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Early life adversity impairs normal hippocampal function and connectivity in various mammalian species, including humans and rodents. According to the 'cumulative model' the number of early adversities can be summed up to determine the risk for developing psychopathology later in life. In contrast, the 'dimensional model' argues that 'Deprivation' and 'Threat' impact different developmental processes that should not be added in determining clinical outcomes. Here we examine these predictions in male and female mice exposed to a single adversity - limited bedding (LB) - versus mice exposed to multiple adversities - unpredictable postnatal stress (UPS) - focusing on microglia-mediated synaptic pruning in the developing hippocampus. Exposure to both LB and UPS reduced the ramification of microglia, impaired their ability to phagocytose synaptic material in vivo and ex vivo, and decreased expression of TREM2. Abnormal phagocytic activity was associated with increased spine density in CA1 pyramidal neurons that was seen in 17-day-old groups and persisted in peri-pubescent 29-day-old LB and UPS mice. Exposure to LB caused more severe impairment in microglial ramification and synaptic engulfment compared to UPS, outcomes that were accompanied by a UPS-specific increase in the expression of several genes implicated in synaptic pruning. We propose that despite being a single stressor, LB represents a more severe form of early deprivation, and that appropriate levels of hippocampal stimulation during the second and third weeks of life are necessary to support normal microglial ramification and synaptic pruning. Further, impaired synaptic pruning during this critical period of hippocampal development contributes to the abnormal hippocampal function and connectivity seen in UPS and LB later in life.

Early adversity can change educational, cognitive, and mental health outcomes. However, the neural processes through which early adversity exerts these effects remain largely unknown. We used generative network modelling of the mouse connectome to test whether unpredictable postnatal stress shifts the constraints that govern the formation of the structural connectome. A model that trades off the wiring cost of long-distance connections with topological homophily (i.e. links between regions with shared neighbours) generated simulations that replicate the organisation of the rodent connectome. The imposition of early life adversity significantly shifted the best-performing parameter combinations toward zero, heightening the stochastic nature of the generative process. Put simply, unpredictable postnatal stress changes the economic constraints that shape network formation, introducing greater randomness into the structural development of the brain. While this change may constrain the development of cognitive abilities, it could also reflect an adaptive mechanism. In other words, neural development could harness heightened stochasticity to make networks more robust to perturbation, thereby facilitating effective responses to future threats and challenges.Significance statementChildren who experience adversity early in life – such as chronic poverty or abuse – show numerous neural differences that are linked to poorer cognition and mental health later in life. To effectively mitigate the burden of adversity, it is critical to identify how these differences arise. In this paper, we use computational modelling to test whether growing up in an impoverished and unpredictable environment changes the development of structural connections in the mouse brain. We found that early adversity appears to introduce more stochasticity in the formation of neural architecture. Our findings point to a potential mechanism for how early adversity could change the course of child development.

Early adversity (EA) impairs myelin development in a manner that persists later in life across diverse mammalian species including humans, non-human primates, and rodents. These observations, coupled with the highly conserved nature of myelin development suggest that animal models can provide important insights into the molecular mechanisms by which EA impairs myelin development later in life and the impact of these changes on network connectivity, cognition, and behavior. However, this area of translational research has received relatively little attention and no comprehensive review is currently available to address these issues. This is particularly important given some recent mechanistic studies in rodents and the availability of new agents to increase myelination. The goals of this review are to highlight the need for additional pre-clinical work in this area and to provide specific examples that demonstrate the potential of this work to generate novel therapeutic interventions that are highly needed.

Translational work in rodents elucidates basic mechanisms that drive complex behaviors relevant to psychiatric and neurological conditions. Nonetheless, numerous promising studies in rodents later fail in clinical trials, highlighting the need for improving the translational utility of preclinical studies in rodents. Imaging of small rodents provides an important strategy to address this challenge, as it enables a whole-brain unbiased search for structural and dynamic changes that can be directly compared to human imaging. The functional significance of structural changes identified using imaging can then be further investigated using molecular and genetic tools available for the mouse. Here, we describe a pipeline for unbiased search and characterization of structural changes and network properties, based on diffusion MRI data covering the entire mouse brain at an isotropic resolution of 100 µm. We first used unbiased whole-brain voxel-based analyses to identify volumetric and microstructural alterations in the brain of adult mice exposed to unpredictable postnatal stress (UPS), which is a mouse model of complex early life stress (ELS). Brain regions showing structural abnormalities were used as nodes to generate a grid for assessing structural connectivity and network properties based on graph theory. The technique described here can be broadly applied to understand brain connectivity in other mouse models of human disorders, as well as in genetically modified mouse strains. Graphic abstract

Large number of promising preclinical psychiatric studies in rodents later fail in clinical trials, raising concerns about the efficacy of this approach to generate novel pharmacological interventions. In this mini-review we argue that over-reliance on behavioral tests that are brief and highly sensitive to external factors play a critical role in this failure and propose that automated home-cage monitoring offers several advantages that will increase the translational utility of preclinical psychiatric research in rodents. We describe three of the most commonly used approaches for automated home cage monitoring in rodents [e.g., operant wall systems (OWS), computerized visual systems (CVS), and automatic motion sensors (AMS)] and review several commercially available systems that integrate the different approaches. Specific examples that demonstrate the advantages of automated home-cage monitoring over traditional tests of anxiety, depression, cognition, and addiction-like behaviors are highlighted. We conclude with recommendations on how to further expand this promising line of preclinical research.

The mechanisms by which childhood maltreatment increases anxiety is unclear, but a propensity for increased defensive behavior in rodent models of early life stress (ELS) suggests that work in rodents may clarify important mechanistic details about this association. A key challenge in studying the effects of ELS on defensive behavior in rodents is the plethora of inconsistent results. This is particularly prominent with the maternal separation (MS) literature, one of the most commonly used ELS models in rodents. To address this issue we conducted a systematic review and meta-analysis, examining the effects of MS on exploratory-defensive behavior in mice and rats using the open field test (OFT) and the elevated plus maze (EPM). This search yielded a total of 49 studies, 24 assessing the effect of MS on behavior in the EPM, 11 tested behavior in the OFT, and 14 studies provided data on both tasks. MS was associated with increased defensive behavior in rats (EPM: Hedge’s g = −0.48, p = 0.02; OFT: Hedge’s g = −0.33, p = 0.05), effect sizes that are consistent with the anxiogenic effect of early adversity reported in humans. In contrast, MS did not alter exploratory behavior in mice (EPM: Hedge’s g = −0.04, p = 0.75; OFT: Hedge’s g = −0.03, p = 0.8). There was a considerable amount of heterogeneity between studies likely related to the lack of standardization of the MS protocol. Together, these findings suggest important differences in the ability of MS to alter circuits that regulate defensive behaviors in mice and rats.

The mechanisms by which childhood maltreatment increases anxiety is unclear, but a propensity for increased defensive behavior in rodent models of early life stress (ELS) suggests that work in rodents may clarify important mechanistic details about this association. A key challenge in studying the effects of ELS on defensive behavior in rodents is the plethora of inconsistent results. This is particularly prominent with the maternal separation (MS) literature, one of the most commonly used ELS models in rodents. To address this issue we conducted a systematic review and meta-analysis, examining the effects of MS on exploratory-defensive behavior in mice and rats using the open field test (OFT) and the elevated plus maze (EPM). This search yielded a total of 49 studies, 24 assessing the effect of MS on behavior in the EPM, 11 tested behavior in the OFT, and 14 studies provided data on both tasks. MS was associated with increased defensive behavior in rats (EPM: Hedge’s g = −0.48, p = 0.02; OFT: Hedge’s g = −0.33, p = 0.05), effect sizes that are consistent with the anxiogenic effect of early adversity reported in humans. In contrast, MS did not alter exploratory behavior in mice (EPM: Hedge’s g = −0.04, p = 0.75; OFT: Hedge’s g = −0.03, p = 0.8). There was a considerable amount of heterogeneity between studies likely related to the lack of standardization of the MS protocol. Together, these findings suggest important differences in the ability of MS to alter circuits that regulate defensive behaviors in mice and rats.

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 and their possible contribution to specific developmental and behavioral abnormalities seen in BDS mice and in other animal models of ELS. The possible utility of these findings for developing novel PET imaging to assess microglial function in individuals exposed to childhood maltreatment is also discussed.

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.

Childhood maltreatment (CM) is a heterogeneous group of childhood adversities that can range from different forms of abuse (physical, sexual, emotional) or neglect (physical, emotional, cognitive), to severe bullying by peers. With an annual estimated cost of $500 billion in the United States alone, CM is recognized as one of the most significant risk factors for a range of psychiatric and medical conditions (White and Kaffman, 2019). Further, rates of numerous psychiatric, neurological, and medical conditions differ significantly between males and females (Gillies and McArthur, 2010), inspiring decades of research on how sex moderates consequences of CM (Gershon et al., 2008). Although vulnerability to CM has been reported to vary by sex, very few findings have been consistent across studies. Moreover, most work to date has focused on how sex alters the frequencies of different psychopathologies in maltreated individuals, with little attention to whether different developmental processes may underlie these psychopathologies in males and females (White and Kaffman, 2019). The primary goal of this editorial was to advocate for more effective research strategies to address these questions. We first examine the rationale for studying sex as an important moderator of consequences of CM, briefly summarize some of the most consistent clinical findings, and discuss the implications of sex in treatment response. We then highlight important obstacles that contribute to the large number of inconsistent findings and make five recommendations on how to move forward.

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.

International audience; Children exposed to abuse or neglect show abnormal hippocampal development and similar findings have been reported in rodent models. Using brief daily separation (BDS), a mouse model of early life stress, we previously showed that exposure to BDS impairs hippocampal function in adulthood and perturbs synaptic maturation, synaptic pruning, axonal growth and myelination in the developing hippocampus. Given that microglia are involved in these developmental processes, we tested whether BDS impairs microglial activity in the hippocampus of 14 (during BDS) and 28-day old mice (one week after BDS). We found that BDS increased the density and altered the morphology of microglia in the hippocampus of 14-day old pups, effects that were no longer present on postnatal day (PND) 28. Despite the normal cell number and morphology seen at PND28, the molecular signature of hippocampal microglia, assessed using the NanoString immune panel, was altered at both ages. We showed that during normal hippocampal development, microglia undergo significant changes between PND14 and PND28, including reduced cell density, decreased ex vivo phagocytic activity, and an increase in the expression of genes involved in inflammation and cell migration. However, microglia harvested from the hippocampus of 28-day old BDS mice showed an increase in phagocytic activity and reduced expression of genes that normally increase across development. Promoter analysis indicated that alteration in the transcriptional activity of PU.1, Creb1, Sp1, and RelA accounted for most of the transcriptional changes seen during normal microglia development and for most of the BDS-induced changes at PND14 and PND28. These findings are the first to demonstrate that early life stress dysregulates microglial function in the developing hippocampus and to identify key transcription factors that are likely to mediate these changes.

Childhood maltreatment represents a major risk factor for the development of numerous childhood psychopathologies that in many cases linger as chronic mental illnesses in adulthood. Exposing rodents or non-human primates to early life stress increases anxiety-like behaviors and impairs cognitive function in adulthood, suggesting that animal models may provide important insights into parallel developmental processes in humans. Using an unbiased genomic screen, we found that expression of lipopolysaccharide binding protein (LBP), a member of the innate immune system, is dramatically decreased in the hippocampus of pups exposed to early life stress. LBP levels peak in the normally developing hippocampus at a period of intense synaptic pruning, during which LBP is colocalized with the synaptic marker PSD95 and is found in close proximity to processes of microglia cells. Expression of LBP declines to low levels seen in adulthood at around postnatal day 30. Importantly, 30-day-old LBP knockout (k.o.) mice show increased spine density and abnormal spine morphology, suggesting that peak levels of LBP during the second and third weeks of life are necessary for normal synaptic pruning in the hippocampus. Finally, LBP k.o. mice show impaired hippocampal-dependent memory and increased anxiety-like behaviors in a manner that resembles that seen in animals exposed to early life stress. These findings describe a novel role for LBP in normal hippocampal development and raise the possibility that at least some of the behavioral sequelae of early life stress are mediated by reduced expression of LBP during a critical period of neurodevelopment.

Recent studies have indicated a gene by environment interaction between serotonin transporter gene (5-HTTLPR) polymorphism and childhood abuse on depressive symptoms. In addition, persistent elevation of cerebrospinal fluid (CSF) corticotropin-releasing factor (CRF) concentrations following early-life adversity has been posited to underlie the subsequent development of major depression. This pilot study tested the hypothesis that elevations of juvenile CSF CRF concentrations are, in part, determined by an interaction between polymorphisms of the 5-HTTLPR and early-life stress. Nine juvenile male bonnet macaques (Macaca radiata) had been raised under variable foraging demand (VFD) conditions, a nonhuman primate model of early-life stress, whereas nine subjects were normatively raised under LFD (low foraging demand) conditions. Genotyping revealed that four (44.4%) of the VFD-reared monkeys possessed at least one “s” allele whereas five VFD monkeys were of the l/l genotype. Of the nine LFD subjects, two (22%) had the s/l genotype and seven had the l/l genotype. A “juvenile” CSF sample was obtained at approximately three years of age. CSF CRF concentrations were elevated specifically in the VFD “s/s” and “s/l” allele group in comparison to each of the remaining three groups, indicating a gene by environment (GxE) interaction.

Parental care plays an important role in the emotional and cognitive development of the offspring. Children who have been exposed to abuse or neglect are more likely to develop numerous psychopathologies, while good parent-infant bonding is associated with improved resiliency to stress. Similar observations have also been reported in non-human primates and rodents, suggesting that at least some neurodevelopmental aspects of parent-offspring interactions are conserved among mammals and could therefore be studied in animals. We present data to suggest that frequency of licking and grooming provided by the dam during a critical period in development plays an important role in modifying neurodevelopment. These findings are examined in the broader context in which exposure to other sensory modalities such as vision or hearing during a specific period in development shapes brain development with functional consequences that persist into adulthood. We also discuss recent rodent work showing that increased frequency of licking and grooming provided by the dam during the first week of life is associated with changes in DNA methylation of promoter elements that control expression of these genes and behavior. The stability of DNA methylation in postmitotic cells provides a possible molecular scaffold by which changes in gene expression and behavioral traits induced by postnatal maternal care are maintained throughout life. Finally, the relevance of findings reported in rodents to those noted in non-human primates and humans are assessed and the research and clinical implicathose noted in non-human primates and humans are tions of these observations for future work are explored.

Early life stress is thought to contribute to psychiatric disorders, but the precise mechanisms underlying this link are poorly understood. As neonatal stress decreases adult hippocampal neurogenesis, which, in turn, functionally contributes to many behavioral phenotypes relevant to psychiatric disorders, we examined how in vivo neonatal maternal separation (NMS) impacts the capacity of adult hippocampal neural precursor cells via epigenetic alterations in vitro.Rat pups were separated from their dams for 3 hours daily from postnatal day (PND) 2 to PND 14 or were never separated from the dam (as control animals). We isolated adult neural precursor cells from the hippocampal dentate gyrus at PND 56 and assessed rates of proliferation, apoptosis, and differentiation in cell culture. We also evaluated the effect of DNA methylation at the retinoic acid receptor (RAR) promoter stemming from NMS on adult neural precursor cells.NMS attenuated neural differentiation of adult neural precursor cells but had no detectible effect on proliferation, apoptosis, or astroglial differentiation. The DNA methyltransferase (DNMT) inhibitor, 5-aza-dC, reversed a reduction by NMS of neural differentiation of adult neural precursor cells. NMS increased DNMT1 expression and decreased expression of RARα. An RARα agonist increased neural differentiation and an antagonist reduced retinoic acid-induced neural differentiation. NMS increased the methylated portion of RARα promoter, and the DNMT inhibitor reversed a reduction by NMS of RARα messenger RNA expression.NMS attenuates the capacity of adult hippocampal neural precursor cells to differentiate into neurons by decreasing expression of RARα through DNMT1-mediated methylation of its promoter.

Background: Early life stress (ELS) is cited as a risk for mood and anxiety disorders, potentially through altered serotonin neurotransmission. We examined the effects of ELS, utilizing the variable foraging demand (VFD) macaque model, on adolescent monoamine metabolites. We sought to replicate an increase in cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) observed in two previous VFD cohorts. We hypothesized that elevated cisternal 5-HIAA was associated with reduced neurotrophic effects , conceivably due to excessive negative feedback at somatodendritic 5-HT1A autoreceptors. A putatively decreased serotonin neurotransmission would be reflected by reductions in hippocampal volume and white matter (WM) fractional anisotropy (FA). Methods: When infants were 2-6 months of age, bonnet macaque mothers were exposed to VFD. We employed cisternal CSF taps to measure monoamine metabolites in VFD (N = 22) and non-VFD (N = 14) offspring (mean age = 2.61 years). Metabolites were correlated with hippocampal volume obtained by MRI and WM FA by diffusion tensor imaging in young adulthood in 17 males [10 VFD (mean age = 4.57 years)].Results: VFD subjects exhibited increased CSF 5-HIAA compared to non-VFD controls. An inverse correlation between right hippocampal volume and 5-HIAA was noted in VFD- but not controls. CSF HVA and MHPG correlated inversely with hippocampal volume only in VFD. CSF 5-HIAA correlated inversely with FA of the WM tracts of the anterior limb of the internal capsule (ALIC) only in VFD. Conclusions: Elevated cisternal 5-HIAA in VFD may reflect increased dorsal raphe serotonin, potentially inducing excessive autoreceptor activation, inducing a putative serotonin deficit in terminal fields. Resultant reductions in neurotrophic activity are reflected by smaller right hippocampal volume. Convergent evidence of reduced neurotrophic activity in association with high CSF 5-HIAA in VFD was reflected by reduced FA of the ALIC.

Children that are exposed to abuse or neglect show abnormal hippocampal function. However, the developmental mechanisms by which early life stress (ELS) impairs normal hippocampal development have not been elucidated. Here we propose that exposure to ELS blunts normal hippocampal growth by inhibiting the availability of ribosomal RNA (rRNA). In support of this hypothesis, we show that the normal mouse hippocampus undergoes a growth-spurt during the second week of life, followed by a gradual decrease in DNA and RNA content that persists into adulthood. This developmental pattern is associated with accelerated ribosomal RNA (rRNA) synthesis during the second week of life, followed by a gradual decline in rRNA levels that continue into adulthood. Levels of DNA methylation at the ribosomal DNA (rDNA) promoter are lower during the second week of life compared to earlier development or adulthood. Exposure to brief daily separation (BDS), a mouse model of early life stress, increased DNA methylation at the ribosomal DNA promoter, decreased rRNA levels, and blunted hippocampal growth during the second week of life. Exposure to acute (3 hrs) maternal separation decreased rRNA and increased DNA methylation at the rDNA proximal promoter, suggesting that exposure to stress early in life can rapidly regulate the availability of rRNA levels in the developing hippocampus. Given the critical role that rRNA plays in supporting normal growth and development, these findings suggest a novel molecular mechanism to explain how stress early in life impairs hippocampus development in the mouse.

National Institute for Mental Health NIMH NARSAD Mid-investigator Award Background: Children exposed to early life stress (ELS) exhibit enlarged amygdala volume in comparison to controls. the primary goal of this study was to examine amygdala volumes in bonnet macaques subjected to maternal variable foraging demand (VFD) rearing, a well-established model of ELS. Preliminary analyses examined the interaction of ELS and the serotonin transporter gene on amygdala volume. Secondary analyses were conducted to examine the association between amygdala volume and other stress-related variables previously found to distinguish VFD and non-VFD reared animals.Methods: Twelve VFD-reared and nine normally reared monkeys completed MRI scans on a 3T system (mean age = 5.2 years).Results: Left amygdala volume was larger in VFD vs. control macaques. Larger amygdala volume was associated with: high cerebrospinal fluid concentrations of corticotropin releasing-factor (CRF) determined when the animals were in adolescence (mean age = 2.7 years); reduced fractional anisotropy (FA) of the anterior limb of the internal capsule (ALIC) during young adulthood (mean age = 5.2 years) and timid anxiety-like responses to an intruder during full adulthood (mean age = 8.4 years). Right amygdala volume varied inversely with left hippocampal neurogenesis assessed in late adulthood (mean age = 8.7 years). Exploratory analyses also showed a gene-by-environment effect, with VFD-reared macaques with a single short allele of the serotonin transporter gene exhibiting larger amygdala volume compared to VFD-reared subjects with only the long allele and normally reared controls.Conclusion: These data suggest that the left amygdala exhibits hypertrophy after ELS, particularly in association with the serotonin transporter gene, and that amygdala volume variation occurs in concert with other key stress-related behavioral and neurobiological parameters observed across the lifecycle. Future research is required to understand the mechanisms underlying these diverse and persistent changes associated with ELS and amygdala volume. Suny Downstate Med Ctr, Dept Psychiat & Behav Sci, Brooklyn, NY 11203 USA Universidade Federal de São Paulo, Dept Psiquiatria, São Paulo, Brazil Mt Sinai Sch Med, Dept Psychiat, New York, NY USA Mt Sinai Sch Med, Dept Neurosci, New York, NY USA Mt Sinai Sch Med, Dept Radiol, New York, NY USA New York State Psychiat Inst & Hosp, New York, NY 10032 USA Michael E Debakey VA Med Ctr, Mental Hlth Care Line, Houston, TX USA Baylor Coll Med, Menninger Dept Psychiat & Behav Sci, Houston, TX 77030 USA Yale Univ, Sch Med, Dept Psychiat, New Haven, CT USA Natl Ctr PTSD, Clin Neurosci Div, West Haven, CT USA New York State Psychiat Inst & Hosp, Dept Mol Imaging & Neuropathol, New York, NY 10032 USA Columbia Univ, Coll Phys & Surg, Dept Psychiat, New York, NY USA Columbia Univ, Coll Phys & Surg, Dept Pathol & Cell Biol, New York, NY USA Comprehensive NeuroSci Corp, Westchester, NY USA Univ Miami Hlth Sytems, Dept Psychiat & Behav Sci, Miami, FL USA Emory Univ, Sch Med, Dept Psychiat & Behav Sci, Emory, GA USA Universidade Federal de São Paulo, Dept Psiquiatria, São Paulo, Brazil National Institute for Mental Health: R01MH65519-01 National Institute for Mental Health: R01MH098073 NIMH: R21MH066748 NIMH: R01MH59990A Web of Science

The movement of many transcription factors, kinases and replication factors between the nucleus and cytoplasm is important in regulating their activity1. In some cases, phosphorylation of a protein regulates its entry into the nucleus2; in others, it causes the protein to be exported to the cytoplasm3,4,5,6. The mechanism by which phosphorylation promotes protein export from the nucleus is poorly understood. Here we investigate how the export of the yeast transcription factor Pho4 is regulated in response to changes in phosphate availability. We show that phosphorylation of Pho4 by a nuclear complex of a cyclin with a cyclin-dependent kinase, Pho80–Pho85, triggers its export from the nucleus. We also find that the shuttling receptor used by Pho4 for nuclear export is the importin-β-family member Msn5 (refs 7, 8), which is required for nuclear export of Pho4 in vivo and binds only to phosphorylated Pho4 in the presence of the GTP-bound form of yeast Ran in vitro. Our results reveal a simple mechanism by which phosphorylation can control the nuclear export of a protein.

PHO4, a transcription factor required for induction of the PHO5 gene in response to phosphate starvation, is phosphorylated by the PHO80-PHO85 cyclin-CDK (cyclin-dependent kinase) complex when yeast are grown in phosphate-rich medium. PHO4 was shown to be concentrated in the nucleus when yeast were starved for phosphate and was predominantly cytoplasmic when yeast were grown in phosphate-rich medium. The sites of phosphorylation on PHO4 were identified, and phosphorylation was shown to be required for full repression of PHO5 transcription when yeast were grown in high phosphate. Thus, phosphorylation of PHO4 by PHO80-PHO85 turns off PHO5 transcription by regulating the nuclear localization of PHO4.

Alterations in neurodevelopment are thought to modify risk of numerous psychiatric disorders, including schizophrenia, autism, ADHD, mood and anxiety disorders, and substance abuse. However, little is known about the cellular and molecular changes that guide these neurodevelopmental changes and how they contribute to mental illness. In this review, we suggest that elucidating this process in humans requires the use of model organisms. Furthermore, we advocate that such translational work should focus on the role that genes and/or environmental factors play in the development of circuits that regulate specific physiological and behavioral outcomes in adulthood. This emphasis on circuit development, as a fundamental unit for understanding behavior, is distinct from current approaches of modeling psychiatric illnesses in animals in two important ways. First, it proposes to replace the diagnostic and statistical manual of mental disorders (DSM) diagnostic system with measurable endophenotypes as the basis for modeling human psychopathology in animals. We argue that a major difficulty in establishing valid animal models lies in their reliance on the DSM/International Classification of Diseases conceptual framework, and suggest that the Research Domain Criteria project, recently proposed by the NIMH, provides a more suitable system to model human psychopathology in animals. Second, this proposal emphasizes the developmental origin of many (though clearly not all) psychiatric illnesses, an issue that is often glossed over in current animal models of mental illness. We suggest that animal models are essential to elucidate the mechanisms by which neurodevelopmental changes program complex behavior in adulthood. A better understanding of this issue, in animals, is the key for defining human psychopathology, and the development of earlier and more effective interventions for mental illness.

The capacity to interact with conspecifics is essential for stable social networks, reproduction, and survival in mammals. In rodents, social exploration and play behavior increase during the juvenile period, suggesting that this timeframe represents an important window for socialization. However, the cellular and molecular mechanisms necessary to support this developmental process have not been elucidated. Neurogenesis during the juvenile period, like that in adults, is mainly confined to the subgranular and subventricular zones. Nevertheless, the levels of neurogenesis are significantly higher during the juvenile period, suggesting unique functions not shared with adult neurogenesis. Here we use a transgenic mouse approach that allows for ablation of neurogenesis during different developmental phases. We find that ablating neurogenesis during either juvenile or adult phases altered anxiety and memory in adult female mice, demonstrating an age-independent function of new neurons for certain behaviors. Blocking neurogenesis during the juvenile period resulted in a profound impairment in the ability of these mice to interact with other adult females or to retrieve pups, without causing gross olfactory deficits. Interestingly, ablating neurogenesis in adult females had no effect on these social behaviors. This work defines a novel role for juvenile neurogenesis in establishing brain circuits necessary for socialization, and demonstrates that juvenile and adult neurogenesis make different contributions to social competency in adult female mice. Additional work is needed to determine whether ablation of juvenile neurogenesis in the subgranular zone and/or the subventricular zone is responsible for the social abnormalities seen after global elimination of juvenile neurogenesis.

Deep brain stimulation (DBS) of the anterior limb of the internal capsule (ALIC) may be effective in treating depression. Parental verbal abuse has been linked to decreased fractional anisotropy (FA) of white matter and reduced FA correlated with depression and anxiety scores. Utilizing a nonhuman primate model of mood and anxiety disorders following disrupted mother-infant attachment, we examined whether adverse rearing conditions lead to white matter impairment of the ALIC. We examined white matter integrity using Diffusion Tensor Imaging (DTI) on a 3T-MRI. Twenty-one adult male Bonnet macaques participated in this study: 12 were reared under adverse [variable foraging demand (VFD)] conditions whereas 9 were reared under normative conditions. We examined ALIC, posterior limb of the internal capsule (PLIC) and occipital white matter. VFD rearing was associated with significant reductions in FA in the ALIC with no changes evident in the PLIC or occipital cortex white matter. Adverse rearing in monkeys persistently impaired frontal white matter tract integrity, a novel substrate for understanding affective susceptibility.

To the Editor: Munafo et al. (1) conducted a meta-analysis of a subset of studies that examined the interaction between the serotonin transporter (5-HTTLPR) gene and stressful life events (SLEs) in conferring risk for depression. 5-HTTLPR has two common alleles of varying length, which are designated “s” for short and “l” for long. They concluded that the prior “positive results for the 5-HTTLPR × SLE interactions in logistic regression models are compatible with chance findings” and stated further that “the 5-HTTLPR and SLE interaction effect is negligible.” These conclusions, however, were based on assumptions in the simulation model that are inconsistent with prior research findings and a bias in sampling strategy that call into question the authors’ conclusions. In the simulation reported in the Munafo article, the environmental effect was specified as having two levels—unexposed (E1) and exposed (E2)—corresponding to zero and one + SLE. As can be seen in Figure 1, in the original report by Caspi et al. (2) the presence of only one SLE conferred no risk for depression, regardless of genotype. Risk for depression in association with the “s” allele of 5-HTTLPR only began to increase significantly in the presence of three or more SLEs and was most pronounced in individuals with four or more SLEs. Collapsing subjects across the various levels of exposure to SLEs added significant noise in the model and compromised efforts to detect the 5-HTTLPR × SLE interaction in the meta-analysis. Figure 1 Results of multiple regression analyses estimating the association between number of stressful life events (between ages 21 years and 26 years) and the probability of major depressive disorder by age 26 as a function of serotonin transporter protein genotype. ... The nonrepresentative nature of the sample of studies included in the meta-analysis is also a limitation of this report. Munafo et al. identified 14 studies of 33 published reports that met their criteria for inclusion in the meta-analysis but were unfortunately only able to obtain data from 5 of the 14 studies. The meta-analysis was conducted with data from less than one-half the studies that met the stated inclusion criteria, with a trend for negative studies to be over-represented in the meta-analysis. Of the 14 studies meeting the inclusion criteria for the meta-analysis, 75% (3/4) of the negative studies and only 20% (2/10) of the positive studies were included in the analysis (Fisher exact test: p < .10). There has been a proliferation of studies examining this gene × environment interaction over the past 2 years and, to date, no comprehensive meta-analysis of all studies. Since the publication of the article by Munafo et al., a second meta-analysis was published that similarly concluded that there is no evidence that the serotonin transporter genotype alone or in interaction with SLEs is associated with an elevated risk for depression (3). Although a larger number of studies were included in the second meta-analysis, 12 studies were published after the dataset for this second meta-analysis was closed, with only 3 of the 12 studies including adequate data in the published reports to be examined in the second meta-analysis (K.R. Merikangas, written communication, July 2009). Seven of the nine studies excluded because they were published after the dataset was closed were full or partial replications (4–10), as were four other earlier studies that were not included in the second meta-analysis because the data were either not received or received in an incompatible format (11–14). Like the publication by Munafo et al., the second meta-analysis also included an excess representation of nonreplications. It was conducted with data from one-half of the 26 studies that met the inclusion criteria for the meta-analysis (3), with a trend again for negative studies to be over-represented. Of the 26 studies meeting the inclusion criteria for the second meta-analysis, 78% (7/9) of the negative studies and only 35% (6/17) of the positive studies were included in the analysis (Fisher exact test: p < .10). Most studies in the literature (17/26) have replicated in part or fully the finding that individuals with the “s” allele of 5-HTTLPR are at higher risk for depression after exposure to multiple SLEs or experiences of child maltreatment, but to date a comprehensive meta-analysis of published results has not been completed. The serotonin transporter is a protein critical to the regulation of serotonin levels in the brain, on the basis of its ability to remove serotonin from the synapse and terminate its action. Serotonin transporter protein (5-HTT) knockout mice show stress-induced anxious- and depressive-like behaviors and increased dendritic spine density in the amygdala (15). This latter finding is interesting in light of the fact that the “s” allele of 5-HTTLPR has been associated with increased amygdala activation to negative stimuli in multiple imaging genomic studies (16). In experimental stress-induction paradigms, the “s” allele of 5-HTTLPR has also been associated with increased hypothalamic pituitary adrenal axis activity in both humans (17) and nonhuman primates (18) and heightened brain activity in stress-responsive brain regions (19). A comprehensive meta-analysis is required to determine the strength of the 5-HTTLPR × SLE interaction in conferring risk for depression. In addition, we believe more work is needed to unravel the mechanisms by which stress might confer vulnerability to depression in individuals with the “s” allele of 5-HTTLPR, to further characterize allelic variants of this gene, and identify additional genetic (e.g., BDNF) and environmental (e.g., social supports) factors that can modify the magnitude of the 5-HTTLPR × SLE interaction.

Male bonnet monkeys (Macaca radiata) were subjected to the variable foraging demand (VFD) early stress paradigm as infants, MRI scans were completed an average of 4 years later, and behavioral assessments of anxiety and ex-vivo corpus callosum (CC) measurements were made when animals were fully matured. VFD rearing was associated with smaller CC size, CC measurements were found to correlate with fearful behavior in adulthood, and ex-vivo CC assessments showed high consistency with earlier MRI measures. Region of interest (ROI) hippocampus and whole brain voxel-based morphometry assessments were also completed and VFD rearing was associated with reduced hippocampus and inferior and middle temporal gyri volumes. The animals were also characterized according to serotonin transporter genotype (5-HTTLPR), and the effect of genotype on imaging parameters was explored. The current findings highlight the importance of future research to better understand the effects of stress on brain development in multiple regions, including the corpus callosum, hippocampus, and other regions involved in emotion processing. Nonhuman primates provide a powerful model to unravel the mechanisms by which early stress and genetic makeup interact to produce long-term changes in brain development, stress reactivity, and risk for psychiatric disorders.

A better understanding of the molecular and cellular mechanisms by which early life stress (ELS) modifies brain development and adult behavior is necessary for diagnosing and treating psychopathology associated with exposure to ELS. For historical reasons most of the work in rodents has been done in rats and attempts to establish robust and reproducible paradigms in the mouse have proven to be challenging. Here we show that under normal rearing conditions, increased levels of postnatal maternal care are associated with a decrease in anxiety-like behavior in BALB/cByj offspring. Brief daily pup-dam separation (BDS) during the postnatal period was associated with increased postnatal maternal care but was surprisingly associated with increased anxiety-like behavior in adult offspring, providing the first example in which offspring receiving higher levels of postnatal maternal care are more anxious in adulthood. Plasma corticosterone levels were elevated in BDS pups even three hours after the pups were reunited with the dam, suggesting that this paradigm represents a form of early life stress. We also show that levels of total RNA and DNA in the hippocampus reach a peak at postnatal day 14 and that exposure to BDS seems to inhibit this developmental growth spurt. We propose that exposure to stress during the postnatal period overrides the ability of high levels of postnatal maternal care to program anxiety-like behavior by inhibiting the normal growth spurt that characterizes this period.

Childhood maltreatment in the United States was recently recognized as a major public health problem by several influential sources including the World Health Organization and the Institute of Medicine (1,2). An extensive survey conducted by the National Incidence of Child Abuse and Neglect (NIS3) revealed that roughly 1.5 million children were abused or neglected in 1993. This number of documented cases most likely underestimates the true prevalence, given that many cases of maltreatment go unrecognized (2). Moreover, according to the three available NIS reports, the incidence of childhood maltreatment has been steadily increasing over the past 3 decades (see also NIS4 for a good summary of this issue). Although increased reporting might explain some of the data, it is unlikely to explain this alarming trend fully (3). In the absence of effective interventions, maltreated children go on to develop a host of behavioral, emotional, cognitive, and medical sequelae that are chronic and in many cases refractory to treatment (2,4–6). The relationship between early life adversity (ELA) and mental illness has now been documented with both retrospective and prospective studies (reviewed in [2]), and several reports have consistently documented that more than one-half (!) of the individuals with chronic mental illness have been physically, verbally, or sexually abused early in life (7,8). Although most clinicians and researchers will endorse the notion that ELA is associated with increased risk for chronic mental illness, few appreciate the true magnitude of this problem. Better awareness of the burden that exposure to ELA places on adult psychiatric services represents the first step necessary towards transforming current psychiatric interventions. This paradigm shift should substitute the current focus on symptom-reduction with one that focuses on prevention and incorporates a neurodevelopmental framework to diagnose and treat ELA-associated psychopathology. These interventions will require a sound biological understanding of normal neurodevelopment and how ELA interferes with this process.

▪ Abstract Information can be transferred between the nucleus and the cytoplasm by translocating macromolecules across the nuclear envelope. Communication of extracellular or intracellular changes to the nucleus frequently leads to a transcriptional response that allows cells to survive in a continuously changing environment. Eukaryotic cells have evolved ways to regulate this movement of macromolecules between the cytoplasm and the nucleus such that the transfer of information occurs only under conditions in which a transcriptional response is required. This review focuses on the ways in which cells regulate movement of proteins across the nuclear envelope and the significance of this regulation for controlling diverse biological processes.

The transcription factor Pho4 is phosphorylated and localized predominantly to the cytoplasm when budding yeast are grown in phosphate-rich medium and is unphosphorylated and localized to the nucleus upon phosphate starvation. We have investigated the requirements for nuclear import of Pho4 and find that Pho4 enters the nucleus via a nonclassical import pathway that utilizes the importin β family member Pse1/Kap121. Pse1 binds directly to Pho4 and is required for its import in vivo. We have defined the nuclear localization signal on Pho4 and demonstrate that it is required for Pse1 binding in vitro and is sufficient for PSE1-dependent import in vivo. Phosphorylation of Pho4 inhibits its interaction with Pse1, providing a mechanism by which phosphorylation may regulate import of Pho4 in vivo.

Induction of the yeast gene PHO5 is mediated by the transcription factors PHO2 and PHO4. PHO5 transcription is not detectable in high phosphate; it is thought that the negative regulators PHO80 and PHO85 inactivate PHO2 and PHO4. Here it is reported that PHO80 has homology to yeast cyclins and interacts with PHO85, a p34cdc2/CDC28-related protein kinase. The PHO80-PHO85 complex phosphorylates PHO4; this phosphorylation is correlated with negative regulation of PHO5. These results demonstrate the existence of a cyclin-cdk complex that is used for a regulatory process other than cell-cycle control and identify a physiologically relevant substrate for this complex.