New perspectives on central amygdala function

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.

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

Importance

The amygdala, a key limbic structure, plays a critical role in 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.

Objective

To characterize the associations between developmental variables and amygdala subregion volumes during preadolescence.

Design Setting and Participants

Cross-sectional Adolescent Brain Cognitive Development (ABCD®) Study data was collected from 3,953 9- and 10-year-old children between September 1, 2016, and October 15, 2018. Data analysis was conducted between June 1, 2023, and July 30, 2024.

Main Outcomes and Measures

Using the CIT168 Amygdala Atlas, nine amygdala subregion volumes were quantified from high-quality MRI scans. 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.

Results

The study population consisted of 3,953 preadolescents (mean [SD] age, 120 [7.41] months; 1,763 [44.6%] female; 57 [1.4%] Asian, 527 [13.3%] Black, 740 [18.7%] Hispanic, 2,279 [57.7%] white, and 350 [8.9%] from other racial/ethnic groups [identified by parents as American Indian/Native American, Alaska Native, Native Hawaiian, Guamanian, Samoan, other Pacific Islander, or other race]). 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 dorsal amygdala subregions and smaller apportionment in the basolateral ventral paralaminar subregion. Higher BMIz was associated with smaller volumes in large laterobasal subregions, with increased relative apportionment in smaller subregions.

Conclusions and Relevance

This cross-sectional study suggests that age, but not pubertal stage, is associated with near-global expansion of the amygdala at ages 9 and 10, while sex and BMIz are linked to distinct changes in amygdala subregions that explain observed differences in total volumes. These findings provide a foundational context for understanding how developmental variables influence amygdala structure in preadolescents, with implications for understanding future risk for brain disorders.

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.

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.

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.

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.

Opioid withdrawal: role in addiction and neural mechanisms

Withdrawal from opioids involves a negative affective state that promotes maintenance of drug-seeking behavior and relapse. As such, understanding the neurobiological mechanisms underlying withdrawal from opioid drugs is critical as scientists and clinicians seek to develop new treatments and therapies. In this review, we focus on the neural systems known to mediate the affective and somatic signs and symptoms of opioid withdrawal, including the mesolimbic dopaminergic system, basolateral amygdala, extended amygdala, and brain and hormonal stress systems. Evidence from preclinical studies suggests that these systems are altered following opioid exposure and that these changes mediate behavioral signs of negative affect such as aversion and anxiety during withdrawal. Adaptations in these systems also parallel the behavioral and psychological features of opioid use disorder (OUD), highlighting the important role of withdrawal in the development of addictive behavior. Implications for relapse and treatment are discussed as well as promising avenues for future research, with the hope of promoting continued progress toward characterizing neural contributors to opioid withdrawal and compulsive opioid use.

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

The ability to evaluate and select a preferred option among a variety of available offers is an essential aspect of goal-directed behavior. Dysregulation of this valuation process is characteristic of alcohol use disorder, with the central amygdala being implicated in persistent alcohol pursuit. However, the mechanism by which the central amygdala encodes and promotes the motivation to seek and consume alcohol remains unclear. We recorded single-unit activity in male Long-Evans rats as they consumed 10% ethanol or 14.2% sucrose. We observed significant activity at the time of approach to alcohol or sucrose, as well as lick-entrained activity during the ongoing consumption of both alcohol and sucrose. We then evaluated the ability of central amygdala optogenetic manipulation time-locked to consumption to alter ongoing intake of alcohol or sucrose, a preferred non-drug reward. In closed two-choice scenarios where rats could drink only sucrose, alcohol, or quinine-adulterated alcohol with or without central amygdala stimulation, rats drank more of stimulation-paired options. Microstructural analysis of licking patterns suggests these effects were mediated by changes in motivation, not palatability. Given a choice among different options, central amygdala stimulation enhanced consumption if the stimulation was associated with the preferred reward while closed-loop inhibition only decreased consumption if the options were equally valued. However, optogenetic stimulation during consumption of the less-preferred option, alcohol, was unable to enhance overall alcohol intake while sucrose was available. Collectively, these findings indicate that the central amygdala processes the motivational value of available offers to promote pursuit of the most preferred available option.

Activation of the central but not the medial and cortical amygdala during anticipation for daily nursing in the rabbit

Rabbits have remarkable nursing behavior: after parturition, does visit daily their pups for nursing only once with circadian periodicity. Before the nursing events, they present increased activity and arousal, which shift according to the timing of scheduled nursing, either during the day or night. Brain areas related to maternal behavior and neuroendocrine cells for milk secretion are also entrained. The daily return of the doe for nursing at approximately the same hour suggests a motivational drive with circadian periodicity. Previously, we reported the activation of the mesolimbic system at the time of nursing, but not 12 h before that. Aiming at a better understanding of the mechanism of this anticipatory behavior, we explored the participation of the limbic regions of the amygdala and the bed nucleus of the stria terminalis, as well as the possible activation of the hypothalamic-pituitaryadrenal axis, specifically the corticotropin-releasing factor cells in the hypothalamic paraventricular nucleus of does at different times before and after nursing. The medial and cortical amygdala, the bed nucleus of the stria terminalis, and corticotropin cells showed activation only after nursing. However, the central amygdala was also activated before nursing. We conclude that the medial and the cortical amygdala form part of the afferent olfactory pathway for entrainment, and the central amygdala participates in the anticipatory motivational circuit of the control of periodic nursing. The lack of activation of corticotropin cells before nursing is consistent with the possible harmful effects of the doe's high glucocorticoid levels on the developing pups.

Transcriptomics reveals amygdala neuron regulation by fasting and ghrelin thereby promoting feeding

The central amygdala (CeA) consists of numerous genetically defined inhibitory neurons that control defensive and appetitive behaviors including feeding. Transcriptomic signatures of cell types and their links to function remain poorly understood. Using single-nucleus RNA sequencing, we describe nine CeA cell clusters, of which four are mostly associated with appetitive and two with aversive behaviors. To analyze the activation mechanism of appetitive CeA neurons, we characterized serotonin receptor 2a (Htr2a)-expressing neurons (CeA^Htr2a) that comprise three appetitive clusters and were previously shown to promote feeding. In vivo calcium imaging revealed that CeA^Htr2a neurons are activated by fasting, the hormone ghrelin, and the presence of food. Moreover, these neurons are required for the orexigenic effects of ghrelin. Appetitive CeA neurons responsive to fasting and ghrelin project to the parabrachial nucleus (PBN) causing inhibition of target PBN neurons. These results illustrate how the transcriptomic diversification of CeA neurons relates to fasting and hormone-regulated feeding behavior.

Neurocircuitry of Predatory Hunting

Predatory hunting is an important type of innate behavior evolutionarily conserved across the animal kingdom. It is typically composed of a set of sequential actions, including prey search, pursuit, attack, and consumption. This behavior is subject to control by the nervous system. Early studies used toads as a model to probe the neuroethology of hunting, which led to the proposal of a sensory-triggered release mechanism for hunting actions. More recent studies have used genetically-trackable zebrafish and rodents and have made breakthrough discoveries in the neuroethology and neurocircuits underlying this behavior. Here, we review the sophisticated neurocircuitry involved in hunting and summarize the detailed mechanism for the circuitry to encode various aspects of hunting neuroethology, including sensory processing, sensorimotor transformation, motivation, and sequential encoding of hunting actions. We also discuss the overlapping brain circuits for hunting and feeding and point out the limitations of current studies. We propose that hunting is an ideal behavioral paradigm in which to study the neuroethology of motivated behaviors, which may shed new light on epidemic disorders, including binge-eating, obesity, and obsessive-compulsive disorders.

Mutant β1-adrenergic receptor improves REM sleep and ameliorates tau accumulation in a mouse model of tauopathy

Sleep is essential for our well-being, and chronic sleep deprivation has unfavorable health consequences. We recently demonstrated that two familial natural short sleep (FNSS) mutations, DEC2-P384R and Npsr1-Y206H, are strong genetic modifiers of tauopathy in PS19 mice, a model of tauopathy. To gain more insight into how FNSS variants modify the tau phenotype, we tested the effect of another FNSS gene variant, Adrb1-A187V, by crossing mice with this mutation onto the PS19 background. We found that the Adrb1-A187V mutation helped restore rapid eye movement (REM) sleep and alleviated tau aggregation in a sleep-wake center, the locus coeruleus (LC), in PS19 mice. We found that ADRB1+ neurons in the central amygdala (CeA) sent projections to the LC, and stimulating CeAADRB1+ neuron activity increased REM sleep. Furthermore, the mutant Adrb1 attenuated tau spreading from the CeA to the LC. Our findings suggest that the Adrb1-A187V mutation protects against tauopathy by both mitigating tau accumulation and attenuating tau spreading.

Advances in AAV technology for delivering genetically encoded cargo to the nonhuman primate nervous system

Modern neuroscience approaches including optogenetics, calcium imaging, and other genetic manipulations have facilitated our ability to dissect specific circuits in rodent models to study their role in neurological disease. These approaches regularly use viral vectors to deliver genetic cargo (e.g., opsins) to specific tissues and genetically-engineered rodents to achieve cell-type specificity. However, the translatability of these rodent models, cross-species validation of identified targets, and translational efficacy of potential therapeutics in larger animal models like nonhuman primates remains difficult due to the lack of efficient primate viral vectors. A refined understanding of the nonhuman primate nervous system promises to deliver insights that can guide the development of treatments for neurological and neurodegenerative diseases. Here, we outline recent advances in the development of adeno-associated viral vectors for optimized use in nonhuman primates. These tools promise to help open new avenues for study in translational neuroscience and further our understanding of the primate brain.

Altered neurotransmission in stress-induced depressive disorders: The underlying role of the amygdala in depression

Depression is the second leading cause of disability in the world population, for which currently available pharmacological therapies either have poor efficacy or have some adverse effects. Accumulating evidence from clinical and preclinical studies demonstrates that the amygdala is critically implicated in depressive disorders, though the underlying pathogenesis mechanism needs further investigation. In this literature review, we overviewed depression and the key role of Gamma-aminobutyric acid (GABA) and Glutamate neurotransmission in depression. Notably, we discussed a new cholecystokinin-dependent plastic changes mechanism under stress and a possible antidepressant response of cholecystokinin B receptor (CCKBR) antagonist. Moreover, we discussed the fundamental role of the amygdala in depression, to discuss and understand the pathophysiology of depression and the inclusive role of the amygdala in this devastating disorder.

Plastic and stimulus-specific coding of salient events in the central amygdala

The central amygdala (CeA) is implicated in a range of mental processes including attention, motivation, memory formation and extinction and in behaviours driven by either aversive or appetitive stimuli1-7. How it participates in these divergent functions remains elusive. Here we show that somatostatin-expressing (Sst+) CeA neurons, which mediate much of CeA functions3,6,8-10, generate experience-dependent and stimulus-specific evaluative signals essential for learning. The population responses of these neurons in mice encode the identities of a wide range of salient stimuli, with the responses of separate subpopulations selectively representing the stimuli that have contrasting valences, sensory modalities or physical properties (for example, shock and water reward). These signals scale with stimulus intensity, undergo pronounced amplification and transformation during learning, and are required for both reward and aversive learning. Notably, these signals contribute to the responses of dopamine neurons to reward and reward prediction error, but not to their responses to aversive stimuli. In line with this, Sst+ CeA neuron outputs to dopamine areas are required for reward learning, but are dispensable for aversive learning. Our results suggest that Sst+ CeA neurons selectively process information about differing salient events for evaluation during learning, supporting the diverse roles of the CeA. In particular, the information for dopamine neurons facilitates reward evaluation.

Experience-dependent changes in affective valence of taste in male mice

Taste plays an essential role in the evaluation of food quality by detecting potential harm and benefit in what animals are about to eat and drink. While the affective valence of taste signals is supposed to be innately determined, taste preference can also be drastically modified by previous taste experiences of the animals. However, how the experience-dependent taste preference is developed and the neuronal mechanisms involved in this process are poorly understood. Here, we investigate the effects of prolonged exposure to umami and bitter tastants on taste preference using two-bottle tests in male mice. Prolonged umami exposure significantly enhanced umami preference with no changes in bitter preference, while prolonged bitter exposure significantly decreased bitter avoidance with no changes in umami preference. Because the central amygdala (CeA) is postulated as a critical node for the valence processing of sensory information including taste, we examined the responses of cells in the CeA to sweet, umami, and bitter tastants using in vivo calcium imaging. Interestingly, both protein kinase C delta (Prkcd)-positive and Somatostatin (Sst)-positive neurons in the CeA showed an umami response comparable to the bitter response, and no difference in cell type-specific activity patterns to different tastants was observed. Meanwhile, fluorescence in situ hybridization with c-Fos antisense probe revealed that a single umami experience significantly activates the CeA and several other gustatory-related nuclei, and especially CeA Sst-positive neurons were strongly activated. Intriguingly, after prolonged umami experience, umami tastant also significantly activates the CeA neurons, but the Prkcd-positive neurons instead of Sst-positive neurons were highly activated. These results suggest a relationship between amygdala activity and experience-dependent plasticity developed in taste preference and the involvement of the genetically defined neural populations in this process.

Toll-like receptor 3 neuroimmune signaling and behavior change: A strain comparison between Lewis and Wistar rats

There are many unanswered questions about the interaction between the immune system and behavior change, including the contributions of individual differences. The present study modeled individual differences in the immune system by comparing inbred Lewis rats, which have dysregulated stress and immune systems, to their genetically diverse parent strain, Wistar rats. The objective was to examine the consequences of an immune challenge on behavior and neuroimmune signaling in both strains. Peripheral administration of the toll-like receptor 3 (TLR3) agonist and viral memetic polyinosinic-polycytidylic acid (poly(I:C)) induced behavior changes in both strains, reducing locomotor activity and increasing avoidance behavior (time on the dark side of the light-dark box). Furthermore, poly(I:C) induced hyperarousal and increased avoidance behavior more in female Lewis than female Wistar rats. Baseline strain differences were also observed: Lewis rats had higher avoidance behavior and lower startle response than Wistars. Lewis rats also had lower levels of peripheral inflammation, as measured by spleen weight. Finally, poly(I:C) increased expression of genes in the TLR3 pathway, cytokine genes, and CD11b, a gene associated with proinflammatory actions of microglia, in the prelimbic cortex and central amygdala, with greater expression of cytokine genes in male rats. Lewis rats had lower baseline expression of some neuroimmune genes, particularly CD11b. Overall, we found constitutive strain differences in immune profiles and baseline differences in behavior, yet poly(I:C) generally induced similar behavior changes in males while hyperarousal and avoidance behavior were heightened in female Lewis rats.

Topographic representation of current and future threats in the mouse nociceptive amygdala

Adaptive behaviors arise from an integration of current sensory context and internal representations of past experiences. The central amygdala (CeA) is positioned as a key integrator of cognitive and affective signals, yet it remains unknown whether individual populations simultaneously carry current- and future-state representations. We find that a primary nociceptive population within the CeA of mice, defined by CGRP-receptor (Calcrl) expression, receives topographic sensory information, with spatially defined representations of internal and external stimuli. While Calcrl+ neurons in both the rostral and caudal CeA respond to noxious stimuli, rostral neurons promote locomotor responses to externally sourced threats, while caudal CeA Calcrl+ neurons are activated by internal threats and promote passive coping behaviors and associative valence coding. During associative fear learning, rostral CeA Calcrl+ neurons stably encode noxious stimulus occurrence, while caudal CeA Calcrl+ neurons acquire predictive responses. This arrangement supports valence-aligned representations of current and future threats for the generation of adaptive behaviors.

Beyond Fear, Extinction, and Freezing: Strategies for Improving the Translational Value of Animal Conditioning Research

Translational neuroscience for anxiety has had limited success despite great progress in understanding the neurobiology of Pavlovian fear conditioning and extinction. This chapter explores the idea that conditioning paradigms have had a modest impact on translation because studies in animals and humans are misaligned in important ways. For instance, animal conditioning studies typically use imminent threats to assess short-duration fear states with single behavioral measures (e.g., freezing), whereas human studies typically assess weaker or more prolonged anxiety states with physiological (e.g., skin conductance) and self-report measures. A path forward may be more animal research on conditioned anxiety phenomena measuring dynamic behavioral and physiological responses in more complex environments. Exploring transitions between defensive brain states during extinction, looming threats, and post-threat recovery may be particularly informative. If care is taken to align paradigms, threat levels, and measures, this strategy may reveal stable patterns of non-conscious defense in animals and humans that correlate better with conscious anxiety. This shift in focus is also warranted because anxiety is a bigger problem than fear, even in disorders defined by dysfunctional fear or panic reactions.

Medial Temporal Lobe Tau Aggregation Relates to Divergent Cognitive and Emotional Empathy Abilities in Alzheimer's Disease

BACKGROUND

In Alzheimer's disease (AD), the gradual accumulation of amyloid-β (Aβ) and tau proteins may underlie alterations in empathy.

OBJECTIVE

To assess whether tau aggregation in the medial temporal lobes related to differences in cognitive empathy (the ability to take others' perspectives) and emotional empathy (the ability to experience others' feelings) in AD.

METHODS

Older adults (n = 105) completed molecular Aβ positron emission tomography (PET) scans. Sixty-eight of the participants (35 women) were Aβ positive and symptomatic with diagnoses of mild cognitive impairment, dementia of the Alzheimer's type, logopenic variant primary progressive aphasia, or posterior cortical atrophy. The remaining 37 (22 women) were asymptomatic Aβ negative healthy older controls. Using the Interpersonal Reactivity Index, we compared current levels of informant-rated cognitive empathy (Perspective-Taking subscale) and emotional empathy (Empathic Concern subscale) in the Aβ positive and negative participants. The Aβ positive participants also underwent molecular tau-PET scans, which were used to investigate whether regional tau burden in the bilateral medial temporal lobes related to empathy.

RESULTS

Aβ positive participants had lower perspective-taking and higher empathic concern than Aβ negative healthy controls. Medial temporal tau aggregation in the Aβ positive participants had divergent associations with cognitive and emotional empathy. Whereas greater tau burden in the amygdala predicted lower perspective-taking, greater tau burden in the entorhinal cortex predicted greater empathic concern. Tau burden in the parahippocampal cortex did not predict either form of empathy.

CONCLUSIONS

Across AD clinical syndromes, medial temporal lobe tau aggregation is associated with lower perspective-taking yet higher empathic concern.

Cellular mechanisms underlying central sensitization in a mouse model of chronic muscle pain

Chronic pain disorders are often associated with negative emotions, including anxiety and depression. The central nucleus of the amygdala (CeA) has emerged as an integrative hub for nociceptive and affective components during central pain development. Prior adverse injuries are precipitating factors thought to transform nociceptors into a primed state for chronic pain. However, the cellular basis underlying the primed state and the subsequent development of chronic pain remains unknown. Here, we investigated the cellular and synaptic alterations of the CeA in a mouse model of chronic muscle pain. In these mice, local infusion of pregabalin, a clinically approved drug for fibromyalgia and other chronic pain disorders, into the CeA or chemogenetic inactivation of the somatostatin-expressing CeA (CeA-SST) neurons during the priming phase prevented the chronification of pain. Further, electrophysiological recording revealed that the CeA-SST neurons had increased excitatory synaptic drive and enhanced neuronal excitability in the chronic pain states. Finally, either chemogenetic inactivation of the CeA-SST neurons or pharmacological suppression of the nociceptive afferents from the brainstem to the CeA-SST neurons alleviated chronic pain and anxio-depressive symptoms. These data raise the possibility of targeting treatments to CeA-SST neurons to prevent central pain sensitization.

Dopaminergic circuits underlying associative aversive learning

Associative aversive learning enables animals to predict and avoid threats and thus is critical for survival and adaptive behavior. Anxiety disorders are characterized with deficits in normal aversive learning mechanisms and hence understanding the neural circuits underlying aversive learning and memory has high clinical relevance. Recent studies have revealed the dopamine system as one of the key modulators of aversive learning. In this review, we highlight recent advances that provide insights into how distinct dopaminergic circuits contribute to aversive learning and memory.

Masseter muscle contraction and cervical muscle sensitization by nerve growth factor cause mechanical hyperalgesia in masticatory muscle with activation of the trigemino-lateral parabrachial nucleus system in female rats

OBJECTIVE

To establish a new rat model of craniofacial myalgia, and to clarify which central nervous system pathways are activated in the model.

BACKGROUND

Craniofacial myalgia, represented by myogenous temporomandibular disorder and tension-type headache with pericranial tenderness, is more common in female patients. The pain is thought to be a type of multifactorial disorder with several coexisting causes. To our knowledge, there are no models of craniofacial muscle hyperalgesia caused by multiple types of stimuli.

METHODS

We injected nerve growth factor into the trapezius muscle of female and male rats and repeatedly stimulated the masseter muscle (MM) electrically for 10 days. We determined the mechanical head-withdrawal threshold of MM and extent of phosphorylated extracellular signal-related kinase 1/2 (pERK) immunoreactivity in various regions of the lower brainstem. We conducted retrograde tract-tracing to determine the projection of mechanosensitive MM-innervating secondary neurons to the lateral parabrachial nucleus. Finally, we administered morphine in rats to determine whether increases of pERK immunoreactivity were dependent on noxious inputs.

RESULTS

In female rats, but not male rats, the mechanical head-withdrawal threshold was decreased significantly from days 9 to 12. The number of pERK-immunoreactive neurons in the brainstem was increased significantly in female rats in the group with both stimuli compared to rats in other groups with a single stimulus. Mechanosensitive MM-innervating neurons in the brainstem projected to the parabrachial nucleus. Morphine administration blocked the increase in the number of pERK-immunoreactive neurons in both the brainstem and parabrachial nucleus.

CONCLUSIONS

We established a model of craniofacial myalgia by combining trapezius and MM stimuli in female rats. We found mechanical hyperalgesia of the MM and activation of the pain pathway from the brainstem to parabrachial nucleus. The model reflects the characteristics of patients with craniofacial myalgia and might be helpful to clarify the pathogenic mechanisms underlying these disorders.

Anxiety in children and youth with autism spectrum disorder and the association with amygdala subnuclei structure

Autism spectrum disorder (ASD) is clinically characterized by social and communication difficulties as well as repetitive behaviors. Many children with ASD also suffer from anxiety, which has been associated with alterations in amygdala structure. In this work, the association between amygdala subnuclei volumes and anxiety was assessed in a cohort of 234 participants (mean age = 11.0 years, SD = 3.9, 95 children with ASD, 139 children were non-autistic). Children underwent magnetic resonance imaging. Amygdala subnuclei volumes were extracted automatically. Anxiety was assessed using the Screen for Child Anxiety Related Disorders, the Child Behavior Checklist, and the Strength and Difficulties Questionnaire. Children with ASD had higher anxiety scores relative to non-autistic children on all anxiety measures (all, p < 0.05). Anxiety levels were significantly predicted in children with ASD by right basal (right: B = 0.235, p = 0.002) and paralaminar (PL) (B = −0.99, p = 0.009) volumes. Basal nuclei receive multisensory information from cortical and subcortical areas and have extensive projections within the limbic system while the PL nuclei are involved in emotional processing. Alterations in basal and PL nuclei in children with ASD and the association with anxiety may reflect morphological changes related to in the neurocircuitry of anxiety in ASD.

Lay abstract

Autism spectrum disorder (ASD) is clinically characterized by social communication difficulties as well as restricted and repetitive patterns of behavior. In addition, children with ASD are more likely to experience anxiety compared with their peers who do not have ASD. Recent studies suggest that atypical amygdala structure, a brain region involved in emotions, may be related to anxiety in children with ASD. However, the amygdala is a complex structure composed of heterogeneous subnuclei, and few studies to date have focused on how amygdala subnuclei relate to in anxiety in this population. The current sample consisted of 95 children with ASD and 139 non-autistic children, who underwent magnetic resonance imaging (MRI) and assessments for anxiety. The amygdala volumes were automatically segmented. Results indicated that children with ASD had elevated anxiety scores relative to peers without ASD. Larger basal volumes predicted greater anxiety in children with ASD, and this association was not seen in non-autistic children. Findings converge with previous literature suggesting ASD children suffer from higher levels of anxiety than non-autistic children, which may have important implications in treatment and interventions. Our results suggest that volumetric estimation of amygdala’s subregions in MRI may reveal specific anxiety-related associations in children with ASD.

Optogenetic fMRI for Brain-Wide Circuit Analysis of Sensory Processing

Sensory processing is a complex neurological process that receives, integrates, and responds to information from one's own body and environment, which is closely related to survival as well as neurological disorders. Brain-wide networks of sensory processing are difficult to investigate due to their dynamic regulation by multiple brain circuits. Optogenetics, a neuromodulation technique that uses light-sensitive proteins, can be combined with functional magnetic resonance imaging (ofMRI) to measure whole-brain activity. Since ofMRI has increasingly been used for investigating brain circuits underlying sensory processing for over a decade, we systematically reviewed recent ofMRI studies of sensory circuits and discussed the challenges of optogenetic fMRI in rodents.