Ventral hippocampal afferents to the nucleus accumbens regulate susceptibility to depression

Projections from ventral hippocampus to nucleus accumbens' cholinergic neurons are altered in depression

The cholinergic interneurons (ChIs) of the nucleus accumbens (NAc) have a critical role in the activity of this region, specifically in the context of major depressive disorder. To understand the circuitry regulating this behavior, we sought to determine the areas that directly project to these interneurons by utilizing the monosynaptic cell-specific tracing technique. Mapping showed monosynaptic projections that are exclusive to NAc ChIs. To determine if some of these projections are altered in a depression mouse model, we used mice that do not express the calcium-binding protein p11 specifically in ChIs (ChAT-p11 cKO) and display a depressive-like phenotype. Our data demonstrated that while the overall projection areas remain similar between wild type and ChAT-p11 cKO mice, the number of projections from the ventral hippocampus (vHIP) is significantly reduced in the ChAT-p11 cKO mice. Furthermore, using optogenetics and electrophysiology we showed that glutamatergic projections from vHIP to NAc ChIs are severely altered in mutant mice. These results show that specific alterations in the circuitry of the accumbal ChIs could play an important role in the regulation of depressive-like behavior, reward-seeking behavior in addictions, or psychiatric symptoms in neurodegenerative diseases.

Prophylactic (R,S)-Ketamine and (2S,6S)-Hydroxynorketamine Decrease Fear Expression by Differentially Modulating Fear Neural Ensembles

BACKGROUND

We previously reported that a single injection of (R,S)-ketamine or its metabolite (2S,6S)-hydroxynorketamine (HNK) prior to stress attenuated learned fear. However, whether these drugs attenuate learned fear through divergent or convergent effects on neural activity remains to be determined.

METHODS

129S6/SvEv male mice were injected with saline, (R,S)-ketamine, or (2S,6S)-HNK 1 week before a 3-shock contextual fear conditioning paradigm. Five days later, mice were re-exposed to the aversive context and euthanized 1 hour later to quantify active cells. Brains were processed for c-fos immunoreactivity, and neural networks were built with a novel, wide-scale imaging pipeline.

RESULTS

We found that (R,S)-ketamine and (2S,6S)-HNK attenuated learned fear. Fear-related neural activity was altered in dorsal CA3 following (2S,6S)-HNK; ventral CA3 and CA1, infralimbic and prelimbic regions, insular cortex, retrosplenial cortex, piriform cortex, nucleus reuniens, and periaqueductal gray following both (R,S)-ketamine and (2S,6S)-HNK; and in the paraventricular nucleus of the thalamus (PVT) following (R,S)-ketamine. Dorsal CA3 and ventral hippocampus activation correlated with freezing in the (R,S)-ketamine group, and retrosplenial cortex activation correlated with freezing in both (R,S)-ketamine and (2S,6S)-HNK groups. (R,S)-ketamine increased connectivity between cortical and subcortical regions while (2S,6S)-HNK increased connectivity within these regions.

CONCLUSIONS

This work identifies novel nodes in fear networks that involve the nucleus reuniens, piriform cortex, insular cortex, periaqueductal gray, and retrosplenial cortex that can be targeted with neuromodulatory strategies or pharmaceutical compounds to treat fear-induced disorders. This approach could be used to optimize target engagement and dosing strategies of existing medications.

Reward integration in prefrontal-cortical and ventral-hippocampal nucleus accumbens inputs cooperatively modulates engagement

The nucleus accumbens, a highly integrative brain region controlling motivated behavior, receives various glutamatergic inputs, yet the relative functional specialization of these inputs is unclear. While circuit neuroscience commonly seeks specificity, redundancy can be highly adaptive and is a critical motif in circuit organization. Using dual-site fiber photometry in an operant reward task in mice, we simultaneously recorded from two accumbal glutamatergic afferents to assess circuit specialization. We identify a common neural motif integrating reward history in medial prefrontal cortex and ventral hippocampus inputs. By systematically degrading task complexity, dissociating reward from choice and action, we identify circuit-specificity in the behavioral conditions that recruit encoding. While input from the prefrontal cortex invariantly encodes reward, encoding in ventral hippocampal input is uniquely anchored to unrewarded outcomes. Optogenetic stimulation demonstrates that both inputs co-operatively modulate task engagement. We illustrate how similar encoding, differentially gated by behavioral state, supports state-sensitive tuning of reward-motivated behavior.

Application of Optogenetic Neuromodulation in Regulating Depression

Depression is a multifaceted disorder with a largely unresolved etiology influenced by a complex interplay of pathogenic factors. Despite decades of research, it remains a major condition that significantly diminishes patients' quality of life. Advances in optogenetics have introduced a powerful tool for exploring the neural mechanisms underlying depression. By selectively expressing optogenes in specific cell types in mice, researchers can study the roles of these cells through targeted light stimulation, offering new insights into central nervous system disorders. The use of viral vectors to express opsins in distinct neuronal subtypes enables precise activation or inhibition of these neurons via light. When combined with behavioral, morphological, and electrophysiological analyses, optogenetics provides an invaluable approach to investigating the neural mechanisms of psychiatric conditions. This review synthesizes current research on the application of optogenetics to understand the mechanisms of depression. This study aims to enhance our knowledge of optogenetic strategies for regulating depression and advancing antidepressant research.

VTA dopaminergic neurons involved in chronic spared nerve injury pain-induced depressive-like behavior

Affective disorders, such as depression, are commonly associated with the development of chronic pain, but the underlying mechanisms still remain unclear. The dopaminergic system, located in the midbrain, is considered one of the regions where algesia and emotional processing overlap. This suggests a structural basis hypothesis for the comorbidity of chronic pain and depression, highlighting the interplay between nociceptive and affective processing. But there are more and more evidences show that somatic and head/facial pain involve different neuronal overlap. In previous study, the research show that VTA dopaminergic system involved in pIONT surgery induced depressive-like behaviors in mice. But there still no evidence shows if chronic somatic pain will induce depressive-like behaviors and which neuronal circle pathway is underly. In this study, we assessed depressive-like behaviors and performed artificial interference of VTA (ventral tegmental area) dopaminergic neurons in a mouse model of chronic peripheral neuropathic pain induced by the spared nerve injury (SNI) model. After a 4-week duration of hyperalgesia and allodynia resulting from SNI surgery, social withdraw and other depressive-like behaviors were observed in the SNI group. Furthermore, the dopaminergic cells' excitability in VTA were significantly increased in SNI mice. The excitability alteration was improved play a key role in the development and modulation of the chronic peripheral neuropathic pain-induced depressive-like behaviors. It has been shown pain and affections have structural and functional circuits to interact with each other, therefore the neuroplastic changes and functional role of VTA dopaminergic neurons within these circuits may serve as potential targets for understanding and therapeutically addressing the development of depressive-like symptoms accompanied by prolonged pain syndromes in humans.

Melatonin Alleviates Behavioral and Neurodevelopmental Abnormalities in Offspring Caused by Prenatal Stress

BACKGROUND

Prenatal stress (PNS) is a significant risk factor impacting the lifelong health of offspring, and it has been widely recognized as being closely linked to the increased prevalence of neurodevelopmental disorders and psychiatric illnesses. However, effective pharmacological interventions to mitigate its detrimental effects remain limited. Melatonin (Mel), an endogenous hormone, has demonstrated considerable potential in treating neurological diseases due to its anti-inflammatory, antioxidant, and neuroprotective properties, as well as its favorable safety profile and broad clinical applicability.

OBJECTIVE

This study aims to investigate the protective effects and mechanisms of melatonin on neurodevelopmental and behavioral abnormalities in offspring induced by prenatal stress.

METHODS

Using a prenatal stress mouse model, we evaluated the effects of melatonin on emotional and cognitive deficits in offspring. Neurogenesis and synaptic development were assessed, and RNA sequencing was performed to analyze microglial gene enrichment and immune-related pathways. Both in vivo and in vitro experiments were conducted to validate the findings, focusing on the PI3K/AKT/NF-κB signaling pathway in microglia.

RESULTS

Melatonin administration alleviated emotional and cognitive deficits in offspring mice exposed to prenatal stress, addressing abnormalities in neurogenesis and synaptic development. Additionally, RNA sequencing revealed that melatonin suppresses microglial gene enrichment and the upregulation of immune-related pathways. Both in vivo and in vitro validation indicated that melatonin modulates the PI3K/AKT/NF-κB signaling pathway in microglia, reducing the elevated expression of CXCL10 in the dentate gyrus, thereby restoring normal neuro-supportive functions and optimizing the neurodevelopmental environment.

CONCLUSION

These findings suggest that melatonin significantly improves neurodevelopmental disorders and behavioral abnormalities caused by prenatal stress by inhibiting pathological microglial activation and promoting hippocampal neurogenesis and synaptic plasticity. This provides new insights into melatonin's potential as a neuroprotective agent for treating prenatal stress-related disorders.

LRP1-mediated p-tau propagation contributes to cognitive impairment after chronic neuropathic pain in rats

Trigeminal neuralgia (TN) is a prevalent chronic neuropathic pain syndrome characterized by severe pain, often accompanied by cognitive dysfunction and cerebral degeneration. However, its mechanisms remain poorly understood. Hyperphosphorylation of tau protein (p-tau) is often seen in neurodegenerative disorders such as Alzheimer's disease (AD). LRP1 expression on brain neurons and microglial cells is believed to facilitate the propagation of p-tau. We established a TN rat model via infraorbital nerve chronic constrictive injury (ION-CCI). Once the model was established, we investigated the association between p-tau and cognitive impairment in TN rats by evaluating behavioral and degenerative markers. During the initial phase, we noted an increase in p-tau level in the prefrontal cortex and hippocampal tissues of TN rats. The accompanied impaired learning and memory abilities suggested cognitive dysfunction. Blocking p-tau synthesis by orally administering a protein phosphatase and by injecting adenoviral vectors targeting LRP1 into the lateral ventricle of rats ameliorated cognitive impairment. This suggests that cognitive decline in TN rats is linked to elevated p-tau levels. Our findings show that LRP1-mediated p-tau propagation may drive cognitive impairment associated with neuropathic pain in TN rats.

Ventral Hippocampal CA1 GADD45B Regulates Susceptibility to Social Stress by Influencing NMDA Receptor-Mediated Synaptic Plasticity

Growth arrest DNA damage-inducible protein 45 β (GADD45B) has been reported to be a regulatory factor for active DNA demethylation and is implicated in the modulation of synaptic plasticity and chronic stress-related psychopathological processes. However, its precise role and mechanism of action in stress susceptibility remain elusive. In this study, we found a significant reduction in GADD45B expression specifically in the ventral, but not the dorsal hippocampal CA1 (dCA1) of stress-susceptible mice. Furthermore, we demonstrated that GADD45B negatively regulates susceptibility to social stress and NMDA receptor-dependent long-term potentiation (LTP) in the ventral hippocampal CA1 (vCA1). Importantly, through pharmacological inhibition using the NMDA receptor antagonist MK801, we provided further evidence supporting the hypothesis that GADD45B potentially modulates susceptibility to social stress by influencing NMDA receptor-mediated LTP. Collectively, these results suggested that modulation of NMDA receptor-mediated synaptic plasticity is a pivotal mechanism underlying the regulation of susceptibility to social stress by GADD45B.

Resting-state fMRI reveals altered functional connectivity associated with resilience and susceptibility to chronic social defeat stress in mouse brain

Chronic stress is a causal antecedent condition for major depressive disorder and associates with altered patterns of neural connectivity. There are nevertheless important individual differences in susceptibility to chronic stress. How functional connectivity (FC) amongst interconnected, depression-related brain regions associates with resilience and susceptibility to chronic stress is largely unknown. We used resting-state functional magnetic resonance imaging (rs-fMRI) to examine FC between established depression-related regions in susceptible (SUS) and resilient (RES) adult mice following chronic social defeat stress (CSDS). Seed-seed FC analysis revealed that the ventral dentate gyrus (vDG) exhibited the greatest number of FC group differences with other stress-related limbic brain regions. SUS mice showed greater FC between the vDG and subcortical regions compared to both control (CON) or RES groups. Whole brain vDG seed-voxel analysis supported seed-seed findings in SUS mice but also indicated significantly decreased FC between the vDG and anterior cingulate area compared to CON mice. Interestingly, RES mice exhibited enhanced FC between the vDG and anterior cingulate area compared to SUS mice. Moreover, RES mice showed greater FC between the infralimbic prefrontal cortex and the nucleus accumbens shell compared to CON mice. These findings indicate unique differences in FC patterns in phenotypically distinct SUS and RES mice that could represent a neurobiological basis for depression, anxiety, and negative-coping behaviors that are associated with exposure to chronic stress.

Human mood disorder risk gene Synaptotagmin-14 contributes to mania-like behaviors in mice

Bipolar disorder (BD) and major depressive disorder (MDD) are the most prevalent mood disorders and cause considerable burden worldwide. Compelling evidence suggests a pronounced overlap between these two disorders in clinical symptoms, treatment strategies, and genetic etiology. Here we leverage a BD GWAS (1822 cases and 4650 controls) and a MDD GWAS (5303 cases and 5337 controls), followed by independent replications, to investigate their shared genetic basis among Han Chinese. We have herein identified a lead SNP rs126277 at the 1q32.2 locus, which also exhibited nominal associations with mood disorders and several relevant sub-clinical phenotypes (e.g., mania) in European populations. Bulk tissue and single-cell eQTL analyses suggest that the risk G-allele of rs126277 predicted lower SYT14 mRNA expression in human brains. We generated mice lacking Syt14 (Syt14-/-) and mice with insufficient expression of Syt14 in the hippocampus (Syt14-KD), and found that depletion of Syt14 resulted in mania-like behaviors including hyperactivity and anti-depressive behaviors, resembling aspects of mood disorders. We also confirmed that deficiency of this gene in the hippocampus was sufficient to induce hyperactivity in mice. RNA-sequencing analyses of the hippocampus of Syt14-/- mice revealed significant upregulation of Per1 as well as downregulation of Slc7a11 and Ptprb. Ultrastructural analyses showed significant alteration of the number of vesicles within 50 nm to the active zone and the width of synaptic cleft in the ventral hippocampus of Syt14-/- mice compared with the control mice. Overall, we have identified a novel mood disorder risk gene SYT14, and confirmed its impact on mania-like behaviors. While the current study identifies an essential mood disorder risk gene, further investigations elucidating the detailed mechanisms by which SYT14 contributes to the pathogenesis of the illnesses are needed.

Lactobacillus fermentum ATCC 9338 Supplementation Prevents Depressive-Like Behaviors Through Glucocorticoid Receptor and N-Methyl-D-aspartate2b in Chronic Unpredictable Mild Stress Mouse Model

Depression is a long-term, related to stress neuropsychiatric disorder, leading to psychological health issues including worthlessness, anhedonia, sleep and appetite disturbances, dysregulated HPA axis, neuronal cell death, and alterations in the gut microbiota (GM). Dysregulated HPA axis increases level of glucocorticoids that induce proinflammatory response with activation of abnormal kynurenine pathway via metabolizing indoleamine-2,3-dioxygenase (IDO). Kynurenine pathway leads to excitotoxicity of N-methyl-D-aspartate (NMDA) receptor responsible for neuronal cell death. Further, probiotics supplementation gained attention from researchers and clinicians to treat neuropsychiatric diseases. GM alteration remains a key reason for depression; however, there is limited information about the role of probiotics on depression involving glucocorticoid receptor and NMDA excitotoxicity through IDO. Chronic unpredictable mild stress (CUMS) model was prepared to check the role of Lactobacillus fermentum ATCC 9338 (LF) and 1-methyl-D-tryptophan (1-MT) in depression. Herein, mice were placed into experimental groups: control, CUMS stressed, CUMS vehicle, CUMS LF, CUMS 1-MT, and CUMS UT (untreated). Results showed that peroral administration of 1 × 108 CFU/day/mouse LF and intraperitoneal dose of 1-MT (15 mg/kg BW/day) alleviate depressive-like behavior and improve motor coordination and walking patterns. Mice supplemented with LF and 1-MT exhibited a decreased expression of GR and NMDAR2b in the cortex, hippocampus, and medulla. Acetylcholinesterase, SOD, and CAT activities were improved in CUMS mice with supplementation of LF and 1-MT. The GM abundance in LF mice was similar to that in control mice. Such study suggests the roles of LF and 1-MT in depression and oxidative stress, and helpful to understand their therapeutic potential through the HPA axis and IDO.

Neural circuits mediating chronic stress: Implications for major depressive disorder

Major depressive disorder (MDD), also known as depression, is a prevalent mental disorder that leads to severe disease burden worldwide. Over the past two decades, significant progress has been made in understanding the pathogenesis and developing novel treatments for MDD. Among the complicated etiologies of MDD, chronic stress is a major risk factor. Exploring the underlying brain circuit mechanisms of chronic stress regulation has been an area of active research for recent years. A growing body of preclinical and clinical research has revealed that abnormalities in the brain circuits are closely associated with failures in coping with stress in depressed individuals. Nevertheless, neural circuit mechanisms underlying chronic stress processing and the onset of depression remain a major puzzle. Here, we review recent literature focusing on circuit- and cell-type-specific dissection of depression-like behaviors in chronic stress-related animal models of MDD and outline the key questions.

Memory-related neurophysiological mechanisms in the hippocampus underlying stress susceptibility

Stress-induced psychiatric symptoms, such as increased anxiety, decreased sociality, and depression, differ considerably across individuals. The cognitive model of depression proposes that biased negative memory is a crucial determinant in the development of mental stress-induced disorders. Accumulating evidence from both clinical and animal studies has demonstrated that such biased memory processing could be triggered by the hippocampus, a region well known to be involved in declarative memories. This review mainly describes how memory-related neurophysiological mechanisms in the hippocampus and their interactions with other related brain regions are involved in the regulation of stress susceptibility and discusses potential interventions to prevent and treat stress-related psychiatric symptoms. Further neurophysiological insights based on memory mechanisms are expected to devise personalized prevention and therapy to confer stress resilience.

Behavioral Animal Models and Neural-Circuit Framework of Depressive Disorder

Depressive disorder is a chronic, recurring, and potentially life-endangering neuropsychiatric disease. According to a report by the World Health Organization, the global population suffering from depression is experiencing a significant annual increase. Despite its prevalence and considerable impact on people, little is known about its pathogenesis. One major reason is the scarcity of reliable animal models due to the absence of consensus on the pathology and etiology of depression. Furthermore, the neural circuit mechanism of depression induced by various factors is particularly complex. Considering the variability in depressive behavior patterns and neurobiological mechanisms among different animal models of depression, a comparison between the neural circuits of depression induced by various factors is essential for its treatment. In this review, we mainly summarize the most widely used behavioral animal models and neural circuits under different triggers of depression, aiming to provide a theoretical basis for depression prevention.

Rasd2 regulates depression-like behaviors via DRD2 neurons in the prelimbic cortex afferent to nucleus accumbens core circuit

Depressive symptoms, such as anhedonia, decreased social interaction, and lack of motivation, implicate brain reward systems in the pathophysiology of depression. Exposure to chronic stress impairs the function of brain reward circuits and is well-known to be involved in the etiology of depression. A transcriptomic analysis found that stress alters the expression of Rasd2 in mice prefrontal cortex (PFC). Similarly, in our previous study, acute fasting decreased Rasd2 expression in mice PFC, and RASD2 modulated dopamine D2 receptor (DRD2)-mediated antidepressant-like effects in ovariectomized mice. This research suggests the role of RASD2 in stress-induced depression and its underlying neural mechanisms that require further investigation. Here, we show that 5-day unpredictable mild stress (5-d UMS) exposure reduces RASD2 expression in both the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) of mice, while overexpression (but not knock-down) of Rasd2 in the NAc core (NAcc) alleviates 5-d UMS-induced depression-like behaviors and activates the DRD2-cAMP-PKA-DARPP-32 signaling pathway. Further studies investigated neuronal projections between the mPFC (Cg1, PrL, and IL) and NAcc, labeled by the retrograde tracer Fluorogold. Depression-like behaviors induced by 5-d UMS were only related to inhibition of the PrL-NAcc circuit. DREADD (Designer receptors exclusively activated by designer drug) analysis found that the activation of PrL-NAcc glutaminergic projection alleviated depression-like behaviors and increased DRD2- and RASD2-positive neurons in the NAcc. Using Drd2-cre transgenic mice, we constructed mice with Rasd2 overexpression in DRD2PrL-NAcc neurons, finding that Rasd2 overexpression ameliorated 5-d UMS-induced depression-like behaviors. These findings demonstrate a critical role for RASD2 modulation of DRD2PrL-NAcc neurons in 5-d UMS-induced depression-like behaviors. In addition, the study identifies a new potential strategy for precision medical treatment of depression.

Regulation of adult-born and mature neurons in stress response and antidepressant action in the dentate gyrus of the hippocampus

The dentate gyrus (DG) of the hippocampus has been implicated in the regulation of stress responses, and in the pathophysiology and treatment of depression. This review discusses the cellular changes caused by chronic stress and the cellular role of the DG in stress-induced behavioral changes and its antidepressant-like effects. Regarding adult-born neurogenic processes in the DG, chronic stress, such as repeated social defeat, suppresses cell proliferation during and immediately after stress; however, this effect is transient. The subsequent differentiation and survival processes are differentially regulated depending on the timing and sensitivity of stress. The activation of young adult-born neurons during stress contributes to stress resilience, while the transient increase in the survival of adult-born neurons after the cessation of stress seems to promote stress susceptibility. In mature granule neurons, the predominant cells in the DG, synaptic plasticity is suppressed by chronic stress. However, a group of mature granule neurons is activated by chronic stress. Chronic antidepressant treatment can transform mature granule neurons to a phenotype resembling that of immature neurons, characterized as "dematuration". Adult-born neurons suppress the activation of mature granule neurons during stress, indicating that local neural interactions within the DG are important for the stress response. Elucidating the stress-associated context- and timing-dependent cellular changes and functions in the DG will provide insights into stress-related psychiatric diseases.

Chronic Pain and Comorbid Emotional Disorders: Neural Circuitry and Neuroimmunity Pathways

Chronic pain is a multidimensional experience that not only involves persistent nociception but is also frequently accompanied by significant emotional disorders, such as anxiety and depression, which complicate its management and amplify its impact. This review provides an in-depth exploration of the neurobiological mechanisms underlying the comorbidity of chronic pain and emotional disturbances. Key areas of focus include the dysregulation of major neurotransmitter systems (serotonin, gamma-aminobutyric acid, and glutamate) and the resulting functional remodeling of critical neural circuits implicated in pain processing, emotional regulation, and reward. Given the contribution of neuroimmune mechanisms to pain chronicity and mood disorders, we further conducted an in-depth investigation into the role of neuroimmune factors, including resident immune cells, infiltrating immune cells, and the release of inflammatory mediators. This review further discusses current therapeutic strategies, encompassing pharmacological interventions, neuromodulation, and integrative approaches, and emphasizes the necessity of targeted treatments that address both pain and emotional components. Finally, it identifies gaps in the current understanding and outlines future research directions aimed at elucidating the complex interplay between chronic pain and emotional disorders, thereby laying the foundation for more effective and holistic treatment paradigms.

A Neural Circuit From Paraventricular Nucleus of the Thalamus to the Nucleus Accumbens Mediates Inflammatory Pain in Mice

BACKGROUND

Pain is a prevalent comorbidity in numerous clinical conditions and causes suffering; however, the mechanism of pain is intricate, and the neural circuitry underlying pain in the brain remains incompletely elucidated. More research into the perception and modulation of pain within the central nervous system is essential. The nucleus accumbens (NAc) plays a pivotal role in the regulation of animal behavior, and extensive research has unequivocally demonstrated its significant involvement in the occurrence and development of pain. NAc receives projections from various other neural nuclei within the brain, including the paraventricular nucleus of the thalamus (PVT). In this experiment, we demonstrate that the specific glutamatergic neural circuit projection from PVT to NAc (PVTGlut→NAc) is implicated in the modulation of inflammatory pain in mice.

METHODS

We compared the difference in pain thresholds between complete Freund's adjuvant (CFA)-induced inflammatory pain models and controls. Then in a well-established mouse model of CFA-induced inflammatory pain, immunofluorescence staining was utilized to evaluate changes in c-Fos protein expression within PVT neurons. To investigate the role of PVTGlut→NAc in the modulation of pain, we used optogenetics to modulate this neural circuit, and nociceptive behavioral tests were employed to investigate the functional role of the PVTGlut→NAc circuit in the modulation of inflammatory pain.

RESULTS

In the mice with the inflammatory pain group, both the paw withdrawal latencies (PWLs) and paw withdrawal thresholds (PWTs) of the right hind paw were decreased compared to the control group. In addition, compared to the control group, CFA-induced inflammatory pain led to increased c-Fos protein expression in PVT, which means that some of the neurons in this area of the brain region have been activated. Following the injection of retrograde transport fluorescent-labeled virus into NAc, glutamatergic neurons projecting from the PVT to NAc were observed, confirming the projection relationship between PVT and NAc. In the experiments in optogenetic regulation, normal mice exhibited pain behavior when the PVTGlut→NAc circuit was stimulated by a 473 nm blue laser, resulting in decreased PWLs and PWTs compared to the control group, which means activating this neural circuit can lead to painful behaviors. In the CFA-induced pain group, inhibition of the PVTGlut→NAc circuit by a 589 nm yellow laser alleviated pain behavior, leading to increased PWLs and PWTs compared to the control group, representing the fact that inhibition of this neural circuit relieves pain behaviors.

CONCLUSIONS

The findings unveil a pivotal role of the PVTGlut→NAc circuit in modulating inflammatory pain induced by CFA in mice.

Understanding the neural code of stress to control anhedonia

Anhedonia, the diminished drive to seek, value, and learn about rewards, is a core feature of major depressive disorder1-3. The neural underpinnings of anhedonia and how this emotional state drives behaviour remain unclear. Here we investigated the neural code of anhedonia by taking advantage of the fact that when mice are exposed to traumatic social stress, susceptible animals become socially withdrawn and anhedonic, whereas others remain resilient. By performing high-density electrophysiology to record neural activity patterns in the basolateral amygdala (BLA) and ventral CA1 (vCA1), we identified neural signatures of susceptibility and resilience. When mice actively sought rewards, BLA activity in resilient mice showed robust discrimination between reward choices. By contrast, susceptible mice exhibited a rumination-like signature, in which BLA neurons encoded the intention to switch or stay on a previously chosen reward. Manipulation of vCA1 inputs to the BLA in susceptible mice rescued dysfunctional neural dynamics, amplified dynamics associated with resilience, and reversed anhedonic behaviour. Finally, when animals were at rest, the spontaneous BLA activity of susceptible mice showed a greater number of distinct neural population states. This spontaneous activity allowed us to decode group identity and to infer whether a mouse had a history of stress better than behavioural outcomes alone. This work reveals population-level neural dynamics that explain individual differences in responses to traumatic stress, and suggests that modulating vCA1-BLA inputs can enhance resilience by regulating these dynamics.

Ventral hippocampus to nucleus accumbens shell circuit regulates approach decisions during motivational conflict

Successful resolution of approach-avoidance conflict (AAC) is fundamentally important for survival, and its dysregulation is a hallmark of many neuropsychiatric disorders, and yet the underlying neural circuit mechanisms are not well elucidated. Converging human and animal research has implicated the anterior/ventral hippocampus (vHPC) as a key node in arbitrating AAC in a region-specific manner. In this study, we sought to target the vHPC CA1 projection pathway to the nucleus accumbens (NAc) to delineate its contribution to AAC decision-making, particularly in the arbitration of learned reward and punishment signals, as well as innate signals. To this end, we used pathway-specific chemogenetics in male and female Long Evans rats to inhibit the NAc shell projecting vHPC CA1 neurons while rats underwent a test in which cues of positive and negative valence were presented concurrently to elicit AAC. Additional behavioral assays of social preference and memory, reward and punishment cue processing, anxiety, and novelty processing were administered to further interrogate the conditions under which the vCA1-NAc shell pathway is recruited. Chemogenetic inhibition of the vCA1-NAc shell circuit resulted in animals exhibiting increased decision-making time and avoidance bias specifically in the face of motivational conflict, as the same behavioral phenotype was absent in separate conditioned cue preference and avoidance tests. vCA1-NAc shell inhibition also led to a reduction in seeking social interaction with a novel rat but did not alter anxiety-like behaviors. The vCA1-NAc shell circuit is therefore critically engaged in biasing decisions to approach in the face of social novelty and approach-avoidance conflict. Dysregulation of this circuit could lead to the precipitation of addictive behaviors in substance abuse, or maladaptive avoidance in situations of approach-avoidance conflict.

Omics Approaches to Investigate the Pathogenesis of Suicide

Suicide is the second leading cause of death in U.S. adolescents and young adults and is generally associated with a psychiatric disorder. Suicidal behavior has a complex etiology and pathogenesis. Moderate heritability suggests genetic causes. Associations between childhood and recent life adversity indicate contributions from epigenetic factors. Genomic contributions to suicide pathogenesis remain largely unknown. This article is based on a workshop held to design strategies to identify molecular drivers of suicide neurobiology that would be putative new treatment targets. The panel determined that while bulk tissue studies provide comprehensive information, single-nucleus approaches that identify cell type-specific changes are needed. While single-nuclei techniques lack information on cytoplasm, processes, spines, and synapses, spatial multiomic technologies on intact tissue detect cell alterations specific to brain tissue layers and subregions. Because suicide has genetic and environmental drivers, multiomic approaches that combine cell type-specific epigenome, transcriptome, and proteome provide a more complete picture of pathogenesis. To determine the direction of effect of suicide risk gene variants on RNA and protein expression and how these interact with epigenetic marks, single-nuclei and spatial multiomics quantitative trait loci maps should be integrated with whole-genome sequencing and genome-wide association databases. The workshop concluded with a recommendation for the formation of an international suicide biology consortium that will bring together brain banks and investigators with expertise in cutting-edge omics technologies to delineate the biology of suicide and identify novel potential treatment targets to be tested in cellular and animal models for drug and biomarker discovery to guide suicide prevention.

Data-Driven Analysis Identifies Novel Modulation of Social Behavior in Female Mice Witnessing Chronic Social Defeat Stress

BACKGROUND

Chronic social defeat stress is a widely used depression model in male mice. Several proposed adaptations extend this model to females with variable, often marginal effects. We examined if the widely used male-defined metrics of stress are suboptimal in females witnessing defeat.

METHODS

Using a data-driven method, we comprehensively classified social interaction behavior in 761 male and female mice after chronic social witness/defeat stress, examining social modulation of behavior and associations with conventional metrics (i.e., social interaction ratio).

RESULTS

Social stress induced distinct behavioral adaptation patterns in defeated males and witness females. Social interaction ratio led to underpowered analyses in witness females with limited utility to differentiate susceptibility/resilience. Data-driven analyses revealed changes in social adaptation in witness females that were captured in attenuated velocity change from no target to target trials. We explored the utility of this metric in 4 female social stress models and in male witnesses. Combining social interaction ratio and velocity change optimally differentiated susceptibility/resilience in witness females and revealed resilient-specific adaptation in a resilience-associated neural circuit in female mice.

CONCLUSIONS

Chronic witness stress induced behavioral changes in females that were qualitatively distinct from those observed in defeated males and not adequately sampled by standard male-defined metrics. Modulation of locomotion is a robust and easily implementable metric for rigorous research in witness female mice. Overall, our findings highlight the need to critically evaluate sex differences in behavior and implement sex-based considerations in preclinical model design.

Dissecting the Hippocampal Regulation of Approach-Avoidance Conflict: Integrative Perspectives From Optogenetics, Stress Response, and Epigenetics

Psychiatric disorders are multifactorial conditions without clear biomarkers, influenced by genetic, environmental, and developmental factors. Understanding these disorders requires identifying specific endophenotypes that help break down their complexity. Here, we undertake an in-depth analysis of one such endophenotype, namely imbalanced approach-avoidance conflict (AAC), reviewing its significant dependency on the hippocampus. Imbalanced AAC is a transdiagnostic endophenotype, being a feature of many psychiatric conditions in humans. However, it is predominantly examined in preclinical research through paradigms that subject rodents to conflict-laden scenarios. This review offers an original perspective by discussing the AAC through three distinct lights: optogenetic modulation of the AAC, which updates our understanding of the hippocampal contribution to behavioral inhibition; the impact of environmental stress, which exacerbates conflict and strengthens the stress-psychopathology axis; and inherent epigenetic aspects, which uncover crucial molecular underpinnings of environmental (mal) adaptation. By integrating these perspectives, in this review we aim to underline a cross-species causal nexus between heightened hippocampal activity and avoidance behavior. In addition, we suggest a rationale to explore epigenetic pharmacology as a potential strategy to tackle AAC-related psychopathology. This review assumes greater significance when viewed through the lens of advancing AAC-centric diagnostics in human subjects. Unlike traditional questionnaires, which struggle to accurately measure individual differences in AAC-related dimensions, new approaches using virtual reality and computer games show promise in better focusing the magnitude of AAC contribution to psychopathology.

The extraordinary "ordinary magic" of resilience

In this essay, I will briefly sample different instances of the utilization of the concept of resilience, attempting to complement a comprehensive representation of the field in the special issue of Development and Psychopathology inspired by the 42nd Minnesota Symposium on Child Psychology, hosted by the Institute of Child Development at the University of Minnesota and held in October of 2022. Having established the general context of the field, I will zoom in on some of its features, which I consider "low-hanging fruit" and which can be harvested in a systematic way to advance the study of resilience in the context of the future of developmental psychopathology.

Circuit mechanisms underlying sexually dimorphic outcomes of early life stress

Stress during early life influences brain development and can affect social, motor, and emotional processes. We describe a striking sex difference in the effects of early life stress (ELS), which produces anhedonia and anxiety-like behaviors in female adolescent mice, as reported previously, but repetitive behavioral pathology and social deficits in male adolescent mice. Notably, this parallels sex differences seen in the prevalence of psychiatric symptoms: depression and anxiety disorders are more common in girls and women, whereas neurodevelopmental disorders like autism spectrum disorder and Tourette syndrome are markedly more common in boys and men. We characterized the effects of ELS on the medial prefrontal cortex (mPFC) and on its projections to the dorsal striatum (dStr) and lateral septum (LS). ELS males, but not females, developed hyperactivity in the cortico-striatal circuit and hypoactivity in the cortico-septal circuit. Chemogenetic manipulation of cortico-striatal projection neurons modulates repetitive behavioral pathology and social behaviors in stressed males, and anhedonia in stressed females. Activation of cortico-septal projection neurons rescues social deficits in stressed males. We conclude that early life stress produces sexually dimorphic behavioral effects, with potential relevance to human psychiatric symptoms, through its differential effects on cortico-striatal and cortico-septal circuits.

Semen Cuscutae flavonoids activated the cAMP-PKA-CREB-BDNF pathway and exerted an antidepressant effect in mice

Background

Semen Cuscutae flavonoids (SCFs) constitute a class of metabolites of Semen Cuscutae, a botanical drug that was recently found to have an anti-depression effect. This study aimed to evaluate the anti-depression effects of SCFs in chronic unpredictable mild stress (CUMS)-induced mice and to interrogate the underlying mechanisms.

Materials and methods

The CUMS mice were used for assessing the effects of SCFs treatments on depression. Mice were randomly divided into five groups. Four groups were subjected to the CUMS induction and concomitantly administered orally with either the vehicle or with a high-, medium-, and low-dose of SCFs, once per day for 4 weeks. One group was kept untreated as a control. The mice were then assessed for their statuses of a number of depression-related parameters, including body weight, food intake, sucrose preference test (SPT), open field test (OFT), tail suspension test (TST), and forced swim test (FST). In addition, a day after the completion of these tests, biopsies from the hippocampus were harvested and used to perform metabolomics by HPLC-MS/MS and to assess the levels of cAMP by ELISA and the levels of PKA, CREB, p-CREB, and BDNF by Western blot analyses.

Results

SCFs resulted in significant increases in both body weight and food intake and in the amelioration of the depressive-like behaviors in CUMS mice. A high-dose SCFs treatment led to significant alterations in 72 metabolites, of which 26 were identified as potential biomarkers for the SCFs treatment. These metabolites are associated with lipid, amino acid, and nucleotide metabolism. Among 26 metabolites, cAMP was positively correlated with body weight, SPT, OFT-total distance, and OFT-central residence time, while negatively correlated with immobility time in TST and FST, linking a change in cAMP with the SCFs treatment and the significant improvement in depressive symptoms in CUMS mice. Further analyses revealed that the levels of cAMP, PKA, CREB, p-CREB, and BDNF were reduced in the hippocampus of CUMS mice but were all increased following the SCFs treatments.

Conclusion

SCFs could ameliorate hippocampal metabolic disturbances and depressive behaviors and cause the activation of the cAMP-PKA-CREB-BDNF signaling pathway in the hippocampus of CUMS mice.

Anxiety disorders: Treatments, models, and circuitry mechanisms

Anxiety disorders are one of the most prevalent mental health conditions worldwide, imposing a significant burden on individuals affected by them and society in general. Current research endeavors aim to enhance the effectiveness of existing anxiolytic drugs and reduce their side effects through optimization or the development of new treatments. Several anxiolytic novel drugs have been produced as a result of discovery-focused research. However, many drug candidates that show promise in preclinical rodent model studies fail to offer any substantive clinical benefits to patients. This review provides an overview of the diagnosis and classification of anxiety disorders together with a systematic review of anxiolytic drugs with a focus on their targets, therapeutic applications, and side effects. It also provides a concise overview of the constraints and disadvantages associated with frequently administered anxiolytic drugs. Additionally, the study comprehensively reviews animal models used in anxiety studies and their associated molecular mechanisms, while also summarizing the brain circuitry related to anxiety. In conclusion, this article provides a valuable foundation for future anxiolytic drug discovery efforts.

Mapping of c-Fos Expression in Rat Brain Sub/Regions Following Chronic Social Isolation: Effective Treatments of Olanzapine, Clozapine or Fluoxetine

The c-Fos as a marker of cell activation is used to identify brain regions involved in stimuli processing. This review summarizes a pattern of c-Fos immunoreactivity and the overlapping brain sub/regions which may provide hints for the identification of neural circuits that underlie depressive- and anxiety-like behaviors of adult male rats following three and six weeks of chronic social isolation (CSIS), relative to controls, as well as the antipsychotic-like effects of olanzapine (Olz), and clozapine (Clz), and the antidepressant-like effect of fluoxetine (Flx) in CSIS relative to CSIS alone. Additionally, drug-treated controls relative to control rats were also characterized. The overlapping rat brain sub/regions with increased expression of c-Fos immunoreactivity following three or six weeks of CSIS were the retrosplenial granular cortex, c subregion, retrosplenial dysgranular cortex, dorsal dentate gyrus, paraventricular nucleus of the thalamus (posterior part, PVP), lateral/basolateral (LA/BL) complex of the amygdala, caudate putamen, and nucleus accumbens shell. Increased activity of the nucleus accumbens core following exposure of CSIS rats either to Olz, Clz, and Flx treatments was found, whereas these treatments in controls activated the LA/BL complex of the amygdala and PVP. We also outline sub/regions that might represent potential neuroanatomical targets for the aforementioned antipsychotics or antidepressant treatments.

The Impacts of Adolescent Cannabinoid Exposure on Striatal Anxiety- and Depressive-Like Pathophysiology Are Prevented by the Antioxidant N-Acetylcysteine

Background

Exposure to Δ9-tetrahydrocannabinol (THC) is an established risk factor for later-life neuropsychiatric vulnerability, including mood- and anxiety-related symptoms. The psychotropic effects of THC on affect and anxiogenic behavioral phenomena are known to target the striatal network, particularly the nucleus accumbens, a neural region linked to mood and anxiety disorder pathophysiology. THC may increase neuroinflammatory responses via the redox system and dysregulate inhibitory and excitatory neural balance in various brain circuits, including the striatum. Thus, interventions that can induce antioxidant effects may counteract the neurodevelopmental impacts of THC exposure.

Methods

In the current study, we used an established preclinical adolescent rat model to examine the impacts of adolescent THC exposure on various behavioral, molecular, and neuronal biomarkers associated with increased mood and anxiety disorder vulnerability. Moreover, we investigated the protective properties of the antioxidant N-acetylcysteine against THC-related pathology.

Results

We demonstrated that adolescent THC exposure induced long-lasting anxiety- and depressive-like phenotypes concomitant with differential neuronal and molecular abnormalities in the two subregions of the nucleus accumbens, the shell and the core. In addition, we report for the first time that N-acetylcysteine can prevent THC-induced accumbal pathophysiology and associated behavioral abnormalities.

Conclusions

The preventive effects of this antioxidant intervention highlight the critical role of redox mechanisms underlying cannabinoid-induced neurodevelopmental pathology and identify a potential intervention strategy for the prevention and/or reversal of these pathophysiological sequelae.

Acute stress activates basolateral amygdala neurons expressing corticotropin-releasing hormone receptor type 1 (CRHR1): Topographical distribution and projection-specific activation in male and female rats

Although the basolateral amygdala (BLA) and corticotropin releasing hormone receptor type I (CRHR1) signaling are both central to the stress response, the spatial and circuit-specific distribution of CRHR1 have not been identified in the BLA at a high resolution. We used transgenic male and female CRHR1-Cre-tdTomato rats to topographically map the distribution of BLACRHR1 neurons and identify whether they are activated by acute stress. Additionally, we used the BLA circuits projecting to the central amygdala (CeA) and nucleus accumbens (NAc) as a model to test circuit-specific expression of CRHR1 in the BLA. We established several key findings. First, CRHR1 had the strongest expression in the lateral amygdala and in caudal portions of the BLA. Second, acute restraint stress increased FOS expression of CRHR1 neurons, and stress-induced activation was particularly strong in medial subregions of the BLA. Third, stress significantly increased FOS expression on BLA-NAc, but not BLA-CeA projectors, and BLA-NAc activation was more robust in males than females. Finally, CRHR1 was expressed on a subset of BLA-CeA and BLA-NAc projection neurons. Collectively, this expands our understanding of BLA molecular- and circuit-specific activation patterns following acute stress.

Identification and experimental validation of hub genes underlying depressive-like behaviors induced by chronic social defeat stress

Introduction: Major depressive disorder (MDD), characterized by severe neuropsychiatric symptoms and significant cognitive deficits, continues to present both etiological and therapeutic challenges. However, the specific underlying mechanisms and therapeutic targets remain unclear. Methods: We analyzed human postmortem dorsolateral prefrontal cortex (dlPFC) samples from MDD patients using datasets GSE53987 and GSE54568, identifying three key genes: AGA, FBXO38, and RGS5. To model depressive-like behavior, we employed chronic social defeat stress (CSDS) and subsequently measured the expression of AGA, FBXO38, and RGS5 in the dlPFC using qPCR and Western blot analysis following CSDS exposure. Results: CSDS significantly induced depressive-like behavior, and both the protein and transcriptional expression levels of AGA, FBXO38, and RGS5 in the dlPFC of mice were markedly reduced after stress, consistent with findings from datasets GSE53987 and GSE54568. Conclusion: Our research suggests that AGA, FBXO38, and RGS5 are potential biomarkers for MDD and could serve as valuable targets for MDD risk prediction.

Sex-biased neural encoding of threat discrimination in nucleus accumbens afferents drives suppression of reward behavior

Learning to predict threat is essential, but equally important-yet often overlooked-is learning about the absence of threat. Here, by recording neural activity in two nucleus accumbens (NAc) glutamatergic afferents during aversive and neutral cues, we reveal sex-biased encoding of threat cue discrimination. In male mice, NAc afferents from the ventral hippocampus are preferentially activated by threat cues. In female mice, these ventral hippocampus-NAc projections are activated by both threat and nonthreat cues, whereas NAc afferents from medial prefrontal cortex are more strongly recruited by footshock and reliably discriminate threat from nonthreat. Chemogenetic pathway-specific inhibition identifies a double dissociation between ventral hippocampus-NAc and medial prefrontal cortex-NAc projections in cue-mediated suppression of reward-motivated behavior in male and female mice, despite similar synaptic connectivity. We suggest that these sex biases may reflect sex differences in behavioral strategies that may have relevance for understanding sex differences in risk of psychiatric disorders.

Characterization of transcriptional profiles associated with stress-induced neuronal activation in Arc-GFP mice

Chronic stress has become a predominant factor associated with a variety of psychiatric disorders, such as depression and anxiety, in both human and animal models. Although multiple studies have looked at transcriptional changes after social defeat stress, these studies primarily focus on bulk tissues, which might dilute important molecular signatures of social interaction in activated cells. In this study, we employed the Arc-GFP mouse model in conjunction with chronic social defeat (CSD) to selectively isolate activated nuclei (AN) populations in the ventral hippocampus (vHIP) and prefrontal cortex (PFC) of resilient and susceptible animals. Nuclear RNA-seq of susceptible vs. resilient populations revealed distinct transcriptional profiles linked predominantly with neuronal and synaptic regulation mechanisms. In the vHIP, susceptible AN exhibited increased expression of genes related to the cytoskeleton and synaptic organization. At the same time, resilient AN showed upregulation of cell adhesion genes and differential expression of major glutamatergic subunits. In the PFC, susceptible mice exhibited upregulation of synaptotagmins and immediate early genes (IEGs), suggesting a potentially over-amplified neuronal activity state. Our findings provide a novel view of stress-exposed neuronal activation and the molecular response mechanisms in stress-susceptible vs. resilient animals, which may have important implications for understanding mental resilience.

Ventral subiculum promotes wakefulness through several pathways in male mice

The ventral subiculum (vSUB), the major output structure of the hippocampal formation, regulates motivation, stress integration, and anxiety-like behaviors that rely on heightened arousal. However, the roles and underlying neural circuits of the vSUB in wakefulness are poorly known. Using in vivo fiber photometry and multichannel electrophysiological recordings in mice, we found that the vSUB glutamatergic neurons exhibited high activities during wakefulness. Moreover, activation of vSUB glutamatergic neurons caused an increase in wakefulness and anxiety-like behaviors and induced a rapid transition from sleep to wakefulness. In addition, optogenetic stimulation of vSUB glutamatergic terminals and retrograde-targeted chemogenetic activation of vSUB glutamatergic neurons revealed that vSUB promoted arousal by innervating the lateral hypothalamus (LH), nucleus accumbens (NAc) shell, and prefrontal cortex (PFC). Nevertheless, local microinjection of dopamine D1 or D2/D3 receptor antagonist blocked the wake-promoting effect induced by chemogenetic activation of vSUB pathways. Finally, chemogenetic inhibition of vSUB glutamatergic neurons decreased arousal. Altogether, our findings reveal a prominent contribution of vSUB glutamatergic neurons to the control of wakefulness through several pathways.

A Prelimbic Cortex-Thalamus Circuit Bidirectionally Regulates Innate and Stress-Induced Anxiety-Like Behavior

Anxiety-related disorders respond to cognitive behavioral therapies, which involved the medial prefrontal cortex (mPFC). Previous studies have suggested that subregions of the mPFC have different and even opposite roles in regulating innate anxiety. However, the specific causal targets of their descending projections in modulating innate anxiety and stress-induced anxiety have yet to be fully elucidated. Here, we found that among the various downstream pathways of the prelimbic cortex (PL), a subregion of the mPFC, PL-mediodorsal thalamic nucleus (MD) projection, and PL-ventral tegmental area (VTA) projection exhibited antagonistic effects on anxiety-like behavior, while the PL-MD projection but not PL-VTA projection was necessary for the animal to guide anxiety-related behavior. In addition, MD-projecting PL neurons bidirectionally regulated remote but not recent fear memory retrieval. Notably, restraint stress induced high-anxiety state accompanied by strengthening the excitatory inputs onto MD-projecting PL neurons, and inhibiting PL-MD pathway rescued the stress-induced anxiety. Our findings reveal that the activity of PL-MD pathway may be an essential factor to maintain certain level of anxiety, and stress increased the excitability of this pathway, leading to inappropriate emotional expression, and suggests that targeting specific PL circuits may aid the development of therapies for the treatment of stress-related disorders.

Heightened lateral habenula activity during stress produces brainwide and behavioral substrates of susceptibility

Some individuals are susceptible to the experience of chronic stress and others are more resilient. While many brain regions implicated in learning are dysregulated after stress, little is known about whether and how neural teaching signals during stress differ between susceptible and resilient individuals. Here, we seek to determine if activity in the lateral habenula (LHb), which encodes a negative teaching signal, differs between susceptible and resilient mice during stress to produce different outcomes. After, but not before, chronic social defeat stress (CSDS), the LHb is active when susceptible mice are in the proximity of the aggressor strain. During stress itself, LHb activity is higher in susceptible mice during aggressor proximity, and activation of the LHb during stress biases mice towards susceptibility. This manipulation generates a persistent and widespread increase in the balance of subcortical versus cortical activity in susceptible mice. Taken together, our results indicate that heightened activity in the LHb during stress produces lasting brainwide and behavioral substrates of susceptibility.

Sex-Specific Mechanisms Underlie Long-Term Potentiation at Hippocampus→Medium Spiny Neuron Synapses in the Medial Shell of the Nucleus Accumbens

Sex differences have complicated our understanding of the neurobiological basis of many behaviors that are key for survival. As such, continued elucidation of the similarities and differences between sexes is necessary to gain insight into brain function and vulnerability. The connection between the hippocampus (Hipp) and nucleus accumbens (NAc) is a crucial site where modulation of neuronal activity mediates reward-related behavior. Our previous work demonstrated that long-term potentiation (LTP) of Hipp→NAc synapses is rewarding, and mice can establish learned associations between LTP of these synapses and the contextual environment in which LTP occurred. Here, we investigated sex differences in the mechanisms underlying Hipp→NAc LTP using whole-cell electrophysiology and pharmacology. We observed similarities in basal synaptic strength between males and females and found that LTP occurs postsynaptically with similar magnitudes in both sexes. However, key sex differences emerged as LTP in males required NMDA receptors (NMDAR), whereas LTP in females utilized an NMDAR-independent mechanism involving L-type voltage-gated Ca2+ channels (VGCCs) and estrogen receptor α (ERα). We also uncovered sex-similar features as LTP in both sexes depended on CaMKII activity and occurred independently of dopamine-1 receptor (D1R) activation. Our results have elucidated sex-specific molecular mechanisms for LTP in an integral pathway that mediates reward-related behaviors, emphasizing the importance of considering sex as a variable in mechanistic studies. Continued characterization of sex-specific mechanisms underlying plasticity will offer novel insight into the neurophysiological basis of behavior, with significant implications for understanding how diverse processes mediate behavior and contribute to vulnerability to developing psychiatric disorders.

Neurobiology and systems biology of stress resilience

Stress resilience is the phenomenon that some people maintain their mental health despite exposure to adversity or show only temporary impairments followed by quick recovery. Resilience research attempts to unravel the factors and mechanisms that make resilience possible and to harness its insights for the development of preventative interventions in individuals at risk for acquiring stress-related dysfunctions. Biological resilience research has been lagging behind the psychological and social sciences but has seen a massive surge in recent years. At the same time, progress in this field has been hampered by methodological challenges related to finding suitable operationalizations and study designs, replicating findings, and modeling resilience in animals. We embed a review of behavioral, neuroimaging, neurobiological, and systems biological findings in adults in a critical methods discussion. We find preliminary evidence that hippocampus-based pattern separation and prefrontal-based cognitive control functions protect against the development of pathological fears in the aftermath of singular, event-type stressors [as found in fear-related disorders, including simpler forms of posttraumatic stress disorder (PTSD)] by facilitating the perception of safety. Reward system-based pursuit and savoring of positive reinforcers appear to protect against the development of more generalized dysfunctions of the anxious-depressive spectrum resulting from more severe or longer-lasting stressors (as in depression, generalized or comorbid anxiety, or severe PTSD). Links between preserved functioning of these neural systems under stress and neuroplasticity, immunoregulation, gut microbiome composition, and integrity of the gut barrier and the blood-brain barrier are beginning to emerge. On this basis, avenues for biological interventions are pointed out.

Histone H1x in mouse ventral hippocampus associates with, but does not cause behavioral adaptations to stress

Prior research has identified differential protein expression levels of linker histone H1x within the ventral hippocampus (vHipp) of stress-susceptible versus stress-resilient mice. These mice are behaviorally classified based on their divergent responses to chronic social stress. Here, we sought to determine whether elevated vHipp H1x protein levels directly contribute to these diverging behavioral adaptations to stress. First, we demonstrated that stress-susceptible mice uniquely express elevated vHipp H1x protein levels following chronic stress. Given that linker histones coordinate heterochromatin compaction, we hypothesize that elevated levels of H1x in the vHipp may impede pro-resilience transcriptional adaptations and prevent development of the resilient phenotype following social stress. To test this, 8-10-week-old male C57BL/6 J mice were randomly assigned to groups undergoing 10 days of chronic social defeat stress (CSDS) or single housing, respectively. Following CSDS, mice were classified as susceptible versus resilient based on their social interaction behaviors. We synthesized a viral overexpression (OE) vector for H1x and transduced all stressed and single housed mice with either H1x or control GFP within vHipp. Following viral delivery, we conducted social, anxiety-like, and memory-reliant behavior tests on distinct cohorts of mice. We found no behavioral adaptations following H1x OE compared to GFP controls in susceptible, resilient, or single housed mice. In sum, although we confirm elevated vHipp protein levels of H1x associate with susceptibility to social stress, we observe no significant behavioral consequence of H1x OE. Thus, we conclude elevated levels of H1x are associated with, but are not singularly sufficient to drive development of behavioral adaptations to stress.

Effects of paternal deprivation on empathetic behavior and the involvement of oxytocin receptors in the anterior cingulate cortex

Paternal deprivation (PD) impairs social cognition and sociality and increases levels of anxiety-like behavior. However, whether PD affects the levels of empathy in offspring and its underlying mechanisms remain unknown. The present study found that PD increased anxiety-like behavior in mandarin voles (Microtus mandarinus), impaired sociality, reduced the ability of emotional contagion, and the level of consolation behavior. Meanwhile, PD reduced OT neurons in the paraventricular nucleus (PVN) in both male and female mandarin voles. PD decreased the level of OT receptor (OTR) mRNA in the anterior cingulate cortex (ACC) of male and female mandarin voles. Besides, OTR overexpression in the ACC reversed the PD-induced changes in anxiety-like behavior, social preference, emotional contagion, and consolation behavior. Interference of OTR expression in the ACC increased levels of anxiety-like behaviors, while it reduced levels of sociality, emotional contagion, and consolation. These results revealed that the OTR in the ACC is involved in the effects of PD on empathetic behaviors, and provide mechanistic insight into how social experiences affect empathetic behaviors.

Optogenetic behavioral studies in depression research: A systematic review

Optogenetics has made substantial contributions to our understanding of the mechanistic underpinnings of depression. This systematic review employs quantitative analysis to investigate the impact of optogenetic stimulation in mice and rats on behavioral alterations in social interaction, sucrose consumption, and mobility. The review analyses optogenetic behavioral studies using standardized behavioral tests to detect behavioral changes induced via optogenetic stimulation in stressed or stress-naive mice and rats. Behavioral changes were evaluated as either positive, negative, or not effective. The analysis comprises the outcomes of 248 behavioral tests of 168 studies described in 37 articles, including negative and null results. Test outcomes were compared for each behavior, depending on the animal cohort, applied type of stimulation and the stimulated neuronal circuit and cell type. The presented synthesis contributes toward a comprehensive picture of optogenetic behavioral research in the context of depression.

Dorsal peduncular cortex activity modulates affective behavior and fear extinction in mice

The medial prefrontal cortex (mPFC) is critical to cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with specialized contributions from its subdivisions. The rodent mPFC is divided into the dorsomedial prefrontal cortex (dmPFC), spanning the anterior cingulate cortex (ACC) and dorsal prelimbic cortex (PL), and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, infralimbic cortex (IL), and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics and optogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, fear and stress responses in C57BL/6J mice. Acute chemogenetic activation of DP/DTT significantly increased anxiety-like behavior in the open field and elevated plus maze tests, as well as passive coping in the tail suspension test. DP/DTT activation also led to an increase in serum corticosterone levels and facilitated auditory fear extinction learning and retrieval. Activation of DP/DTT projections to the dorsomedial hypothalamus (DMH) acutely decreased freezing at baseline and during extinction learning, but did not alter affective behavior. These findings point to the DP/DTT as a new regulator of affective behavior and fear extinction in mice.

Phytomedicine Fructus Aurantii-derived two absorbed compounds unlock antidepressant and prokinetic multi-functions via modulating 5-HT3/GHSR

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Aurantii (FA), a well-known phytomedicine, has been employed to evoke antidepressant and prokinetic multi-functions. Therein, systematically identifying bioactive components and the referred mechanism is essential for FA.

AIM OF THE STUDY

This study was planned to answer "2 W" (What and Why), such as which components and pathways contribute to FA's multi-functions. We aimed to identify bioactive compounds as the key for opening the lock of FA's multi-functions, and the molecule mechanisms are their naturally matched lock cylinder.

MATERIALS AND METHODS

The phytochemical content of FA extract was determined, and the compounds were identified in rats pretreated with FA using liquid chromatography with mass spectrometry (LC-MS). The contribution strategy was used to assess bioactive compounds' efficacy (doses = their content in FA) in model rats with the mechanism. The changes in functional brain regions were determined via 7.0 T functional magnetic resonance imaging-blood oxygen level-dependent (fMRI-BOLD).

RESULT

Eight phytochemicals' content was detected, and merely six components were identified in rats in vivo. Meranzin hydrate + hesperidin (MH), as the primary contributor of FA, exerted antidepressant and prokinetic effects (improvement of indexes for immobility time, gastric emptying, intestinal transit, CRH, ghrelin, ACTH, DA, NA, 5-HT, CORT, and 5-HT3) by regulating 5-HT3/Growth hormone secretagogue receptor (GHSR) pathway. These results were validated by 5-HT2A, 5-HT3, and GHSR receptor antagonists combined with molecule docking. MH restored the excessive BOLD activation of the left accumbens nucleus, left corpus callosum and hypothalamus preoptic region.

CONCLUSION

Absorbed MH accounts for FA's anti-depressant and prokinetic efficacy in acutely-stressed rats, primarily via 5-HT3/GHSR shared regulation.

Tet1/DLL3/Notch1 signal pathway affects hippocampal neurogenesis and regulates depression-like behaviour in mice

Ten-eleven translocation protein 1 (Tet1) is associated with the regulation of depression-like behaviour in mice. However, the mechanism by which Tet1 affects neurogenesis in mice to regulate depression-like behaviours remains unclear. In this study, the chronic social defeat stress (CSDS) paradigm was constructed by overexpressing Tet1 protein in the mouse hippocampus, and 5-ethynyl-2'-deoxyuridine (EdU, 50 mg/kg) was injected on the seventh day to explore the mechanism of the regulation of the Tet1/Delta-like protein 3 (DLL3)/Notch1 protein pathway in mice hippocampal neurogenesis and its influence on depression-like behaviour. Following CSDS, the expression level of Tet1 decreased significantly. Moreover, due to the downregulation of Tet1 protein, the maintenance of the DNA methylation and demethylation balance was affected, resulting in a significant increase in the methylation levels of Notch1 and DLL3 and a significant decrease in the protein expression levels of DLL3, Notch1, and brain-derived neurotrophic factor (BDNF). At the same time, the proliferation and differentiation of neurones were affected, which was related to a significant decrease in the number of EdU+, doublecortin (DCX)+, and Ki67+ cells in the hippocampus of the CSDS model mice. When the Tet1 protein was overexpressed in the mouse hippocampus, DLL3 and Notch1 protein expression levels were upregulated, promoting hippocampal neurogenesis and alleviating depression-like behaviour in mice. These findings suggest that regulation of the hippocampal Tet1/DLL3/Notch1 protein pathway to influence neurogenesis may be a therapeutic strategy for depression.

FBXL20 promotes synaptic impairment in depression disorder via degrading vesicle-associated proteins

BACKGROUND

Synaptic plasticity changes in presynaptic terminals or postsynaptic membranes play a critical role in cognitive impairments and emotional disorders, but the underlying molecular mechanisms in depression remain largely unknown.

METHODS

The regulation effects of F-box and leucine-rich repeat protein 20 (FBXL20), vesicular glutamate transporter 1 (VGLUT1) and vesicle-associated membrane protein 1 (VAMP1) on synaptic plasticity and depressive-like behaviors examined by proteomics analysis, viral stereotaxic injection, transmission electron microscope and biochemical methods. The glutamate release detected by fluorescent probe in cultured primary pyramidal neurons.

RESULTS

We found that chronic unpredictable mild stress (CUMS) induced significant synaptic deficits within hippocampus of depressed rats, accompanied with the decreased expression of VGLUT1 and VAMP1. Moreover, knockdown of VGLUT1 or VAMP1 in hippocampal pyramidal neurons resulted in abnormal glutamatergic neurotransmitter release. In addition, we found that the E3 ubiquitin ligase FBXL20 was increased within hippocampus, which may promote ubiquitination and degradation of VGLUT1 and VAMP1, and thus resulted in the reduction of glutamatergic neurotransmitter release, the disruptions of synaptic transmission and the induction of depression-like behaviors in rats. In contrast, shRNA knockdown of FBXL20 within the hippocampus of depressed rats significantly ameliorated synaptic damage and depression-like behaviors.

LIMITATION

Only one type of depression model was used in the present study, while other animal models should be used in the future to confirm the underlying mechanisms reported here.

CONCLUSIONS

This study provides new insights that inhibiting FBXL20 pathway in depressed rats may be an effective strategy to rescue synaptic transmission and depression-like behaviors.

Discrete prefrontal neuronal circuits determine repeated stress-induced behavioral phenotypes in male mice

Chronic stress is a major risk factor for psychiatric disorders, including depression. Although depression is a highly heterogeneous syndrome, it remains unclear how chronic stress drives individual differences in behavioral responses. In this study, we developed a subtyping-based approach wherein stressed male mice were divided into four subtypes based on their behavioral patterns of social interaction deficits and anhedonia, the core symptoms of psychiatric disorders. We identified three prefrontal cortical neuronal projections that regulate repeated stress-induced behavioral phenotypes. Among them, the medial prefrontal cortex (mPFC)→anterior paraventricular thalamus (aPVT) pathway determines the specific behavioral subtype that exhibits both social deficits and anhedonia. Additionally, we identified the circuit-level molecular mechanism underlying this subtype: KDM5C-mediated epigenetic repression of Shisa2 transcription in aPVT projectors in the mPFC led to social deficits and anhedonia. Thus, we provide a set of biological aspects at the cellular, molecular, and epigenetic levels that determine distinctive stress-induced behavioral phenotypes.

Obesogenic diet induces circuit-specific memory deficits in mice

Obesity is associated with neurocognitive dysfunction, including memory deficits. This is particularly worrisome when obesity occurs during adolescence, a maturational period for brain structures critical for cognition. In rodent models, we recently reported that memory impairments induced by obesogenic high-fat diet (HFD) intake during the periadolescent period can be reversed by chemogenetic manipulation of the ventral hippocampus (vHPC). Here, we used an intersectional viral approach in HFD-fed male mice to chemogenetically inactivate specific vHPC efferent pathways to nucleus accumbens (NAc) or medial prefrontal cortex (mPFC) during memory tasks. We first demonstrated that HFD enhanced activation of both pathways after training and that our chemogenetic approach was effective in normalizing this activation. Inactivation of the vHPC-NAc pathway rescued HFD-induced deficits in recognition but not location memory. Conversely, inactivation of the vHPC-mPFC pathway restored location but not recognition memory impairments produced by HFD. Either pathway manipulation did not affect exploration or anxiety-like behaviour. These findings suggest that HFD intake throughout adolescence impairs different types of memory through overactivation of specific hippocampal efferent pathways and that targeting these overactive pathways has therapeutic potential.

Targeting cAMP in D1-MSNs in the nucleus accumbens, a new rapid antidepressant strategy

Studies have suggested that the nucleus accumbens (NAc) is implicated in the pathophysiology of major depression; however, the regulatory strategy that targets the NAc to achieve an exclusive and outstanding anti-depression benefit has not been elucidated. Here, we identified a specific reduction of cyclic adenosine monophosphate (cAMP) in the subset of dopamine D1 receptor medium spiny neurons (D1-MSNs) in the NAc that promoted stress susceptibility, while the stimulation of cAMP production in NAc D1-MSNs efficiently rescued depression-like behaviors. Ketamine treatment enhanced cAMP both in D1-MSNs and dopamine D2 receptor medium spiny neurons (D2-MSNs) of depressed mice, however, the rapid antidepressant effect of ketamine solely depended on elevating cAMP in NAc D1-MSNs. We discovered that a higher dose of crocin markedly increased cAMP in the NAc and consistently relieved depression 24 h after oral administration, but not a lower dose. The fast onset property of crocin was verified through multicenter studies. Moreover, crocin specifically targeted at D1-MSN cAMP signaling in the NAc to relieve depression and had no effect on D2-MSN. These findings characterize a new strategy to achieve an exclusive and outstanding anti-depression benefit by elevating cAMP in D1-MSNs in the NAc, and provide a potential rapid antidepressant drug candidate, crocin.

Identifying and modulating neural signatures of stress susceptibility and resilience enables control of anhedonia

Anhedonia is a core aspect of major depressive disorder. Traditionally viewed as a blunted emotional state in which individuals are unable to experience joy, anhedonia also diminishes the drive to seek rewards and the ability to value and learn about them 1-4.The neural underpinnings of anhedonia and how this emotional state drives related behavioral changes remain unclear. Here, we investigated these questions by taking advantage of the fact that when mice are exposed to traumatic social stress, susceptible animals become socially withdrawn and anhedonic, where they cease to seek high-value rewards, while others remain resilient. By performing high density electrophysiological recordings and comparing neural activity patterns of these groups in the basolateral amygdala (BLA) and ventral CA1 (vCA1) of awake behaving animals, we identified neural signatures of susceptibility and resilience to anhedonia. When animals actively sought rewards, BLA activity in resilient mice showed stronger discrimination between upcoming reward choices. In contrast, susceptible mice displayed a rumination-like signature, where BLA neurons encoded the intention to switch or stay on a previously chosen reward. When animals were at rest, the spontaneous BLA activity of susceptible mice was higher dimensional than in controls, reflecting a greater number of distinct neural population states. Notably, this spontaneous activity allowed us to decode group identity and to infer if a mouse had a history of stress better than behavioral outcomes alone. Finally, targeted manipulation of vCA1 inputs to the BLA in susceptible mice rescued dysfunctional neural dynamics, amplified dynamics associated with resilience, and reversed their anhedonic behavior. This work reveals population-level neural signatures that explain individual differences in responses to traumatic stress, and suggests that modulating vCA1-BLA inputs can enhance resilience by regulating these dynamics.

Corticotropin-releasing hormone neurons control trigeminal neuralgia-induced anxiodepression via a hippocampus-to-prefrontal circuit

Anxiety and depression are frequently observed in patients suffering from trigeminal neuralgia (TN), but neural circuits and mechanisms underlying this association are poorly understood. Here, we identified a dedicated neural circuit from the ventral hippocampus (vHPC) to the medial prefrontal cortex (mPFC) that mediates TN-related anxiodepression. We found that TN caused an increase in excitatory synaptic transmission from vHPCCaMK2A neurons to mPFC inhibitory neurons marked by the expression of corticotropin-releasing hormone (CRH). Activation of CRH+ neurons subsequently led to feed-forward inhibition of layer V pyramidal neurons in the mPFC via activation of the CRH receptor 1 (CRHR1). Inhibition of the vHPCCaMK2A-mPFCCRH circuit ameliorated TN-induced anxiodepression, whereas activating this pathway sufficiently produced anxiodepressive-like behaviors. Thus, our studies identified a neural pathway driving pain-related anxiodepression and a molecular target for treating pain-related psychiatric disorders.