Animal models of early life stress: implications for understanding resilience

Enhancing translation: A need to leverage complex preclinical models of addictive drugs to accelerate substance use treatment options

Preclinical models of addictive drugs have been developed for decades to model aspects of the clinical experience in substance use disorders (SUDs). These include passive exposure as well as volitional intake models across addictive drugs and have been utilized to also measure withdrawal symptomatology and potential neurobehavioral mechanisms underlying relapse to drug seeking or taking. There are a number of Food and Drug Administration (FDA)-approved medications for SUDs, however, many demonstrate low clinical efficacy as well as potential sex differences, and we also note gaps in the continuum of care for certain aspects of clinical experiences in individuals who use drugs. In this review, we provide a comprehensive update on both frequently utilized and novel behavioral models of addiction with a focus on translational value to the clinical experience and highlight the need for preclinical research to follow epidemiological trends in drug use patterns to stay abreast of clinical treatment needs. We then note areas in which models could be improved to enhance the medications development pipeline through efforts to enhance translation of preclinical models. Next, we describe neuroscience efforts that can be leveraged to identify novel biological mechanisms to enhance medications development efforts for SUDs, focusing specifically on advances in brain transcriptomics approaches that can provide comprehensive screening and identification of novel targets. Together, the confluence of this review demonstrates the need for careful selection of behavioral models and methodological parameters that better approximate the clinical experience combined with cutting edge neuroscience techniques to advance the medications development pipeline for SUDs.

Line- and sex-dependent effects of juvenile stress on contextual fear- and anxiety-related behavior in high- and low-alcohol-preferring mouse lines

Juvenile stress (JS) is a known risk factor for the development of alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD), both of which are frequently co-morbid. Data suggest there may be common, genetically-influenced biological responses to stress that contribute to the development of both AUD and PTSD. The present study investigated the impact of JS on contextual fear learning and extinction, as well as corticosterone (CORT) responses before and after JS, before and after contextual fear conditioning (CFC), and after fear extinction in male and female high-alcohol-preferring (HAP2) and low-alcohol-preferring (LAP2) mouse lines. We also measured unconditioned anxiety-related behavior in the light-dark-transition test before CFC. HAP2 and LAP2 mice did not differ in fear acquisition, but HAP2 mice showed faster fear extinction compared to LAP2 mice. No effects of JS were seen in HAP2 mice, whereas in LAP2 mice, JS reduced fear acquisition in males and facilitated fear extinction in females. Females showed greater fear-related behavior relative to males, regardless of subgroup. HAP2 males demonstrated more anxiolytic-like responses than LAP2 males and LAP2 females demonstrated more anxiolytic-like responses than LAP2 males in the light-dark transition test. HAP2 and LAP2 mice did not differ in CORT during the juvenile stage; however, adult LAP2 mice showed greater CORT levels than HAP2 mice at baseline and after CFC and extinction testing. These findings build upon prior work in these unique mouse lines that differ in genetic propensity toward alcohol preference and provide new information regarding contextual fear learning and extinction mechanisms theorized to contribute to co-morbid AUD and PTSD.

Early resource scarcity causes cortical astrocyte enlargement and sex-specific changes in the orbitofrontal cortex transcriptome in adult rats

Astrocyte morphology affects function, including the regulation of glutamatergic signaling. This morphology changes dynamically in response to the environment. However, how early life manipulations alter adult cortical astrocyte morphology is underexplored. Our lab uses brief postnatal resource scarcity, the limited bedding and nesting (LBN) manipulation, in rats. We previously found that LBN augments maternal behaviors and promotes later resilience to adult addiction-related behaviors, reducing impulsivity, risky decision-making, and morphine self-administration. These behaviors rely on glutamatergic transmission in the medial orbitofrontal (mOFC) and medial prefrontal (mPFC) cortex. Here we tested whether LBN changed astrocyte morphology in the mOFC and mPFC of adult rats using a novel viral approach that, unlike traditional markers, fully labels astrocytes. Prior exposure to LBN causes an increase in the surface area and volume of astrocytes in the mOFC and mPFC of adult males and females relative to control-raised rats. We next used bulk RNA sequencing of OFC tissue to assess transcriptional changes that could increase astrocyte size in LBN rats. LBN caused mainly sex-specific changes in differentially expressed genes. Pathway analysis revealed that OFC glutamatergic signaling is altered by LBN in males and females, but the gene changes in that pathway differed across sex. This may represent a convergent sex difference where glutamatergic signaling, which affects astrocyte morphology, is altered by LBN via sex-specific mechanisms. Collectively, these studies highlight that astrocytes may be an important cell type that mediates the effect of early resource scarcity on adult brain function.

Sex Differences in Stress Response: Classical Mechanisms and Beyond

Neuropsychiatric disorders, which are associated with stress hormone dysregulation, occur at different rates in men and women. Moreover, nowadays, preclinical and clinical evidence demonstrates that sex and gender can lead to differences in stress responses that predispose males and females to different expressions of similar pathologies. In this curated review, we focus on what is known about sex differences in classic mechanisms of stress response, such as glucocorticoid hormones and corticotrophin-releasing factor (CRF), which are components of the hypothalamicpituitary- adrenal (HPA) axis. Then, we present sex differences in neurotransmitter levels, such as serotonin, dopamine, glutamate and GABA, as well as indices of neurodegeneration, such as amyloid β and Tau. Gonadal hormone effects, such as estrogens and testosterone, are also discussed throughout the review. We also review in detail preclinical data investigating sex differences caused by recentlyrecognized regulators of stress and disease, such as the immune system, genetic and epigenetic mechanisms, as well neurosteroids. Finally, we discuss how understanding sex differences in stress responses, as well as in pharmacology, can be leveraged into novel, more efficacious therapeutics for all. Based on the supporting evidence, it is obvious that incorporating sex as a biological variable into preclinical research is imperative for the understanding and treatment of stress-related neuropsychiatric disorders, such as depression, anxiety and Alzheimer's disease.

Early resource scarcity causes cortical astrocyte enlargement and sex-specific changes in the orbitofrontal cortex transcriptome in adult rats

Astrocyte morphology affects function, including the regulation of glutamatergic signaling. This morphology changes dynamically in response to the environment. However, how early life manipulations alter adult cortical astrocyte morphology is underexplored. Our lab uses brief postnatal resource scarcity, the limited bedding and nesting (LBN) manipulation, in rats. We previously found that LBN promotes later resilience to adult addiction-related behaviors, reducing impulsivity, risky decision-making, and morphine self-administration. These behaviors rely on glutamatergic transmission in the medial orbitofrontal (mOFC) and medial prefrontal (mPFC) cortex. Here we tested whether LBN changed astrocyte morphology in the mOFC and mPFC of adult rats using a novel viral approach that, unlike traditional markers, fully labels astrocytes. Prior exposure to LBN causes an increase in the surface area and volume of astrocytes in the mOFC and mPFC of adult males and females relative to control-raised rats. We next used bulk RNA sequencing of OFC tissue to assess transcriptional changes that could increase astrocyte size in LBN rats. LBN caused mainly sex-specific changes in differentially expressed genes. However, Park7, which encodes for the protein DJ-1 that alters astrocyte morphology, was increased by LBN across sex. Pathway analysis revealed that OFC glutamatergic signaling is altered by LBN in males and females, but the gene changes in that pathway differed across sex. This may represent a convergent sex difference where glutamatergic signaling, which affects astrocyte morphology, is altered by LBN via sex-specific mechanisms. Collectively, these studies highlight that astrocytes may be an important cell type that mediates the effect of early resource scarcity on adult brain function.

Ecological validity of social defeat stressors in mouse models of vulnerability and resilience

Laboratory mouse models offer opportunities to bridge the gap between basic neuroscience and applied stress research. Here we consider the ecological validity of social defeat stressors in mouse models of emotional vulnerability and resilience. Reports identified in PubMed from 1980 to 2020 are reviewed for the ecological validity of social defeat stressors, sex of subjects, and whether results are discussed in terms of vulnerability alone, resilience alone, or both vulnerability and resilience. Most of the 318 reviewed reports (95%) focus on males, and many reports (71%) discuss vulnerability and resilience. Limited ecological validity is associated with increased vulnerability and decreased resilience. Elements of limited ecological validity include frequent and repeated exposure to defeat stressors without opportunities to avoid or escape from unfamiliar conspecifics that are pre-screened and selected for aggressive behavior. These elements ensure defeat and may be required to induce vulnerability, but they are not representative of naturalistic conditions. Research aimed at establishing causality is needed to determine whether ecologically valid stressors build resilience in both sexes of mice.

Photobiomodulation attenuates oligodendrocyte dysfunction and prevents adverse neurological consequences in a rat model of early life adversity

Rationale: Adverse experiences in early life including abuse, trauma and neglect, have been linked to poor physical and mental health outcomes. Emerging evidence implies that those who experienced early life adversity (ELA) are more likely to develop cognitive dysfunction and depressive-like symptoms in adulthood. The molecular mechanisms responsible for the negative consequences of ELA, however, remain unclear. In the absence of effective management options, anticipatory guidance is the mainstay of ELA prevention. Furthermore, there is no available treatment that prevents or alleviates the neurologic sequelae of ELA, especially traumatic stress. Hence, the present study aims to investigate the mechanisms for these associations and evaluate whether photobiomodulation (PBM), a non-invasive therapeutic procedure, can prevent the negative cognitive and behavioral manifestations of ELA in later life. Methods: ELA was induced by repeated inescapable electric foot shock of rats from postnatal day 21 to 26. On the day immediately following the last foot shock, 2-min daily PBM treatment was applied transcranially for 7 consecutive days. Cognitive dysfunction and depression-like behaviors were measured by a battery of behavioral tests in adulthood. Subsequently, oligodendrocyte progenitor cells (OPCs) differentiation, the proliferation and apoptosis of oligodendrocyte lineage cells (OLs), mature oligodendrocyte, myelinating oligodendrocyte, the level of oxidative damage, reactive oxygen species (ROS) and total antioxidant capacity were measured and analyzed using immunofluorescence staining, capillary-based immunoassay (ProteinSimple®) and antioxidant assay kit. Results: The rats exposed to ELA exhibited obvious oligodendrocyte dysfunction, including a reduction in OPCs differentiation, diminished generation and survival of OLs, decreased OLs, and decreased matured oligodendrocyte. Furthermore, a deficit in myelinating oligodendrocytes was observed, in conjunction with an imbalance in redox homeostasis and accumulated oxidative damage. These alternations were concomitant with cognitive dysfunction and depression-like behaviors. Importantly, we found that early PBM treatment largely prevented these pathologies and reversed the neurologic sequelae resulting from ELA. Conclusions: Collectively, these findings provide new insights into the mechanism by which ELA affects neurological outcomes. Moreover, our findings support that PBM may be a promising strategy to prevent ELA-induced neurologic sequelae that develops later in life.

Exposure to humans after weaning does not reduce the behavioural reactivity of extensively reared Merino lambs

Human-directed fear in extensively reared sheep is often high due to the aversive nature of common husbandry procedures and infrequent interactions with humans. This study investigated whether additional human exposure provided to weaned lambs reduced human-directed fear and behavioural reactivity. Ninety Merino lambs were either exposed to low or moderately stressful human exposure sessions, or had no additional human contact, and their fear responses and behavioural reactivity to humans, a startle stimulus and confinement were tested. Overall, the imposed interventions did not reduce behavioural reactivity during these tests, suggesting fear towards humans had not been altered.

Effects of Positive Reinforcement Training and Novel Object Exposure on Salivary Cortisol Levels under Consideration of Individual Variation in Captive African Elephants (Loxodonta africana)

Simple Summary

Regular training for medical or enrichment purposes and the provision of environmental enrichment, such as varied feeding schedules and novel objects, are part of the management of African elephants in zoos. The present study aimed to find out whether training and enrichment in the form of a novel object induced physiological changes in captive African elephants. We repeatedly sampled the saliva of ten animals (three zoos) before and after training and the exposure to a novel object for the analysis of cortisol and as a measure of stress and arousal. We found high salivary cortisol levels before and low levels after training. A novel object, in contrast, moderately increased the salivary cortisol levels. Moreover, males and young elephants showed lower salivary cortisol levels than females and old elephants, respectively. The zoo, handling method (free vs. protected contact to keepers), reproductive and social status, however, did not influence the salivary cortisol levels of the animals studied. We conclude that the relatively high cortisol values before training could be due to anticipation of the training event. A novel object, in contrast, may have evoked arousal, which led to the observed cortisol increase. In addition, understanding why animals differ in stress responses will help to manage stress in zoo elephants with the goal of ensuring their welfare.

Abstract

Dealing with potential stress in species that have high husbandry requirements, such as elephants, is a challenge for zoos. The objective of the present study was to determine whether positive reinforcement training (PRT) and exposure to a novel object (NOV) for enrichment induced a salivary cortisol response indicative of activation of the hypothalamic–pituitary–adrenal (HPA) axis and which factors determine individual variation in this regard in captive African elephants. We repeatedly sampled the saliva of ten animals (three zoos) for the analysis of cortisol (SACort) before and up to 60 min (in 10–15 min intervals) after the onset of PRT (three repeats) or NOV (nine repeats), which lasted 10 min. There was considerable individual variation in SACort in response to PRT or NOV. Using mixed models, we were able to control these and to reveal that PRT was associated with high SACort before and relatively low SACort after PRT, while NOV induced a moderate SACort increase. The individual differences in SACort were related to age and sex (NOV), while the effects of zoo, handling method (free vs. protected contact) and reproductive and social status were variable. We conclude that positive affective states, such as anticipation or arousal, should be taken into account when interpreting the differences in the SACort responses between PRT and NOV. In addition, understanding the individuality of stress will support management decisions aimed at promoting captive elephant welfare.

Predicting their past: Machine language learning can discriminate the brains of chimpanzees with different early-life social rearing experiences

Early life experiences, including separation from caregivers, can result in substantial, persistent effects on neural, behavioral, and physiological systems as is evidenced in a long-standing literature and consistent findings across species, populations, and experimental models. In humans and other animals, differential rearing conditions can affect brain structure and function. We tested for whole brain patterns of morphological difference between 108 chimpanzees reared typically with their mothers (MR; N = 54) and those reared decades ago in a nursery with peers, human caregivers, and environmental enrichment (NR; N = 54). We applied support vector machine (SVM) learning to archival MRI images of chimpanzee brains to test whether we could, with any degree of significant probability, retrospectively classify subjects as MR and NR based on variation in gray matter within the entire brain. We could accurately discriminate MR and NR chimpanzee brains with nearly 70% accuracy. The combined brain regions discriminating the two rearing groups were widespread throughout the cortex. We believe this is the first report using machine language learning as an analytic method for discriminating nonhuman primate brains based on early rearing experiences. In this sense, the approach and findings are novel, and we hope they stimulate application of the technique to studies on neural outcomes associated with early experiences. The findings underscore the potential for infant separation from caregivers to leave a long-term mark on the developing brain.

Impact of Early Life Stress on Reward Circuit Function and Regulation

Early life stress - including experience of child maltreatment, neglect, separation from or loss of a parent, and other forms of adversity - increases lifetime risk of mood, anxiety, and substance use disorders. A major component of this risk may be early life stress-induced alterations in motivation and reward processing, mediated by changes in the nucleus accumbens (NAc) and ventral tegmental area (VTA). Here, we review evidence of the impact of early life stress on reward circuit structure and function from human and animal models, with a focus on the NAc. We then connect these results to emerging theoretical models about the indirect and direct impacts of early life stress on reward circuit development. Through this review and synthesis, we aim to highlight open research questions and suggest avenues of future study in service of basic science, as well as applied insights. Understanding how early life stress alters reward circuit development, function, and motivated behaviors is a critical first step toward developing the ability to predict, prevent, and treat stress-related psychopathology spanning mood, anxiety, and substance use disorders.

Maternal fluoxetine reduces hippocampal inflammation and neurogenesis in adult offspring with sex-specific effects of periadolescent oxytocin

Untreated perinatal depression can have severe consequences for the mother and her children. However, both the efficacy to mothers and safety to exposed infants of pharmacological antidepressants such as selective serotonin reuptake inhibitors (SSRIs), have been questioned. We previously reported that maternal SSRI exposure increased hippocampal IL-1β levels, which may be tied to limited efficacy of SSRIs during the postpartum to the dam but is not yet known whether maternal postpartum SSRIs affect the neuroinflammatory profile of adult offspring. In addition, although controversial, perinatal SSRI exposure has been linked to increased risk of autism spectrum disorder (ASD) in children. Oxytocin (OT) is under investigation as a treatment for ASD, but OT is a large neuropeptide that has difficulty crossing the blood-brain barrier (BBB). Triozan^TM is a nanoformulation that can facilitate OT to cross the BBB. Thus, we investigated the impact of maternal postpartum SSRIs and offspring preadolescent OT treatment on adult offspring neuroinflammation, social behavior, and neurogenesis in the hippocampus. Using a model of de novo postpartum depression, corticosterone (CORT) was given in the postpartum to the dam with or without treatment with the SSRI, fluoxetine (FLX) for 21 days postpartum. Offspring were then subsequently treated with either OT, OT + Triozan^TM, or vehicle for 10 days prior to adolescence (PD25-34). Maternal FLX decreased hippocampal IL-10 and IL-13 and neurogenesis in both sexes, whereas maternal CORT increased hippocampal IL-13 in both sexes. Maternal CORT treatment shifted the neuroimmune profile towards a more proinflammatory profile in offspring hippocampus, whereas oxytocin, independent of formulation, normalized this profile. OT treatment increased hippocampal neurogenesis in adult males but not in adult females, regardless of maternal treatment. OT treatment increased the time spent with a novel social stimulus animal (social investigation) in both adult male and female offspring, although this effect depended on maternal CORT. These findings underscore that preadolescent exposure to OT can reverse some of the long-lasting effects of postpartum maternal CORT and FLX treatments in the adult offspring. In addition, we found that maternal treatments that reduce (CORT) or increase (FLX) hippocampal inflammation in dams resulted in opposing patterns of hippocampal inflammation in adult offspring.

Early life adversity promotes resilience to opioid addiction-related phenotypes in male rats and sex-specific transcriptional changes

Experiencing some early life adversity can have an "inoculating" effect that promotes resilience in adulthood. However, the mechanisms underlying stress inoculation are unknown, and animal models are lacking. Here we used the limited bedding and nesting (LBN) model of adversity to evaluate stress inoculation of addiction-related phenotypes. In LBN, pups from postnatal days 2 to 9 and their dams were exposed to a low-resource environment. In adulthood, they were tested for addiction-like phenotypes and compared to rats raised in standard housing conditions. High levels of impulsivity are associated with substance abuse, but in males, LBN reduced impulsive choice compared to controls. LBN males also self-administered less morphine and had a lower breakpoint on a progressive ratio reinforcement schedule than controls. These effects of LBN on addiction-related behaviors were not found in females. Because the nucleus accumbens (NAc) mediates these behaviors, we tested whether LBN altered NAc physiology in drug-naïve and morphine-exposed rats. LBN reduced the frequency of spontaneous excitatory postsynaptic currents in males, but a similar effect was not observed in females. Only in males did LBN prevent a morphine-induced increase in the AMPA/NMDA ratio. RNA sequencing was performed to delineate the molecular signature in the NAc associated with LBN-derived phenotypes. LBN produced sex-specific changes in transcription, including in genes related to glutamate transmission. Collectively, these studies reveal that LBN causes a male-specific stress inoculation effect against addiction-related phenotypes. Identifying factors that promote resilience to addiction may reveal novel treatment options for patients.

Enhancing the Selection and Performance of Working Dogs

Dogs perform a variety of integral roles in our society, engaging in work ranging from assistance (e.g., service dogs, guide dogs) and therapy to detection (e.g., search-and-rescue dogs, explosive detection dogs) and protection (e.g., military and law enforcement dogs). However, success in these roles, which requires dogs to meet challenging behavioral criteria and to undergo extensive training, is far from guaranteed. Therefore, enhancing the selection process is critical for the effectiveness and efficiency of working dog programs and has the potential to optimize how resources are invested in these programs, increase the number of available working dogs, and improve working dog welfare. In this paper, we review two main approaches for achieving this goal: (1) developing selection tests and criteria that can efficiently and effectively identify ideal candidates from the overall pool of candidate dogs, and (2) developing approaches to enhance performance, both at the individual and population level, via improvements in rearing, training, and breeding. We summarize key findings from the empirical literature regarding best practices for assessing, selecting, and improving working dogs, and conclude with future steps and recommendations for working dog organizations, breeders, trainers, and researchers.

Allostatic load: Developmental and conceptual considerations in a multi-system physiological indicator of chronic stress exposure

Developmental researchers studying how stress affects health have often focused on specific, individual, physiological parameters such as cortisol. Yet, recent theories of stress biology emphasize that the stress response is multi-faceted and engages distinct yet interconnected physiological systems, including metabolic, immune, and cardiovascular systems that respond to one another. Moreover, advocates of a systems approach also argue that the confluence of changes across several physiological systems presents a health risk, even when one indicator alone is not predictive of health outcomes. Allostatic load is one potential multi-system indicator of stress, capturing the cumulative, physiological burden of chronic stress exposure on the body. At the same time, studying allostatic load during early development raises several issues, including how allostatic load is operationalized, the clinical importance of commonly used biomarkers during distinct periods of development, and the fundamental role of timing. In this review paper, we discuss the potential of allostatic load in the context of studies of stress in developmental science, review developmental studies that have assessed allostatic load, and articulate critical conceptual questions regarding the study of allostatic load during the childhood years.

Evaluation of the HPA Axis' Response to Pharmacological Challenges in Experimental and Clinical Early-Life Stress-Associated Depression

Early-life stress (ELS) is associated with a higher risk of psychopathologies in adulthood, such as depression, which may be related to persistent changes in the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to evaluate the effects of ELS on the functioning of the HPA axis in clinical and experimental situations. Clinically, patients with current depressive episodes, with and without ELS, and healthy controls, composed the sample. Subjects took a capsule containing placebo, fludrocortisone, prednisolone, dexamethasone or spironolactone followed by an assessment of plasma cortisol the morning after. Experimentally, male Wistar rats were submitted to ELS protocol based on variable, unpredictable stressors from postnatal day (PND)1 to PND21. On PND65 animals were behaviorally evaluated through the forced-swimming test (FST). At PND68, pharmacological challenges started, using mifepristone, dexamethasone, spironolactone, or fludrocortisone, and corticosterone levels were determined 3 h after injections. Cortisol response of the patients did not differ significantly from healthy subjects, regardless of their ELS history, and it was lower after fludrocortisone, prednisolone, and dexamethasone compared with placebo, indicating the suppression of plasma cortisol by all these treatments. Animals exposed to ELS presented altered phenotype as indicated by an increased immobility time in the FST when compared with control, but no significant long-lasting effects of ELS were observed on the HPA axis response. Limitations on the way the volunteers were sampled may have contributed to the lack of ELS effects on the HPA axis, pointing out the need for further research to understand these complex phenomena.

Chronic stress has lasting effects on improved cued discrimination early in extinction

Chronic stress typically leads to deficits in fear extinction when tested soon after chronic stress ends. Given the importance of extinction in updating fear memories, the current study examined whether fear extinction was impaired in rats that were chronically stressed and then given a break from the end of chronic stress to the start of fear conditioning and extinction. Male rats were chronically stressed by restraint (6 h/d/21 d) and tested soon (termed immediate, STR-IMM), or 3 or 6 wk after a rest period from restraint (termed rest or "R," STR-R3, STR-R6). In Experiment 1, STR-R3 and STR-R6 discriminated between the cue and nonshock context better than STR-IMM or control. Interestingly, STR-IMM showed high freezing to the nonshock context. Consequently, Experiment 2 investigated whether STR-IMM generalized across contexts, which was not supported. Experiment 3 determined whether STR-IMM were susceptible to second-order conditioning to a novel context, but showed that the level of second-order conditioning was similar for all groups. These findings reveal that rats exposed to chronic stress and then given a rest period of 3 or 6 wk, express unique fear extinction profiles compared to control and STR-IMM. Specifically, STR-R demonstrated excellent cue and context discrimination during extinction, and perhaps showed a stress inoculation effect. For STR-IMM, the heightened freezing under these extensive acclimation parameters was not attributed to generalization nor to second-order fear conditioning to "safe" contexts and, instead, may reflect hypervigilance.

Moderate early life stress improves adult zebrafish (Danio rerio) working memory but does not affect social and anxiety-like responses

Early life stress (ELS) is defined as a short or chronic period of trauma, environmental or social deprivation, which can affect different neurochemical and behavioral patterns during adulthood. Zebrafish (Danio rerio) have been widely used as a model system to understand human neurodevelopmental disorders and display translationally relevant behavioral and stress-regulating systems. In this study, we aimed to investigate the effects of moderate ELS by exposing young animals (6-weeks postfertilization), for 3 consecutive days, to three stressors, and analyzing the impact of this on adult zebrafish behavior (16-week postfertilization). The ELS impact in adults was assessed through analysis of performance on tests of unconditioned memory (free movement pattern Y-maze test), exploratory and anxiety-related task (novel tank diving test), and social cohesion (shoaling test). Here, we show for the first time that moderate ELS increases the number of alternations in turn-direction compared to repetitions in the unconditioned Y-maze task, suggesting increased working memory, but has no effect on shoal cohesion, locomotor profile, or anxiety-like behavior. Overall, our data suggest that moderate ELS may be linked to adaptive flexibility which contributes to build "resilience" in adult zebrafish by improving working memory performance.

Moderate maternal separation mitigates the altered synaptic transmission and neuronal activation in amygdala by chronic stress in adult mice

Exposure to moderate level of stress during the perinatal period helps the organisms to cope well with stressful events in their later life, an effect known as stress inoculation. Amygdala is one of the kernel brain regions mediating stress-coping in the brain. However, little is known about whether early life stress may affect amygdala to have its inoculative effect. Here, we observed that moderate maternal separation (MS) from postnatal day 3 to day 21 (D3–21, 1 h per day) significantly alleviated the increased anxiety-like behavior induced by chronic social defeat stress (CSDS) in adulthood, suggesting an obvious inoculative effect of moderate MS. Further studies revealed that MS prevented CSDS-evoked augmentation of glutamatergic transmission onto principal neurons (PNs) in the basolateral amygdala (BLA) by inhibiting presynaptic glutamate release. By contrast, it did not affect GABAergic transmission in BLA PNs, as indicated by unaltered frequency and amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Moreover, the CSDS-induced increase of neuronal excitability was also mitigated by MS in BLA PNs. In conclusion, our results suggest that MS may have its inoculative effect through alleviating the influences of later life stress on the glutamatergic transmission and neuronal activity in amygdala neurons.

Bridging the species gap in translational research for neurodevelopmental disorders

The prevalence and societal impact of neurodevelopmental disorders (NDDs) continue to increase despite years of research in both patient populations and animal models. There remains an urgent need for translational efforts between clinical and preclinical research to (i) identify and evaluate putative causes of NDD, (ii) determine their underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches, and (iv) translate basic research into safe and effective clinical practices. Given the complexity behind potential causes and behaviors affected by NDDs, modeling these uniquely human brain disorders in animals will require that we capitalize on unique advantages of a diverse array of species. While much NDD research has been conducted in more traditional animal models such as the mouse, ultimately, we may benefit from creating animal models with species that have a more sophisticated social behavior repertoire such as the rat (Rattus norvegicus) or species that more closely related to humans, such as the rhesus macaque (Macaca mulatta). Here, we highlight the rat and rhesus macaque models for their role in previous psychological research discoveries, current efforts to understand the neurobiology of NDDs, and focus on the convergence of behavior outcome measures that parallel features of human NDDs.

Neurobiological Markers of Resilience to Depression Following Childhood Maltreatment: The Role of Neural Circuits Supporting the Cognitive Control of Emotion

BACKGROUND

Childhood adversity is strongly linked to negative mental health outcomes, including depression and anxiety. Leveraging cognitive neuroscience to identify mechanisms that contribute to resilience in children with a history of maltreatment may provide viable intervention targets for the treatment or prevention of psychopathology. We present a conceptual model of a potential neurobiological mechanism of resilience to depression and anxiety following childhood adversity. Specifically, we argue that neural circuits underlying the cognitive control of emotion may promote resilience, wherein a child's ability to recruit the frontoparietal control network to modulate amygdala reactivity to negative emotional cues-such as during cognitive reappraisal-buffers risk for internalizing symptoms following exposure to adversity.

METHODS

We provide preliminary support for this model of resilience in a longitudinal sample of 151 participants 8 to 17 years of age with (n = 79) and without (n = 72) a history of childhood maltreatment who completed a cognitive reappraisal task while undergoing functional magnetic resonance imaging.

RESULTS

Among maltreated youths, those who were better able to recruit prefrontal control regions and modulate amygdala reactivity during reappraisal exhibited lower risk for depression over time. By contrast, no association was observed between neural functioning during reappraisal and depression among youths without a history of maltreatment.

CONCLUSIONS

These preliminary findings support the hypothesis that children who are better able to regulate emotion through recruitment of the frontoparietal network exhibit greater resilience to depression following childhood maltreatment. Interventions targeting cognitive reappraisal and other cognitive emotion regulation strategies may have potential for reducing vulnerability to depression among children exposed to adversity.

The Biology of Human Resilience: Opportunities for Enhancing Resilience Across the Life Span

Recent scientific and technological advances have brought us closer to being able to apply a true biopsychosocial approach to the study of resilience in humans. Decades of research have identified a range of psychosocial protective factors in the face of stress and trauma. Progress in resilience research is now advancing our understanding of the biology underlying these protective factors at multiple phenotypic levels, including stress response systems, neural circuitry function, and immune responses, in interaction with genetic factors. It is becoming clear that resilience involves active and unique biological processes that buffer the organism against the impact of stress, not simply involve a reversal of pathological mechanisms. Here, we provide an overview of recent progress in the field, highlighting key psychosocial milestones and accompanying biological changes during development, and into adulthood and old age. Continued advances in our understanding of psychological, social, and biological determinants of resilience will contribute to the development of novel interventions and help optimize the type and timing of intervention for those most at risk, resulting in a possible new framework for enhancing resilience across the life span.

Midlife reversibility of early-established biobehavioral risk factors: A research agenda

Epidemiological evidence links exposure to early life adversities-such as childhood maltreatment-with impaired health and well-being in adulthood. Since these effects are usually unrecognized or untreated in childhood, preventive and remediating interventions in adults are needed. Our focus on adulthood prompted three major questions. First, does our increased understanding of mechanisms accounting for the long-term effects of early life adversities help delineate underlying dimensions that underscore key similarities and differences among these adversities? Second, can adults accurately report on adversities they experienced in childhood? Third, can we identify malleable risk processes in adulthood that might be targets for preventive intervention? Supported by the National Institute on Aging, the U.K. Economic and Social and the Biotechnology and Biological Sciences Research Councils, a network of researchers in human and animal development addressed these questions through meetings and literature review. A small number of dimensions may adequately distinguish among a range of co-occurring childhood adversities. Widely used adult ascertainments of childhood adversity are poorly related to prospective ascertainment. Strategies for preventive interventions should be aimed both at adults who were actually exposed to adversity as well as those who recall adversity, but the targeted risk processes may be different. Now is an opportune time to support research on adult interventions based on unfolding research on critical periods of sensitivity to adversity in fetal and child development, on improved understanding of risk mechanisms that may persist across the life span, and on new insights on enhancing neuroplasticity in adults. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Resilience priming: Translational models for understanding resiliency and adaptation to early life adversity

Despite the increasing attention to early life adversity and its long-term consequences on health, behavior, and the etiology of neurodevelopmental disorders, our understanding of the adaptations and interventions that promote resiliency and rescue against such insults are underexplored. Specifically, investigations of the perinatal period often focus on negative events/outcomes. In contrast, positive experiences (i.e. enrichment/parental care//healthy nutrition) favorably influence development of the nervous and endocrine systems. Moreover, some stressors result in adaptations and demonstrations of later-life resiliency. This review explores the underlying mechanisms of neuroplasticity that follow some of these early life experiences and translates them into ideas for interventions in pediatric settings. The emerging role of the gut microbiome in mediating stress susceptibility is also discussed. Since many negative outcomes of early experiences are known, it is time to identify mechanisms and mediators that promote resiliency against them. These range from enrichment, quality parental care, dietary interventions and those that target the gut microbiota.

Understanding Resilience and Preventing and Treating PTSD

Resilience is defined as the dynamic ability to adapt successfully in the face of adversity, trauma, or significant threat. Some of the key early studies of resilience were observational studies in children. They were followed by research in adults, studies testing interventions to promote resilience in different populations, and a recent upsurge of studies on the underlying genomic and neurobiological mechanisms. Neural and molecular studies in preclinical models of resilience are also increasingly identifying active stress adaptations in resilient animals. Knowledge gained from animal and human studies of resilience can be harnessed to develop new preventive interventions to enhance resilience in at-risk populations. Further, treatment interventions focused on enhancing potentially modifiable protective factors that are consistently linked to psychological resilience can enrich currently available treatment interventions for individuals with posttraumatic stress disorder (PTSD). Translating our expanding knowledge of the neurobiology of resilience additionally promises to yield novel therapeutic strategies for treating this disabling condition. This review summarizes the vast field of resilience research spanning genomic, psychosocial, and neurobiological levels, and discusses how findings have led and can lead to new preventive and treatment interventions for PTSD.

Understanding the effects of emotional reactivity on depression and suicidal thoughts and behaviors: Moderating effects of childhood adversity and resilience

BACKGROUND

Early adulthood is a period of increased risk for depression and suicide. Emotional reactivity (a tendency to react to stress with increases in negative affect and maladaptive interpretations of events) is an important risk factor for these outcomes that has been under-studied. We hypothesized that elevated emotional reactivity would be associated with higher levels of depressive symptoms and suicidal thoughts and behaviors. Further, we hypothesized that experiences of childhood maltreatment would amplify this relationship, whereas the presence of resilience would act as a buffer.

METHODS

1703 young adults (Mean Age = 19.56 years), 71% female) completed well-validated self-report questionnaires at a single time point.

RESULTS

Higher emotional reactivity was directly associated with higher levels of depressive symptoms and suicidal thoughts and behaviors. Further, resilience levels significantly moderated the relationships between emotional reactivity and depressive symptoms and suicidal thoughts and behaviors. Finally, childhood trauma significantly moderated the relationship between emotional reactivity and suicidal thoughts and behaviors only.

LIMITATIONS

This study was cross-sectional in design and relied upon self-report measures only.

CONCLUSIONS

The current study demonstrates an association between emotional reactivity, depressive symptoms, and suicidal thoughts and behaviors during emerging adulthood. Whereas a history of childhood maltreatment may amplify the relationship between emotional reactivity, depression, and suicidal thoughts and behaviors, certain qualities associated with resilience may buffer against the effects of emotional reactivity. Future studies can identify the resilience-promoting factors that are most protective and develop and test interventions that can potentially augment those factors.

Childhood trauma and insulin resistance in patients suffering from depressive disorders

OBJECTIVE

Insulin resistance (IR) is a metabolic dysfunction often co-morbid with major depressive disorder (MDD). The paths to development of MDD remain largely unspecified, highlighting a need for identification of risk factors. Here, we tested whether specific subscales of childhood trauma as well as family history of type-2 diabetes (Fam-Hx-Dm2) are risk factors for development of metabolic dysfunction and severity of depressive symptoms.

RESEARCH DESIGN AND METHODS

We used a sample of 45 adults suffering from MDD that was well-characterized for insulin resistance and sensitivity as assessed by measures of fasting plasma glucose (FPG) plasma insulin (FPI) levels, body mass index (BMI), weight, homeostasis model assessment of insulin sensitivity (HOMA), Matsuda index as well as both glucose and insulin responses to oral glucose challenges. Severity of depressive symptoms was assessed with the Hamilton Depression Rating Scale (HDRS-21). Physical, sexual and emotional abuse as well as physical and emotional neglect were assessed with the Childhood Trauma Questionnaire. First- or second-degree relatives with type-2 diabetes defined fam-Hx-DM2.

RESULTS

Individuals reporting higher rates of emotional abuse were more likely to have greater IR as showed by elevated FPI levels and HOMA. No association was found with any of the other subscales of childhood trauma (e.g., physical abuse). Similarly, Fam-Hx-DM2 was associated with greater degree of IR as shown by elevated FPI, HOMA, but also FPG, weight and BMI. Moreover, we report a relationship and interaction between Fam-Hx-DM2 and emotional abuse on severity of depressive symptoms. Specifically, emotional abuse and Fam-HX-DM2 predicted severity of depressive symptoms at HDRS-21. Also, severity of depressive symptoms was greater with higher reported rates of emotional abuse but only in patients with negative Fam-Hx-Dm2. Individuals reporting higher emotional abuse and negative Fam-Hx-Dm2 also showed higher FPG levels. Conversely, individuals reporting higher emotional abuse and positive Fam-Hx-Dm2 showed higher FPI levels. This data suggest that Fam-Hx-Dm2 may define two different metabolic endophenotypes.

CONCLUSIONS

Our findings suggest that Fam-HX-DM2 and emotional abuse represent separate risk factors for developing metabolic dysfunction (i.e.: IR) in patients suffering from MDD, and that the effects of emotional abuse on psychiatric illness may depend upon the personal characteristics, including Fam-Hx-DM2.

Juvenile stress induces behavioral change and affects perineuronal net formation in juvenile mice

Background

Many neuropsychiatric disorders develop in early life. Although the mechanisms involved have not been elucidated, it is possible that functional abnormalities of parvalbumin-positive interneurons (PV neurons) are present. Several previous studies have shown that juvenile stress is implicated in the development of neuropsychiatric disorders. We aimed to clarify the effects of juvenile stress on behavior and on the central nervous system. We investigated behavioral abnormalities of chronically-stressed mice during juvenilehood and the effect of juvenile stress on PV neurons and WFA-positive perineuronal nets (PNNs), which are associated with vulnerability and plasticity in the mouse brain.

Results

Due to juvenile stress, mice showed neurodevelopmental disorder-like behavior. Juvenile stressed mice did not show depressive-like behaviors, but on the contrary, they showed increased activity and decreased anxiety-like behavior. In the central nervous system of juvenile stressed mice, the fluorescence intensity of WFA-positive PNNs decreased, which may signify increased vulnerability.

Conclusion

This study suggested that juvenile stressed mice showed behavioral abnormalities, resembling those seen in neuropsychiatric disorders, and increased brain vulnerability.

Development of an optogenetic toolkit for neural circuit dissection in squirrel monkeys

Optogenetic tools have opened a rich experimental landscape for understanding neural function and disease. Here, we present the first validation of eight optogenetic constructs driven by recombinant adeno-associated virus (AAV) vectors and a WGA-Cre based dual injection strategy for projection targeting in a widely-used New World primate model, the common squirrel monkey Saimiri sciureus. We observed opsin expression around the local injection site and in axonal projections to downstream regions, as well as transduction to thalamic neurons, resembling expression patterns observed in macaques. Optical stimulation drove strong, reliable excitatory responses in local neural populations for two depolarizing opsins in anesthetized monkeys. Finally, we observed continued, healthy opsin expression for at least one year. These data suggest that optogenetic tools can be readily applied in squirrel monkeys, an important first step in enabling precise, targeted manipulation of neural circuits in these highly trainable, cognitively sophisticated animals. In conjunction with similar approaches in macaques and marmosets, optogenetic manipulation of neural circuits in squirrel monkeys will provide functional, comparative insights into neural circuits which subserve dextrous motor control as well as other adaptive behaviors across the primate lineage. Additionally, development of these tools in squirrel monkeys, a well-established model system for several human neurological diseases, can aid in identifying novel treatment strategies.

Why and how the early-life environment affects development of coping behaviours

Understanding the ways in which individuals cope with threats, respond to challenges, make use of opportunities and mediate the harmful effects of their surroundings is important for predicting their ability to function in a rapidly changing world. Perhaps one of the most essential drivers of coping behaviour of adults is the environment experienced during their early-life development. Although the study of coping, defined as behaviours displayed in response to environmental challenges, has a long and rich research history in biology, recent literature has repeatedly pointed out that the processes through which coping behaviours develop in individuals are still largely unknown. In this review, we make a move towards integrating ultimate and proximate lines of coping behaviour research. After broadly defining coping behaviours (1), we review why, from an evolutionary perspective, the development of coping has become tightly linked to the early-life environment (2), which relevant developmental processes are most important in creating coping behaviours adjusted to the early-life environment (3), which influences have been shown to impact those developmental processes (4) and what the adaptive significance of intergenerational transmission of coping behaviours is, in the context of behavioural adaptations to a fast changing world (5). Important concepts such as effects of parents, habitat, nutrition, social group and stress are discussed using examples from empirical studies on mammals, fish, birds and other animals. In the discussion, we address important problems that arise when studying the development of coping behaviours and suggest solutions.

Early weaning increases aggression and stereotypic behaviour in cats

Behaviour problems are common in companion felines, and problematic behaviour may be a sign of chronic stress. In laboratory animals, early weaning increases the risk for aggression, anxiety, and stereotypic behaviour. However, very few studies have focused on early weaning in one of the world’s most popular pets, the domestic cat, although weaning soon after the critical period of socialisation is common practice. To study the effects of early weaning (<12 weeks) on behaviour, a large data set (N = 5726, 40 breeds) was collected from home-living domestic cats through a questionnaire survey. The results show that weaning before 8 weeks of age increases the risk for aggression, but not fearful behaviour. Moreover, cats weaned after 14 weeks of age have a lower probability for aggression towards strangers than early weaned cats and a lower probability for stereotypic behaviour (excessive grooming) than cats weaned at 12 weeks. The effect of weaning age on stereotypic behaviour is partially explained by the effects on aggression. These findings indicate that early weaning has a detrimental effect on behaviour, and suggest delayed weaning as a simple and inexpensive approach to significantly improve the welfare of millions of domestic cats.

An adverse early life environment can enhance stress resilience in adulthood

Chronic stress is a major risk factor for depression. Interestingly, not all individuals develop psychopathology after chronic stress exposure. In contrast to the prevailing view that stress effects are cumulative and increase stress vulnerability throughout life, the match/mismatch hypothesis of psychiatric disorders. The match/mismatch hypothesis proposes that individuals who experience moderate levels of early life psychosocial stress can acquire resilience to renewed stress exposure later in life. Here, we have tested this hypothesis by comparing the developmental effects of 2 opposite early life conditions, when followed by 2 opposite adult environments. Male Balb/c mice were exposed to either adverse early life conditions (limited nesting and bedding material) or a supportive rearing environment (early handling). At adulthood, the animals of each group were either housed with an ovariectomized female (supportive environment) or underwent chronic social defeat stress (socially adverse environment) for 3 weeks. At the end of the adult manipulations, all of the animals were returned to standard housing conditions. Then, we compared the neuroendocrine, behavioral and molecular effects of the interaction between early and adult environment. Our study shows that early life adversity does not necessarily result in increased vulnerability to stress. Specific endophenotypes, like hypothalamic-pituitary-adrenal axis activity, anxiety-related behavior and glucocorticoid receptor expression levels in the hippocampus were not significantly altered when adversity is experienced during early life and in adulthood, and are mainly affected by either early life or adult life adversity alone. Overall our data support the notion that being raised in a stressful environment prepares the offspring to better cope with a challenging adult environment and emphasize the role of early life experiences in shaping adult responsiveness to stress.

Differential Behavioral and Neurobiological Effects of Chronic Corticosterone Treatment in Adolescent and Adult Rats

Adolescence is a critical period with ongoing maturational processes in stress-sensitive systems. While adolescent individuals show heightened stress-induced hormonal responses compared to adults, it is unclear whether and how the behavioral and neurobiological consequences of chronic stress would differ between the two age groups. Here we address this issue by examining the effects of chronic exposure to the stress hormone, corticosterone (CORT), in both adolescent and adult animals. Male Sprague-Dawley (SD) rats were injected intraperitoneally with CORT (40 mg/kg) or vehicle for 21 days during adolescence (post-natal day (PND) 29–49) or adulthood (PND 71–91) and then subjected to behavioral testing or sacrifice for western blot analyses. Despite of similar physical and neuroendocrine effects in both age groups, chronic CORT treatment produced a series of behavioral and neurobiological effects with striking age differences. While CORT-treated adult animals exhibited decreased sucrose preference, increased anxiety levels and cognitive impairment, CORT-treated adolescent animals demonstrated increased sucrose preference, decreased anxiety levels, and increased sensorimotor gating functions. These differential behavioral alterations were accompanied by opposite changes in the two age groups in the expression levels of brain-derived neurotrophic factor (BDNF), the phosphorylation of the obligatory subunit of the NMDA receptor, GluN1, and PSD-95 in rat hippocampus. These results suggest that prolonged glucocorticoid exposure during adolescence produces different behavioral and neurobiological effects from those in adulthood, which may be due to the complex interaction between glucocorticoids and the ongoing neurodevelopmental processes during this period.

Chronic Early-life Stress in Rat Pups Alters Basal Corticosterone, Intestinal Permeability, and Fecal Microbiota at Weaning: Influence of Sex

Background/Aims

Wistar rat dams exposed to limited nesting stress (LNS) from post-natal days (PND) 2 to 10 display erratic maternal behavior, and their pups show delayed maturation of the hypothalamic-pituitary-adrenal axis and impaired epithelial barrier at PND10 and a visceral hypersensitivity at adulthood. Little is known about the impact of early life stress on the offspring before adulthood and the influence of sex. We investigated whether male and female rats previously exposed to LNS displays at weaning altered corticosterone, intestinal permeability, and microbiota.

Methods

Wistar rat dams and litters were maintained from PND2 to 10 with limited nesting/bedding materials and thereafter reverted to normal housing up to weaning (PND21). Control litters had normal housing. At weaning, we monitored body weight, corticosterone plasma levels (enzyme immunoassay), in vivo intestinal to colon permeability (fluorescein isothiocyanate-dextran 4 kDa) and fecal microbiota (DNA extraction and amplification of the V4 region of the 16S ribosomal RNA gene).

Results

At weaning, LNS pups had hypercorticosteronemia and enhanced intestinal permeability with females > males while body weights were similar. LNS decreased fecal microbial diversity and induced a distinct composition characterized by increased abundance of Gram positive cocci and reduction of fiber-degrading, butyrate-producing, and mucus-resident microbes.

Conclusions

These data indicate that chronic exposure to LNS during the first week post-natally has sustained effects monitored at weaning including hypercorticosteronemia, a leaky gut, and dysbiosis. These alterations may impact on the susceptibility to develop visceral hypersensitivity in adult rats and have relevance to the development of irritable bowel syndrome in childhood.

Low-Grade Inflammation and Ambulatory Cortisol in Adolescents: Interaction Between Interviewer-Rated Versus Self-Rated Acute Stress and Chronic Stress

OBJECTIVE

To determine whether the association between self-rated or interviewer-rated recent acute stress exposures and low-grade inflammation and daily cortisol production in adolescents is moderated by chronic stress ratings.

METHODS

Acute and chronic stress exposures were assessed in 261 adolescents aged 13 to 16 years using a semistructured life stress interview. The negative impact of acute stressors was independently rated by both adolescents (self-rated) and interviewers (interviewer-rated). Markers of inflammation (interleukin (IL)-6, IL-1ra, C-reactive protein) were measured from peripheral blood samples obtained via antecubital venipuncture. Participants collected 4 saliva samples at home on each of 6 consecutive days for the analysis of diurnal salivary cortisol profiles.

RESULTS

There were no main effects of acute stressors (self- and interviewer-rated) and chronic family or peer stress on adolescent inflammation markers and cortisol (p values > .10). However, the interaction between interviewer-rated acute stress and chronic family stress was significantly associated with adolescent inflammation markers (IL-6, IL-1ra). Specifically, as chronic family stress increased, the association between acute stressor impact (interviewer-rated) and inflammation markers became more positive (IL-6 (B = .054, SE = .023, p = .022); IL-1ra (B = .030, SE = .014, p = .034)). Interactions between self-rated acute stress and chronic family stress were not associated with any biological measures (p values > .10). Interactions between acute stressor impact (both self- and interviewer-rated) and chronic peer stress were also not significantly associated with any biological measures (p values > .05).

CONCLUSIONS

Among adolescents, interviewer-based ratings of acute stressor impact may allow for better prediction of health-relevant inflammation markers than adolescents' own ratings.

Repeated daily restraint stress induces adaptive behavioural changes in both adult and juvenile mice

Chronic stress is known to be a risk factor for the development of depression and anxiety, disorders which often begin during adolescence. Restraint stress is a commonly used stressor in adult rodents, however the effects of repeated restraint stress in juvenile mice have not been well characterised. Here we have shown for the first time the behavioural and hormonal effects of repeated restraint stress in both adult and juvenile BALB/c and C57BL/6 mice. Repeated daily restraint stress (2h/day for 3, 7 or 14days) provoked a robust physiological response evident as increased corticosterone levels and decreased body weight after 14days. However, habituation of the stress-response was evident during repeated exposure to the stressor in both adult and juvenile mice. The behavioural changes seen in response to repeated restraint stress were complex. In juvenile mice, repeated restraint stress evoked an increase in exploratory behaviours in the elevated plus maze, a decrease in time spent immobile in the forced swim test and a decrease in sucrose preference. In adult mice fewer behavioural changes were seen. Interestingly BALB/c and C57BL/6 mice showed qualitatively similar response to 3days repeated restraint stress. The behavioural changes we observed, as a result of prior stress exposure, may represent an adaptive stress-coping response or resilience. Both the hormonal and behavioural effects of stress were more pronounced in juvenile mice than in adults. This wider range of behavioural responses seen in juvenile mice might reflect a greater ability to engage in adaptive stress-coping strategies that likely have beneficial effects evident in future stress challenges.

Moderate Childhood Stress Buffers Against Depressive Response to Proximal Stressors: A Multi-Wave Prospective Study of Early Adolescents

Although the majority of research in the field has focused on childhood stressors as a risk factor for psychopathology, a burgeoning body of literature has focused on the possible steeling effect of moderate types of stressful events. The current study investigated the effects of proximal life stressors on prospective changes in depressive symptoms, and whether a history of moderate childhood adversity would moderate this relationship in a multi-wave study of a diverse community sample of early adolescents (N = 163, 52 % female, 51 % Caucasian). Hierarchical linear modeling was run with four waves of data. Adolescents with greater moderately severe early life events evinced a blunted depressive symptom response to changes in proximal stressful events in the previous 9 months, compared to those with fewer early moderately severe experiences of adversity. These results held after controlling for between-subject factors such as race, gender, severe early life stress, and average stress over the four waves of data. Findings indicate that greater exposure to moderate childhood stressors may buffer against the negative effects of subsequent stressors, suggesting the importance of a nuanced developmental approach to studying the effects of early life stress.

Neural Efficiency in Expert Cognitive-Motor Performers During Affective Challenge

Skilled individuals demonstrate a spatially localized or relatively lower response in brain activity characterized as neural efficiency when performing within their domain of expertise. Elite athletes are experts in their chosen sport and thus must be not only adept in the motor domain but must be resilient to performing under the stress of high-level competition. Such stability of performance suggests this population processes emotion and mental stress in an adaptive and efficient manner. This study sought to determine if athletes with a history of successful performance under circumstances of mental stress demonstrate neural efficiency during affective challenges compared to age-matched controls. Using functional magnetic resonance imaging, the blood-oxygen level-dependent response was recorded during emotional challenge induced by sport-specific and general unpleasant images. The athletes demonstrated neural efficiency in brain regions critical to emotion regulation (prefrontal cortex) and affect (insula) independently of their domain of expertise, suggesting adaptive processing of negative events and less emotional reactivity to unpleasant stimuli.

Research involving anxiety in non-human primates has potential implications for the assessment and treatment of anxiety in autism spectrum disorder: A translational literature review

OBJECTIVE

The purpose of this translational review (i.e. moving from basic primate research toward possible human applications) was to summarize non-human primate literature on anxiety to inform the development of future assessments of anxiety in non-verbal individuals with autism spectrum disorder (ASD).

METHODS

Systematic searches of databases identified 67 studies that met inclusion criteria. Each study was analysed and summarised in terms of (a) strategies used to evoke anxiety, (b) non-verbal behavioural indicators of anxiety and (c) physiological indicators of anxiety.

RESULTS

Eighteen strategies were used to evoke anxiety, 48 non-verbal behavioural indicators and 17 physiological indicators of anxiety were measured.

CONCLUSIONS

A number of the strategies used with non-human primates, if modified carefully, could be considered in the ongoing effort to study anxiety in individuals with ASD. Potential applications to the assessment of anxiety in humans with ASD are discussed.

Limited Nesting Stress Alters Maternal Behavior and In Vivo Intestinal Permeability in Male Wistar Pup Rats

A few studies indicate that limited nesting stress (LNS) alters maternal behavior and the hypothalamic pituitary adrenal (HPA) axis of dams and offspring in male Sprague Dawley rats. In the present study, we evaluated the impact of LNS on maternal behavior in Wistar rats, and on the HPA axis, glycemia and in vivo intestinal permeability of male and female offspring. Intestinal permeability is known to be elevated during the first week postnatally and influenced by glucocorticoids. Dams and neonatal litters were subjected to LNS or normal nesting conditions (control) from days 2 to 10 postnatally. At day 10, blood was collected from pups for determination of glucose and plasma corticosterone by enzyme immunoassay and in vivo intestinal permeability by oral gavage of fluorescein isothiocyanate-dextran 4kDa. Dams exposed to LNS compared to control showed an increase in the percentage of time spent building a nest (118%), self-grooming (69%), and putting the pups back to the nest (167%). LNS male and female pups exhibited a reduction of body weight by 5% and 4%, adrenal weights/100g body weight by 17% and 18%, corticosterone plasma levels by 64% and 62% and blood glucose by 11% and 12% respectively compared to same sex control pups. In male LNS pups, intestinal permeability was increased by 2.7-fold while no change was observed in females compared to same sex control. There was no sex difference in any of the parameters in control pups except the body weight. These data indicate that Wistar dams subjected to LNS during the first postnatal week have an altered repertoire of maternal behaviors which affects the development of the HPA axis in both sexes and intestinal barrier function in male offspring.

Early life stress dampens stress responsiveness in adolescence: Evaluation of neuroendocrine reactivity and coping behavior

Stressful experiences during early life (ELS) can affect brain development, thereby exerting a profound and long-lasting influence on mental development and psychological health. The stress inoculation hypothesis presupposes that individuals who have early experienced an attenuated form of stressors may gain immunity to its more virulent forms later in life. Increasing evidence demonstrates that ELS may promote the development of subsequent stress resistance, but the mechanisms underlying such adaptive changes are not fully understood. The present study evaluated the impact of fragmented dam-pup interactions by limiting the bedding and nesting material in the cage during postnatal days 2-9, a naturalistic animal model of chronic ELS, on the physiological and behavioral responses to different stressors in adolescent mice and characterized the possible underlying mechanisms. We found that ELS mice showed less social interaction deficits after chronic social defeat stress and acute restraint-tailshock stress-induced impaired long-term potentiation (LTP) and enhanced long-term depression (LTD) in hippocampal CA1 region compared with control mice. The effects of ELS on LTP and LTD were rescued by adrenalectomy. While ELS did not cause alterations in basal emotional behaviors, it significantly enhanced stress coping behaviors in both the tail suspension and the forced swimming tests. ELS mice exhibited a significant decrease in corticosterone response and trafficking of glucocorticoid receptors to the nucleus in response to acute restraint stress. Altogether, our data support the hypothesis that stress inoculation training, via early exposure to manageable stress, may enhance resistance to other unrelated extreme stressors in adolescence.

Annual Research Review: Threats to the validity of child psychiatry and psychology

BACKGROUND

Suggestions have been made that many claims concern false-positive findings in the field of child psychology and psychiatry.

FINDINGS

The literature was searched for concepts and findings on the validity of child psychiatry and psychology. Substantial progress has been made in some, but not all, areas and considerable challenges remain in all.

CONCLUSIONS

The two major threats to validity concern the inability to examine brain tissues in life and the evidence that there is a high overlap among disorders. We emphasize the need to follow published guidelines on preplanned analyses and we note the dangers associated with unregulated flexibility in data analysis. We note the very important clinical and developmental findings that have been ignored, perhaps partly because of an excessive focus on technologies. Nevertheless, we are positive about both the accomplishments and the ways in which challenges are being met.

Striatal dopamine D2/3 receptor regulation by stress inoculation in squirrel monkeys

Intermittent mildly stressful situations provide opportunities to learn, practice, and improve coping in a process called stress inoculation. Stress inoculation also enhances cognitive control and response inhibition of impulsive motivated behavior. Cognitive control and motivation have been linked to striatal dopamine D2 and/or D3 receptors (DRD2/3) in rodents, monkeys, and humans. Here, we study squirrel monkeys randomized early in life to stress inoculation with or without maternal companionship and a no-stress control treatment condition. Striatal DRD2/3 availability in adulthood was measured in vivo by [¹¹C]raclopride binding using positron emission tomography (PET). DRD2/3 availability was greater in caudate and putamen compared to ventral striatum as reported in PET studies of humans and other non-human primates. DRD2/3 availability in ventral striatum was also consistently greater in stress inoculated squirrel monkeys compared to no-stress controls. Squirrel monkeys exposed to stress inoculation in the presence of their mother did not differ from squirrel monkeys exposed to stress inoculation without maternal companionship. Similar effects in different social contexts extend the generality of our findings and together suggest that stress inoculation increases striatal DRD2/3 availability as a correlate of cognitive control in squirrel monkeys.

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Stress inoculation entails intermittent exposure to mildly stressful situations.

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Stress inoculation promotes coping, emotion regulation, and cognitive control of behavior.

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Cognitive control has been linked to striatal dopamine D2/3 receptors (DRD2/3).

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Stress inoculation increases striatal DRD2/3 availability and enhances cognitive control in squirrel monkeys.

Child Care and Cortisol Across Infancy and Toddlerhood: Poverty, Peers, and Developmental Timing

Evidence suggests that relations between child care and children's development-behaviorally and physiologically-likely differ between children from high-versus low-risk contexts. Using data from the Family Life Project (N = 1,155), the authors tested (a) whether within- and between-child differences in children's child care experiences (i.e., quantity, type, caregiver responsivity, and peer exposure) were predictive of their cortisol levels across infancy and toddlerhood and (b) whether these relations differed for children experiencing different levels of environmental risk. They found some evidence of such interactive effects. For children from high-risk contexts, within-child increases in child care hours were predictive of cortisol decreases. The inverse was evident for children from low-risk contexts. This relation grew across toddlerhood. Whereas a history of greater center-based child care was predictive of heightened cortisol levels for low-risk families, this was not the case for children from high-risk families. Irrespective of risk, greater peer exposure (between children) was associated with lower cortisol levels.