Direct Ventral Hippocampal-Prefrontal Input Is Required for Anxiety-Related Neural Activity and Behavior

Contribution of prefrontal cortex and ventral hippocampus to anxiety in young epileptic mice

Children with epilepsy are particularly vulnerable to anxiety disorders, where these disorders are frequently underdiagnosed and untreated. Despite the high prevalence of anxiety in epilepsy, the underlying neurobiological mechanisms are not fully understood. The medial prefrontal cortex (mPFC) and ventral hippocampus (vHPC) are key brain regions implicated in the genesis and modulation of anxiety, and their interactions play a crucial role in emotional processing including anxiety. We utilized a pilocarpine-induced epilepsy model in young mice (7 weeks old) to assess anxiety-like behaviors using the open field test (OFT), light/dark box, and elevated plus maze (EPM). Local field potential (LFP) recordings were conducted to examine theta power and coherence between the mPFC and vHPC. LFP recordings revealed significantly altered theta power variation in both the mPFC and vHPC during exposure to anxiogenic contexts, suggesting the involvement of these regions in anxiety in the young epileptic mice. Notably, theta-frequency synchrony between the mPFC and vHPC was not significantly altered in the young epileptic mice, indicating that altered theta power rather than inter-regional synchrony may underlie anxiety behaviors in young epileptic mice. Furthermore, we demonstrated that chemogenetic inhibition of excitatory neurons in the mPFC and vHPC reduced anxiety levels in young epileptic mice. Altogether, our findings highlight the critical contributions of mPFC and vHPC to the pathogenesis of comorbid anxiety in epilepsy. These findings underscore the potential therapeutic significance of modulating the activity in these two regions as means to alleviate anxiety in a youth epilepsy population.

Anxiety disorders: Treatments, models, and circuitry mechanisms

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

The extraordinary "ordinary magic" of resilience

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

Astrocytes in the Ventral Hippocampus Bidirectionally Regulate Innate and Stress-Induced Anxiety-Like Behaviors in Male Mice

The mechanisms of anxiety disorders, the most common mental illness, remain incompletely characterized. The ventral hippocampus (vHPC) is critical for the expression of anxiety. However, current studies primarily focus on vHPC neurons, leaving the role for vHPC astrocytes in anxiety largely unexplored. Here, genetically encoded Ca2+ indicator GCaMP6m and in vivo fiber photometry calcium imaging are used to label vHPC astrocytes and monitor their activity, respectively, genetic and chemogenetic approaches to inhibit and activate vHPC astrocytes, respectively, patch-clamp recordings to measure glutamate currents, and behavioral assays to assess anxiety-like behaviors. It is found that vHPC astrocytic activity is increased in anxiogenic environments and by 3-d subacute restraint stress (SRS), a well-validated mouse model of anxiety disorders. Genetic inhibition of vHPC astrocytes exerts anxiolytic effects on both innate and SRS-induced anxiety-related behaviors, whereas hM3Dq-mediated chemogenetic or SRS-induced activation of vHPC astrocytes enhances anxiety-like behaviors, which are reversed by intra-vHPC application of the ionotropic glutamate N-methyl-d-aspartate receptor antagonists. Furthermore, intra-vHPC or systemic application of the N-methyl-d-aspartate receptor antagonist memantine, a U.S. FDA-approved drug for Alzheimer's disease, fully rescues SRS-induced anxiety-like behaviors. The findings highlight vHPC astrocytes as critical regulators of stress and anxiety and as potential therapeutic targets for anxiety and anxiety-related disorders.

Distinct ventral hippocampal inhibitory microcircuits regulating anxiety and fear behaviors

In emotion research, anxiety and fear have always been interconnected, sharing overlapping brain structures and neural circuitry. Recent investigations, however, have unveiled parallel long-range projection pathways originating from the ventral hippocampus, shedding light on their distinct roles in anxiety and fear. Yet, the mechanisms governing the emergence of projection-specific activity patterns to mediate different negative emotions remain elusive. Here, we show a division of labor in local GABAergic inhibitory microcircuits of the ventral hippocampus, orchestrating the activity of subpopulations of pyramidal neurons to shape anxiety and fear behaviors in mice. These findings offer a comprehensive insight into how distinct inhibitory microcircuits are dynamically engaged to encode different emotional states.

Ventral hippocampal parvalbumin interneurons gate the acute anxiolytic action of the serotonergic psychedelic DOI

There has been a recent renewal of interest in the therapeutic potential of serotonergic psychedelics. Here, we uncover the essential role of ventral hippocampus (vHpc) GABAergic interneurons in the anxiolytic effect evoked by the serotonergic psychedelic 2,5-dimethoxy-4-iodoamphetamine (DOI). Integrating anatomical, pharmacological, and genetic approaches, we show that 5-HT2A receptors in the CA1/subiculum (CA1/sub) region of the vHpc are required for the anxiolytic action of DOI. In vivo electrophysiology and opto-tagging experiments indicate that DOI enhances the firing rate of hippocampal fast-spiking parvalbumin (PV)-positive interneurons, most of which express the 5-HT2A receptors. Restoration of 5-HT2A receptors in PV-positive interneurons in a loss-of-function background reinstated the anxiolytic responses evoked by DOI in the vHpc CA1/sub region. Collectively, our results localize the acute anxiolytic action of a serotonergic psychedelic to 5-HT2A receptors in the ventral hippocampus and specifically identify PV-positive fast-spiking cells as a cellular trigger for the psychedelic-induced relief of anxiety-like behavior.

Adaptive closed-loop modulation of cortical theta oscillations: Insights into the neural dynamics of navigational decision-making

Navigational decision-making tasks, such as spatial working memory (SWM), rely highly on information integration from several cortical and sub-cortical regions. Performance in SWM tasks is associated with theta rhythm, including low-frequency oscillations related to movement and memory. The interaction of the ventral hippocampus (vHPC) and medial prefrontal cortex (mPFC), reflected in theta synchrony, is essential in various steps of information processing during SWM. We used a closed-loop neurofeedback (CLNF) system to upregulate theta power in the mPFC and investigate its effects on circuit dynamics and behavior in animal models. Specifically, we hypothesized that enhancing the power of the theta rhythm in the mPFC might improve SWM performance. Animals were divided into three groups: closed-loop (CL), random-loop (RL), and OFF (without stimulation). We recorded local field potential (LFP) in the mPFC while electrical reward stimulation contingent on cortical theta activity was delivered to the lateral hypothalamus (LH), which is considered one of the central reward-associated regions. We also recorded LFP in the vHPC to evaluate the related subcortical neural changes. Results revealed a sustained increase in the theta power in both mPFC and vHPC for the CL group. Our analysis also revealed an increase in mPFC-vHPC synchronization in the theta range over the stimulation sessions in the CL group, as measured by coherence and cross-correlation in the theta frequency band. The reinforcement of this circuit improved spatial decision-making performance in the subsequent behavioral results. Our findings provide direct evidence of the relationship between specific theta upregulation and SWM performance and suggest that theta oscillations are integral to cognitive processes. Overall, this study highlights the potential of adaptive CLNF systems in investigating neural dynamics in various brain circuits.

The Role of the Medial Prefrontal Cortex in Spatial Margin of Safety Calculations

Naturalistic observations show that animals pre-empt danger by moving to locations that increase their success in avoiding future threats. To test this in humans, we created a spatial margin of safety (MOS) decision task that quantifies pre-emptive avoidance by measuring the distance subjects place themselves to safety when facing different threats whose attack locations vary in predictability. Behavioral results show that human participants place themselves closer to safe locations when facing threats that attack in spatial locations with more outliers. Using both univariate and multivariate pattern analysis (MVPA) on fMRI data collected during a 2 h session on participants of both sexes, we demonstrate a dissociable role for the vmPFC in MOS-related decision-making. MVPA results revealed that the posterior vmPFC encoded for more unpredictable threats with univariate analyses showing a functional coupling with the amygdala and hippocampus. Conversely, the anterior vmPFC was more active for the more predictable attacks and showed coupling with the striatum. Our findings converge in showing that during pre-emptive danger, the anterior vmPFC may provide a safety signal, possibly via foreseeable outcomes, while the posterior vmPFC drives unpredictable danger signals.

Exposure to 1-nitropyrene after weaning induces anxiety-like behavior partially by inhibiting steroid hormone synthesis in prefrontal cortex

1-Nitropyrene (1-NP) is a neurodevelopmental toxicant. This study was to evaluate the impact of exposure to 1-NP after weaning on anxiety-like behavior. Five-week-old mice were administered with 1-NP (0.1 or 1 mg/kg) daily for 4 weeks. Anxiety-like behaviour was measured using elevated-plus maze (EPM) and open field test (OFT). In EPM test, time spending in open arm and times entering open arm were reduced in 1-NP-treated mice. In OFT test, time spent in the center region and times entering the center region were diminished in 1-NP-treated mice. Prefrontal dendritic length and number of dendrite branches were decreased in 1-NP-treated mice. Prefrontal PSD95, an excitatory postsynaptic membrane protein, and gephyrin, an inhibitory postsynaptic membrane protein, were downregulated in 1-NP-treated mice. Further analysis showed that peripheral steroid hormones, including serum testosterone (T) and estradiol (E2), testicular T, and ovarian E2, were decreased in 1-NP-treated mice. Interestingly, T and E2 were diminished in 1-NP-treated prefrontal cortex. Prefrontal T and E2 synthases were diminished in 1-NP-treated mice. Mechanistically, GCN2-eIF2α, a critical pathway that regulates ribosomal protein translation, was activated in 1-NP-treated prefrontal cortex. These results indicate that exposure to 1-NP after weaning induces anxiety-like behaviour partially by inhibiting steroid hormone synthesis in prefrontal cortex.

Ventral subiculum promotes wakefulness through several pathways in male mice

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

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.

Evaluating the effects of tDCS on depressive and anxiety symptoms from a transdiagnostic perspective: a systematic review and meta-analysis of randomized controlled trials

Depressive and anxiety symptoms are prevalent among patients with various clinical conditions, resulting in diminished emotional well-being and impaired daily functioning. The neural mechanisms underlying these symptoms, particularly across different disorders, remain unclear, limiting the effectiveness of conventional treatments. Therefore, it is crucial to elucidate the neural underpinnings of depressive and anxiety symptoms and investigate novel, effective treatments across clinical conditions. Transcranial direct current stimulation (tDCS) is a neuromodulatory technique that can help understand the neural underpinnings of symptoms and facilitate the development of interventions, addressing the two research gaps at both neural and clinical levels. Thus, this systematic review and meta-analysis aims to evaluate the existing evidence regarding the therapeutic efficacy of tDCS in reducing depressive and anxiety symptoms among individuals with diverse clinical diagnoses. This review evaluated evidence from fifty-six randomized, sham-controlled trials that administered repeated tDCS sessions with a parallel design, applying a three-level meta-analytic model. tDCS targeting the left dorsolateral prefrontal cortex (DLPFC) at 2-mA intensity demonstrates moderate efficacy in alleviating depressive symptoms, identifying the left DLPFC as a transdiagnostic neural mechanism of depressive symptoms across clinical conditions. In comparison, the findings on anxiety symptoms demonstrate greater heterogeneity. tDCS over the left DLPFC is effective in reducing depressive symptoms and shows promising effects in alleviating anxiety symptoms among individuals with diverse diagnoses. These findings enhance our understanding of the neuropsychological basis of depressive and anxiety symptoms, laying the groundwork for the development of more effective tDCS interventions applicable across clinical conditions.

Apocynin Prevents Cigarette Smoke-Induced Anxiety-Like Behavior and Preserves Microglial Profiles in Male Mice

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death globally and is primarily caused by cigarette smoking (CS). Neurocognitive comorbidities such as anxiety and cognitive impairments are common among people with COPD. CS-induced lung inflammation and oxidative stress may "spill-over" into the systemic circulation, driving the onset of these comorbidities. We investigated whether a prophylactic treatment with the NADPH Oxidase 2 (NOX2) inhibitor, apocynin, could prevent CS-induced neurocognitive impairments. Adult male BALB/c mice were exposed to CS (9 cigarettes/day, 5 days/week) or room air (sham) for 8 weeks with co-administration of apocynin (5 mg/kg, intraperitoneal injection once daily) or vehicle (0.01% DMSO in saline). Following 7 weeks of CS exposure, mice underwent behavioral testing to assess recognition and spatial memory (novel object recognition and Y maze, respectively) and anxiety-like behaviors (open field and elevated plus maze). Mice were then euthanized, and blood, lungs, and brains were collected. Apocynin partially improved CS-induced lung neutrophilia and reversed systemic inflammation (C-reactive protein) and oxidative stress (malondialdehyde). Apocynin exerted an anxiolytic effect in CS-exposed mice, which was associated with restored microglial profiles within the amygdala and hippocampus. Thus, targeting oxidative stress using apocynin can alleviate anxiety-like behaviors and could represent a novel strategy for managing COPD-related anxiety disorders.

Prefrontal Regulation of Social Behavior and Related Deficits: Insights From Rodent Studies

The prefrontal cortex (PFC) is well known as the executive center of the brain, combining internal states and goals to execute purposeful behavior, including social actions. With the advancement of tools for monitoring and manipulating neural activity in rodents, substantial progress has been made in understanding the specific cell types and neural circuits within the PFC that are essential for processing social cues and influencing social behaviors. Furthermore, combining these tools with translationally relevant behavioral paradigms has also provided novel insights into the PFC neural mechanisms that may contribute to social deficits in various psychiatric disorders. This review highlights findings from the past decade that have shed light on the PFC cell types and neural circuits that support social information processing and distinct aspects of social behavior, including social interactions, social memory, and social dominance. We also explore how the PFC contributes to social deficits in rodents induced by social isolation, social fear conditioning, and social status loss. These studies provide evidence that the PFC uses both overlapping and unique neural mechanisms to support distinct components of social cognition. Furthermore, specific PFC neural mechanisms drive social deficits induced by different contexts.

Serotonergic psychedelic 5-MeO-DMT alters plasticity-related gene expression and generates anxiolytic effects in stressed mice

Serotonergic psychedelics have potential therapeutic effects in treating anxiety and mood disorders, often after a single dose, and are suggested to have plasticity-inducing action. However, a comprehensive mechanism of action is still lacking. Here, we investigated how a single dose of the short-acting 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) acts on gene expression from microdissected brain regions (anterior cingulate cortex - ACC; basolateral amygdala - BLA; ventral hippocampus CA1 region - vCA1 and dentate gyrus-DG) of naive and stressed mice. Specifically, we compared gene expression of Arc, Zif268, BDNF, CREB, mTORC1, NR2A, TRIP8b, and NFkB in mice injected with 5-MeO-DMT or saline at different time points (1 h, 5 h, or 5 days prior). 5-MeO-DMT altered mRNA expression of immediate early genes Arc and ZiF268 in the ACC, BLA, and vCA1, while NR2A expression was decreased after 5 h in the vCA1. We also found a long-term increase in TRIP8b, a gene related to the modulation of neuronal activity, in the vCA1 after 5 days. Behaviorally, 5-MeO-DMT treated mice showed mixed anxiolytic and anxiogenic effects in the elevated plus maze and open field test 24 h or 5 days after treatment. However, pre-treated mice subjected to acute stress showed both lower corticosterone levels and robust anxiolytic effects of 5-MeO-DMT administration. Together, our findings provide insights into the molecular actions of 5-MeO-DMT in the brain related to anxiolytic effects of behavior.

Impaired neuronal macroautophagy in the prelimbic cortex contributes to comorbid anxiety-like behaviors in rats with chronic neuropathic pain

A large proportion of patients with chronic pain experience co-morbid anxiety. The medial prefrontal cortex (mPFC) is proposed to underlie this comorbidity, but the molecular and neuronal mechanisms are not fully understood. Here, we reported that impaired neuronal macroautophagy in the prelimbic cortical (PrL) subregion of the mPFC paralleled the occurrence of anxiety-like behaviors in rats with chronic spared nerve injury (SNI). Intriguingly, such macroautophagy impairment was mainly observed in a FOS/c-Fos+ neuronal subpopulation in the PrL. Chemogenetic inactivation of this comorbid anxiety-related neuronal ensemble relieved pain-induced anxiety-like behaviors. Rescuing macroautophagy impairment in this neuronal ensemble relieved chronic pain-associated anxiety and mechanical allodynia and restored synaptic homeostasis at the molecular level. By contrast, artificial disruption of macroautophagy induced early-onset co-morbid anxiety in neuropathic rats, but not general anxiety in normal rats. Taken together, our work identifies causal linkage between PrL neuronal macroautophagy dysfunction and comorbid anxiety in neuropathic pain and provides novel insights into the role of PrL by differentiating its contribution in pain-induced comorbid anxiety from its modulation over general anxiety-like behaviors.Abbreviation: AAV: adeno-associated viruses; ACC: anterior cingulate cortex; ATG5: autophagy related 5; ATG7: autophagy related 7; ATG12: autophagy related 12; CAMK2/CaMKII: calcium/calmodulin-dependent protein kinase II; CNO: clozapine-N-oxide; CQ: chloroquine; DIA: data independent acquisition; DIO: double floxed inverse orf; DLG4/PSD-95: discs large MAGUK scaffold protein 4; Dox: doxycycline; GABA: γ-aminobutyric acid; GFP: green fluorescent protein; GO: gene ontology; Gi: inhibitory guanine nucleotide-binding proteins; HsCHRM4/M4D: human cholinergic receptor muscarinic 4; HsSYN: human synapsin; KEGG: Kyoto encyclopedia of genes and genomes; LAMP1: lysosomal-associated membrane protein 1; LC3-II: PE conjugated microtubule-associated protein 1 light chain3; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mPFC: medial prefrontal cortex; P2A: 2A self-cleaving peptide; PPI: protein-protein interaction networks; PrL: prelimbic cortex; RBFOX3/NeuN: RNA binding protein, fox-1 homolog (C. elegans) 3; rtTA: reverse tetracycline-transactivator; SDS-PAGE: sodium dodecylsulfate-polyacrylamide gel electrophoresis; SHANK3: SH3 and multiple ankyrin repeat domains 3; SLC1A1/EAAC1: solute carrier family 1 (neuronal/epithelial high affinity glutamate transporter, systemXag), member 1; SNAP23: synaptosomal-associated protein 23; SNI:spared nerve injury; SQSTM1/p62: sequestosome 1; SYT3: synaptotagmin 3; TRE: tetracycline-responsive element; TRE3G: third-generation tetracycline-responsive element.

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.

Neural basis of cognitive control signals in anterior cingulate cortex during delay discounting

Cognitive control involves allocating cognitive effort according to internal needs and task demands and the Anterior Cingulate Cortex (ACC) is hypothesized to play a central role in this process. We investigated the neural basis of cognitive control in the ACC of rats performing an adjusting-amount delay discounting task. Decision-making in this this task can be guided by using either a lever-value tracking strategy, requiring a 'resource-based' form of cognitive effort or a lever-biased strategy requiring a 'resistance-based' form of cognitive effort. We found that ACC ensembles always tightly tracked lever value on each trial, indicative of a resource-based control signal. These signals were prevalent in the neural recordings and were influenced by the delay. A shorter delay was associated with devaluing of the immediate option and a longer delay was associated with overvaluing of the immediate option. In addition, ACC theta (6-12Hz) oscillations were observed at the choice point of rats exhibiting a resistance-based strategy. These data provide candidates of neural activity patterns in the ACC that underlie the use of 'resource-based' and 'resistance-based' cognitive effort. Furthermore, these data illustrate how strategies can be engaged under different conditions in individual subjects.

Reconfiguration of Behavioral Signals in the Anterior Cingulate Cortex Based on Emotional State

Behaviors and their execution depend on the context and emotional state in which they are performed. The contextual modulation of behavior likely relies on regions such as the anterior cingulate cortex (ACC) that multiplex information about emotional/autonomic states and behaviors. The objective of the present study was to understand how the representations of behaviors by ACC neurons become modified when performed in different emotional states. A pipeline of machine learning techniques was developed to categorize and classify complex, spontaneous behaviors in male rats from the video. This pipeline, termed Hierarchical Unsupervised Behavioural Discovery Tool (HUB-DT), discovered a range of statistically separable behaviors during a task in which motivationally significant outcomes were delivered in blocks of trials that created three unique "emotional contexts." HUB-DT was capable of detecting behaviors specific to each emotional context and was able to identify and segregate the portions of a neural signal related to a behavior and to emotional context. Overall, ∼10× as many neurons responded to behaviors in a contextually dependent versus a fixed manner, highlighting the extreme impact of emotional state on representations of behaviors that were precisely defined based on detailed analyses of limb kinematics. This type of modulation may be a key mechanism that allows the ACC to modify the behavioral output based on emotional states and contextual demands.

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

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

Functional connectivity changes of the hippocampal subregions in anti-N-methyl-D-aspartate receptor encephalitis

The hippocampus plays an important role in the pathophysiological mechanism of Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis. Nevertheless, the connection between the resting-state activity of the hippocampal subregions and neuropsychiatric disorders in patients remains unclear. This study aimed to explore the changes in functional connectivity (FC) in the hippocampal subregions of patients with anti-NMDAR encephalitis and its association with clinical symptoms and cognitive performance. Twenty-three patients with anti-NMDAR encephalitis and 23 healthy controls (HC) were recruited. All participants underwent resting-state functional magnetic resonance imaging (rs-fMRI) scans and completed clinical cognitive scales. Based on the Brainnetome Atlas, the rostral (anterior) and caudal (posterior) hippocampi of both the left and right hemispheres were selected as regions of interest (ROIs) for FC analysis. First, a one-sample t-test was used to observe the whole-brain connectivity distribution of hippocampal subregions within the patient and HC groups at a threshold of p < 0.05. The two-sample t-test was used to compare the differences in hippocampal ROIs connectivity between groups, followed by a partial correlation analysis between the FC values of brain regions with statistical differences and clinical variables. This study observed that the distribution of whole-brain functional connectivity in the rostral and caudal hippocampi aligned with the connectivity differences between the anterior and posterior hippocampi. Compared to the HC group, the patients showed significantly decreased FC between the bilateral rostral hippocampus and the left inferior orbitofrontal gyrus and between the right rostral hippocampus and the right cerebellum. However, a significant increase in FC was observed between the right rostral hippocampus and left superior temporal gyrus, the left caudal hippocampus and right superior frontal gyrus, and the right caudal hippocampus and left gyrus rectus. Partial correlation analysis showed that FC between the left inferior orbitofrontal gyrus and the right rostral hippocampus was significantly negatively correlated with the California Verbal Learning Test (CVLT) and Brief Visuospatial Memory Test (BVMT) scores. The FC between the right rostral hippocampus and the left superior temporal gyrus was negatively correlated with BVMT scores. FC abnormalities in the hippocampal subregions of patients with anti-NMDAR encephalitis were associated with cognitive impairment, emotional changes, and seizures. These results may help explain the pathophysiological mechanisms and clinical manifestations of anti-NMDAR encephalitis and NMDAR dysfunction-related diseases such as schizophrenia.

Selective vulnerability of the ventral hippocampus-prelimbic cortex axis parvalbumin interneuron network underlies learning deficits of fragile X mice

High-penetrance mutations affecting mental health can involve genes ubiquitously expressed in the brain. Whether the specific patterns of dysfunctions result from ubiquitous circuit deficits or might reflect selective vulnerabilities of targetable subnetworks has remained unclear. Here, we determine how loss of ubiquitously expressed fragile X mental retardation protein (FMRP), the cause of fragile X syndrome, affects brain networks in Fmr1y/- mice. We find that in wild-type mice, area-specific knockout of FMRP in the adult mimics behavioral consequences of area-specific silencing. By contrast, the functional axis linking the ventral hippocampus (vH) to the prelimbic cortex (PreL) is selectively affected in constitutive Fmr1y/- mice. A chronic alteration in late-born parvalbumin interneuron networks across the vH-PreL axis rescued by VIP signaling specifically accounts for deficits in vH-PreL theta-band network coherence, ensemble assembly, and learning functions of Fmr1y/- mice. Therefore, vH-PreL axis function exhibits a selective vulnerability to loss of FMRP in the vH or PreL, leading to learning and memory dysfunctions in fragile X mice.

Jnk1 and downstream signalling hubs regulate anxiety-like behaviours in a zebrafish larvae phenotypic screen

Current treatments for anxiety and depression show limited efficacy in many patients, indicating the need for further research into the underlying mechanisms. JNK1 has been shown to regulate anxiety- and depressive-like behaviours in mice, however the effectors downstream of JNK1 are not known. Here we compare the phosphoproteomes from wild-type and Jnk1-/- mouse brains and identify JNK1-regulated signalling hubs. We next employ a zebrafish (Danio rerio) larvae behavioural assay to identify an antidepressant- and anxiolytic-like (AA) phenotype based on 2759 measured stereotypic responses to clinically proven antidepressant and anxiolytic (AA) drugs. Employing machine learning, we classify an AA phenotype from extracted features measured during and after a startle battery in fish exposed to AA drugs. Using this classifier, we demonstrate that structurally independent JNK inhibitors replicate the AA phenotype with high accuracy, consistent with findings in mice. Furthermore, pharmacological targeting of JNK1-regulated signalling hubs identifies AKT, GSK-3, 14-3-3 ζ/ε and PKCε as downstream hubs that phenocopy clinically proven AA drugs. This study identifies AKT and related signalling molecules as mediators of JNK1-regulated antidepressant- and anxiolytic-like behaviours. Moreover, the assay shows promise for early phase screening of compounds with anti-stress-axis properties and for mode of action analysis.

Dissociable contributions of the amygdala and ventral hippocampus to stress-induced changes in defensive behavior

BACKGROUND

Severe stress can produce multiple persistent changes in defensive behavior relevant to psychiatric illness. While much is known about the circuits supporting stress-induced associative fear, how stress-induced circuit plasticity supports non-associative changes in defensive behavior remains unclear.

METHODS

Mice were exposed to an acute severe stressor, and subsequently, both associative and non-associative defensive behavioral responses were assessed. A mixture of local protein synthesis inhibition, pan-neuronal chemogenetic inhibition, and projection-specific chemogenetic inhibition were utilized to isolate the roles of the basolateral amygdala (BLA) and ventral hippocampus (vHC) to the induction and expression of associative and non-associative defensive behavioral changes.

RESULTS

Stress-induced protein synthesis in the BLA was necessary for enhancements in stress sensitivity but not enhancements in anxiety-related behaviors, whereas protein synthesis in the vHC was necessary for enhancements in anxiety-related behavior but not enhancements in stress sensitivity. Like protein synthesis, neuronal activity of the BLA and vHC were found to differentially support the expression of these same defensive behaviors. Additionally, projection-specific inhibition of BLA-vHC connections failed to alter these behaviors, indicating that these defensive behaviors are regulated by distinct BLA and vHC circuits. Lastly, contributions of the BLA and vHC to stress sensitivity and anxiety-related behavior were independent of their contributions to associative fear.

CONCLUSIONS

Stress-induced plasticity in the BLA and vHC were found to support dissociable non-associative behavioral changes, with BLA supporting enhancements in stress sensitivity and vHC supporting increased anxiety-related behavior. These findings demonstrate that independent BLA and vHC circuits are critical for stress-induced defensive behaviors, and that differential targeting of BLA and vHC circuits may be needed in disease treatment.

The chemokine XCL1 functions as a pregnancy hormone to program offspring innate anxiety

Elevated levels of cytokines in maternal circulation increase the offspring's risk for neuropsychiatric disease. Because of their low homeostatic levels, circulating maternal cytokines during normal pregnancies have not been considered to play a role in fetal brain development and offspring behavior. Here we report that the T/NK cell chemotactic cytokine XCL1, a local paracrine immune signal, can function as a pregnancy hormone and is required for the proper development of placenta and male offspring approach-avoidance behavior. We found that circulating XCL1 levels were at a low pregestational level throughout pregnancy except for a midgestational rise and fall. Blunted elevation in maternal plasma XCL1 in dams with a genetic 5HT1A receptor deficit or following neutralization by anti-XCL1 antibodies increased the expression of tissue damage associated factors in WT fetal placenta and led to increased innate anxiety and stress reactivity in the WT male offspring. Therefore, chemokines like XCL1 may act as pregnancy hormones to regulate placenta development and offspring emotional behavior.

Integration of Prior Expectations and Suppression of Prediction Errors During Expectancy-Induced Pain Modulation: The Influence of Anxiety and Pleasantness

Pain perception arises from the integration of prior expectations with sensory information. Although recent work has demonstrated that treatment expectancy effects (e.g., placebo hypoalgesia) can be explained by a Bayesian integration framework incorporating the precision level of expectations and sensory inputs, the key factor modulating this integration in stimulus expectancy-induced pain modulation remains unclear. In a stimulus expectancy paradigm combining emotion regulation in healthy male and female adults, we found that participants' voluntary reduction in anticipatory anxiety and pleasantness monotonically reduced the magnitude of pain modulation by negative and positive expectations, respectively, indicating a role of emotion. For both types of expectations, Bayesian model comparisons confirmed that an integration model using the respective emotion of expectations and sensory inputs explained stimulus expectancy effects on pain better than using their respective precision. For negative expectations, the role of anxiety is further supported by our fMRI findings that (1) functional coupling within anxiety-processing brain regions (amygdala and anterior cingulate) reflected the integration of expectations with sensory inputs and (2) anxiety appeared to impair the updating of expectations via suppressed prediction error signals in the anterior cingulate, thus perpetuating negative expectancy effects. Regarding positive expectations, their integration with sensory inputs relied on the functional coupling within brain structures processing positive emotion and inhibiting threat responding (medial orbitofrontal cortex and hippocampus). In summary, different from treatment expectancy, pain modulation by stimulus expectancy emanates from emotion-modulated integration of beliefs with sensory evidence and inadequate belief updating.

Amygdala-hippocampus somatostatin interneuron beta-synchrony underlies a cross-species biomarker of emotional state

Emotional responses arise from limbic circuits including the hippocampus and amygdala. In the human brain, beta-frequency communication between these structures correlates with self-reported mood and anxiety. However, both the mechanism and significance of this biomarker as a readout vs. driver of emotional state remain unknown. Here, we show that beta-frequency communication between ventral hippocampus and basolateral amygdala also predicts anxiety-related behavior in mice, both on long timescales (∼30 min) and immediately preceding behavioral choices. Genetically encoded voltage indicators reveal that this biomarker reflects synchronization between somatostatin interneurons across both structures. Indeed, synchrony between these neurons dynamically predicts approach-avoidance decisions, and optogenetically shifting the phase of synchronization by just 25 ms is sufficient to bidirectionally modulate anxiety-related behaviors. Thus, back-translation establishes a human biomarker as a causal determinant (not just predictor) of emotional state, revealing a novel mechanism whereby interregional synchronization that is frequency, phase, and cell type specific controls emotional processing.

Dynamic effects of ventral hippocampal NRG3/ERBB4 signaling on nicotine withdrawal-induced responses

Tobacco smoking remains a leading cause of preventable death in the United States, with approximately a 5% success rate for smokers attempting to quit. High relapse rates have been linked to several genetic factors, indicating that the mechanistic relationship between genes and drugs of abuse is a valuable avenue for the development of novel smoking cessation therapies. For example, various single nucleotide polymorphisms (SNPs) in the gene for neuregulin 3 (NRG3) and its cognate receptor, the receptor tyrosine-protein kinase erbB-4 (ERBB4), have been linked to nicotine addiction. Our lab has previously shown that ERBB4 plays a role in anxiety-like behavior during nicotine withdrawal (WD); however, the neuronal mechanisms and circuit-specific effects of NRG3-ERBB4 signaling during nicotine and WD are unknown. The present study utilizes genetic, biochemical, and functional approaches to examine the anxiety-related behavioral and functional role of NRG3-ERBB4 signaling, specifically in the ventral hippocampus (VH) of male and female mice. We report that 24hWD from nicotine is associated with altered synaptic expression of VH NRG3 and ERBB4, and genetic disruption of VH ErbB4 leads to an elimination of anxiety-like behaviors induced during 24hWD. Moreover, we observed attenuation of GABAergic transmission as well as alterations in Ca2+-dependent network activity in the ventral CA1 area of VH ErbB4 knock-down mice during 24hWD. Our findings further highlight contributions of the NRG3-ERBB4 signaling pathway to anxiety-related behaviors seen during nicotine WD.

Association between resting-state connectivity patterns in the defensive system network and treatment response in spider phobia-a replication approach

Although highly effective on average, exposure-based treatments do not work equally well for all patients with anxiety disorders. The identification of pre-treatment response-predicting patient characteristics may enable patient stratification. Preliminary research highlights the relevance of inhibitory fronto-limbic networks as such. We aimed to identify pre-treatment neural signatures differing between exposure treatment responders and non-responders in spider phobia and to validate results through rigorous replication. Data of a bi-centric intervention study comprised clinical phenotyping and pre-treatment resting-state functional connectivity (rsFC) data of n = 79 patients with spider phobia (discovery sample) and n = 69 patients (replication sample). RsFC data analyses were accomplished using the Matlab-based CONN-toolbox with harmonized analyses protocols at both sites. Treatment response was defined by a reduction of >30% symptom severity from pre- to post-treatment (Spider Phobia Questionnaire Score, primary outcome). Secondary outcome was defined by a reduction of >50% in a Behavioral Avoidance Test (BAT). Mean within-session fear reduction functioned as a process measure for exposure. Compared to non-responders and pre-treatment, results in the discovery sample seemed to indicate that responders exhibited stronger negative connectivity between frontal and limbic structures and were characterized by heightened connectivity between the amygdala and ventral visual pathway regions. Patients exhibiting high within-session fear reduction showed stronger excitatory connectivity within the prefrontal cortex than patients with low within-session fear reduction. Whereas these results could be replicated by another team using the same data (cross-team replication), cross-site replication of the discovery sample findings in the independent replication sample was unsuccessful. Results seem to support negative fronto-limbic connectivity as promising ingredient to enhance response rates in specific phobia but lack sufficient replication. Further research is needed to obtain a valid basis for clinical decision-making and the development of individually tailored treatment options. Notably, future studies should regularly include replication approaches in their protocols.

Obesogenic diet induces circuit-specific memory deficits in mice

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

Di (2-ethylhexyl) phthalate alters neurobehavioral responses and oxidative status, architecture, and GFAP and BDNF signaling in juvenile rat's brain: Protective role of Coenzyme10

Di-(2-ethylhexyl) phthalate (DEHP), a phthalate plasticizer, is widely spread in the environment, presenting hazards to human health and food safety. Hence, this study examined the probable preventive role of coenzyme10 (CQ10) (10 mg/kg.b.wt) against DEHP (500 mg/kg.wt) - induced neurotoxic and neurobehavioral impacts in juvenile (34 ± 1.01g and 3 weeks old) male Sprague Dawley rats in 35-days oral dosing trial. The results indicated that CQ10 significantly protected against DEHP-induced memory impairment, anxiety, depression, spatial learning disorders, and repetitive/stereotypic-like behavior. Besides, the DEHP-induced depletion in dopamine and gamma amino butyric acid levels was significantly restored by CQ10. Moreover, CQ10 significantly protected against the exhaustion of CAT, GPx, SOD, GSH, and GSH/GSSG ratio, as well as the increase in malondialdehyde, Caspas-3, interleukin-6, and tumor necrosis factor-alpha brain content accompanying with DEHP exposure. Furthermore, CQ10 significantly protected the brain from the DEHP-induced neurodegenerative alterations. Also, the increased immunoexpression of brain-derived neurotrophic factor, not glial fibrillary acidic protein, in the cerebral, hippocampal, and cerebellar brain tissues due to DEHP exposure was alleviated with CQ10. This study's findings provide conclusive evidence that CQ10 has the potential to be used as an efficient natural protective agent against the neurobehavioral and neurotoxic consequences of DEHP.

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

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

Projection-Targeted Photopharmacology Reveals Distinct Anxiolytic Roles for Presynaptic mGluR2 in Prefrontal- and Insula-Amygdala Synapses

Dissecting how membrane receptors regulate neural circuit function is critical for deciphering basic principles of neuromodulation and mechanisms of therapeutic drug action. Classical pharmacological and genetic approaches are not well-equipped to untangle the roles of specific receptor populations, especially in long-range projections which coordinate communication between brain regions. Here we use viral tracing, electrophysiological, optogenetic, and photopharmacological approaches to determine how presynaptic metabotropic glutamate receptor 2 (mGluR2) activation in the basolateral amygdala (BLA) alters anxiety-related behavior. We find that mGluR2-expressing neurons from the ventromedial prefrontal cortex (vmPFC) and posterior insular cortex (pIC) preferentially target distinct cell types and subregions of the BLA to regulate different forms of avoidant behavior. Using projection-specific photopharmacological activation, we find that mGluR2-mediated presynaptic inhibition of vmPFC-BLA, but not pIC-BLA, connections can produce long-lasting decreases in spatial avoidance. In contrast, presynaptic inhibition of pIC-BLA connections decreased social avoidance, novelty-induced hypophagia, and increased exploratory behavior without impairing working memory, establishing this projection as a novel target for the treatment of anxiety disorders. Overall, this work reveals new aspects of BLA neuromodulation with therapeutic implications while establishing a powerful approach for optical mapping of drug action via photopharmacology.

Hippocampal Involvement in Safety Signal Learning Varies With Anxiety Among Healthy Adults

Background

Safety signal learning (SSL), based on conditioned inhibition of fear in the presence of learned safety, can effectively attenuate threat responses in animal models and humans. Difficulty regulating threat responses is a core feature of anxiety disorders, suggesting that SSL may provide a novel mechanism for fear reduction. Cross-species evidence suggests that SSL involves functional connectivity between the anterior hippocampus and the dorsal anterior cingulate cortex. However, the neural mechanisms supporting SSL have not been examined in relation to trait anxiety or while controlling for the effect of novelty.

Methods

Here, we investigated the neural mechanisms involved in SSL and associations with trait anxiety in a sample of 64 healthy (non-clinically anxious) adults (ages 18-30 years; 43 female, 21 male) using physiological, behavioral, and neuroimaging (functional magnetic resonance imaging) data collected during an SSL task.

Results

During SSL, compared with individuals with lower trait anxiety, individuals with higher trait anxiety showed less fear reduction as well as altered hippocampal activation and hippocampal-dorsal anterior cingulate cortex functional connectivity, and lower inferior frontal gyrus and ventrolateral prefrontal cortex activation. Importantly, the findings show that SSL reduces threat responding, across learning and over and above the effect of novelty, and involves hippocampal activation.

Conclusions

These findings provide new insights into the nature of SSL and suggest that there may be meaningful variation in SSL and related neural correlates as a function of trait anxiety, with implications for better understanding fear reduction and optimizing interventions for individuals with anxiety disorders.

Temporal association activates projections from the perirhinal cortex and ventral CA1 to the prelimbic cortex and from the prelimbic cortex to the basolateral amygdala

In trace fear conditioning, the prelimbic cortex exhibits persistent activity during the interval between the conditioned and unconditioned stimuli, which maintains a conditioned stimulus representation. Regions cooperating for this function or encoding the conditioned stimulus before the interval could send inputs to the prelimbic cortex, supporting learning. The basolateral amygdala has conditioned stimulus- and unconditioned stimulus-responsive neurons, convergently activated. The prelimbic cortex could directly project to the basolateral amygdala to associate the transient memory of the conditioned stimulus with the unconditioned stimulus. We investigated the neuronal circuit supporting temporal associations using contextual fear conditioning with a 5-s interval, in which 5 s separates the contextual conditioned stimulus from the unconditioned stimulus. Injecting retrobeads, we quantified c-Fos in prelimbic cortex- or basolateral amygdala-projecting neurons from 9 regions after contextual fear conditioning with a 5-s interval or contextual fear conditioning, in which the conditioned and unconditioned stimuli overlap. The contextual fear conditioning with a 5-s interval activated ventral CA1 and perirhinal cortex neurons projecting to the prelimbic cortex and prelimbic cortex neurons projecting to basolateral amygdala. Both fear conditioning activated ventral CA1 and lateral entorhinal cortex neurons projecting to basolateral amygdala and basolateral amygdala neurons projecting to prelimbic cortex. The perirhinal cortex → prelimbic cortex and ventral CA1 → prelimbic cortex connections are the first identified prelimbic cortex afferent projections participating in temporal associations. These results help to understand time-linked memories, a process required in episodic and working memories.

Removal of a partial genomic duplication restores synaptic transmission and behavior in the MyosinVA mutant mouse Flailer

BACKGROUND

Copy number variations, and particularly duplications of genomic regions, have been strongly associated with various neurodegenerative conditions including autism spectrum disorder (ASD). These genetic variations have been found to have a significant impact on brain development and function, which can lead to the emergence of neurological and behavioral symptoms. Developing strategies to target these genomic duplications has been challenging, as the presence of endogenous copies of the duplicate genes often complicates the editing strategies.

RESULTS

Using the ASD and anxiety mouse model Flailer, which contains a partial genomic duplication working as a dominant negative for MyoVa, we demonstrate the use of DN-CRISPRs to remove a 700 bp genomic region in vitro and in vivo. Importantly, DN-CRISPRs have not been used to remove genomic regions using sgRNA with an offset greater than 300 bp. We found that editing the flailer gene in primary cortical neurons reverts synaptic transport and transmission defects. Moreover, long-term depression (LTD), disrupted in Flailer animals, is recovered after gene editing. Delivery of DN-CRISPRs in vivo shows that local delivery to the ventral hippocampus can rescue some of the mutant behaviors, while intracerebroventricular delivery, completely recovers the Flailer animal phenotype associated to anxiety and ASD.

CONCLUSIONS

Our results demonstrate the potential of DN-CRISPR to efficiently remove larger genomic duplications, working as a new gene therapy approach for treating neurodegenerative diseases.

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

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

High emotional reactivity is associated with activation of a molecularly distinct hippocampal-amygdala circuit modulated by the glucocorticoid receptor

Emotions are characterized not only by their valence but also by whether they are stable or labile. Yet, we do not understand the molecular or circuit mechanisms that control the dynamic nature of emotional responses. We have shown that glucocorticoid receptor overexpression in the forebrain (GRov) leads to a highly reactive mouse with increased anxiety behavior coupled with greater swings in emotional responses. This phenotype is established early in development and persists into adulthood. However, the neural circuitry mediating this lifelong emotional lability remains unknown. In the present study, optogenetic stimulation in ventral dentate gyrus (vDG) of GRov mice led to a greater range and a prolonged duration of anxiety behavior. cFos expression analysis showed that the amplified behavioral response to vDG activation in GRov mice is coupled to increased neuronal activity in specific brain regions. Relative to wild type mice, GRov mice displayed glutamatergic/GABAergic activation imbalance in ventral CA1 (vCA1) and selectively increased glutamatergic activation in the basal posterior amygdaloid complex. Moreover, forebrain GR overexpression led to increased activation of molecularly distinct subpopulations of neurons within the hippocampus and the posterior basolateral amygdala (pBLA) as evident from the increased cFos co-labeling in the calbindin1+ glutamatergic neurons in vCA1 and in the DARPP-32/Ppp1r1b+ glutamatergic neurons in pBLA. We propose that a molecularly distinct hippocampal-amygdala circuit is shaped by stress early in life and tunes the dynamics of emotional responses.

The role of the hippocampus in the consolidation of emotional memories during sleep

Episodic memory relies on the hippocampus, a heterogeneous brain region with distinct functions. Spatial representations in the dorsal hippocampus (dHPC) are crucial for contextual memory, while the ventral hippocampus (vHPC) is more involved in emotional processing. Here, we review the literature in rodents highlighting the anatomical and functional properties of the hippocampus along its dorsoventral axis that underlie its role in contextual and emotional memory encoding, consolidation, and retrieval. We propose that the coordination between the dorsal and vHPC through theta oscillations during rapid eye movement (REM) sleep, and through sharp-wave ripples during non-REM (NREM) sleep, might facilitate the transfer of contextual information for integration with valence-related processing in other structures of the network. Further investigation into the physiology of the vHPC and its connections with other brain areas is needed to deepen the current understanding of emotional memory consolidation during sleep.

Effect of Human Infant Gut Microbiota on Mouse Behavior, Dendritic Complexity, and Myelination

The mammalian gut microbiome influences numerous developmental processes. In human infants it has been linked with cognition, social skills, hormonal responses to stress, and brain connectivity. Yet, these associations are not necessarily causal. The present study tested whether two microbial stool communities, common in human infants, affected behavior, myelination, dendritic morphology, and spine density when used to colonize mouse models. Humanized animals were more like specific-pathogen free mice than germ-free mice for most phenotypes, although in males, both humanized groups were less social. Both humanized groups had thinner myelin sheaths in the hippocampus, than did germ-free animals. Humanized animals were similar to each other except for dendritic morphology and spine density where one group had greater dendritic length in the prefrontal cortex, greater dendritic volume in the nucleus accumbens, and greater spine density in both regions, compared to the other. Results add to a body of literature suggesting the gut microbiome impacts brain development.

Teaser

Fecal transplants from human infants with highly abundant Bifidobacterium , an important inhabitant of the intestinal tract of breastfed newborns, may promote brain connectivity in mice.

Pathway specific interventions reveal the multiple roles of ventral hippocampus projections in cognitive functions

Since the 1950s study of Scoville and Milner on the case H.M., the hippocampus has attracted neuroscientists' attention. The hippocampus has been traditionally divided into dorsal and ventral parts, each of which projects to different brain structures and mediates various functions. Despite a predominant interest in its dorsal part in animal models, especially regarding episodic-like and spatial cognition, recent data highlight the role of the ventral hippocampus (vHPC), as the main hippocampal output, in cognitive processes. Here, we review recent studies conducted in rodents that have used advanced in vivo functional techniques to specifically monitor and manipulate vHPC efferent pathways and delineate the roles of these specific projections in learning and memory processes. Results highlight that vHPC projections to basal amygdala are implicated in emotional memory, to nucleus accumbens in social memory and instrumental actions and to prefrontal cortex in all the above as well as in object-based memory. Some of these hippocampal projections also modulate feeding and anxiety-like behaviours providing further evidence that the "one pathway-one function" view is outdated and future directions are proposed to better understand the role of hippocampal pathways and shed further light on its connectivity and function.

Context-invariant socioemotional encoding by prefrontal ensembles

The prefrontal cortex plays a key role in social interactions, anxiety-related avoidance, and flexible context- dependent behaviors, raising the question: how do prefrontal neurons represent socioemotional information across different environments? Are contextual and socioemotional representations segregated or intermixed, and does this cause socioemotional encoding to remap or generalize across environments? To address this, we imaged neuronal activity in the medial prefrontal cortex of mice engaged in social interactions or anxiety-related avoidance within different environments. Neuronal ensembles representing context and social interaction overlapped more than expected while remaining orthogonal. Anxiety-related representations similarly generalized across environments while remaining orthogonal to contextual information. This shows how prefrontal cortex multiplexes parallel information streams using the same neurons, rather than distinct subcircuits, achieving context-invariant encoding despite context-specific reorganization of population-level activity.

Thalamic nucleus reuniens coordinates prefrontal-hippocampal synchrony to suppress extinguished fear

Traumatic events result in vivid and enduring fear memories. Suppressing the retrieval of these memories is central to behavioral therapies for pathological fear. The medial prefrontal cortex (mPFC) and hippocampus (HPC) have been implicated in retrieval suppression, but how mPFC-HPC activity is coordinated during extinction retrieval is unclear. Here we show that after extinction training, coherent theta oscillations (6-9 Hz) in the HPC and mPFC are correlated with the suppression of conditioned freezing in male and female rats. Inactivation of the nucleus reuniens (RE), a thalamic hub interconnecting the mPFC and HPC, reduces extinction-related Fos expression in both the mPFC and HPC, dampens mPFC-HPC theta coherence, and impairs extinction retrieval. Conversely, theta-paced optogenetic stimulation of RE augments fear suppression and reduces relapse of extinguished fear. Collectively, these results demonstrate a role for RE in coordinating mPFC-HPC interactions to suppress fear memories after extinction.

Rewarded Maze Training Increases Approach Behavior in Rats Through Neurogenesis-Dependent Growth of Ventral Hippocampus-Prelimbic Circuits

Background

Learning complex navigation routes increases hippocampal volume in humans, but it is not clear whether this growth impacts behaviors outside the learning situation or what cellular mechanisms are involved.

Methods

We trained rats with pharmacogenetic suppression of adult neurogenesis and littermate controls in 3 mazes over 3 weeks and tested novelty approach behavior several days after maze exposure. We then measured hippocampus and prelimbic cortex volumes using magnetic resonance imaging and assessed neuronal and astrocyte morphology. Finally, we investigated the activation and behavioral role of the ventral CA1 (vCA1)-to-prelimbic pathway using immediate-early genes and DREADDs (designer receptors exclusively activated by designer drugs).

Results

Maze training led to volume increase of both the vCA1 region of the hippocampus and the prelimbic region of the neocortex compared with rats that followed fixed paths. Growth was also apparent in individual neurons and astrocytes in these 2 regions, and behavioral testing showed increased novelty approach in maze-trained rats in 2 different tests. Suppressing adult neurogenesis prevented the effects on structure and approach behavior after maze training without affecting maze learning itself. The vCA1 neurons projecting to the prelimbic area were more activated by novelty in maze-trained animals, and suppression of this pathway decreased approach behavior.

Conclusions

Rewarded navigational learning experiences induce volumetric and morphologic growth in the vCA1 and prelimbic cortex and enhance activation of the circuit connecting these 2 regions. Both the structural and behavioral effects of maze training require ongoing adult neurogenesis, suggesting a role for new neurons in experience-driven increases in novelty exploration.

Ventral CA1 Population Codes for Anxiety

The ventral hippocampus is a critical node in the distributed brain network that controls anxiety. Using miniature microscopy and calcium imaging, we recorded ventral CA1 (vCA1) neurons in freely moving mice as they explored variants of classic behavioral assays for anxiety. Unsupervised behavioral segmentation revealed clusters of behavioral motifs that corresponded to exploratory and vigilance-like states. We discovered multiple vCA1 population codes that represented the anxiogenic features of the environment, such as bright light and openness, as well as the moment-to-moment anxiety state of the animals. These population codes possessed distinct generalization properties: neural representations of anxiogenic features were different for open field and elevated plus/zero maze tasks, while neural representations of moment-to-moment anxiety state were similar across both experimental contexts. Our results suggest that anxiety is not tied to the aversive compartments of these mazes but is rather defined by a behavioral state and its corresponding population code that generalizes across environments.

Transmembrane protein 184B (TMEM184B) promotes expression of synaptic gene networks in the mouse hippocampus

In Alzheimer's Disease (AD) and other dementias, hippocampal synaptic dysfunction and loss contribute to the progression of memory impairment. Recent analysis of human AD transcriptomes has provided a list of gene candidates that may serve as drivers of disease. One such candidate is the membrane protein TMEM184B. To evaluate whether TMEM184B contributes to neurological impairment, we asked whether loss of TMEM184B in mice causes gene expression or behavior alterations, focusing on the hippocampus. Because one major risk factor for AD is age, we compared young adult (5-month-old) and aged (15-month-old) wild type and Tmem184b-mutant mice to assess the dual contributions of age and genotype. TMEM184B loss altered expression of pre- and post-synaptic transcripts by 5 months and continued through 15 months, specifically affecting genes involved in synapse assembly and neural development. Wnt-activated enhancer elements were enriched among differentially expressed genes, suggesting an intersection with this pathway. Few differences existed between young adult and aged mutants, suggesting that transcriptional effects of TMEM184B loss are relatively constant. To understand how TMEM184B disruption may impact behaviors, we evaluated memory using the novel object recognition test and anxiety using the elevated plus maze. Young adult Tmem184b-mutant mice show normal object discrimination, suggesting a lack of memory impairment at this age. However, mutant mice showed decreased anxiety, a phenotype seen in some neurodevelopmental disorders. Taken together, our data suggest that TMEM184B is required for proper synaptic gene expression and anxiety-related behavior and is more likely to be linked to neurodevelopmental disorders than to dementia.

Stress induces behavioral abnormalities by increasing expression of phagocytic receptor MERTK in astrocytes to promote synapse phagocytosis

Childhood neglect and/or abuse can induce mental health conditions with unknown mechanisms. Here, we identified stress hormones as strong inducers of astrocyte-mediated synapse phagocytosis. Using in vitro, in vivo, and human brain organoid experiments, we showed that stress hormones increased the expression of the Mertk phagocytic receptor in astrocytes through glucocorticoid receptor (GR). In post-natal mice, exposure to early social deprivation (ESD) specifically activated the GR-MERTK pathway in astrocytes, but not in microglia. The excitatory post-synaptic density in cortical regions was reduced in ESD mice, and there was an increase in the astrocytic engulfment of these synapses. The loss of excitatory synapses, abnormal neuronal network activities, and behavioral abnormalities in ESD mice were largely prevented by ablating GR or MERTK in astrocytes. Our work reveals the critical roles of astrocytic GR-MERTK activation in evoking stress-induced abnormal behaviors in mice, suggesting GR-MERTK signaling as a therapeutic target for stress-induced mental health conditions.

Node of Ranvier remodeling in chronic psychosocial stress and anxiety

Differential expression of myelin-related genes and changes in myelin thickness have been demonstrated in mice after chronic psychosocial stress, a risk factor for anxiety disorders. To determine whether and how stress affects structural remodeling of nodes of Ranvier, another form of myelin plasticity, we developed a 3D reconstruction analysis of node morphology in C57BL/6NCrl and DBA/2NCrl mice. We identified strain-dependent effects of chronic social defeat stress on node morphology in the medial prefrontal cortex (mPFC) gray matter, including shortening of paranodes in C57BL/6NCrl stress-resilient and shortening of node gaps in DBA/2NCrl stress-susceptible mice compared to controls. Neuronal activity has been associated with changes in myelin thickness. To investigate whether neuronal activation is a mechanism influencing also node of Ranvier morphology, we used DREADDs to repeatedly activate the ventral hippocampus-to-mPFC pathway. We found reduced anxiety-like behavior and shortened paranodes specifically in stimulated, but not in the nearby non-stimulated axons. Altogether, our data demonstrate (1) nodal remodeling of the mPFC gray matter axons after chronic stress and (2) axon-specific regulation of paranodes in response to repeated neuronal activity in an anxiety-associated pathway. Nodal remodeling may thus contribute to aberrant circuit function associated with anxiety disorders.

Dexmedetomidine alleviates anxiety-like behaviors in female mice with musculoskeletal pain through SIRT1/p53 axis

BACKGROUND

Musculoskeletal pain is the most common form of chronic pain. Anxiety increases pain intensity and appears to have a major impact on the prevalence and also disability of musculoskeletal pain in women. We examined the effect of dexmedetomidine (DEX) on anxiety-like behaviors associated with musculoskeletal pain and the underlying molecular mechanism in female mice.

METHODS

Musculoskeletal pain was induced by injection of acidified saline into the gastrocnemius muscle in adult female mice, and the von Frey filament test is used to measure mechanical sensitivity. DEX and EX527 (SIRT1 inhibitor) were administered after modelling. Behavioral tests were used for anxiety and motor activity tests. SIRT1, p53 and acetyl-p53 were quantified by Western blot.

RESULTS

Adult female mice with musculoskeletal pain exhibit increased fear-like behavior by reducing SIRT1 expression in the medial prefrontal cortex (mPFC). While administration of DEX was able to alleviate mechanical hypersensitivity and anxiety-like behaviors by blocking SIRT1 decline and acetyl-p53 upregulation in mPFC, EX527 inhibited acetyl-p53 rise and reversed the antinociceptive and anxiolytic effects of DEX.

CONCLUSION

DEX may alleviate anxiety-like behaviors in mice with musculoskeletal pain via the SIRT1/p53 axis. These results suggest that DEX may have a potential therapeutic role in musculoskeletal pain-induced anxiety.

Somatostatin peptide signaling dampens cortical circuits and promotes exploratory behavior

We sought to characterize the unique role of somatostatin (SST) in the prelimbic (PL) cortex in mice. We performed slice electrophysiology in pyramidal and GABAergic neurons to characterize the pharmacological mechanism of SST signaling and fiber photometry of GCaMP6f fluorescent calcium signals from SST neurons to characterize the activity profile of SST neurons during exploration of an elevated plus maze (EPM) and open field test (OFT). We used local delivery of a broad SST receptor (SSTR) agonist and antagonist to test causal effects of SST signaling. SSTR activation hyperpolarizes layer 2/3 pyramidal neurons, an effect that is recapitulated with optogenetic stimulation of SST neurons. SST neurons in PL are activated during EPM and OFT exploration, and SSTR agonist administration directly into the PL enhances open arm exploration in the EPM. This work describes a broad ability for SST peptide signaling to modulate microcircuits within the prefrontal cortex and related exploratory behaviors.