Neurogenetic Approaches to Stress and Fear in Humans as Pathophysiological Mechanisms for Posttraumatic Stress Disorder

The basal forebrain to lateral habenula circuitry mediates social behavioral maladaptation

Elucidating the neural basis of fear allows for more effective treatments for maladaptive fear often observed in psychiatric disorders. Although the basal forebrain (BF) has an essential role in fear learning, its function in fear expression and the underlying neuronal and circuit substrates are much less understood. Here we report that BF glutamatergic neurons are robustly activated by social stimulus following social fear conditioning in male mice. And cell-type-specific inhibition of those excitatory neurons largely reduces social fear expression. At the circuit level, BF glutamatergic neurons make functional contacts with the lateral habenula (LHb) neurons and these connections are potentiated in conditioned mice. Moreover, optogenetic inhibition of BF-LHb glutamatergic pathway significantly reduces social fear responses. These data unravel an important function of the BF in fear expression via its glutamatergic projection onto the LHb, and suggest that selective targeting BF-LHb excitatory circuitry could alleviate maladaptive fear in relevant disorders.

Stress and Susceptibility: A Systematic Review of Prenatal Epigenetic Risks for Developing Post-Traumatic Stress Disorder

This review aims to systematically assess the current literature about prenatal epigenetic markers that lead to post-traumatic stress disorder susceptibility across the lifespan. Studies included in this review met several research criteria: Studies included (1) participants with a PTSD diagnosis according to the DSM-5, (2) prenatal epigenetic marker data that could be analyzed, and (3) explicit references to postnatal PTSD susceptibility. Our study sample fit within a timeframe of 2002 (the earliest recorded studies of prenatal susceptibility to post-traumatic stress disorder in the databases used) and February 2021 when the literature search for this review was terminated. Studies for this review were collated from PubMed, MEDLINE, Science Direct, and Boston College School of Social Work Library databases. A systematic search was conducted in these databases using basic keyword terms, such as "PSTD resilience" and "PTSD vulnerability," and then adding clarifying terms to refine specific searches, such as "epigenetics," "genetics," "epigenetic markers," "haplotypes," and "mRNA methylation." Based on these criteria and research methods, 33 studies remained for inclusion in the review sample. This review suggests that BDNF Val66-Met, a polymorphism of FKBP5, and an altered messenger ribonucleic acid methylation marker in NR3C1 present most often in cases of PTSD. These epigenetic markers might be implicated in central neurological processes related to post-traumatic stress disorder symptomatology.

Is Fear Extinction Impairment Central to Psychopathology?

As discussed in this chapter, there have been enormous advances in our understanding of how anxiety disorders develop, are maintained, and can be treated. Many of these advances have been the result of translational studies using fear conditioning and extinction models. Despite these successes, we recognize, as a field, that there are important limitations in the extent to which extinction can explain how anxiety disorders and behaviors remit. Clinically speaking, the outstanding challenge for treatment of anxiety disorders is to improve the current suboptimal success rates. Over the past 30 years, we have not improved our treatment success rates despite employing many pharmacological and pharmacological strategies. While extinction and related fear circuitry mechanisms most certainly appear to play a role in treatment of anxiety disorders, they are also apparently insufficient to fully accommodate the varied responses individuals exhibit with this treatment approach. Increasingly diverse and innovative approaches are needed that accommodate the multitude of change mechanisms involved in treating anxiety. However, this is not to suggest ignoring the key role that extinction and memory updating processes play in overcoming anxiety.

Genetic Specificity of Hippocampal Subfield Volumes, Relative to Hippocampal Formation, Identified in 2148 Young Adult Twins and Siblings

The hippocampus is a complex brain structure with key roles in cognitive and emotional processing and with subregion abnormalities associated with a range of disorders and psychopathologies. Here we combine data from two large independent young adult twin/sibling cohorts to obtain the most accurate estimates to date of genetic covariation between hippocampal subfield volumes and the hippocampus as a single volume. The combined sample included 2148 individuals, comprising 1073 individuals from 627 families (mean age = 22.3 years) from the Queensland Twin IMaging (QTIM) Study, and 1075 individuals from 454 families (mean age = 28.8 years) from the Human Connectome Project (HCP). Hippocampal subfields were segmented using FreeSurfer version 6.0 (CA4 and dentate gyrus were phenotypically and genetically indistinguishable and were summed to a single volume). Multivariate twin modeling was conducted in OpenMx to decompose variance into genetic and environmental sources. Bivariate analyses of hippocampal formation and each subfield volume showed that 10%-72% of subfield genetic variance was independent of the hippocampal formation, with greatest specificity found for the smaller volumes; for example, CA2/3 with 42% of genetic variance being independent of the hippocampus; fissure (63%); fimbria (72%); hippocampus-amygdala transition area (41%); parasubiculum (62%). In terms of genetic influence, whole hippocampal volume is a good proxy for the largest hippocampal subfields, but a poor substitute for the smaller subfields. Additive genetic sources accounted for 49%-77% of total variance for each of the subfields in the combined sample multivariate analysis. In addition, the multivariate analyses were sufficiently powered to identify common environmental influences (replicated in QTIM and HCP for the molecular layer and CA4/dentate gyrus, and accounting for 7%-16% of total variance for 8 of 10 subfields in the combined sample). This provides the clearest indication yet from a twin study that factors such as home environment may influence hippocampal volumes (albeit, with caveats).

Unsuppressed Striatal Activity and Genetic Risk for Schizophrenia Associated With Individual Cognitive Performance Under Social Competition

BACKGROUND AND HYPOTHESIS

Social competition affects human behaviors by inducing psychosocial stress. The neural and genetic mechanisms of individual differences of cognitive-behavioral response to stressful situations in a competitive context remain unknown. We hypothesized that variation in stress-related brain activation and genetic heterogeneity associated with psychiatric disorders may play roles towards individually differential responses under stress.

STUDY DESIGN

A total of 419 healthy subjects and 66 patients with schizophrenia were examined functional magnetic resonance imaging during working memory task including social competition stressors. We explored the correlation between stress-induced brain activity and individual working memory performance. The partial least squares regression was performed to examine the genetic correlates between stress-related activity and gene expression data from Allen Human Brain Atlas. Polygenic risk score (PRS) was used to assess individual genetic risk for schizophrenia.

STUDY RESULTS

Greater suppression of bilateral striatal activity was associated with better behavioral improvement in working memory manipulation under social competition (left: rPearson = -0.245, P = 4.0 × 10-6, right: rPearson = -0.234, P = 1.0 × 10-5). Genes transcriptionally related to stress-induced activation were linked to genetic risk for schizophrenia (PFDR < 0.005). Participants with decreased accuracy under social competition exhibited higher PRS of schizophrenia (t = 2.328, P = .021). Patients with schizophrenia showed less suppressed striatal activity under social stress (F = 13.493, P = 3.5 × 10-4).

CONCLUSIONS

Striatal activity change and genetic risk for schizophrenia might play a role in the individually behavioral difference in working memory manipulation under stress.

Childhood maltreatment history and attention bias variability in healthy adult women: role of inflammation and the BDNF Val66Met genotype

Childhood maltreatment has been associated with greater attention bias to emotional information, but the findings are controversial. Recently, a novel index of attention bias, i.e., attention bias variability (ABV), has been developed to better capture trauma-related attentional dysfunction. However, ABV in relation to childhood trauma has not been studied. Here, we examined the association of childhood maltreatment history with attention bias/ABV in 128 healthy adult women. Different types of childhood maltreatment were assessed with the Childhood Trauma Questionnaire. Attention bias/ABV was measured by the dot-probe task. Possible mechanisms whereby childhood maltreatment affects attention bias/ABV were also explored, focusing on blood proinflammatory markers and the BDNF Val66Met polymorphism. We observed a significant positive correlation between childhood emotional abuse and ABV (P = 0.002). Serum high-sensitivity tumor necrosis factor-α levels were significantly positively correlated with ABV (P < 0.001), but not with childhood maltreatment. Jonckheere-Terpstra trend test showed a significant tendency toward greater ABV with increasing numbers of the BDNF Met alleles (P = 0.021). A two-way analysis of variance further revealed that the genotype-by-emotional abuse interaction for ABV was significant (P = 0.022); individuals with the Val/Met and Met/Met genotypes exhibited even greater ABV when childhood emotional abuse was present. These results indicate that childhood emotional abuse can have a long-term negative impact on emotional attention control. Increased inflammation may be involved in the mechanism of ABV, possibly independently of childhood maltreatment. The BDNF Met allele may dose-dependently increase ABV by interacting with childhood emotional abuse.

Transcriptomic organization of the human brain in post-traumatic stress disorder

Despite extensive study of the neurobiological correlates of post-traumatic stress disorder (PTSD), little is known about its molecular determinants. Here, differential gene expression and network analyses of four prefrontal cortex subregions from postmortem tissue of people with PTSD demonstrate extensive remodeling of the transcriptomic landscape. A highly connected downregulated set of interneuron transcripts is present in the most significant gene network associated with PTSD. Integration of this dataset with genotype data from the largest PTSD genome-wide association study identified the interneuron synaptic gene ELFN1 as conferring significant genetic liability for PTSD. We also identified marked transcriptomic sexual dimorphism that could contribute to higher rates of PTSD in women. Comparison with a matched major depressive disorder cohort revealed significant divergence between the molecular profiles of individuals with PTSD and major depressive disorder despite their high comorbidity. Our analysis provides convergent systems-level evidence of genomic networks within the prefrontal cortex that contribute to the pathophysiology of PTSD in humans.

Prefrontal Disinhibition in Social Fear: A Vital Action of Somatostatin Interneurons

Social fear and avoidance of social partners and social situations represent the core behavioral symptom of Social Anxiety Disorder (SAD), a prevalent psychiatric disorder worldwide. The pathological mechanism of SAD remains elusive and there are no specific and satisfactory therapeutic options currently available. With the development of appropriate animal models, growing studies start to unravel neuronal circuit mechanisms underlying social fear, and underscore a fundamental role of the prefrontal cortex (PFC). Prefrontal cortical functions are implemented by a finely wired microcircuit composed of excitatory principal neurons (PNs) and diverse subtypes of inhibitory interneurons (INs). Disinhibition, defined as a break in inhibition via interactions between IN subtypes that enhances the output of excitatory PNs, has recently been discovered to serve as an efficient strategy in cortical information processing. Here, we review the rodent animal models of social fear, the prefrontal IN diversity, and their circuits with a particular emphasis on a novel disinhibitory microcircuit mediated by somatostatin-expressing INs in gating social fear behavior. The INs subtype distinct and microcircuit-based mechanism advances our understanding of the etiology of social fear and sheds light on developing future treatment of neuropsychiatric disorders associated with social fear.

Psychological and Physiological Stress in Hens With Bone Damage

Abnormalities in bone development in humans and non-humans can lead to impaired physical and psychological health; however, evidence is lacking regarding the role of individual psychosocial factors in the development of poor bone conditions. Addressing this lack of knowledge, we used low-productive laying hens (n = 93) and assessed behavioral responses to an open-field test [at 17, 18, 29, 33 weeks of age (wa)], an aerial predator test (at 39 wa), and a social reinstatement test (at 42 wa). Bone condition was assessed using a palpation technique on five occasions (at 16, 29, 33, 45, 58 wa), with half of the hens experiencing damage (deviations, fractures, or both) at 29 wa and all hens by 58 wa. Corticosterone (CORT) concentration in feathers (at 16, 33, 58 wa) and body weight (at 23, 47, 58 wa) were also investigated. We hypothesized that lighter birds (at 23 wa) with higher CORT (at 16 wa) and open field-induced fear collected before the onset of lay (at 17 and 18 wa) are associated with a worse bone condition when in lay. We also hypothesized that those birds with more damage at the peak of laying (at 29 wa) would be lighter at 47 and 58 wa and more fearful by showing higher open field-induced (at 29 and 33 wa) and predator-induced fear responses, however, acting less socially toward conspecifics. These hens were also expected to have higher CORT (at 33 and 58 wa). Our results show no association between open-field fear level and fear behavior, CORT concentration, or body weight on the one hand (all measured before starting to lay) and bone damage at 29 wa on the other. When in lay, bone damage was associated with more pecking and less crossing zones when faced with an open-field situation at 29 wa and improved sociality at 42 wa. This study provides the first evidence of a relationship of bone health with fear, sociality, and stress response. When in poor bone condition, our hens had enhanced psychological stress measured by fear behavior reactivity but not physiological stress measured as feather CORT concentration.

Anxiety Sensitivity Prospectively Predicts Increased Acute Posttraumatic Stress and Related Symptoms After Sexual Assault

Anxiety sensitivity is a potential risk factor for posttraumatic stress symptoms (PTSS) and has been hypothesized to contribute to PTSS development. However, few prospective studies have evaluated whether anxiety sensitivity predicts PTSS. In a subsample of 48 women sexual assault survivors enrolled as part of a larger prospective observational study, elevated anxiety sensitivity measured via a brief assessment 1 week after experiencing a sexual assault was concurrently associated with PTSS at 1 week and prospectively predicted PTSS 6 weeks after the event, with small-to-medium effect sizes, η2 p = .10, even after covarying for trauma history. Heightened anxiety sensitivity at 1-week postevent also interacted with time to predict anxiety and depression both before and after sexual assault, with medium-to-large effect sizes, ηp 2 = .21- .24. This is consistent with research linking anxiety sensitivity to PTSS, but this was the first prospective study of which we are aware to demonstrate that anxiety sensitivity in the acute posttrauma period predicts PTSS among women who have recently experienced sexual assault. Future research should use the full Anxiety Sensitivity Index to replicate findings in a larger sample and explore whether targeting anxiety sensitivity could mitigate the development of PTSS in this vulnerable population.

Effects of RU486 treatment after single prolonged stress depend on the post-stress interval

The Single Prolonged Stress protocol is considered a model for PTSD, as it induces long lasting changes in rat behaviour and endocrine regulation. Previous work demonstrated that some of these changes can be prevented by treatment with the glucocorticoid receptor antagonist RU486, administered a week after the stressor. The current study evaluated the effects of an earlier intervention with RU486, as evaluated 1 week after SPS-exposure. Most RU486 effects occurred independent of prior stress, except for the reversal of a stress-induced increase in locomotor behaviour. The accompanying changes in gene expression depended on gene, brain region, and time. DNA methylation of the robustly down-regulated Fkbp5 gene was dissociated of changes in mRNA expression. The findings reinforce the long term effects of GR antagonist treatment, but also emphasize the need to evaluate changes over time to allow the identification of robust correlates between gene expression and behavioural/endocrine outcome of stressful experiences.

Adverse childhood experiences, posttraumatic stress, and FKBP5 methylation patterns in postpartum women and their newborn infants

BACKGROUND

Genetic variation and epigenetic mechanisms involving the stress-related gene FKBP5 have been implicated in the intergenerational transmission of trauma-related effects in adult offspring of trauma-exposed caregivers, but these processes have not been fully explored in postpartum women and their newborn infants.

METHODS

Women recruited from a prenatal care clinic during their third trimester of pregnancy (N = 114) completed a battery of instruments assessing adverse childhood experiences (ACEs), adversity in adulthood, posttraumatic stress disorder (PTSD) symptoms, negative emotional state, and emotion dysregulation. FKBP5 rs1360780 genotype and intron 7 methylation were derived from saliva collected from postpartum mothers and their newborn infants within 24 h of delivery.

RESULTS

Allele-specific associations of methylation with maternal ACEs and prenatal trauma-related symptoms were evident; however, relations differed between mothers and newborns. In mothers carrying the stress sensitive T-allele (CT and TT genotypes), maternal FKBP5 methylation negatively correlated with threat-based ACEs and maternal PTSD symptoms during pregnancy, but not deprivation-based ACEs. In infants homozygous for the C allele (CC genotype), infant FKBP5 methylation positively correlated with maternal threat-based ACEs and prenatal PTSD symptom severity, but not deprivation-based ACEs or adversity in adulthood.

CONCLUSIONS

Our results provide evidence that links maternal threat-based ACEs and trauma-related symptoms during pregnancy with allele-specific epigenetic patterns in postpartum women and their newborn infants. These findings provide mechanistic insight into the potential intergenerational impact of ACEs and the effect of maternal PTSD symptoms during pregnancy.

The BDNF Val66Met polymorphism affects negative memory bias in civilian women with PTSD

Memory abnormalities are considered a core feature of posttraumatic stress disorder (PTSD). Studies attempting to quantify such memory dysfunction in PTSD have reported that individuals with this disorder exhibit selective memory bias toward negative material. The low expression Met allele of brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has been associated with the aetiology of PTSD and with memory abnormalities. It is therefore possible that the BDNF Val66Met polymorphism can moderate the relationship between PTSD and memory bias. Here we examined this association in 50 civilian women with PTSD and 70 non-trauma-exposed healthy control women. All subjects were genotyped for the BDNF Val66Met (rs6265) polymorphism. Negative memory bias was assessed using a recognition memory task. Patients showed significantly greater negative memory bias compared to controls. In patients, negative memory bias significantly increased with increasing numbers of Met alleles; while no significant relationship was seen in controls. Further pairwise analyses revealed that patients with the Met allele had significantly greater negative memory bias than controls. These results suggest that the relationship between PTSD and negative memory bias can be moderated by the BDNF Val66Met polymorphism. More studies are needed to further clarify the relationship between this polymorphism and memory abnormalities in PTSD.

Correlation between hypothalamic-pituitary-adrenal axis gene polymorphisms and posttraumatic stress disorder symptoms

BACKGROUND

The hypothalamic-pituitary-adrenal (HPA) axis is the main neuroendocrine system that controls stress responses, including fear learning. To further understand the correlation between the HPA axis and stress- and fear-related symptoms in humans, the current study investigated the relationship between HPA axis gene polymorphisms and a stress- and fear-related disorder, posttraumatic stress disorder (PTSD). This is the first study that systematically investigates the correlations between HPA axis genes and distinct PTSD symptom clusters.

METHODS

Participants included 1132 Chinese earthquake survivors (772 women and 360 men). PTSD symptoms were measured by the PTSD Checklist for DSM-5 (PCL-5), and the severity (total symptoms) and symptom clusters were calculated according to the hybrid seven-factor model of DSM-5 PTSD. We genotyped eight single nucleotide polymorphisms (SNPs) of three HPA axis genes, including FKBP5, CRHR1 and CRHR2.

RESULTS

The main effects of the CRHR2 SNP rs2267715 were associated with PTSD severity (P = 0.0035) and all PTSD symptom clusters except dysphoric arousal (P ranging from 0.0011 to 0.048). In women, a gene-environment interaction (G × E) effect of FKBP5 (rs3800373 × trauma exposure) was correlated with PTSD severity (P = 0.038), externalizing behaviors, anxious arousal and dysphoric arousal symptoms (P ranging from 0.014 to 0.028); the G × E effect of CRHR1 (rs4458044 × trauma exposure) was associated with anxious arousal symptoms (P = 0.016). In men, a gene-gene interaction (G × G) effect of FKBP5-CRHR1 (rs9470080 × rs4458044) was associated with PTSD severity (P = 0.0091), intrusion, negative affect, externalizing behaviors and anxious arousal (P ranging 0.012-0.049).

CONCLUSION

Our results systematically revealed that the main effects and G × E and G × G effects of some genetic polymorphisms of HPA axis genes are involved in the severity and distinct symptom clusters of PTSD.

Distinct Profiles of Cell-Free MicroRNAs in Plasma of Veterans with Post-Traumatic Stress Disorder

Dysregulation of circulating microRNAs (miRNAs) in body fluids has been reported in psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder, and post-traumatic stress disorder (PTSD). Recent studies of various diseases showed that extracellular vesicles (EV) in body fluids can provide different spectra of circulating miRNAs and disease-associated signatures from whole fluid or EV-depleted fraction. However, the association of miRNAs in EVs to PTSD has not been studied. In this study, we performed a comprehensive profiling of miRNAs in whole plasma, extracellular vesicles (EV) and EV-depleted plasma (EVD) samples collected from combat veterans with PTSD and matched controls by utilizing a next-generation sequencing (NGS) platform. In total, 520 circulating miRNAs were quantified from 24 male Iraq and Afghanistan combat veterans with (n = 12) and without (n = 12) PTSD. The overall miRNA profiles in whole plasma, EV and EVD fractions were different and miRNAs affected by PTSD were also distinct in each sample type. The concentration changes of miR-203a-3p in EV and miR-339-5p in EVD were confirmed in an independent validation cohort that consisted of 20 veterans (10 with and 10 without PTSD) using qPCR. The target genes of these two miRNAs were involved in signaling pathways and comorbid conditions associated with PTSD (e.g., neurotransmitter systems such as dopaminergic and serotonergic signaling, inflammatory response, and cardiovascular diseases). Our findings suggest that PTSD may have different impacts on miRNAs encapsulated in vesicles and outside of vesicles. Further studies using larger samples are needed to evaluate the utility of these miRNAs as diagnostic biomarkers for PTSD.

Volumetric brain correlates of approach-avoidance behavior and their relation to chronic back pain

Avoiding any harm, such as painful experiences, is an important ability for our physical and mental health. This avoidance behavior might be overactive under chronic pain, and the cortical and subcortical brain volumetry, which also often changes in chronic pain states, might be a significant correlate of this behavior. In the present study, we thus investigated the association between volumetric brain differences using 3 T structural magnetic resonance imaging and pain- versus pleasure-related approach-avoidance behavior using an Approach Avoidance Task in the laboratory in chronic back pain (N = 42; mean age: 51.34 years; 23 female) and healthy individuals (N = 43; mean age: 45.21 years; 15 female). We found significant differences in hippocampal, amygdala and accumbens volumes in patients compared to controls. The patients` hippocampal volume was significantly positively related to pain avoidance, the amygdala volume to positive approach, and the accumbens volume negatively to a bias to pain avoidance over positive approach. These associations were significantly moderated by pain symptom duration. Cortical structure may thus contribute to an overacting pain avoidance system in chronic back pain, and could, together with a reduction in approaching positive stimuli, be related to maladaptive choice and decision-making processes in chronic pain.

Region- and time-dependent gene regulation in the amygdala and anterior cingulate cortex of a PTSD-like mouse model

Posttraumatic stress disorder is developed by exposure to a threatening and/or a horrifying event and characterized by the presence of anxiety, hyperarousal, avoidance, and sleep abnormality for a prolonged period of time. To elucidate the potential molecular mechanisms, we constructed a mouse model by electric foot shock followed by situational reminders and performed transcriptome analysis in brain tissues. The stressed mice acquired anxiety-like behavior after 2 weeks and exaggerated startle response after 4 weeks. Avoidance latency and freezing behavior were sustained up to 5 weeks post stress and abnormal static behavior was observed during the sleep period. RNA sequencing was performed in two of the emotional regulatory regions, anterior cingulate cortex and amygdala, at 2 and 5 weeks post stress. More than 1000 differentially expressed genes were identified at 2 weeks in both regions. The number of the regulated genes remained constant in amygdala at 5 weeks post stress, whereas those in anterior cingulate cortex were plummeted. Although synaptic remodeling and endocrine system were the most enriched signaling pathways in both anterior cingulate cortex and amygdala, the individual gene expression profile was regulated in a region- and time-dependent manner. In addition, several genes associated with PTSD involved in Hypothalamic-Pituitary-Adrenal axis were differentially regulated. These findings suggested that global gene expression profile was dynamically regulated in accordance with the disease development stage, and therefore targeting the distinct signaling molecules in different region and development stage might be critical for effective treatment to PTSD.

A Disinhibitory Microcircuit Mediates Conditioned Social Fear in the Prefrontal Cortex

Fear behavior is under tight control of the prefrontal cortex, but the underlying microcircuit mechanism remains elusive. In particular, it is unclear how distinct subtypes of inhibitory interneurons (INs) within prefrontal cortex interact and contribute to fear expression. We employed a social fear conditioning paradigm and induced robust social fear in mice. We found that social fear is characterized by activation of dorsal medial prefrontal cortex (dmPFC) and is largely diminished by dmPFC inactivation. With a combination of in vivo electrophysiological recordings and fiber photometry together with cell-type-specific pharmacogenetics, we further demonstrated that somatostatin (SST) INs suppressed parvalbumin (PV) INs and disinhibited pyramidal cells and consequently enhanced dmPFC output to mediate social fear responses. These results reveal a previously unknown disinhibitory microcircuit in prefrontal cortex through interactions between IN subtypes and suggest that SST INs-mediated disinhibition represents an important circuit mechanism in gating social fear behavior.