The role of the central nucleus of the amygdala in mediating fear and anxiety in the primate

Noradrenergic alterations associated with early life stress

Significant stress in childhood or adolescence is linked to both structural and functional changes in the brain in human and analogous animal models. In addition, neuromodulators, such as noradrenaline (NA), show life-long alterations in response to these early life stressors, which may impact upon the sensitivity and time course of key adrenergic activities, such as rapid autonomic stress responses (the 'fight or flight response'). The locus-coeruleus noradrenergic (LC-NA) network, a key stress-responsive network in the brain, displays numerous changes in response to significant early- life stress. Here, we review the relationship between NA and the neurobiological changes associated with early life stress and set out future lines of research that can illuminate how brain circuits and circulating neurotransmitters adapt in response to childhood stressors.

Translation of monosynaptic circuits underlying amygdala fMRI neurofeedback training

fMRI neurofeedback using autobiographical memory recall to upregulate the amygdala is associated with resting-state functional connectivity (rsFC) changes between the amygdala and the salience and default mode networks (SN and DMN, respectively). We hypothesize the existence of anatomical circuits underlying these rsFC changes. Using a cross-species brain parcellation, we identified in non-human primates locations homologous to the regions of interest (ROIs) from studies showing pre-to-post-neurofeedback changes in rsFC with the left amygdala. We injected bidirectional tracers in the basolateral, lateral, and central amygdala nuclei of adult macaques and used bright- and dark-field microscopy to identify cells and axon terminals in each ROI (SN: anterior cingulate, ventrolateral, and insular cortices; DMN: temporal pole, middle frontal gyrus, angular gyrus, precuneus, posterior cingulate cortex, parahippocampal gyrus, hippocampus, and thalamus). We also performed additional injections in specific ROIs to validate the results following amygdala injections and delineate potential disynaptic pathways. Finally, we used high-resolution diffusion MRI data from four post-mortem macaque brains and one in vivo human brain to translate our findings to the neuroimaging domain. Different amygdala nuclei had significant monosynaptic connections with all the SN and DMN ipsilateral ROIs. Amygdala connections with the DMN contralateral ROIs are disynaptic through the hippocampus and parahippocampal gyrus. Diffusion MRI in both species benefitted from using the ground-truth tracer data to validate its findings, as we identified false-negative ipsilateral and false-positive contralateral connectivity results. This study provides the foundation for future causal investigations of amygdala neurofeedback modulation of the SN and DMN through these anatomic connections.

Stress-sensitive neural circuits change the gut microbiome via duodenal glands

Negative psychological states impact immunity by altering the gut microbiome. However, the relationship between brain states and microbiome composition remains unclear. We show that Brunner's glands in the duodenum couple stress-sensitive brain circuits to bacterial homeostasis. Brunner's glands mediated the enrichment of gut Lactobacillus species in response to vagus nerve stimulation. Cell-specific ablation of the glands markedly suppressed Lactobacilli counts and heightened vulnerability to infection. In the forebrain, we mapped a vagally mediated, polysynaptic circuit connecting the central nucleus of the amygdala to Brunner's glands. Chronic stress suppressed central amygdala activity and phenocopied the effects of gland lesions. Conversely, excitation of either the central amygdala or parasympathetic vagal neurons activated Brunner's glands and reversed the effects of stress on the gut microbiome and immunity. The findings revealed a tractable brain-body mechanism linking psychological states to host defense.

Inhibition of Protein Synthesis Attenuates Formation of Traumatic Memory and Normalizes Fear-Induced c-Fos Expression in a Mouse Model of Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a debilitating psychosomatic condition characterized by impairment of brain fear circuits and persistence of exceptionally strong associative memories resistant to extinction. In this study, we investigated the neural and behavioral consequences of inhibiting protein synthesis, a process known to suppress the formation of conventional aversive memories, in an established PTSD animal model based on contextual fear conditioning in mice. Control animals were subjected to the conventional fear conditioning task. Utilizing c-Fos neural activity mapping, we found that the retrieval of PTSD and normal aversive memories produced activation of an overlapping set of brain structures. However, several specific areas, such as the infralimbic cortex and the paraventricular thalamic nucleus, showed an increase in the PTSD group compared to the normal aversive memory group. Administration of protein synthesis inhibitor before PTSD induction disrupted the formation of traumatic memories, resulting in behavior that matched the behavior of mice with usual aversive memory. Concomitant with this behavioral shift was a normalization of brain c-Fos activation pattern matching the one observed in usual fear memory. Our findings demonstrate that inhibiting protein synthesis during traumatic experiences significantly impairs the development of PTSD in a mouse model. These data provide insights into the neural underpinnings of protein synthesis-dependent traumatic memory formation and open prospects for the development of new therapeutic strategies for PTSD prevention.

An Amygdalar-Vagal-Glandular Circuit Controls the Intestinal Microbiome

Psychological states can regulate intestinal mucosal immunity by altering the gut microbiome. However, the link between the brain and microbiome composition remains elusive. We show that Brunner's glands in the duodenal submucosa couple brain activity to intestinal bacterial homeostasis. Brunner's glands mediated the enrichment of gut probiotic species in response to stimulation of abdominal vagal fibers. Cell-specific ablation of the glands triggered transmissible dysbiosis associated with an immunodeficiency syndrome that led to mortality upon gut infection with pathogens. The syndrome could be largely prevented by oral or intra-intestinal administration of probiotics. In the forebrain, we identified a vagally-mediated, polysynaptic circuit connecting the glands of Brunner to the central nucleus of the amygdala. Intra-vital imaging revealed that excitation of central amygdala neurons activated Brunner's glands and promoted the growth of probiotic populations. Our findings unveil a vagal-glandular neuroimmune circuitry that may be targeted for the modulation of the gut microbiome. The glands of Brunner may be the critical cells that regulate the levels of Lactobacilli species in the intestine.

Adolescent social anxiety is associated with diminished discrimination of anticipated threat and safety in the bed nucleus of the stria terminalis

Social anxiety-which typically emerges in adolescence-lies on a continuum and, when extreme, can be devastating. Socially anxious individuals are prone to heightened fear, anxiety, and the avoidance of contexts associated with potential social scrutiny. Yet most neuroimaging research has focused on acute social threat. Much less attention has been devoted to understanding the neural systems recruited during the uncertain anticipation of potential encounters with social threat. Here we used a novel fMRI paradigm to probe the neural circuitry engaged during the anticipation and acute presentation of threatening faces and voices in a racially diverse sample of 66 adolescents selectively recruited to encompass a range of social anxiety and enriched for clinically significant levels of distress and impairment. Results demonstrated that adolescents with more severe social anxiety symptoms experience heightened distress when anticipating encounters with social threat, and reduced discrimination of uncertain social threat and safety in the bed nucleus of the stria terminalis (BST), a key division of the central extended amygdala (EAc). Although the EAc-including the BST and central nucleus of the amygdala-was robustly engaged by the acute presentation of threatening faces and voices, the degree of EAc engagement was unrelated to the severity of social anxiety. Together, these observations provide a neurobiologically grounded framework for conceptualizing adolescent social anxiety and set the stage for the kinds of prospective-longitudinal and mechanistic research that will be necessary to determine causation and, ultimately, to develop improved interventions for this often-debilitating illness.

Distinct eLPBChAT projections for methamphetamine withdrawal anxiety and primed reinstatement of conditioned place preference

Methamphetamine (METH) withdrawal anxiety symptom and relapse have been significant challenges for clinical practice, however, the underlying neuronal basis remains unclear. Our recent research has identified a specific subpopulation of choline acetyltransferase (ChAT+) neurons localized in the external lateral portion of parabrachial nucleus (eLPBChAT), which modulates METH primed-reinstatement of conditioned place preference (CPP). Here, the anatomical structures and functional roles of eLPBChAT projections in METH withdrawal anxiety and primed reinstatement were further explored. Methods: In the present study, a multifaceted approach was employed to dissect the LPBChAT+ projections in male mice, including anterograde and retrograde tracing, acetylcholine (Ach) indicator combined with fiber photometry recording, photogenetic and chemogenetic regulation, as well as electrophysiological recording. METH withdrawal anxiety-like behaviors and METH-primed reinstatement of conditioned place preference (CPP) were assessed in male mice. Results: We identified that eLPBChAT send projections to PKCδ-positive (PKCδ+) neurons in lateral portion of central nucleus of amygdala (lCeAPKCδ) and oval portion of bed nucleus of the stria terminalis (ovBNSTPKCδ), forming eLPBChAT-lCeAPKCδ and eLPBChAT-ovBNSTPKCδ pathways. At least in part, the eLPBChAT neurons positively innervate lCeAPKCδ neurons and ovBNSTPKCδ neurons through regulating synaptic elements of presynaptic Ach release and postsynaptic nicotinic acetylcholine receptors (nAChRs). METH withdrawal anxiety and METH-primed reinstatement of CPP respectively recruit eLPBChAT-lCeAPKCδ pathway and eLPBChAT-ovBNSTPKCδ pathway in male mice. Conclusion: Our findings put new insights into the complex neural networks, especially focusing on the eLPBChAT projections. The eLPBChAT is a critical node in the neural networks governing METH withdrawal anxiety and primed-reinstatement of CPP through its projections to the lCeAPKCδ and ovBNSTPKCδ, respectively.

Understanding the heterogeneity of anxiety using a translational neuroscience approach

Anxiety disorders affect millions of people worldwide and present a challenge in neuroscience research because of their substantial heterogeneity in clinical presentation. While a great deal of progress has been made in understanding the neurobiology of fear and anxiety, these insights have not led to effective treatments. Understanding the relationship between phenotypic heterogeneity and the underlying biology is a critical first step in solving this problem. We show translation, reverse translation, and computational modeling can contribute to a refined, cross-species understanding of fear and anxiety as well as anxiety disorders. More specifically, we outline how animal models can be leveraged to develop testable hypotheses in humans by using targeted, cross-species approaches and ethologically informed behavioral paradigms. We discuss reverse translational approaches that can guide and prioritize animal research in nontraditional research species. Finally, we advocate for the use of computational models to harmonize cross-species and cross-methodology research into anxiety. Together, this translational neuroscience approach will help to bridge the widening gap between how we currently conceptualize and diagnose anxiety disorders, as well as aid in the discovery of better treatments for these conditions.

Nuclei-specific hypothalamus networks predict a dimensional marker of stress in humans

The hypothalamus is part of the hypothalamic-pituitary-adrenal axis which activates stress responses through release of cortisol. It is a small but heterogeneous structure comprising multiple nuclei. In vivo human neuroimaging has rarely succeeded in recording signals from individual hypothalamus nuclei. Here we use human resting-state fMRI (n = 498) with high spatial resolution to examine relationships between the functional connectivity of specific hypothalamic nuclei and a dimensional marker of prolonged stress. First, we demonstrate that we can parcellate the human hypothalamus into seven nuclei in vivo. Using the functional connectivity between these nuclei and other subcortical structures including the amygdala, we significantly predict stress scores out-of-sample. Predictions use 0.0015% of all possible brain edges, are specific to stress, and improve when using nucleus-specific compared to whole-hypothalamus connectivity. Thus, stress relates to connectivity changes in precise and functionally meaningful subcortical networks, which may be exploited in future studies using interventions in stress disorders.

Neigh G, Jovanovic T, Michopoulos V. HIV Interacts with Posttraumatic Stress Disorder to Impact Fear Psychophysiology in Trauma-Exposed Black Women

Background

The prevalence of posttraumatic stress disorder (PTSD) among people living with HIV (PLWH) is higher than in the general population and can impact health behaviors. The influence of HIV on PTSD psychophysiology requires further investigation due to implications for the treatment of PTSD in PLWH.

Objective

Utilizing fear-potentiated startle (FPS), we aimed to interrogate the influence of PTSD and HIV on fear responses.

Materials and Methods

Women (18-65 years of age) recruited from the Women's Interagency HIV Study in Atlanta, GA (n = 70, 26 without HIV and 44 with HIV), provided informed consent and completed a semistructured interview to assess trauma exposure and PTSD symptom severity. Participants also underwent an FPS paradigm to assess fear acquisition and extinction: Psychophysiological indices that measure how individuals learn new fear and then subsequently attempt to suppress this fear.

Results

Women with PTSD, who did not have HIV, exhibited a greater startle response compared to women without PTSD or HIV during late acquisition to both the danger cue, reinforced conditioned stimulus (CS+, p = 0.013)), and the safety cue, non-reinforced conditioned stimulus (CS-, p = 0.046)), whereas women living with HIV (WLH) and PTSD demonstrated blunted fear responses compared to women with PTSD only. During extinction, WLH comorbid with PTSD exhibited an increased fear response during the extinction period in comparison to all other groups (p = 0.023). Women without PTSD demonstrated a reduction in the fear response during extinction regardless of HIV status.

Conclusion

Our findings indicate that HIV further modifies fear psychophysiology in WLH with comorbid PTSD, highlighting the importance of considering HIV status in conjunction with PTSD treatment.

Differential functional organization of amygdala-medial prefrontal cortex networks in macaque and human

Over the course of evolution, the amygdala (AMG) and medial frontal cortex (mPFC) network, involved in behavioral adaptation, underwent structural changes in the old-world monkey and human lineages. Yet, whether and how the functional organization of this network differs remains poorly understood. Using resting-state functional magnetic resonance imagery, we show that the functional connectivity (FC) between AMG nuclei and mPFC regions differs between humans and awake macaques. In humans, the AMG-mPFC FC displays U-shaped pattern along the corpus callosum: a positive FC with the ventromedial prefrontal (vmPFC) and anterior cingulate cortex (ACC), a negative FC with the anterior mid-cingulate cortex (MCC), and a positive FC with the posterior MCC. Conversely, in macaques, the negative FC shifted more ventrally at the junction between the vmPFC and the ACC. The functional organization divergence of AMG-mPFC network between humans and macaques might help understanding behavioral adaptation abilities differences in their respective socio-ecological niches.

Transcranial focused ultrasound of the amygdala modulates fear network activation and connectivity

BACKGROUND

Current noninvasive brain stimulation methods are incapable of directly modulating subcortical brain regions critically involved in psychiatric disorders. Transcranial Focused Ultrasound (tFUS) is a newer form of noninvasive stimulation that could modulate the amygdala, a subcortical region implicated in fear.

OBJECTIVE

We investigated the effects of active and sham tFUS of the amygdala on fear circuit activation, skin conductance responses (SCR), and self-reported anxiety during a fear-inducing task. We also investigated amygdala tFUS' effects on amygdala-fear circuit resting-state functional connectivity.

METHODS

Thirty healthy individuals were randomized in this double-blinded study to active or sham tFUS of the left amygdala. We collected fMRI scans, SCR, and self-reported anxiety during a fear-inducing task (participants viewed red or green circles which indicated the risk of receiving an aversive stimulus), as well as resting-state scans, before and after tFUS.

RESULTS

Compared to sham tFUS, active tFUS was associated with decreased (pre to post tFUS) blood-oxygen-level-dependent fMRI activation in the amygdala (F(1,25) = 4.86, p = 0.04, η2 = 0.16) during the fear task, and lower hippocampal (F(1,27) = 4.41, p = 0.05, η2 = 0.14), and dorsal anterior cingulate cortex (F(1,27) = 6.26, p = 0.02; η2 = 0.19) activation during the post tFUS fear task. The decrease in amygdala activation was correlated with decreased subjective anxiety (r = 0.62, p = 0.03). There was no group effect in SCR changes from pre to post tFUS (F(1,23) = 0.85, p = 0.37). The active tFUS group also showed decreased amygdala-insula (F(1,28) = 4.98, p = 0.03) and amygdala-hippocampal (F(1,28) = 7.14, p = 0.01) rsFC, and increased amygdala-ventromedial prefrontal cortex (F(1,28) = 3.52, p = 0.05) resting-state functional connectivity.

CONCLUSIONS

tFUS can change functional connectivity and brain region activation associated with decreased anxiety. Future studies should investigate tFUS' therapeutic potential for individuals with clinical levels of anxiety.

Childhood abuse influences clinical features of major depressive disorder by modulating the functional network of the right amygdala subregions

Childhood trauma and the amygdala play essential roles in major depressive disorder (MDD) mechanisms. However, the neurobiological mechanism among them remains unclear. Therefore, we explored the relationship among the amygdala subregion's abnormal functional connectivity (FC), clinical features, and childhood trauma in MDD. We obtained resting-state functional magnetic resonance imaging (fMRI) in 115 MDD patients and 91 well-matched healthy controls (HC). Amygdala subregions were defined according to the Human Brainnetome Atlas. The case vs. control difference in FCs was extracted. After controlling for age, sex, and education years, the mediations between the detected abnormal FCs and clinical features were analyzed, including the onset age of MDD and the Hamilton Depression Scale-24 (HAMD-24) reductive rate. Compared with HC subjects, we found, only the right amygdala subregions, namely the right medial amygdala (mAmyg.R) and the right lateral amygdala (lAmyg.R), showed a significant decrease in whole-brain FCs in MDD patients. Only childhood abuse experiences were significantly associated with amygdala subregion connectivity and clinical features in MDD patients. Additionally, The FCs between the mAmyg.R and extensive frontal, temporal, and subcortical regions mediated between the early life abuses and disease onset or treatment outcome. The findings indicate that the abnormal connectivity of the right amygdala subregions is involved in MDD's pathogenesis and clinical characteristics.

Motivation as a Lens for Understanding Information-seeking Behaviors

Most prior research characterizes information-seeking behaviors as serving utilitarian purposes, such as whether the obtained information can help solve practical problems. However, information-seeking behaviors are sensitive to different contexts (i.e., threat vs. curiosity), despite having equivalent utility. Furthermore, these search behaviors can be modulated by individuals' life history and personality traits. Yet the emphasis on utilitarian utility has precluded the development of a unified model, which explains when and how individuals actively seek information. To account for this variability and flexibility, we propose a unified information-seeking framework that examines information-seeking through the lens of motivation. This unified model accounts for integration across individuals' internal goal states and the salient features of the environment to influence information-seeking behavior. We propose that information-seeking is determined by motivation for information, invigorated either by instrumental utility or hedonic utility, wherein one's personal or environmental context moderates this relationship. Furthermore, we speculate that the final common denominator in guiding information-seeking is the engagement of different neuromodulatory circuits centered on dopaminergic and noradrenergic tone. Our framework provides a unified framework for information-seeking behaviors and generates several testable predictions for future studies.

Structural Neuroimaging of Hippocampus and Amygdala Subregions in Posttraumatic Stress Disorder: A Scoping Review

Numerous studies have explored the relationship between posttraumatic stress disorder (PTSD) and the hippocampus and the amygdala because both regions are implicated in the disorder's pathogenesis and pathophysiology. Nevertheless, those key limbic regions consist of functionally and cytoarchitecturally distinct substructures that may play different roles in the etiology of PTSD. Spurred by the availability of automatic segmentation software, structural neuroimaging studies of human hippocampal and amygdala subregions have proliferated in recent years. Here, we present a preregistered scoping review of the existing structural neuroimaging studies of the hippocampus and amygdala subregions in adults diagnosed with PTSD. A total of 3513 studies assessing subregion volumes were identified, 1689 of which were screened, and 21 studies were eligible for this review (total N = 2876 individuals). Most studies examined hippocampal subregions and reported decreased CA1, CA3, dentate gyrus, and subiculum volumes in PTSD. Fewer studies investigated amygdala subregions and reported altered lateral, basal, and central nuclei volumes in PTSD. This review further highlights the conceptual and methodological limitations of the current literature and identifies future directions to increase understanding of the distinct roles of hippocampal and amygdalar subregions in posttraumatic psychopathology.

Gestational protein restriction alters early amygdala neurochemistry in male offspring

BACKGROUND

Gestational protein intake restriction-induced long-lasting harmful outcomes in the offspring's organs and systems. However, few studies have focused on this event's impact on the brain's structures and neurochemical compounds.

AIM

The present study investigated the effects on the amygdala neurochemical composition and neuronal structure in gestational protein-restricted male rats' offspring.

METHODS

Dams were maintained on isocaloric standard rodent laboratory chow with regular protein [NP, 17%] or low protein content [LP, 6%]. Total cells were quantified using the Isotropic fractionator method, Neuronal 3D reconstruction, and dendritic tree analysis using the Golgi-Cox technique. Western blot and high-performance liquid chromatography performed neurochemical studies.

RESULTS

The gestational low-protein feeding offspring showed a significant decrease in birth weight up to day 14, associated with unaltered brain weight in youth or adult progenies. The amygdala cell numbers were unchanged, and the dendrites length and dendritic ramifications 3D analysis in LP compared to age-matched NP progeny. However, the current study shows reduced amygdala content of norepinephrine, epinephrine, and dopamine in LP progeny. These offspring observed a significant reduction in the amygdala glucocorticoid (GR) and mineralocorticoid (MR) receptor protein levels. Also corticotrophin-releasing factor (CRF) amygdala protein content was reduced in 7 and 14-day-old LP rats.

CONCLUSION

The observed amygdala neurochemical changes may represent adaptation during embryonic development in response to elevated fetal exposure to maternal corticosteroid levels. In this way, gestational malnutrition stress can alter the amygdala's neurochemical content and may contribute to known behavioral changes induced by gestational protein restriction.

DREADD-mediated amygdala activation is sufficient to induce anxiety-like responses in young nonhuman primates

Anxiety disorders are among the most prevalent psychiatric disorders, with symptoms often beginning early in life. To model the pathophysiology of human pathological anxiety, we utilized Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in a nonhuman primate model of anxious temperament to selectively increase neuronal activity of the amygdala. Subjects included 10 young rhesus macaques; 5 received bilateral infusions of AAV5-hSyn-HA-hM3Dq into the dorsal amygdala, and 5 served as controls. Subjects underwent behavioral testing in the human intruder paradigm following clozapine or vehicle administration, prior to and following surgery. Behavioral results indicated that clozapine treatment post-surgery increased freezing across different threat-related contexts in hM3Dq subjects. This effect was again observed approximately 1.9 years following surgery, indicating the long-term functional capacity of DREADD-induced neuronal activation. [11C]deschloroclozapine PET imaging demonstrated amygdala hM3Dq-HA specific binding, and immunohistochemistry revealed that hM3Dq-HA expression was most prominent in basolateral nuclei. Electron microscopy confirmed expression was predominantly on neuronal membranes. Together, these data demonstrate that activation of primate amygdala neurons is sufficient to induce increased anxiety-related behaviors, which could serve as a model to investigate pathological anxiety in humans.

Ultra-high field imaging of the amygdala - A narrative review

The amygdala is an evolutionarily conserved core structure in emotion processing and one of the key regions of interest in affective neuroscience. Results of neuroimaging studies focusing on the amygdala are, however, often heterogeneous since it is composed of functionally and neuroanatomically distinct subnuclei. Fortunately, ultra-high-field imaging offers several advances for amygdala research, most importantly more accurate representation of functional and structural properties of subnuclei and their connectivity. Most clinical studies using ultra-high-field imaging focused on major depression, suggesting either overall rightward amygdala atrophy or distinct bilateral patterns of subnuclear atrophy and hypertrophy. Other pathologies are only sparsely covered. Connectivity analyses identified widespread networks for learning and memory, stimulus processing, cognition, and social processes. They provide evidence for distinct roles of the central, basal, and basolateral nucleus, and the extended amygdala in fear and emotion processing. Amid largely sparse and ambiguous evidence, we propose theoretical and methodological considerations that will guide ultra-high-field imaging in comprehensive investigations to help disentangle the ambiguity of the amygdala's function, structure, connectivity, and clinical relevance.

Stimulation of lateral parabrachial (LPB) to central amygdala (CeA) pituitary adenylate cyclase-activating polypeptide (PACAP) neurons induces anxiety-like behavior and mechanical allodynia

BACKGROUND

Anxiety disorders are the most prevalent psychiatric disorders, and they are highly comorbid with chronic pain conditions. The central nucleus of the amygdala (CeA) is known not only for its role in the regulation of anxiety but also as an important site for the negative affective dimension of pain. Pituitary adenylate cyclase activating polypeptide (PACAP), a neuropeptide whose terminals are abundant in the CeA, is strongly implicated in the stress response as well as in pain processing. Here, using Cre-dependent viral vectors, we explored in greater detail the role of the PACAP projection to the CeA that originates in the lateral parabrachial nucleus (LPB).

METHODS

We first performed a circuit mapping experiment by injecting an anterograde Cre-dependent virus expressing a fluorescent reporter in the LPB of PACAP-Cre mice and observing their projections. Then, we used a chemogenetic approach (a Cre-dependent Designer Receptors Activated by Designer Drugs, DREADDs) to assess the effects of the direct stimulation of the PACAP LPB to CeA projection on general locomotor activity, anxiety-like behavior (using a defensive withdrawal test), and mechanical pain sensitivity (using the von Frey test).

RESULTS

We found that the CeA, together with other areas, is one of the major downstream projection targets of PACAP neurons originating in the lateral parabrachial nucleus (LPB). In the DREADD experiment, we then found that the selective activation of this neuronal pathway is sufficient to increase both anxiety-like behavior and mechanical pain sensitivity in mice, without affecting general locomotor activity.

CONCLUSION

In conclusion, our data suggest that the dysregulation of this circuit may contribute to a variety of anxiety disorders and chronic pain states, and that PACAP may represent an important therapeutic target for the treatment of these conditions.

Multiple routes of communication within the amygdala-mPFC network: A comparative approach in humans and macaques

The network formed by the amygdala (AMG) and the medial Prefrontal Cortex (mPFC), at the interface between our internal and external environment, has been shown to support some important aspects of behavioral adaptation. Whether and how the anatomo-functional organization of this network evolved across primates remains unclear. Here, we compared AMG nuclei morphological characteristics and their functional connectivity with the mPFC in humans and macaques to identify potential homologies and differences between these species. Based on selected studies, we highlight two subsystems within the AMG-mPFC circuits, likely involved in distinct temporal dynamics of integration during behavioral adaptation. We also show that whereas the mPFC displays a large expansion but a preserved intrinsic anatomo-functional organization, the AMG displays a volume reduction and morphological changes related to specific nuclei. We discuss potential commonalities and differences in the dialogue between AMG nuclei and mPFC in humans and macaques based on available data.

DREADD-mediated amygdala activation is sufficient to induce anxiety-like responses in young nonhuman primates

Anxiety disorders are among the most prevalent psychiatric disorders, with symptoms often beginning early in life. To model the pathophysiology of human pathological anxiety, we utilized Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in a nonhuman primate model of anxious temperament to selectively increase neuronal activity of the amygdala. Subjects included 10 young rhesus macaques; 5 received bilateral infusions of AAV5-hSyn-HA-hM3Dq into the dorsal amygdala, and 5 served as controls. Subjects underwent behavioral testing in the human intruder paradigm following clozapine or vehicle administration, prior to and following surgery. Behavioral results indicated that clozapine treatment post-surgery increased freezing across different threat-related contexts in hM3Dq subjects. This effect was again observed approximately 1.9 years following surgery, indicating the long-term functional capacity of DREADD-induced neuronal activation. [11C]deschloroclozapine PET imaging demonstrated amygdala hM3Dq-HA specific binding, and immunohistochemistry revealed that hM3Dq-HA expression was most prominent in basolateral nuclei. Electron microscopy confirmed expression was predominantly on neuronal membranes. Together, these data demonstrate that activation of primate amygdala neurons is sufficient to induce increased anxiety-related behaviors, which could serve as a model to investigate pathological anxiety in humans.

Volume changes of hippocampal and amygdala subfields in patients with mild cognitive impairment and Alzheimer's disease

BACKGROUND

Automated segmentation of hippocampal and amygdala subfields could improve classification accuracy of Mild Cognitive Impairments (MCI) and Alzheimer's Disease (AD) individuals.

METHODS

We applied T1-weighted magnetic resonance imaging (MRI) for 21 AD, 39 MCI and 32 normal control (NC) participants at 3-Tesla MRI. Twelve hippocampal subfields and 9 amygdala subfields in each hemisphere were analyzed using FreeSurfer 6.0.

RESULTS

Smaller volumes were observed in right/left whole hippocampus, right/left hippocampal tail, right/left subiculum, right Cornu ammonis 1(CA1), right/left molecular layer, right granule cell-molecular layer-dentate gyrus (GC-ML-DG), right CA4, right fimbria, right whole amygdala, right/left accessory basal, right anterior amygdala area, left central, left medial and right/left cortical nucleus of AD group compared to both MCI and NC groups (p < 0.001). The volumes of right presubiculum, right CA3, right hippocampus-amygdala-transition-area (HATA), right lateral, right basal, right central, right medial, right cortico-amygdaloid transition (CAT) and right paralaminar nucleus were significantly larger in NC than AD group (p ≤ 0.001), while the volumes of right subiculum, right CA1, right molecular layer, right whole hippocampus, right whole amygdala, right basal and right accessory basal were significantly larger in NC than MCI group (p ≤ 0.002). Trend analysis showed that most hippocampus and amygdala subfields have a trend of atrophy with the decline of cognitive function. Six core components were identified by the hierarchical clustering. The combined Receiver operating characteristic (ROC) analysis achieved the diagnostic performances (AUC: 0.81) in differentiating AD from MCI; (AUC: 0.79) in differentiating MCI from NC and (AUC: 0.97) in differentiating AD from NC.

CONCLUSIONS

Volumetric differences of hippocampus and amygdala were at a finer subfields scale, and the volumes of right basal nucleus, left parasubiculum, left medial nucleus, left GC-ML-DG, left hippocampal fissure, and right fimbria can be employed as neuroimaging biomarkers to assist the clinical diagnosis of MCI and AD.

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

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

The role of puberty on physical and brain development: A longitudinal study in male Rhesus Macaques

This study examined the role of male pubertal maturation on physical growth and development of neurocircuits that regulate stress, emotional and cognitive control using a translational nonhuman primate model. We collected longitudinal data from male macaques between pre- and peri-puberty, including measures of physical growth, pubertal maturation (testicular volume, blood testosterone -T- concentrations) and brain structural and resting-state functional MRI scans to examine developmental changes in amygdala (AMY), hippocampus (HIPPO), prefrontal cortex (PFC), as well as functional connectivity (FC) between those regions. Physical growth and pubertal measures increased from pre- to peri-puberty. The indexes of pubertal maturation -testicular size and T- were correlated at peri-puberty, but not at pre-puberty (23 months). Our findings also showed ICV, AMY, HIPPO and total PFC volumetric growth, but with region-specific changes in PFC. Surprisingly, FC in these neural circuits only showed developmental changes from pre- to peri-puberty for HIPPO-orbitofrontal FC. Finally, testicular size was a better predictor of brain structural maturation than T levels -suggesting gonadal hormones-independent mechanisms-, whereas T was a strong predictor of functional connectivity development. We expect that these neural circuits will show more drastic pubertal-dependent maturation, including stronger associations with pubertal measures later, during and after male puberty.

RGS14 expression in CA2 hippocampus, amygdala, and basal ganglia: Implications for human brain physiology and disease

RGS14 is a multifunctional scaffolding protein that is highly expressed within postsynaptic spines of pyramidal neurons in hippocampal area CA2. Known roles of RGS14 in CA2 include regulating G protein, H-Ras/ERK, and calcium signaling pathways to serve as a natural suppressor of synaptic plasticity and postsynaptic signaling. RGS14 also shows marked postsynaptic expression in major structures of the limbic system and basal ganglia, including the amygdala and both the ventral and dorsal subdivisions of the striatum. In this review, we discuss the signaling functions of RGS14 and its role in postsynaptic strength (long-term potentiation) and spine structural plasticity in CA2 hippocampal neurons, and how RGS14 suppression of plasticity impacts linked behaviors such as spatial learning, object memory, and fear conditioning. We also review RGS14 expression in the limbic system and basal ganglia and speculate on its possible roles in regulating plasticity in these regions, with a focus on behaviors related to emotion and motivation. Finally, we explore the functional implications of RGS14 in various brain circuits and speculate on its possible roles in certain disease states such as hippocampal seizures, addiction, and anxiety disorders.

Estrogen receptor beta in the central amygdala regulates the deleterious behavioral and neuronal consequences of repeated social stress in female rats

While over 95% of the population has reported experiencing extreme stress or trauma, females of reproductive age develop stress-induced neuropsychiatric disorders at twice the rate of males. This suggests that ovarian hormones may facilitate neural processes that increase stress susceptibility and underlie the heightened rates of these disorders, like depression and anxiety, that result from stress exposure in females. However, there is contradicting evidence in the literature regarding estrogen's role in stress-related behavioral outcomes. Estrogen signaling through estrogen receptor beta (ERβ) has been traditionally thought of as anxiolytic, but recent studies suggest estrogen exhibits distinct effects in the context of stress. Furthermore, ERβ is found abundantly in many stress-sensitive brain loci, including the central amygdala (CeA), in which transcription of the vital stress hormone, corticotropin releasing factor (CRF), can be regulated by an estrogen response element. Therefore, these experiments sought to identify the role of CeA ERβ activity during stress on behavioral outcomes in naturally cycling, adult, female Sprague-Dawley rats. Rats were exposed to an ethological model of vicarious social stress, witness stress (WS), in which they experienced the sensory and psychological aspects of an aggressive social defeat encounter between two males. Following WS, rats exhibited stress-induced anxiety-like behaviors in the marble burying taskand brain analysis revealed increased ERβ and CRF specifically within the CeA following exposure to stress cues. Subsequent experiments were designed to target this receptor in the CeA using microinjections of the ERβ antagonist, PHTPP, prior to each stress session. During WS, estrogen signaling through ERβ was responsible for the behavioral sensitization to repeated social stress. Sucrose preference, acoustic startle, and marble burying tasks determined that blocking ERβ in the CeA during WS prevented the development of depressive-, anxiety-like, and hypervigilant behaviors. Additionally, brain analysis revealed a long-term decrease of intra-CeA CRF expression in PHTPP-treated rats. These experiments indicate that ERβ signaling in the CeA, likely through its effects on CRF, contributes to the development of negative valence behaviors that result from exposure to repeated social stress in female rats.

Current Perspectives on Selective Dopamine D3 Receptor Antagonists/Partial Agonists as Pharmacotherapeutics for Opioid and Psychostimulant Use Disorders

Over three decades of evidence indicate that dopamine (DA) D3 receptors (D3R) are involved in the control of drug-seeking behavior and may play an important role in the pathophysiology of substance use disorders (SUD). The expectation that a selective D3R antagonist/partial agonist would be efficacious for the treatment of SUD is based on the following key observations. First, D3R are distributed in strategic areas belonging to the mesolimbic DA system such as the ventral striatum, midbrain, and ventral pallidum, which have been associated with behaviors controlled by the presentation of drug-associated cues. Second, repeated exposure to drugs of abuse produces neuroadaptations in the D3R system. Third, the synthesis and characterization of highly potent and selective D3R antagonists/partial agonists have further strengthened the role of the D3R in SUD. Based on extensive preclinical and preliminary clinical evidence, the D3R shows promise as a target for the development of pharmacotherapies for SUD as reflected by their potential to (1) regulate the motivation to self-administer drugs and (2) disrupt the responsiveness to drug-associated stimuli that play a key role in reinstatement of drug-seeking behavior triggered by re-exposure to the drug itself, drug-associated environmental cues, or stress. The availability of PET ligands to assess clinically relevant receptor occupancy by selective D3R antagonists/partial agonists, the definition of reliable dosing, and the prospect of using human laboratory models may further guide the design of clinical proof of concept studies. Pivotal clinical trials for more rapid progression of this target toward regulatory approval are urgently required. Finally, the discovery that highly selective D3R antagonists, such as R-VK4-116 and R-VK4-40, do not adversely affect peripheral biometrics or cardiovascular effects alone or in the presence of oxycodone or cocaine suggests that this class of drugs has great potential in safely treating psychostimulant and/or opioid use disorders.

Genetically engineered mesenchymal stem cells with dopamine synthesis for Parkinson's disease in animal models

Although striatal delivery of three critical genes for dopamine synthesis by viruses is a potential clinical approach for treating Parkinson's disease (PD), the approach makes it difficult to finely control dopamine secretion amounts and brings safety concerns. Here, we generate genetically engineered mesenchymal stem cells encoding three critical genes for dopamine synthesis (DOPA-MSCs). DOPA-MSCs retain their MSC identity and stable ability to secrete dopamine during passaging. Following transplantation, DOPA-MSCs reinstate striatal dopamine levels and correct motor function in PD rats. Importantly, after grafting into the caudate and putamen, DOPA-MSCs provide homotopic reconstruction of midbrain dopamine pathways by restoring striatal dopamine levels, and safely and long-term (up to 51 months) correct motor disorders and nonmotor deficits in acute and chronic PD rhesus monkey models of PD even with advanced PD symptoms. The long-term benefits and safety results support the idea that the development of dopamine-synthesized engineered cell transplantation is an important strategy for treating PD.

The unbalanced behavioral activation and inhibition system sensitivity in internet gaming disorder: Evidence from resting-state Granger causal connectivity analysis

BACKGROUND

Patients with behavioral or substance addiction show an unbalanced behavioral activation system (BAS) and behavioral inhibition system (BIS) sensitivity. However, the relationship between internet gaming disorder (IGD) and BAS/BIS is obscure and the neurobiological mechanism underlying this relationship remains unclear.

METHODS

We recruited 154 IGDs and 229 recreational game users (RGUs) in the current study. First, we explored the relationship between BAS/BIS and IGD. Second, subjects were subdivided into subgroups by BAS/BIS sensitivity. Third, whole-brain Granger causal connectivity (GCC) of striatum and amygdala subdivisions was estimated for the subgroup. Fourth, mediation analysis was performed to explore the role of connectivity in the relationship between IGD and BAS/BIS sensitivity.

RESULTS

We found the IGD group scored higher than the RGU on BIS and BASf (fun-seeking) sensitivity. Then, we identified 4 (2*2) subgroups: low/high risk of IGD with low/high BAS/BIS sensitivity groups. Two-way ANCOVA main results of interaction effects showed that in the high BAS/BIS group, the RGU exhibited increased strength in the GCC from the left putamen to the right cuneus, and the IGD exhibited decreased strength in the GCC from the right medial frontal gyrus to the caudate, from the left superior frontal gyrus to the centromedial amygdala, and from the right superior parietal lobule to the left laterobasal amygdala. Moreover, the GCC from the centromedial amygdala to the middle frontal gyrus mediated the directional relationship between BIS and IAT (Young's internet addiction test) scores.

CONCLUSIONS

The IGD individuals exhibited higher BIS and BAS-fun seeking sensitivity. Moreover, IGD with unbalanced BAS/BIS sensitivity exhibited alternative connectivity patterns involving amygdala and striatum subdivisions. These findings suggest a neurobiological mechanism for an alternation between IGD and RGU with different BAS/BIS sensitivity.

The central extended amygdala guides survival-relevant tradeoffs: Implications for understanding common psychiatric disorders

To thrive in challenging environments, individuals must pursue rewards while avoiding threats. Extensive studies in animals and humans have identified the central extended amygdala (EAc)-which includes the central nucleus of the amygdala (Ce) and bed nucleus of the stria terminalis (BST)-as a conserved substrate for defensive behavior. These studies suggest the EAc influences defensive responding and assembles fearful and anxious states. This has led to the proliferation of a view that the EAc is fundamentally a defensive substrate. Yet mechanistic work in animals has implicated the EAc in numerous appetitive and consummatory processes, yielding fresh insights into the microcircuitry of survival- and emotion-relevant response selection. Coupled with the EAc's centrality in a conserved network of brain regions that encode multisensory environmental and interoceptive information, these findings suggest a broader role for the EAc as an arbiter of survival- and emotion-relevant tradeoffs for action selection. Determining how the EAc optimizes these tradeoffs promises to improve our understanding of common psychiatric illnesses such as anxiety, depression, alcohol- and substance-use disorders, and anhedonia.

Prefrontal influences on the function of the neural circuitry underlying anxious temperament in primates

Anxious temperament, characterized by heightened behavioral and physiological reactivity to potential threat, is an early childhood risk factor for the later development of stress-related psychopathology. Using a well-validated nonhuman primate model, we tested the hypothesis that the prefrontal cortex (PFC) is critical in regulating the expression of primate anxiety-like behavior, as well as the function of subcortical components of the anxiety-related neural circuit. We performed aspiration lesions of a narrow 'strip' of the posterior orbitofrontal cortex (OFC) intended to disrupt both cortex and axons entering, exiting and coursing through the pOFC, particularly those of the uncinate fasciculus (UF), a white matter tract that courses adjacent to and through this region. The OFC is of particular interest as a potential regulatory region because of its extensive reciprocal connections with amygdala, other subcortical structures and other frontal lobe regions. We validated this lesion method by demonstrating marked lesion-induced decreases in the microstructural integrity of the UF, which contains most of the fibers that connect the ventral PFC with temporal lobe structures as well as with other frontal regions. While the lesions resulted in modest decreases in threat-related behavior, they substantially decreased metabolism in components of the circuit underlying threat processing. These findings provide evidence for the importance of structural connectivity between the PFC and key subcortical structures in regulating the functions of brain regions known to be involved in the adaptive and maladaptive expression of anxiety.

Developmental Delays in Socio-Emotional Brain Functions in Persons with an Intellectual Disability: Impact on Treatment and Support

Intellectual disability is a neurodevelopmental disorder with a related co-occurrence of mental health issues and challenging behaviors. In addition to purely cognitive functions, socio-emotional competencies may also be affected. In this paper, the lens of developmental social neuroscience is used to better understand the origins of mental disorders and challenging behaviors in people with an intellectual disability. The current concept of intelligence is broadened by socio-emotional brain functions. The emergence of these socio-emotional brain functions is linked to the formation of the respective neuronal networks located within the different parts of the limbic system. Thus, high order networks build on circuits that process more basic information. The socio-emotional skills can be assessed and complement the results of a standardized IQ-test. Disturbances of the brain cytoarchitecture and function that occur at a certain developmental period may increase the susceptibility to certain mental disorders. Insights into the current mental and socio-emotional functioning of a person may support clinicians in the calibration of treatment and support. Acknowledging the trajectories of the socio-emotional brain development may result in a more comprehensive understanding of behaviors and mental health in people with developmental delays and thus underpin supports for promotion of good mental health in this highly vulnerable population.

Pedunculopontine Nucleus Dysconnectivity Correlates With Gait Impairment in Parkinson’s Disease: An Exploratory Study

Background

Gait impairment is a debilitating and progressive feature of Parkinson’s disease (PD). Increasing evidence suggests that gait control is partly mediated by cholinergic signaling from the pedunculopontine nucleus (PPN).

Objective

We investigated whether PPN structural connectivity correlated with quantitative gait measures in PD.

Methods

Twenty PD patients and 15 controls underwent diffusion tensor imaging to quantify structural connectivity of the PPN. Whole brain analysis using tract-based spatial statistics and probabilistic tractography were performed using the PPN as a seed region of interest for cortical and subcortical target structures. Gait metrics were recorded in subjects’ medication ON and OFF states, and were used to determine if specific features of gait dysfunction in PD were related to PPN structural connectivity.

Results

Tract-based spatial statistics revealed reduced structural connectivity involving the corpus callosum and right superior corona radiata, but did not correlate with gait measures. Abnormalities in PPN structural connectivity in PD were lateralized to the right hemisphere, with pathways involving the right caudate nucleus, amygdala, pre-supplementary motor area, and primary somatosensory cortex. Altered connectivity of the right PPN-caudate nucleus was associated with worsened cadence, stride time, and velocity while in the ON state; altered connectivity of the right PPN-amygdala was associated with reduced stride length in the OFF state.

Conclusion

Our exploratory analysis detects a potential correlation between gait dysfunction in PD and a characteristic pattern of connectivity deficits in the PPN network involving the right caudate nucleus and amygdala, which may be investigated in future larger studies.

Altered hippocampus and amygdala subregion connectome hierarchy in major depressive disorder

The hippocampus and amygdala limbic structures are critical to the etiology of major depressive disorder (MDD). However, there are no high-resolution characterizations of the role of their subregions in the whole brain network (connectome). Connectomic examination of these subregions can uncover disorder-related patterns that are otherwise missed when treated as single structures. 38 MDD patients and 40 healthy controls (HC) underwent anatomical and diffusion imaging using 7-Tesla MRI. Whole-brain segmentation was performed along with hippocampus and amygdala subregion segmentation, each representing a node in the connectome. Graph theory analysis was applied to examine the importance of the limbic subregions within the brain network using centrality features measured by node strength (sum of weights of the node's connections), Betweenness (number of shortest paths that traverse the node), and clustering coefficient (how connected the node's neighbors are to one another and forming a cluster). Compared to HC, MDD patients showed decreased node strength of the right hippocampus cornu ammonis (CA) 3/4, indicating decreased connectivity to the rest of the brain, and decreased clustering coefficient of the right dentate gyrus, implying it is less embedded in a cluster. Additionally, within the MDD group, the greater the embedding of the right amygdala central nucleus (CeA) in a cluster, the greater the severity of depressive symptoms. The altered role of these limbic subregions in the whole-brain connectome is related to diagnosis and depression severity, contributing to our understanding of the limbic system involvement in MDD and may elucidate the underlying mechanisms of depression.

Longitudinal assessment of early-life white matter development with quantitative relaxometry in nonhuman primates

Alterations in white matter (WM) development are associated with many neuropsychiatric and neurodevelopmental disorders. Most MRI studies examining WM development employ diffusion tensor imaging (DTI), which relies on estimating diffusion patterns of water molecules as a reflection of WM microstructure. Quantitative relaxometry, an alternative method for characterizing WM microstructural changes, is based on molecular interactions associated with the magnetic relaxation of protons. In a longitudinal study of 34 infant non-human primates (NHP) (Macaca mulatta) across the first year of life, we implement a novel, high-resolution, T1-weighted MPnRAGE sequence to examine WM trajectories of the longitudinal relaxation rate (qR1) in relation to DTI metrics and gestational age at scan. To the best of our knowledge, this is the first study to assess developmental WM trajectories in NHPs using quantitative relaxometry and the first to directly compare DTI and relaxometry metrics during infancy. We demonstrate that qR1 exhibits robust logarithmic growth, unfolding in a posterior-anterior and medial-lateral fashion, similar to DTI metrics. On a within-subject level, DTI metrics and qR1 are highly correlated, but are largely unrelated on a between-subject level. Unlike DTI metrics, gestational age at birth (time in utero) is a strong predictor of early postnatal qR1 levels. Whereas individual differences in DTI metrics are maintained across the first year of life, this is not the case for qR1. These results point to the similarities and differences in using quantitative relaxometry and DTI in developmental studies, providing a basis for future studies to characterize the unique processes that these measures reflect at the cellular and molecular level.

Dysfunctions of brain oxytocin signaling: Implications for poor mothering

Good mothering has profound impact on both the mother's and the young's well-being. Consequently, experiencing inadequate maternal care - or even neglect - in the first stages of life is a major risk factor for the development of psychiatric disorders, and even for poor parenting towards the future offspring. Thus, understanding the neurobiological basis of maternal neglect becomes crucial. Along with other neurotransmitters and neuropeptides, oxytocin (OXT) has long been known as one of the main modulators of maternal behavior. In rodents, disruptions of central OXT transmission have been associated with poor maternal responses, like impaired onset of nursing behaviors, and reduced care and defense of the pups. Importantly, such behavioral and molecular deficits can be transmitted through generations, creating a vicious circle of low-quality maternal behavior. Similarly, evidence from human studies shows that OXT signaling is defective in conditions of inadequate mothering and child neglect. On those premises, this review aims at providing a comprehensive overview of animal and human studies linking perturbed OXT transmission to poor maternal behavior. Considering the important fallouts of inadequate maternal responses, we believe that unraveling the alterations in OXT transmission might provide useful insights for a better understanding of maternal neglect and, ultimately, for future intervention approaches.

Repeated vagus nerve stimulation produces anxiolytic effects via upregulation of AMPAR function in centrolateral amygdala of male rats

Repeated vagus nerve stimulation (rVNS) exerts anxiolytic effect by activation of noradrenergic pathway. Centrolateral amygdala (CeL), a lateral subdivision of central amygdala, receives noradrenergic inputs, and its neuronal activity is positively correlated to anxiolytic effect of benzodiazepines. The activation of β-adrenergic receptors (β-ARs) could enhance glutamatergic transmission in CeL. However, it is unclear whether the neurobiological mechanism of noradrenergic system in CeL mediates the anxiolytic effect induced by rVNS. Here, we find that rVNS treatment produces an anxiolytic effect in male rats by increasing the neuronal activity of CeL. Electrophysiology recording reveals that rVNS treatment enhances the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR)-mediated excitatory neurotransmission in CeL, which is mimicked by β-ARs agonist isoproterenol or blocked by β-ARs antagonist propranolol. Moreover, chemogenetic inhibition of CeL neurons or pharmacological inhibition of β-ARs in CeL intercepts both enhanced glutamatergic neurotransmission and the anxiolytic effects by rVNS treatment. These results suggest that the amplified AMPAR trafficking in CeL via activation of β-ARs is critical for the anxiolytic effects induced by rVNS treatment.

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rVNS amplifies the noradrenergic system in CeL and results in anxiolysis.

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rVNS treatment enhances AMPAR-mediated excitatory neurotransmission CeL via β-ARs.

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Pharmacological inhibition β-ARs in CeL intercept the anxiolytic effects by rVNS.

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Exciting CeL neurons lead to an increase in inhibitory inputs into CeM neurons.

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Inhibiting CeL neurons abate inhibitory inputs into CeM and anxiolysis by rVNS.

Fast Detection of Snakes and Emotional Faces in the Macaque Amygdala

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

Social housing status impacts rhesus monkeys' affective responding in classic threat processing tasks

Individuals’ social contexts are broadly recognized to impact both their psychology and neurobiology. These effects are observed in people and in nonhuman animals who are the subjects for comparative and translational science. The social contexts in which monkeys are reared have long been recognized to have significant impacts on affective processing. Yet, the social contexts in which monkeys live as adults are often ignored and could have important consequences for interpreting findings, particularly those related to biopsychiatry and behavioral neuroscience studies. The extant nonhuman primate neuropsychological literature has historically tested individually-housed monkeys, creating a critical need to understand how social context might impact the outcomes of such experiments. We evaluated affective responding in adult rhesus monkeys living in four different social contexts using two classic threat processing tasks—a test of responsivity to objects and a test of responsivity to an unfamiliar human. These tasks have been commonly used in behavioral neuroscience for decades. Relative to monkeys with full access to a social partner, individually-housed monkeys had blunted reactivity to threat and monkeys who had limited contact with their partner were more reactive to some threatening stimuli. These results indicate that monkeys’ social housing contexts impact affective reactivity and point to the potential need to reconsider inferences drawn from prior studies in which the impacts of social context have not been considered.

Amygdala-driven apnea and the chemoreceptive origin of anxiety

Although the amygdala plays an important part in the pathogenesis of anxiety and generation of exteroceptive fear, recent discoveries have challenged the directionality of this brain-behavior relationship with respect to interoceptive fear. Here we highlight several paradoxical findings including: (1) amygdala lesion patients who experience excessive fear and panic following inhalation of carbon dioxide (CO₂), (2) clinically anxious patients who have significantly smaller (rather than larger) amygdalae and a pronounced hypersensitivity toward CO₂, and (3) epilepsy patients who exhibit apnea immediately following stimulation of their amygdala yet have no awareness that their breathing has stopped. The above findings elucidate an entirely novel role for the amygdala in the induction of apnea and inhibition of CO₂-induced fear. Such a role is plausible given the strong inhibitory connections linking the central nucleus of the amygdala with respiratory and chemoreceptive centers in the brainstem. Based on this anatomical arrangement, we propose a model of Apnea-induced Anxiety (AiA) which predicts that recurring episodes of apnea are being unconsciously elicited by amygdala activation, resulting in transient spikes in CO₂ that provoke fear and anxiety, and lead to characteristic patterns of escape and avoidance behavior in patients spanning the spectrum of anxiety. If this new conception of AiA proves to be true, and activation of the amygdala can repeatedly trigger states of apnea outside of one's awareness, then it remains possible that the chronicity of anxiety disorders is being interoceptively driven by a chemoreceptive system struggling to maintain homeostasis in the midst of these breathless states.

Amygdala or hippocampus damage only minimally impacts affective responding to threat

Decades of research studying the behavioral effects of damage to structures in medial temporal lobe of rhesus monkeys have documented that such damage, particularly damage to the amygdala, causes animals to become hyporesponsive to threat and hyper-social. This phenotype, a subset of the behaviors known as "Klüver-Bucy Syndrome," is one of the most well-known phenomena in behavioral neuroscience. Carrying on the tradition of evaluating hyposensitivity to threat in monkeys with temporal lobe lesions, we evaluated the responses of rhesus monkeys with bilateral ibotenic acid lesions of the amygdala or hippocampus and procedure-matched control animals to the presentation of an unfamiliar human intruder and threatening objects of varying complexity. All animals behaved as expected-calibrating their responses to the ostensible threat value of the stimuli such that they were most responsive to the most potent stimuli and least responsive to the least potent stimuli. Contrary to an earlier report (Mason et al., 2006), lesion status did not impact the pattern of responses across multiple dependent measures (overt behaviors, position in cage, etc.). The only lesion induced difference consistent with hyposensitivity to threat was that monkeys with amygdala lesions retrieved food rewards placed near reptile-like objects more rapidly than did control animals. These findings call into question the assumption that amygdala damage causes robust, stereotyped changes to affective behavior. They also highlight the importance of replication in neuroscientific studies using nonhuman primates. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

A spatial and cellular distribution of rabies virus infection in the mouse brain revealed by fMOST and single-cell RNA sequencing

BACKGROUND

Neurotropic virus infection can cause serious damage to the central nervous system (CNS) in both humans and animals. The complexity of the CNS poses unique challenges to investigate the infection of these viruses in the brain using traditional techniques.

METHODS

In this study, we explore the use of fluorescence micro-optical sectioning tomography (fMOST) and single-cell RNA sequencing (scRNA-seq) to map the spatial and cellular distribution of a representative neurotropic virus, rabies virus (RABV), in the whole brain. Mice were inoculated with a lethal dose of a recombinant RABV encoding enhanced green fluorescent protein (EGFP) under different infection routes, and a three-dimensional (3D) view of RABV distribution in the whole mouse brain was obtained using fMOST. Meanwhile, we pinpointed the cellular distribution of RABV by utilizing scRNA-seq.

RESULTS

Our fMOST data provided the 3D view of a neurotropic virus in the whole mouse brain, which indicated that the spatial distribution of RABV in the brain was influenced by the infection route. Interestingly, we provided evidence that RABV could infect multiple nuclei related to fear independent of different infection routes. More surprisingly, our scRNA-seq data revealed that besides neurons RABV could infect macrophages and the infiltrating macrophages played at least three different antiviral roles during RABV infection.

CONCLUSION

This study draws a comprehensively spatial and cellular map of typical neurotropic virus infection in the mouse brain, providing a novel and insightful strategy to investigate the pathogenesis of RABV and other neurotropic viruses.

The Effect of 12 Hz Extremely Low-frequency Electromagnetic Field on Visual Memory of Male Macaque Monkeys

Introduction

Today, humans live in a world surrounded by electromagnetic fields. Numerous studies have been conducted to discover the biological, physiological, and behavioral effects of electromagnetic fields on humans and animals. Given the biological similarities between monkeys and humans, The present research aimed to examine Visual Memory (VM), hormonal, genomic, and anatomic changes, in the male rhesus macaques exposed to an Extremely Low-Frequency Magnetic Field (ELF-MF).

Methods

Four male rhesus macaques (Macaca mulatta) were used. For the behavioral tests, the animals should be fasting for 17 hours. For the tests such as visual memory, the animal's cooperation was necessary. Using the radiation protocol, we exposed two monkeys to a 12-Hz electromagnetic field with a magnitude of 0.7 μT (electromagnetic radiation) four hours a day for a month. Before and after the exposure, a visual memory test was conducted using a coated device (visible reward) on a movable stand. Ten milliliters of blood was obtained from the femoral artery of each monkey, and half of it was used to examine cortisol serum levels using the MyBioSource kit (made in the USA). The other half of the blood was used to extract lymphocytes for assaying expressions of Glucocorticoid Receptor (GR) genes before and after radiation using the PCR method. Anatomic studies of the amygdala were carried out based on pre- and post-radiation Magnetic Resonance Imaging (MRI).

Results

Research results indicated that visual memory in male primates increased significantly after exposure to the 12-Hz frequency. Hormonal analysis at the 12-Hz frequency showed a decrease in cortisol serum levels. However, visual memory and serum cortisol levels did not change considerably in male primates in the control group. There was no considerable amygdala volumetric difference after exposure to the 12-Hz frequency. The expression of the GR genes decreased in the 12-Hz group compared to the control group.

Conclusion

In short, these results indicated that ELF might benefit memory enhancement because exposure to the 12-HZ ELF can enhance visual memory. This outcome may be due to a decrease in plasma cortisol and or expression of GR genes. Moreover, direct amygdala involvement in this regard cannot be recommended.

Highlights

The effects of Extremely Low-Frequency Electromagnetic Fields (ELF-EMF) of 12 Hz on monkeys were studied.The results showed a reduction in the serum cortisol levels and the expression of GR genes.The amygdala anatomical area changes were not significant in the experimental group.In the experimental group, visual memory (delay of 30- and 60-s evaluation) improved after exposure to a frequency of 12 Hz.

Plain Language Summary

Extremely low-frequency electromagnetic fields are among the most important factors affecting humans. This study aimed to determine the fields of 12-Hz frequency on the visual memory changes of male monkeys. The importance of research is due to the cognitive similarity of monkeys to humans. The findings of the research can be attributed to humans. Behavioral, hormonal, genetic, and anatomical studies indicated improvement in visual memory (test monkeys versus control monkeys). This study demonstrates the effect of the 12-Hz frequency on the monkey's visual memory. Researchers can study 12-Hz frequency in other cognitive indices.

Changes in the Orexin System in Rats Exhibiting Learned Helplessness Behaviors

Orexin-A (OX-A) and orexin-B (OX-B) are neuropeptides produced in the hypothalamus. Preclinical and clinical studies suggest that depression and anxiety are associated with the orexin system. In the current study, we used the learned helplessness (LH) animal model of depression to identify rats displaying LH behaviors (LH rats) and those that did not (No-LH rats). We compared the number of orexin-containing neurons in the hypothalamus of LH, No-LH, and control rats. Orexin peptides, orexin receptor 1 (OXR1) and 2 (OXR2) in brain areas involved in major depression and serum OX-A and corticosterone (CORT) concentrations were quantified and compared between rat groups. We found that LH and No-LH rats displayed higher serum OX-A concentrations compared with control rats. Comparison between LH and No-LH rats revealed that No-LH rats had significantly higher OX-A levels in the brain, more OX-A neurons, and more OX-A neuron activation. LH rats had more OX-B neurons and more OX-B neuron activation. Orexin peptides and receptors in the brain areas involved in major depression exhibited different patterns in LH and NoLH rats. Our findings revealed that activation of OX-A neurons could promote resilient behaviors under stressful situations and OX-A and OX-B neuropeptides exhibit dissimilar functions in LH behaviors.

Anxiety and ultrastructural consequences of chronic mild stress in rats

Detrimental consequences following exposure to severe stress, either acute or chronic are well recognized. Chronic mild stress (CMS) is also a leading cause of emotional distress and neuropsychiatric conditions such as anxiety disorders. However, the neurobiological substrates of the latter, particularly at the ultrastructural levels have not been adequately investigated. In this study, adult male Wistar rats were subjected to 4 h daily mild restraint for 20 days and their behavior in open field and elevated plus maze (EPM) were evaluated 24 h after the last restraint. Anxiety-like behavior was evident in CMS exposed rats by increases in rearing and grooming in the open field and the avoidance of open arms in the EPM. Concomitant ultrastructural alterations such as chromatolysis, agglutination of synaptic vesicles or mitochondrial damage were also observed in the central nucleus of amygdala (CNA), an area intimately involved in emotional and fear response, in CMS exposed rats. These results while confirming detrimental consequences of CMS, also suggest that ultrastructural alterations in CNA may be a basis for CMS-induced anxiety.

Evidence in primates supporting the use of chemogenetics for the treatment of human refractory neuropsychiatric disorders

Non-human primate (NHP) models are essential for developing and translating new treatments that target neural circuit dysfunction underlying human psychopathology. As a proof-of-concept for treating neuropsychiatric disorders, we used a NHP model of pathological anxiety to investigate the feasibility of decreasing anxiety by chemogenetically (DREADDs [designer receptors exclusively activated by designer drugs]) reducing amygdala neuronal activity. Intraoperative MRI surgery was used to infect dorsal amygdala neurons with AAV5-hSyn-HA-hM4Di in young rhesus monkeys. In vivo microPET studies with [11C]-deschloroclozapine and postmortem autoradiography with [3H]-clozapine demonstrated selective hM4Di binding in the amygdala, and neuronal expression of hM4Di was confirmed with immunohistochemistry. Additionally, because of its high affinity for DREADDs, and its approved use in humans, we developed an individualized, low-dose clozapine administration strategy to induce DREADD-mediated amygdala inhibition. Compared to controls, clozapine selectively decreased anxiety-related freezing behavior in the human intruder paradigm in hM4Di-expressing monkeys, while coo vocalizations and locomotion were unaffected. These results are an important step in establishing chemogenetic strategies for patients with refractory neuropsychiatric disorders in which amygdala alterations are central to disease pathophysiology.

Whole Brain Mapping of Neurons Innervating Extraorbital Lacrimal Glands in Mice and Rats of Both Genders

The extraorbital lacrimal glands (ELGs) secret tears to maintain a homeostatic environment for ocular surfaces, and pheromones to mediate social interactions. Although its distinct gender-related differences in mice and rats have been identified, its comprehensive histology together with whole-brain neuronal network remain largely unknown. The primary objective of the present study was to investigate whether sex-specific differences take place in histological and physiological perspectives. Morphological and histological data were obtained via magnetic resonance imaging (MRI), hematoxylin-eosin (HE) staining in mice and rats of both genders. The innervating network was visualized by a pseudorabies virus (PRV) mediated retrograde trans-multi-synaptic tracing system for adult C57BL6/J mice of both genders. In terms of ELGs' anatomy, mice and rats across genders both have 7 main lobes, with one exception observed in female rats which have only 5 lobes. Both female rats and mice generally have relatively smaller shape size, absolute weight, and cell size than males. Our viral tracing revealed a similar trend of innervating patterns antero-posteriorly, but significant gender differences were also observed in the hypothalamus (HY), olfactory areas (OLF), and striatum (STR). Brain regions including piriform area (Pir), post-piriform transition area (TR), central amygdalar nucleus (CEA), medial amygdalar nucleus (MEA), lateral hypothalamic area (LHA), parasubthalamic nucleus (PSTN), pontin reticular nucleus (caudal part) (PRNc), and parabrachial nucleus, (PB) were commonly labeled. In addition, chemical isotope labeling-assisted liquid chromatography-mass spectrometry (CIL-LC-MS) and nuclear magnetic resonance spectroscopy (NMR spectroscopy) were performed to reveal the fatty acids and metabolism of the ELGs, reflecting the relationship between pheromone secretion and brain network. Overall, our results revealed basic properties and the input neural networks for ELGs in both genders of mice, providing a structural basis to analyze the diverse functions of ELGs.

Modelling behaviors relevant to brain disorders in the nonhuman primate: Are we there yet?

Recent years have seen a profound resurgence of activity with nonhuman primates (NHPs) to model human brain disorders. From marmosets to macaques, the study of NHP species offers a unique window into the function of primate-specific neural circuits that are impossible to examine in other models. Examining how these circuits manifest into the complex behaviors of primates, such as advanced cognitive and social functions, has provided enormous insights to date into the mechanisms underlying symptoms of numerous neurological and neuropsychiatric illnesses. With the recent optimization of modern techniques to manipulate and measure neural activity in vivo, such as optogenetics and calcium imaging, NHP research is more well-equipped than ever to probe the neural mechanisms underlying pathological behavior. However, methods for behavioral experimentation and analysis in NHPs have noticeably failed to keep pace with these advances. As behavior ultimately lies at the junction between preclinical findings and its translation to clinical outcomes for brain disorders, approaches to improve the integrity, reproducibility, and translatability of behavioral experiments in NHPs requires critical evaluation. In this review, we provide a unifying account of existing brain disorder models using NHPs, and provide insights into the present and emerging contributions of behavioral studies to the field.