, but deficiency in extinction may lead to PTSD. While the amygdala and its neural circuits are critical for fear extinction, the molecular identity and organizational logic of cell types that lie at the core of these circuits remain unclear. Here we report that mice deficient for amygdala-enriched gastrin-releasing peptide gene (Grp-/-) exhibit enhanced neuronal activity in the basolateral amygdala (BLA) and stronger fear conditioning, as well as deficient extinction in stress-enhanced fear learning (SEFL). rAAV2-retro-based tracing combined with visualization of the GFP knocked in the Grp gene showed that BLA receives GRPergic or conditioned stimulus projections from the indirect auditory thalamus-to-auditory cortex pathway, ventral hippocampus and ventral tegmental area. Transcription of dopamine-related genes was decreased in BLA of Grp-/- mice following SEFL extinction recall, suggesting that the GRP may mediate fear extinction regulation by dopamine. Impact statementMice deficient for the amygdala-enriched gastrin-releasing peptide gene are susceptible to stress-enhanced fear, a behavioral protocol with relevance to PTSD, and show a decrease in dopamine-related gene transcription.

A single, severe episode of stress can bring about myriad responses amongst individuals, ranging from cognitive enhancement to debilitating and persistent anxiety; however, the biological mechanisms that contribute to resilience versus susceptibility to stress are poorly understood. The dentate gyrus (DG) of the hippocampus and the basolateral nucleus of the amygdala (BLA) are key limbic regions that are susceptible to the neural and hormonal effects of stress. Previous work has also shown that these regions contribute to individual variability in stress responses; however, the molecular mechanisms underlying the role of these regions in susceptibility and resilience are unknown. In this study, we profiled the transcriptomic signatures of the DG and BLA of rats with divergent behavioral outcomes after a single, severe stressor. We subjected rats to three hours of immobilization with exposure to fox urine and conducted a behavioral battery one week after stress to identify animals that showed persistent, high anxiety-like behavior. We then conducted bulk RNA sequencing of the DG and BLA from susceptible, resilient, and unexposed control rats. Differential gene expression analyses revealed that the molecular signatures separating each of the three groups were distinct and non-overlapping between the DG and BLA. In the amygdala, key genes associated with insulin and hormonal signaling corresponded with vulnerability. Specifically, Inhbb, Rab31, and Ncoa3 were upregulated in the amygdala of stress-susceptible animals compared to resilient animals. In the hippocampus, increased expression of Cartpt - which encodes a key neuropeptide involved in reward, reinforcement, and stress responses - was strongly correlated with vulnerability to anxiety-like behavior. However, few other genes distinguished stress-susceptible animals from control animals, while a larger number of genes separated stress-resilient animals from control and stress-susceptible animals. Of these, Rnf112, Tbx19, and UBALD1 distinguished resilient animals from both control and susceptible animals and were downregulated in resilience, suggesting that an active molecular response in the hippocampus facilitates protection from the long-term consequences of severe stress. These results provide novel insight into the mechanisms that bring about individual variability in the behavioral responses to stress and provide new targets for the advancement of therapies for stress-induced neuropsychiatric disorders.

The amygdala plays an important role in the regulation of stress and anxiety. However, little is known about the relationship between amygdala connectivity and subsequent stress-induced behavior. The current study investigated whether amygdala connectivity measured before experiencing stress is a predisposing neural feature of subsequent stress-induced behavior while individuals face an emergent and unexpected event like the COVID-19 outbreak. Using an fMRI cohort established before the pandemic in Wuhan, Hubei, we found that resting-state functional connectivity (rsFC) of the right amygdala with the dorsomedial prefrontal cortex (dmPFC) was negatively correlated with the stress-induced behavior of these volunteers during the COVID-2019 outbreak in Hubei. Furthermore, the self-connection of the right amygdala, inferred using dynamic causal modeling, was negatively correlated with stress-induced behavior in this cohort. A significant correlation between the right amygdala-dmPFC rsFC and self-connection of the right amygdala was found. Additionally, after three months of the COVID-19 outbreak in Hubei when the stressor weakened - and in another cohort collected in regions outside Hubei where the individuals experienced a lower level of stress - the relationship between the amygdala-dmPFC rsFC and the stress-induced behavior disappeared. Our findings support that amygdala connectivity is a predisposing neural feature of stress-induced behavior in the COVID-19 outbreak in Hubei, suggesting the amygdala connectivity before stress predicts subsequent behavior while facing an emergent and unexpected event. And thus our findings provide an avenue for identifying individuals vulnerable to stress using intrinsic brain function before stress as an indicator.

Early life stress (ELS) is one of the strongest risk factors for developing psychiatric disorders in humans. As conserved key stress hormones of vertebrates, glucocorticoids (GCs) are thought to play an important role in mediating the effects of ELS exposure in shaping adult phenotypes. In this process, early exposure to high level of GCs may induce molecular changes that alter developmental trajectory of an animal and primes differential adult responses. However, comprehensive characterization of identities of molecules that are targeted by developmental GC exposure is currently lacking. In our study, we describe lifelong molecular consequences of high level of developmental GC exposure using an optogenetic zebrafish model. First, we developed a new double-hit stress model using zebrafish by combining exposure to a high endogenous GC level during development and acute adulthood stress exposure. Our results establish that similar to ELS-exposed humans and rodents, developmental GC exposed zebrafish model shows altered behavior and stress hypersensitivity in adulthood. Second, we generated time-series gene expression profiles of the brains in larvae, in adult, and upon stress exposure to identify molecular alterations induced by high developmental GC exposure at different developmental stages. Third, we identify a set of GC-primed genes that show altered expression upon acute stress exposure only in animals exposed to a high developmental GC. Interestingly, our datasets of GC primed genes are enriched in risk factors identified for human psychiatric disorders. Lastly, we identify potential epigenetic regulatory elements and associated post-transcriptional modifications following high developmental GC exposure. Thus, we present a translationally relevant zebrafish model for studying stress hypersensitivity and alteration of behavior induced by exposure to elevated GC levels during development. Our study provides comprehensive datasets delineating potential molecular targets underlying the impact of developmental high GC exposure on adult responses.

Traumatic stress can cause long-lasting changes in cognition and affect, sometimes leading to diagnoses such as post-traumatic stress disorder (PTSD). The stress-enhanced fear learning (SEFL) model recapitulates understudied components of PTSD, such as stress-induced sensitization of fear learning. The SEFL procedure entails exposing mice to footshock stress followed later by fear conditioning in a different context. When tested later for recall of fear conditioning, previously stressed mice exhibit enhanced freezing compared to non-stressed controls. Studies have shown that dorsal and ventral dentate gyrus (DG) generates neural ensemble representations of contextual fear, such that fear recall involves reactivation of a sparse set of "engram cells" that were active during fear memory acquisition. How stress affects these hippocampal ensemble representations is unknown. We used SEFL and activity-dependent neuronal tagging with FosTRAP2 mice to investigate effects of stress on fear memory ensembles in rostral and caudal hippocampal DG. FosTRAP2/Ai6 mice received footshock stress or equivalent context exposure without shock in Context A on day 1. Five days later, mice received 1-shock conditioning in Context B and immediately received an injection of 4-OHT (55mg/kg) to tag fear acquisition neurons with the zsGreen reporter. One day later, mice were tested for fear recall in Context B and were perfused 90 minutes after testing. Confirming prior studies, prior stress potentiated 1-shock conditioning in Context B, with stressed mice displaying higher freezing in the Context B test session than non-stressed mice. At the level of neural activity, results showed stress had no effect on the number of zsGreen+ fear ensemble cells or the number of cfos+ recall-activated cells in rostral or caudal DG. However, stress increased reactivation (percentage of zsGreen+ cells expressing cfos) in the caudal but not rostral DG. The results suggest stress potentiates later fear learning by enhancing fear representations in caudal hippocampus, a region of the hippocampus specialized for integrating emotional and motivational valence into memory.

The molecular mechanisms that link stress and circadian rhythms still remain unclear. The habenula (Hb) is a key brain region involved in regulating diverse types of emotion-related behaviours while the suprachiasmatic nucleus (SCN) is the bodys central clock. To investigate the effects of chronic social stress on transcription patterns, we performed gene expression analysis in the Hb and SCN of stress naive and stress exposed mice. Our analysis revealed a large number of differentially expressed genes and enrichment of synaptic and cell signalling pathways between resilient and stress-naive mice at ZT16 in both the Hb and SCN. This transcriptomic signature was nighttime-specific and observed only in stress-resilient mice. In contrast, there were relatively few differences between the stress-susceptible and stress-naive groups across timepoints. Our results reinforce the functional link between diurnal gene expression patterns and differential responses to stress, thereby highlighting the importance of temporal expression patterns in homeostatic stress responses.

A positive coping style is recognized as a stable disposition to foster emotional wellness and resilience, enabling an adaptive process of assessing and dealing with environmental challenges. Such an adaptive process is believed to rely on a nuanced interplay of the hippocampal system and the primary stress hormone cortisol activity. As a hallmark of diurnal cortisol rhythm, cortisol awakening response (CAR) is sensitive to upcoming stress and subserves the preparation of the hippocampal system for rapid behavioral adaption. Yet, little is known about how the hippocampal system and CAR contribute to the merit of positive coping on emotional wellness. By two studies, we investigate the effects of positive coping on childrens emotional wellness and CAR, as well as longitudinal changes in hippocampal-neocortical functional systems involved in emotional processing. Behaviorally, positive coping predicted better emotional regulation ability, but lower anxiety and lower response caution in emotional decision-making. At the endocrine and neurocognitive level, positive coping was associated with greater CAR, which further predicted higher connectivity of the hippocampus with ventrolateral prefrontal cortex (vlPFC) and stimulus-sensitive neocortex one year later. Furthermore, CAR mediated an indirect association between positive coping and longitudinal increases in hippocampal-neocortical connectivity. Positive coping and CAR together could account for the maturity of vlPFC through longitudinal changes in hippocampal-neocortical connectivity. Overall, our findings suggest a cognitive-neuroendocrinal framework in which positive coping shapes hippocampal-neocortical maturation via stress hormone response to support emotional wellness. SignificanceThe role of the hippocampal system in regulating stress response is well recognized, but its contribution to emotional well-being is not yet understood. Here we show that the protective effects of positive coping on emotional well-being are contingent on two factors: the cortisol awakening response (CAR), which is sensitive to upcoming stress, and hippocampal development. We found that positive coping practices promoted emotional wellness, enhanced emotional decision-making and increased CAR in young children. Longitudinal neuroimaging analysis revealed that positive coping-related CAR predicted greater hippocampal connectivity with stimulus-sensitive neocortex one year later. Importantly, CAR acted as a mediator of the promotive influence of positive coping on the longitudinal development of hippocampal-neocortical connectivity, which contributed to the maturity of prefrontal control systems. Our findings emphasize the importance of hippocampal-neocortical development in resilient coping and emotional wellness.

Chronic stress is a physiological state marked by dysregulation of the hypo-pituitary-adrenal axis and high circulating levels of stress hormones, such as corticosterone in mice or cortisol in humans. This dysregulated state may result in the development of mood disorders but the process by which this occurs is still unknown. The bed nucleus of the stria terminalis (BNST) serves as an integration center for stress signaling and is therefore likely an important area for the development of mood disorders. This project utilized a chronic variable mild stress (CVMS) paradigm to persistently stress mice for 6 weeks followed by RNA-Sequencing of the anterodorsal (ad) BNST and electrophysiology of corticotropin releasing hormone-expressing cells in the adBNST. Our results show significant sex-biases in the transcriptome of the adBNST as well as effects of CVMS on the transcriptome of the adBNST specifically in males. Female biased genes are related to synaptic transmission while male biased genes are related to RNA processing. Stress sensitive genes in males are related to synaptic transmission and synapse formation. Additionally, electrophysiology data showed that CVMS suppressed the M-current in males but not females. However, CVMS increased the strength of excitatory post-synaptic currents in females but not males. This suggests significant differences in how males and females process chronic stress. It also suggests that the BNST is more sensitive to chronic stress in males than in females.