Anxiety is a common non-motor symptom of Parkinson's disease (PD), but its neurobiological mechanism is obscure. 5-hydroxytryptamine7 (5-HT7) receptor is associated with anxiety and is widely distributed in brain regions related to emotion regulation, including anterior part of basolateral amygdaloid nucleus (BLA), and monosynaptic glutamatergic BLA to ventral hippocampus (vHPC) (BLAGlu-vHPC) pathway modulates anxiety-related behaviors. Measurable pathological and pathophysiological changes within the amygdala and hippocampus have also been reported in PD patients and parkinsonian animals. Thus, we hypothesized that BLA 5-HT7 receptors might regulate PD-related anxiety through BLAGlu-vHPC pathway. In this study, we found that down-regulation of BLA 5-HT7 receptors by RNA interference produced anxiolytic effects in sham and 6-hydroxydopamine-lesioned rats. And intra-BLA injection of 5-HT7 receptor agonist AS19 and antagonist SB269970 induced anxiogenic and anxiolytic responses in the two groups of rats. Further, intra-BLA injection of AS19 and SB269970 increased and decreased the mean firing rate of BLA glutamatergic neurons and vHPC extracellular glutamate levels in sham and the lesioned rats, respectively. Compared to sham rats, the effects of AS19 and SB269970 on the anxiety-related behaviors, firing activity and transmitter levels were decreased in the lesioned rats, which are associated with decreased expression of 5-HT7 receptors on BLAGlu-vHPC pathway after substantia nigra pars compacta lesion. Collectively, these results suggest that activation and blockade of 5-HT7 receptors on the BLAGlu-vHPC pathway are involved in the regulation of PD-related anxiety, and dopaminergic lesion decreases the expression of 5-HT7 receptors on this neural pathway.

JOURNAL/nrgr/04.03/01300535-202506000-00024/figure1/v/2024-08-05T133530Z/r/image-tiff The conventional perception of astrocytes as mere supportive cells within the brain has recently been called into question by empirical evidence, which has revealed their active involvement in regulating brain function and encoding behaviors associated with emotions. Specifically, astrocytes in the basolateral amygdala have been found to play a role in the modulation of anxiety-like behaviors triggered by chronic stress. Nevertheless, the precise molecular mechanisms by which basolateral amygdala astrocytes regulate chronic stress-induced anxiety-like behaviors remain to be fully elucidated. In this study, we found that in a mouse model of anxiety triggered by unpredictable chronic mild stress, the expression of excitatory amino acid transporter 2 was upregulated in the basolateral amygdala. Interestingly, our findings indicate that the targeted knockdown of excitatory amino acid transporter 2 specifically within the basolateral amygdala astrocytes was able to rescue the anxiety-like behavior in mice subjected to stress. Furthermore, we found that the overexpression of excitatory amino acid transporter 2 in the basolateral amygdala, whether achieved through intracranial administration of excitatory amino acid transporter 2 agonists or through injection of excitatory amino acid transporter 2-overexpressing viruses with GfaABC1D promoters, evoked anxiety-like behavior in mice. Our single-nucleus RNA sequencing analysis further confirmed that chronic stress induced an upregulation of excitatory amino acid transporter 2 specifically in astrocytes in the basolateral amygdala. Moreover, through in vivo calcium signal recordings, we found that the frequency of calcium activity in the basolateral amygdala of mice subjected to chronic stress was higher compared with normal mice. After knocking down the expression of excitatory amino acid transporter 2 in the basolateral amygdala, the frequency of calcium activity was not significantly increased, and anxiety-like behavior was obviously mitigated. Additionally, administration of an excitatory amino acid transporter 2 inhibitor in the basolateral amygdala yielded a notable reduction in anxiety level among mice subjected to stress. These results suggest that basolateral amygdala astrocytic excitatory amino acid transporter 2 plays a role in in the regulation of unpredictable chronic mild stress-induced anxiety-like behavior by impacting the activity of local glutamatergic neurons, and targeting excitatory amino acid transporter 2 in the basolateral amygdala holds therapeutic promise for addressing anxiety disorders.

Camouflage is a critical survival strategy that helps to evade predation and increase hunting success. Background matching and disruptive colouration are different camouflage strategies that are subject to different selective pressures and can drive divergence in their associated traits such as colour pattern and behaviour. This study tested whether two closely related reef fish species (Hypoplectrus spp.) with distinct colour patterns exhibit different predator escape responses and differential gene expression in the brain indicative of divergent camouflage strategies. Combining field and laboratory experiments, we show that barred hamlets, characterised by disruptive colouration, are dynamic in their escape responses, while black hamlets, with their darker colouration, had a preference for hiding. The behavioural differences between these species seem to be limited to divergent predator escape responses since other behaviours such as activity or sociability did not differ. Importantly, the observed behavioural differences were accompanied by transcriptomic differences in their brains, particularly in regions associated with the perception of looming threats and less so in the region involved in conditioning. Differential expression in the diencephalon suggests enhanced neuronal plasticity in barred hamlets, which might allow for rapid adjustments in their escape response, while black hamlets exhibited upregulation in genes linked to immune response and oxygen transport in the optic tectum. Overall, our findings suggest that the two species utilise different camouflage strategies, which might contribute to the maintenance of colour pattern differences and thereby influence the speciation and diversification of these closely related sympatric reef fishes.

Environmental contexts serve as powerful cues for episodic memory, allowing humans to recall events tied to specific settings. While rats can learn context-specific associations and temporal order, their ability to manage multiple contexts and rapidly adapt to changes in context remains unclear. This study investigated whether rats could order objects across two distinct contexts. Eight Lister Hooded rats were trained in a dual-context maze, where each context contained a pair of objects. In each trial, rats entered the maze, selected an object, and then re-entered either the same or a different context to complete the trial in the correct temporal order. Six rats successfully learned object order within a single context, but only two reached criterion in the more complex two-context condition. Group error analyses revealed a partial reliance on a procedural learning strategy and a tendency to favour one context, where prior location influenced object selection in subsequent trials. While two rats successfully adapted to the two-context condition beyond these simple strategies, most struggled with context switching, exhibiting perseveration difficulties-a trait also observed in some humans. These findings highlight the evolutionary foundations of context-guided memory and reveal remarkable individual variability in the ability to flexibly navigate multiple contexts.

Meditation training has been shown to improve physical and mental health and promote neural plasticity, but more research is needed on the relationships between these effects. This study analyzed the Resting State Functional Connectivity (RSFC) of posterior cingulate cortex (PCC) among 94 chronically stressed but otherwise healthy adults randomized 1:1:1 to receive eight weeks of in-person one-on-one interventions focused either on meditation (n = 32), yoga (n = 31), or stress education (n = 31). We found only in the meditation arm, there was a significant reduction of PCC RSFC with the left hippocampus (p < 0.05, FWE corrected). Post-intervention changes of PCC-hippocampal RSFC were significantly (all p ≤ 0.01) correlated with changes of perceived stress (r = 0.54), allostatic load index (r = 0.58), and NF-κB anti-inflammatory gene expression (r = -0.55), suggesting the neural effects of meditation are closely associated with biomarkers of physical wellness. No significant changes with PCC RSFC were observed within the yoga or stress education arm, suggesting this neurobiological mechanism might be unique to meditation training.

A connection between stress-related illnesses and alcohol use disorders is extensively documented. Fear conditioning is a standard procedure used to study stress learning and links it to the activation of amygdala circuitry. However, the connection between the changes in amygdala circuitry and function induced by alcohol and fear conditioning is not well established.

We introduce a computational model to test the mechanistic relationship between amygdala functional and circuit adaptations during fear conditioning and the impact of acute vs. repeated alcohol exposure. Using firing rate formalism, the model generates electrophysiological and behavioral responses in fear conditioning protocols via plasticity of amygdala inputs. The influence of alcohol is modeled by accounting for known modulation of connections within amygdala circuits, which consequently affect plasticity. Thus, the model connects the electrophysiological and behavioral experiments. We hypothesize that alterations within amygdala circuitry produced by alcohol cause abnormal plasticity of amygdala inputs such that fear extinction is slower to achieve and less robust.

In accordance with prior experimental results, both acute and prior repeated alcohol decrease the speed and robustness of fear extinction in our simulations. The model predicts that, first, the delay in fear extinction caused by alcohol is mostly induced by greater activation of the basolateral amygdala (BLA) after fear acquisition due to alcohol-induced modulation of synaptic weights. Second, both acute and prior repeated alcohol shift the amygdala network away from the robust extinction regime by inhibiting activity in the central amygdala (CeA). Third, our model predicts that fear memories formed during acute or after chronic alcohol are more connected to the context.

The model suggests how circuit changes induced by alcohol may affect fear behaviors and provides a framework for investigating the involvement of multiple neuromodulators in this neuroadaptive process.

Concern about falling (CAF) is common in multiple sclerosis (MS), impacting motor function, cognition, and emotional well-being. However, the underlying neural correlates remain understudied. Given the multifactorial nature of CAF, we hypothesized that neural correlates may involve interactions between brain regions involved in emotional (e.g., amygdala), motor (e.g., cerebellum), and cognitive functions (e.g., hippocampus). This study explored associations between CAF and resting-state functional connectivity (FC) in amygdala-hippocampal and amygdala-cerebellar circuits in MS.

Participants with relapsing-remitting MS completed the Falls Efficacy Scale-International to assess CAF, followed by a functional MRI scan. Region of interest (ROI)-to-ROI analyses examined associations between CAF and FC in amygdala-hippocampal and amygdala-cerebellar circuits. Significant connections were identified using false discovery rate (FDR) correction at α = 0.05.

Forty-one individuals participated in our study. CAF was significantly associated with greater amygdala-hippocampal FC (T(39) ≥ 3.76, q ≤ 0.001) and lower amygdala-cerebellar FC (T(39) ≤ -2.52, q ≤ 0.026).

These findings highlight distinct neural patterns linked to CAF in MS. Higher CAF was associated with greater amygdala-hippocampal connectivity, suggesting that neural circuits underlying fear-related memories and emotional processing may play a crucial role in perceived fall risk. In contrast, lower amygdala-cerebellar connectivity in individuals with heightened CAF may reflect diminished integration of emotional and motor output, potentially compromising the ability to assess environmental hazards and situations where falls are likely to occur. Further understanding these neural underpinnings may help develop targeted interventions to reduce CAF and its negative impact on people with MS.

Autism spectrum disorder (ASD) is associated with disruptions in social behavior and the neural circuitry behind it. Very little data is available on the mechanisms that are responsible for the lack of motivation to reunite with conspecifics during isolation. It is as important to investigate the neural changes that reduce motivation to end social isolation, as those underlying the reactions to social stimuli. Using a rodent model of prenatal valproic acid (VPA) exposure, we investigated how social isolation affects the neural activation of key brain nuclei involved in social processing and stress regulation. Juvenile male C57BL/6 mice were treated prenatally with VPA or saline (CTR) and subjected to 24 h of social isolation from their cage mates, with neural activity assessed via c-Fos immunohistochemistry. Based on correlational activations we reconstructed and analyzed the functional connectome of the observed brain regions. Control animals exhibited elevated c-Fos expression in the regions central to the mesolimbic reward system (MRS), social brain network (SBN), and stress-related networks, with the interpeduncular nucleus (IPN) at the core, compared to VPA-treated animals. Functional network analysis revealed a more widespread but less specific pattern of connectivity in VPA-treated animals. These findings suggest that prenatal VPA exposure disrupts certain neural circuits related to social behavior and stress regulation, offering an insight into the altered perception of social isolation in ASD models, and highlighting potential therapeutic targets.

The often co-morbid conditions of depression and anxiety are the most common mental illnesses and are more prevalent among females than males. Chronic stress paradigms in rodents serve as valuable preclinical models for investigating the factors contributing to these disorders and their neural underpinnings. A variety of chronic stressors are associated with the development of sexually differentiated effects on anxiety- and depressive-like responses in rodents. This review summarizes and discusses common behavioral tasks used to assess anxiety-like (e.g., elevated plus maze, open field) and depressive-like (e.g., sucrose preference, forced swim) behaviors in rodents and discusses evidence of sex differences in these responses. Preclinical chronic stress models also aid in identifying potential mechanisms underlying behavioral changes, including dendritic synaptic alterations in neural circuits affected by stress. Robust sex differences have been observed in stress-responsive brain regions such as the prefrontal cortex, hippocampus, and amygdala. Therefore, applying chronic stress paradigms and assessing their neural effects in rodents may provide crucial insights into the biological basis of sexually differentiated mental illnesses in humans.

Hyponatremia is the most common clinical electrolyte disorder. Once thought to be asymptomatic in response to adaptation by the brain, recent evidence suggests that chronic hyponatremia (CHN) may induce neurological manifestations, including psychological symptoms. However, the specific psychological symptoms induced by CHN, the mechanisms underlying these symptoms, and their potential reversibility remain unclear. Therefore, this study aimed to determine whether monoaminergic neurotransmission is associated with innate anxiety-like behaviors potentiated by CHN in a mouse model of CHN secondary to the syndrome of inappropriate antidiuresis. In the present study, using a mouse model of the syndrome of inappropriate antidiuresis presenting with CHN, we showed that the sustained reduction of serum sodium ion concentrations potentiated innate anxiety-like behaviors in the light/dark transition and open field tests. We also found that serotonin and dopamine levels in the amygdala were significantly lower in mice with CHN than in controls. Additionally, phosphorylation of extracellular signal-regulated kinase (ERK) in the amygdala was significantly reduced in mice with CHN. Notably, after correcting for CHN, the increased innate anxiety-like behaviors, decreased serotonin and dopamine levels, and reduced phosphorylation of ERK in the amygdala were normalized. These findings further underscore the importance of treating CHN and highlight potential therapeutic strategies for alleviating anxiety in patients with CHN, which will improve their quality of life.

A key function of brain systems mediating emotion is to learn to anticipate unpleasant experiences. Although organisms readily associate sensory stimuli with aversive outcomes, higher-order forms of emotional learning and memory require inference to extrapolate the circumstances surrounding directly experienced aversive events to other indirectly related sensory patterns that were not part of the original experience. This type of learning requires internal models of emotion, which flexibly track directly experienced and inferred aversive associations. Although the brain mechanisms of simple forms of aversive learning have been well studied in areas such as the amygdala1-4, whether and how the brain forms and represents internal models of emotionally relevant associations are not known5. Here we report that neurons in the rodent dorsomedial prefrontal cortex (dmPFC) encode a flexible internal model of emotion by linking sensory stimuli in the environment with aversive events, whether they were directly or indirectly associated with that experience. These representations form through a multi-step encoding mechanism involving recruitment and stabilization of dmPFC cells that support inference. Although dmPFC population activity encodes all salient associations, dmPFC neurons projecting to the amygdala specifically represent and are required to express inferred associations. Together, these findings reveal how internal models of emotion are encoded in the dmPFC to regulate subcortical systems for recall of inferred emotional memories.

Understanding how threats drive fear memory formation is crucial to understanding how organisms adapt to environments and treat threat-related disorders such as PTSD. While traditional Pavlovian conditioning studies have provided valuable insights, the exclusive reliance on electric shock as a threat stimulus has limited our understanding of diverse threats. To address this, we developed a conditioning paradigm using a looming visual stimulus as an unconditioned stimulus (US) in mice and identified a distinct neural circuit for visual threat conditioning. Parabrachial CGRP neurons were necessary for both conditioning and memory retrieval. Upstream neurons in the posterior insular cortex (pIC) responded to looming stimuli, and their projections to the parabrachial nucleus (PBN) induced aversive states and drove conditioning. However, this pIC-to-PBN pathway was not required for foot-shock conditioning. These findings reveal how non-nociceptive visual stimuli can drive aversive states and fear memory formation, expanding our understanding of aversive US processing beyond traditional models.

Ketamine has anesthetic, analgesic, and antidepressant properties which may involve multiple neuromodulatory systems. In humans, the opioid receptor (OR) antagonist naltrexone blocks the antidepressant effect of ketamine. This mechanism may differentiate ketamine from other NMDA receptor antagonists. Animal models that reflect OR-dependent behavioral effects of ketamine may shed light on the brain regions and circuits that contribute to ketamine's antidepressant mechanism in humans.

We screened male and female wild-type mice for a behavioral response to ketamine that could be reversed by OR antagonists in several assays, including locomotor activation, analgesia, and the forced swim test. Whole-brain imaging of cFos expression in ketamine-treated mice, pretreated with naltrexone or vehicle, was used to identify brain areas mediating ketamine / OR interactions. Region-specific pharmacological and genetic interference with μOR (MOR) signaling was used to test predictions of whole-brain imaging results in a subset of behavioral assays.

Among a series of behavioral assays, only locomotor-activation was sensitive to ketamine and blocked by an MOR-selective antagonist. Locomotor activation produced by the NMDA receptor antagonist, MK-801, was not OR-dependent. Whole-brain imaging revealed cFos expression in neurons of the central amygdala (CeA) showed the greatest difference between ketamine in the presence versus absence of naltrexone. CeA neurons expressing both MOR and PKCδ were strongly activated by naltrexone, and selectively interrupting MOR function in the CeA either pharmacologically or genetically blocked the locomotor effects of ketamine.

These data suggest that ketamine acts at MORs expressed in CeA neurons to produce acute hyperlocomotion.

Anxiety disorders, marked by excessive fear and worry, are particularly prevalent in autism, affecting up to 45 % of individuals with the condition. Since the 1960s, advances in neuroscience, psychology, and psychopharmacology have enhanced understanding and treatment of anxiety disorders in general population. Standardized diagnostic criteria development facilitated accurate classification of anxiety disorders. Neurobiological research identified key brain regions forming the basis of the amygdala-centred fear circuit model. Pharmacological advancements introduced selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) as safer, first-line treatments. However, these medications show limited efficacy and significant side effects in autistic individuals, highlighting the need for alternative treatments. Cognitive-behavioural therapy (CBT) has gained empirical support, helping to reduce avoidance behaviours, but modifications are often needed for autistic individuals. Emerging therapies, including Mindfulness-Based Stress Reduction for Autism Spectrum Disorder (MASSI) and virtual reality-based interventions, are being explored for individuals with more treatment-resistant anxiety. Ongoing clinical trials are assessing medications used for other psychiatric disorders to determine their efficacy in anxiety treatment for autism. Recent genetic and neuroimaging research has revealed altered brain connectivity and genetic susceptibility in anxiety, promoting the development of personalized treatments. Despite these advances, challenges remain in optimizing interventions and addressing treatment resistance, necessitating continued research and innovation.

How do our brains determine whether something is good or bad? The brain's ability to evaluate stimuli as positive or negative - by attributing valence - is fundamental to survival and decision-making. Different brain regions have been associated with valence encoding, including the nucleus accumbens (NAc). The NAc is predominantly composed of GABAergic medium spiny neurons (MSNs), which segregate into two distinct populations based on their dopamine receptor expression: D1-receptor-expressing (D1-MSNs) and D2-receptor-expressing neurons (D2-MSNs). Classical models propose a binary functional role, where D1-MSNs exclusively mediated reward and positive valence, while D2-MSNs processed aversion and negative valence. However, we now recognize that NAc MSN subpopulations operate in a more complex manner than previously thought, often working cooperatively rather than antagonistically in valence-related behaviors. This review synthesizes our current knowledge of valence-encoding neurocircuitry, with emphasis on the NAc. We examine electrophysiological, calcium imaging, optogenetic, chemogenetic and pharmacological studies detailing the contribution of NAc medium spiny neurons for rewarding and aversive responses. Finally, we explore emerging technical innovations that promise to advance our understanding of how the mammalian brain encodes valence and translates it into behavior.

Understanding how innate predispositions and learned experiences interact to shape behavior is a central question in systems neuroscience. Traditionally, innate behaviors, that is, those present without prior learning and governed by evolutionarily conserved neural circuits, have been studied separately from learned behaviors, which depend on experience and neural plasticity. This division has led to a compartmentalized view of behavior and neural circuit organization. Increasing evidence suggests that innate and learned behaviors are not independent, but rather deeply intertwined, with plasticity evident even in circuits classically considered 'innate'. In this opinion, we highlight examples across species that illustrate the dynamic interaction between these behavioral domains and discuss the implications for unifying theoretical and empirical frameworks. We argue that a more integrative approach, namely one that acknowledges the reciprocal influences of innate and learned processes, is essential for advancing our understanding of how neuronal activity drives complex behaviors.

Post-stroke anxiety (PSA) manifests as anxiety symptoms after stroke, with unclear mechanisms and limited treatment strategies. Endocannabinoids, reported to mitigate fear, anxiety, and stress, undergo dynamic alterations after stroke linked to prognosis intricately. However, endocannabinoid metabolism in ischemic microenvironment and their associations with post-stroke anxiety-like behavior remain largely uncovered. Our findings indicated that endocannabinoid metabolism was dysregulated after stroke, characterized by elevated N-palmitoylethanolamide (PEA) hydrolase N-acylethanolamine-acid amidase (NAAA) in activated microglia from ischemic area, accompanied by rapid PEA exhaustion. Microglial PEA metabolite exhaustion is directly associated with more severe pathological damage, anxiety symptoms and pain sensitivity. Naaa knockout or pharmacological supplementation to boost PEA pool content can effectively promote stroke recovery and alleviate anxiety-like behaviors. In addition, maintaining PEA pool content in ischemic area reduces overactivated microglia by confronting against mitochondria dysfunction and inflammasome cascade triggered IL-18 release and diffusion to contralateral hemisphere. Meanwhile, maintenance of microglial PEA pool content in ischemic-damaged lesion can preserve contralateral vCA1 synaptic integrity, enhancing anxiolytic pBLA-vCA1Calb1+ circuit activity by alleviating microglial phagocytosis-mediated synaptic loss. Thus, we conclude that microglial NAAA-regulated lipid signaling in the ischemic focus remodels contralateral anxiolytic circuit to participate in post-stroke anxiety progression. Blocking PEA signaling breakdown promotes stroke recovery and mitigates anxiety-like symptoms.

The predatory imminence continuum (PIC) of antipredator defensive behavior has been a helpful strategy for modeling anxiety and fear-related disorders in nonclinical research. The PIC is divided into three different sequential stages that reflect defensive behavioral strategy in response to predatory imminence. However, the PIC was experimentally addressed with a series of shock-based fear conditioning experiments rather than predatory threats. In this article, we consider the PIC in a more naturalistic behavioral setting, focusing on analyzing the neural systems of animals responding to terrestrial and aerial predators. Of relevance, there is a sequential engagement of the distinct neural circuits along each phase of the PIC. In the preencounter phase, prefrontal cortical networks are particularly involved in planning and organizing behavioral responses to ambiguous threats. As the predatory cues or the real predator is detected, there is an engagement of amygdalar and hippocampal > hypothalamic pathways in conjunction with the periaqueductal gray, which organize fear responses. This dynamic particularly reveals how specific neural circuits are set into action to subserve distinct defensive responses. Moreover, we further explore the neural circuits governing other fearful situations outside the context of the PIC, including agonistic social encounters and interoceptive challenges. This analysis reveals an interesting overlap between the neural systems responding to these threats and those involved in response to predatory threats. The present review clarifies how defensive circuits respond to natural threats and provides a more realistic view of the neural systems underlying anxiety and fear responses.

Chronic low-grade inflammation and exposure to stress are key contributing factors in the etiology and progression of many neuropsychiatric disorders. Dietary emulsifiers, such as carboxymethylcellulose (CMC) and polysorbate-80 (P80), are commonly added to processed foods and drinks and are classified by the Food and Drug Administration (FDA) as generally recognized as safe (GRAS). Recently, however, we and others have reported that these additives at translationally relevant doses cause low-grade intestinal inflammation, microbiota dysbiosis, and alterations in gene expression in brain areas that mediate behavioral and neuroendocrine responses to stress-provoking stimuli.

To test whether emulsifier exposure sensitizes behavioral, hormonal, and neuronal responses to stress, C57BL/6 J male mice were given water +1 % emulsifier (CMC or P80) or water alone for 12 weeks after which they were exposed to social defeat stress. We previously found increased PTGS2 (COX-2) gene expression in the amygdala following emulsifier consumption. To determine whether inflammation, potentially through the COX pathway, is a potential mechanism driving emulsifier-induced increases in stress sensitivity, we administered the COX inhibitor aspirin (25 mg/kg/day) in conjunction with emulsifiers for the last six weeks of treatment.

In defeated mice, CMC increased circulating corticosterone, while both emulsifiers increased social avoidance behavior and altered defeat-induced c-Fos immunofluorescence in various brain regions. Moreover, behavioral and hormonal alterations were attenuated by aspirin.

These data demonstrate that ingestion of at least some dietary emulsifiers at concentrations analogous to those ingested by humans increases sensitivity to social stress in mice and that the COX pathway may be a mechanistic candidate by which emulsifier-induced increases in sensitivity to social stress occur.

Spontaneous rescue behavior enhances the well-being and survival of social animals, yet the neural mechanisms underlying the recognition and response to conspecifics in need remain unclear. Here, we report that observer mice experience distress when encountering anesthetized conspecifics, prompting spontaneous rescue-like behavior toward the unconscious mice. This behavior facilitates the earlier awakening of anesthetized mice while simultaneously alleviating stress in the helper mice. Our findings reveal that endogenous oxytocin (OXT) release from the hypothalamic paraventricular nucleus (PVN) to the oxytocin receptor (OXTR) in the central nucleus of the amygdala (CeA) regulates the emotional component of rescue-like behavior. In contrast, OXT release from the PVN to OXTR in the dorsal bed nucleus of the stria terminalis (dBNST) mediates the motor component of the behavior. Furthermore, we demonstrate that these two pathways exhibited distinct temporal dynamics and functional roles. The OXTPVN-OXTRCeA pathway is activated in a transient and intense manner, acting as a trigger for rescue-like behavior, whereas the OXTPVN-OXTRdBNST pathway responds in a sustained manner, ensuring the continuation of the behavior. These findings highlight the remarkable ability of rodents to engage in targeted helping behavior and suggest that distinct subcortical oxytocinergic pathways selectively and synergistically regulate the motor and emotional aspects of rescue-like behavior.

Hypothalamic VMHdmSF1 neurons are activated by predator cues and are necessary and sufficient for instinctive defensive responses. However, such data do not distinguish which features of a predator encounter are encoded by VMHdmSF1 neural activity. To address this issue, we imaged VMHdmSF1 neurons at single-cell resolution in freely behaving mice exposed to a natural predator in varying contexts. Our results reveal that VMHdmSF1 neurons do not encode different defensive behaviors but rather represent predator identity and multiple predator-evoked internal states, including threat-evoked fear/anxiety, arousal or neophobia, predator imminence, and safety. Notably, threat and safety are encoded bi-directionally by anti-correlated subpopulations. Strikingly, individual differences in predator defensiveness are correlated with individual differences in VMHdmSF1 response dynamics. Thus, different threat-related internal state variables are encoded by distinct neuronal subpopulations within a genetically defined, anatomically restricted hypothalamic cell class.

Extinction learning is regarded as a core mechanism underlying exposure therapy. Under this assumption, studies have looked at the predictive value of the extinction learning paradigm for exposure therapy outcomes. However, predicting factors of long-term exposure therapy success have not been established. Participants with a specific phobia (SP) for spiders were included in a double-blind randomized controlled trial. Participants were randomly assigned to receive exposure therapy (n = 25, 24 females) or an active control intervention, progressive muscle relaxation (PMR; n = 18, 15 females). Symptom levels were measured with the Fear of Spiders questionnaire (FSQ) at baseline (T0), after the intervention (T1), and at six- (T2) and twelve (T3) months follow-up. At baseline, participants completed a three-day fMRI fear conditioning, extinction learning, and extinction recall paradigm. Indices of extinction were defined as self-reported threat expectancy and fear, and neural activation during stimulus presentations and threat omission in the ventromedial prefrontal cortex and nucleus accumbens, based on prior data. Mixed model analysis revealed that the exposure therapy group had an overall stronger decrease in phobic symptoms over time than the PMR group (β = 10.95, p < .001). However, none of the indices of extinction learning were predictive for FSQ scores after exposure therapy at the longest follow-up measurement (T3). In sum, the current results show the long-term effectiveness of a single session of exposure therapy for reducing a specific fear of spiders but no baseline characteristics were identified that predicted individual differences in exposure therapy success after one year.

Accumulating evidence supports a role for altered circuit function in impaired valence processing and altered affective states as a core feature of psychiatric illnesses. We review the circuit mechanisms underlying normal valence processing and highlight evidence supporting altered function of the basolateral amygdala, valence processing, and affective states across psychiatric illnesses. The mechanisms controlling network activity that governs valence processing are reviewed in the context of potential pathophysiological mechanisms mediating circuit dysfunction and impaired valence processing in psychiatric illnesses. Finally, we review emerging data demonstrating experience-dependent, biased information routing through the basolateral amygdala promoting negative valence processing and discuss the potential relevance to impaired affective states and psychiatric illnesses.

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.

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.

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.

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.

The amygdala exhibits distinct different activity patterns to threat and safety stimuli. Animal studies have demonstrated that the fear (i.e., threat) and extinction (i.e., safety) memory are encoded by the amygdala and its interaction with the ventromedial prefrontal cortex (vmPFC). Recent studies in both animals and humans suggest that the inter-regional interaction between amygdala and vmPFC can be supported by theta oscillations during fear processing. However, the mechanism by which the human vmPFC-amygdala pathway dynamically supports neural representations of the same stimulus remains elusive, as it alternatively reflects threat and safety situations. To investigate this phenomenon, we conducted intracranial EEG recordings in drug-resistant epilepsy patients (n = 8) with implanted depth electrodes who performed a fear conditioning and extinction task. This task was designed with a fixed structure whereby specific CS+ stimulus could be either safe (never paired with US) or threatening (possibly paired with US) based on an implicit rule during fear acquisition. Our findings showed that the stimulus embodying potential threat information was accompanied by increased theta activities in amygdala during both fear acquisition and early extinction. Furthermore, the learning of safety information was associated with enhanced theta-related direction from the vmPFC to the amygdala. This study provided directly electrophysiological evidence supporting the dynamic oscillatory modulation of threat and safety representations in the human amygdala-vmPFC circuit, and suggests that amygdala safety processing depends on theta inputs from the vmPFC in both fear acquisition and extinction.

Ischemic stroke, brain tissue infarction following obstructed cerebral blood flow, leads to long-term neurological deficits and death. While neocortex is a commonly affected region with established preclinical models, less is known about deeper brain strokes, despite having unique neurological outcomes. We induced focal ischemic stroke while simultaneously monitoring neuronal activity in awake behaving Thy1-GCaMP6f mice by delivering and collecting light through bilateral fiberoptic implants. Unilateral hippocampal stroke resulted in atypical wandering behavior coincident with ipsilesional terminal spreading depolarization (sustained increase in GCaMP6f fluorescence). Ischemia induced seizures that propagated to the contralesional hippocampus triggering a transient spreading depolarization, predominantly in females. Hippocampal stroke impaired contextual fear conditioning acquired pre-stroke. Yet, 7 days post-stroke, contextual fear conditioning was only improved in mice with contralesional spreading depolarization. Blunting peri-stroke contralesional spreading depolarization prevented recovery of hippocampus-dependent learning. Together, we show that regionally isolated deleterious and beneficial spreading depolarizations can occur concurrently in the murine brain during acute stroke.

Post-traumatic stress disorder (PTSD) is a psychiatric disorder caused by traumatic past experiences, rooted in the neurocircuits of fear memory formation. Memory processes include encoding, storing, and recalling to forgetting, suggesting the potential to erase fear memories through timely interventions. Conventional strategies such as medications or electroconvulsive therapy often fail to provide permanent relief and come with significant side-effects. This review explores how fear memory may be erased, particularly focusing on the mnemonic phases of reconsolidation and extinction. Reconsolidation strengthens memory, while extinction weakens it. Interfering with memory reconsolidation could diminish the fear response. Alternatively, the extinction of acquired memory could reduce the fear memory response. This review summarizes experimental animal models of PTSD, examines the nature and epidemiology of reconsolidation to extinction, and discusses current behavioral therapy aimed at transforming fear memories to treat PTSD. In sum, understanding how fear memory updates holds significant promise for PTSD treatment.

Recent laboratory research showed that vagus nerve stimulation promotes fear extinction, the inhibitory core mechanism of exposure treatment, presumably via activation of the noradrenergic brain system. However, a translation of this stimulation technique to clinical practice is lacking. We therefore investigated the potential of vagal stimulation to inhibit excessive fear responses and facilitate responding to in-vivo and laboratory exposure in individuals with specific phobia. Spider-phobic participants were subjected to three standardized in-vivo exposures towards a living tarantula, complemented by an exposure in vitro (between exposure in vivo I and II). Transcutaneous auricular vagus nerve stimulation (taVNS) was applied during in-vitro exposure, presenting pictures of the exposed tarantula, other spiders and neutral tools in the laboratory. Fear was assessed by self-reports and behavioral avoidance (in-vivo exposures), and amygdala-mediated autonomic and behavioral fear components (exposure in vitro). Vagal stimulation facilitated the reduction of behavioral avoidance across repeated in-vivo exposures. During laboratory exposure, taVNS inhibited fear tachycardia and corrugator muscle activity specifically in response to pictures of the previously exposed tarantula - an effect that became stronger with increasing stimulation duration. Psychophysiological indices of noradrenergic transmission in the basolateral amygdala were elevated during taVNS and correlated to subsequent attenuation of behavioral avoidance. Our results suggest, that taVNS exerts stimulus-specific and dose-dependent inhibition of multiple automatic response components of excessive fear, highlighting taVNS as a valuable adjunct to exposure-based treatment. A translational mechanism of action is supported, proposing that taVNS exhibits its effects by noradrenergic activation of fear extinction circuitry, particularly targeting the basolateral amygdala.

Clinical observation has identified cerebellar cognitive affective syndrome, which is characterized by various non-motor dysfunctions such as social disorders and anxiety. Increasing evidence has revealed reciprocal mono-/poly-synaptic connections of cerebello-cerebral circuits, forming the concept of the cerebellar connectome. In this study, we demonstrate that neurons in the cerebellar nuclei (CN) of male mice project to a subset of zona incerta (ZI) neurons through long-range glutamatergic and GABAergic transmissions, both capable of encoding acute stress. Furthermore, activating or inhibiting glutamatergic and GABAergic transmissions in the CN → ZI pathway can positively or negatively regulate anxiety and place preference through presynaptic plasticity-dependent mechanisms, as well as mediate motor-induced alleviation of anxiety. Our data support the close relationship between the cerebellum and emotional processes and suggest that targeting cerebellar outputs may be an effective approach for treating anxiety.

Because of the important roles of both serotonin (5-HT) and the cerebellum in regulating anxiety, we asked whether 5-HT signaling within the cerebellum is involved in anxiety behavior. Physiological 5-HT levels were measured in vivo by expressing a fluorescent sensor for 5-HT in lobule VII of the cerebellum, while using fiber photometry to measure sensor fluorescence during anxiety behavior on the elevated zero maze. Serotonin increased in lobule VII when male mice were less anxious and decreased when mice were more anxious. To establish a causal role for this serotonergic input in anxiety behavior, we photostimulated or photoinhibited serotonergic terminals in lobule VII while mice were in an elevated zero maze. Photostimulating these terminals reduced anxiety behavior in mice, while photoinhibiting them enhanced anxiety behavior. Our findings add to evidence that cerebellar lobule VII is a topographical locus for anxiety behavior and establish that 5-HT input into this lobule is necessary and sufficient to bidirectionally influence anxiety behavior. These results represent progress toward understanding how the cerebellum regulates anxiety behavior and provide new evidence for a functional connection between the cerebellum and the serotonin system within the anxiety circuit.

Fear, whether innate or learned, is an essential emotion required for survival. The learning, and subsequent memory, of fearful events enhances our ability to recognise and respond to threats, aiding adaptation to new, ever-changing environments. Considerable research has leveraged associative learning protocols such as contextual or auditory forms of fear conditioning in rodents, to understand fear learning, memory consolidation and extinction phases of memory. Such assays have led to detailed characterisation of the underlying neurocircuitry and neurobiology supporting fear learning processes. Given fear processing is conserved across rodents and humans, fear conditioning experiments provide translational insights into fundamental memory processes and fear-related pathologies. This review examines associative learning protocols used to measure fear learning, memory and extinction, before providing an overview on the underlying complex neurocircuitry including the amygdala, hippocampus and medial prefrontal cortex. This is followed by an in-depth commentary on the neurobiology, particularly synaptic plasticity mechanisms, which regulate fear learning, memory and extinction. Next, we consider how fear conditioning assays in rodents can inform our understanding of disrupted fear memory in human disorders such as post-traumatic stress disorder (PTSD), anxiety and psychiatric disorders including schizophrenia. Lastly, we critically evaluate fear conditioning protocols, highlighting some of the experimental and theoretical limitations and the considerations required when conducting such assays, alongside recent methodological advancements in the field. Overall, rodent-based fear conditioning assays remain central to making progress in uncovering fundamental memory phenomena and understanding the aetiological mechanisms that underpin fear associated disorders, alongside the development of effective therapeutic strategies.

The medial prefrontal cortex (mPFC) is critical for learning and decision-making processes, including responding to threats. The protracted maturation of the mPFC extends into early adulthood. Although prominent models suggest that increasing top-down control by the mPFC eventually allows adult behavioral repertoires to emerge, it is unclear how progressive strengthening can produce nonlinear behavioral changes observed across development. We use fiber photometry and optogenetics to establish causal links between frontolimbic pathway activity and threat avoidance strategies in juvenile, adolescent and adult mice. We uncover multiple developmental switches in the roles of mPFC pathways targeting the nucleus accumbens and basolateral amygdala. These changes are accompanied by axonal pruning, strengthening of synaptic connectivity and altered functional connectivity with downstream cell types, which occur in the mPFC-basolateral amygdala and mPFC-nucleus accumbens pathways at different rates. Our results reveal how developing mPFC pathways pass through distinct architectures that may make them optimally adapted to age-specific challenges.

Fear and associated learning and memory are critical for developing defensive behavior. Excessive fear and anxiety are important components of post-traumatic stress disorder. However, the neurobiology of fear conditioning, especially tone-related fear memory retrieval, has not been clearly defined, which limits specific intervention development for patients with excessive fear and anxiety. Here, we show that auditory fear memory retrieval stimuli activate multiple brain regions including the lateral septum (LS). Inhibition of the LS and the connection between basolateral amygdala (BLA) and LS or between LS and ventromedial nucleus of the hypothalamus (VMH) attenuates tone-related fear conditioning and memory retrieval. Inhibiting GABAergic neurons or dopaminergic neurons in the LS also attenuates tone-related fear conditioning. Our data further show that fear conditioning is inhibited by blocking orexin B signaling in the LS. Our results indicate that the neural circuitries BLA-LS and LS-VMH are critical for tone-related fear conditioning and memory retrieval, and that GABAergic neurons, dopaminergic neurons and orexin signaling in the LS participate in this auditory fear conditioning.

The atypical antipsychotic clozapine targets multiple receptor systems beyond the dopaminergic pathway and influences prepulse inhibition (PPI), a critical translational measure of sensorimotor gating. Since PPI is modulated by atypical antipsychotics such as risperidone and clozapine, we hypothesized that p11-an adaptor protein associated with anxiety- and depressive-like behaviors and G-protein-coupled receptor function-might modulate these effects. In this study, we assessed the role of p11 in clozapine's PPI-enhancing effect by testing wild-type and global p11 knockout (KO) mice in response to haloperidol, risperidone, and clozapine. We also performed structural and functional brain imaging. Contrary to our expectation that anxiety-like p11-KO mice would exhibit an augmented startle response and heightened sensitivity to clozapine, PPI tests showed that p11-KO mice were unresponsive to the PPI-enhancing effects of risperidone and clozapine. Imaging revealed distinct regional brain volume differences and reduced hippocampal connectivity in p11-KO mice, with significantly blunted clozapine-induced connectivity changes in the CA1 region. Our findings highlight a novel role for p11 in modulating clozapine's effects on sensorimotor gating and hippocampal connectivity, offering new insight into its functional pathways.

Learning by experience that certain cues in the environment predict danger is crucial for survival. How dopamine (DA) circuits drive this form of associative learning is not fully understood. Here, in male mice, we demonstrate that DA neurons projecting to a unique subregion of the dorsal striatum, the posterior tail of the striatum (TS), encode a prediction error (PE) signal during associative fear learning. These DA neurons are necessary specifically during acquisition of fear learning, but not once the fear memory is formed, and are not required for forming cue-reward associations. Notably, temporally-precise inhibition or excitation of DA terminals in TS impairs or enhances fear learning, respectively. Furthermore, neuronal activity in TS is crucial for the acquisition of associative fear learning and learning-induced activity patterns in TS critically depend on DA input. Together, our results reveal that DA PE signaling in a non-canonical nigrostriatal circuit is important for driving associative fear learning.

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).

Emotional arousal plays a critical role in determining what is remembered from experiences. It is hypothesized that activation of the amygdala by emotional stimuli enhances memory consolidation in its downstream brain regions. However, the physiological basis of the inter-regional interaction and its functions remain unclear. Here, by adding emotional information to a perceptual recognition task that relied on a frontal-sensory cortical circuit in mice, we demonstrated that the amygdala not only associates emotional information with perceptual information but also enhances perceptual memory retention via amygdalo-frontal cortical projections. Furthermore, emotional association increased reactivation of coordinated activity across the amygdalo-cortical circuit during non-rapid eye movement (NREM) sleep but not during rapid eye movement (REM) sleep. Notably, this increased reactivation was associated with amygdala high-frequency oscillations. Silencing of amygdalo-cortical inputs during NREM sleep selectively disrupted perceptual memory enhancement. Our findings indicate that inter-regional reactivation triggered by the amygdala during NREM sleep underlies emotion-induced perceptual memory enhancement.

Anxiety is a physiological, emotional response that anticipates distal threats. When kept under control, anxiety is a beneficial response, helping animals to maintain heightened attention in environments with potential dangers. However, an overestimation of potential threats can lead to an excessive expression of anxiety that, in humans, may evolve into anxiety disorders. Pharmacological treatments show variable efficacy among patients, highlighting the need for more efforts to better understand the pathogenesis of anxiety disorders. Mounting evidence suggests that astrocytes, a type of glial cells, are active partners of neurons in brain circuits and in the regulation of behaviors under both physiological and pathological conditions. In this review, I summarize the current literature on the role of astrocytes from different brain regions in modulating anxious states, with the goal of exploring novel cerebral mechanisms to identify potential innovative therapeutic targets for the treatment of anxiety disorders.

Anxiety and fear are emotions often intertwined in response to aversive stimuli, complicating efforts to differentiate them and understand their distinct consequences. This study explores the common genetic and environmental factors contributing to the co-occurrence of anxiety disorders and dimensions of the revised Reinforcement Sensitivity Theory (rRST). A sample of 356 monozygotic (22.5 % males; M = 25.73, SD = 8.3) and 386 dizygotic (33.9 % males; M = 24.21, SD = 8.33) twins from the Serbian Twin Advanced Registry was analyzed. The Psychiatric Diagnostic Screening Questionnaire (PDSQ) provided scales for panic disorder, agoraphobia, social phobia, and generalized anxiety disorder (GAD), while the Reinforcement Sensitivity Questionnaire (RSQ) measured the Behavioral Inhibition System (BIS), Behavioral Activation System (BAS), and Fight/Flight/Freeze System (FFFS). Common additive genetic effects accounted for most of the variance in BIS, Fight, and panic, agoraphobia, and social phobia, while specific additive genetic effects were highest for Flight. Shared environmental effects were most pronounced for Fight across all models, with additional shared influences on BAS and BIS for panic, and BAS and Freeze for agoraphobia and social phobia. Nonshared environmental effects were the highest specific contributors across variables. Genetic overlap between anxiety disorders and rRST dimensions suggests pleiotropy, with unique environmental factors playing an important role in disorder development. While anxiety and fear may stem from distinct etiologies, their shared symptomatology complicates differentiation, highlighting the importance of considering both genetic and environmental influences in anxiety disorders.