Neurobiology of Stress

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.

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.

Identifying the neural circuits engaged and reshaped by chronic stress is critical for understanding how adaptive responses shift to maladaptive behaviors that contribute to stress-related disorders. Our previous work demonstrates that chronic unpredictable stress (CUS) induces a persistent increase in the firing activity of proopiomelanocortin (POMC) neurons in the arcuate nucleus (ARC). This hyperactivity is due, in part, to a reduction in GABAergic synaptic transmission onto POMC neurons, indicating a disruption in inhibitory control. However, the sources of GABAergic inputs responsible for this effect of chronic stress are unknown. Although AgRP neurons provide local GABAergic input onto POMC neurons and are suppressed by chronic stress, chemogenetic activation of AgRP neurons during stress exposure failed to reduce POMC neuron hyperactivity. GABAergic projections originating from the dorsomedial hypothalamus (DMH) represent another source of inhibitory input to POMC neurons. We found that CUS decreased the firing activity of DMH GABAergic neurons with sex differences, with females exhibiting greater vulnerability to stress-induced suppression. Chemogenetic activation of these neurons during chronic stress markedly attenuated POMC neuron hyperactivity in both sexes, indicating that DMH GABAergic neurons function as a critical upstream regulator of POMC neuron activity under chronic stress. These findings suggest that reduced inhibitory input from DMH GABAergic neurons, rather than local GABAergic AgRP neurons, drives POMC neuron hyperactivity. The weakening of the DMHGABA[->]ARCPOMC circuit activity may represent a novel mechanism underlying maladaptive stress responses and a potential therapeutic target for stress-related disorders.

Post-traumatic stress disorder (PTSD) has been linked to various alterations within the immune system, yet the metabolic programming of immune cells remains unexplored. In the current cross-sectional study, we interrogated immunometabolic function by applying cell-specific metabolic flow cytometry, serum biomarker profiling, and targeted gene expression analysis in peripheral blood mononuclear cells from patients with PTSD (N=34) compared with healthy controls (N=32). PTSD was associated with higher glycolysis- and oxidative pentose phosphate pathway-related markers across adaptive and innate immune cell subsets, as well as elevated circulating interleukin-6. Expression of inflammatory- and stress-related genes was largely comparable between groups. Together, these data provide preliminary evidence for immunometabolic alterations in PTSD at both cellular and systemic levels. These results could contribute to understanding potential pathophysiological mechanisms and support further investigation of immunometabolism in PTSD.

Chronic stress increases risk for metabolic disorders, including diabetes mellitus. Additionally, projections from the infralimbic cortex (IL) to the rostral ventrolateral medulla (RVLM) regulate endocrine stress responses. However, the neurobiological basis for chronic stress effects on glucose homeostasis has not been identified. The current study tests the hypothesis that the IL-RVLM circuit is necessary to prevent glucose intolerance. Accordingly, male and female rats with Cre-dependent expression of tetanus toxin light chain (TeLC) to inhibit neurotransmitter release from RVLM-projecting IL neurons were subject to chronic variable stress (CVS) or remained as No CVS controls. Animals were then acutely challenged with a fasted intraperitoneal glucose tolerance test (GTT). Endocrine metabolic function was evaluated during GTT via time courses of glucose, insulin, glucagon, and corticosterone. In No CVS females expressing TeLC, inhibition of IL-RVLM circuit signaling impaired glucose tolerance characterized by elevated glucose and decreased insulin sensitivity. Following chronic stress, females had impaired glucoregulation characterized by decreased glucose clearance and elevated corticosterone. When combined with TeLC, chronically-stressed females showed shifts in the ratio of insulin to glucagon compared to CVS GFP females, suggesting circuit function impacts the pancreatic mechanisms mediating glucose homeostasis during chronic stress. In No CVS males, TeLC increased glucagon only. However, CVS TeLC males had impaired glucose tolerance, reduced insulin sensitivity, and decreased corticosterone. These data indicate that the IL-RVLM circuit mediates glucoregulation in a manner dependent on both sex and stress history. Collectively, the IL-RVLM circuit is necessary for the sex-specific maintenance of glucose homeostasis following chronic stress.

Development of the brain networks is highly vulnerable to stressful events. Early life stress (ELS) has been linked to multifaceted cognitive and emotional deficits in adulthood. Despite a growing body of evidence showing ELS-induced structural and functional changes in the prefrontal cortex (PFC) and basolateral amygdala (BLA), a circuit crucial for emotional processing, our knowledge of the resulting changes in the network dynamics is incomplete. Here, we investigate how maternal separation (MS) affects prefrontal-amygdala network in terms of neuronal avalanches, spatiotemporal clusters of activity, using simultaneous multielectrode recordings in the medial PFC (mPFC) and the BLA of urethane-anaesthetized juvenile (postnatal day (p) 14 - p15) and young adult (p50 - p 60) rats. Firstly, we show that MS leads to an intensified spread of activity within both regions as reflected in the higher mean branching ratios of the avalanches. Next, we demonstrate that most of the avalanches occur locally in one region, however, a small percentage of avalanches has clusters of activity in both regions simultaneously. We show that in MS animals prefrontal clusters followed by activity in the amygdala tend to be larger compared to controls and each event in the mPFC is followed by smaller number of events in the BLA, pointing towards impaired spread of activity from the mPFC to the BLA. Interestingly, avalanche spread from the BLA to the mPFC remains unaffected by MS. Abovementioned effects manifest only in adulthood and, intriguingly, only in males highlighting prolonged developmental and sex-dependent nature of ELS outcome. Significance statementBrain criticality implies that the brain self-organizers towards critical state, characterized by sustained activity propagation reflected in the unitary branching ratios of neuronal avalanches. Here we show how adverse events during early periods of network maturation, namely ELS, can disrupt developmental trajectories of the critical dynamics in the mPFC-BLA circuit in a sex-specific manner. This study broadens our understanding of the critical dynamics emergence in the prefrontal-limbic network and highlights ELS as a potential criticality control parameter.

The medial prefrontal cortex (mPFC) and ventral tegmental area (VTA) form a highly interconnected circuit involved in emotional regulation, stress reactivity, and cognitive processing. While prior research has established the anatomical and functional interactions between these regions, the precise organization and molecular identity of VTA neurons involved in unidirectional and bidirectional mPFC connectivity remains poorly defined, particularly under stress. We combined dual anterograde and retrograde viral tracing in male and female mice to label VTA neurons according to their connectivity with the mPFC. This approach identified three distinct subpopulations including mPFC-projecting, mPFC-receiving, and bidirectionally-connected neurons which accounted for nearly half of the labelled VTA population. Each group displayed molecular heterogeneity, with most cells expressing dopaminergic (TH) and glutamatergic (VGLUT2) transcripts rather than single dopaminergic or GABAergic (GAD1) markers. Acute and chronic stress exposure revealed sex- and circuit-specific patterns of c-Fos activation. In males, acute and chronic stress generated opposing rostrocaudally organized activation profiles, whereas females showed a more uniform increase in activity. Spatial clustering analyses further revealed that stress induces distinct hotspot organization within the VTA, with chronic stress promoting cohesive hotspot organization and consistent local enrichment of bidirectionally connected neurons despite a limited global activation. Together, these findings uncover a molecularly diverse mPFC-VTA circuitry with bidirectional connectivity that undergoes sex-dependent spatial and functional rearrangement under stress, providing new insights on circuit-level mechanisms of stress-related disorders.

Human-dog interaction is widely used to alleviate stress, yet the accompanying cortical and autonomic dynamics during acute stress and recovery remain incompletely characterized. In this study, 70 adult dog owners completed a standardized stress protocol while prefrontal cortex activity was continuously monitored with functional near-infrared spectroscopy (fNIRS), alongside subjective stress and salivary cortisol measures. Participants then underwent a recovery phase involving interaction with a companion dog, manipulating contact type (direct in person vs. indirect video conferencing), and familiarity (own vs. unfamiliar dog). Stress responses were quantified through heart rate (HR), heart rate variability (HRV), low- and high-frequency spectral power (LF, HF, and LF/HF), and prefrontal functional connectivity (FC) based on maximum cross-correlation coefficients between fNIRS channels. As expected, HR, HRV-derived indices, and FC increased from baseline to the stress phase, confirming robust engagement of autonomic and prefrontal networks. During the recovery phase, all dog interaction conditions demonstrated reductions in HR, LF/HF ratio, and FC toward or below baseline, consistent with physiological and neural stress recovery; direct interaction was associated with particularly pronounced parasympathetic enhancement and a drop in FC that fell significantly below baseline in some cases. Across groups, HRV, LF/HF, and FC were the most consistent predictors of subjective stress ratings, whereas associations with cortisol were limited. These findings suggest that human-dog interaction promotes coordinated autonomic and prefrontal recovery from acute stress, and that fNIRS-derived metrics might provide a marker of stress modulation that can distinguish high-cognitive load and low cognitive demand states beyond traditional stress indices.

Negative cognitive biases in depression are more pronounced in females than in males. This sex difference emerges during adolescence, a sensitive developmental stage when chronic stress exposure increases the risk of depression in adulthood. The neurobiology linking adolescent stress to sex-specific cognitive bias and resting-state network reorganization in adults remain poorly understood. The study aimed to investigate the longitudinal effects of chronic restraint stress (CRS) during adolescence on cognitive bias and functional connectome in emerging adulthood. 28 Wistar rats (sex-balanced; aged five weeks on arrival) were trained on a judgment bias task with distinct tactile cues signalling differential rewards. Cognitive bias was quantified from responses to ambiguous probe trials. Following training, animals were randomly and equally assigned to CRS or control groups (sex-balanced). Offline resting-state functional MRI scans were conducted at adolescent baseline (pre-CRS) and again in adulthood (post-CRS), followed by probe trials to assess neural and behavioural changes. Following CRS, females showed a greater tendency to shift toward negative bias than males (ratio of odds ratio=3.67). Furthermore, CRS significantly reduced functional connectivity between the left cerebellar-auditory and hypothalamic-thalamic networks only in females. Repeated-measures correlation between cognitive bias and network connectivity were not statistically significant across sex-by-group strata, potentially due to offline imaging and small sample size. However, intra-individual association revealed sex-specific trends, with CRS females showing moderately positive correlations and CRS males exhibiting a weak negative association. The results could inform stratified connectome-based interventions targeting adolescent stress exposures to potentially reduce the risk of adult depression. Six keywords: Resting-State Functional MRI, Chronic Restraint Stress, Judgement Bias, Open Field Test, Sex Differences

Nucleus accumbens (NAc) dopamine 2 receptor expressing medium spiny neurons (D2-MSNs) are involved in stress and aversive learning, where repeated stress increases excitatory spine density. Whether this plasticity reflects cue-specific learning or generalized stress response remains unknown. Using Pavlovian fear conditioning in Tac1-Cre/Tdtomato mice, we dissociated associative plasticity from the effects of foot shock stress. Acute fear conditioning produced distinct physiological outcomes between stress in the presence or absence of a cue. Conditioning for 7 days consolidated cue learning and increased excitatory transmission frequency via an increase in the total spine density. However, repeated exposure to foot shock did not lead to this synaptic remodeling. Our results suggest that morphological changes supporting synaptic plasticity on NAc D2-MSNs are due to cue-dependent learning, but not foot shock stress alone. We propose that NAc D2-MSNs encode learning and response to threat cues, which may heighten later stress responsivity.

PTSD is defined by a core of inter-connected symptom clusters. It is currently unclear whether this pattern of interconnections remains stable across the lifespan or differs across key developmental periods. Synthesising seven international trauma-exposed samples (N=5,470), we compared network interrelationships among core self-reported and/or caregiver-reported PTSD symptom clusters (re-experiencing, avoidance and arousal) in preschoolers, school-aged children, adolescents, and adults. For self-report from school-age to adulthood, within-cluster connectivity (associations among symptoms within the same cluster) was consistently stronger than between-cluster connectivity (associations among symptoms from different clusters) across all age groups. This was especially true for the re-experiencing symptom cluster. These inter-relationships appeared stable across with lifecourse with no significant age-related differences. In contrast, caregiver reports from preschool to adolescence, showed stronger within-cluster connectivity among arousal symptoms but these only emerged in school-aged children and adolescents. Longitudinal analyses across approximately the first year post-trauma of self-report symptoms indicated that adults overall symptom connectivity increased over time, whereas school-aged childrens and adolescents networks became sparser. These findings suggest that while PTSD network architecture is broadly stable across different age groups, reporter discrepancies and temporal dynamics warrant close attention, especially with regards to less visible, internalised symptoms such as re-experiencing.

Astrocytes are now widely recognized as important modulators of synaptic plasticity and socio-emotional behaviors. Recent studies highlight their involvement in anxiety- and depressive-like behaviors, particularly via oxytocin (OXT) signaling. While the specific contributions of astrocytes remain largely unexplored, the role of OXT receptor (OXTR) signaling in the lateral septum (LS) in regulating social fear expression has been well characterized. Here, we studied the differential contribution of astrocytic OXTR signaling using a social fear conditioning (SFC+) paradigm. We found the highest abundance of astrocytes, and especially of OXTR-expressing (OXTR+) astrocytes, within the caudal LC (LSc) compared to the rostral LS in both male and female mice. Interestingly, female mice displayed a significantly higher number of astrocytes and OXTR+ astrocytes in the LSc in comparison to males. However, social fear acquisition resulted in dynamic changes in LSc astrocytic morphology and calcium activity in male mice. Furthermore, we showed that pre-SFC acquisition pharmacology-induced loss of local astrocytic function facilitated the extinction of social fear in males. In support, astrocyte-specific OXTR knockdown in the LSc also facilitated social fear extinction in both males and females. Taken together, our study identifies OXTR-signaling in LSc astrocytes as a crucial component in the mechanisms underlying the regulation of social fear in a sex-dependent manner.

BackgroundEarly-life adversity can alter emotional and social development and increase vulnerability to later life stress. We investigated how early adverse experiences (EAE) and later adverse experiences (LAE) shape adult emotional contagion (EC) responses in female and male rats. MethodsEAE was induced using the limited bedding and nesting model during the first postnatal week. LAE was induced via footshocks during adolescence. In adulthood, male and female rats underwent an EC test in which observers witnessed a conspecific receiving footshocks. ResultsAdolescence-footshock exposed observers showed cingulate cortex-associated increased immobility, proximity, and attention toward distressed conspecifics during adulthood, compared to adult-exposed and sham animals, both in male and female animals. While EAE did alter maternal care, pup stress physiology, and pup weight, we found evidence that it did not alter immobility during EC. However, female demonstrators paired with EAE observers showed increased immobility, linked to a reduced rate and lower frequency of the observers 50-kHz vocalizations. Mediation analysis revealed that a shift toward lower-frequency 50-kHz vocalizations specifically mediated this effect, suggesting a sex-specific pathway by which early adversity shapes social behavior. ConclusionsEarly and adolescent adversity influenced distinct aspects of emotional contagion: EAE mediated an observer-to-demonstrator emotional transfer during EC, while LAE impacted a demonstrator-to-observer transfer, with no evidence of additive effects. Our results highlight developmentally specific and sex-dependent mechanisms by which early and later adversity alter social-affective responses in adulthood.

BackgroundThe Michigan Freshman Study on Stress and Resilience aims to identify factors that predict the emergence of depression and/or anxiety symptoms in college freshmen. We previously showed that a combination of psychiatric instruments (Affect Score) strongly predicts who will develop such symptoms during the freshman year. Here, we ask: a) Can we replicate the predictive power of the Affect Score in an independent cohort? and b) Can the neuroendocrine profile during the Trier Social Stress Test (TSST) serve as an additional predictor? MethodsA new cohort of subjects (N= 357) was used for Affect Score replication. The TSST study involved 337 subjects (Females 184, Males 153). Self-report questionnaires at the start of the year were used to derive the Affect Score. GAD-7 and PHQ-9 were used to monitor anxiety and depression, respectively. TSST measures involved plasma ACTH and Cortisol and heart rate monitoring. ResultsThe Affect Score proved to be a highly replicable predictor of future depression and anxiety. In the TSST, subjects not currently depressed but who developed depression at another timepoint during the year showed a higher and delayed peak of the CORT response. Female subjects not currently anxious but who developed anxiety at another timepoint had an elevated CORT response throughout the TSST. This hyperresponsiveness was not correlated with Affect Score and was an independent predictor of anxiety. Present addressMichigan Neuroscience Institute, University of Michigan, A. Alfred Taubman Biomedical Science Research Building, Rm 2009, Ann Arbor, MI, 48109-9901, USA Author ContributionsHK performed research, analyzed data, wrote the paper; CAT designed research, performed research, wrote the paper; VM-W designed research, performed research; LG, FL, AO, KA and LW performed research; CS coded and analyzed data; JFL designed research; SJW Jr designed research; HA designed research, wrote the paper. FundingThis work was supported by the Office of Naval Research (ONR) Grant N00014-09-1-0598, N00014-12-1-0366 and N00014-19-1-2149, the Pritzker Neuropsychiatric Disorders Research Consortium Fund, LLC and the Hope for Depression Research Foundation. This project was also supported by Grant Number P30DK020572 (MDRC) from the National Institute of Diabetes and Digestive and Kidney Diseases. Competing interestsThe authors declare no competing interests. ConclusionsThe Affect Score is a powerful predictor of depression and anxiety in college freshmen. The combination of Affect Score and TSST is strongly predictive of anxiety in females.

The overlapping effects on neuronal plasticity of acute increase in glucocorticoid levels and the BDNF-TRKB signaling indicate a deep interconnection between the two pathways. Moreover, chronic stress with elevated glucocorticoids levels and downregulation of TRKB signaling associated with reduced BDNF are both involved in the pathophysiology of different psychiatric disorders. However, the mechanism by which TRKB and glucocorticoid receptors are recruited together in the modulation of neuronal plasticity is not clear yet. In this study we investigated the molecular mechanisms underlying the interplay of glucocorticoids and TRKB signaling in vitro and in vivo. We found that although not binding directly to TRKB, glucocorticoids promote TRKB dimerization and signaling similarly to BDNF. Moreover, the glucocorticoid receptor physically interacts with TRKB, modulating its dimerization and activity both in presence and in absence of glucocorticoids and contributing to TRKB-mediated plasticity. The transmembrane domain of TRKB is important for the interaction and for mediating the behavioral effects of TRKB and glucocorticoid receptor modulation, suggesting at least a partial overlap between the two signaling pathways. These results shed light on the interconnected effects of glucocorticoid and TRKB signaling highlighting the need for a more comprehensive understanding of the role and the dysfunction of different players contributing to synaptic plasticity.

Menopause is a major psychoneuroendocrine transition which can impact emotional functioning and mental health. Although emotion regulation (ER) is fundamental for mental health, intrinsic neural connectivity supporting ER during the menopausal transition remains unexplored. Addressing this gap, this study provides the first examination of intrinsic effective connectivity within an ER-related network across menopausal stages. Resting-state fMRI data were acquired from 76 healthy premenopausal (n = 32), perimenopausal (n = 19), and postmenopausal (n = 25) women. Effective connectivity within a predefined ER network was examined using spectral dynamic causal modeling. Further, we assessed how intrinsic connectivity predicts self-reported ER ability within each group. While self-reported ER ability did not differ across groups, resting-state effective connectivity within the ER network varied in a stage-dependent manner, with most heterogeneous effects observed between pre- and perimenopause, suggesting a non-monotonic trajectory. Perimenopause was characterized by distinct changes in frontal interactions, reflecting a redistribution rather than a gradual shift toward postmenopausal connectivity. Differences regarding postmenopause were restricted to greater weighting of temporo-parietal network components. Connectivity-ER ability associations revealed stage-specific predictive profiles, with distributed fronto-temporal connectivity predicting ER ability in premenopause, frontal-restricted connectivity in perimenopause, and a single frontal connection with reversed predictive direction in postmenopause. Our findings demonstrate that comparable levels of trait-based ER ability are associated with divergent intrinsic network configurations rather than a uniform architecture. Identifying perimenopause as distinct transition window of intrinsic network organization advances hormone-sensitive models of intrinsic connectivity and provides a framework for understanding how baseline network organization may adapt during psychoneuroendocrine transitions in women.

Stressors are commonly used in rats to induce models of anxiety or depression. The effectiveness of these stressors is often evaluated using specific behavioural tests. In a previous meta-analysis of chronic variable stress (CVS) procedures, we predicted that longer and more intensive stress procedures would result in larger effect sizes in behavioural tests. However, we found that the duration or intensity of CVS procedures did not correlate strongly with the magnitude of the effect sizes reported in behaviouraltests. In that study, we were concerned that the large and unexplained diversity in CVS procedure design, both in terms of duration and the types of stressors used, made it challenging to detect the factors that were influencing effect size. In an effort to address this, we explore here the use of a much simpler stress procedure - chronic restraint stress (CRS) - to study the relationship between the duration of CRS procedures and the effect sizes obtained in subsequent behavioural tests. We searched PubMed for articles using CRS procedures with rats, systematically documented the total duration of restraint, and carried out a meta-analysis of the effect sizes obtained in four behavioural tests: the forced swim test (FST), the sucrose preference test (SPT), the elevated plus maze (EPM) and the open field test (OFT). We found that chronic restraint stress increased immobility in the FST, decreased sucrose preference in the SPT, decreased time spent in the open arms of the EPM but had no effect on time spent in the centre of the OFT. However, the effect sizes in all behavioural tests, except the SPT, were not moderated by the duration of the CRS procedure, indicating that longer CRS procedures are associated with larger effect sizes in the SPT but not in the FST or EPM.

BackgroundChronic stress exposure is a risk factor for several psychiatric disorders, including post-traumatic stress disorder (PTSD) and major depression (MDD), with the prefrontal cortex (PFC) playing a key role in mediating this stress susceptibility. However, most individuals who are exposed to chronic stress are resilient and do not develop psychopathology. Recent evidence suggests that glial cells, especially astrocytes, play an important role in controlling stress-induced anxiety- and depression-like behavior, yet their role in contributing to stress resilience is not understood. MethodsUsing fiber photometry, chemogenetics, and RNA-sequencing in male mice, we establish a role for PFC astrocytes in stress resilience. ResultsWe demonstrate that stress-induced increases in astrocytic calcium activity are both necessary and sufficient for resilience. Bioinformatic analysis reveals robust transcriptional responses in PFC astrocytes that differ between susceptible vs. resilient mice and are unique when compared to astrocytic transcriptional changes in other limbic regions. Comparison with human RNA-sequencing data indicates that molecular changes observed in PFC astrocytes from susceptible mice converge with gene expression changes observed in MDD patients. ConclusionsTogether, these data support targeting astrocytes as a potential therapy for negative behavioral consequences following stress exposure and reveal potential molecular mechanisms within PFC astrocytes that could contribute to depressive-like behaviors.

The fear circuit orchestrates defensive responses to environmental threats and is essential for survival. Dysregulation of this system is thought to contribute to the pathophysiology of several psychiatric disorders. Within this fear circuit, the corticolimbic network, particularly the amygdala and the medial prefrontal cortex (mPFC), is strongly modulated by serotonin. Previous studies have shown that Htr3a knockout (Htr3a-KO) mice exhibit deficits in the extinction of cued fear memory; however, the circuit level mechanisms underlying these impairments remain unknown. Here, we investigated this question by recording local field potentials evoked by auditory conditioned stimuli (CS) in the prelimbic (PrL), infralimbic (IL), and basolateral amygdala (BLA) of head-fixed wild-type (WT) and Htr3a-KO mice prior to fear conditioning and during fear memory retrieval. Behaviorally, Htr3a-KO mice displayed a delayed attenuation of fear-induced freezing during cued fear memory retrieval, whereas WT mice showed a rapid attenuation in freezing. Electrophysiologically, Htr3a-KO mice exhibited reduced fear-evoked theta power in the PrL, IL, and BLA, along with diminished mPFC-BLA theta synchrony. Moreover, theta-phase modulation of gamma oscillations within the BLA, which has been shown to increase during fear states, was perturbed in the absence of Htr3a signaling. Together, these findings indicate that Htr3a is critical for maintaining proper oscillatory dynamics within the mPFC-BLA circuit and for supporting effective attenuation of learned fear. Highlights- Attenuation of fear responses during fear memory retrieval sessions is protracted in Htr3a knock-out mice - The fear-induced theta response in the medial prefrontal cortex and the basolateral amygdala is less powerful in the Htr3a knock-out mice than in wild-type - Htr3a knock-out mice show a deficit in fear-induced synchronization as well as in theta modulation of gamma power in the cortico-limbic network - These results suggest that malfunction of the Htr3a receptor cause alterations in fear network circuit mechanisms that might be linked to deficits in fear responses attenuation

Bilaterian animals exhibit operational (functional) asymmetry--population-level, directional left-right differences in physiology and behavior, including responses to spatially symmetric environmental challenges. Whether such symmetry-to-asymmetry conversion can be driven at the systems level by neurohormonal regulators remains unclear. Here we tested whether a spatially symmetric neuroendocrine challenge--water deprivation (WD)--can elicit a directional left-right physiological response in rats using hindlimb postural asymmetry (HL-PA), a binary readout that quantifies left- versus right-sided hindlimb flexion. Twenty-four hours of WD induced robust HL-PA with right hindlimb flexion, revealed under anesthesia. The asymmetry persisted after complete thoracic spinal cord transection, suggesting that humoral signaling, rather than descending neural commands, may maintain the postural bias. Because dehydration recruits the hypothalamic-neurohypophysial arginine vasopressin (AVP) system, we next tested AVP receptor involvement. Both a V1B antagonist (SSR-149415) and a V1A/V2 antagonist (conivaptan) abolished WD-induced HL-PA, supporting an AVP-dependent mechanism that likely operates at least two anatomical sites. AVP signaling may involve pituitary V1B-dependent endocrine output and spinal V1A actions; consistent with the latter, expression of AVP V1A receptors is right-biased in lumbar spinal cord. Together, these findings identify WD as a symmetric systemic challenge capable of imposing a directional peripheral set-point, and implicate vasopressin signaling in symmetry breaking and left-right physiological regulation. Visual summary O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=133 SRC="FIGDIR/small/708998v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@10d6b3corg.highwire.dtl.DTLVardef@1fb4b5aorg.highwire.dtl.DTLVardef@11003c0org.highwire.dtl.DTLVardef@66671c_HPS_FORMAT_FIGEXP M_FIG C_FIG