New perspectives on central amygdala function

Memristor-based circuit design of interweaving mechanism of emotional memory in a hippocamp-brain emotion learning model

Endowing robots with human-like emotional and cognitive abilities has garnered widespread attention, driving deep investigations into the complexities of these processes. However, few studies have examined the intricate circuits that govern the interplay between emotion and memory. This work presents a memristive circuit design that generates emotional memory, mimicking human emotional responses and memories while enabling interaction between emotions and cognition. Leveraging the hippocampal-brain emotion learning (BEL) architecture, the memristive circuit comprises seven comprehensive modules: the thalamus, sensory cortex, orbitofrontal cortex, amygdala, dentate gyrus (DG), CA3, and CA1. This design incorporates a compact biological framework, facilitating the collaborative encoding of emotional memories by the amygdala and hippocampus and allowing for flexible adjustment of circuit parameters to accommodate diverse personality traits. The proposed memristor-based circuit effectively mimics the complex interplay between emotions and memory, providing a valuable foundation for advancing the development of robots capable of replicating human-like emotional responses and cognitive integration.

Ketamine evokes acute behavioral effects via μ-opioid receptor expressing neurons of the central amygdala

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Central amygdala astrocyte plasticity underlies GABAergic dysregulation in ethanol dependence

Dependence is a hallmark of alcohol use disorder characterized by excessive alcohol intake and withdrawal symptoms. The central nucleus of the amygdala (CeA) is a key brain structure underlying the synaptic and behavioral consequences of ethanol dependence. While accumulating evidence suggests that astrocytes regulate synaptic transmission and behavior, there is a limited understanding of the role astrocytes play in ethanol dependence. The present study used a combination of viral labeling, super resolution confocal microscopy, 3D image analysis, and slice electrophysiology to determine the effects of chronic intermittent ethanol (CIE) exposure on astrocyte plasticity in the CeA. During withdrawal from CIE exposure, we observed increased GABA transmission, an upregulation in astrocytic GAT3 levels, and an increased proximity of astrocyte processes near CeA synapses. Furthermore, GAT3 levels and synaptic proximity were positively associated with voluntary ethanol drinking in dependent rats. Slice electrophysiology confirmed that the upregulation in astrocytic GAT3 levels was functional, as CIE exposure unmasked a GAT3-sensitive tonic GABA current in the CeA. A causal role for astrocytic GAT3 in ethanol dependence was assessed using viral-mediated GAT3 overexpression and knockdown approaches. However, GAT3 knockdown or overexpression had no effect on somatic withdrawal symptoms, dependence-escalated ethanol intake, aversion-resistant drinking, or post-dependent ethanol drinking in male or female rats. Moreover, intra-CeA pharmacological inhibition of GAT3 did not alter dependent ethanol drinking. Together, these findings indicate that ethanol dependence induces GABAergic dysregulation and astrocyte plasticity in the CeA. However, these changes in astrocytic GAT3 do not appear to be necessary for the drinking related phenotypes associated with dependence.

Neuroanatomical and neurochemical organization of brainstem and forebrain circuits involved in breathing regulation

Breathing regulation depends on a highly intricate and precise network within the brainstem, requiring the identification of all neuronal elements in the brainstem respiratory circuits and a comprehensive understanding of their organization into distinct functional compartments. These compartments play a pivotal role by providing essential input to three main targets: cranial motoneurons that regulate airway control, spinal motoneurons that activate the inspiratory and expiratory muscles, and higher brain structures that influence breathing behavior and integrate it with other physiological and behavioral processes. This review offers a comprehensive examination of the phenotypes, connections, and functional roles of the major compartments within the brainstem and forebrain respiratory circuits. In addition, it summarizes the diverse neurotransmitters used by neurons in these regions, highlighting their contributions to the coordination and modulation of respiratory activity.

Food and water intake are regulated by distinct central amygdala circuits revealed using intersectional genetics

The central amygdala (CeA) plays a crucial role in defensive and appetitive behaviours. It contains genetically defined GABAergic neuron subpopulations distributed over three anatomical subregions, capsular (CeC), lateral (CeL), and medial (CeM). The roles that these molecularly- and anatomically-defined CeA neurons play in appetitive behavior remain unclear. Using intersectional genetics in mice, we found that neurons driving food or water consumption are confined to the CeM. Separate CeM subpopulations exist for water only versus water or food consumption. In vivo calcium imaging revealed that CeMHtr2a neurons promoting feeding are responsive towards appetitive cues with little regard for their physical attributes. CeMSst neurons involved in drinking are sensitive to the physical properties of salient stimuli. Both CeM subtypes receive inhibitory input from CeL and send projections to the parabrachial nucleus to promote appetitive behavior. These results suggest that distinct CeM microcircuits evaluate liquid and solid appetitive stimuli to drive the appropriate behavioral responses.

From the pancreas to the amygdala: New brain area critical for ingestive and motivated behavior control exerted by amylin

Amylin, a pancreatic peptide, has a well-established role in feeding behavior control. Amylin analogues are clinically utilized in patients with diabetes and are under investigation as potential anti-obesity pharmacotherapies. The neural circuits underlying actions of amylin on behavior are not well understood. While amylin was found to bind to the central amygdala (CeA) of rodents and primates and we found that all components of amylin receptors are present in the CeA, their potential role in physiology or behavior remains unknown. Here, we investigated the impact of this potential pancreas - CeA amylin-mediated communication - on ingestive and motivated behaviors. Activation of CeA amylin receptors resulted in a robust hypophagia, reduced food-motivated behavior, and altered macronutrient preference in male and female rats. Clinically used amylin analogue, pramlintide, reduced meal size and frequency by acting on the CeA. Disruption of CeA amylin signaling led to hyperphagia and body weight gain in a sex divergent manner. Importantly, CeA amylin signaling was required for appetite suppression induced by peripherally applied amylin, highlighting translational relevance of this brain site. Our data indicate the CeA is a critical neural substrate for amylin signaling.

Amygdala subregion volumes and apportionment in preadolescents - Associations with age, sex, and body mass index

The amygdala, a key limbic structure, is critical to emotional, social, and appetitive behaviors that develop throughout adolescence. Composed of a heterogeneous group of nuclei, questions remain about potential differences in the maturation of its subregions during development. In 3953 9- and 10-year-olds from the Adolescent Brain Cognitive Development℠ Study, the CIT168 Atlas was used to segment nine amygdala subregions. Linear mixed-effects models were used to examine the effects of age, sex, pubertal stage, and body mass index z-score (BMIz) on subregion volumes and their relative apportionment within the amygdala. Distinct associations were observed between age, sex, and BMIz with whole amygdala volume, subregion volumes, and subregion apportionment. Pubertal stage was not related to amygdala subregion volumes. Age was associated with near-global expansion of amygdala subregions during this developmental period. Female sex was linked to smaller volumes in most amygdala subregions, with larger relative apportionment in the dorsal subregions and smaller apportionment in the basolateral ventral paralaminar subregion. Higher BMIz was associated with smaller volumes in large basolateral subregions, with increased relative apportionment in smaller subregions. These findings provide a foundational context for understanding how developmental variables influence amygdala structure, with implications for understanding future risk for brain disorders.

Amygdala Subregion Volumes and Apportionment in Preadolescents - Associations with Age, Sex, and Body Mass Index

The amygdala, a key limbic structure, is critical to emotional, social, and appetitive behaviors that develop throughout adolescence. Composed of a heterogeneous group of nuclei, questions remain about potential differences in the maturation of its subregions during development. In 3,953 9- and 10-year-olds from the Adolescent Brain Cognitive Development Study, the CIT168 Amygdala Atlas was used to segment nine amygdala subregions. Linear mixed-effects models were used to examine the effects of age, sex, pubertal stage, and body mass index z-score (BMIz) on subregion volumes and their relative apportionment within the amygdala. Distinct associations were observed between age, sex, and BMIz and whole amygdala volume, subregion volumes, and subregion apportionment. Pubertal stage was not related to amygdala subregion volumes. Age was associated with near-global expansion of amygdala subregions during this developmental period. Female sex was linked to smaller volumes in most amygdala subregions, with larger relative apportionment in the dorsal subregions and smaller apportionment in the basolateral ventral paralaminar subregion. Higher BMIz was associated with smaller volumes in large basolateral subregions, with increased relative apportionment in smaller subregions. These findings provide a foundational context for understanding how developmental variables influence amygdala structure, with implications for understanding future risk for brain disorders.

Whole-brain mapping in adult zebrafish and identification of the functional brain network underlying the novel tank test

Zebrafish have gained prominence as a model organism in neuroscience over the past several decades, generating key insight into the development and functioning of the vertebrate brain. However, techniques for whole brain mapping in adult stage zebrafish are lacking. Here, we describe a pipeline built using open-source tools for whole-brain activity mapping in adult zebrafish. Our pipeline combines advances in histology, microscopy, and machine learning to capture cfos activity across the entirety of the brain. Following tissue clearing, whole brain images are captured using light-sheet microscopy and registered to the recently created adult zebrafish brain atlas (AZBA) for automated segmentation. By way of example, we used our pipeline to measure brain activity after zebrafish were subject to the novel tank test, one of the most widely used behaviors in adult zebrafish. Cfos levels peaked 15 minutes following behavior and several regions, including those containing serotoninergic and dopaminergic neurons, were active during exploration. Finally, we generated a novel tank test functional brain network. This revealed that several regions of the subpallium form a cohesive sub-network during exploration. Functional interconnections between the subpallium and other regions appear to be mediated primarily by ventral nucleus of the ventral telencephalon (Vv), the olfactory bulb, and the anterior part of the parvocellular preoptic nucleus (PPa). Taken together, our pipeline enables whole-brain activity mapping in adult zebrafish while providing insight into neural basis for the novel tank test.Significance statement Zebrafish have grown in popularity as a model organism over the past several decades due to their low cost, ease of genetic manipulation, and similarity to other vertebrates like humans and rodents. However, to date, tools for whole-brain mapping in adult stage animals has been lacking. Here, we present an open-source pipeline for whole-brain mapping in adult zebrafish. We demonstrate the use of our pipeline by generating a functional brain network for one of the most widely used behavioral assays in adult zebrafish, the novel tank test. We found that exploration of a novel tank engages the olfactory bulb and a network of subpallial regions that correspond to the mammalian subpallial amygdala and basal ganglia.

Integration of Glucagon-Like Peptide 1 Receptor Actions Through the Central Amygdala

Understanding the detailed mechanism of action of glucagon-like peptide 1 receptor (GLP-1R) agonists on distinct topographic and genetically defined brain circuits is critical for improving the efficacy and mitigating adverse side effects of these compounds. In this mini-review, we propose that the central nucleus of the amygdala (CeA) is a critical mediator of GLP-1R agonist-driven hypophagia. Here, we review the extant literature demonstrating CeA activation via GLP-1R agonists across multiple species and through multiple routes of administration. The precise role of GLP-1Rs within the CeA is unclear but the site-specific GLP-1Rs may mediate distinct behavioral and physiological hallmarks of GLP-1R agonists on food intake. Thus, we propose important novel directions and methods to test the role of the CeA in mediating GLP-1R actions.

Update on the connectivity of the paraventricular nucleus of the thalamus and its position within limbic corticostriatal circuits

The paraventricular nucleus of the thalamus (PVT) is generating interest because evidence establishes a role for this midline thalamic nucleus in behavior. Early tracing studies demonstrated that afferent fibers from the PVT and limbic cortex converge with dopamine fibers within subcompartments of the ventral striatum. Subsequent tracing studies expanded on these observations by establishing that the PVT provides a dense projection to a continuum of striatal-like regions that include the nucleus accumbens and the extended amygdala. These findings have been complemented by recent tracing evidence examining the organization of the PVT's efferent and afferent connections. An updated view of the organization of projection neurons in PVT is provided with a focus on the input-output relationship of these neurons. The review emphasizes recent findings demonstrating that the PVT is composed of intermixed populations of neurons with axons that collateralize to densely innervate limbic striatal regions while being reciprocally connected with limbic cortical areas that innervate the same regions of the striatum. An updated perspective of the PVT's anatomical relationship with limbic corticostriatal circuits is presented to stimulate research on how the PVT regulates behavioral responses associated with emotion and motivation.

Cannabinoid Modulation of Central Amygdala Population Dynamics During Threat Investigation

Cannabinoids modulate innate avoidance, threat-reactivity, and stress adaptations via modulation amygdala-associated circuits; however, the mechanisms by which cannabinoids modulate amygdala representation of threat-related behavior are not known. We show that cannabinoid administration increases the activity of central amygdala (CeA) somatostatin neurons (SOM) and alters basal network dynamics in a manner supporting generation of antagonistic sub-ensembles within the SOM population. Moreover, diverging neuronal population trajectory dynamics and enhanced antagonistic sub-ensemble representation of threat-related behaviors, and enhanced threat-related location representation, were also observed. Lastly, cannabinoid administration increased the proportion of SOM neurons exhibiting multidimensional representation of threat-related behaviors and behavior-location conjunction. While cannabinoid receptor activation ex vivo suppressed excitatory inputs to SOM neurons, our data suggest preferential suppression of local GABA release subserves cannabinoid activation of CeA SOM neurons. These data provide insight into how cannabinoid-mediated presynaptic suppression transforms postsynaptic population dynamics and reveal cellular mechanisms by which cannabinoids could affect threat-reactivity.

Structural and functional alterations in different types of delusions across schizophrenia spectrum: A systematic review

BACKGROUND

Despite the high clinical role of delusions as a transnosological psychopathological phenomenon, the number of experimental studies on the different types of delusions across schizophrenia spectrum is still relatively small, and their results are somehow inconsistent. We aimed to understand the current state of knowledge regarding the structural and functional brain alterations in delusions to determine whether particular types of delusions are associated with specific brain changes and to identify common alterations underlying the formation and persistence of delusions regardless of their content.

METHODS

For this systematic review, we followed PRISMA guidelines to search in PubMed for English papers published between 1953 and September 30, 2023. The initial inclusion criteria for screening purposes were articles that investigated delusions or subclinical delusional beliefs in schizophrenia spectrum disorders, high clinical or genetic risk for schizophrenia using fMRI, sMRI or/and dwMRI methods. Exclusion criteria during the screening phase were articles that investigated lesion-induced or substance-induced delusions, delusions in Alzheimer's disease and other neurocognitive disorders, single case studies and non-human studies. The publication metadata were uploaded to the web-tool for working on systematic reviews, Rayyan. For each of the studies, a table was filled out with detailed information.

RESULTS

We found 1752 records, of which 95 full-text documents were reviewed and included in the current paper. Both nonspecific and particular types of delusions were associated with widespread structural and functional alterations. The most prominent areas affected across all types of delusions were the superior temporal cortex (predominantly left language processing areas), anterior cingulate/medial prefrontal cortex and insula. The most reproducible findings in paranoia may be alterations in the functioning of the amygdala and its interactions with other regions. Somatic delusions and delusional infestation were mostly characterized by alterations in the insula and thalamus.

DISCUSSION

The data are ambiguous; however, in general the predictive processing framework seems to be the most widely accepted approach to explaining different types of delusions. Aberrant prediction errors signaling during processing of social, self-generated and sensory information may lead to inaccuracies in assessing the intentions of others, self-relevancy of ambiguous stimuli, misattribution of self-generated actions and unusual sensations, which could provoke delusional ideation with persecutory, reference, control and somatic content correspondingly. However, currently available data are still insufficient to draw conclusions about the specific biological mechanisms of predictive coding account of delusions. Thus, further studies exploring more homogeneous groups and interaction of diagnoses by types of delusions are needed. There are also some limitations in this review. Studies that investigate delusions induced by lesions, substance abuse or neurodegeneration and studies using modalities other than fMRI, sMRI or dwMRI were not included in the review. Due to the relatively small number of publications, we systematized them based on a certain type of delusions, while the results could also be affected by the diagnosis of patients, the presence and type of therapy, illness duration etc.

Valence and salience encoding in the central amygdala

The central amygdala (CeA) has emerged as an important brain region for regulating both negative (fear and anxiety) and positive (reward) affective behaviors. The CeA has been proposed to encode affective information in the form of valence (whether the stimulus is good or bad) or salience (how significant is the stimulus), but the extent to which these two types of stimulus representation occur in the CeA is not known. Here, we used single cell calcium imaging in mice during appetitive and aversive conditioning and found that majority of CeA neurons (~65%) encode the valence of the unconditioned stimulus (US) with a smaller subset of cells (~15%) encoding the salience of the US. Valence and salience encoding of the conditioned stimulus (CS) was also observed, albeit to a lesser extent. These findings show that the CeA is a site of convergence for encoding oppositely valenced US information.

Insights into the Neurobiology of Behavioral Inhibition from Nonhuman Primate Models

Children with extreme behavioral inhibition (BI) are at a significantly greater risk to develop anxiety disorders later in life. We and others have identified similar early-life temperamental BI in nonhuman primates (NHPs), including rhesus monkeys. NHP models of BI provide a unique opportunity to study the neurobiology of BI in a species that shares biological, developmental, and socioemotional similarities with humans. Rhesus monkey models have identified a distributed brain circuit that includes the central extended amygdala (EAc) as being critical for the genesis of BI. By leveraging multimodal neuroimaging, brain lesions, RNA-sequencing, and viral vector manipulations in rhesus monkeys, these studies have identified specific brain regions, genetic factors, and molecular mechanisms that causally contribute to BI. Here, we discuss these findings from NHPs and how they fit into a translational framework that can contribute to our understanding of the neural circuits that give rise to the risk to develop anxiety and depressive disorders.

Regulator of G protein signalling 14 (RGS14) protein expression profile in the adult mouse brain

Regulator of G protein signalling 14 (RGS14) is a multifunctional signalling protein that serves as a natural suppressor of synaptic plasticity in the mouse brain. Our previous studies showed that RGS14 is highly expressed in postsynaptic dendrites and spines of pyramidal neurons in hippocampal area CA2 of the developing mouse brain. However, our more recent work with monkey brain shows that RGS14 is found in multiple neuron populations throughout hippocampal area CA1 and CA2, caudate nucleus, putamen, globus pallidus, substantia nigra and amygdala. In the mouse brain, we also have observed RGS14 protein in discrete limbic regions linked to reward behaviour and addiction, including the central amygdala and the nucleus accumbens, but a comprehensive mapping of RGS14 protein expression in the adult mouse brain is lacking. Here, we report that RGS14 is more broadly expressed in mouse brain than previously known. Intense RGS14 staining is observed in specific neuron populations of the hippocampal formation, amygdala, septum, bed nucleus of stria terminalis and ventral striatum/nucleus accumbens. RGS14 is also observed in axon fibre tracts including the dorsal fornix, fimbria, stria terminalis and the ventrohippocampal commissure. Moderate RGS14 staining is observed in various other adjacent regions not previously reported. These findings show that RGS14 is expressed in brain regions that govern aspects of core cognitive functions such as sensory perception, emotion, memory, motivation and execution of actions and suggest that RGS14 may serve to suppress plasticity and filter inputs in these brain regions to set the overall tone on experience-to-action processes.

Central amygdala-to-pre-Bötzinger complex neurotransmission is direct and inhibitory

Breathing behaviour is subject to emotional regulation, but the underlying mechanisms remain unclear. Here, we demonstrate a direct relationship between the central amygdala, a major output hub of the limbic system associated with emotional brain function, and the brainstem pre-Bötzinger complex, which generates the fundamental rhythm and pattern for breathing. The connection between these two sites is monosynaptic and inhibitory, involving GABAergic central amygdala neurons whose axonal projections act predominantly via ionotropic GABAA receptors to produce inhibitory postsynaptic currents in pre-Bötzinger neurons. This pathway may provide a mechanism to inhibit breathing in the context of freezing to assess threats and plan defensive action. The existence of this pathway may further explain how epileptic seizures invading the amygdala cause long-lasting apnea, which can be fatal. Although their ultimate importance awaits further behavioural tests, these results elucidate a link between emotional brain function and breathing, which underlies survival-related behaviour in mammals and pertains to human anxiety disorders.

Translational Insights From Cell Type Variation Across Amygdala Subnuclei in Rhesus Monkeys and Humans

OBJECTIVE

Theories of amygdala function are central to our understanding of psychiatric and neurodevelopmental disorders. However, limited knowledge of the molecular and cellular composition of the amygdala impedes translational research aimed at developing new treatments and interventions. The aim of this study was to characterize and compare the composition of amygdala cells to help bridge the gap between preclinical models and human psychiatric and neurodevelopmental disorders.

METHODS

Tissue was dissected from multiple amygdala subnuclei in both humans (N=3, male) and rhesus macaques (N=3, male). Single-nucleus RNA sequencing was performed to characterize the transcriptomes of individual nuclei.

RESULTS

The results reveal substantial heterogeneity between regions, even when restricted to inhibitory or excitatory neurons. Consistent with previous work, the data highlight the complexities of individual marker genes for uniquely targeting specific cell types. Cross-species analyses suggest that the rhesus monkey model is well-suited to understanding the human amygdala, but also identify limitations. For example, a cell cluster in the ventral lateral nucleus of the amygdala (vLa) is enriched in humans relative to rhesus macaques. Additionally, the data describe specific cell clusters with relative enrichment of disorder-related genes. These analyses point to the human-enriched vLa cell cluster as relevant to autism spectrum disorder, potentially highlighting a vulnerability to neurodevelopmental disorders that has emerged in recent primate evolution. Further, a cluster of cells expressing markers for intercalated cells is enriched for genes reported in human genome-wide association studies of neuroticism, anxiety disorders, and depressive disorders.

CONCLUSIONS

Together, these findings shed light on the composition of the amygdala and identify specific cell types that can be prioritized in basic science research to better understand human psychopathology and guide the development of potential treatments.

An Honest Reckoning With the Amygdala and Mental Illness

Anxiety disorders are a leading source of human misery, morbidity, and premature mortality. Existing treatments are far from curative for many, underscoring the need to clarify the underlying neural mechanisms. Although many brain regions contribute, the amygdala has received the most intense scientific attention. Over the past several decades, this scrutiny has yielded a detailed understanding of amygdala function, but it has failed to produce new clinical assays, biomarkers, or cures. Rising to this urgent public health challenge demands an honest reckoning with the functional-neuroanatomical complexity of the amygdala and a shift from theories anchored on "the amygdala" to models centered on specific amygdala nuclei and cell types. This review begins by examining evidence from studies of rodents, monkeys, and humans for the "canonical model," the idea that the amygdala plays a central role in fear- and anxiety-related states, traits, and disorders. Next, the authors selectively highlight work indicating that the canonical model, while true, is overly simplistic and fails to adequately capture the actual state of the evidentiary record, the breadth of amygdala-associated functions and illnesses, or the complexity of the amygdala's functional architecture. The authors describe the implications of these facts for basic and clinical neuroimaging research. The review concludes with some general recommendations for grappling with the complexity of the amygdala and accelerating efforts to understand and more effectively treat amygdala-related psychopathology.

Dopaminergic circuits controlling threat and safety learning

The ability to learn from experience that certain cues and situations are associated with threats or safety is crucial for survival and adaptive behavior. Understanding the neural substrates of threat and safety learning has high clinical significance because deficits in these forms of learning characterize anxiety disorders. Traditionally, dopamine neurons were thought to uniformly support reward learning by signaling reward prediction errors. However, the dopamine system is functionally more diverse than was initially appreciated and is also critical for processing threat and safety. In this review, I highlight recent studies demonstrating that dopamine neurons generate prediction errors for threat and safety, and describe how dopamine projections to the amygdala, medial prefrontal cortex (mPFC), and striatum regulate associative threat and safety learning.

Sex Differences in Neural Circuits Underlying Fear Processing

Neural circuitry involved in anxiety and fear-related disorders exhibits strong sexual modulation. A limited number of studies integrating female and male data have revealed differences in neural networks, and distinct interconnectivity between these brain areas. Despite the efforts to incorporate female or mixed-sex data, there is compelling evidence that sex, as a biological variable, significantly influences fear processing. This chapter presents primary findings on sex differences in fear circuitry. It is imperative to consider this factor to ensure scientific research's integrity and understand how fear is processed in the central nervous system.

Developmental Shifts in Amygdala Function

Mammals have evolved with strategies to optimize survival and thrive in their native environment. This includes both physical and behavioral adaptations, and extends to their social environment. However, within a social context, the roles of an animal change across development, and their behavior and biology must update to match these changes. The amygdala has a key role in social and emotional processing and expression, and displays developmental changes in early juvenile, adolescent, and adult transitions. Furthermore, the amygdala is highly sensitive to the social environment. This chapter will describe the primary amygdala developmental changes, how this maps onto major changes in social and emotional domains, and propose a framework where developmental stage of intra-amygdala circuits and its regulation by cortical inputs biases the animal toward developmentally appropriate social and emotional behavior. This developmental plasticity also presents an opportunity for retuning the developmental trajectory in the presence of ongoing challenges during maturation, such as constant threat or resource scarcity, so there can be realignment of behavior to match environmental demands.

Valence and Salience Encoding in the Central Amygdala

The central amygdala (CeA) has emerged as an important brain region for regulating both negative (fear and anxiety) and positive (reward) affective behaviors. The CeA has been proposed to encode affective information in the form of valence (whether the stimulus is good or bad) or salience (how significant is the stimulus), but the extent to which these two types of stimulus representation occur in the CeA is not known. Here, we used single cell calcium imaging in mice during appetitive and aversive conditioning and found that majority of CeA neurons (~65%) encode the valence of the unconditioned stimulus (US) with a smaller subset of cells (~15%) encoding the salience of the US. Valence and salience encoding of the conditioned stimulus (CS) was also observed, albeit to a lesser extent. These findings show that the CeA is a site of convergence for encoding oppositely valenced US information.

Behavioral outputs and overlapping circuits between conditional fear and active avoidance

Aversive learning can produce a wide variety of defensive behavioral responses depending on the circumstances, ranging from reactive responses like freezing to proactive avoidance responses. While most of this initial learning is behaviorally supported by an expectancy of an aversive outcome and neurally supported by activity within the basolateral amygdala, activity in other brain regions become necessary for the execution of defensive strategies that emerge in other aversive learning paradigms such as active avoidance. Here, we review the neural circuits that support both reactive and proactive defensive behaviors that are motivated by aversive learning, and identify commonalities between the neural substrates of these distinct (and often exclusive) behavioral strategies.

Whole-brain mapping in adult zebrafish and identification of a novel tank test functional connectome

Identifying general principles of brain function requires the study of structure-function relationships in a variety of species. Zebrafish have recently gained prominence as a model organism in neuroscience, yielding important insights into vertebrate brain function. Although methods have been developed for mapping neural activity in larval animals, we lack similar techniques for adult zebrafish that have the advantage of a fully developed neuroanatomy and larger behavioral repertoire. Here, we describe a pipeline built around open-source tools for whole-brain activity mapping in freely swimming adult zebrafish. Our pipeline combines recent advances in histology, microscopy, and machine learning to capture cfos activity across the entirety of the adult brain. Images captured using light-sheet microscopy are registered to the recently created adult zebrafish brain atlas (AZBA) for automated segmentation using advanced normalization tools (ANTs). We used our pipeline to measure brain activity after zebrafish were subject to the novel tank test. We found that cfos levels peaked 15 minutes following behavior and that several regions containing serotoninergic, dopaminergic, noradrenergic, and cholinergic neurons were active during exploration. Finally, we generated a novel tank test functional connectome. Functional network analysis revealed that several regions of the medial ventral telencephalon form a cohesive sub-network during exploration. We also found that the anterior portion of the parvocellular preoptic nucleus (PPa) serves as a key connection between the ventral telencephalon and many other parts of the brain. Taken together, our work enables whole-brain activity mapping in adult zebrafish for the first time while providing insight into neural basis for the novel tank test.

Subregion-specific transcriptomic profiling of rat brain reveals sex-distinct gene expression impacted by adolescent stress

Stress during adolescence clearly impacts brain development and function. Sex differences in adolescent stress-induced or exacerbated emotional and metabolic vulnerabilities could be due to sex-distinct gene expression in hypothalamic, limbic, and prefrontal brain regions. However, adolescent stress-induced whole-genome expression changes in key subregions of these brain regions were unclear. In this study, female and male adolescent Sprague Dawley rats received one-hour restraint stress daily from postnatal day (PD) 32 to PD44. Corticosterone levels, body weights, food intake, body composition, and circulating adiposity and sex hormones were measured. On PD44, brain and blood samples were collected. Using RNA-sequencing, sex-specific differences in stress-induced differentially expressed (DE) genes were identified in subregions of the hypothalamus, limbic system, and prefrontal cortex. Canonical pathways reflected well-known sex-distinct maladies and diseases, substantiating the therapeutic potential of the DE genes found in the current study. Thus, we proposed specific sex distinct, adolescent stress-induced transcriptional changes found in the current study as examples of the molecular bases for sex differences witnessed in stress induced or exacerbated emotional and metabolic disorders. Future behavioral studies and single-cell studies are warranted to test the implications of the DE genes identified in this study in sex-distinct stress-induced susceptibilities.

Suppression of excitatory synaptic transmission in the centrolateral amygdala via presynaptic histamine H3 heteroreceptors

The central histaminergic system has a pivotal role in emotional regulation and psychiatric disorders, including anxiety, depression and schizophrenia. However, the effect of histamine on neuronal activity of the centrolateral amygdala (CeL), an essential node for fear and anxiety processing, remains unknown. Here, using immunostaining and whole-cell patch clamp recording combined with optogenetic manipulation of histaminergic terminals in CeL slices prepared from histidine decarboxylase (HDC)-Cre rats, we show that histamine selectively suppresses excitatory synaptic transmissions, including glutamatergic transmission from the basolateral amygdala, on both PKC-δ- and SOM-positive CeL neurons. The histamine-induced effect is mediated by H3 receptors expressed on VGLUT1-/VGLUT2-positive presynaptic terminals in CeL. Furthermore, optoactivation of histaminergic afferent terminals from the hypothalamic tuberomammillary nucleus (TMN) also significantly suppresses glutamatergic transmissions in CeL via H3 receptors. Histamine neither modulates inhibitory synaptic transmission by presynaptic H3 receptors nor directly excites CeL neurons by postsynaptic H1, H2 or H4 receptors. These results suggest that histaminergic afferent inputs and presynaptic H3 heteroreceptors may hold a critical position in balancing excitatory and inhibitory synaptic transmissions in CeL by selective modulation of glutamatergic drive, which may not only account for the pathophysiology of psychiatric disorders but also provide potential psychotherapeutic targets. KEY POINTS: Histamine selectively suppresses the excitatory, rather than inhibitory, synaptic transmissions on both PKC-δ- and SOM-positive neurons in the centrolateral amygdala (CeL). H3 receptors expressed on VGLUT1- or VGLUT2-positive afferent terminals mediate the suppression of histamine on glutamatergic synaptic transmission in CeL. Optogenetic activation of hypothalamic tuberomammillary nucleus (TMN)-CeL histaminergic projections inhibits glutamatergic transmission in CeL via H3 receptors.

Regulator of G Protein Signaling 14 protein expression profile in the adult mouse brain

Regulator of G protein signaling 14 (RGS14) is a multifunctional signaling protein that serves as a natural suppressor of synaptic plasticity in the mouse brain. Our previous studies showed that RGS14 is highly expressed in postsynaptic dendrites and spines of pyramidal neurons in hippocampal area CA2 of the developing mouse brain. However, our more recent work with adult rhesus macaque brain shows that RGS14 is found in multiple neuron populations throughout hippocampal area CA1 and CA2, caudate nucleus, putamen, globus pallidus, substantia nigra, and amygdala in the adult rhesus monkey brain. In the mouse brain, we also have observed RGS14 protein in discrete limbic regions linked to reward behavior and addiction, including the central amygdala and the nucleus accumbens, but a comprehensive mapping of RGS14 protein expression in the adult mouse brain is lacking. Here, we report that RGS14 is more broadly expressed in mouse brain than previously known. Intense RGS14 staining is observed in specific neuron populations of the hippocampal formation, amygdala, septum, bed nucleus of stria terminalis and ventral striatum/nucleus accumbens. RGS14 is also observed in axon fiber tracts including the dorsal fornix, fimbria, stria terminalis, and the ventrohippocampal commissure. Moderate RGS14 staining is observed in various other adjacent regions not previously reported. These findings show that RGS14 is expressed in brain regions that govern aspects of core cognitive functions such as sensory perception, emotion, memory, motivation, and execution of actions, and suggests that RGS14 may serve to suppress plasticity and filter inputs in these brain regions to set the overall tone on experience-to-action processes.

Central Amygdala Astrocyte Plasticity Underlies GABAergic Dysregulation in Ethanol Dependence

Dependence is a hallmark of alcohol use disorder characterized by excessive alcohol intake and withdrawal symptoms. The central nucleus of the amygdala (CeA) is a key brain structure underlying the synaptic and behavioral consequences of ethanol dependence. While accumulating evidence suggests that astrocytes regulate synaptic transmission and behavior, there is a limited understanding of the role astrocytes play in ethanol dependence. The present study used a combination of viral labeling, super resolution confocal microscopy, 3D image analysis, and slice electrophysiology to determine the effects of chronic intermittent ethanol (CIE) exposure on astrocyte plasticity in the CeA. During withdrawal from CIE exposure, we observed increased GABA transmission, an upregulation in astrocytic GAT3 levels, and an increased proximity of astrocyte processes near CeA synapses. Furthermore, GAT3 levels and synaptic proximity were positively associated with voluntary ethanol drinking in dependent rats. Slice electrophysiology confirmed that the upregulation in astrocytic GAT3 levels was functional, as CIE exposure unmasked a GAT3-sensitive tonic GABA current in the CeA. A causal role for astrocytic GAT3 in ethanol dependence was assessed using viral-mediated GAT3 overexpression and knockdown approaches. However, GAT3 knockdown or overexpression had no effect on somatic withdrawal symptoms, dependence-escalated ethanol intake, aversion-resistant drinking, or post-dependent ethanol drinking in male or female rats. Moreover, intra-CeA pharmacological inhibition of GAT3 also did not alter dependent ethanol drinking. Together, these findings indicate that ethanol dependence induces GABAergic dysregulation and astrocyte plasticity in the CeA. However, astrocytic GAT3 does not appear necessary for the drinking related phenotypes associated with dependence.

The human hypothalamus coordinates switching between different survival actions

Comparative research suggests that the hypothalamus is critical in switching between survival behaviors, yet it is unclear if this is the case in humans. Here, we investigate the role of the human hypothalamus in survival switching by introducing a paradigm where volunteers switch between hunting and escape in response to encounters with a virtual predator or prey. Given the small size and low tissue contrast of the hypothalamus, we used deep learning-based segmentation to identify the individual-specific hypothalamus and its subnuclei as well as an imaging sequence optimized for hypothalamic signal acquisition. Across 2 experiments, we employed computational models with identical structures to explain internal movement generation processes associated with hunting and escaping. Despite the shared structure, the models exhibited significantly different parameter values where escaping or hunting were accurately decodable just by computing the parameters of internal movement generation processes. In experiment 2, multi-voxel pattern analyses (MVPA) showed that the hypothalamus, hippocampus, and periaqueductal gray encode switching of survival behaviors while not encoding simple motor switching outside of the survival context. Furthermore, multi-voxel connectivity analyses revealed a network including the hypothalamus as encoding survival switching and how the hypothalamus is connected to other regions in this network. Finally, model-based fMRI analyses showed that a strong hypothalamic multi-voxel pattern of switching is predictive of optimal behavioral coordination after switching, especially when this signal was synchronized with the multi-voxel pattern of switching in the amygdala. Our study is the first to identify the role of the human hypothalamus in switching between survival behaviors and action organization after switching.

Encoding and context-dependent control of reward consumption within the central nucleus of the amygdala

Dysregulation of the central amygdala is thought to underlie aberrant choice in alcohol use disorder, but the role of central amygdala neural activity during reward choice and consumption is unclear. We recorded central amygdala neurons in male rats as they consumed alcohol or sucrose. We observed activity changes at the time of reward approach, as well as lick-entrained activity during ongoing consumption of both rewards. In choice scenarios where rats could drink sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala optogenetic stimulation, rats drank more of stimulation-paired options when the two bottles contained identical options. Given a choice among different options, central amygdala stimulation usually enhanced consumption of stimulation-paired rewards. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance alcohol intake while sucrose was available. These findings indicate that the central amygdala contributes to refining motivated pursuit toward the preferred available option.

Leveraging interindividual variability in threat conditioning of inbred mice to model trait anxiety

Trait anxiety is a major risk factor for stress-induced and anxiety disorders in humans. However, animal models accounting for the interindividual variability in stress vulnerability are largely lacking. Moreover, the pervasive bias of using mostly male animals in preclinical studies poorly reflects the increased prevalence of psychiatric disorders in women. Using the threat imminence continuum theory, we designed and validated an auditory aversive conditioning-based pipeline in both female and male mice. We operationalised trait anxiety by harnessing the naturally occurring variability of defensive freezing responses combined with a model-based clustering strategy. While sustained freezing during prolonged retrieval sessions was identified as an anxiety-endophenotype behavioral marker in both sexes, females were consistently associated with an increased freezing response. RNA-sequencing of CeA, BLA, ACC, and BNST revealed massive differences in phasic and sustained responders' transcriptomes, correlating with transcriptomic signatures of psychiatric disorders, particularly post-traumatic stress disorder (PTSD). Moreover, we detected significant alterations in the excitation/inhibition balance of principal neurons in the lateral amygdala. These findings provide compelling evidence that trait anxiety in inbred mice can be leveraged to develop translationally relevant preclinical models to investigate mechanisms of stress susceptibility in a sex-specific manner.

EZH2-dependent epigenetic reprogramming in the central nucleus of amygdala regulates adult anxiety in both sexes after adolescent alcohol exposure

Alcohol use and anxiety disorders occur in both males and females, but despite sharing similar presentation and classical symptoms, the prevalence of alcohol use disorder (AUD) is lower in females. While anxiety is a symptom and comorbidity shared by both sexes, the common underlying mechanism that leads to AUD and the subsequent development of anxiety is still understudied. Using a rodent model of adolescent intermittent ethanol (AIE) exposure in both sexes, we investigated the epigenetic mechanism mediated by enhancer of zeste 2 (EZH2), a histone methyltransferase, in regulating both the expression of activity-regulated cytoskeleton-associated protein (Arc) and an anxiety-like phenotype in adulthood. Here, we report that EZH2 protein levels were significantly higher in PKC-δ positive GABAergic neurons in the central nucleus of amygdala (CeA) of adult male and female rats after AIE. Reducing protein and mRNA levels of EZH2 using siRNA infusion in the CeA prevented AIE-induced anxiety-like behavior, increased H3K27me3, decreased H3K27ac at the Arc synaptic activity response element (SARE) site, and restored deficits in Arc mRNA and protein expression in both male and female adult rats. Our data indicate that an EZH2-mediated epigenetic mechanism in the CeA plays an important role in regulating anxiety-like behavior and Arc expression after AIE in both male and female rats in adulthood. This study suggests that EZH2 may serve as a tractable drug target for the treatment of adult psychopathology after adolescent alcohol exposure.

Nausea-induced suppression of feeding is mediated by central amygdala Dlk1-expressing neurons

The motivation to eat is suppressed by satiety and aversive stimuli such as nausea. The neural circuit mechanisms of appetite suppression by nausea are not well understood. Pkcδ neurons in the lateral subdivision of the central amygdala (CeA) suppress feeding in response to satiety signals and nausea. Here, we characterized neurons enriched in the medial subdivision (CeM) of the CeA marked by expression of Dlk1. CeADlk1 neurons are activated by nausea, but not satiety, and specifically suppress feeding induced by nausea. Artificial activation of CeADlk1 neurons suppresses drinking and social interactions, suggesting a broader function in attenuating motivational behavior. CeADlk1 neurons form projections to many brain regions and exert their anorexigenic activity by inhibition of neurons of the parabrachial nucleus. CeADlk1 neurons are inhibited by appetitive CeA neurons, but also receive long-range monosynaptic inputs from multiple brain regions. Our results illustrate a CeA circuit that regulates nausea-induced feeding suppression.

Rhesus infant nervous temperament predicts peri-adolescent central amygdala metabolism & behavioral inhibition measured by a machine-learning approach

Anxiety disorders affect millions of people worldwide and impair health, happiness, and productivity on a massive scale. Developmental research points to a connection between early-life behavioral inhibition and the eventual development of these disorders. Our group has previously shown that measures of behavioral inhibition in young rhesus monkeys (Macaca mulatta) predict anxiety-like behavior later in life. In recent years, clinical and basic researchers have implicated the central extended amygdala (EAc)-a neuroanatomical concept that includes the central nucleus of the amygdala (Ce) and the bed nucleus of the stria terminalis (BST)-as a key neural substrate for the expression of anxious and inhibited behavior. An improved understanding of how early-life behavioral inhibition relates to an increased lifetime risk of anxiety disorders-and how this relationship is mediated by alterations in the EAc-could lead to improved treatments and preventive strategies. In this study, we explored the relationships between infant behavioral inhibition and peri-adolescent defensive behavior and brain metabolism in 18 female rhesus monkeys. We coupled a mildly threatening behavioral assay with concurrent multimodal neuroimaging, and related those findings to various measures of infant temperament. To score the behavioral assay, we developed and validated UC-Freeze, a semi-automated machine-learning (ML) tool that uses unsupervised clustering to quantify freezing. Consistent with previous work, we found that heightened Ce metabolism predicted elevated defensive behavior (i.e., more freezing) in the presence of an unfamiliar human intruder. Although we found no link between infant-inhibited temperament and peri-adolescent EAc metabolism or defensive behavior, we did identify infant nervous temperament as a significant predictor of peri-adolescent defensive behavior. Our findings suggest a connection between infant nervous temperament and the eventual development of anxiety and depressive disorders. Moreover, our approach highlights the potential for ML tools to augment existing behavioral neuroscience methods.

Opioid receptor expressing neurons of the central amygdala gate behavioral effects of ketamine in mice

Ketamine has anesthetic, analgesic, and antidepressant properties which may involve multiple neuromodulatory systems. In humans, the opioid receptor (OR) antagonist naltrexone blocks the antidepressant effect of ketamine. It is unclear whether naltrexone blocks a direct effect of ketamine at ORs, or whether normal functioning of the OR system is required to realize the full antidepressant effects of treatment. In mice, the effect of ketamine on locomotion, but not analgesia or the forced swim test, was sensitive to naltrexone and was therefore used as a behavioral readout to localize the effect of naltrexone in the brain. We performed whole-brain imaging of cFos expression in ketamine-treated mice, pretreated with naltrexone or vehicle, and identified the central amygdala (CeA) as the area with greatest difference in cFos intensity. CeA neurons expressing both μOR (MOR) and PKCμ were strongly activated by naltrexone but not ketamine, and selectively interrupting MOR function in the CeA either pharmacologically or genetically blocked the locomotor effects of ketamine. These data suggest that MORs expressed in CeA neurons gate behavioral effects of ketamine but are not direct targets of ketamine.

65 years of research on dopamine's role in classical fear conditioning and extinction: A systematic review

Dopamine, a catecholamine neurotransmitter, has historically been associated with the encoding of reward, whereas its role in aversion has received less attention. Here, we systematically gathered the vast evidence of the role of dopamine in the simplest forms of aversive learning: classical fear conditioning and extinction. In the past, crude methods were used to augment or inhibit dopamine to study its relationship with fear conditioning and extinction. More advanced techniques such as conditional genetic, chemogenic and optogenetic approaches now provide causal evidence for dopamine's role in these learning processes. Dopamine neurons encode conditioned stimuli during fear conditioning and extinction and convey the signal via activation of D1-4 receptor sites particularly in the amygdala, prefrontal cortex and striatum. The coordinated activation of dopamine receptors allows for the continuous formation, consolidation, retrieval and updating of fear and extinction memory in a dynamic and reciprocal manner. Based on the reviewed literature, we conclude that dopamine is crucial for the encoding of classical fear conditioning and extinction and contributes in a way that is comparable to its role in encoding reward.

An active inference perspective for the amygdala complex

The amygdala is a heterogeneous network of subcortical nuclei with central importance in cognitive and clinical neuroscience. Various experimental designs in human psychology and animal model research have mapped multiple conceptual frameworks (e.g., valence/salience and decision making) to ever more refined amygdala circuitry. However, these predominantly bottom up-driven accounts often rely on interpretations tailored to a specific phenomenon, thus preventing comprehensive and integrative theories. We argue here that an active inference model of amygdala function could unify these fractionated approaches into an overarching framework for clearer empirical predictions and mechanistic interpretations. This framework embeds top-down predictive models, informed by prior knowledge and belief updating, within a dynamical system distributed across amygdala circuits in which self-regulation is implemented by continuously tracking environmental and homeostatic demands.

Effect of a single psilocybin treatment on Fos protein expression in male rat brain

Psilocybin has received attention as a treatment for depression, stress disorders and drug and alcohol addiction. To help determine the mechanisms underlying its therapeutic effects, here we examined acute effects of a range of behaviourally relevant psilocybin doses (0.1-3 mg/kg SC) on regional expression of Fos, the protein product of the immediate early gene, c-fos in brain areas involved in stress, reward and motivation in male rats. We also determined the cellular phenotypes activated by psilocybin, in a co-labeling analysis with NeuN, a marker of mature neurons, or Olig1, a marker of oligodendrocytes. In adult male Sprague-Dawley rats, psilocybin increased Fos expression dose dependently in several brain regions, including the frontal cortex, nucleus accumbens, central and basolateral amygdala and locus coeruleus. These effects were most marked in the central amygdala. Double labeling experiments showed that Fos was expressed in both neurons and oligodendrocytes. These results extend previous research by determining Fos expression in multiple brain areas at a wider psilocybin dose range, and the cellular phenotypes expressing Fos. The data also highlight the amygdala, especially the central nucleus, a key brain region involved in emotional processing and learning and interconnected with other brain areas involved in stress, reward and addiction, as a potentially important locus for the therapeutic effects of psilocybin. Overall, the present findings suggest that the central amygdala may be an important site through which the initial brain activation induced by psilocybin is translated into neuroplastic changes, locally and in other regions that underlie its extended therapeutic effects.

Molecular diversity and functional dynamics in the central amygdala

The central amygdala (CeA) is crucial in integrating sensory and associative information to mediate adaptive responses to emotional stimuli. Recent advances in genetic techniques like optogenetics and chemogenetics have deepened our understanding of distinct neuronal populations within the CeA, particularly those involved in fear learning and memory consolidation. However, challenges remain due to overlapping genetic markers complicating neuron identification. Furthermore, a comprehensive understanding of molecularly defined cell types and their projection patterns, which are essential for elucidating functional roles, is still developing. Recent advancements in transcriptomics are starting to bridge these gaps, offering new insights into the functional dynamics of CeA neurons. In this review, we provide an overview of the expanding genetic markers for amygdala research, encompassing recent developments and current trends. We also discuss how novel transcriptomic approaches are redefining cell types in the CeA and setting the stage for comprehensive functional studies.

Top-down control of flight by a non-canonical cortico-amygdala pathway

Survival requires the selection of appropriate behaviour in response to threats, and dysregulated defensive reactions are associated with psychiatric illnesses such as post-traumatic stress and panic disorder1. Threat-induced behaviours, including freezing and flight, are controlled by neuronal circuits in the central amygdala (CeA)2; however, the source of neuronal excitation of the CeA that contributes to high-intensity defensive responses is unknown. Here we used a combination of neuroanatomical mapping, in vivo calcium imaging, functional manipulations and electrophysiology to characterize a previously unknown projection from the dorsal peduncular (DP) prefrontal cortex to the CeA. DP-to-CeA neurons are glutamatergic and specifically target the medial CeA, the main amygdalar output nucleus mediating conditioned responses to threat. Using a behavioural paradigm that elicits both conditioned freezing and flight, we found that CeA-projecting DP neurons are activated by high-intensity threats in a context-dependent manner. Functional manipulations revealed that the DP-to-CeA pathway is necessary and sufficient for both avoidance behaviour and flight. Furthermore, we found that DP neurons synapse onto neurons within the medial CeA that project to midbrain flight centres. These results elucidate a non-canonical top-down pathway regulating defensive responses.

Multiple Memory Subsystems: Reconsidering Memory in the Mind and Brain

The multiple-memory-systems framework-that distinct types of memory are supported by distinct brain systems-has guided learning and memory research for decades. However, recent work challenges the one-to-one mapping between brain structures and memory types central to this taxonomy, with key memory-related structures supporting multiple functions across substructures. Here we integrate cross-species findings in the hippocampus, striatum, and amygdala to propose an updated framework of multiple memory subsystems (MMSS). We provide evidence for two organizational principles of the MMSS theory: First, opposing memory representations are colocated in the same brain structures; second, parallel memory representations are supported by distinct structures. We discuss why this burgeoning framework has the potential to provide a useful revision of classic theories of long-term memory, what evidence is needed to further validate the framework, and how this novel perspective on memory organization may guide future research.

Aberrant functional and causal connectivity of the amygdala in herpes zoster and post-herpetic neuralgia patients

OBJECTIVE

Resting-state functional magnetic resonance imaging (rs-fMRI) and Granger causality analysis (GCA) were used to observe the characteristics of amygdala and whole-brain effect connections in patients with herpes zoster (HZ) and post-herpetic neuralgia (PHN) and to determine their relationship with clinical features.

METHODS

Rs-fMRI scans were performed on 50 HZ; 50 PHN; and 50 age-, sex- and education-year-matched healthy controls (HCs). Bilateral amygdala subregions were used as seeds for functional connectivity (FC). GCA was used to analyze the effective connection of brain regions that were significantly different among groups. Then, the correlation between FC, and GCA values and clinical indices was investigated.

RESULTS

PHN had impaired FC between the amygdala subregion with the putamen, cortex, anterior cingulate cortex (ACC) to HCs and reduced FC of medial amygdala (MeA) with the parieto-occipital lobe and motor cortex to HZ; HZ had reduced FC of the lateral amygdala (LA) with the insula to HCs. GCA values from the bilateral LA to the bilateral ACC, left MeA to the bilateral ACC and left putamen, and right ACC to the bilateral MeA were reduced in PHN patients compared to HCs. Compared with HCs, the GCA values from the left MeA to the left ACC and right putamen were reduced in HZ. The GCA values from the amygdala subregion to the ACC were positively correlated with HAMA or HAMD scores in PHN.

CONCLUSION

PHN showed reduced FC between the amygdala subregions and cortico-putamen and decreased effective connectivity from the amygdala subregion to the ACC and putamen.

ADVANCES IN KNOWLEDGE

HZ and PHN patients had significant changes in effective connectivity in brain regions, including diverse functional areas emanating from and projecting to the amygdala. The current findings will provide a new perspective for understanding the neuropathophysiological mechanism HZ and PHN.

Optogenetic and chemogenetic approaches reveal differences in neuronal circuits that mediate initiation and maintenance of social interaction

For social interaction to be successful, two conditions must be met: the motivation to initiate it and the ability to maintain it. This study uses both optogenetic and chemogenetic approaches to reveal the specific neural pathways that selectively influence those two social interaction components.

5-HT1A receptor in the central amygdala and 5-HT2A receptor in the basolateral amygdala are involved in social hierarchy in male mice

Most social animals self-organize into dominance hierarchies that strongly influence their behavior and health. The serotonin (5-HT) system is believed to play an important role in the formation of social hierarchy. 5-HT receptors are abundantly expressed in the amygdala, which is considered as the central node for the perception and learning of social hierarchy. In this study, we assessed the functions of various 5-HT receptor subtypes related to social rank determination in different subregions of the amygdala using the confrontation tube test in mice. We revealed that most adult C57BL/6 J male mice exhibited a linear social rank after a few days of cohousing. The tube test ranks were slightly related to anxiety-like behavioral performance. After the tube test, the amygdala and 5-HT neurons in the dorsal raphe nucleus were activated in lower-rank individuals. Quantitative real-time polymerase chain reaction analysis revealed that despite the high expression of 5-HT1A receptor mRNA in the central amygdala (CeA), 5-HT2A receptor mRNA expression was downregulated in the basolateral amygdala (BLA) in higher-rank individuals. The dominant-subordinate relationship between mouse pairs could be switched via pharmacological modulation of these receptors in CeA and BLA, suggesting that these expression changes are essential for establishing social ranks. Our findings provide novel insights into the divergent functions of 5-HT receptors in the amygdala related to social hierarchy, which is closely related to our health and welfare.

Radiotherapy-Induced Neurocognitive Impairment Is Driven by Heightened Apoptotic Priming in Early Life and Prevented by Blocking BAX

Although external beam radiotherapy (xRT) is commonly used to treat central nervous system (CNS) tumors in patients of all ages, young children treated with xRT frequently experience life-altering and dose-limiting neurocognitive impairment (NI) while adults do not. The lack of understanding of mechanisms responsible for these differences has impeded the development of neuroprotective treatments. Using a newly developed mouse model of xRT-induced NI, we found that neurocognitive function is impaired by ionizing radiation in a dose- and age-dependent manner, with the youngest animals being most affected. Histologic analysis revealed xRT-driven neuronal degeneration and cell death in neurogenic brain regions in young animals but not adults. BH3 profiling showed that neural stem and progenitor cells, neurons, and astrocytes in young mice are highly primed for apoptosis, rendering them hypersensitive to genotoxic damage. Analysis of single-cell RNA sequencing data revealed that neural cell vulnerability stems from heightened expression of proapoptotic genes including BAX, which is associated with developmental and mitogenic signaling by MYC. xRT induced apoptosis in primed neural cells by triggering a p53- and PUMA-initiated, proapoptotic feedback loop requiring cleavage of BID and culminating in BAX oligomerization and caspase activation. Notably, loss of BAX protected against apoptosis induced by proapoptotic signaling in vitro and prevented xRT-induced apoptosis in neural cells in vivo as well as neurocognitive sequelae. On the basis of these findings, preventing xRT-induced apoptosis specifically in immature neural cells by blocking BAX, BIM, or BID via direct or upstream mechanisms is expected to ameliorate NI in pediatric patients with CNS tumor.

SIGNIFICANCE

Age- and differentiation-dependent apoptotic priming plays a pivotal role in driving radiotherapy-induced neurocognitive impairment and can be targeted for neuroprotection in pediatric patients.

Diverse processing of pharmacological and natural rewards by the central amygdala

The central amygdala (CeA) with its medial (CeM) and lateral (CeL) nuclei is the brain hub for processing stimuli with emotional context. CeL nucleus gives a strong inhibitory input to the CeM, and this local circuitry assigns values (positive or negative) to incoming stimuli, guiding appropriate behavior (approach or avoid). However, the particular involvement of CeA in processing such emotionally relevant information and adaptations of the CeA circuitry are not yet well understood. In this study, we examined synaptic plasticity in the CeA after exposure to two types of rewards, pharmacological (cocaine) and natural (sugar). We found that both rewards engage CeM, where they generate silent synapses resulting in the strengthening of the network. However, only cocaine triggers plasticity in the CeL, which leads to the weakening of its excitatory inputs. Finally, chemogenetic inhibition of CeM attenuates animal preference for sugar, while activation delays cocaine-induced increase in locomotor activity.

Distinct Circuits From the Central Lateral Amygdala to the Ventral Part of the Bed Nucleus of Stria Terminalis Regulate Different Fear Memory

BACKGROUND

The ability to differentiate stimuli that predict fear is critical for survival; however, the underlying molecular and circuit mechanisms remain poorly understood.

METHODS

We combined transgenic mice, in vivo transsynaptic circuit-dissecting anatomical approaches, optogenetics, pharmacological methods, and electrophysiological recording to investigate the involvement of specific extended amygdala circuits in different fear memory.

RESULTS

We identified the projections from central lateral amygdala (CeL) protein kinase C δ (PKCδ)-positive neurons and somatostatin (SST)-positive neurons to GABAergic (gamma-aminobutyric acidergic) and glutamatergic neurons in the ventral part of the bed nucleus of stria terminalis (vBNST). Prolonged optogenetic activation or inhibition of the PKCδCeL-vBNST pathway specifically reduced context fear memory, whereas the SSTCeL-vBNST pathway mainly reduced tone fear memory. Intriguingly, optogenetic manipulation of vBNST neurons that received the projection from PKCδCeL neurons exerted bidirectional regulation of context fear, whereas manipulation of vBNST neurons that received the projection from SSTCeL neurons could bidirectionally regulate both context and tone fear memory. We subsequently demonstrated the presence of δ and κ opioid receptor protein expression within the CeL-vBNST circuits, potentially accounting for the discrepancy between prolonged activation of GABAergic circuits and inhibition of downstream vBNST neurons. Finally, administration of an opioid receptor antagonist cocktail on the PKCδCeL-vBNST or SSTCeL-vBNST pathway successfully restored context or tone fear memory reduction induced by prolonged activation of the circuits.

CONCLUSIONS

Together, these findings establish a functional role for distinct CeL-vBNST circuits in the differential regulation and appropriate maintenance of fear.

From aversive associations to defensive programs: experience-dependent synaptic modifications in the central amygdala

Plasticity elicited by fear conditioning (FC) is thought to support the storage of aversive associative memories. Although work over the past decade has revealed FC-induced plasticity beyond canonical sites in the basolateral complex of the amygdala (BLA), it is not known whether modifications across distributed circuits make equivalent or distinct contributions to aversive memory. Here, we review evidence demonstrating that experience-dependent synaptic plasticity in the central nucleus of the amygdala (CeA) has a circumscribed role in memory expression per se, guiding the selection of defensive programs in response to acquired threats. We argue that the CeA may be a key example of a broader phenomenon by which synaptic plasticity at specific nodes of a distributed network makes a complementary contribution to distinct memory processes.

Pedunculopontine Chx10+ neurons control global motor arrest in mice

Arrest of ongoing movements is an integral part of executing motor programs. Behavioral arrest may happen upon termination of a variety of goal-directed movements or as a global motor arrest either in the context of fear or in response to salient environmental cues. The neuronal circuits that bridge with the executive motor circuits to implement a global motor arrest are poorly understood. We report the discovery that the activation of glutamatergic Chx10-derived neurons in the pedunculopontine nucleus (PPN) in mice arrests all ongoing movements while simultaneously causing apnea and bradycardia. This global motor arrest has a pause-and-play pattern with an instantaneous interruption of movement followed by a short-latency continuation from where it was paused. Mice naturally perform arrest bouts with the same combination of motor and autonomic features. The Chx10-PPN-evoked arrest is different to ventrolateral periaqueductal gray-induced freezing. Our study defines a motor command that induces a global motor arrest, which may be recruited in response to salient environmental cues to allow for a preparatory or arousal state, and identifies a locomotor-opposing role for rostrally biased glutamatergic neurons in the PPN.