PROJECT SUMMARY/ABSTRACT Alterations in neuroplasticity are strongly implicated in stress-related psychopathology. This proposal will use nonhuman primates (NHP) to investigate the extent to which altered neuroplasticity systems in the central nucleus of the amygdala (Ce) underlie anxious temperament (AT), the early risk phenotype for anxiety and depressive disorders. We will also investigate the effects of increasing neuroplasticity via an understudied, direct prefrontal cortex to Ce pathway, which will inform the development of pathway specific treatments focused on modulating Ce function. Anxiety disorders (ADs) commonly emerge during childhood, are highly prevalent, result in significant disability, and childhood onset predicts more severe and prolonged symptomatology. Despite current treatments, many individuals with ADs continue to be highly symptomatic and interventions aimed at mechanisms mediating the childhood onset of ADs would be ideal. To gain insights into the mechanisms underlying childhood ADs, and to conceptualize more effective interventions, we developed a NHP model of AT that is directly translatable to humans. Our studies demonstrate remarkable similarities between human and monkey AT, have elaborated AT’s neural circuit, and using RNA sequencing (RNA-Seq) have characterized molecular alterations in the Ce. To facilitate molecular, mechanistic studies, we developed intraoperative real-time MRI methods to reliably deliver viral vectors to select neural targets, including the Ce. Our work led us to posit a neurodevelopmental hypothesis suggesting that reduced neuroplasticity mechanisms in the Ce serve to maintain high levels of AT and its ultimate conversion to anxiety and depressive disorders. While much is known from rodent studies about the BDNF (brain-derived neurotrophic factor)-TrkB system in mediating fear, depressive behaviors, and antidepressant effects, our RNA-Seq and viral vector overexpression data from young primates also points to alterations in NT3 (neurotrophin 3)-TrkC signaling within the Ce as a pathway that contributes to pathological anxiety. To further explore the role of Ce NT3/TrkC and BDNF/TrkB systems in early-life pathological anxiety, we will use viral vectors to modulate neuroplasticity systems in the Ce and in a prefrontal pathway that directly regulates Ce. To assess effects we will use a unique combination of measures including: behavioral, neuroimaging, postmortem analyses, and RNA-Seq. Paralleling the in vivo experiments, we will use Ce-like neurons derived from rhesus induced pluripotent stem cells (iPSCs), to investigate mechanisms at a cellular level. The experiments in this proposal will provide evidence in primates for the involvement of altered Ce neuroplasticity in mediating early-life anxiety and will establish a translational rationale for exploring new therapeutic approaches in patients with anxiety and depression.