Amygdala Function Research Articles

Allergen-induced anxiety-like behavior is associated with disruption of medial prefrontal cortex - amygdala circuit

Anxiety is prevalent in asthma, and is associated with disease severity and poor quality of life. However, no study to date provides direct experimental evidence for the effect of allergic inflammation on the structure and function of medial prefrontal cortex (mPFC) and amygdala, which are essential regions for modulating anxiety and its behavioral expression. We assessed the impact of ovalbumin (OVA)-induced allergic inflammation on the appearance of anxiety-like behavior, mPFC and amygdala volumes using MRI, and the mPFC-amygdala circuit activity in sensitized rats. Our findings exhibited that the OVA challenge in sensitized rats induced anxiety-like behavior, and led to more activated microglia and astrocytes in the mPFC and amygdala. We also found a negative correlation between anxiety-like behavior and amygdala volume. Moreover, OVA challenge in sensitized rats was associated with increases in mPFC and amygdala activity, elevation of amygdala delta-gamma coupling, and the enhancement of functional connectivity within mPFC-amygdala circuit – accompanied by an inverted direction of information transferred from the amygdala to the mPFC. We indicated that disrupting the dynamic interactions of the mPFC-amygdala circuit may contribute to the induction of anxiety-related behaviors with asthma. These findings could provide new insight to clarify the underlying mechanisms of allergic inflammation-induced psychiatric disorders related to asthma.

Human Plasma BDNF Is Associated With Amygdala-Prefrontal Cortex Functional Connectivity and Problem Drinking Behaviors.

BackgroundPreclinical studies suggest that decreased levels of brain-derived neurotrophic factor in the amygdala play a role in anxiety and alcohol use disorder. The association between brain-derived neurotrophic factor levels and amygdala function in humans with alcohol use disorder is still unclear, although neuroimaging studies have also implicated the amygdala in alcohol use disorder and suggest that alcohol use disorder is associated with disrupted functional connectivity between the amygdala and prefrontal cortex during aversive states.MethodsThe current study investigated whether plasma brain-derived neurotrophic factor levels in individuals with and without alcohol use disorder (n = 57) were associated with individual differences in amygdala reactivity and amygdala-prefrontal cortex functional connectivity during 2 forms of aversive responding captured via functional magnetic resonance imaging: anxiety elicited by unpredictable threat of shock and fear elicited by predictable threat of shock. We also examined whether brain-derived neurotrophic factor and brain function were associated with binge drinking episodes and alcohol use disorder age of onset.ResultsDuring anxiety, but not fear, lower levels of plasma brain-derived neurotrophic factor were associated with less connectivity between the left amygdala and the medial prefrontal cortex and the inferior frontal gyrus. In addition, within individuals with alcohol use disorder (only), lower levels of brain-derived neurotrophic factor and amygdala-medial prefrontal cortex functional connectivity during anxiety were associated with more binge episodes within the past 60 days and a lower age of alcohol use disorder onset. There were no associations between brain-derived neurotrophic factor levels and focal amygdala task reactivity.ConclusionsTogether, the results indicate that plasma brain-derived neurotrophic factor levels are related to amygdala circuit functioning in humans, particularly during anxiety, and these individual differences may relate to drinking behaviors.

Dual and Opposing Functions of the Central Amygdala in the Modulation of Pain

SUMMARYPain perception is essential for survival and can be amplified or suppressed by expectations, experiences, and context. The neural mechanisms underlying bidirectional modulation of pain remain largely unknown. Here, we demonstrate that the central nucleus of the amygdala (CeA) functions as a pain rheostat, decreasing or increasing pain-related behaviors in mice. This dual and opposing function of the CeA is encoded by opposing changes in the excitability of two distinct subpopulations of GABAergic neurons that receive excitatory inputs from the parabrachial nucleus (PB). Thus, cells expressing protein kinase C-delta (CeA-PKCδ) are sensitized by nerve injury and increase pain-related responses. In contrast, cells expressing somatostatin (CeA-Som) are inhibited by nerve injury and their activity drives antinociception. Together, these results demonstrate that the CeA can amplify or suppress pain in a cell-type-specific manner, uncovering a previously unknown mechanism underlying bidirectional control of pain in the brain.

Promising Neuroimaging Biomarkers in Depression.

The neuroimaging has been applied in the study of pathophysiology in major depressive disorder (MDD). In this review article, several kinds of methodologies of neuroimaging would be discussed to summarize the promising biomarkers in MDD. For the magnetic resonance imaging (MRI) and magnetoencephalography field, the literature review showed the potentially promising roles of frontal lobes, such as anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC) and orbitofrontal cortex (OFC). In addition, the limbic regions, such as hippocampus and amygdala, might be the potentially promising biomarkers for MDD. The structures and functions of ACC, DLPFC, OFC, amygdala and hippocampus might be confirmed as the biomarkers for the prediction of antidepressant treatment responses and for the pathophysiology of MDD. The functions of cognitive control and emotion regulation of these regions might be crucial for the establishment of biomarkers. The near-infrared spectroscopy studies demonstrated that blood flow in the frontal lobe, such as the DLPFC and OFC, might be the biomarkers for the field of near-infrared spectroscopy. The electroencephalography also supported the promising role of frontal regions, such as the ACC, DLPFC and OFC in the biomarker exploration, especially for the sleep electroencephalogram to detect biomarkers in MDD. The positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in MDD demonstrated the promising biomarkers for the frontal and limbic regions, such as ACC, DLPFC and amygdala. However, additional findings in brainstem and midbrain were also found in PET and SPECT. The promising neuroimaging biomarkers of MDD seemed focused in the fronto-limbic regions.

Impact of Chronic BDNF Depletion on GABAergic Synaptic Transmission in the Lateral Amygdala.

Brain-derived neurotrophic factor (BDNF) has previously been shown to play an important role in glutamatergic synaptic plasticity in the amygdala, correlating with cued fear learning. While glutamatergic neurotransmission is facilitated by BDNF signaling in the amygdala, its mechanism of action at inhibitory synapses in this nucleus is far less understood. We therefore analyzed the impact of chronic BDNF depletion on GABAA-mediated synaptic transmission in BDNF heterozygous knockout mice (BDNF+/−). Analysis of miniature and evoked inhibitory postsynaptic currents (IPSCs) in the lateral amygdala (LA) revealed neither pre- nor postsynaptic differences in BDNF+/− mice compared to wild-type littermates. In addition, long-term potentiation (LTP) of IPSCs was similar in both genotypes. In contrast, facilitation of spontaneous IPSCs (sIPSCs) by norepinephrine (NE) was significantly reduced in BDNF+/− mice. These results argue against a generally impaired efficacy and plasticity at GABAergic synapses due to a chronic BDNF deficit. Importantly, the increase in GABAergic tone mediated by NE is reduced in BDNF+/− mice. As release of NE is elevated during aversive behavioral states in the amygdala, effects of a chronic BDNF deficit on GABAergic inhibition may become evident in response to states of high arousal, leading to amygdala hyper-excitability and impaired amygdala function.

Amygdala and affective responses to infant pictures: Comparing depressed and non-depressed mothers and non-mothers.

In many mammalian species, new mothers show heightened positive responsiveness to infants and their cues when they give birth. As is evident from non-human and human studies, the amygdala is a brain region implicated in both the maternal and affective neural circuitry, and is involved in processing socioemotionally salient stimuli. In humans, infants are socially salient stimuli to women, and mothers in particular. Neuroimaging studies investigating the maternal response to infant cues have identified infant-related amygdala function as an important factor in maternal anxiety/depression, in the quality of mothering and in individual differences in the motivation to mother. The present study investigated the effects of maternal status and depression on the subjective affective response and amygdala responsiveness to unfamiliar infants using functional magnetic resonance imaging. Smiling infant pictures were used in a 2×2 design comparing four groups of women: mothers and non-mothers, with and without depression (total of 101 women: postpartum depression [PPD]=32, non-PPD=25, major depression [MDD]=15, non-MDD=29). We undertook an anatomically defined region of interest analysis of the amygdala response for a priori defined group comparisons. We found that mothers rated infants more positively than non-mothers and non-mothers rated non-infant stimuli (scenery) more positively than mothers. In the amygdala, we found that depression elevated response to smilingunfamiliarinfants in mothers but had no effect in non-mothers. Within the depressed groups, mothers (PPD) showed an elevated amygdala response to unfamiliar smiling infants compared to depressed non-mothers. Hence, our results indicate that women with PPD show an enhanced amygdala response to affectively positive infant pictures but not to affectively positive (but non-salient) pictures of scenery. Women with depression outside of the postpartum period show no change in amygdala responsiveness to either stimulus categories.

Increases in dendritic spine density in BLA without metabolic changes in a rodent model of PTSD.

Imaging studies have shown abnormal amygdala function in patients with posttraumatic stress disorder (PTSD). In addition, alterations in synaptic plasticity have been associated with psychiatric disorders and previous reports have indicated alterations in the amygdala morphology, especially in basolateral (BLA) neurons, are associated with stress-related disorders. Since, some individuals exposed to a traumatic event develop PTSD, the goals of this study were to evaluate the early effects of PTSD on amygdala glucose metabolism and analyze the possible BLA dendritic spine plasticity in animals with different levels of behavioral response. We employed the inescapable footshock protocol as an experimental model of PTSD and the animals were classified according to the duration of their freezing behavior into distinct groups: "extreme behavioral response" (EBR) and "minimal behavioral response". We evaluated the amygdala glucose metabolism at baseline (before the stress protocol) and immediately after the situational reminder using the microPET and the radiopharmaceutical 18F-FDG. The BLA dendritic spines were analyzed according to their number, density, shape and morphometric parameters. Our results show the EBR animals exhibited longer freezing behavior and increased proximal dendritic spines density in the BLA neurons. Neither the amygdaloid glucose metabolism, the types of dendritic spines nor their morphometric parameters showed statistically significant differences. The extreme behavior response induced by this PTSD protocol produces an early increase in BLA spine density, which is unassociated with either additional changes in the shape of spines or metabolic changes in the whole amygdala of Wistar rats.

Early life stress: It’s all in the timing

The effects of childhood maltreatment on adult amygdala function depend on when the maltreatment occurs.

Cross-species convergence in pupillary response: understanding human anxiety via non-human primate amygdala lesion.

Few studies have used matched affective paradigms to compare humans and non-human primates. In monkeys with amygdala lesions and youth with anxiety disorders, we examined cross-species pupillary responses during a saccade-based, affective attentional capture task. Given evidence of enhanced amygdala function in anxiety, we hypothesized that opposite patterns would emerge in lesioned monkeys and anxious participants. A total of 53 unmedicated youths (27 anxious, 26 healthy) and 8 adult male rhesus monkeys (Macaca mulatta) completed matched behavioral paradigms. Four monkeys received bilateral excitotoxic amygdala lesions and four served as unoperated controls. Compared to healthy youth, anxious youth exhibited increased pupillary constriction in response to emotional and non-emotional distractors (F(1,48) = 6.28, P=0.02, η2p= 0.12). Pupillary response was associated significantly with anxiety symptoms severity (F(1,48) = 5.59, P=0.02, η2p= 0.10). As hypothesized, lesioned monkeys exhibited the opposite pattern i.e. decreased pupillary constriction in response to distractors, compared to unoperated control monkeys (F(1,32) = 24.22, P<0.001, η2= 0.33). Amygdala lesioned monkeys and youth with anxiety disorders show opposite patterns of pupil constriction in the context of an affective distractor task. Such findings suggest the presence of altered amygdala circuitry functioning in anxiety. Future lesion and human neuroimaging work might examine the way in which specific amygdala sub-nuclei and downstream circuits mediate these effects.

Association of Prepubertal and Postpubertal Exposure to Childhood Maltreatment With Adult Amygdala Function

Abnormalities in amygdala response to threatening faces have been observed in anxiety disorders, autism, bipolar disorder, depression, posttraumatic stress disorder, and schizophrenia. Abnormally hyperactive and hypoactive responses have typically been associated with anxiety and inhibition vs risk taking and inappropriate social behaviors. Maltreatment is a major risk factor for most of these disorders and is associated with abnormal amygdala function. To identify the type and age of exposure to childhood maltreatment that are associated with hyperactive and hypoactive amygdala responses in young adulthood. Data collection for this retrospective cohort study took place from November 8, 2010, to August 23, 2012. Data analyses were conducted from September 20, 2012, to June 27, 2018. Participants were recruited from the urban and suburban Boston vicinity without diagnostic restrictions based on exposure history. The Maltreatment and Abuse Chronology of Exposure (MACE) scale was used to retrospectively assess type and age of exposure to childhood maltreatment. Activation and pattern information functional magnetic resonance imaging were used to assess bilateral amygdala response to angry and fearful faces vs neutral faces or shapes, and sensitive exposure periods were identified using cross-validated artificial intelligence predictive analytics (50 averaged randomized iterations with training on 63.3% and testing on 36.7% of the sample). Of the 202 participants (mean [SD] age, 23.2 [1.7] years; 118 [58.4%] female), 52 (25.7%) reported no exposure to maltreatment and 150 (74.3%) reported exposure to 1 or more maltreatment types. Eight participants (15.1%) with a MACE score of 0 and 51 (34.2%) with a MACE score of 1 or higher had a history of major depression (odds ratio, 2.40; 95% CI, 1.05-6.06; P = .03); 8 unexposed participants (15.1%) and 46 with MACE scores of 1 or higher (30.9%) had a history of 1 or more anxiety disorders (odds ratio, 2.45; 95% CI, 1.03-6.50; P = .03). Retrospective self-report of physical maltreatment between 3 and 6 years of age and peer emotional abuse at 13 and 15 years were associated with amygdala activation to emotional faces vs shapes. Early exposure was associated with blunted response (β = -0.17, P < .001), whereas later exposure was associated with augmented response (β = 0.16, P < .001). Prepubertal vs postpubertal maltreatment was associated with an opposite response on the voxelwise response pattern in clustering stimuli of the same type (eg, mean [SD] emotional ellipse areas for physical maltreatment at age 4 years vs nonverbal emotional abuse at 13 years: 1.41 [1.05] vs 0.25 [0.10], P < .001) and in distinguishing between stimuli of different types (eg, mean [SD] emotional vs neutral faces distance for peer emotional abuse at age 6 years vs 13 years: 1.89 [0.75] vs 0.80 [0.39], P < .001). The findings suggest that prepubertal vs postpubertal developmental differences in the association between maltreatment and amygdala response to threatening or salient stimuli exist. Understanding the role of adversity in different sensitive exposure periods and the potential adaptive significance of attenuated vs enhanced amygdala response may help explain why maltreatment may be a risk factor for many different disorders and foster creation of targeted interventions to preempt the emergence of psychopathology in at-risk youths.

The Science of Auricular Microsystem Acupuncture: Amygdala Function in Psychiatric, Neuromusculoskeletal, and Functional Disorders.

Addressing dysfunction of the amygdala via the auricular acupuncture microsystem has vast potential. Widespread medical consequences of amygdala dysregulation have been well-defined scientifically. Clinical results and a significant quantity of existing amygdala research support the rationale for addressing amygdala function through auricular-acupuncture techniques. Further scientific inquiry into their mechanisms of action, clinical applications, and expansion of both professional and public education of the merits of these techniques is warranted.

Investigations of Amygdala Function Using Neurophysiological Recording and Stimulation

Investigations of Amygdala Function Using Neurophysiological Recording and Stimulation

Amygdala functioning during threat acquisition and extinction differentiates antisocial subtypes.

Extensive work implicates abnormal amygdala response during threatening stimuli in youth with antisocial behaviour. However, no research has examined whether youth identified in Primary and Secondary psychopathy subtypes would show differences in amygdala activity in response to threat acquisition and extinction. Latent profile analysis (LPA) was used to identify distinct antisocial groups based on participants' scores on callous-unemotional (CU) traits, anxiety, and familial abuse in a sample of 136 high-risk adolescents (mean age=17.7, SD=1.6; 86% male). Functional MRI was then used to assess amygdala activation patterns during a classical differential delay threat-conditioning task. In addition to the Primary and Secondary subtypes, we identified groups mainly high on anxiety and others who were mainly high on abuse. Participants in the Primary group showed lower right amygdala activity in response to neutral male faces compared to the low, Anxious, and Secondary groups, whereas participants in the group with history of abuse exhibited higher right amygdala activity during threat acquisition compared to the rest of the groups. During threat extinction, the Primary group showed lower right amygdala activity compared to the Secondary and abuse groups. This is the first study to reveal amygdala activation in identified psychopathy-related variants during threat conditioning. We found that stratifying the sample based on the identified variants revealed amygdala functioning patterns that furthered our understanding of emotion-based deficits among high-risk adolescents.

Deletion of Dtnbp1 in mice impairs threat memory consolidation and is associated with enhanced inhibitory drive in the amygdala

Schizophrenia is a severe and highly heritable disorder. Dystrobrevin-binding protein 1 (DTNBP1), also known as dysbindin-1, has been implicated in the pathophysiology of schizophrenia. Specifically, dysbindin-1 mRNA and protein expression are decreased in the brains of subjects with this disorder. Mice lacking dysbinidn-1 also display behavioral phenotypes similar to those observed in schizophrenic patients. However, it remains unknown whether deletion of dysbindin-1 impacts functions of the amygdala, a brain region that is critical for emotional processing, which is disrupted in patients with schizophrenia. Here, we show that dysbindin-1 is expressed in both excitatory and inhibitory neurons of the basolateral amygdala (BLA). Deletion of dysbindin-1 in male mice (Dys−/−) impaired cued and context-dependent threat memory, without changes in measures of anxiety. The behavioral deficits observed in Dys−/− mice were associated with perturbations in the BLA, including the enhancement of GABAergic inhibition of pyramidal neurons, increased numbers of parvalbumin interneurons, and morphological abnormalities of dendritic spines on pyramidal neurons. Our findings highlight an important role for dysbindin-1 in the regulation of amygdalar function and indicate that enhanced inhibition of BLA pyramidal neuron activity may contribute to the weakened threat memory expression observed in Dys−/− mice.

Stress reactivity after traumatic brain injury: implications for comorbid post-traumatic stress disorder.

Most people have or will experience traumatic stress at some time over the lifespan, but only a subset of traumatized individuals develop post-traumatic stress disorder (PTSD). Clinical research supports high rates of traumatic brain injury (TBI)-PTSD comorbidity and demonstrates TBI as a significant predictor of the development of PTSD. Biological factors impacted following brain injury that may contribute to increased PTSD risk are unknown. Heightened stress reactivity and dysregulated hypothalamic-pituitary-adrenal (HPA) axis function are common to both TBI and PTSD, and affect amygdalar structure and function, which is implicated in PTSD. In this review, we summarize a growing body of literature that shows HPA axis dysregulation, as well as enhanced fear and amygdalar function after TBI. We present the hypothesis that altered stress reactivity as a result of brain injury impacts the amygdala and defense systems to be vulnerable to increased fear and PTSD development from traumatic stress. Identifying biological mechanisms that underlie this vulnerability, such as dysregulated HPA axis function, may lead to better targeted treatments and preventive measures to support psychological health after TBI.

Mild Traumatic Brain Injury (TBI) Alters Endocannabinoids in the Amygdala of Female Alcohol Drinking Rats

Traumatic brain injury (TBI) is a growing national health concern; nearly 2.5 million Americans sustain a TBI each year, and this number has increased since 2000 by nearly 60%. Most TBIs are ‘mild TBIs (mTBI)’, which predispose individuals to develop detrimental symptoms like cognitive impairment, anxiety, depression, and increased propensity for addictive behaviors.Alcohol is a known risk factor for incurring TBI, and our labs have demonstrated deleterious effects of alcohol on TBI outcomes and recovery. The amygdala is an important neural structure implicated in emergence of negative affective states and addiction. Mild TBI and alcohol each alter amygdala function and endocannabinoid (eCB) signaling, providing a potential neurobiological mechanism for post‐TBI psychiatric sequelae that are exacerbated by post‐TBI alcohol drinking.This study's aims were 1) to determine the effect of mTBI and operant alcohol self‐administration on endocannabinoid system protein expression in the central (CeA) and basolateral amygdala (BLA) of female rats and 2) to determine mTBI and operant alcohol self‐administration on endocannabinoid levels in the BLA. We hypothesized that mTBI would increase degradative eCB enzyme monoacylglycerol lipase (MAGL) expression and decrease endocannabinoid signaling in amygdaloid sub‐nuclei in alcohol drinking animals. Adult female Wistar rats were trained to self‐administer alcohol using an operant task. Following stabilization of alcohol responding, all rats underwent a 5‐mm left lateral craniotomy. Three days later, mild‐to‐moderate TBI (25ms, 28–32 PSI) or sham injury was delivered via lateral fluid percussion over the sensorimotor cortex. Operant alcohol self‐administration was measured every two days post‐injury, and animals were sacrificed 1 hour, 5 days, or 11 days post‐TBI. Following sacrifice, brains were excised, CeA and BLA were bilaterally dissected, and micropunches were used for either Western blot analysis of eCB protein expression (eCB synthetic and degradative enzymes and cannabinoid receptors) or quantification of endocannabinoid (i.e., 2‐arachidonyl glycerol [2‐AG], anandamide) levels via liquid chromatography and mass spectroscopy.Western blot analysis revealed downregulation of the synthetic 2‐AG enzyme, diacylglycerol lipase alpha, in BLA of female alcohol drinking mTBI rats 11 d post injury. Alcohol self‐administration decreased 2‐AG degradative enzyme, MAGL, expression in the BLA 11 d post injury. No changes in endocannabinoid protein expression were observed in alcohol‐naïve rats.Collectively, our results suggest that mTBI may decrease basolateral amygdalar 2‐AG synthesis in alcohol drinking rats, and these alterations may represent a mechanism by which mTBI increases alcohol drinking.Support or Funding InformationAA026468‐01A1 (ZFS), AA007577 (PEM), and AA023305 (NWG)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Genetic Correlation between Child Callous-Unemotional Behaviors and Fear Recognition Deficit: Evidence for a Neurocognitive Endophenotype.

This study investigates emotion recognition deficits as candidate neurocognitive endophenotypes for callous-unemotional (CU) behaviors. Using a twin design, we tested genetic correlations between child CU behaviors and poor processing of fearful and sad facial expressions. Participants were 504 twin pairs (209 MZ pairs; 295 DZ pairs) from the Quebec Newborn Twin Study, a longitudinal study of a population-based sample of twins. Teachers in kindergarten and first grade rated children's CU behaviors and other behavior problems (attention deficit and hyperactivity symptoms, physical aggression, and depressive symptoms). In first grade (mean age 7years), the children completed the visual subtest of the Diagnostic Analysis of Nonverbal Accuracy Scale 2 (DANVA-II) to assess emotion recognition from facial stimuli. Using structural equation modeling, we examined the genetic-environmental etiology of the association between fear/sadness recognition and child CU behaviors, controlling for other behavior problems and recognition of other emotions. We found a significant genetic correlation between poor fear recognition and CU behaviors that was independent of other behavior problems. Poor recognition of sadness was not significantly associated with CU behaviors after taking into account other behavior problems. Our results suggest that CU behaviors and fear recognition have a partly shared genetic aetiology. This provides support for poor fear recognition as a key neurocognitive endophenotype for CU behaviors. Future research should test a hypothesized causal chain from specific genes, through amygdala functioning and fear recognition, to CU behaviors, and identify specific environmental factors (including intervention) that may disrupt this chain.

(247) Studying Pain Neural Circuits with Viral Vector rAAV2-Retro in the Brain

Prefrontal cortex (PFC) activity could modulate amygdala function and alter cognitive performance or the emotional-affective dimension of pain. The PFC-thalamic circuitry could be also altered by locus coeruleus (LC) activity as a modulatory mechanism for pain. A serotype of rAAV has been recently described that is capable of selectively transfecting projection neurons in a retrograde fashion, termed rAAV2-Retro, however this property has not been documented for many circuits in rat brain. We hypothesize that the variant rAAV2-Retro could be used to target distant projections between brain regions using Cre and Flex technology in a circuit-specific manner. We evaluated prefrontal cortex projections of the anterior cingulate cortex (ACC), basomedial amygdala (BLA), ventral tegmental area (VTA), and locus coeruleus (LC). First, we administered rAAV2-Retro-CAG-GFP (1.8 × 1012 viral particles) in the prefrontal cortex and collected brain region tissues 4 or 8 weeks after injection to conduct immunohistochemistry and determine retrograde transduction efficiency. We observed robust GFP expression in ACC, BLA, and VTA in all treated rats (n=6) 4 weeks after viral injection using GFP fluorescence and anti-GFP antibodies (with a neuronal marker, NeuN) and in the LC 8 weeks after viral injection. Second, we injected rAAV2-retro-CAG-Cre in prefrontal cortex and rAAV8-FLEX-CAG-tdTomato in the BLA. We collected BLA tissues 4 weeks after injection for immunohistochemistry to determine gene induction efficiency. We confirmed Cre expression in BLA 4 weeks after viral injection in the prefrontal cortex (rAAV2-retro-CAG-Cre) using an anti-Cre antibody (with NeuN). We observed that tdTomato was robustly expressed in BLA (tdTomato fluorescence and anti-DSred antibody) when rAAV2-retro-CAG-Cre was injected in prefrontal cortex and rAAV8-FLEX-CAG-tdTomato in the BLA, but not in control groups (rAAV8-FLEX-CAG-tdTomato in BLA only). We conclude that rAAV2-Retro could be efficiently used to target brain projections to the prefrontal cortex using Cre-Flex approaches for circuit-specific modulation. Acknowledgements: NIGMS grant GM113852.

A model of amygdala function following plastic changes at specific synapses during extinction

The synaptic networks in the amygdala have been the subject of intense interest in recent times, primarily because of the role of this structure in emotion. Fear and its extinction depend on the workings of these networks, with particular interest in extinction because of its potential to ameliorate adverse symptoms associated with post-traumatic stress disorder. Here we place emphasis on the extinction networks revealed by recent techniques, and on the probable plasticity properties of their synaptic connections. We use modules of neurons representing each of the principal components identified as involved in extinction. Each of these modules consists of neural networks, containing specific ratios of excitatory and specialized inhibitory neurons as well as synaptic plasticity mechanisms appropriate for the component of the amygdala they represent. While these models can produce dynamic output, here we concentrate on the equilibrium outputs and do not model the details of the plasticity mechanisms. Pavlovian fear conditioning generates a fear memory in the lateral amygdala module that leads to activation of neurons in the basal nucleus fear module but not in the basal nucleus extinction module. Extinction protocols excite infralimbic medial prefrontal cortex neurons (IL) which in turn excite so-called extinction neurons in the amygdala, leading to the release of endocannabinoids from them and an increase in efficacy of synapses formed by lateral amygdala neurons on them. The model simulations show how such a mechanism could explain experimental observations involving the role of IL as well as endocannabinoids in different temporal phases of extinction.

Non-invasive Vagal Nerve Stimulation Paired with Stress Exposure in Posttraumatic Stress Disorder (PTSD)

Non-invasive Vagal Nerve Stimulation (nVNS) is a new device that has promise for the study of vagal nerve physiology as well as clinical application in patients with psychiatric disorders. Posttraumatic stress disorder (PTSD) is a psychiatric disorder that can follow exposure to psychological trauma and is associated with intrusive memories, nightmares, avoidance, and problems with sleep and concentration. Exposure to reminders of the traumatic event can activate PTSD symptoms. We and others have shown changes in brain circuits in PTSD, including decreased medial prefrontal and increased amygdala function, as well as increased peripheral sympathetic and inflammatory responses, impaired autonomic tone, and an increased risk for coronary heart disease. In the current study, subjects with a history of exposure to psychological trauma undergo both trauma-specific and neutral stressors (math stress, public speaking) paired with nVNS or sham stimulation to the neck in conjunction with High Resolution Positron Emission Tomographic (HR-PET) with radiolabelled water imaging of the brain and measurement of stress biomarkers (e.g., inflammatory markers, cortisol, norepinephrine), as well as assessment of cardiovascular and autonomic parameters using wearable sensory devices. Pre-ejection Period (PEP) (the time interval between electrical depolarization of the left ventricle and the opening of the aortic valve) shortening is a marker of increased sympathetic tone, as is seen with stress. Other outcomes include peripheral vasoconstriction and rate pressure product (RPP). Preliminary findings show decreased inflammatory markers, blocked shortening of PEP, and increased medial prefrontal (anterior cingulate) function with nVNS paired to traumatic scripts but not sham controls. These findings suggest that nVNS has effects on both central and peripheral stress response systems in humans that may counteract the effects of stress. This research has implications for new treatments involving electrical stimulation in PTSD.