Midbrain projection to the basolateral amygdala encodes anxiety-like but not depression-like behaviors

Dopamine D1-D2 signalling in hippocampus arbitrates approach and avoidance

The hippocampus1-6, as well as dopamine circuits7-9, coordinates decision-making in anxiety-eliciting situations. Yet, little is known about how dopamine modulates hippocampal representations of emotionally salient stimuli to inform appropriate resolution of approach versus avoidance conflicts. Here we studied dopaminoceptive neurons in the male mouse ventral hippocampus (vHipp), molecularly distinguished by their expression of dopamine D1 or D2 receptors. We show that these neurons are transcriptionally distinct and topographically organized across vHipp subfields and cell types. In the ventral subiculum where they are enriched, both D1 and D2 neurons are recruited during anxiogenic exploration, yet with distinct profiles related to investigation and behavioural selection. In turn, they mediate opposite approach-avoidance responses, and are differentially modulated by dopaminergic transmission in that region. Together, these results suggest that vHipp dopamine dynamics gate exploratory behaviours under contextual uncertainty, implicating dopaminoception in the complex computation engaged in the vHipp to govern emotional states.

Multidimensional mechanisms of anxiety and depression in Parkinson's disease: Integrating neuroimaging, neurocircuits, and molecular pathways

Anxiety and depression are common non-motor symptoms of Parkinson's disease (PD) that significantly affect patients' quality of life. In recent years, our understanding of PD has advanced through multifaceted studies on the pathological mechanisms associated with anxiety and depression in PD. These classic psychiatric symptoms involve complex pathophysiology, with both distinct features and connections to the mechanisms underlying the aetiology of PD. Furthermore, the co-occurrence of anxiety and depression in PD blurs the boundaries between them. Therefore, a comprehensive summary of the pathogenic mechanisms associated with anxiety and depression will aid in better addressing the emergence of these classic psychiatric symptoms in PD. This article integrates neuroanatomical, neural projection, neurotransmitter, neuroinflammatory, brain-gut axis, neurotrophic, hypothalamic-pituitary-adrenal axis, and genetic perspectives to provide a comprehensive description of the core pathological alterations underlying anxiety and depression in PD, aiming to provide an up-to-date perspective and broader therapeutic prospects for PD patients suffering from anxiety or depression.

Brain-derived uroguanylin as a regulator of postprandial brown adipose tissue activation: a potential therapeutic approach for metabolic disorders

Background

Preclinical and clinical research of insulin resistance and glucose homeostasis in metabolic disorders are essential. In this study, we aim to determine the expression of uroguanylin (UGN) in the mouse and human brain, its regulatory mechanisms, and its significance to patients with obesity and type 2 diabetes (T2D).

Methods

UGN expression, regulation, and its correlation with feeding status and obesity in the mouse and human brain were analyzed at the mRNA level using RT-PCR, qPCR, and in situ hybridization and at the protein level using Western blot, ELISA, and immunohistochemistry. Brown adipose tissue (BAT) activity was measured using infrared thermography. The volume of interscapular brown adipose tissue in mice was assessed by magnetic resonance imaging.

Results

UGN was expressed in both the mouse and human brain, and its expression was regulated by feeding. In the human prefrontal cortex, UGN was expressed in several interneuron subpopulations across all cortical layers. In Brodmann area (BA) 10, prouroguanylin (proUGN) expression was not regulated by feeding in obesity, whereas this regulation still persisted in BA9. In mice, centrally applied UGN and its analog linaclotide, affecting the hypothalamus, induced both acute and chronic activation of BAT, which decreases the plasma glucose concentration. However, in obesity, proUGN expression was reduced in the human hypothalamus, suggesting reduced postprandial glucose consumption in BAT. Similarly, centrally applied analog of glucagon-like peptide 1 (GLP-1-liraglutide) affected proUGN expression and was associated with increased basal BAT activity but reduced BAT activation after a meal in patients with T2D receiving GLP-1 therapy.

Conclusion

Postprandial BAT activation is regulated by brain-derived UGN, which could serve as a novel therapeutic approach to enhance BAT activity in patients with obesity and T2D to improve postprandial glucose regulation.

Activation of orexin receptor 2 plays anxiolytic effect in male mice

Anxiety disorders are the most common psychiatric illnesses. Present drugs can provide temporary relief for anxiety, however, they also come with side effects and safety concerns such as dependence, suicide, overdose and so on. Therefore, it is critical to discover new anxiolytic targets. An ongoing area of interest in the field of psychiatric diseases is the orexin system. Emerging body of evidences show that orexin receptor 1 (OX1R) has promising potential as novel anxiolytic target. However, little attention has been paid to orexin receptor 2 (OX2R) in anxiety. In this study, by using behavioral test, stereotaxic surgery and microinjection, virus-mediated knockdown of OX2R and pharmacological method, we found that: (1) Intraperitoneal injection of OX2R antagonist Seltorexant induced increased baseline anxiety-like behaviors in male mice. (2) Intraperitoneal injection of OX2R agonist YNT-185 reduced baseline anxiety-like behaviors in male mice. (3) Intraperitoneal injection of YNT-185 alleviated morphine withdrawal-induced anxiety-like behaviors in male mice. (4) Microinjection of YNT-185 into the VTA played anxiolytic effect in male mice. (5) Virus-mediated OX2R knockdown in the VTA induced anxiety-like behaviors in male mice.

Social stress increases anxiety by GluA1-dependent synaptic strengthening of ventral tegmental area inputs to the basolateral amygdala

BACKGROUND

Brain defensive mechanisms evolved to maintain low levels of state anxiety. However, risk factors such as stress exposure shifts activity within defensive circuits, resulting in increased anxiety. The amygdala is a crucial node for maintaining adaptive anxiety levels, and amygdala hyperactivity can lead to pathological anxiety through mechanisms that are not well understood.

METHODS

We used chronic social defeat stress (CSD) in mice. We combined anatomical tracing methods, patch-clamp recordings and optogenetics to probe how synaptic inputs from the ventral tegmental area (VTA) to the basolateral amygdala (BLA) are affected by CSD. We performed in vivo fiber photometry recordings to track inputs onto basolateral amygdala. Array tomography and electron microscopy were used to unravel the structural composition of VTA-BLA synapses.

RESULTS

We identified the VTA as a source of glutamatergic inputs to the BLA potentiated by stress. In turn, inputs from mPFC were not potentiated. BLA-projecting VTA glutamatergic neurons are activated by social stress, increasing their excitability and synaptic strength. In vivo potentiation of VTA glutamatergic inputs in the BLA is sufficient to increase anxiety. We showed that stress-induced synaptic strengthening is mediated by insertion of GluA1-containing AMPA receptors. Impeding GluA1 subunit trafficking in BLA neurons with VTA upstream inputs prevents stress-induced increase in synaptic firing and anxiety.

CONCLUSIONS

Potentiation of VTA inputs increases synaptic integration, enhancing amygdala activity and promoting maladaptive anxiety. Understanding the impact of amygdala hyperactivity could lead to targeted therapies, restoring circuit balance and offering new precision medicine approaches for anxiety disorders.

Design and validation of novel brain-penetrant HCN channel inhibitors to ameliorate social stress-induced susceptible phenotype

Major Depressive Disorder (MDD) is a devastating, multifactorial disease with limited pharmacological treatment options. Patients with MDD exhibit alterations in their dopamine (DA) signaling pathways through the midbrain ventral tegmental area (VTA). A similar observation is also detected in preclinical models of stress - mice exhibit behavioral and physiological impairments following chronic social defeat stress (CSDS). Prior studies demonstrate that CSDS-susceptible mice have increased VTA DA neuronal excitability, in part driven by an upregulation in hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels. Inhibiting HCN channels with known inhibitors such as Cilobradine alleviates the negative behavioral effects of CSDS. Here, we aimed to identify Cilobradine analogs with improved neural tropism and inhibitory efficacy. Two compounds, MS7710 and MS7712, differing by their left-hand side moieties, have a similar, potent inhibitory effect on VTA DA Ih currents as compared to Cilobradine, and a greater inhibitory effect than Cilobradine on VTA DA firing rate. We demonstrate that MS7710 and MS7712 have superior brain/plasma concentration ratios as compared to Cilobradine. They were efficacious at inhibiting VTA DA neuron firing rate and bursting activity in CSDS-susceptible male mice at lower doses than Cilobradine, which was recapitulated in female CSDS-susceptible mice with MS7710. Finally, we define that a single intraperitoneal injection of MS7710 ameliorates CSDS-induced social interaction deficits and reward-associated cognitive inflexibility for at least two weeks in male and female mice. These findings yield a novel HCN channel inhibitor with improved neural tropism and stress-alleviating effects that could provide a basis for future antidepressant drug discovery.

Effects of KCNQ potassium channel modulation on ventral tegmental area activity and connectivity in individuals with depression and anhedonia

Up to half of individuals with depression do not respond to first-line treatments, possibly due to a lack of treatment interventions informed by neurobiology. A novel therapeutic approach for depression has recently emerged from translational work targeting aberrant activity of ventral tegmental area (VTA) dopamine neurons via modulation of the KCNQ voltage-gated potassium channels. In this study, individuals with major depressive disorder (MDD) with elevated anhedonia were randomized to five weeks of the KCNQ channel opener, ezogabine (up to 900 mg/day) or placebo. Participants completed functional MRI during a monetary anticipation task and resting-state at baseline and at end-of-treatment. The clinical results were reported previously. Here, we examined VTA activity during monetary anticipation and resting-state functional connectivity between the VTA and the ventromedial prefrontal cortex (mesocortical pathway) and ventral striatum (mesolimbic pathway) at baseline and end-of-treatment. Results indicated a significant drug-by-time interaction in VTA activation during anticipation (F(1,34) = 4.36, p = 0.044), where VTA activation was reduced from pre-to-post ezogabine, compared to placebo. Mesocortical functional connectivity was also higher in depressed participants at baseline compared to a healthy control group (t(56) = 2.68, p = 0.01) and associated with VTA hyper-activity during task-based functional MRI at baseline (R = 0.352, p = 0.033). Mesocortical connectivity was also reduced from pre-to-post ezogabine, compared to placebo (significant drug-by-time interaction, F(1,33) = 4.317, p = 0.046). Together this translational work is consistent with preclinical findings highlighting VTA hyper-activity in depression, and suggesting a mechanism of action for KCNQ channel openers in normalizing this hyper-activity in individuals with both depression and anhedonia.

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.

Dopamine modulation of basolateral amygdala activity and function

The basolateral amygdala (BLA) is central to emotional processing, fear learning, and memory. Dopamine (DA) significantly influences BLA function, yet its precise effects are not clear. We present a mathematical model exploring how DA modulation of BLA activity depends on the network's current state. Specifically, we model the firing rates of interconnected neural groups in the BLA and their responses to external stimuli and DA modulation. BLA projection neurons are separated into two groups according to their responses-fear and safety. These groups are connected by mutual inhibition though interneurons. We contrast 'differentiated' BLA states, where fear and safety projection neurons exhibit distinct activity levels, with 'non-differentiated' states. We posit that differentiated states support selective responses and short-term emotional memory. On the other hand, non-differentiated states represent either the case in which BLA is disengaged, or the activation of the fear and safety neurons is at a similar moderate or high level. We show that, while DA further disengages BLA in the low activity state, it destabilizes the moderate activity non-differentiated BLA state. We show that in the latter non-differentiated state the BLA is hypersensitive, and the polarity of its responses (fear or safety) to salient stimuli is highly random. We hypothesize that this non-differentiated state is related to anxiety and Post-Traumatic Stress Disorder (PTSD).

Cross-species dissection of the modular role of the ventral tegmental area in depressive disorders

Depressive disorders, including major depressive disorder (MDD), represent one of the most prevalent set of disorders worldwide. MDD is characterized by a range of cognitive, behavioral, and neurobiological changes that contribute to the vast array of symptom profiles that make this disorder particularly difficult to treat. A multitude of established evidence suggests a role for the dopamine system, stemming in part from the ventral tegmental area (VTA), in mediating symptoms and behavioral changes that underlie depression. Developments in cutting-edge technologies in pre-clinical models of depressive phenotypes, such as retrograde tracing, electrophysiological recordings, immunohistochemistry, and molecular profiling, have allowed a deeper characterization of singular VTA neuron molecular, physiological, and projection properties. These developments have highlighted that the VTA is not a homogenous cell population but instead comprises vast cellular diversity that underscores its modular role across various functions related to reward processing, aversion, salience processing, learning and motivation. In this review, we begin by introducing the various cell types and brain regions that comprise the VTA circuitry. Then, we introduce the role of the VTA in reward processing as it compares to aversion processing. Next, we characterize distinct neural pathways within the VTA circuitry to understand the effects of chronic social and non-social stress and tie together how these neurobiological changes manifest into specific behavioral phenotypes. Finally, we relate these preclinical findings to clinical findings to parse the heterogeneity of depressive phenotypes and explain the efficacy of recent novel pharmacological interventions that may target the VTA in MDD.

Deficit of neuronal EAAT2 impairs hippocampus CA3 neuron's activity and may induce depressive like behaviors

INTRODUCTION

Major depressive disorder (MDD) is a severe neuropsychiatric disease that is accompanied by hippocampal dysfunction. Currently, the complex neuronal types and molecules involved in the various hippocampal subfields in patients with depression remain unclear.

OBJECTIVES

We focused on the role of hippocampal excitatory amino acid transporter 2 (EAAT2) in chronic stress.

METHODS

We studied two chronic stress models, the chronic unpredictable mild stress (CUMS) and the chronic social defeat stress (CSDS) models, and performed pharmacological inhibition, genetic manipulations to examine overexpression of neuron-specific solute carrier family 1 member 2 (SLC1A2), the gene encoding EAAT2, in the dorsal CA3 and conditional Slc1a2 knockout in CA3, whole-cell recording, and behavioral tests.

RESULTS

Our results indicated that decreased EAAT2 expression and specific inhibition were associated with depression-like behavior and enhanced CA3 pyramidal neuron activity. In addition, neuron-specific EAAT2 overexpression in the CA3 yielded antidepressant-like effects and inhibited CA3 pyramidal neuron hyperactivity, whereas conditional CA3 EAAT2 knockout showed opposite effects at both behavioral and functional levels. We also found that the single-nucleotide polymorphism, rs77619780, in the SLCA1A2 gene was associated with lower MDD risk.

CONCLUSION

Our findings revealed that EAAT2 deficit in the CA3 induces depression-like behavior, which offers novel insight into MDD pathophysiology.

Investigating the effect of Arvcf reveals an essential role on regulating the mesolimbic dopamine signaling-mediated nicotine reward

The mesolimbic dopamine system is crucial for drug reinforcement and reward learning, leading to addiction. We previously demonstrated that Arvcf was associated significantly with nicotine and alcohol addiction through genome-wide association studies. However, the role and mechanisms of Arvcf in dopamine-mediated drug reward processes were largely unknown. In this study, we first showed that Arvcf mediates nicotine-induced reward behavior by using conditioned place preference (CPP) model on Arvcf-knockout (Arvcf-KO) animal model. Then, we revealed that Arvcf was mainly expressed in VTA dopaminergic neurons whose expression could be upregulated by nicotine treatment. Subsequently, our SnRNA-seq analysis revealed that Arvcf was directly involved in dopamine biosynthesis in VTA dopaminergic neurons. Furthermore, we found that Arvcf-KO led to a significant reduction in both the dopamine synthesis and release in the nucleus accumbens (NAc) on nicotine stimulation. Specifically, we demonstrated that inhibition of Arvcf in VTA dopaminergic neurons decreased dopamine release within VTA-NAc circuit and suppressed nicotine reward-related behavior, while overexpression of Arvcf led to the opposite results. Taken together, these findings highlight the role of Arvcf in regulating dopamine signaling and reward learning, and its enhancement of dopamine release in the VTA-NAc circuit as a novel mechanism for nicotine reward.

Low-dose proton induced genetic alteration in cingulate cortex and declined its relevant cognitive function in behaviors

Environmental radiation poses health risks to the central nervous system (CNS) as well as the internal organs. While the technology for managing radiation has improved, the effects of low-dose radiation in the long term are still considered as a health-related risky factor. The clinical and space radiation studies suggested cognitive threat from proton, but the inconsistent behavioral responses to low-dose proton made their cognitive effects elusive. Here, we examined the low-dose proton-induced functional changes by measuring genetic and behavioral responses. Total 54 mice (C57BL/6, 7 weeks, males) were used for this study. The genetic effects were tested using the brain tissue (cingulate cortex, CC), one of core regions for cognition, and the behavioral responses were evaluated by open field (OFT) and radial maze tests (RMT). In 4 weeks after irradiation, all genes (HSPA, GFAP, MBP, NEFL, NEFM) showed peak inflammatory responses (p < 2.05×10-3), and these reactions were resolved in 3 months, returning to the initial level of foldchanges. The behavioral changes were identified between 4 weeks and 3 months, which was after the peak genetic inflammatory period. The moving distance and the speed were maintained up to 4 weeks, but both motional factors decreased with significance after 4 weeks (p < 0.126×10-3). Unlike the results in OFT, no parameters in RMT showed a significant difference among the groups. Considering the overall results, low-dose protons induced reversible genetic alteration in the central regions over time, and their delayed effects on cognitive behaviors were limited, with consequences varying depending on the functional types of cognition. Our current findings are expected to provide critical information for the development of substantive regulations for astronauts' health and clinical use of proton.

Subanesthetic propofol alleviates chronic stress-induced anxiety by enhancing VTADA neurons' activity

Anxiety, a common mental disorder, imposes significant clinical and economic burdens. Previous studies indicate that propofol has anxiolytic effects at anesthetic doses. However, the risks associated with general anesthesia limit its application in anxiety treatment. The feasibility of using subanesthetic doses of propofol to alleviate chronic stress-induced anxiety and the underlying neural mechanisms remain unknown. Here, we found that subanesthetic dose (20 mg/kg and 40 mg/kg) of propofol alleviated anxiety-like behaviors induced by chronic unpredictable mild stress (CUMS) in mice, and the anxiolytic effects were maintained for at least 6 h. In vivo calcium imaging study showed that propofol significantly enhanced Ca2+ signals in ventral tegmental area dopaminergic (VTADA) neurons. Whole-cell patch-clamp recordings confirmed that subanesthetic propofol increased the excitability of VTADA neurons while inhibiting VTA GABAergic (VTAGABA) neurons. Propofol suppressed spontaneous inhibitory postsynaptic currents (sIPSCs) in VTADA neurons, accompanied by a decline in the ability of GABAergic neurons to transmit inhibitory signals. These findings suggests that a subanesthetic dose of propofol enhances the excitability of VTADA neurons through disinhibition, demonstrating its potential for the treatment of CUMS-associated anxiety-like behaviors.

Pde4b-regulated cAMP signaling pathway in the AUDGABA-S1TrSst circuit underlies acute-stress-induced anxiety-like behavior

Acute-stress-induced anxiety helps animals avoid danger, but the neural and molecular mechanisms controlling this behavior remain largely elusive. Here, we find that acute physical stress activates many neurons in the primary somatosensory cortex, trunk region (S1Tr). Single-cell sequencing reveals that the S1Tr c-fos-positive neurons activated by acute stress are largely GABAergic somatostatin (Sst) neurons. These S1TrSst neurons desensitize during subsequent anxiety-like behavior tests. Inhibiting or inducing apoptosis of S1TrSst neurons mimics acute-stress effects and induces anxiety, while activating these neurons reduces acute-stress-induced anxiety. S1TrSst cells receive inputs from secondary auditory cortex, dorsal area (AUD) GABAergic neurons to modulate this anxiety. Spatial transcriptome sequencing and targeted Pde4b protein knockdown show that acute stress reduces Pde4b-regulated cAMP signaling in AUDGABA-S1TrSst projections, leading to decreased S1TrSst neuron activity in subsequent behavioral tests. Our study reports a neural and molecular mechanism for acute-stress-induced anxiety, providing a basis for treating anxiety disorders.

The biology of addiction

The tools of modern genetics and neurobiology have propelled a renaissance of research that has advanced our understanding of the pathophysiology of drug addiction. We know that an individual's risk for addiction is determined by interactions between genetics and environment and that only a minute fraction of chemical agents share the ability to act on this vulnerability to induce a state of addiction. Repeated exposure to these drugs causes addiction through repeated activation of dopaminergic transmission (and many other actions) in the brain, inducing changes at the molecular, cellular, and synaptic levels that, over time, rewire the circuitry throughout the limbic system. In this Review, I discuss how we are gaining a clearer picture of this drug-induced plasticity-some of which is shared by all addictive drugs, whereas other aspects are specific to certain drug classes-and of the ways in which these adaptations mediate the range of behavioral abnormalities that define the addicted state. Despite the challenges, there is reason for optimism in translating this rich biological understanding of addiction into improved treatments for the many individuals burdened by this illness around the world.

Hindbrain networks: Exploring the hidden anxiety circuits in rodents

Anxiety disorders are multifaceted conditions that engage numerous brain regions and circuits. While the hindbrain is pivotal in fundamental biological functions, its role in modulating emotions has been underappreciated. This review will uncover critical targets and circuits within the hindbrain that are essential for both anxiety and anxiolytic effects, expanding on research obtained through behavioral tests. The bidirectional neural pathways between the hindbrain and other brain regions, with a spotlight on vagal afferent signaling, provide a crucial framework for unraveling the neural mechanisms underlying anxiety. Exploring neural circuits within the hindbrain can help to unravel the neurobiological mechanisms of anxiety and elucidate differences in the expression of these circuits between genders, thereby providing valuable insights for the development of future anxiolytic drugs.

Cafeteria Diet Abstinence Induces Depressive Behavior and Disrupts Endocannabinoid Signaling in Dopaminergic Areas: A Preclinical Study

BACKGROUND

Alterations of dopamine (DA) transmission in the brain reward system can be associated with an addictive-like state defined as food addiction (FA), common in obese individuals. Subjects affected by FA experience negative feelings when abstinent from their preferred diet and may develop mood disorders, including depression, sustained by alterations in brain DA pathways.

OBJECTIVE

This study aims to investigate the impact of long-term abstinence from a palatable diet on depressive-like behavior in rats, exploring neurochemical alterations in monoamine and endocannabinoid signaling in DA-enriched brain regions, including ventral tegmental area, dorsolateral striatum, substantia nigra and medial prefrontal cortex.

METHODS

Rats underwent exposure and subsequent abstinence from a palatable cafeteria diet. During abstinence, animals were treated with fatty acid amide hydrolase (FAAH) inhibitor PF-3845 (10 mg/kg, intraperitoneal administration every other day). Lastly, animals were subjected to a forced swimming test, and their brains were dissected and processed for high-performance liquid chromatography measurement of monoamines and western blot analyses of markers of the endocannabinoid machinery.

RESULTS

After the withdrawal from the palatable diet, animals showed depressive-like behavior, coupled with significant variations in the concentration of brain monoamines and in the expression of endocannabinoid signalling machinery proteins in cited brain areas. Treatment with PF-3845 exerted an antidepressant- like effect and restored part of the alterations in monoaminergic and endocannabinoid systems.

CONCLUSION

Overall, our results suggest that abstinence from a cafeteria diet provokes emotional disturbances linked to neuroadaptive changes in monoamines and endocannabinoid signalling in brain areas partaking to DA transmission that could partially be restored by the enhancement of endocannabinoid signalling through FAAH inhibition.

Male and female behavioral variability and morphine response in C57BL/6J, DBA/2J, and their BXD progeny following chronic stress exposure

Drug addiction is a multifactorial syndrome in which genetic predispositions and exposure to environmental stressors constitute major risk factors for the early onset, escalation, and relapse of addictive behaviors. While it is well known that stress plays a key role in drug addiction, the genetic factors that make certain individuals particularly sensitive to stress and, thereby, more vulnerable to becoming addicted are unknown. In an effort to test a complex set of gene x environment interactions-specifically gene x chronic stress-here we leveraged a systems genetics resource: BXD recombinant inbred mice (BXD5, BXD8, BXD14, BXD22, BXD29, and BXD32) and their parental mouse lines, C57BL/6J and DBA/2J. Utilizing the chronic social defeat stress (CSDS) and chronic variable stress (CVS) paradigms, we first showed sexual dimorphism in social and exploratory behaviors between the mouse strains. Further, we observed an interaction between genetic background and vulnerability to prolonged exposure to non-social stressors. Finally, we found that DBA/2J and C57BL/6J mice pre-exposed to stress displayed differences in morphine sensitivity. Our results support the hypothesis that genetic variation influences chronic stress-induced behavioral outcomes such as social and approach-avoidance behaviors, reward responses, as well as morphine sensitivity, and is likely to modulate the development of drug addiction.

Secure attachment to caregiver prevents adult depressive symptoms in a sex-dependent manner: A translational study

Although clinically relevant, evidence for a protective effect of early secure attachment against the development of depressive symptoms in adulthood is still inconsistent. This study used a translational approach to overcome this limitation. The analysis of a non-clinical adult population revealed a moderating effect of secure attachment on depressive symptoms in women only. Thus, we tested the causal link between early attachment with caregiver and adult depressive-like phenotypes in a mouse model of early adversities that is especially effective in females. Repeated cross fostering (RCF) in the first postnatal days prevented the development of pups' secure attachment with the caregiver as tested in a rodent version of the "strange situation"-the standard human test-induced depressive-like behaviors and altered activity of the ventral tegmental area dopamine neurons in adulthood. Finally, a stable alternative caregiver during the RCF experience prevented all these effects, modeling human "earned attachment."

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

Some individuals are susceptible to 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, the LHb is active when susceptible mice are in proximity of the aggressor strain. During stress, activity is higher in susceptible mice during aggressor interactions, and activation biases mice toward susceptibility. This manipulation generates a persistent and widespread increase in the balance of subcortical vs. 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.

Neurokinin-1 receptors in the nucleus accumbens shell influence sensitivity to social defeat stress and stress-induced alcohol consumption in male mice

Chronic social defeat stress (SDS) is a widely employed preclinical model of depression involving repeated exposure to physical defeats using a resident-intruder model in male mice. Exposure to SDS induces depressive-like phenotypes including anhedonia, social withdrawal, and increased drug and alcohol consumption. Previously, we found that expression of the neurokinin-1 receptor (NK1R) is increased in the nucleus accumbens (NAC) of mice that are sensitive to this stressor and increase their alcohol intake. The NK1R is the endogenous receptor for the neuropeptide substance P (SP) and plays a prominent role in stress, anxiety, and addiction. In the present study, we assessed changes in NK1R protein levels in the NAC shell and implemented viral vector strategies to demonstrate a functional role of the NK1R in sensitivity to SDS. Specifically, we found that NK1R protein levels were increased in the NAC shell following SDS exposure. Next, we found that NK1R overexpression in the NAC shell increased the sensitivity to SDS and stress-induced alcohol consumption. Together, these experiments provide evidence for a role of the NK1R in the NAC shell in the sensitivity to SDS and the subsequent escalation in alcohol intake.

Associations between mesolimbic connectivity, and alcohol use from adolescence to adulthood

Dopaminergic projections from the ventral tegmental area (VTA) to limbic regions play a key role in the initiation and maintenance of substance use; however, the relationship between mesolimbic resting-state functional connectivity (RSFC) and alcohol use during development remains unclear. We examined the associations between alcohol use and VTA RSFC to subcortical structures in 796 participants (12-21 years old at baseline, 51 % female) across 9 waves of longitudinal data from the National Consortium on Alcohol and Neurodevelopment in Adolescence. Linear mixed effects models included interactions between age, sex, and alcohol use, and best fitting models were selected using log-likelihood ratio tests. Results demonstrated a positive association between alcohol use and VTA RSFC to the nucleus accumbens. Age was associated with VTA RSFC to the amygdala and hippocampus, and an age-by-alcohol use interaction on VTA-globus pallidus connectivity was driven by a positive association between alcohol and VTA-globus pallidus RSFC in adolescence, but not adulthood. On average, male participants exhibited greater VTA RSFC to the amygdala, nucleus accumbens, caudate, hippocampus, globus pallidus, and thalamus. Differences in VTA RSFC related to age, sex, and alcohol, may inform our understanding of neurobiological risk and resilience for alcohol use and other psychiatric disorders.

Neural Network Excitation/Inhibition: A Key to Empathy and Empathy Impairment

Empathy is an ability to fully understand and feel the mental states of others. We emphasize that empathy is elicited by the transmission of pain, fear, and sensory information. In clinical studies, impaired empathy has been observed in most psychiatric conditions. However, the precise impairment mechanism of the network systems on the pathogenesis of empathy impairment in psychiatric disorders is still unclear. Multiple lines of evidence suggest that disturbances in the excitatory/inhibitory balance in neurologic disorders are key to empathetic impairment in psychiatric disorders. Therefore, we here describe the roles played by the anterior cingulate cortex- and medial prefrontal cortex-dependent neural circuits and their impairments in psychiatric disorders, including anxiety, depression, and autism. In addition, we review recent studies on the role of microglia in neural network excitation/inhibition imbalance, which contributes to a better understanding of the neural network excitation/inhibition imbalance and may open up innovative psychiatric therapies.

Projections from subfornical organ to bed nucleus of the stria terminalis modulate inflammation-induced anxiety-like behaviors in mice

Peripheral inflammation is closely related to the pathogenesis of sickness behaviors and psychiatric disorders such as anxiety and depression. The circumventricular organs (CVOs) are important brain sites to perceive peripheral inflammatory signals, but few studies have reported their role in inflammation-induced anxiety or depression. Using a mouse model of lipopolysaccharide (LPS)-induced inflammation, we identified a previously unreported role of the subfornical organ (SFO), one of the CVOs, in combating inflammation-induced anxiety. LPS treatment induced anxiety-like and sickness behaviors in mice. Although both the SFO and the organum vasculosum of the lamina terminalis (a CVO) neurons were activated after LPS treatment, only manipulating SFO neurons modulated LPS-induced anxiety-like behaviors. Activating or inhibiting SFO neurons alleviated or aggravated LPS-induced anxiety-like behaviors. In addition, SFO exerted this effect through glutamatergic projections to the bed nucleus of the stria terminalis. Manipulating SFO neurons did not affect LPS-induced sickness behaviors. Thus, we uncovered an active role of SFO neurons in counteracting peripheral inflammation-induced anxiety.

Infralimbic-basolateral amygdala circuit associated with depression-like not anxiety-like behaviors induced by chronic neuropathic pain and the antidepressant effects of electroacupuncture

Chronic pain, such as neuropathic pain, can lead to anxiety, depression, and other negative emotions, thereby forming comorbidities and increasing the risk of chronic pain over time. Both the infralimbic amygdala (IL) and the basolateral amygdala (BLA) are significantly associated with negative emotions and pain, and they are known to have reciprocal connections. However, the role of IL-BLA circuit pathways in neuropathic pain-induced anxiety and depression remains unexplored. Electroacupuncture (EA) is frequently employed in the treatment of chronic pain and emotional disorders. However, The mechanism by which EA mediates its analgesic and emotion-alleviating effects via the IL-BLA circuit remains uncertain. Here, we used chemogenetic manipulation combined with behavioral tests to detect pain induced anxiety-like and depression-like behaviors. We observed that activation of the IL-BLA circuit by chemogenetic activation induced depression-like behavior of mice. Additionally, we discovered that chemogenetic activation of the IL-BLA circuit successfully prevented the beneficial effects of EA on depression-like behavior brought on by chronic pain in mice with spared nerve injury (SNI). We discovered that SNI-induced depression-like behavior could be mitigated by inhibiting the circuit, and EA had a comparable depressive-relieving effect. Furthermore, the IL-BLA circuit's activation or inhibition had no effect on the anxiety-like feelings brought on by SNI. Overall, our findings identify a specific neural circuit that selectively regulates pain-induced depression-like emotions, without affecting pain-induced anxiety-like emotions. This discovery offers a precise target for future treatments of comorbid pain and depression and provides a plausible explanation for the efficacy of EA in treating depression-like emotions associated with chronic pain.

Effects of inulin-type oligosaccharides (JSO) from Cichorium intybus L. on behavioral deficits induced by chronic restraint stress in mice and associated molecular alterations

Depression and anxiety are serious psychiatric disorders with significant physical and mental health impacts, necessitating the development of safe and effective treatments. This study aimed to evaluate the efficacy of Jiangshi oligosaccharide (JSO), a type of inulin-based oligosaccharide, in alleviating anxiety and depression and to investigate the underlying molecular mechanisms. Using a mouse model of chronic restraint stress (CRS), JSO was administered orally at doses of 50, 100, and 200 mg/kg for 21 days. Behavioral tests, including the novelty-suppressed feeding test (NSFT), open field test (OFT), elevated plus maze test (EPMT), tail suspension test (TST), and forced swimming test (FST), demonstrated that JSO significantly improved anxiety- and depressive-like behaviors (P< 0.05). Notably, JSO reduced feeding latency in the NSFT, increased time spent in the center in the OFT, enhanced time and entries into open arms in the EPMT, and decreased immobility time in the TST and FST (P< 0.01). Histological and molecular analyses revealed that JSO treatment attenuated neuronal loss in the hippocampus (Hip) and medial prefrontal cortex (mPFC) and reduced the expression of inflammatory markers such as Iba-1 and GFAP in these regions. JSO significantly downregulated the mRNA and protein expression of pro-inflammatory factors (IL-1β, TNF-α, IL-6) while increasing anti-inflammatory markers (IL-10, TGF-β) (P< 0.05). Furthermore, JSO inhibited the c-GAS-STING-NLRP3 axis and apoptosis-related proteins (Bax/Bcl-2, Caspase-3/8/9) while promoting the expression of brain-derived neurotrophic factor (BDNF), PSD-95, and synaptophysin (SYP), indicating improved neuronal survival and synaptic plasticity (P< 0.01). These findings suggest that JSO exerts potent anti-anxiety and antidepressant effects by modulating neuroinflammation, synaptic function, and neuronal apoptosis in the Hip and mPFC of CRS mice. This study highlighted JSO as a potential therapeutic agent for stress-induced anxiety and depression.

Transient nicotine exposure in early adolescent male mice freezes their dopamine circuits in an immature state

How nicotine acts on developing neurocircuitry in adolescence to promote later addiction vulnerability remains largely unknown, but may hold the key for informing more effective intervention efforts. We found transient nicotine exposure in early adolescent (PND 21-28) male mice was sufficient to produce a marked vulnerability to nicotine in adulthood (PND 60 + ), associated with disrupted functional connectivity in dopaminergic circuits. These mice showed persistent adolescent-like behavioral and physiological responses to nicotine, suggesting that nicotine exposure in adolescence prolongs an immature, imbalanced state in the function of these circuits. Chemogenetically resetting the balance between the underlying dopamine circuits unmasked the mature behavioral response to acute nicotine in adolescent-exposed mice. Together, our results suggest that the perseverance of a developmental imbalance between dopamine pathways may alter vulnerability profiles for later dopamine-dependent psychopathologies.

Basolateral amygdala parvalbumin and cholecystokinin-expressing GABAergic neurons modulate depressive and anxiety-like behaviors

The basolateral amygdala (BLA) is increasingly recognized as a key regulator of depression and anxiety-like behaviors. However, the specific contribution of individual BLA neurons to these behaviors remains poorly understood. Building on our previous study, which demonstrated increased activity in glutamatergic BLA neurons in response to aversive stimuli and that enhancing inhibition in the BLA can alleviate depressive-like behaviors, we investigated the role of individual BLA GABAergic neurons (BLAGABA) in depressive and anxiety-like phenotypes. To address this question, we employed a comprehensive array of techniques, including c-fos staining, fiber photometry recording, optogenetic and chemogenetic manipulation, and behavior analysis. Our findings indicate that BLAGABA neurons show decreased activity during tail suspension and after chronic social defeat stress (CSDS) during social interaction. High-frequency activation of BLAGABA neurons attenuated depressive and anxiety-like behaviors, while low-frequency activation had no effect. Fiber photometry recordings revealed increased activity in BLA GABAergic neurons expressing somatostatin (SST), parvalbumin (PV), and cholecystokinin (CCK) during footshock aversive stimuli. Moreover, we found increased activity in PV and SST neurons and decreased activity in CCK-GABA neurons in the BLA during tail suspension stress. However, after CSDS, BLAPV neurons displayed decreased activity, while SST and CCK neurons showed no changes during the social interaction test. Behavioral analysis demonstrated that chemogenetic inhibition of PV and CCK-GABA neurons induced depressive and anxiety-like behaviors. whereas SST neuron inhibition had no effect. Conversely, chemogenetic activation of BLAPV neurons alleviated depressive behaviors, and activation of BLACCK-GABA neurons alleviated at least partly both depressive and anxiety-like behaviors. This study provides compelling evidence that BLAPV neurons play a critical role in regulating depressive-like behaviors, and that BLACCK-GABA neurons are involved, at least in part, in modulating both depressive-like and anxiety-like behaviors in mice.

Nighttime-specific differential gene expression in suprachiasmatic nucleus and habenula is associated with resilience to chronic social stress

The molecular mechanisms that link stress and biological rhythms still remain unclear. The habenula (Hb) is a key brain region involved in regulating diverse types of emotion-related behaviours while the suprachiasmatic nucleus (SCN) is the body's central clock. To investigate the effects of chronic social stress on transcription patterns, we performed gene expression analysis in the Hb and SCN of stress-naïve and stress-exposed mice. Our analysis revealed a large number of differentially expressed genes and enrichment of synaptic and cell signalling pathways between resilient and stress-naïve mice at zeitgeber 16 (ZT16) in both the Hb and SCN. This transcriptomic signature was nighttime-specific and observed only in stress-resilient mice. In contrast, there were relatively few differences between the stress-susceptible and stress-naïve groups across time points. Our results reinforce the functional link between circadian gene expression patterns and differential responses to stress, thereby highlighting the importance of temporal expression patterns in homoeostatic stress responses.

Neuronal HIPK2-HDAC3 axis regulates mitochondrial fragmentation to participate in stroke injury and post-stroke anxiety like behavior

Post-stroke anxiety (PSA) seriously affects the prognosis of patients, which is an urgent clinical problem to be addressed. However, the pathological mechanism of PSA is largely unclear. Here, we found that neuronal HIPK2 expression was upregulated in the ischemic lesion after stroke. The upregulation of HIPK2 promotes Drp1 oligomerization through the HDAC3-dependent pathway, leading to excessive mitochondrial damage. This subsequently triggers the release of cellular cytokines such as IL-18 from neurons under ischemic stress. Microglia are capable of responding to IL-18, which promotes their activation and enhances their phagocytosis, ultimately resulting in the loss of synapses and neurons, thereby exacerbating the pathological progression of PSA. HIPK2 knockdown or inhibition suppresses excessive pruning of neuronal synapses by activated microglia in the contralateral vCA1 region to compromise inactivated anxiolytic pBLA-vCA1Calb1+ circuit, relieving anxiety-like behavior after stroke. Furthermore, we discovered that early remimazolam administration can remodel HIPK2-HDAC3 axis, ameliorating the progression of PSA. In conclusion, our study revealed that the neuronal HIPK2-HDAC3 axis in the ischemic focus regulates mitochondrial fragmentation to balance inflammation stress reservoir to participate in anxiety susceptibility after stroke.

Isoflurane anesthesia decreases excitability of inhibitory neurons in the basolateral amygdala leading to anxiety‑like behavior in aged mice

Anxiety after surgery can be a major factor leading to postoperative cognitive dysfunction, particularly in elderly patients. The role of inhibitory neurons in the basolateral amygdala (BLA) in anxiety-like behaviors in aged mice following isoflurane anesthesia remains unclear. Therefore, the present study aimed to investigate the role of inhibitory neurons in isoflurane-treated mice. A total of 30 C57BL/6 mice (age, 13 months) were allocated into the control and isoflurane anesthesia groups (15 mice/group) and were then subjected to several neurological assessments. Behavioral testing using an elevated plus maze test showed that aged mice in the isoflurane anesthesia group displayed significant anxiety-like behavior, since they spent more time in the closed arm, exhibited more wall climbing behavior and covered more distance. In addition, whole-cell patch-clamp recording revealed that the excitability of the BLA excitatory neurons was notably increased following mice anesthesia with isoflurane, while that of inhibitory neurons was markedly reduced. Following mice treatment with diazepam, the excitability of the BLA inhibitory neurons was notably increased compared with that of the excitatory neurons, which was significantly attenuated. Overall, the results of the current study indicated that anxiety-like behavior could occur in aged mice after isoflurane anesthesia, which could be caused by a reduced excitability of the inhibitory neurons in the BLA area. This process could enhance excitatory neuronal activity in aged mice, thus ultimately promoting the onset of anxiety-like behaviors.

Distinct Neuromodulatory Effects of Endogenous Orexin and Dynorphin Corelease on Projection-Defined Ventral Tegmental Dopamine Neurons

Dopamine (DA) neurons in the ventral tegmental area (VTA) respond to motivationally relevant cues, and circuit-specific signaling drives different aspects of motivated behavior. Orexin (ox; also known as hypocretin) and dynorphin (dyn) are coexpressed lateral hypothalamic (LH) neuropeptides that project to the VTA. These peptides have opposing effects on the firing activity of VTADA neurons via orexin 1 (Ox1R) or kappa opioid (KOR) receptors. Given that Ox1R activation increases VTADA firing, and KOR decreases firing, it is unclear how the coreleased peptides contribute to the net activity of DA neurons. We tested if optical stimulation of LHox/dyn neuromodulates VTADA neuronal activity via peptide release and if the effects of optically driven LHox/dyn release segregate based on VTADA projection targets including the basolateral amygdala (BLA) or the lateral or medial shell of the nucleus accumbens (lAcbSh, mAchSh). Using a combination of circuit tracing, optogenetics, and patch-clamp electrophysiology in male and female orexincre mice, we showed a diverse response of LHox/dyn optical stimulation on VTADA neuronal firing, which is not mediated by fast transmitter release and is blocked by antagonists to KOR and Ox1R signaling. Additionally, where optical stimulation of LHox/dyn inputs in the VTA inhibited firing of the majority of BLA-projecting VTADA neurons, optical stimulation of LHox/dyn inputs in the VTA bidirectionally affects firing of either lAcbSh- or mAchSh-projecting VTADA neurons. These findings indicate that LHox/dyn corelease may influence the output of the VTA by balancing ensembles of neurons within each population which contribute to different aspects of reward seeking.

Ketamine ameliorates post-traumatic social avoidance by erasing the traumatic memory encoded in VTA-innervated BLA engram cells

Erasing traumatic memory during memory reconsolidation is a promising retrieval-extinction strategy for post-traumatic stress disorder (PTSD). Here, we developed an acute social defeat stress (SDS) mouse model with short-term and re-exposure-evoked long-term social avoidance. SDS-associated traumatic memories were identified to be stored in basolateral amygdala (BLA) engram cells. A single intraperitoneal administration of subanesthetic-dose ketamine within, but not beyond, the re-exposure time window significantly alleviates SDS-induced social avoidance, which reduces the activity and quantity of reactivated BLA engram cells. Furthermore, activation or inhibition of dopaminergic projections from the ventral tegmental area to the BLA effectively mimics or blocks the therapeutic effect of re-exposure with ketamine and is dopamine D2 receptor dependent. Single-cell RNA sequencing reveals that re-exposure with ketamine triggered significant changes in memory-related pathways in the BLA. Together, our research advances the understanding of how ketamine mitigates PTSD symptoms and offers promising avenues for developing more effective treatments for trauma-related disorders.

Parkinson's LRRK2-G2019S risk gene mutation drives sex-specific behavioral and cellular adaptations to chronic variable stress

Anxiety is a psychiatric non-motor symptom of Parkinson's that can appear in the prodromal period, prior to significant loss of midbrain dopamine neurons and motor symptoms. Parkinson's-related anxiety affects females more than males, despite the greater prevalence of Parkinson's in males. How stress, anxiety and Parkinson's are related and the basis for a sex-specific impact of stress in Parkinson's are not clear. We addressed this using young adult male and female mice carrying a G2019S knockin mutation of leucine-rich repeat kinase 2 (Lrrk2 G2019S) and Lrrk2 WT control mice. In humans, LRRK2 G2019S significantly elevates the risk of late-onset Parkinson's. To assess within-sex differences between Lrrk2 G2019S and control mice in stress-induced anxiety-like behaviors in young adulthood, we used a within-subject design whereby Lrrk2 G2019S and Lrrk2 WT control mice underwent tests of anxiety-like behaviors before (baseline) and following a 28 day (d) variable stress paradigm. There were no differences in behavioral measures between genotypes in males or females at baseline, indicating that the mutation alone does not produce anxiety-like responses. Following chronic stress, male Lrrk2 G2019S mice were affected similarly to male wildtypes except for novelty-suppressed feeding, where stress had no impact on Lrrk2 G2019S mice while significantly increasing latency to feed in Lrrk2 WT control mice. Female Lrrk2 G2019S mice were impacted by chronic stress similarly to wildtype females across all behavioral measures. Subsequent post-stress analyses compared cFos immunolabeling-based cellular activity patterns across several stress-relevant brain regions. The density of cFos-activated neurons across brain regions in both male and female Lrrk2 G2019S mice was generally lower compared to stressed Lrrk2 WT mice, except for the nucleus accumbens of male Lrrk2 G2019S mice, where cFos-labeled cell density was significantly higher than all other groups. Together, these data suggest that the Lrrk2 G2019S mutation differentially impacts anxiety-like behavioral responses to chronic stress in males and females that may reflect sex-specific adaptations observed in circuit activation patterns in some, but not all stress-related brain regions.

Establishing connectivity through microdissections of midbrain stimulation-related neural circuits

Comprehensive understanding of the neural circuits involving the ventral tegmental area is essential for elucidating the anatomofunctional mechanisms governing human behaviour, in addition to the therapeutic and adverse effects of deep brain stimulation for neuropsychiatric diseases. Although the ventral tegmental area has been targeted successfully with deep brain stimulation for different neuropsychiatric diseases, the axonal connectivity of the region is not fully understood. Here, using fibre microdissections in human cadaveric hemispheres, population-based high-definition fibre tractography and previously reported deep brain stimulation hotspots, we find that the ventral tegmental area participates in an intricate network involving the serotonergic pontine nuclei, basal ganglia, limbic system, basal forebrain and prefrontal cortex, which is implicated in the treatment of obsessive-compulsive disorder, major depressive disorder, Alzheimer's disease, cluster headaches and aggressive behaviours.

The rostromedial tegmental nucleus gates fat overconsumption through ventral tegmental area output in male rats

Excessive consumption of palatable foods that are rich in fats and sugars has contributed to the increasing prevalence of obesity worldwide. Similar to addictive drugs, such foods activate the brain's reward circuit, involving mesolimbic dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and the prefrontal cortex. Neuroadaptations occurring in this circuit are hypothesized to contribute to uncontrolled consumption of such foods, a common feature of most of eating disorders and obesity. The rostromedial tegmental nucleus (RMTg), also named tail of the VTA (tVTA), is an inhibitory structure projecting to the VTA and the lateral hypothalamus (LH), two key brain regions in food intake regulation. Prior research has demonstrated that the RMTg responds to addictive drugs and influences their impact on mesolimbic activity and reward-related behaviors. However, the role of the RMTg in food intake regulation remains largely unexplored. The present study aimed to investigate the role of the RMTg and its projections to the VTA and the LH in regulating food intake in rats. To do so, we examined eating patterns of rats with either bilateral excitotoxic lesions of the RMTg or specific lesions of RMTg-VTA and RMTg-LH pathways. Rats were exposed to a 6-week 'free choice high-fat and high-sugar' diet, followed by a 4-week palatable food forced abstinence and a 24 h re-access period. Our results indicate that an RMTg-VTA pathway lesion increases fat consumption following 6 weeks of diet and at time of re-access. The RMTg-LH pathway lesion produces a milder effect with a decrease in global calorie intake. These findings suggest that the RMTg influences palatable food consumption and relapse through its projections to the VTA.

CRISPR/Cas9-mediated neuronal deletion of 5-lipoxygenase alleviates deficits in mouse models of epilepsy

INTRODUCTION

Our previous work reveals a critical role of activation of neuronal Alox5 in exacerbating brain injury post seizures. However, whether neuronal Alox5 impacts the pathological process of epilepsy remains unknown.

OBJECTIVES

To prove the feasibility of neuron-specific deletion of Alox5 via CRISPR-Cas9 in the blockade of seizure onset and epileptic progression.

METHODS

Here, we employed a Clustered regularly interspaced short-palindromic repeat-associated proteins 9 system (CRISPR/Cas9) system delivered by adeno-associated virus (AAV) to specifically delete neuronal Alox5 gene in the hippocampus to explore its therapeutic potential in various epilepsy mouse models and possible mechanisms.

RESULTS

Neuronal depletion of Alox5 was successfully achieved in the brain. AAV delivery of single guide RNA of Alox5 in hippocampus resulted in reducing seizure severity, delaying epileptic progression and improving epilepsy-associated neuropsychiatric comorbidities especially anxiety, cognitive deficit and autistic-like behaviors in pilocarpine- and kainic acid-induced temporal lobe epilepsy (TLE) models. In addition, neuronal Alox5 deletion also reversed neuron loss, neurodegeneration, astrogliosis and mossy fiber sprouting in TLE model. Moreover, a battery of tests including analysis of routine blood test, hepatic function, renal function, routine urine test and inflammatory factors demonstrated no noticeable toxic effect, suggesting that Alox5 deletion possesses the satisfactory biosafety. Mechanistically, the anti-epileptic effect of Alox5 deletion might be associated with reduction of glutamate level to restore excitatory/inhibitory balance by reducing CAMKII-mediated phosphorylation of Syn ISer603.

CONCLUSION

Our findings showed the translational potential of AAV-mediated delivery of CRISPR-Cas9 system including neuronal Alox5 gene for an alternative promising therapeutic approach to treat epilepsy.

A population of Insula neurons encodes for social preference only after acute social isolation in mice

The Insula functions as a multisensory relay involved in socio-emotional processing with projections to sensory, cognitive, emotional, and motivational regions. Notably, the interhemispheric projection from the Insula to the contralateral Insula is a robust yet underexplored connection. Using viral-based tracing neuroanatomy, ex vivo and in vivo electrophysiology, in vivo fiber photometry along with targeted circuit manipulation, we elucidated the nature and role of InsulaIns communication in social and anxiety processing in mice. In this study, we 1) characterized the anatomical and molecular profile of the InsulaIns neurons, 2) demonstrated that stimulation of this neuronal subpopulation induces excitation in the Insula interhemispheric circuit, 3) revealed that InsulaIns neurons are essential for social discrimination after 24 h of isolation in male mice. In conclusion, our findings highlight InsulaIns neurons as a distinct class of neurons within the insula and offer new insights into the neuronal mechanisms underlying social behavior.

Dimethyl fumarate ameliorates chronic stress-induced anxiety-like behaviors by decreasing neuroinflammation and neuronal activity in the amygdala

BACKGROUND

Chronic stress-induced neuroinflammation plays a pivotal role in the development and exacerbation of mental disorders, such as anxiety and depression. Dimethyl Fumarate (DMF), an effective therapeutic agent approved for the treatment of multiple sclerosis, has been widely reported to display anti-inflammatory and anti-oxidative effects. However, the impact of DMF on chronic stress-induced anxiety disorders and the exact underlying mechanisms remain largely unknown.

METHODS

We established a mouse model of chronic social defeat stress (CSDS). DMF was administered orally 1 h before daily stress session for 10 days in CSDS + DMF group. qRT-PCR and western blotting were used to analyze mRNA and protein expression of NLRP3, Caspase-1 and IL-1β. Immunofluorescence staining was carried out to detect the expression of Iba 1 and c-fos positive cells as well as morphological change of Iba 1+ microglia. Whole-cell patch-clamp recording was applied to evaluate synaptic transmission and intrinsic excitability of neurons.

RESULTS

DMF treatment significantly alleviated CSDS-induced anxiety-like behaviors in mice. Mechanistically, DMF treatment prevented CSDS-induced neuroinflammation by inhibiting the activation of microglia and NLRP3/Caspase-1/IL-1β signaling pathway in basolateral amygdala (BLA), a brain region important for emotional processing. Furthermore, DMF treatment effectively reversed the CSDS-caused disruption of excitatory and inhibitory synaptic transmission balance, as well as the increased intrinsic excitability of BLA neurons.

CONCLUSIONS

Our findings provide new evidence that DMF may exert anxiolytic effect by preventing CSDS-induced activation of NLRP3/Caspase-1/IL-1β signaling pathway and alleviating hyperactivity of BLA neurons.

BLA-involved circuits in neuropsychiatric disorders

The basolateral amygdala (BLA) is the subregion of the amygdala located in the medial of the temporal lobe, which is connected with a wide range of brain regions to achieve diverse functions. Recently, an increasing number of studies have focused on the participation of the BLA in many neuropsychiatric disorders from the neural circuit perspective, aided by the rapid development of viral tracing methods and increasingly specific neural modulation technologies. However, how to translate this circuit-level preclinical intervention into clinical treatment using noninvasive or minor invasive manipulations to benefit patients struggling with neuropsychiatric disorders is still an inevitable question to be considered. In this review, we summarized the role of BLA-involved circuits in neuropsychiatric disorders including Alzheimer's disease, perioperative neurocognitive disorders, schizophrenia, anxiety disorders, depressive disorders, posttraumatic stress disorders, autism spectrum disorders, and pain-associative affective states and cognitive dysfunctions. Additionally, we provide insights into future directions and challenges for clinical translation.

Stress-induced anxiety-related behavior in mice is driven by enhanced excitability of ventral tegmental area GABA neurons

Introduction

Stress and trauma are significant risk factors for many neuropsychiatric disorders and diseases, including anxiety disorders. Stress-induced anxiety symptoms have been attributed to enhanced excitability in circuits controlling fear, anxiety, and aversion. A growing body of evidence has implicated GABAergic neurons of the ventral tegmental area (VTA) in aversion processing and affective behavior.

Methods

We used an unpredictable footshock (uFS) model, together with electrophysiological and behavioral approaches, to investigate the role of VTA GABA neurons in anxiety-related behavior in mice.

Results

One day after a single uFS session, C57BL/6J mice exhibited elevated anxiety-related behavior and VTA GABA neuron excitability. The enhanced excitability of VTA GABA neurons was correlated with increased glutamatergic input and a reduction in postsynaptic signaling mediated via GABAA and GABAB receptors. Chemogenetic activation of VTA GABA neurons was sufficient to increase anxiety-related behavior in stress-naïve mice. In addition, chemogenetic inhibition of VTA GABA neurons suppressed anxiety-related behavior in mice exposed to uFS.

Discussion

These data show that VTA GABA neurons are an early substrate for stress-induced anxiety-related behavior in mice and suggest that approaches mitigating enhanced excitability of VTA GABA neurons may hold promise for the treatment of anxiety provoked by stress and trauma.

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.

Intermittent hypoxia exacerbates anxiety in high-fat diet-induced diabetic mice by inhibiting TREM2-regulated IFNAR1 signaling

BACKGROUND

Type 2 diabetes mellitus (T2DM) and obstructive sleep apnea (OSA) are mutual risk factors, with both conditions inducing cognitive impairment and anxiety. However, whether OSA exacerbates cognitive impairment and anxiety in patients with T2DM remains unclear. Moreover, TREM2 upregulation has been suggested to play a protective role in attenuating microglia activation and improving synaptic function in T2DM mice. The aim of this study was to explore the regulatory mechanisms of TREM2 and the cognitive and anxiety-like behavioral changes in mice with OSA combined with T2DM.

METHODS

A T2DM with OSA model was developed by treating mice with a 60% kcal high-fat diet (HFD) combined with intermittent hypoxia (IH). Spatial learning memory capacity and anxiety in mice were investigated. Neuronal damage in the brain was determined by the quantity of synapses density, the number and morphology of brain microglia, and pro-inflammatory factors. For mechanism exploration, an in vitro model of T2DM combined with OSA was generated by co-treating microglia with high glucose (HG) and IH. Regulation of TREM2 on IFNAR1-STAT1 pathway was determined by RNA sequencing and qRT-PCR.

RESULTS

Our results showed that HFD mice exhibited significant cognitive dysfunction and anxiety-like behavior, accompanied by significant synaptic loss. Furthermore, significant activation of brain microglia and enhanced microglial phagocytosis of synapses were observed. Moreover, IH was found to significantly aggravate anxiety in the HFD mice. The mechanism of HG treatment may potentially involve the promotion of TREM2 upregulation, which in turn attenuates the proinflammatory microglia by inhibiting the IFNAR1-STAT1 pathway. Conversely, a significant reduction in TREM2 in IH-co-treated HFD mice and HG-treated microglia resulted in the further activation of the IFNAR1-STAT1 pathway and consequently increased proinflammatory microglial activation.

CONCLUSIONS

HFD upregulated the IFNAR1-STAT1 pathway and induced proinflammatory microglia, leading to synaptic damage and causing anxiety and cognitive deficits. The upregulated TREM2 inT2DM mice brain exerted a negative regulation of the IFNAR1-STAT1 pathway. Mice with T2DM combined with OSA exacerbated anxiety via the downregulation of TREM2, causing heightened IFNAR1-STAT1 pathway activation and consequently increasing proinflammatory microglia.

Mediodorsal thalamus projection to medial prefrontal cortical mediates social defeat stress-induced depression-like behaviors

Clinical studies have shown that the mediodorsal thalamus (MD) may play an important role in the development of depression. However, the molecular and circuit mechanisms by which the mediodorsal thalamus (MD) participates in the pathological processes of depression remain unclear. Here, we show that in male chronic social defeat stress (CSDS) mice, the calcium signaling activity of glutamatergic neurons in MD is reduced. By combining conventional neurotracer and transneuronal virus tracing techniques, we identify a synaptic circuit connecting MD and medial prefrontal cortex (mPFC) in the mouse. Brain slice electrophysiology and fiber optic recordings reveal that the reduced activity of MD glutamatergic neurons leads to an excitatory-inhibitory imbalance of pyramidal neurons in mPFC. Furthermore, activation of MD glutamatergic neurons restores the electrophysiological properties abnormal in mPFC. Optogenetic activation of the MD-mPFC circuit ameliorates anxiety and depression-like behaviors in CSDS mice. Taken together, these data support the critical role of MD-mPFC circuit on CSDS-induced depression-like behavior and provide a potential mechanistic explanation for depression.

A widespread electrical brain network encodes anxiety in health and depressive states

In rodents, anxiety is charactered by heightened vigilance during low-threat and uncertain situations. Though activity in the frontal cortex and limbic system are fundamental to supporting this internal state, the underlying network architecture that integrates activity across brain regions to encode anxiety across animals and paradigms remains unclear. Here, we utilize parallel electrical recordings in freely behaving mice, translational paradigms known to induce anxiety, and machine learning to discover a multi-region network that encodes the anxious brain-state. The network is composed of circuits widely implicated in anxiety behavior, it generalizes across many behavioral contexts that induce anxiety, and it fails to encode multiple behavioral contexts that do not. Strikingly, the activity of this network is also principally altered in two mouse models of depression. Thus, we establish a network-level process whereby the brain encodes anxiety in health and disease.

Neurobiological basis of stress resilience

A majority of humans faced with severe stress maintain normal physiological and behavioral function, a process referred to as resilience. Such stress resilience has been modeled in laboratory animals and, over the past 15 years, has transformed our understanding of stress responses and how to approach the treatment of human stress disorders such as depression, post-traumatic stress disorder (PTSD), and anxiety disorders. Work in rodents has demonstrated that resilience to chronic stress is an active process that involves much more than simply avoiding the deleterious effects of the stress. Rather, resilience is mediated largely by the induction of adaptations that are associated uniquely with resilience. Such mechanisms of natural resilience in rodents are being characterized at the molecular, cellular, and circuit levels, with an increasing number being validated in human investigations. Such discoveries raise the novel possibility that treatments for human stress disorders, in addition to being geared toward reversing the damaging effects of stress, can also be based on inducing mechanisms of natural resilience in individuals who are inherently more susceptible. This review provides a progress report on this evolving field.

Mesolimbic Neural Response Dynamics Predict Future Individual Alcohol Drinking in Mice

BACKGROUND

Individual variability in response to rewarding stimuli is a striking but understudied phenomenon. The mesolimbic dopamine system is critical in encoding the reinforcing properties of both natural reward and alcohol; however, how innate or baseline differences in the response dynamics of this circuit define individual behavior and shape future vulnerability to alcohol remain unknown.

METHODS

Using naturalistic behavioral assays, a voluntary alcohol drinking paradigm, in vivo fiber photometry, in vivo electrophysiology, and chemogenetics, we investigated how differences in mesolimbic neural circuit activity contribute to the individual variability seen in reward processing and, by proxy, alcohol drinking.

RESULTS

We first characterized heterogeneous behavioral and neural responses to natural reward and defined how these baseline responses predicted future individual alcohol-drinking phenotypes in male mice. We then determined spontaneous ventral tegmental area dopamine neuron firing profiles associated with responses to natural reward that predicted alcohol drinking. Using a dual chemogenetic approach, we mimicked specific mesolimbic dopamine neuron firing activity before or during voluntary alcohol drinking to link unique neurophysiological profiles to individual phenotype. We show that hyperdopaminergic individuals exhibit a lower neuronal response to both natural reward and alcohol that predicts lower levels of alcohol consumption in the future.

CONCLUSIONS

These findings reveal unique, circuit-specific neural signatures that predict future individual vulnerability or resistance to alcohol and expand the current knowledge base on how some individuals are able to titrate their alcohol consumption whereas others go on to engage in unhealthy alcohol-drinking behaviors.

The avBNSTGABA-VTA and avBNSTGABA-DRN pathways are respectively involved in the regulation of anxiety-like behaviors in parkinsonian rats

The anteroventral bed nucleus of stria terminalis (avBNST) is a key brain region which involves negative emotional states, such as anxiety. The most neurons in the avBNST are GABAergic, and it sends GABAergic projections to the ventral tegmental area (VTA) and the dorsal raphe nucleus (DRN), respectively. The VTA and DRN contain dopaminergic and serotonergic cell groups in the midbrain which regulate anxiety-like behaviors. However, it is unclear the role of GABAergic projections from the avBNST to the VTA and the DRN in the regulation of anxiety-like behaviors, particularly in Parkinson's disease (PD)-related anxiety. In the present study, unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra pars compacta in rats induced anxiety-like behaviors, and decreased level of dopamine (DA) in the basolateral amygdala (BLA). Chemogenetic activation of avBNSTGABA-VTA or avBNSTGABA-DRN pathway induced anxiety-like behaviors and decreased DA or 5-HT release in the BLA in sham and 6-OHDA rats, while inhibition of avBNSTGABA-VTA or avBNSTGABA-DRN pathway produced anxiolytic-like effects and increased level of DA or 5-HT in the BLA. These findings suggest that avBNST inhibitory projections directly regulate dopaminergic neurons in the VTA and serotonergic neurons in the DRN, and the avBNSTGABA-VTA and avBNSTGABA-DRN pathways respectively exert impacts on PD-related anxiety-like behaviors.

Selective disruption of mTORC1 and mTORC2 in VTA astrocytes induces depression and anxiety-like behaviors in mice

Dysfunction of the mechanistic target of rapamycin (mTOR) signaling pathway is implicated in neuropsychiatric disorders including depression and anxiety. Most studies have been focusing on neurons, and the function of mTOR signaling pathway in astrocytes is less investigated. mTOR forms two distinct complexes, mTORC1 and mTORC2, with key scaffolding protein Raptor and Rictor, respectively. The ventral tegmental area (VTA), a vital component of the brain reward system, is enrolled in regulating both depression and anxiety. In the present study, we aimed to examine the regulation effect of VTA astrocytic mTOR signaling pathway on depression and anxiety. We specifically deleted Raptor or Rictor in VTA astrocytes in mice and performed a series of behavioral tests for depression and anxiety. Deletion of Raptor and Rictor both decreased the immobility time in the tail suspension test and the latency to eat in the novelty suppressed feeding test, and increased the horizontal activity and the movement time in locomotor activity. Deletion of Rictor decreased the number of total arm entries in the elevated plus-maze test and the vertical activity in locomotor activity. These data suggest that VTA astrocytic mTORC1 plays a role in regulating depression-related behaviors and mTORC2 is involved in both depression and anxiety-related behaviors. Our results indicate that VTA astrocytic mTOR signaling pathway might be new targets for the treatment of psychiatric disorders.