Prefrontal Cortex Drives Distinct Projection Neurons in the Basolateral Amygdala

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

The role of the prefrontal cortex in modulating aggression in humans and rodents

Accumulating evidence suggests that the prefrontal cortex (PFC) plays an important role in aggression. However, the findings regarding the key neural mechanisms and molecular pathways underlying the modulation of aggression by the PFC are relatively scattered, with many inconsistencies and areas that would benefit from exploration. Here, we highlight the relationship between the PFC and aggression in humans and rodents and describe the anatomy and function of the human PFC, along with homologous regions in rodents. At the molecular level, we detail how the major neuromodulators of the PFC impact aggression. At the circuit level, this review provides an overview of known and potential subcortical projections that regulate aggression in rodents. Finally, at the disease level, we review the correlation between PFC alterations and heightened aggression in specific human psychiatric disorders. Our review provides a framework for PFC modulation of aggression, resolves several intriguing paradoxes from previous studies, and illuminates new avenues for further study.

Activation of the mPFC-NAc Pathway Reduces Motor Impulsivity but Does Not Affect Risk-Related Decision-Making in Innately High-Impulsive Male Rats

Attention-deficit/hyperactivity disorder (ADHD) and substance use disorders (SUD) are characterized by exacerbated motor and risk-related impulsivities, which are associated with decreased cortical activity. In rodents, the medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) have been separately implicated in impulsive behaviors, but studies on the specific role of the mPFC-NAc pathway in these behaviors are limited. Here, we investigated whether heightened impulsive behaviors are associated with reduced mPFC activity in rodents and determined the involvement of the mPFC-NAc pathway in motor and risk-related impulsivities. We used the Roman High- (RHA) and Low-Avoidance (RLA) rat lines, which display divergent phenotypes in impulsivity. To investigate alterations in cortical activity in relation to impulsivity, regional brain glucose metabolism was measured using positron emission tomography and [18F]-fluorodeoxyglucose ([18F]FDG). Using chemogenetics, the activity of the mPFC-NAc pathway was either selectively activated in high-impulsive RHA rats or inhibited in low-impulsive RLA rats, and the effects of these manipulations on motor and risk-related impulsivity were concurrently assessed using the rat gambling task. We showed that basal [18F]FDG uptake was lower in the mPFC and NAc of RHA compared to RLA rats. Activation of the mPFC-NAc pathway in RHA rats reduced motor impulsivity, without affecting risk-related decision-making. Conversely, inhibition of the mPFC-NAc pathway had no effect in RLA rats. Our results suggest that the mPFC-NAc pathway controls motor impulsivity, but has limited involvement in risk-related decision-making in our current model. Our findings suggest that reducing fronto-striatal activity may help attenuate motor impulsivity in patients with impulse control dysregulation.

Identification of a stress-responsive subregion of the basolateral amygdala in male rats

The basolateral amygdala (BLA) is reliably activated by psychological stress and hyperactive in conditions of pathological stress or trauma; however, subsets of BLA neurons are also readily activated by rewarding stimuli and can suppress fear and avoidance behaviours. The BLA is highly heterogeneous anatomically, exhibiting continuous molecular and connectivity gradients throughout the entire structure. A critical gap remains in understanding the anatomical specificity of amygdala subregions, circuits, and cell types explicitly activated by acute stress and how they are dynamically activated throughout stimulus exposure. Using a combination of topographical mapping for the activity-responsive protein FOS and fiber photometry to measure calcium transients in real-time, we sought to characterize the spatial and temporal patterns of BLA activation in response to a range of novel stressors (shock, swim, restraint, predator odour) and non-aversive, but novel stimuli (crackers, citral odour). We report four main findings: (1) the BLA exhibits clear spatial activation gradients in response to novel stimuli throughout the medial-lateral and dorsal-ventral axes, with aversive stimuli strongly biasing activation towards medial aspects of the BLA; (2) novel stimuli elicit distinct temporal activation patterns, with stressful stimuli exhibiting particularly enhanced or prolonged temporal activation patterns; (3) changes in BLA activity are associated with changes in behavioural state; and (4) norepinephrine enhances stress-induced activation of BLA neurons via the ß-noradrenergic receptor. Moving forward, it will be imperative to combine our understanding of activation gradients with molecular and circuit-specificity.

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.

Supraspinal glycinergic neurotransmission in pain: A scoping review of current literature

The neurotransmitter glycine is an agonist at the strychnine-sensitive glycine receptors. In addition, it has recently been discovered to act at two new receptors, the excitatory glycine receptor and metabotropic glycine receptor. Glycine's neurotransmitter roles have been most extensively investigated in the spinal cord, where it is known to play essential roles in pain, itch, and motor function. In contrast, less is known about supraspinal glycinergic functions, and their contributions to pain circuits are largely unrecognized. As glycinergic neurons are absent from cortical regions, a clearer understanding of how supraspinal glycine modulates pain could reveal new pharmacological targets. This review aims to synthesize the published research on glycine's role in the adult brain, highlighting regions where glycine signaling may modulate pain responses. This was achieved through a scoping review methodology identifying several key regions of supraspinal pain circuitry where glycine signaling is involved. Therefore, this review unveils critical research gaps for supraspinal glycine's potential roles in pain and pain-associated responses, encouraging researchers to consider glycinergic neurotransmission more widely when investigating neural mechanisms of pain.

Unraveling the Prefrontal Cortex-Basolateral Amygdala Pathway's Role on Schizophrenia's Cognitive Impairments: A Multimodal Study in Patients and Mouse Models

BACKGROUND AND HYPOTHESIS

This study investigated the role of the medial prefrontal cortex (mPFC)-basolateral amygdala (BLA) pathway in schizophrenia (SCZ)-related cognitive impairments using various techniques.

STUDY DESIGN

This study utilized clinical scales, magnetic resonance imaging, single-cell RNA sequencing, and optogenetics to investigate the mPFC-BLA pathway in SCZ patients. In the mouse model, 6-week-old methylazoxymethanol acetate-induced mice demonstrated significant cognitive deficits, which were addressed through stereotaxic injections of an adeno-associated viral vector to unveil the neural connection between the mPFC and BLA.

STUDY RESULTS

Significant disparities in brain volume and neural activity, particularly in the dorsolateral prefrontal cortex (DLPFC) and BLA regions, were found between SCZ patients and healthy controls. Additionally, we observed correlations indicating that reduced volumes of the DLPFC and BLA were associated with lower cognitive function scores. Activation of the mPFC-BLA pathway notably improved cognitive performance in the SCZ model mice, with the targeting of excitatory or inhibitory neurons alone failing to replicate this effect. Single-cell transcriptomic profiling revealed gene expression differences in excitatory and inhibitory neurons in the BLA of SCZ model mice. Notably, genes differentially expressed in the BLA of these model mice were also found in the blood exosomes of SCZ patients.

CONCLUSIONS

Our research provides a comprehensive understanding of the role of the PFC-BLA pathway in SCZ, underscoring its significance in cognitive impairment and offering novel diagnostic and therapeutic avenues. Additionally, our research highlights the potential of blood exosomal mRNAs as noninvasive biomarkers for SCZ diagnosis, underscoring the clinical feasibility and utility of this method.

Chronic restraint stress induces depression-like behaviors and alterations in the afferent projections of medial prefrontal cortex from multiple brain regions in mice

INTRODUCTION

The medial prefrontal cortex (mPFC) forms output pathways through projection neurons, inversely receiving adjacent and long-range inputs from other brain regions. However, how afferent neurons of mPFC are affected by chronic stress needs to be clarified. In this study, the effects of chronic restraint stress (CRS) on the distribution density of mPFC dendrites/dendritic spines and the projections from the cortex and subcortical brain regions to the mPFC were investigated.

METHODS

In the present study, C57BL/6 J transgenic (Thy1-YFP-H) mice were subjected to CRS to establish an animal model of depression. The infralimbic (IL) of mPFC was selected as the injection site of retrograde AAV using stereotactic technique. The effects of CRS on dendrites/dendritic spines and afferent neurons of the mPFC IL were investigaed by quantitatively assessing the distribution density of green fluorescent (YFP) positive dendrites/dendritic spines and red fluorescent (retrograde AAV recombinant protein) positive neurons, respectively.

RESULTS

The results revealed that retrograde tracing virus labeled neurons were widely distributed in ipsilateral and contralateral cingulate cortex (Cg1), second cingulate cortex (Cg2), prelimbic cortex (PrL), infralimbic cortex, medial orbital cortex (MO), and dorsal peduncular cortex (DP). The effects of CRS on the distribution density of mPFC red fluorescence positive neurons exhibited regional differences, ranging from rostral to caudal or from top to bottom. Simultaneously, CRS resulted a decrease in the distribution density of basal, proximal and distal dendrites, as well as an increase in the loss of dendritic spines of the distal dendrites in the IL of mPFC. Furthermore, varying degrees of red retrograde tracing virus fluorescence signals were observed in other cortices, amygdala, hippocampus, septum/basal forebrain, hypothalamus, thalamus, mesencephalon, and brainstem in both ipsilateral and contralateral brain. CRS significantly reduced the distribution density of red fluorescence positive neurons in other cortices, hippocampus, septum/basal forebrain, hypothalamus, and thalamus. Conversely, CRS significantly increased the distribution density of red fluorescence positive neurons in amygdala.

CONCLUSION

Our results suggest a possible mechanism that CRS leads to disturbances in synaptic plasticity by affecting multiple inputs to the mPFC, which is characterized by a decrease in the distribution density of dendrites/dendritic spines in the IL of mPFC and a reduction in input neurons of multiple cortices to the IL of mPFC as well as an increase in input neurons of amygdala to the IL of mPFC, ultimately causing depression-like behaviors.

Mimicking opioid analgesia in cortical pain circuits

The anterior cingulate cortex plays a pivotal role in the cognitive and affective aspects of pain perception. Both endogenous and exogenous opioid signaling within the cingulate mitigate cortical nociception, reducing pain unpleasantness. However, the specific functional and molecular identities of cells mediating opioid analgesia in the cingulate remain elusive. Given the complexity of pain as a sensory and emotional experience, and the richness of ethological pain-related behaviors, we developed a standardized, deep-learning platform for deconstructing the behavior dynamics associated with the affective component of pain in mice-LUPE (Light aUtomated Pain Evaluator). LUPE removes human bias in behavior quantification and accelerated analysis from weeks to hours, which we leveraged to discover that morphine altered attentional and motivational pain behaviors akin to affective analgesia in humans. Through activity-dependent genetics and single-nuclei RNA sequencing, we identified specific ensembles of nociceptive cingulate neuron-types expressing mu-opioid receptors. Tuning receptor expression in these cells bidirectionally modulated morphine analgesia. Moreover, we employed a synthetic opioid receptor promoter-driven approach for cell-type specific optical and chemical genetic viral therapies to mimic morphine's pain-relieving effects in the cingulate, without reinforcement. This approach offers a novel strategy for precision pain management by targeting a key nociceptive cortical circuit with on-demand, non-addictive, and effective analgesia.

Pathophysiology in cortico-amygdala circuits and excessive aversion processing: the role of oligodendrocytes and myelination

Stress-related psychiatric illnesses, such as major depressive disorder, anxiety and post-traumatic stress disorder, present with alterations in emotional processing, including excessive processing of negative/aversive stimuli and events. The bidirectional human/primate brain circuit comprising anterior cingulate cortex and amygdala is of fundamental importance in processing emotional stimuli, and in rodents the medial prefrontal cortex-amygdala circuit is to some extent analogous in structure and function. Here, we assess the comparative evidence for: (i) Anterior cingulate/medial prefrontal cortex<->amygdala bidirectional neural circuits as major contributors to aversive stimulus processing; (ii) Structural and functional changes in anterior cingulate cortex<->amygdala circuit associated with excessive aversion processing in stress-related neuropsychiatric disorders, and in medial prefrontal cortex<->amygdala circuit in rodent models of chronic stress-induced increased aversion reactivity; and (iii) Altered status of oligodendrocytes and their oligodendrocyte lineage cells and myelination in anterior cingulate/medial prefrontal cortex<->amygdala circuits in stress-related neuropsychiatric disorders and stress models. The comparative evidence from humans and rodents is that their respective anterior cingulate/medial prefrontal cortex<->amygdala circuits are integral to adaptive aversion processing. However, at the sub-regional level, the anterior cingulate/medial prefrontal cortex structure-function analogy is incomplete, and differences as well as similarities need to be taken into account. Structure-function imaging studies demonstrate that these neural circuits are altered in both human stress-related neuropsychiatric disorders and rodent models of stress-induced increased aversion processing. In both cases, the changes include altered white matter integrity, albeit the current evidence indicates that this is decreased in humans and increased in rodent models. At the cellular-molecular level, in both humans and rodents, the current evidence is that stress disorders do present with changes in oligodendrocyte lineage, oligodendrocytes and/or myelin in these neural circuits, but these changes are often discordant between and even within species. Nonetheless, by integrating the current comparative evidence, this review provides a timely insight into this field and should function to inform future studies-human, monkey and rodent-to ascertain whether or not the oligodendrocyte lineage and myelination are causally involved in the pathophysiology of stress-related neuropsychiatric disorders.

Neuronal Ensembles in the Amygdala Allow Social Information to Motivate Later Decisions

Social experiences carry tremendous weight in our decision-making, even when social partners are not present. To determine mechanisms, we trained female mice to respond for two food reinforcers. Then, one food was paired with a novel conspecific. Mice later favored the conspecific-associated food, even in the absence of the conspecific. Chemogenetically silencing projections from the prelimbic subregion (PL) of the medial prefrontal cortex to the basolateral amygdala (BLA) obstructed this preference while leaving social discrimination intact, indicating that these projections are necessary for socially driven choice. Further, mice that performed the task had greater densities of dendritic spines on excitatory BLA neurons relative to mice that did not. We next induced chemogenetic receptors in cells active during social interactions-when mice were encoding information that impacted later behavior. BLA neurons stimulated by social experience were necessary for mice to later favor rewards associated with social conspecifics but not make other choices. This profile contrasted with that of PL neurons stimulated by social experience, which were necessary for choice behavior in social and nonsocial contexts alike. The PL may convey a generalized signal allowing mice to favor particular rewards, while units in the BLA process more specialized information, together supporting choice motivated by social information.

Prefrontal Regulation of Safety Learning during Ethologically Relevant Thermal Threat

Learning and adaptation during sources of threat and safety are critical mechanisms for survival. The prelimbic (PL) and infralimbic (IL) subregions of the medial prefrontal cortex (mPFC) have been broadly implicated in the processing of threat and safety. However, how these regions regulate threat and safety during naturalistic conditions involving thermal challenge still remains elusive. To examine this issue, we developed a novel paradigm in which adult mice learned that a particular zone that was identified with visuospatial cues was associated with either a noxious cold temperature ("threat zone") or a pleasant warm temperature ("safety zone"). This led to the rapid development of avoidance behavior when the zone was paired with cold threat or approach behavior when the zone was paired with warm safety. During a long-term test without further thermal reinforcement, mice continued to exhibit robust avoidance or approach to the zone of interest, indicating that enduring spatial-based memories were formed to represent the thermal threat and thermal safety zones. Optogenetic experiments revealed that neural activity in PL and IL was not essential for establishing the memory for the threat zone. However, PL and IL activity bidirectionally regulated memory formation for the safety zone. While IL activity promoted safety memory during normal conditions, PL activity suppressed safety memory especially after a stress pretreatment. Therefore, a working model is proposed in which balanced activity between PL and IL is favorable for safety memory formation, whereas unbalanced activity between these brain regions is detrimental for safety memory after stress.

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.

Excitatory subtypes of the lateral amygdala neurons are differentially involved in regulation of synaptic plasticity and excitation/inhibition balance in aversive learning in mice

The amygdala plays a crucial role in aversive learning. In Pavlovian fear conditioning, sensory information about an emotionally neutral conditioned stimulus (CS) and an innately aversive unconditioned stimulus is associated with the lateral amygdala (LA), and the CS acquires the ability to elicit conditioned responses. Aversive learning induces synaptic plasticity in LA excitatory neurons from CS pathways, such as the medial geniculate nucleus (MGN) of the thalamus. Although LA excitatory cells have traditionally been classified based on their firing patterns, the relationship between the subtypes and functional properties remains largely unknown. In this study, we classified excitatory cells into two subtypes based on whether the after-depolarized potential (ADP) amplitude is expressed in non-ADP cells and ADP cells. Their electrophysiological properties were significantly different. We examined subtype-specific synaptic plasticity in the MGN-LA pathway following aversive learning using optogenetics and found significant experience-dependent plasticity in feed-forward inhibitory responses in fear-conditioned mice compared with control mice. Following aversive learning, the inhibition/excitation (I/E) balance in ADP cells drastically changed, whereas that in non-ADP cells tended to change in the reverse direction. These results suggest that the two LA subtypes are differentially regulated in relation to synaptic plasticity and I/E balance during aversive learning.

A longitudinal study of childhood maltreatment, subcortical development, and subcortico-cortical structural maturational coupling from early to late adolescence

BACKGROUND

Examining neurobiological mechanisms that may transmit the effects of childhood maltreatment on mental health in youth is crucial for understanding vulnerability to psychopathology. This study investigated associations between childhood maltreatment, adolescent structural brain development, and mental health trajectories into young-adulthood.

METHODS

Structural magnetic resonance imaging data was acquired from 144 youth at three time points (age 12, 16, and 18 years). Childhood maltreatment was reported to occur prior to the first scan. Linear mixed models were utilized to examine the association between total childhood maltreatment, neglect, abuse and (i) amygdala and hippocampal volume development, and (ii) maturational coupling between amygdala/hippocampus volume and the thickness of prefrontal regions. We also examined whether brain development mediated the association between maltreatment and depressive and anxiety symptoms trajectories from age 12 to 28.

RESULTS

Total maltreatment, and neglect, were associated with positive maturational coupling between the amygdala and caudal anterior cingulate cortex (cACC), whereby at higher and lower levels of amygdala growth, maltreatment was associated with lower and higher PFC thinning, respectively. Neglect was also associated with maturational coupling of the hippocampus with prefrontal regions. While positive amygdala-cACC maturational coupling was associated with greater increases in anxiety symptoms, it did not significantly mediate the association between maltreatment and anxiety symptom trajectories.

CONCLUSION

We found maltreatment to be associated with altered patterns of coupling between subcortical and prefrontal regions during adolescence, suggesting that maltreatment is associated with the development of socio-emotional neural circuitry. The implications of these findings for mental health require further investigation.

Dynamic switching of neural oscillations in the prefrontal-amygdala circuit for naturalistic freeze-or-flight

The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) are involved in the regulation of defensive behavior under threat, but their engagement in flexible behavior shifts remains unclear. Here, we report the oscillatory activities of mPFC-BLA circuit in reaction to a naturalistic threat, created by a predatory robot in mice. Specifically, we found dynamic frequency tuning among two different theta rhythms (~5 or ~10 Hz) was accompanied by agile changes of two different defensive behaviors (freeze-or-flight). By analyzing flight trajectories, we also found that high beta (~30 Hz) is engaged in the top-down process for goal-directed flights and accompanied by a reduction in fast gamma (60 to 120 Hz, peak near 70 Hz). The elevated beta nested the fast gamma activity by its phase more strongly. Our results suggest that the mPFC-BLA circuit has a potential role in oscillatory gear shifting allowing flexible information routing for behavior switches.

Accelerated social representational drift in the nucleus accumbens in a model of autism

Impaired social interaction is one of the core deficits of autism spectrum disorder (ASD) and may result from social interactions being less rewarding. How the nucleus accumbens (NAc), as a key hub of reward circuitry, encodes social interaction and whether these representations are altered in ASD remain poorly understood. We identified NAc ensembles encoding social interactions by calcium imaging using miniaturized microscopy. NAc population activity, specifically D1 receptor-expressing medium spiny neurons (D1-MSNs) activity, predicted social interaction epochs. Despite a high turnover of NAc neurons modulated by social interaction, we found a stable population code for social interaction in NAc which was dramatically degraded in Cntnap2-/- mouse model of ASD. Surprisingly, non-specific optogenetic inhibition of NAc core neurons increased social interaction time and significantly improved sociability in Cntnap2-/- mice. Inhibition of D1- or D2-MSNs showed reciprocal effects, with D1 inhibition decreasing social interaction and D2 inhibition increasing interaction. Therefore, social interactions are preferentially, specifically and dynamically encoded by NAc neurons and social representations are degraded in this autism model.

Update on neurobiological mechanisms of fear: illuminating the direction of mechanism exploration and treatment development of trauma and fear-related disorders

Fear refers to an adaptive response in the face of danger, and the formed fear memory acts as a warning when the individual faces a dangerous situation again, which is of great significance to the survival of humans and animals. Excessive fear response caused by abnormal fear memory can lead to neuropsychiatric disorders. Fear memory has been studied for a long time, which is of a certain guiding effect on the treatment of fear-related disorders. With continuous technological innovations, the study of fear has gradually shifted from the level of brain regions to deeper neural (micro) circuits between brain regions and even within single brain regions, as well as molecular mechanisms. This article briefly outlines the basic knowledge of fear memory and reviews the neurobiological mechanisms of fear extinction and relapse, which aims to provide new insights for future basic research on fear emotions and new ideas for treating trauma and fear-related disorders.

Anterior basolateral amygdala neurons comprise a remote fear memory engram

Introduction

Threatening environmental cues often generate enduring fear memories, but how these are formed and stored remains actively investigated. Recall of a recent fear memory is thought to reflect reactivation of neurons, in multiple brain regions, activated during memory formation, indicating that anatomically distributed and interconnected neuronal ensembles comprise fear memory engrams. The extent to which anatomically specific activation-reactivation engrams persist during long-term fear memory recall, however, remains largely unexplored. We hypothesized that principal neurons in the anterior basolateral amygdala (aBLA), which encode negative valence, acutely reactivate during remote fear memory recall to drive fear behavior.

Methods

Using adult offspring of TRAP2 and Ai14 mice, persistent tdTomato expression was used to "TRAP" aBLA neurons that underwent Fos-activation during contextual fear conditioning (electric shocks) or context only conditioning (no shocks) (n = 5/group). Three weeks later, mice were re-exposed to the same context cues for remote memory recall, then sacrificed for Fos immunohistochemistry.

Results

TRAPed (tdTomato +), Fos +, and reactivated (double-labeled) neuronal ensembles were larger in fear- than context-conditioned mice, with the middle sub-region and middle/caudal dorsomedial quadrants of aBLA displaying the greatest densities of all three ensemble populations. Whereas tdTomato + ensembles were dominantly glutamatergic in context and fear groups, freezing behavior during remote memory recall was not correlated with ensemble sizes in either group.

Discussion

We conclude that although an aBLA-inclusive fear memory engram forms and persists at a remote time point, plasticity impacting electrophysiological responses of engram neurons, not their population size, encodes fear memory and drives behavioral manifestations of long-term fear memory recall.

INVOLVEMENT OF CORTICAL PROJECTIONS TO BASOLATERAL AMYGDALA IN CONTEXT-INDUCED REINSTATEMENT OF ETHANOL-SEEKING IN RATS

Ethanol is the most consumed substance of abuse in the world, and its misuse may lead to the development of alcohol use disorder (AUD). High relapse rates remain a relevant problem in the treatment of AUD. Exposure to environmental cues previously associated with ethanol intake could trigger ethanol-seeking behavior. However, the neural mechanisms involved in this phenomenon are not entirely clear. In this context, cortical projections to the basolateral amygdala (BLA) play a role in appetitive and aversive learned behaviors. Therefore, we aimed to evaluate the activation of the cortical projections from the prelimbic (PL), orbitofrontal (OFC), and infralimbic (IL), to the BLA in the context-induced reinstatement of ethanol-seeking. Male Long-Evans rats were trained to self-administer 10% ethanol in Context A. Subsequently, lever pressing in the presence of the discrete cue was extinguished in Context B. After nine extinction sessions, rats underwent intracranial surgery for the unilateral injection of red fluorescent retrograde tracer into the BLA. The context-induced reinstatement of ethanol-seeking was assessed by re-exposing the rats to Context A or B under extinction conditions. Finally, we combined retrograde neuronal tracing with Fos to identify activated cortical inputs to BLA during the reinstatement of ethanol-seeking behavior. We found that PL, but not OFC or IL, retrogradely-labeled neurons from BLA presented increased Fos expression during the re-exposure to the ethanol-associated context, suggesting that PL projection to BLA is involved in the context-induced reinstatement of ethanol-seeking behavior.

Medial prefrontal cortex input to basolateral amygdala controls acute stress-induced short-term anxiety-like behavior in mice

Anxiety is a normal and transitory emotional state that allows the organisms to cope well with the real or perceived threats, while excessive or prolonged anxiety is a key characteristic of anxiety disorders. We have recently revealed that prolonged anxiety induced by chronic stress is associated with the circuit-varying dysfunction of basolateral amygdala projection neurons (BLA PNs). However, it is not yet known whether similar mechanisms also emerge for acute stress-induced, short-lasting increase of anxiety. Here, using a mouse model of acute restraint stress (ARS), we found that ARS mice showed increased anxiety-like behavior at 2 h but not 24 h after stress, and this effect was accompanied by a transient increase of the activity of BLA PNs. Specifically, ex vivo patch-clamp recordings revealed that the increased BLA neuronal activity did not differ among the distinct BLA neuronal populations, regardless of their projection targets being the dorsomedial prefrontal cortex (dmPFC) or elsewhere. We further demonstrated that such effects were mainly mediated by the enhanced presynaptic glutamate release in dmPFC-to-BLA synapses but not lateral amygdala-to-BLA ones. Furthermore, while optogenetically weakening the presynaptic glutamate release in dmPFC-to-BLA synapses ameliorated ARS-induced anxiety-like behavior, strengthening the release increased in unstressed mice. Together, these findings suggest that acute stress causes short-lasting increase in anxiety-like behavior by facilitating synaptic transmission from the prefrontal cortex to the amygdala in a circuit-independent fashion.

Insights into the encoding of memories through the circuitry of fear

Associative learning induces physical changes to a network of cells, known as the memory engram. Fear is widely used as a model to understand the circuit motifs that underpin associative memories. Recent advances suggest that the distinct circuitry engaged by different conditioned stimuli (e.g. tone vs. context) can provide insights into what information is being encoded in the fear engram. Moreover, as the fear memory matures, the circuitry engaged indicates how information is remodelled after learning and hints at potential mechanisms for consolidation. Finally, we propose that the consolidation of fear memories involves plasticity of engram cells through coordinated activity between brain regions, and the inherent characteristics of the circuitry may mediate this process.

Determinants of functional synaptic connectivity among amygdala-projecting prefrontal cortical neurons in male mice

The medial prefrontal cortex (mPFC) mediates a variety of complex cognitive functions via its vast and diverse connections with cortical and subcortical structures. Understanding the patterns of synaptic connectivity that comprise the mPFC local network is crucial for deciphering how this circuit processes information and relays it to downstream structures. To elucidate the synaptic organization of the mPFC, we developed a high-throughput optogenetic method for mapping large-scale functional synaptic connectivity in acute brain slices. We show that in male mice, mPFC neurons that project to the basolateral amygdala (BLA) display unique spatial patterns of local-circuit synaptic connectivity, which distinguish them from the general mPFC cell population. When considering synaptic connections between pairs of mPFC neurons, the intrinsic properties of the postsynaptic cell and the anatomical positions of both cells jointly account for ~7.5% of the variation in the probability of connection. Moreover, anatomical distance and laminar position explain most of this fraction in variation. Our findings reveal the factors determining connectivity in the mPFC and delineate the architecture of synaptic connections in the BLA-projecting subnetwork.

Identification of a novel fatty acid binding protein-5-CB2 receptor-dependent mechanism regulating anxiety behaviors in the prefrontal cortex

The endocannabinoid (eCB) system represents a promising neurobiological target for novel anxiolytic pharmacotherapies. Previous clinical and preclinical evidence has revealed that genetic and/or pharmacological manipulations altering eCB signaling modulate fear and anxiety behaviors. Water-insoluble eCB lipid anandamide requires chaperone proteins for its intracellular transport to degradation, a process that requires fatty acid-binding proteins (FABPs). Here, we investigated the effects of a novel FABP-5 inhibitor, SBFI-103, on fear and anxiety-related behaviors using rats. Acute intra-prelimbic cortex administration of SBFI-103 induced a dose-dependent anxiolytic response and reduced contextual fear expression. Surprisingly, both effects were reversed when a cannabinoid-2 receptor (CB2R) antagonist, AM630, was co-infused with SBFI-103. Co-infusion of the cannabinoid-1 receptor antagonist Rimonabant with SBFI-103 reversed the contextual fear response yet showed no reversal effect on anxiety. Furthermore, in vivo neuronal recordings revealed that intra-prelimbic region SBFI-103 infusion altered the activity of putative pyramidal neurons in the basolateral amygdala and ventral hippocampus, as well as oscillatory patterns within these regions in a CB2R-dependent fashion. Our findings identify a promising role for FABP5 inhibition as a potential target for anxiolytic pharmacotherapy. Furthermore, we identify a novel, CB2R-dependent FABP-5 signaling pathway in the PFC capable of strongly modulating anxiety-related behaviors and anxiety-related neuronal transmission patterns.

Compensatory Contextual Fear Memory Pathways Develop in the Infralimbic Cortex within 3 Days after the First Test in the Absence of the Dorsal Hippocampus

The dorsal hippocampus (DH) is primarily involved in the formation of contextual fear-conditioned (CxFC) memory. However, CxFC memory can be formed even in the absence of the DH. In addition to the DH, the infralimbic cortex (IL), a sub-region of the medial prefrontal cortex (mPFC), also plays an important role in the consolidation of CxFC memory. However, role of IL in the development of compensatory CxFC memory is not known. Here, we have examined (a) the development of the compensatory circuitry of CxFC memory within 3 days after the first test in the absence of the DH and (b) the role of IL in the induction of compensatory CxFC memory in the absence of the DH. The DH-lesioned rats re-trained for CxFC 1 day after the first testing exhibited significantly less freezing compared to the control group. However, the DH-lesioned rats, re-trained for CxFC 3 days after the first testing, showed a robust freezing response. It suggests that the fully functional compensatory circuitry of contextual fear memory develops after multiple training separated by 3 days. Furthermore, we observed that reversible inactivation of the IL of the DH-lesioned rats during the first training waned the formation of compensatory CxFC. It suggests that (a) the IL receives contextual fear memory information during the first trial in the absence of the DH and (b) perturbation in fear memory information encoding in the IL during the first trial impairs the development of the compensatory network in the absence of the DH.

Connectivity-based parcellation of the amygdala and identification of its main white matter connections

The amygdala plays a role in emotion, learning, and memory and has been implicated in behavioral disorders. Better understanding of the amygdala circuitry is crucial to develop new therapies for these disorders. We used data from 200 healthy-subjects from the human connectome project. Using probabilistic tractography, we created population statistical maps of amygdala connectivity to brain regions involved in limbic, associative, memory, and reward circuits. Based on the amygdala connectivity with these regions, we applied k-means clustering to parcellate the amygdala into three clusters. The resultant clusters were averaged across all subjects and the main white-matter pathways of the amygdala from each averaged cluster were generated. Amygdala parcellation into three clusters showed a medial-to-lateral pattern. The medial cluster corresponded with the centromedial and cortical nuclei, the basal cluster with the basal nuclei and the lateral cluster with the lateral nuclei. The connectivity analysis revealed different white-matter pathways consistent with the anatomy of the amygdala circuit. This in vivo connectivity-based parcellation of the amygdala delineates three clusters of the amygdala in a mediolateral pattern based on its connectivity with brain areas involved in cognition, memory, emotion, and reward. The human amygdala circuit presented in this work provides the first step for personalized amygdala circuit mapping for patients with behavioral disorders.

Emotional Memory Processing during REM Sleep with Implications for Post-Traumatic Stress Disorder

REM sleep is important for the processing of emotional memories, including fear memories. Rhythmic interactions, especially in the theta band, between the medial prefrontal cortex (mPFC) and limbic structures are thought to play an important role, but the ways in which memory processing occurs at a mechanistic and circuits level are largely unknown. To investigate how rhythmic interactions lead to fear extinction during REM sleep, we used a biophysically based model that included the infralimbic cortex (IL), a part of the mPFC with a critical role in suppressing fear memories. Theta frequency (4-12 Hz) inputs to a given cell assembly in IL, representing an emotional memory, resulted in the strengthening of connections from the IL to the amygdala and the weakening of connections from the amygdala to the IL, resulting in the suppression of the activity of fear expression cells for the associated memory. Lower frequency (4 Hz) theta inputs effected these changes over a wider range of input strengths. In contrast, inputs at other frequencies were ineffective at causing these synaptic changes and did not suppress fear memories. Under post-traumatic stress disorder (PTSD) REM sleep conditions, rhythmic activity dissipated, and 4 Hz theta inputs to IL were ineffective, but higher-frequency (10 Hz) theta inputs to IL induced changes similar to those seen with 4 Hz inputs under normal REM sleep conditions, resulting in the suppression of fear expression cells. These results suggest why PTSD patients may repeatedly experience the same emotionally charged dreams and suggest potential neuromodulatory therapies for the amelioration of PTSD symptoms.SIGNIFICANCE STATEMENT Rhythmic interactions in the theta band between the mPFC and limbic structures are thought to play an important role in processing emotional memories, including fear memories, during REM sleep. The infralimbic cortex (IL) in the mPFC is thought to play a critical role in suppressing fear memories. We show that theta inputs to the IL, unlike other frequency inputs, are effective in producing synaptic changes that suppress the activity of fear expression cells associated with a given memory. Under PTSD REM sleep conditions, lower-frequency (4 Hz) theta inputs to the IL do not suppress the activity of fear expression cells associated with the given memory but, surprisingly, 10 Hz inputs do. These results suggest potential neuromodulatory therapies for PTSD.

Probing the antidepressant potential of psilocybin: integrating insight from human research and animal models towards an understanding of neural circuit mechanisms

Interest in the therapeutic potential of serotonergic psychedelic compounds including psilocybin has surged in recent years. While human clinical research suggests psilocybin holds promise as a rapid and long-lasting antidepressant, little is known about how its acute mechanisms of action mediate enduring alterations in cognition and behavior. Human neuroimaging studies point to both acute and sustained modulation of functional connectivity in key cortically dependent brain networks. Emerging evidence in preclinical models highlights the importance of psilocybin-induced neuroplasticity and alterations in the prefrontal cortex (PFC). Overviewing research in both humans and preclinical models suggests avenues to increase crosstalk between fields. We review how acute modulation of PFC circuits may contribute to long-term structural and functional alterations to mediate antidepressant effects. We highlight the potential for preclinical circuit and behavioral neuroscience approaches to provide basic mechanistic insight into how psilocybin modulates cognitive and affective neural circuits to support further development of psilocybin as a promising new treatment for depression.

The prelimbic cortex but not the anterior cingulate cortex plays an important role in social recognition and social investigation in mice

The prefrontal cortex (PFC) has been implicated in social cognitive functions and emotional behaviors in rodents. Each subregion (prelimbic cortex, PL; infralimbic cortex; and anterior cingulate cortex, ACC) of the PFC appears to play a different role in social and emotional behaviors. However, previous investigations have produced inconsistent data, and few previous studies directly compared the roles of the PFC subregions using the same experimental paradigm. Accordingly, in the present study, we examined the role of the PL and the ACC in short-term social recognition, social investigation, and anxiety-related behaviors in C57BL/6J mice. We subjected mice with a lesioned PL or ACC, as well as those in a sham control group, to tests of social recognition and social novelty where juvenile and adult male mice were used as social stimuli. In the social recognition test, the PL-lesioned mice exhibited habituation but not dishabituation regardless of whether they encountered juvenile or adult mice. In a subsequent social novelty test, they spent less time engaged in social investigation compared with the control mice when adult mice were used as social stimuli. These results suggest that PL lesions impaired both social recognition and social investigation. In contrast, ACC-lesioned mice did not exhibit impaired short-term social recognition or social investigation regardless of the social stimulus. Furthermore, PL lesions and ACC lesions did not affect anxiety-related behavior in the open field test or light-dark transition test. Our findings demonstrate that the PL but not the ACC plays an important role in social recognition and social investigation.

Rostral and caudal basolateral amygdala engage distinct circuits in the prelimbic and infralimbic prefrontal cortex

Connections from the basolateral amygdala (BLA) to medial prefrontal cortex (PFC) regulate memory and emotion and become disrupted in neuropsychiatric disorders. The diverse roles attributed to interactions between the BLA and PFC may reflect multiple circuits nested within a wider network. To examine these circuits, we first used retrograde and anterograde anatomy to show that the rostral BLA (rBLA) and caudal BLA (cBLA) differentially project to prelimbic (PL) and infralimbic (IL) subregions of the mouse PFC. Using ex vivo whole-cell recordings and optogenetics, we then assessed which neuronal subtypes are targeted, showing that rBLA preferentially drives layer 2 (L2) cortico-amygdalar (CA) neurons in PL, whereas cBLA drives layer 5 (L5) pyramidal tract (PT) neurons in IL. We next combined in vivo silicon probe recordings and optogenetics to confirm that cBLA mainly influences IL L5, whereas rBLA primarily activates PL L2, but also evokes polysynaptic activity in PL L5. Lastly, we used soma-tagged optogenetics to explore the local circuits linking superficial and deep layers of PL, showing how rBLA can engage L2 CA neurons to impact L5 PT neuron activity. Together, our findings delineate how subregions of the BLA target distinct networks within the PFC and differentially influence output from PL and IL.

Amygdala neural ensemble mediates mouse social investigation behaviors

Innate social investigation behaviors are critical for animal survival and are regulated by both neural circuits and neuroendocrine factors. Our understanding of how neuropeptides regulate social interest, however, is incomplete at the current stage. In this study, we identified the expression of secretin (SCT) in a subpopulation of excitatory neurons in the basolateral amygdala. With distinct molecular and physiological features, BLA^SCT+ cells projected to the medial prefrontal cortex and were necessary and sufficient for promoting social investigation behaviors, whilst other basolateral amygdala neurons were anxiogenic and antagonized social behaviors. Moreover, the exogenous application of secretin effectively promoted social interest in both healthy and autism spectrum disorder model mice. These results collectively demonstrate a previously unrecognized group of amygdala neurons for mediating social behaviors and suggest promising strategies for social deficits.

Prefrontal Cortex Response to Prenatal Insult and Postnatal Opioid Exposure

The influence of proinflammatory challenges, such as maternal immune activation (MIA) or postnatal exposure to drugs of abuse, on brain molecular pathways has been reported. On the other hand, the simultaneous effects of MIA and drugs of abuse have been less studied and sometimes offered inconsistent results. The effects of morphine exposure on a pig model of viral-elicited MIA were characterized in the prefrontal cortex of males and females using RNA-sequencing and gene network analysis. Interacting and main effects of morphine, MIA, and sex were detected in approximately 2000 genes (false discovery rate-adjusted p-value < 0.05). Among the enriched molecular categories (false discovery rate-adjusted p-value < 0.05 and −1.5 > normalized enrichment score > 1.5) were the cell adhesion molecule pathways associated with inflammation and neuronal development and the long-term depression pathway associated with synaptic strength. Gene networks that integrate gene connectivity and expression profiles displayed the impact of morphine-by-MIA interaction effects on the pathways. The cell adhesion molecules and long-term depression networks presented an antagonistic effect between morphine and MIA. The differential expression between the double-challenged group and the baseline saline-treated Controls was less extreme than the individual challenges. The previous findings advance the knowledge about the effects of prenatal MIA and postnatal morphine exposure on the prefrontal cortex pathways.

Metabotropic Glutamate Receptor 5 in Amygdala Target Neurons Regulates Susceptibility to Chronic Social Stress

BACKGROUND

Metabotropic glutamate receptor 5 (mGluR5) has been implicated in stress-related psychiatric disorders, particularly major depressive disorder. Although growing evidence supports the proresilient role of mGluR5 in corticolimbic circuitry in the depressive-like behaviors following chronic stress exposure, the underlying neural mechanisms, including circuits and molecules, remain unknown.

METHODS

We measured the c-Fos expression and probability of neurotransmitter release in and from basolateral amygdala (BLA) neurons projecting to the medial prefrontal cortex (mPFC) and to the ventral hippocampus (vHPC) after chronic social defeat stress. The role of BLA projections in depressive-like behaviors was assessed using optogenetic manipulations, and the underlying molecular mechanisms of mGluR5 and downstream signaling were investigated by Western blotting, viral-mediated gene transfer, and pharmacological manipulations.

RESULTS

Chronic social defeat stress disrupted neural activity and glutamatergic transmission in both BLA projections. Optogenetic activation of BLA projections reversed the detrimental effects of chronic social defeat stress on depressive-like behaviors and mGluR5 expression in the mPFC and vHPC. Conversely, inhibition of BLA projections of mice undergoing subthreshold social defeat stress induced a susceptible phenotype and mGluR5 reduction. These two BLA circuits appeared to act in an independent way. We demonstrate that mGluR5 overexpression in the mPFC or vHPC was proresilient while the mGluR5 knockdown was prosusceptible and that the proresilient effects of mGluR5 are mediated through distinctive downstream signaling pathways in the mPFC and vHPC.

CONCLUSIONS

These findings identify mGluR5 in the mPFC and vHPC that receive BLA inputs as a critical mediator of stress resilience, highlighting circuit-specific signaling for depressive-like behaviors.

Activation of LH GABAergic inputs counteracts fasting-induced changes in tVTA/RMTG neurons

KEY POINTS

While dopamine neuronal activity changes with motivational state, it is unknown if fasting influences tVTA/RMTg GABAergic neurons, a major inhibitory input to VTA dopamine neurons. In unfasted mice, there were sex differences in inhibitory synaptic transmission onto tVTA/RMTg GABAergic neurons. Activation of LH GABAergic neurons decreases firing of tVTA/RMTg GABAergic neurons through a monosynaptic input. An acute fast decreased the excitability of tVTA/RMTg GABAergic neurons. An acute fast decreases inhibitory synaptic transmission of the LH GABA input to tVTA/RMTg GABAergic neurons in both male and female mice.

ABSTRACT

Dopamine neurons in the ventral tegmental area (VTA) are strongly innervated by GABAergic neurons in the 'tail of the VTA' (tVTA), also known as the rostralmedial tegmental nucleus (RMTg). Disinhibition of dopamine neurons through firing of the GABAergic neurons projecting from the lateral hypothalamus (LH) leads to reward seeking and consumption through dopamine release in the nucleus accumbens. VTA dopamine neurons respond to changes in motivational state, yet less is known of whether tVTA/RMTg GABAergic neurons or the LH GABAergic neurons that project to them are also affected by changes in motivational state, such as fasting. An acute 16 h overnight fast decreased the excitability of tVTA/RMTg GABAergic neurons of male and female mice. In addition, fasting decreased synaptic strength at LH GABA to tVTA/RMTg GABAergic synapses, indicated by reduced amplitude of optically evoked currents, decreased readily releasable pool (RRP) size and replenishment. Optical stimulation of LH GABA terminals suppressed evoked action potentials of tVTA/RMTg GABAergic neurons in unfasted mice, but this effect decreased following fasting. Furthermore, during fasting, LH GABA inputs to tVTA/RMTg neurons maintained functional connectivity during depolarization, as depolarization block was reduced following fasting. Taken together, inhibitory synaptic transmission from LH GABA inputs onto tVTA/RMTg GABAergic neurons decreases following fasting, however ability to functionally inhibit tVTA/RMTg GABAergic neurons is preserved, allowing for possible disinhibition of dopamine neurons and subsequent foraging. Abstract figure legend  The inhibitory synaptic input is represented by the downward arrows. Following fasting, there was a decrease in inhibitory synaptic strength in both males and females. The action potentials represent the excitability, which also decreases in both males and females following fasting. Because both the LH GABA input and excitability of tVTA/RMTg GABA neurons have reduced activity following fasting, we predict that disinhibition of dopamine neurons with stimulation of LH inputs is preserved. This article is protected by copyright. All rights reserved.

Fast Detection of Snakes and Emotional Faces in the Macaque Amygdala

Primate vision is reported to detect snakes and emotional faces faster than many other tested stimuli. Because the amygdala has been implicated in avoidance and emotional behaviors to biologically relevant stimuli and has neural connections with subcortical nuclei involved with vision, amygdalar neurons would be sensitive to snakes and emotional faces. In this study, neuronal activity in the amygdala was recorded from Japanese macaques (Macaca fuscata) during discrimination of eight categories of visual stimuli including snakes, monkey faces, human faces, carnivores, raptors, non-predators, monkey hands, and simple figures. Of 527 amygdalar neurons, 95 responded to one or more stimuli. Response characteristics of the amygdalar neurons indicated that they were more sensitive to the snakes and emotional faces than other stimuli. Response magnitudes and latencies of amygdalar neurons to snakes and monkey faces were stronger and faster than those to the other categories of stimuli, respectively. Furthermore, response magnitudes to the low pass-filtered snake images were larger than those to scrambled snake images. Finally, analyses of population activity of amygdalar neurons suggest that snakes and emotional faces were represented separately from the other stimuli during the 50–100 ms period from stimulus onset, and neutral faces during the 100–150 ms period. These response characteristics indicate that the amygdala processes fast and coarse visual information from emotional faces and snakes (but not other predators of primates) among the eight categories of the visual stimuli, and suggest that, like anthropoid primate visual systems, the amygdala has been shaped over evolutionary time to detect appearance of potentially threatening stimuli including both emotional faces and snakes, the first of the modern predators of primates.

Medial prefrontal cortex-basolateral amygdala circuit dysfunction in chronic alcohol-exposed male rats

Alcohol is a commonly used drug that can produce alcohol use disorders (AUDs). Few individuals with AUDs receive treatment and treatment options are complicated by issues with effectiveness and compliance. Alcohol has been shown to differentially affect specific brain regions and an improved understanding of circuit-specific dysregulation caused by alcohol is warranted. Previous work has implicated both the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) in alcohol-associated plasticity, however studies directly examining the impact of alcohol exposure on this circuit are lacking. The current study employed an optogenetic strategy to investigate the prelimbic mPFC to BLA circuit and changes in circuit activity following chronic intragastric ethanol exposure in male Sprague Dawley rats. We observed monosynaptic connections with light-evoked stimulation of mPFC terminals in the BLA with efficacy and short latency. We also found that mPFC-BLA projections are primarily glutamatergic under basal inhibitory control, with a lesser population of GABAergic projections. We examined optically-evoked glutamate currents in the BLA using repeated trains of stimulation that displayed accommodation, or a reduction in evoked current amplitude over repeated stimulations. We found that following chronic ethanol exposure mPFC-BLA glutamatergic connections were dysregulated such that there were decreases in overall function, notably in synaptic strength and accommodation, with no change in probability of evoked glutamate release. The lesser GABAergic component of the mPFC-BLA circuit was not altered by chronic ethanol exposure. Collectively these data indicate that mPFC-BLA circuitry is a significant target of alcohol-associated plasticity, which may contribute to pathological behavior associated with AUDs.

Brain Networks of Connectionally Unique Basolateral Amygdala Cell Types

Different brain regions structurally interconnected through networks regulate behavior output. Therefore, understanding the functional organization of the brain in health and disease necessitates a foundational anatomic roadmap to its network organization. To provide this to the research community, our lab has systematically traced thousands of pathways in the mouse brain and has applied computational measures to determine the network architecture of major brain systems. Toward this effort, the brain-wide networks of the basolateral amygdalar complex (BLA) were recently generated. The data revealed uniquely connected cell types within the same BLA nucleus that were constituents of distinct neural networks. Here, we elaborate on how these connectionally unique BLA cell types fit within the larger cortico-basal ganglia and limbic networks that were previously described by our team. The significance and utility of high quality, detailed anatomic data is also discussed.

The self on its axis: a framework for understanding depression

The self is experienced differently in depression. It is infused with pervasive low mood, and structured by negative self-related thoughts. The concept of the self has been difficult to define-one of the reasons it is now infrequently an object of enquiry for psychiatry-but findings from functional brain imaging and other neuroscience studies have provided new insights. They have elucidated how the self is supported by complex, hierarchical brain processes. Bodily sensations rise through the spinal cord, brainstem, and subcortical regions through to cortical networks, with the default mode network sitting at the apex, integrating interoceptive signals with information about the extended social environment. We discuss how this forms a "self axis", and demonstrate how this axis is set awry by depression. Our self-axis model of depression establishes a new perspective on the disorder. It emphasises the multi-level nature of depression, and how impacts made at different explanatory levels influence others along the axis. It suggests that diverse treatments might be effective for depression, from lifestyle interventions to psychotherapies to medications: they target different aspects of the self, but changes at one level of the self axis can affect others along it. Our framework for depression establishes a central role for the self, which might again become a useful focus of investigation.

Decreased Phase-Amplitude Coupling Between the mPFC and BLA During Exploratory Behaviour in Chronic Unpredictable Mild Stress-Induced Depression Model of Rats

Depression is a common neuropsychiatric illness observed worldwide, and reduced interest in exploration is one of its symptoms. The control of dysregulated medial prefrontal cortex (mPFC) over the basolateral amygdala (BLA) is related to depression. However, the oscillation interaction in the mPFC-BLA circuit has remained elusive. Therefore, this study used phase-amplitude coupling (PAC), which provides complicated forms of information transmission by the phase of low-frequency rhythm, modulating the amplitude of high-frequency rhythm, and has a potential application for the treatment of neurological disease. The chronic unpredictable mild stress (CUMS) was used to prepare the rat models of depression. Moreover, multichannel in vivo recording was applied to obtain the local field potentials (LFPs) of the mPFC, the BLA in rats in control, and CUMS groups, while they explored the open field. The results showed prominent coupling between the phase of theta oscillation (4-12 Hz) in the mPFC and the amplitude of high-gamma oscillation (70-120 Hz) in the BLA. Compared to the control group, this theta-gamma PAC was significantly decreased in the CUMS group, which was accompanied by the diminished exploratory behaviour. The results indicate that the coupling between the phase of theta in the mPFC and the amplitude of gamma in the BLA is involved in exploratory behaviour, and this decreased coupling may inhibit exploratory behaviour of rats exposed to CUMS.

Serum High-Sensitivity C-Reactive Protein Is Associated with Postoperative Psychiatric Status in Patients with Empty Nose Syndrome

Many patients diagnosed with empty nose syndrome (ENS) later develop mental illness. The literature addressing biomarkers associated with postoperative psychiatric status is limited. This study aimed to assess the association between high-sensitivity C-reactive protein (hs-CRP) and psychiatric status after surgery in ENS. We recruited patients with ENS undergoing endonasal submucosal implantation. Their pre- and postoperative psychiatric status was evaluated using the Beck depression inventory-II (BDI-II) and the Beck Anxiety Inventory (BAI). Serum hs-CRP was analyzed one day before and one year after surgery. Of the 43 patients enrolled, all subjective measurements had improved (symptom scores decreased) significantly by the third month postoperatively and remained plateaued till 12 months. Those with preoperative hs-CRP levels > 2.02 mg/L were likely to remain depressive 1 year postoperatively. The regression model showed that a preoperative hs-CRP level > 2.02 mg/L was significantly correlated with postoperative depression in patients with ENS (odds ratio, 19.9). Hs-CRP level seems to be a feasible predictor of surgical outcome regarding improved depression in patients with ENS. Patients with higher preoperative hs-CRP levels should be monitored closely after surgery.

Oxytocin system driven by experiences modifies social recognition and neuron morphology in female BALB/c mice

The oxytocin (OT) system, affected by life experiences, modulates neuron morphology in a sex-specific manner, leading to sex differences in social interactions. To date, few studies have focused on the OT system and social interactions of female mice. In this study, we used maternal deprivation (MD) and its possible treatment, environmental enrichment (EE), to affect social recognition in female BALB/c mice. We checked neuron morphology, synaptic connections, oxytocinergic (OTergic) neurons in the hypothalamus paraventricular nucleus (PVH), and OT receptor (OTR) in the basolateral amygdala (BLA) and layer II/III of the prelimbic cortex (PL). Our results showed that MD induced social recognition impairments, increased OTR levels in the BLA, and, meanwhile, reduced OTergic neurons in the magnocellular region of the PVH (mPVH). Decreased Nissl bodies, increased cell nuclei, and increased dendrites of projection neurons paralleled the increased OTR levels in the BLA of MD mice. EE restored MD-induced the impairments of novel object recognition and sociability; this effect paralleled a decrease in cell density in the PL and an increase in OTergic neurons in the parvocellular regions of the PVH and synaptic connections in the BLA and layer II/III of the PL. Our findings indicate that early life stress such as MD impairs social recognition, and meanwhile, remodels neuron morphology region-specifically in the female brain, apparently in the BLA but slightly in the PL; and EE could partially restore the deficits induced by MD. The results provide new insights into sex differences in the prevalence of psychological development disorders.

Effects of Acute Stress on the Oscillatory Activity of the Hippocampus-Amygdala-Prefrontal Cortex Network

Displaying a stress response to threatening stimuli is essential for survival. These reactions must be adjusted to be adaptive. Otherwise, even mental illnesses may develop. Describing the physiological stress response may contribute to distinguishing the abnormal responses that accompany the pathology, which may help to improve the development of both diagnoses and treatments. Recent advances have elucidated many of the processes and structures involved in stress response management; however, there is still much to unravel regarding this phenomenon. The main aim of the present research is to characterize the response of three brain areas deeply involved in the stress response (i.e., to an acute stressful experience). Specifically, the electrophysiological activity of the infralimbic division of the medial prefrontal cortex (IL), the basolateral nucleus of the amygdala (BLA), and the dorsal hippocampus (dHPC) was recorded after the infusion of 0.5 µl of corticosterone-releasing factor into the dorsal raphe nucleus (DRN), a procedure which has been validated as a paradigm to cause acute stress. This procedure induced a delayed reduction in slow waves in the three structures, and an increase in faster oscillations, such as those in theta, beta, and gamma bands. The mutual information at low theta frequencies between the BLA and the IL increased, and the delta and slow wave mutual information decreased. The low theta-mid gamma phase-amplitude coupling increased within BLA, as well as between BLA and IL. This electrical pattern may facilitate the activation of these structures, in response to the stressor, and memory consolidation.

Increased mGlu5 mRNA expression in BLA glutamate neurons facilitates resilience to the long-term effects of a single predator scent stress exposure

Post-traumatic stress disorder (PTSD) develops in a subset of individuals exposed to a trauma with core features being increased anxiety and impaired fear extinction. To model the heterogeneity of PTSD behavioral responses, we exposed male Sprague-Dawley rats to predator scent stress once for 10 min and then assessed anxiety-like behavior 7 days later using the elevated plus maze and acoustic startle response. Rats displaying anxiety-like behavior in both tasks were classified as stress Susceptible, and rats exhibiting behavior no different from un-exposed Controls were classified as stress Resilient. In Resilient rats, we previously found increased mRNA expression of mGlu5 in the amygdala and prefrontal cortex (PFC) and CB1 in the amygdala. Here, we performed fluorescent in situ hybridization (FISH) to determine the subregion and cell-type-specific expression of these genes in Resilient rats 3 weeks after TMT exposure. Resilient rats displayed increased mGlu5 mRNA expression in the basolateral amygdala (BLA) and the infralimbic and prelimbic regions of the PFC and increased BLA CB1 mRNA. These increases were limited to glutamatergic cells. To test the necessity of mGlu5 for attenuating TMT-conditioned contextual fear 3 weeks after TMT conditioning, intra-BLA infusions of the mGlu5 negative allosteric modulator MTEP were administered prior to context re-exposure. In TMT-exposed Resilient rats, but not Controls, MTEP increased freezing on the day of administration, which extinguished over two additional un-drugged sessions. These results suggest that increased mGlu5 expression in BLA glutamate neurons contributes to the behavioral flexibility observed in stress-Resilient animals by facilitating a capacity for extinguishing contextual fear associations.

Ethanol modulation of cortico-basolateral amygdala circuits: Neurophysiology and behavior

This review highlights literature relating the anatomy, physiology, and behavioral contributions by projections between rodent prefrontal cortical areas and the basolateral amygdala. These projections are robustly modulated by both environmental experience and exposure to drugs of abuse including ethanol. Recent literature relating optogenetic and chemogenetic dissection of these circuits within behavior both compliments and occasionally challenges roles defined by more traditional pharmacological or lesion-based approaches. In particular, cortico-amygdala circuits help control both aversive and reward-seeking. Exposure to pathology-producing environments or abused drugs dysregulates the relative 'balance' of these outcomes. Modern circuit-based approaches have also shown that overlapping populations of neurons within a given brain region frequently govern both aversion and reward-seeking. In addition, these circuits often dramatically influence 'local' cortical or basolateral amygdala excitatory or inhibitory circuits. Our understanding of these neurobiological processes, particularly in relation to ethanol research, has just begun and represents a significant opportunity.

Prefrontal GABAergic Interneurons Gate Long-Range Afferents to Regulate Prefrontal Cortex-Associated Complex Behaviors

Prefrontal cortical GABAergic interneurons (INs) and their innervations are essential for the execution of complex behaviors such as working memory, social behavior, and fear expression. These behavior regulations are highly dependent on primary long-range afferents originating from the subcortical structures such as mediodorsal thalamus (MD), ventral hippocampus (vHPC), and basolateral amygdala (BLA). In turn, the regulatory effects of these inputs are mediated by activation of parvalbumin-expressing (PV) and/or somatostatin expressing (SST) INs within the prefrontal cortex (PFC). Here we review how each of these long-range afferents from the MD, vHPC, or BLA recruits a subset of the prefrontal interneuron population to exert precise control of specific PFC-dependent behaviors. Specifically, we first summarize the anatomical connections of different long-range inputs formed on prefrontal GABAergic INs, focusing on PV versus SST cells. Next, we elaborate on the role of prefrontal PV- and SST- INs in regulating MD afferents-mediated cognitive behaviors. We also examine how prefrontal PV- and SST- INs gate vHPC afferents in spatial working memory and fear expression. Finally, we discuss the possibility that prefrontal PV-INs mediate fear conditioning, predominantly driven by the BLA-mPFC pathway. This review will provide a broad view of how multiple long-range inputs converge on prefrontal interneurons to regulate complex behaviors and novel future directions to understand how PFC controls different behaviors.

Connectivity characterization of the mouse basolateral amygdalar complex

The basolateral amygdalar complex (BLA) is implicated in behaviors ranging from fear acquisition to addiction. Optogenetic methods have enabled the association of circuit-specific functions to uniquely connected BLA cell types. Thus, a systematic and detailed connectivity profile of BLA projection neurons to inform granular, cell type-specific interrogations is warranted. Here, we apply machine-learning based computational and informatics analysis techniques to the results of circuit-tracing experiments to create a foundational, comprehensive BLA connectivity map. The analyses identify three distinct domains within the anterior BLA (BLAa) that house target-specific projection neurons with distinguishable morphological features. We identify brain-wide targets of projection neurons in the three BLAa domains, as well as in the posterior BLA, ventral BLA, posterior basomedial, and lateral amygdalar nuclei. Inputs to each nucleus also are identified via retrograde tracing. The data suggests that connectionally unique, domain-specific BLAa neurons are associated with distinct behavior networks.

Circuit organization of the rodent medial prefrontal cortex

The prefrontal cortex (PFC) orchestrates higher brain function and becomes disrupted in many mental health disorders. The rodent medial PFC (mPFC) possesses an enormous variety of projection neurons and interneurons. These cells are engaged by long-range inputs from other brain regions involved in cognition, motivation, and emotion. They also communicate in the local network via specific connections between excitatory and inhibitory cells. In this review, we describe the cellular diversity of the rodent mPFC, the impact of long-range afferents, and the specificity of local microcircuits. We highlight similarities with and differences between other cortical areas, illustrating how the circuit organization of the mPFC may give rise to its unique functional roles.

Striatal Direct Pathway Targets Npas1+ Pallidal Neurons

The classic basal ganglia circuit model asserts a complete segregation of the two striatal output pathways. Empirical data argue that, in addition to indirect-pathway striatal projection neurons (iSPNs), direct-pathway striatal projection neurons (dSPNs) innervate the external globus pallidus (GPe). However, the functions of the latter were not known. In this study, we interrogated the organization principles of striatopallidal projections and their roles in full-body movement in mice (both males and females). In contrast to the canonical motor-promoting response of dSPNs in the dorsomedial striatum (DMSdSPNs), optogenetic stimulation of dSPNs in the dorsolateral striatum (DLSdSPNs) suppressed locomotion. Circuit analyses revealed that dSPNs selectively target Npas1+ neurons in the GPe. In a chronic 6-hydroxydopamine lesion model of Parkinson's disease, the dSPN-Npas1+ projection was dramatically strengthened. As DLSdSPN-Npas1+ projection suppresses movement, the enhancement of this projection represents a circuit mechanism for the hypokinetic symptoms of Parkinson's disease that has not been previously considered. In sum, our results suggest that dSPN input to the GPe is a critical circuit component that is involved in the regulation of movement in both healthy and parkinsonian states.SIGNIFICANCE STATEMENT In the classic basal ganglia model, the striatum is described as a divergent structure: it controls motor and adaptive functions through two segregated, opposing output streams. However, the experimental results that show the projection from direct-pathway neurons to the external pallidum have been largely ignored. Here, we showed that this striatopallidal subpathway targets a select subset of neurons in the external pallidum and is motor-suppressing. We found that this subpathway undergoes changes in a Parkinson's disease model. In particular, our results suggest that the increase in strength of this subpathway contributes to the slowness or reduced movements observed in Parkinson's disease.

Reduced anterior cingulate cortex volume induced by chronic stress correlates with increased behavioral emotionality and decreased synaptic puncta density

Clinical and preclinical studies report that chronic stress induces behavioral deficits as well as volumetric and synaptic alterations in corticolimbic brain regions including the anterior cingulate cortex (ACC), amygdala (AMY), nucleus accumbens (NAc) and hippocampus (HPC). Here, we aimed to investigate the volumetric changes associated with chronic restraint stress (CRS) and link these changes to the CRS-induced behavioral and synaptic deficits. We first confirmed that CRS increases behavioral emotionality, defined as collective scoring of anxiety- and anhedonia-like behaviors. We then demonstrated that CRS induced a reduction of total brain volume which negatively correlated with behavioral emotionality. Region-specific analysis identified that only the ACC showed significant decrease in volume following CRS (p < 0.05). Reduced ACC correlated with increased behavioral emotionality (r = -0.56; p = 0.0003). Although not significantly altered by CRS, AMY and NAc (but not the HPC) volumes were negatively correlated with behavioral emotionality. Finally, using structural covariance network analysis to assess shared volumetric variances between the corticolimbic brain regions and associated structures, we found a progressive decreased ACC degree and increased AMY degree following CRS. At the cellular level, reduced ACC volume correlated with decreased PSD95 (but not VGLUT1) puncta density (r = 0.35, p < 0.05), which also correlated with increased behavioral emotionality (r = -0.44, p < 0.01), suggesting that altered synaptic strength is an underlying substrate of CRS volumetric and behavioral effects. Our results demonstrate that CRS effects on ACC volume and synaptic density are linked to behavioral emotionality and highlight key ACC structural and morphological alterations relevant to stress-related illnesses including mood and anxiety disorders.