The only evidence-based behavioral treatment for anxiety and stress-related disorders involves desensitization techniques that rely on principles of extinction learning. However, 40% of patients do not respond to this treatment. Efforts have focused on individual differences in treatment response, but have not examined when, during development, such treatments may be most effective. We examined fear-extinction learning across development in mice and humans. Parallel behavioral studies revealed attenuated extinction learning during adolescence. Probing neural circuitry in mice revealed altered synaptic plasticity of prefrontal cortical regions implicated in suppression of fear responses across development. The results suggest a lack of synaptic plasticity in the prefrontal regions, during adolescence, is associated with blunted regulation of fear extinction. These findings provide insight into optimizing treatment outcomes for when, during development, exposure therapies may be most effective. F ear learning is a highly adaptive, evolutionarily conserved process that allows one to respond appropriately to cues associated with danger. In the case of psychiatric disorders, however, fear may persist long after an environmental threat has passed. This unremitting and often debilitating form of fear is a core component of many anxiety disorders, including posttraumatic stress disorder (PTSD), and involves exaggerated and inappropriate fear responses. Existing treatments, such as exposure therapy, are based on principles of fear extinction, during which cues previously associated with threat are presented in the absence of the initial aversive event until cues are considered safe and fear responses are reduced. Extinction-based exposure therapies have the strongest empirical evidence for benefitting adult patients suffering from PTSD (1), yet a comparative lack of knowledge about the development of fear neural circuitry prohibits similarly successful treatment outcomes in children and adolescents (2). Adolescence, in particular, is a developmental stage when the incidence of anxiety disorders peaks in humans (3-6), and it is estimated that over 75% of adults with fear-related disorders met diagnostic criteria as children and adolescents (7, 8). Because of insufficient or inaccurate diagnoses and a dearth of pediatric and adolescent specialized treatments, fewer than one in five children or adolescents are expected to receive treatment for their anxiety disorders (9), leaving a vast number with inadequate or no treatment (2, 10). The increased frequency of anxiety disorders in pediatric and adolescent populations highlights the importance of understanding neural mechanisms of fear regulation from a developmental perspective, as existing therapies directly rely upon principles of fear-extinction learning. Converging evidence from human and rodent studies suggests that insufficient top-down regulation of subcortical structures (11-14), such as the amygdala, may coincide with diminished prototypical extinction learning (15...

Relatively little is known about neurobiological changes attributable to early-life stressors (e.g., orphanage rearing), even though they have been associated with a heightened risk for later psychopathology. Human neuroimaging and animal studies provide complementary insights into the neural basis of problem behaviors following stress, but too often are limited by dissimilar experimental designs. The current mouse study manipulates the type and timing of a stressor to parallel the early-life stress experience of orphanage rearing, controlling for genetic and environmental confounds inherent in human studies. The results provide evidence of both early and persistent alterations in amygdala circuitry and function following early-life stress. These effects are not reversed when the stressor is removed nor diminished with the development of prefrontal regulation regions. These neural and behavioral findings are similar to our human findings in children adopted from orphanages abroad in that even following removal from the orphanage, the ability to suppress attention toward potentially threatening information in favor of goal-directed behavior was diminished relative to never-institutionalized children. Together, these findings highlight how early-life stress can lead to altered brain circuitry and emotion dysregulation that may increase the risk for psychopathology.anxiety | emotion regulation | infralimbic cortex | c-fos | cross-species E arly-childhood adversity (e.g., abuse, neglect) accounts for over 30% of all anxiety disorders (1) and is associated with later emotional and behavioral dysregulation (2-6). One form of early-life stress (ELS) in humans that has received significant attention is that of orphanage rearing (7-11). It is estimated that eight million children live in orphanages worldwide. Children adopted from these orphanages provide a unique opportunity to assess the effects of ELS with a discrete timing and offset (12, 13). However, it is unclear to what extent emotional and behavioral dysregulation reported in this population is the result of the orphanage experience of disorganized care or attributable to preexisting conditions (e.g., prenatal exposure to substances, maternal malnutrition, and/or congenital disorders) (12). Moreover, we know little about the long-term effects of such early-life experiences and whether they reverse after the stressor is removed. The current study examines these issues using a rodent model of ELS (14, 15) and an outcome measure that uniquely parallels human paradigms to test for immediate and long-term effects of stress across development while controlling for preexisting environmental and genetic factors.To date, most animal studies of stress have either focused on the effects of adult stress or on how early stress impacts later adult brain and behavior. The findings have been mixed depending on the type and timing of the stressor and the specific task and age of testing. Adult-restraint stress leads to reversible decreases in dendritic arborization and volume in...

Fear can be highly adaptive in promoting survival, yet it can also be detrimental when it persists long after a threat has passed. Flexibility of the fear response may be most advantageous during adolescence when animals are prone to explore novel, potentially threatening environments. Two opposing adolescent fear-related behaviours—diminished extinction of cued fear and suppressed expression of contextual fear—may serve this purpose, but the neural basis underlying these changes is unknown. Using microprisms to image prefrontal cortical spine maturation across development, we identify dynamic BLA-hippocampal-mPFC circuit reorganization associated with these behavioural shifts. Exploiting this sensitive period of neural development, we modified existing behavioural interventions in an age-specific manner to attenuate adolescent fear memories persistently into adulthood. These findings identify novel strategies that leverage dynamic neurodevelopmental changes during adolescence with the potential to extinguish pathological fears implicated in anxiety and stress-related disorders.

Anxiety disorders peak in incidence during adolescence, a developmental window that is marked by dynamic changes in gene expression, endocannabinoid signaling, and frontolimbic circuitry. We tested whether genetic alterations in endocannabinoid signaling related to a common polymorphism in fatty acid amide hydrolase (FAAH), which alters endocannabinoid anandamide (AEA) levels, would impact the development of frontolimbic circuitry implicated in anxiety disorders. In a pediatric imaging sample of over 1,000 3-to 21-y-olds, we show effects of the FAAH genotype specific to frontolimbic connectivity that emerge by ∼12 y of age and are paralleled by changes in anxietyrelated behavior. Using a knock-in mouse model of the FAAH polymorphism that controls for genetic and environmental backgrounds, we confirm phenotypic differences in frontoamygdala circuitry and anxiety-related behavior by postnatal day 45 (P45), when AEA levels begin to decrease, and also, at P75 but not before. These results, which converge across species and level of analysis, highlight the importance of underlying developmental neurobiology in the emergence of genetic effects on brain circuitry and function. Moreover, the results have important implications for the identification of risk for disease and precise targeting of treatments to the biological state of the developing brain as a function of developmental changes in gene expression and neural circuit maturation.A nxiety disorders typically emerge during adolescence, when the incidence of mental illness peaks (1, 2). The developmental phase of adolescence is characterized by dynamic changes in gene expression, frontolimbic circuitry (3, 4), and overall tone of the endocannabinoid system, which are implicated in anxiety (5-7).The corticolimbic endocannabinoid system undergoes dynamic changes across development. The onset of adolescence is marked by the highest expression of type 1 cannabinoid receptor (CB1) in both cortical and subcortical brain regions, with CB1 expression declining to adult levels throughout adolescence (8, 9). Across the amygdala and prefrontal cortex, fatty acid amide hydrolase (FAAH) expression shows a transient increase from postnatal day 35 (P35) to P45 during adolescence in mice (10). Consistent with the regulatory role of FAAH, anandamide (AEA) levels show an inverse pattern of a peak at P35 and subsequent decrease during adolescence (10, 11). AEA is an endogenous ligand for the CB1 receptor, suggesting that the concurrent changes in AEA and CB1 expression reflect decreasing endocannabinoid signaling during adolescence (12), which may be associated with increasing risk for anxiety (Fig. 1).A common human polymorphism in the gene encoding FAAH (C385A; rs324420), the primary catabolic enzyme of the prototypical endocannabinoid AEA, regulates FAAH activity. The variant FAAH A385 allele destabilizes the FAAH protein, causing lower levels of FAAH enzymatic activity and/or increased levels of AEA in T lymphocytes and brain (13,14). Phenotypic expression of common polymorphism...