Individual differences in frontolimbic circuitry and anxiety emerge with adolescent changes in endocannabinoid signaling across species

The beautiful adolescent brain: An evolutionary developmental perspective

The adolescent brain has been characterized as a defective car, with no brakes or steering wheel-only an accelerator. This characterization has been used to explain the impulsive and risky behavior of this transient developmental period. But why do adolescents respond to the world the way they do? In this article, we consider adolescent-specific changes in the brain and behavior from a developmental evolutionary viewpoint in how they might be adaptive. We suggest ways in which the adolescent brain has evolved to explore and learn from new and changing environments as the adolescent gains independence from the caregiver and transitions into an adult. We highlight adolescent-specific changes in the brain and behavior in response to emotional and social cues that may facilitate learning to independently secure resources (e.g., food, water, and shelter) and to establish new social bonds beyond the family or pack for their own survival. Specifically, we focus on how rewards, social cues, and threats in the environment influence behavior and may serve an adaptive role for the adolescent.

Examining threat responses through a developmental lens

Adolescence has been characterized by risk taking and fearlessness. Yet, the emergence of anxiety disorders that are associated with fear peaks during this developmental period. Moreover, adolescents show heightened sensitivity to stress relative to children and adults. To address inconsistencies between the common characterization of adolescents as fearless and the evidence of heightened anxiety and stress during this time, we build upon foundational discoveries of threat-related circuitry and behavior in adult rodents by Joseph LeDoux and colleagues. Specifically, the conservation of this circuitry across species has provided opportunities for identifying mechanisms underlying threat responses that we have extended to developing humans and rodents. We elucidate situations in which adolescents show heightened threat responses and others where they appear fearless and link them to developmental changes of threat circuitry during this period. We discuss the potential adaptiveness of these threat responses for survival of the individual and species but also the potential risks for anxiety and stress. We end by offering potential new ways in which behavioral treatments for youth with anxiety and stress-related disorders may be optimized to target the developing vs developed brain.

Endocannabinoid dysregulation and PTSD in urban adolescents: Associations with anandamide concentrations and FAAH genotype

BACKGROUND

The endocannabinoid system, which regulates fear- and anxiety-related behaviors, is dysregulated in adults with posttraumatic stress disorder (PTSD), as indicated by higher circulating anandamide (AEA) concentrations. The C385A (rs324420) polymorphism in the fatty acid amide hydrolase (FAAH) gene, which catabolizes AEA, is linked to higher AEA concentrations and greater PTSD symptoms in adults. Given that adolescence is a critical period during which trauma and psychiatric disorders emerge, understanding this relationship in youth is essential. This study examines PTSD symptoms, AEA concentrations, and FAAH genotype in a diverse adolescent sample.

METHODS

This study included 102 Detroit-area adolescents (M ± SD = 13.33 ± 2.21 years, 54.9% female) and their parents/guardians. The sample consisted of 40.2% White Non-Hispanic, 34.3% Black Non-Hispanic, 6.9% White Hispanic, 4.9% Asian/Pacific Islander, and 12.7% Biracial adolescents. Trauma exposure and PTSD symptoms were assessed using the UCLA PTSD Reaction Index for DSM-5. Plasma concentrations of AEA were measured by liquid chromatography-tandem mass spectrometry, and FAAH genotype was determined from saliva samples and high-throughput screening.

RESULTS

The majority (90%) of adolescents reported trauma exposure, and 20% met PTSD criteria. Higher AEA concentrations were associated with more severe PTSD symptoms (p = 0.009), especially hyperarousal. The FAAH A-allele (present in 52.5% of participants) was associated with higher AEA concentrations (2.11 ± 0.69 pmol/ml, p = 0.013) and greater PTSD severity (22.65 ± 15.931, p = 0.027), particularly those with the reexperiencing cluster, compared to the CC genotype (1.79 ± 0.66 pmol/ml and 15.87 ±+ 13.043, respectively).

CONCLUSION

Elevated AEA concentrations and the FAAH A-allele were associated with greater PTSD symptom severity in urban adolescents. These findings suggest endocannabinoid dysregulation may play a role in adolescent PTSD, highlighting the need for further research and targeted interventions.

Genetic polymorphisms in the 5-HT and endocannabinoid systems moderate the association between childhood trauma and burnout in the general occupational population

BACKGROUND

Interactions between the serotonin (5-HT) and endocannabinoid (eCB) systems have been reported in the psychopathology of stress-related symptoms, while their interplay in regulating the relationship between childhood trauma and burnout remains unclear. In this study, we investigated the interaction of childhood trauma with genetic polymorphisms in these two systems in predicting burnout.

METHODS

Burnout, childhood trauma, and job stress were assessed using rating scales in 992 general occupational individuals. Genetic polymorphisms including HTR2A rs6313, 5-HTT rs6354 and FAAH rs324420, were genotyped. Linear hierarchical regression analysis and PROCESS macro in SPSS were used to examine two- and three-way interactions.

RESULTS

There were significant interactions of job stress × HTR2A rs6313 and childhood abuse × FAAH rs324420 on reduced personal accomplishment. Moreover, we found significant three-way interactions of childhood abuse × FAAH rs324420 × HTR2A rs6313 on cynicism and reduced personal accomplishment, childhood abuse × FAAH rs324420 × 5-HTT rs6354 on emotional exhaustion, and childhood neglect × FAAH rs324420 × 5-HTT rs6354 on reduced personal accomplishment. These results suggest that the FAAH rs324420 A allele carriers, when with some specific genetic polymorphisms of 5-HT system, would show more positive associations between childhood trauma and burnout.

CONCLUSIONS

Genetic polymorphisms in the 5-HT and eCB systems may jointly moderate the impact of childhood trauma on burnout.

The Development of Cannabinoids as Therapeutic Agents in the United States

Cannabis is one of the oldest and widely used substances in the world. Cannabinoids within the cannabis plant, known as phytocannabinoids, mediate cannabis' effects through interactions with the body's endogenous cannabinoid system. This endogenous system, the endocannabinoid system, has important roles in physical and mental health. These roles point to the potential to develop cannabinoids as therapeutic agents while underscoring the risks related to interfering with the endogenous system during nonmedical use. This scoping narrative review synthesizes the current evidence for both the therapeutic and adverse effects of the major (i.e., Δ9-tetrahydrocannabinol and cannabidiol) and lesser studied minor phytocannabinoids, from nonclinical to clinical research. We pay particular attention to the areas where evidence is well established, including analgesic effects after acute exposures and neurocognitive risks after acute and chronic use. In addition, drug development considerations for cannabinoids as therapeutic agents within the United States are reviewed. The proposed clinical study design considerations encourage methodological standards for greater scientific rigor and reproducibility to ultimately extend our knowledge of the risks and benefits of cannabinoids for patients and providers. SIGNIFICANCE STATEMENT: This work provides a review of prior research related to phytocannabinoids, including therapeutic potential and known risks in the context of drug development within the United States. We also provide study design considerations for future cannabinoid drug development.

Genetic variation in endocannabinoid signaling: Anxiety, depression, and threat- and reward-related brain functioning during the transition into adolescence

BACKGROUND

The endocannabinoid system modulates neural activity throughout the lifespan. In adults, neuroimaging studies link a common genetic variant in fatty acid amide hydrolase (FAAH C385A)-an enzyme that regulates endocannabinoid signaling-to reduced risk of anxiety and depression, and altered threat- and reward-related neural activity. However, limited research has investigated these associations during the transition into adolescence, a period of substantial neurodevelopment and increased psychopathology risk.

METHODS

This study included FAAH genotype and longitudinal neuroimaging and neurobehavioral data from 4811 youth (46% female; 9-11 years at Baseline, 11-13 years at Year 2) from the Adolescent Brain Cognitive DevelopmentSM Study. Linear mixed models examined the effects of FAAH and the FAAH x time interaction on anxiety and depressive symptoms, amygdala reactivity to threatening faces, and nucleus accumbens (NAcc) response to happy faces during the emotional n-back task.

RESULTS

A significant main effect of FAAH on depressive symptoms was observed, such that depressive symptoms were lower across both timepoints in those with the AA genotype compared to both AC and CC genotypes (p's<0.05). There were no significant FAAH x time interactions for anxiety, depression, or neural responses (p's>0.05). Additionally, there were no main effects of FAAH on anxiety or neural responses (p's>0.05).

CONCLUSIONS

Our findings add to emerging evidence linking the FAAH C385A variant to lower risk of psychopathology, and extend these findings to a developmental sample. In particular, we found lower depressive symptoms in FAAH AA genotypes compared to AC and CC genotypes. Future research is needed to characterize the role of the FAAH variant and the eCB system more broadly in neurodevelopment and psychiatric risk.

Maturation of cortical input to dorsal raphe nucleus increases behavioral persistence in mice

The ability to persist toward a desired objective is a fundamental aspect of behavioral control whose impairment is implicated in several behavioral disorders. One of the prominent features of behavioral persistence is that its maturation occurs relatively late in development. This is presumed to echo the developmental time course of a corresponding circuit within late-maturing parts of the brain, such as the prefrontal cortex, but the specific identity of the responsible circuits is unknown. Here, we used a genetic approach to describe the maturation of the projection from layer 5 neurons of the neocortex to the dorsal raphe nucleus in mice. Using optogenetic-assisted circuit mapping, we show that this projection undergoes a dramatic increase in synaptic potency between postnatal weeks 3 and 8, corresponding to the transition from juvenile to adult. We then show that this period corresponds to an increase in the behavioral persistence that mice exhibit in a foraging task. Finally, we used a genetic targeting strategy that primarily affected neurons in the medial prefrontal cortex, to selectively ablate this pathway in adulthood and show that mice revert to a behavioral phenotype similar to juveniles. These results suggest that frontal cortical to dorsal raphe input is a critical anatomical and functional substrate of the development and manifestation of behavioral persistence.

A systematic review of evidence on integrated management of psychiatric disorders in youth who use cannabis

Given the risks to mental health associated with cannabis use in youth and the increase in cannabis legalization worldwide and in the U.S., there is a need to understand existing evidence-based approaches to integrated management of psychiatric disorders in youth who use cannabis. This systematic review aimed to appraise the current evidence on integrated treatment for adolescents and young adults with common psychiatric disorders who engage in regular cannabis use. A total of 989 studies were screened for inclusion. Study's titles and abstracts were screened and advanced to full text review for further screening by two independent reviewers. Thirty-five full-text articles were reviewed, with five articles ultimately meeting all criteria for inclusion. Five randomized controlled trials examined the effects of therapeutic interventions in youth with common psychiatric disorders who used cannabis, including two studies on depression, one on bipolar disorder, one on anxiety and one on PTSD were reviewed. No studies were considered high in risk of bias. Overall, there is a paucity of research on the treatment of comorbid adolescent mental health disorders and cannabis use, which limits the ability to draw evidence-based treatment recommendations.

Impact of Childhood Trauma Exposure, Genetic Variation in Endocannabinoid Signaling, and Anxiety on Frontolimbic Pathways in Children

Introduction: The endocannabinoid (eCB) system plays a key role in modulating brain development, including myelination processes. Recent studies link a common variant (C385A, rs324420) in the fatty acid amide hydrolase (FAAH) gene to higher circulating eCB levels, lower anxiety, and altered frontolimbic development. Frontolimbic pathways, which demonstrate a protracted maturational course across childhood and adolescence, are associated with anxiety, and are vulnerable to environmental stressors such as trauma exposure. Here, we examined the impact of trauma exposure, FAAH genotype, and anxiety on frontolimbic white matter microstructure in children. Materials and Methods: We leveraged baseline data from the Adolescent Brain Cognitive Development (ABCD) study (n=9969; mean±standard deviation age=9.92±0.62 years; 47.1% female). Saliva samples were used for genotyping, and caregivers reported on their child's anxiety symptoms and trauma exposure. Fractional anisotropy (FA), a nonspecific measure of white matter integrity, was estimated for frontolimbic tracts. Results: Thirty-six percent of youth experienced one or more potentially traumatic events according to DSM-5 Criterion A (64% controls), and 45% were FAAH A-allele carriers (55% noncarriers). Relative to controls, trauma-exposed youth demonstrated higher anxiety and higher FA of the left uncinate. The FAAH A-allele (vs. CC) was associated with lower FA in the left fornix and left parahippocampal cingulum, and there was an indirect effect of FAAH genotype on anxiety through FA of the left fornix. Moreover, genotype moderated the association between FA of the left cingulum and anxiety. Conclusions: Our findings demonstrate distinct effects of trauma exposure and the FAAH C385A variant on frontolimbic pathways and subsequent anxiety risk in preadolescent children. This line of work may provide important insights into neurodevelopmental mechanisms leading to anxiety risk, and potential targets for intervention.

The endocannabinoid system as a putative target for the development of novel drugs for the treatment of psychiatric illnesses

Cannabis is well established to impact affective states, emotion and perceptual processing, primarily through its interactions with the endocannabinoid system. While cannabis use is quite prevalent in many individuals afflicted with psychiatric illnesses, there is considerable controversy as to whether cannabis may worsen these conditions or provide some form of therapeutic benefit. The development of pharmacological agents which interact with components of the endocannabinoid system in more localized and discrete ways then via phytocannabinoids found in cannabis, has allowed the investigation if direct targeting of the endocannabinoid system itself may represent a novel approach to treat psychiatric illness without the potential untoward side effects associated with cannabis. Herein we review the current body of literature regarding the various pharmacological tools that have been developed to target the endocannabinoid system, their impact in preclinical models of psychiatric illness and the recent data emerging of their utilization in clinical trials for psychiatric illnesses, with a specific focus on substance use disorders, trauma-related disorders, and autism. We highlight several candidate drugs which target endocannabinoid function, particularly inhibitors of endocannabinoid metabolism or modulators of cannabinoid receptor signaling, which have emerged as potential candidates for the treatment of psychiatric conditions, particularly substance use disorder, anxiety and trauma-related disorders and autism spectrum disorders. Although there needs to be ongoing clinical work to establish the potential utility of endocannabinoid-based drugs for the treatment of psychiatric illnesses, the current data available is quite promising and shows indications of several potential candidate diseases which may benefit from this approach.

FAAH rs324420 Polymorphism: Biological Pathways, Impact on Elite Athletic Performance and Insights for Sport Medicine

Gene variation linked to physiological functions is recognised to affect elite athletic performance by modulating training and competition-enabling behaviour. The fatty acid amide hydrolase (FAAH) has been investigated as a good candidate for drug targeting, and recently, its single-nucleotide polymorphism (SNP) rs324420 was reported to be associated with athletic performance. Given the implications, the biological pathways of this genetic polymorphism linked to elite athletic performance, considering sport type, psychological traits and sports injuries, need to be dissected. Thus, a narrative review of the literature concerning the biological mechanisms of this SNP was undertaken. In addition to its role in athletic performance, FAAH rs324420 is also involved in important mechanisms underlying human psychopathologies, including substance abuse and neural dysfunctions. However, cumulative evidence concerning the C385A variant is inconsistent. Therefore, validation studies considering homogeneous sports modalities are required to better define the role of this SNP in elite athletic performance and its impact on stress coping, pain regulation and inflammation control.

Developmental age and fatty acid amide hydrolase genetic variation converge to mediate fear regulation in female mice

Anxiety disorders are more prevalent in females than in males, yet a majority of basic neuroscience studies are performed in males. Furthermore, anxiety disorders peak in prevalence during adolescence, yet little is known about neurodevelopmental trajectories of fear expression, particularly in females. To examine these factors, we fear conditioned juvenile, adolescent, and adult female mice and exposed them to fear extinction and a long-term recall test. For this, we used knock-in mice containing a common human mutation in the gene for fatty acid amide hydrolase (FAAH), the primary catabolic enzyme for the endocannabinoid anandamide (FAAH-IN). This mutation has been shown to impart a low-anxiety phenotype in humans, and in rodents relative to their wild-type littermates. We find an impact of the FAAH polymorphism on developmental changes in fear behavior. Specifically, the FAAH polymorphism appears to induce a state of hypervigilance (increased fear) during adolescence. We also used markerless pose estimation software to classify alternative behaviors outside of freezing. These analyses revealed age differences in vigilance to indicators of threat and in the propensity of mice to explore an aversive environment, though genotypic differences were minimal. These findings address a gap in the literature regarding developmental patterns of fear learning and memory as well as the mechanistic contributions of the endocannabinoid system in females.

Developmentally distinct architectures in top-down circuits

The medial prefrontal cortex (mPFC) plays a key role in learning, mood and decision making, including in how individuals respond to threats 1-6 . mPFC undergoes a uniquely protracted development, with changes in synapse density, cortical thickness, long-range connectivity, and neuronal encoding properties continuing into early adulthood 7-21 . Models suggest that before adulthood, the slow-developing mPFC cannot adequately regulate activity in faster-developing subcortical centers 22,23 . They propose that during development, the enhanced influence of subcortical systems underlies distinctive behavioural strategies of juveniles and adolescents and that increasing mPFC control over subcortical structures eventually allows adult behaviours to emerge. Yet it has remained unclear how a progressive strengthening of top-down control can lead to nonlinear changes in behaviour as individuals mature 24,25 . To address this discrepancy, here we monitored and manipulated activity in the developing brain as animals responded to threats, establishing direct causal links between frontolimbic circuit activity and the behavioural strategies of juvenile, adolescent and adult mice. Rather than a linear strengthening of mPFC synaptic connectivity progressively regulating behaviour, we uncovered multiple developmental switches in the behavioural roles of mPFC circuits targeting the basolateral amygdala (BLA) and nucleus accumbens (NAc). We show these changes are accompanied by axonal pruning coinciding with functional strengthening of synaptic connectivity in the mPFC-BLA and mPFC-NAc pathways, which mature at different rates. Our results reveal how developing mPFC circuits pass through distinct architectures that may make them optimally adapted to the demands of age-specific challenges.

Dissociation of basolateral and central amygdala effective connectivity predicts the stability of emotion-related impulsivity in adolescents and emerging adults with borderline personality symptoms: a resting-state fMRI study

BACKGROUND

Borderline personality disorder (BPD) is associated with altered activity in the prefrontal cortex (PFC) and amygdala, yet no studies have examined fronto-limbic circuitry in borderline adolescents and emerging adults. Here, we examined the contribution of fronto-limbic effective connectivity (EC) to the longitudinal stability of emotion-related impulsivity, a key feature of BPD, in symptomatic adolescents and young adults.

METHODS

We compared resting-state EC in 82 adolescents and emerging adults with and without clinically significant borderline symptoms (n BPD = 40, ages 13-30). Group-specific directed networks were estimated amongst fronto-limbic nodes including PFC, ventral striatum (VS), central amygdala (CeN), and basolateral amygdala (BLA). We examined the association of directed centrality metrics with initial levels and rates of change in emotion-related impulsivity symptoms over a one-year follow-up using latent growth curve models (LGCMs).

RESULTS

In controls, ventromedial prefrontal cortex (vmPFC) and dorsal ACC had a directed influence on CeN and VS, respectively. In the BPD group, bilateral BLA had a directed influence on CeN, whereas in the healthy group CeN influenced BLA. LGCMs indicated that emotion-related impulsivity was stable across a one-year follow-up in the BPD group. Further, higher EC of R CeN to other regions in controls was associated with stronger within-person decreases in emotion-related impulsivity.

CONCLUSIONS

Functional inputs from BLA and vmPFC appear to play competing roles in influencing CeN activity. In borderline adolescents and young adults, BLA may predominate over CeN activity, while in controls the ability of CeN to influence BLA activity predicted more rapid reductions in emotion-related impulsivity.

Resilience to substance use disorder following childhood maltreatment: association with peripheral biomarkers of endocannabinoid function and neural indices of emotion regulation

Childhood maltreatment (CM) is a risk factor for substance use disorders (SUD) in adulthood. Understanding the mechanisms by which people are susceptible or resilient to developing SUD after exposure to CM is important for improving intervention. This case-control study investigated the impact of prospectively assessed CM on biomarkers of endocannabinoid function and emotion regulation in relation to the susceptibility or resilience to developing SUD. Four groups were defined across the dimensions of CM and lifetime SUD (N = 101 in total). After screening, participants completed two experimental sessions on separate days, aimed at assessing the behavioral, physiological, and neural mechanisms involved in emotion regulation. In the first session, participants engaged in tasks assessing biochemical (i.e., cortisol, endocannabinoids), behavioral, and psychophysiological indices of stress and affective reactivity. During the second session, the behavioral and brain mechanisms associated with emotion regulation and negative affect were investigated using magnetic resonance imaging. CM-exposed adults who did not develop SUD, operationally defined as resilient to developing SUD, had higher peripheral levels of the endocannabinoid anandamide at baseline and during stress exposure, compared to controls. Similarly, this group had increased activity in salience and emotion regulation regions in task-based measures of emotion regulation compared to controls, and CM-exposed adults with lifetime SUD. At rest, the resilient group also showed significantly greater negative connectivity between ventromedial prefrontal cortex and anterior insula compared to controls and CM-exposed adults with lifetime SUD. Collectively, these peripheral and central findings point to mechanisms of potential resilience to developing SUD after documented CM exposure.

Effects of cannabidiol on anandamide levels in individuals with cannabis use disorder: findings from a randomised clinical trial for the treatment of cannabis use disorder

Cannabidiol (CBD) has shown promise in treating psychiatric disorders, including cannabis use disorder - a major public health burden with no approved pharmacotherapies. However, the mechanisms through which CBD acts are poorly understood. One potential mechanism of CBD is increasing levels of anandamide, which has been implicated in psychiatric disorders including depression and cannabis use disorder. However, there is a lack of placebo-controlled human trials investigating this in psychiatric disorders. We therefore assessed whether CBD affects plasma anandamide levels compared to placebo, within a randomised clinical trial of CBD for the treatment of cannabis use disorder. Individuals meeting criteria for cannabis use disorder and attempting cannabis cessation were randomised to 28-day administration with placebo (n = 23), 400 mg CBD/day (n = 24) or 800 mg CBD/day (n = 23). We estimated the effects of each CBD dose compared to placebo on anandamide levels from baseline to day 28. Analyses were conducted both unadjusted and adjusted for cannabis use during the trial to account for effects of cannabis on the endocannabinoid system. We also investigated whether changes in plasma anandamide levels were associated with clinical outcomes relevant for cannabis use disorder (cannabis use, withdrawal, anxiety, depression). There was an effect of 800 mg CBD compared to placebo on anandamide levels from baseline to day 28 after adjusting for cannabis use. Pairwise comparisons indicated that anandamide levels unexpectedly reduced from baseline to day 28 in the placebo group (-0.048, 95% CI [-0.089, -0.007]), but did not change in the 800 mg CBD group (0.005, 95% CI [-0.036, 0.047]). There was no evidence for an effect of 400 mg CBD compared to placebo. Changes in anandamide levels were not associated with clinical outcomes. In conclusion, this study found preliminary evidence that 28-day treatment with CBD modulates anandamide levels in individuals with cannabis use disorder at doses of 800 mg/day but not 400 mg/day compared to placebo.

Fatty Acid Amide Hydrolase: An Integrative Clinical Perspective

Introduction: Fatty acid amide hydrolase (FAAH) is one of the main terminating enzymes of the endocannabinoid system (ECS). Since being discovered in 1996, the modulation of FAAH has been viewed as a compelling alternative strategy to obtain the beneficial effect of the ECS. With a considerable amount of FAAH-related publication over time, the next step would be to comprehend the proximity of this evidence for clinical application. Objective: This review intends to highlight the rationale of FAAH modulation and provide the latest evidence from clinical studies. Methods: Publication searches were conducted to gather information focused on FAAH-related clinical evidence with an extension to the experimental research to understand the biological plausibility. The subtopics were selected to be multidisciplinary to offer more perspective on the current state of the arts. Discussion: Experimental and clinical studies have demonstrated that FAAH was highly expressed not only in the central nervous system but also in the peripheral tissues. As the key regulator of endocannabinoid signaling, it would appear that FAAH plays a role in the modulation of mood and emotional response, reward system, pain perception, energy metabolism and appetite regulation, inflammation, and other biological processes. Genetic variants may be associated with some conditions such as substance/alcohol use disorders, obesity, and eating disorder. The advancement of functional neuroimaging has enabled the evaluation of the neurochemistry of FAAH in brain tissues and this can be incorporated into clinical trials. Intriguingly, the application of FAAH inhibitors in clinical trials seems to provide less striking results in comparison with the animal models, although some potential still can be seen. Conclusion: Modulation of FAAH has an immense potential to be a new therapeutic candidate for several disorders. Further exploration, however, is still needed to ensure who is the best candidate for the treatment strategy.

Extinction Learning Across Development: Neurodevelopmental Changes and Implications for Pediatric Anxiety Disorders

Alterations in extinction learning relate to the development and maintenance of anxiety disorders across the lifespan. While exposure therapy, based on principles of extinction, can be highly effective for treating anxiety, many patients do not show sufficient improvement following treatment. In particular, evidence suggests that exposure therapy does not work sufficiently for up to 40% of children who receive this evidence-based treatment.Importantly, fear learning and extinction, as well as the neural circuitry supporting these processes, undergo dynamic changes across development. An improved understanding of developmental changes in extinction learning and the associated neural circuitry may help to identify targets to improve treatment response in clinically anxious children and adolescents. In this chapter, we provide a brief overview of methods used to study fear learning and extinction in developmental populations. We then review what is currently known about the developmental changes that occur in extinction learning and related neural circuitry. We end this chapter with a discussion of the implications of these neurodevelopmental changes for the characterization and treatment of pediatric anxiety disorders.

Fatty acid amide hydrolase C385A polymorphism affects susceptibility to various diseases

The endocannabinoid (eCB) system is an important neuromodulatory system with its extensive network of receptors throughout the human body that has complex actions in the nervous system, immune system, and all of the body's other organs. Fatty acid amide hydrolase (FAAH) is an important membrane-bound homodimeric degrading enzyme that controls the biological activity of N-arachidonoylethanolamide (AEA) in the eCB system and other relevant bioactive lipids. It has been shown that several single nucleotide polymorphisms (SNPs) of FAAH are associated with various phenotypes and diseases including cardiovascular, endocrine, drug abuse, and neuropsychiatric disorders. A common functional and most studied polymorphism of this gene is C385A (rs324420), which results in the replacement of a conserved proline to threonine in the FAAH enzyme structure, leads to a reduction of the activity and expression of FAAH, compromises the inactivation of AEA and causes higher synaptic concentrations of AEA that can be associated with several various phenotypes. The focus of this review is on evidence-based studies on the associations of the FAAH C385A polymorphism and the various diseases or traits. Although there was variability in the results of these reports, the overall consensus is that the FAAH C385A genotype can affect susceptibility to some multifactorial disorders and can be considered a potential therapeutic target.

In vivo brain endocannabinoid metabolism is related to hippocampus glutamate and structure - a multimodal imaging study with PET, 1H-MRS, and MRI

Dysregulation of hippocampus glutamatergic neurotransmission and reductions in hippocampal volume have been associated with psychiatric disorders. The endocannabinoid system modulates glutamate neurotransmission and brain development, including hippocampal remodeling. In humans, elevated levels of anandamide and lower activity of its catabolic enzyme fatty acid amide hydrolase (FAAH) are associated with schizophrenia diagnosis and psychotic symptom severity, respectively (Neuropsychopharmacol, 29(11), 2108-2114; Biol. Psychiatry 88 (9), 727-735). Although preclinical studies provide strong evidence linking anandamide and FAAH to hippocampus neurotransmission and structure, these relationships remain poorly understood in humans. We recruited young adults with and without psychotic disorders and measured FAAH activity, hippocampal glutamate and glutamine (Glx), and hippocampal volume using [11C]CURB positron emission tomography (PET), proton magnetic resonance spectroscopy (1H-MRS) and T1-weighted structural MRI, respectively. We hypothesized that higher FAAH activity would be associated with greater hippocampus Glx and lower hippocampus volume, and that these effects would differ in patients with psychotic disorders relative to healthy control participants. After attrition and quality control, a total of 37 participants (62% male) completed [11C]CURB PET and 1H-MRS of the left hippocampus, and 45 (69% male) completed [11C]CURB PET and hippocampal volumetry. Higher FAAH activity was associated with greater concentration of hippocampal Glx (F1,36.36 = 9.17, p = 0.0045; Cohen's f = 0.30, medium effect size) and smaller hippocampal volume (F1,44.70 = 5.94, p = 0.019, Cohen's f = 0.26, medium effect size). These effects did not differ between psychosis and healthy control groups (no group interaction). This multimodal imaging study provides the first in vivo evidence linking hippocampal Glx and hippocampus volume with endocannabinoid metabolism in the human brain.

Synapse-specific roles for microglia in development: New horizons in the prefrontal cortex

Dysfunction of both microglia and circuitry in the medial prefrontal cortex (mPFC) have been implicated in numerous neuropsychiatric disorders, but how microglia affect mPFC development in health and disease is not well understood. mPFC circuits undergo a prolonged maturation after birth that is driven by molecular programs and activity-dependent processes. Though this extended development is crucial to acquire mature cognitive abilities, it likely renders mPFC circuitry more susceptible to disruption by genetic and environmental insults that increase the risk of developing mental health disorders. Recent work suggests that microglia directly influence mPFC circuit maturation, though the biological factors underlying this observation remain unclear. In this review, we discuss these recent findings along with new studies on the cellular mechanisms by which microglia shape sensory circuits during postnatal development. We focus on the molecular pathways through which glial cells and immune signals regulate synaptogenesis and activity-dependent synaptic refinement. We further highlight how disruptions in these pathways are implicated in the pathogenesis of neurodevelopmental and psychiatric disorders associated with mPFC dysfunction, including schizophrenia and autism spectrum disorder (ASD). Using these disorders as a framework, we discuss microglial mechanisms that could link environmental risk factors including infections and stress with ongoing genetic programs to aberrantly shape mPFC circuitry.

Experimental evidence for a child-to-adolescent switch in human amygdala-prefrontal cortex communication: A cross-sectional pilot study

Interactions between the amygdala and prefrontal cortex are fundamental to human emotion. Despite the central role of frontoamygdala communication in adult emotional learning and regulation, little is known about how top-down control emerges during human development. In the present cross-sectional pilot study, we experimentally manipulated prefrontal engagement to test its effects on the amygdala during development. Inducing dorsal anterior cingulate cortex (dACC) activation resulted in developmentally-opposite effects on amygdala reactivity during childhood versus adolescence, such that dACC activation was followed by increased amygdala reactivity in childhood but reduced amygdala reactivity in adolescence. Bayesian network analyses revealed an age-related switch between childhood and adolescence in the nature of amygdala connectivity with the dACC and ventromedial PFC (vmPFC). Whereas adolescence was marked by information flow from dACC and vmPFC to amygdala (consistent with that observed in adults), the reverse information flow, from the amygdala to dACC and vmPFC, was dominant in childhood. The age-related switch in information flow suggests a potential shift from bottom-up co-excitatory to top-down regulatory frontoamygdala connectivity and may indicate a profound change in the circuitry supporting maturation of emotional behavior. These findings provide novel insight into the developmental construction of amygdala-cortical connections and implications for the ways in which childhood experiences may influence subsequent prefrontal function.

Adolescents are more sensitive than adults to acute behavioral and cognitive effects of THC

Increased cannabis availability has contributed to increased use with concomitant incidence of adverse effects. One risk factor for adverse drug reactions may be age. There is preclinical evidence that acute effects of delta-9-tetrahydrocannabinol (THC), the primary active constituent of cannabis, are greater during adolescence, but this has not been fully studied in humans. The present study sought to determine whether adolescent men and women are more sensitive than adults to acute THC. Adolescents aged 18-20 (N = 12) and adults aged 30-40 (N = 12), with less than 20 total lifetime uses of THC-containing products, received capsules of THC (7.5, 15 mg) and placebo across three study sessions in randomized order under double blind conditions. During each session, subjective, cardiovascular, behavioral, and EEG measures were obtained. Behavioral measures included Simple Reaction Time, Stop Task, Time Production and N-back and EEG measures included P300 amplitudes during an auditory oddball task and eyes-closed resting state. THC affected subjective state and heart rate similarly in both age groups. However, adolescents were more sensitive to performance impairing effects, exhibiting dose-dependent impairments on reaction time, response accuracy, and time perception. On EEG measures, THC dose-dependently decreased P300 amplitude in adolescents but not adults. Adolescents were more sensitive to behavioral and cognitive effects of THC, but not to cardiovascular effects or subjective measures. Thus, at doses that produce comparable ratings of intoxication, adolescents may exhibit greater cognitive impairment and alterations in brain function.

Fatty acid amide hydrolase levels in brain linked with threat-related amygdala activation

Background

Preclinical evidence suggests that increasing levels of the major endocannabinoid anandamide decreases anxiety and fear responses potentially through its effects in the amygdala. Here we used neuroimaging to test the hypothesis that lower fatty acid amide hydrolase (FAAH), the main catabolic enzyme for anandamide, is associated with a blunted amygdala response to threat.

Methods

Twenty-eight healthy participants completed a positron emission tomography (PET) scan with the radiotracer for FAAH, [¹¹C]CURB, as well as a block-design functional magnetic resonance imaging session during which angry and fearful faces meant to activate the amygdala were presented.

Results

[¹¹C]CURB binding in the amygdala as well as in the medial prefrontal cortex, cingulate and hippocampus correlated positively with blood-oxygen-level-dependent (BOLD) signal during processing of angry and fearful faces (p_FWE < 0.05).

Conclusion

Our finding that lower levels of FAAH in amygdala, medial prefrontal cortex, cingulate and hippocampus was associated with a dampened amygdala response to a threatening social cue aligns with preclinical and neuroimaging studies in humans and suggests the involvement of FAAH in modulating stress and anxiety in humans. The current neuroimaging study also lends support for the potential use of FAAH inhibitors to control amygdala hyperactivity, which is known to be involved in the pathophysiology of anxiety and trauma-related disorders.

Molecular Alterations of the Endocannabinoid System in Psychiatric Disorders

The therapeutic benefits of the current medications for patients with psychiatric disorders contrast with a great variety of adverse effects. The endocannabinoid system (ECS) components have gained high interest as potential new targets for treating psychiatry diseases because of their neuromodulator role, which is essential to understanding the regulation of many brain functions. This article reviewed the molecular alterations in ECS occurring in different psychiatric conditions. The methods used to identify alterations in the ECS were also described. We used a translational approach. The animal models reproducing some behavioral and/or neurochemical aspects of psychiatric disorders and the molecular alterations in clinical studies in post-mortem brain tissue or peripheral tissues were analyzed. This article reviewed the most relevant ECS changes in prevalent psychiatric diseases such as mood disorders, schizophrenia, autism, attentional deficit, eating disorders (ED), and addiction. The review concludes that clinical research studies are urgently needed for two different purposes: (1) To identify alterations of the ECS components potentially useful as new biomarkers relating to a specific disease or condition, and (2) to design new therapeutic targets based on the specific alterations found to improve the pharmacological treatment in psychiatry.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

Targeting the Endocannabinoid System in the Treatment of Posttraumatic Stress Disorder: A Promising Case of Preclinical-Clinical Translation?

The endocannabinoid (eCB) system is one the most ubiquitous signaling systems of the brain and offers a rich pharmacology including multiple druggable targets. Preclinical research shows that eCB activity influences functional connectivity between the prefrontal cortex and amygdala and thereby influences an organism's ability to cope with threats and stressful experiences. Animal studies show that CB1 receptor activation within the amygdala is essential for extinction of fear memories. Failure to extinguish traumatic memories is a core symptom of posttraumatic stress disorder, suggesting that potentiating eCB signaling may have a therapeutic potential in this condition. However, it has been unknown whether animal findings in this domain translate to humans. Data to inform this critical question are now emerging and are the focus of this review. We first briefly summarize the biology of the eCB system and the animal studies that support its role in fear extinction and stress responding. We then discuss the pharmacological eCB-targeting strategies that may be exploited for therapeutic purposes: direct CB1 receptor activation, using Δ9-tetrahydrocannabinol or its synthetic analogs; or indirect potentiation, through inhibition of eCB-degrading enzymes, the anandamide-degrading enzyme fatty acid amide hydrolase; or the 2-AG (2-arachidonoyl glycerol)-degrading enzyme monoacylglycerol lipase. We then review recent human data on direct CB1 receptor activation via Δ9-tetrahydrocannabinol and anandamide potentiation through fatty acid amide hydrolase blockade. The available human data consistently support a translation of animal findings on fear memories and stress reactivity and suggest a potential therapeutic utility in humans.

Translation of animal endocannabinoid models of PTSD mechanisms to humans: Where to next?

The endocannabinoid system is known to be involved in mechanisms relevant to PTSD aetiology and maintenance, though this understanding is mostly based on animal models of the disorder. Here we review how human paradigms can successfully translate animal findings to human subjects, with the view that substantially increased insight into the effect of endocannabinoid signalling on stress responding, emotional and intrusive memories, and fear extinction can be gained using modern paradigms and methods for assessing the state of the endocannabinoid system in PTSD.

Cannabinoid polymorphisms interact with plasma endocannabinoid levels to predict fear extinction learning

BACKGROUND

The endocannabinoid system is gaining increasing attention as a favorable target for improving posttraumatic stress disorder (PTSD) treatments. Exposure therapy is the gold-standard treatment for PTSD, and fear extinction learning is a key concept underlying successful exposure.

METHODS

This study examined the role of genetic endocannabinoid polymorphisms in a fear extinction paradigm with PTSD compared to healthy participants (N = 220). Participants provided saliva for genotyping, completed a fear conditioning and extinction task, with blood samples taken before and after the task (n = 57). Skin conductance was the outcome and was analyzed using mixed models.

RESULTS

Results for cannabinoid receptor type 1 polymorphisms suggested that minor alleles of rs2180619 and rs1049353 were associated with poorer extinction learning in PTSD participants. The minor allele of the fatty acid amide hydrolase (FAAH) polymorphism rs324420 was associated with worse extinction in PTSD participants. Subanalysis of healthy participants (n = 57) showed the FAAH rs324420 genotype effect was dependent on plasma arachidonoyl ethanolamide (AEA) level, but not oleoylethanolamide or 2-arachidonoyl glycerol. Specifically, higher but not lower AEA levels in conjunction with the minor allele of FAAH rs324420 were associated with better extinction learning.

CONCLUSIONS

These findings provide translational evidence that cannabinoid receptor 1 and AEA are involved in extinction learning in humans. FAAH rs324420's effect on fear extinction is moderated by AEA plasma level in healthy controls. These findings imply that FAAH inhibitors may be effective for targeting anxiety in PTSD, but this effect needs to be explored further in clinical populations.

Genetic variation in endocannabinoid signaling is associated with differential network-level functional connectivity in youth

The endocannabinoid system is an important regulator of emotional responses such as fear, and a number of studies have implicated endocannabinoid signaling in anxiety. The fatty acid amide hydrolase (FAAH) C385A polymorphism, which is associated with enhanced endocannabinoid signaling in the brain, has been identified across species as a potential protective factor from anxiety. In particular, adults with the variant FAAH 385A allele have greater fronto-amygdala connectivity and lower anxiety symptoms. Whether broader network-level differences in connectivity exist, and when during development this neural phenotype emerges, remains unknown and represents an important next step in understanding how the FAAH C385A polymorphism impacts neurodevelopment and risk for anxiety disorders. Here, we leveraged data from 3,109 participants in the nationwide Adolescent Brain Cognitive Development Study℠ (10.04 ± 0.62 years old; 44.23% female, 55.77% male) and a cross-validated, data-driven approach to examine associations between genetic variation and large-scale resting-state brain networks. Our findings revealed a distributed brain network, comprising functional connections that were both significantly greater (95% CI for p values = [<0.001, <0.001]) and lesser (95% CI for p values = [0.006, <0.001]) in A-allele carriers relative to non-carriers. Furthermore, there was a significant interaction between genotype and the summarized connectivity of functional connections that were greater in A-allele carriers, such that non-carriers with connectivity more similar to A-allele carriers (i.e., greater connectivity) had lower anxiety symptoms (β = -0.041, p = 0.030). These findings provide novel evidence of network-level changes in neural connectivity associated with genetic variation in endocannabinoid signaling and suggest that genotype-associated neural differences may emerge at a younger age than genotype-associated differences in anxiety.

Leveraging big data to map neurodevelopmental trajectories in pediatric anxiety

Anxiety disorders are the most prevalent psychiatric condition among youth, with symptoms commonly emerging prior to or during adolescence. Delineating neurodevelopmental trajectories associated with anxiety disorders is important for understanding the pathophysiology of pediatric anxiety and for early risk identification. While a growing literature has yielded valuable insights into the nature of brain structure and function in pediatric anxiety, progress has been limited by inconsistent findings and challenges common to neuroimaging research. In this review, we first discuss these challenges and the promise of ‘big data’ to map neurodevelopmental trajectories in pediatric anxiety. Next, we review evidence of age-related differences in neural structure and function among anxious youth, with a focus on anxiety-relevant processes such as threat and safety learning. We then highlight large-scale cross-sectional and longitudinal studies that assess anxiety and are well positioned to inform our understanding of neurodevelopment in pediatric anxiety. Finally, we detail relevant challenges of ‘big data’ and propose future directions through which large publicly available datasets can advance knowledge of deviations from normative brain development in anxiety. Leveraging ‘big data’ will be essential for continued progress in understanding the neurobiology of pediatric anxiety, with implications for identifying markers of risk and novel treatment targets.

Endocannabinoids, cannabinoids and the regulation of anxiety

Cannabis has been used for hundreds of years, with its ability to dampen feelings of anxiety often reported as a primary reason for use. Only recently has the specific role cannabinoids play in anxiety been thoroughly investigated. Here we discuss the body of evidence describing how endocannabinoids and exogenous cannabinoids are capable of regulating the generation and termination of anxiety states. Disruption of the endogenous cannabinoid (eCB) system following genetic manipulation, pharmacological intervention or stress exposure reliably leads to the generation of an anxiety state. On the other hand, upregulation of eCB signaling is capable of alleviating anxiety-like behaviors in multiple paradigms. When considering exogenous cannabinoid administration, cannabinoid receptor 1 (CB1) agonists have a biphasic, dose-dependent effect on anxiety such that low doses are anxiolytic while high doses are anxiogenic, a phenomenon that is evident in both rodent models and humans. Translational studies investigating a loss of function mutation in the gene for fatty acid amide hydrolase, the enzyme responsible for metabolizing AEA, have also shown that AEA signaling regulates anxiety in humans. Taken together, evidence reviewed here has outlined a convincing argument for cannabinoids being powerful regulators of both the manifestation and amelioration of anxiety symptoms, and highlights the therapeutic potential of targeting the eCB system for the development of novel classes of anxiolytics. This article is part of the special issue on 'Cannabinoids'.

A common genetic variant in fatty acid amide hydrolase is linked to alterations in fear extinction neural circuitry in a racially diverse, nonclinical sample of adults

Poor fear extinction learning and recall are linked to the development of fear-based disorders, like posttraumatic stress disorder, and are associated with aberrant activation of fear-related neural circuitry. This includes greater amygdala activation during extinction learning and lesser hippocampal and ventromedial prefrontal cortex (vmPFC) activation during recall. Emerging data indicate that genetic variation in fatty acid amide hydrolase (FAAH C385A; rs324420) is associated with increased peripheral endocannabinoid (eCB) levels and lesser threat-related amygdala reactivity. Preclinical studies link increased eCB signaling to better extinction learning and recall, thus FAAH C385A may protect against the development of trauma-related psychopathology by facilitating extinction learning. However, how this FAAH variant affects fear extinction neural circuitry remains unknown. In the present study, we used a novel, immersive-reality fear extinction paradigm paired with functional neuroimaging to assess FAAH C385A effects on fear-related neural circuitry and conditioned fear responding (US expectancy ratings, subjective units of distress, and skin conductance responding) in healthy adults from an urban area (Detroit, MI; N = 59; C/C = 35, A-carrier = 24). We found lesser amygdala activation in A-allele carriers, compared to C/C homozygotes, during early extinction recall. Likewise, we found lesser dorsal anterior cingulate cortex and greater hippocampus activation in early extinction learning in A-carriers compared to C/C homozygotes. We found no effects of FAAH C385A on vmPFC activation or behavioral fear indices. These data support and extend previous findings that FAAH genetic variation, associated with increased eCB signaling and subsequent enhanced fear extinction, may predict individual differences in successful fear learning.

Linking mPFC circuit maturation to the developmental regulation of emotional memory and cognitive flexibility

The medial prefrontal cortex (mPFC) and its abundant connections with other brain regions play key roles in memory, cognition, decision making, social behaviors, and mood. Dysfunction in mPFC is implicated in psychiatric disorders in which these behaviors go awry. The prolonged maturation of mPFC likely enables complex behaviors to emerge, but also increases their vulnerability to disruption. Many foundational studies have characterized either mPFC synaptic or behavioral development without establishing connections between them. Here, we review this rich body of literature, aligning major events in mPFC development with the maturation of complex behaviors. We focus on emotional memory and cognitive flexibility, and highlight new work linking mPFC circuit disruption to alterations of these behaviors in disease models. We advance new hypotheses about the causal connections between mPFC synaptic development and behavioral maturation and propose research strategies to establish an integrated understanding of neural architecture and behavioral repertoires.

Untapped endocannabinoid pharmacological targets: Pipe dream or pipeline?

It has been established that the endogenous cannabinoid (endocannabinoid) system plays key modulatory roles in a wide variety of pathological conditions. The endocannabinoid system comprises both cannabinoid receptors, their endogenous ligands including 2-arachidonoylglycerol (2-AG), N-arachidonylethanolamine (anandamide, AEA), and enzymes that regulate the synthesis and degradation of endogenous ligands which include diacylglycerol lipase alpha (DAGL-α), diacylglycerol lipase beta (DAGL-β), fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), α/β hydrolase domain 6 (ABHD6). As the endocannabinoid system exerts considerable involvement in the regulation of homeostasis and disease, much effort has been made towards understanding endocannabinoid-related mechanisms of action at cellular, physiological, and pathological levels as well as harnessing the various components of the endocannabinoid system to produce novel therapeutics. However, drug discovery efforts within the cannabinoid field have been slower than anticipated to reach satisfactory clinical endpoints and raises an important question into the validity of developing novel ligands that therapeutically target the endocannabinoid system. To answer this, we will first examine evidence that supports the existence of an endocannabinoid system role within inflammatory diseases, neurodegeneration, pain, substance use disorders, mood disorders, as well as metabolic diseases. Next, this review will discuss recent clinical studies, within the last 5 years, of cannabinoid compounds in context to these diseases. We will also address some of the challenges and considerations within the cannabinoid field that may be important in the advancement of therapeutics into the clinic.

In it together? The case for endocannabinoid-noradrenergic interactions in fear extinction

Anxiety and trauma-related disorders, such as post-traumatic stress disorder (PTSD), are debilitating mental illnesses with great personal and socioeconomic costs. Examining memory formation and relevant behavioural responding associated with aversive stimuli may improve our understanding of the neurobiology underlying fear memory processing and PTSD treatment. The neurocircuitry underpinning learned fear and its inhibition through extinction is complex, involving synergistic interactions between different neurotransmitter systems in inter-connected brain areas. Endocannabinoid and noradrenergic transmission have both been implicated separately in fear memory processing and PTSD, but potential interactions between these systems in relation to fear extinction have received little attention to date. Their receptors are expressed together in brain areas crucial for fear extinction, which is enhanced by both cannabinoid and noradrenergic receptor activation in these areas. Moreover, cannabinoid signalling modulates the activity of locus coeruleus noradrenaline (NA) neurons and the release of NA in the medial prefrontal cortex, a brain area that is crucial for fear extinction. Interestingly, endocannabinoid-noradrenergic system interactions have been shown to regulate the encoding and retrieval of fear memory. Thus, noradrenergic regulation of fear extinction may also be driven indirectly in part via cannabinoid receptor signalling. In this perspective paper, we collate the available relevant literature and propose a synergistic role for the endocannabinoid and noradrenergic systems in regulating fear extinction, the study of which may further our understanding of the neurobiological substrates of PTSD and its treatment.

Fatty acid amide hydrolase binding is inversely correlated with amygdalar functional connectivity: a combined positron emission tomography and magnetic resonance imaging study in healthy individuals

Background

Upregulation of the endocannabinoid enzyme fatty acid amide hydrolase (FAAH) has been linked to abnormal activity in frontoamygdalar circuits, a hallmark of posttraumatic stress disorder. We tested the hypothesis that FAAH levels in the amygdala were negatively correlated with functional connectivity between the amygdala and prefrontal cortex, subserving stress and affect control.

Methods

Thirty-one healthy participants completed positron emission tomography (PET) imaging with the FAAH probe [C-11]CURB, and resting-state functional MRI scans. Participants were genotyped for the FAAH polymorphism rs324420, and trait neuroticism was assessed. We calculated amygdala functional connectivity using predetermined regions of interest (including the subgenual ventromedial prefrontal cortex [sgvmPFC] and the dorsal anterior cingulate cortex [dACC]) and a seed-to-voxel approach. We conducted correlation analyses on functional connectivity, with amygdala [C-11]CURB binding as a variable of interest.

Results

The strength of amygdala functional connectivity with the sgvmPFC and dACC was negatively correlated with [C-11]CURB binding in the amygdala (sgvmPFC: r = -0.38, q = 0.04; dACC: r = -0.44; q = 0.03). Findings were partly replicated using the seed-to-voxel approach, which showed a cluster in the ventromedial prefrontal cortex, including voxels in the dACC but not the sgvmPFC (cluster-level, family-wise error rate corrected p < 0.05).

Limitations

We did not replicate earlier findings of a relationship between an FAAH polymorphism (rs324420) and amygdala functional connectivity.

Conclusion

Our data provide preliminary evidence that lower levels of FAAH in the amygdala relate to increased frontoamygdalar functional coupling. Our findings were consistent with the role of FAAH in regulating brain circuits that underlie fear and emotion processing in humans.

Cannabis use and posttraumatic stress disorder comorbidity: Epidemiology, biology and the potential for novel treatment approaches

Cannabis use is increasing among some demographics in the United States and is tightly linked to anxiety, trauma, and stress reactivity at the epidemiological and biological level. Stress-coping motives are highly cited reasons for cannabis use. However, with increased cannabis use comes the increased susceptibility for cannabis use disorder (CUD). Indeed, CUD is highly comorbid with posttraumatic stress disorder (PTSD). Importantly, endogenous cannabinoid signaling systems play a key role in the regulation of stress reactivity and anxiety regulation, and preclinical data suggest deficiencies in this signaling system could contribute to the development of stress-related psychopathology. Furthermore, endocannabinoid deficiency states, either pre-existing or induced by trauma exposure, could provide explanatory insights into the high rates of comorbid cannabis use in patients with PTSD. Here we review clinical and preclinical literature related to the cannabis use-PTSD comorbidity, the role of endocannabinoids in the regulation of stress reactivity, and potential therapeutic implications of recent work in this area.

Genetic analyses of the endocannabinoid pathway in association with affective phenotypic variants

BACKGORUND

Increasing experimental data confirm the crucial role of the endocannabinoid (eCB) system in the regulation of stress response and emotional processes. Despite of the fact, that genetically determined vulnerability for stress is a widely accepted concept in the pathomechanism of affective disorders, replicable human genetic results with interaction analyses of early life trauma and eCB genes are rare. The aim of this study is to test the associations between genetic variants of the eCB pathway, childhood trauma and affective phenotypes.

METHODS

We selected 18,897 SNPs in the eCB pathway of a GWAS dataset in two general population cohorts (BP sample N = 837; MN sample N = 988). Association analyses were performed on the anxious and depressive subscales of the Brief Symptom Inventory (BSI-ANX and BSI-DEP, respectively). Childhood trauma was assessed by the Childhood Adversity Questionnaire (CAQ). Association analyses were performed in the R 2.0. statistical program using the SNPassoc package.

REULTS

Genetic effect was more robust in the BP sample than in the MN sample. The most comprehensive results showed that SNPs in the CACNA1C gene associated with depressive phenotype in interaction with CAQ in both BP (p = 1.2 × 10^-4) and MN samples (p = 1.6 × 10^-4). Direct association analyses (without interaction) provided significant associations between SNPs in different genesets of the two study populations. SNPs in KCNJ3 and GNB5 genes on the BSI-DEP (p = 6.1 × 10^-5; p = 7.1 × 10^-4) and GNG12 gene on the BSI-ANX (p = 7.4 × 10^-6) in the BP sample, while GABAergic, ADCY1 and HTR2A gene variants can be outlined from results of MN sample with less strong p-values.

CONCLUSION

Our results confirmed the prominent role of CACNA1C gene in the pathogenic effect of early life stress in the development of affective vulnerability in two different study populations using GxE interaction analysis. CACNA1C gene, as it encodes for L-type voltage-gated calcium channel, contributes to neuronal excitability, plasticity and neurogenesis being a crucial effector of both eCB signaling and the BDNF-CREB pathway as well. Our findings suggest that childhood trauma related depression may have more robust genetically determined basis than without early life stress.

Effects of optogenetic photoexcitation of infralimbic cortex inputs to the basolateral amygdala on conditioned fear and extinction

Deficiencies in the ability to extinguish fear is a hallmark of Trauma- and stressor-related disorders, Anxiety disorders, and certain other neuropsychiatric conditions. Hence, a greater understanding of the brain mechanisms involved in the inhibition of fear is of significant translational relevance. Previous studies in rodents have shown that glutamatergic projections from the infralimbic prefrontal cortex (IL) to basolateral amygdala (BLA) play a crucial instructional role in the formation of extinction memories, and also indicate that variation in the strength of this input correlates with extinction efficacy. To further examine the relationship between the IL→BLA pathway and extinction we expressed three different titers of the excitatory opsin, channelrhodopsin (ChR2), in IL neurons and photostimulated their projections in the BLA during partial extinction training. The behavioral effects of photoexcitation differed across the titer groups: the low titer had no effect, the medium titer selectively facilitated extinction memory formation, and the high titer produced both an acute suppression of fear and a decrease in fear during (light-free) extinction retrieval. We discuss various possible explanations for these titer-specific effects, including the possibility of IL-mediated inhibition of BLA fear-encoding neurons under conditions of sufficiently strong photoexcitation. These findings further support the role of IL→BLA pathway in regulating fear and highlight the importance of methodological factors in optogenetic studies of neural circuits underling behavior.

Neurobiology of cannabinoid receptor signaling

The endocannabinoid system (ECS) is a highly versatile signaling system within the nervous system. Despite its widespread localization, its functions within the context of distinct neural processes are very well discernable and specific. This is remarkable, and the question remains as to how such specificity is achieved. One key player in the ECS is the cannabinoid type 1 receptor (CB₁), a G protein-coupled receptor characterized by the complexity of its cell-specific expression, cellular and subcellular localization, and its adaptable regulation of intracellular signaling cascades. CB₁ receptors are involved in different synaptic and cellular plasticity processes and in the brain's bioenergetics in a context-specific manner. CB₂ receptors are also important in several processes in neurons, glial cells, and immune cells of the brain. As polymorphisms in ECS components, as well as external impacts such as stress and metabolic challenges, can both lead to dysregulated ECS activity and subsequently to possible neuropsychiatric disorders, pharmacological intervention targeting the ECS is a promising therapeutic approach. Understanding the neurobiology of cannabinoid receptor signaling in depth will aid optimal design of therapeutic interventions, minimizing unwanted side effects.
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Prospective associations, longitudinal patterns of childhood socioeconomic status, and white matter organization in adulthood

The association between childhood socioeconomic status (SES) and brain development is an emerging area of research. The primary focus to date has been on SES and variations in gray matter structure with much less known about the relation between childhood SES and white matter structure. Using a longitudinal study of SES, with measures of income-to-needs ratio (INR) at age 9, 13, 17, and 24, we examined the prospective relationship between childhood SES (age 9 INR) and white matter organization in adulthood using diffusion tensor imaging. We also examined how changes in INR from childhood through young adulthood are associated with white matter organization in adult using a latent growth mixture model. Using tract-based spatial statistics (TBSS) we found that there is a significant prospective positive association between childhood INR and white matter organization in the bilateral uncinate fasciculus, bilateral cingulum bundle, bilateral superior longitudinal fasciculus, and corpus callosum (p < .05, FWE corrected). The probability that an individual was in the high-increasing INR profile across development compared with the low-increasing INR profile was positively associated with white matter organization in the bilateral uncinate fasciculus, left cingulum, and bilateral superior longitudinal fasciculus. The results of the current study have potential implications for interventions given that early childhood poverty may have long-lasting associations with white matter structure. Furthermore, trajectories of socioeconomic status during childhood are important-with individuals that belong to the latent profile that had high increases in INR having greater regional white matter organization in adulthood.

Effects of ∆9-tetrahydrocannabinol on aversive memories and anxiety: a review from human studies

BACKGROUND

Posttraumatic stress disorder (PTSD) may stem from the formation of aberrant and enduring aversive memories. Some PTSD patients have recreationally used Cannabis, probably aiming at relieving their symptomatology. However, it is still largely unknown whether and how Cannabis or its psychotomimetic compound Δ⁹-tetrahydrocannabinol (THC) attenuates the aversive/traumatic memory outcomes. Here, we seek to review and discuss the effects of THC on aversive memory extinction and anxiety in healthy humans and PTSD patients.

METHODS

Medline, PubMed, Cochrane Library, and Central Register for Controlled Trials databases were searched to identify peer-reviewed published studies and randomized controlled trials in humans published in English between 1974 and July 2020, including those using only THC and THC combined with cannabidiol (CBD). The effect size of the experimental intervention under investigation was calculated.

RESULTS

At low doses, THC can enhance the extinction rate and reduce anxiety responses. Both effects involve the activation of cannabinoid type-1 receptors in discrete components of the corticolimbic circuitry, which could couterbalance the low "endocannabinoid tonus" reported in PTSD patients. The advantage of associating CBD with THC to attenuate anxiety while minimizing the potential psychotic or anxiogenic effect produced by high doses of THC has been reported. The effects of THC either alone or combined with CBD on aversive memory reconsolidation, however, are still unknown.

CONCLUSIONS

Current evidence from healthy humans and PTSD patients supports the THC value to suppress anxiety and aversive memory expression without producing significant adverse effects if used in low doses or when associated with CBD. Future studies are guaranteed to address open questions related to their dose ratios, administration routes, pharmacokinetic interactions, sex-dependent differences, and prolonged efficacy.

Age Differences in the Neural Correlates of Anxiety Disorders: An fMRI Study of Response to Learned Threat

OBJECTIVE

Although both pediatric and adult patients with anxiety disorders exhibit similar neural responding to threats, age-related differences have been found in some functional MRI (fMRI) studies. To reconcile disparate findings, the authors compared brain function in youths and adults with and without anxiety disorders while rating fear and memory of ambiguous threats.

METHODS

Two hundred medication-free individuals ages 8-50 were assessed, including 93 participants with an anxiety disorder. Participants underwent discriminative threat conditioning and extinction in the clinic. Approximately 3 weeks later, they completed an fMRI paradigm involving extinction recall, in which they rated their levels of fear evoked by, and their explicit memory for, morph stimuli with varying degrees of similarity to the extinguished threat cues.

RESULTS

Age moderated two sets of anxiety disorder findings. First, as age increased, healthy subjects compared with participants with anxiety disorders exhibited greater amygdala-ventromedial prefrontal cortex (vmPFC) connectivity when processing threat-related cues. Second, age moderated diagnostic differences in activation in ways that varied with attention and brain regions. When rating fear, activation in the vmPFC differed between the anxiety and healthy groups at relatively older ages. In contrast, when rating memory for task stimuli, activation in the inferior temporal cortex differed between the anxiety and healthy groups at relatively younger ages.

CONCLUSIONS

In contrast to previous studies that demonstrated age-related similarities in the biological correlates of anxiety disorders, this study identified age differences. These findings may reflect this study's focus on relatively late-maturing psychological processes, particularly the appraisal and explicit memory of ambiguous threat, and inform neurodevelopmental perspectives on anxiety.

Protective effects of elevated anandamide on stress and fear-related behaviors: translational evidence from humans and mice

Post-traumatic stress disorder (PTSD) is a common, debilitating condition with limited treatment options. Extinction of fear memories through prolonged exposure therapy, the primary evidence-based behavioral treatment for PTSD, has only partial efficacy. In mice, pharmacological inhibition of fatty acid amide hydrolase (FAAH) produces elevated levels of anandamide (AEA) and promotes fear extinction, suggesting that FAAH inhibitors may aid fear extinction-based treatments. A human FAAH 385C->A substitution encodes an FAAH enzyme with reduced catabolic efficacy. Individuals homozygous for the FAAH 385A allele may therefore offer a genetic model to evaluate the impact of elevations in AEA signaling in humans, helping to inform whether FAAH inhibitors have the potential to facilitate fear extinction therapy for PTSD. To overcome the challenge posed by low frequency of the AA genotype (appr. 5%), we prospectively genotyped 423 individuals to examine the balanced groups of CC, AC, and AA individuals (n = 25/group). Consistent with its loss-of-function nature, the A allele was dose dependently associated with elevated basal AEA levels, facilitated fear extinction, and enhanced the extinction recall. Moreover, the A-allele homozygotes were protected against stress-induced decreases in AEA and negative emotional consequences of stress. In a humanized mouse model, AA homozygous mice were similarly protected against stress-induced decreases in AEA, both in the periphery, and also in the amygdala and prefrontal cortex, brain structures critically involved in fear extinction and regulation of stress responses. Collectively, these data suggest that AEA signaling can temper aspects of the stress response and that FAAH inhibition may aid the treatment for stress-related psychiatric disorders, such as PTSD.

Cannabis and the Developing Adolescent Brain

Purpose of Review

This review summarizes (1) recent trends in delta-9-tetrahydrocannabionol [THC] and cannabidiol (CBD) content in cannabis products, (2) neurobiological correlates of cannabis use on the developing adolescent brain, (3) effects of cannabis on psychiatric symptoms and daily functioning in youth (i.e., academic performance, cognition, sleep and driving), (4) cannabis products used to relieve or treat medical issues in youth, and (5) available treatments for cannabis use disorder in adolescence.

Recent findings

Despite marked increases in THC content and availability of cannabis, there has been a decline in perceived risk and an increase in use of THC extract products among youth in the United States. The primary psychiatric symptoms associated with cannabis use in youth are increased risk for addiction, depressive, and psychotic symptoms. Cannabis alters endocannabinoid system function which plays a central role in modulating the neurodevelopment of reward and stress systems. To date, few studies have examined neurobiological mechanisms underlying the psychiatric sequalae of cannabis exposure in youth. Adolescent cannabis exposure results in impaired cognition, sleep, and driving ability. There are very limited FDA-approved cannabinoid medications, none of them supporting their use for the treatment of psychiatric symptoms. Behavioral therapies are currently the mainstay of treating cannabis misuse, with no pharmacotherapies currently approved by the FDA for cannabis use disorder in youth.

Summary

Here, we summarize the most up-to-date knowledge on the neurobiological psychiatric, and daily function effects of the most commonly used cannabinoids, delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). We then review FDA approved medical use of cannabinoid treatments as well as pharmacological and psychological treatments for cannabis use disorder in youth. Our current understanding of the effects of cannabis on the developing brain and treatments for cannabis misuse in youth remain limited. Future research aimed at examining the neurobiological effects of cannabis, with objective measures of exposure, over the course of pediatric development and in relation to psychiatric symptoms are needed.

Elevated Anandamide, Enhanced Recall of Fear Extinction, and Attenuated Stress Responses Following Inhibition of Fatty Acid Amide Hydrolase: A Randomized, Controlled Experimental Medicine Trial

BACKGROUND

Posttraumatic stress disorder, an area of large unmet medical needs, is characterized by persistence of fear memories and maladaptive stress responses. In rodents, elevation of the endocannabinoid anandamide due to inhibition of fatty acid amide hydrolase (FAAH) facilitates fear extinction and protects against the anxiogenic effects of stress. We recently reported that elevated anandamide levels in people homozygous for a loss-of-function FAAH mutation are associated with a similar phenotype, suggesting a translational validity of the preclinical findings.

METHODS

In this double-blind, placebo-controlled experimental medicine study, healthy adults were randomized to an FAAH inhibitor (PF-04457845, 4 mg orally, once daily; n = 16) or placebo (n = 29) for 10 days. On days 9 and 10, participants completed a task battery assessing psychophysiological indices of fear learning, stress reactivity, and stress-induced affective responses.

RESULTS

FAAH inhibition produced a 10-fold increase in baseline anandamide. This was associated with potentiated recall of fear extinction memory when tested 24 hours after extinction training. FAAH inhibition also attenuated autonomic stress reactivity, assessed via electrodermal activity, and protected against stress-induced negative affect, measured via facial electromyography.

CONCLUSIONS

Our data provide preliminary human evidence that FAAH inhibition can improve the recall of fear extinction memories and attenuate the anxiogenic effects of stress, in a direct translation of rodent findings. The beneficial effects of FAAH inhibition on fear extinction, as well as stress- and affect-related behaviors, provide a strong rationale for developing this drug class as a treatment for posttraumatic stress disorder.

Endocannabinoid genetic variation enhances vulnerability to THC reward in adolescent female mice

Adolescence represents a developmental period with the highest risk for initiating cannabis use. Little is known about whether genetic variation in the endocannabinoid system alters mesolimbic reward circuitry to produce vulnerability to the rewarding properties of the exogenous cannabinoid Δ9-tetrahydrocannabinol (THC). Using a genetic knock-in mouse model (FAAHC/A) that biologically recapitulates the human polymorphism associated with problematic drug use, we find that in adolescent female mice, but not male mice, this FAAH polymorphism enhances the mesolimbic dopamine circuitry projecting from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and alters cannabinoid receptor 1 (CB1R) levels at inhibitory and excitatory terminals in the VTA. These developmental changes collectively increase vulnerability of adolescent female FAAHC/A mice to THC preference that persists into adulthood. Together, these findings suggest that this endocannabinoid genetic variant is a contributing factor for increased susceptibility to cannabis dependence in adolescent females.