Childhood maltreatment is associated with a wide range of psychopathologies including anxiety that emerge in childhood and in many cases persist in adulthood. Increased amygdala activation in response to threat and abnormal amygdala connectivity with frontolimbic brain regions, such as the hippocampus and the prefrontal cortex, are some of the most consistent findings seen in individuals exposed to childhood maltreatment. The underlying mechanisms responsible for these changes are difficult to study in humans but can be elucidated using animal models of early-life stress. Such studies are especially powerful in the mouse where precise control of the genetic background and the stress paradigm can be coupled with resting-state fMRI (rsfMRI) to map abnormal connectivity in circuits that regulate anxiety. To address this issue we first compared the effects of two models of early-life stress, limited bedding (LB) and unpredictable postnatal stress (UPS), on anxiety-like behavior in juvenile and adult mice. We found that UPS, but not LB, causes a robust increase in anxiety in juvenile and adult male mice. Next, we used rsfMRI to compare frontolimbic connectivity in control and UPS adult male mice. We found increased amygdala–prefrontal cortex and amygdala–hippocampus connectivity in UPS. The strength of the amygdala–hippocampal and amygdala–prefrontal cortex connectivity was highly correlated with anxiety-like behavior in the open-field test and elevated plus maze. These findings are the first to link hyperconnectivity in frontolimbic circuits and increased anxiety in a mouse model of early-life stress, allowing for more mechanistic understanding of parallel findings in humans.

The role of the innate immune system in mediating some of the consequences of childhood abuse and neglect has received increasing attention in recent years. Most of the work to date has focused on the role that neuroinflammation plays in the long-term adult psychiatric and medical complications associated with childhood maltreatment. The effects of stress-induced neuroinflammation on neurodevelopment have received little attention because until recently this issue has not been studied systematically in animal models of early life stress. The primary goal of this review is to explore the hypothesis that elevated corticosterone during the first weeks of life in mice exposed to brief daily separation (BDS), which is a mouse model of early life stress, disrupts microglial function during a critical period of brain development. We propose that perturbations of microglial function lead to abnormal maturation of several neuronal and non-neuronal cellular processes resulting in behavioral abnormalities that emerge during the juvenile period and persist in adulthood. Here, we highlight recent work demonstrating that exposure to BDS alters microglial cell number, morphology, phagocytic activity, and gene expression in the developing hippocampus in a manner that extends into the juvenile period. These changes in microglial function are associated with abnormalities in developmental processes mediated by microglia including synaptogenesis, synaptic pruning, axonal growth, and myelination. We examine the changes in microglial gene expression in the context of previous work demonstrating developmental and behavioral abnormalities in BDS mice and in other animal models of early life stress. The possible utility of these findings for developing novel PET imaging to assess microglial function in individuals exposed to childhood maltreatment is also discussed.

Most large pharmaceutical companies have downscaled or closed their clinical neuroscience research programs in response to the low clinical success rate for drugs that showed tremendous promise in animal experiments intended to model psychiatric pathophysiology. These failures have raised serious concerns about the role of preclinical research in the identification and evaluation of new pharmacotherapies for psychiatry. In the absence of a comprehensive understanding of the neurobiology of psychiatric disorders, the task of developing “animal models” seems elusive. The purpose of this review is to highlight emerging strategies to enhance the utility of preclinical research in the drug development process. We address this issue by reviewing how advances in neuroscience, coupled with new conceptual approaches, have recently revolutionized the way we can diagnose and treat common psychiatric conditions. We discuss the implications of these new tools for modeling psychiatric conditions in animals and advocate for the use of systematic reviews of preclinical work as a prerequisite for conducting psychiatric clinical trials. We believe that work in animals is essential for elucidating human psychopathology and that improving the predictive validity of animal models is necessary for developing more effective interventions for mental illness.