Mechanisms of late-onset cognitive decline after early-life stress

NRXN3-NLGN1 complex influences the development of depression induced by maternal separation in rats

Early-life stress (ELS) increases the risk of major depressive disorder in children and adolescents. However, the molecular and cellular mechanisms of major depressive disorder (MDD) induced by ELS are poorly understood. Here, we establish a stress model in rats in which maternal separation stress (MS) during the postnatal period increases susceptibility to restraint stress (RS) later in life. In terms of mechanism, MS causes long-lasting synaptic plasticity alterations in rats, which is accompanied by reduced branch and spine lengths in the hippocampus. We identified the role of the cell adhesion factor neurexin 3 (NRXN3) and its ligand neuroligin 1 (NLGN1) as mediators of these effects. NRXN3 and NLGN1 downregulation in the hippocampus occurred prior to the observed synaptic changes and depression-related behaviors. In conclusion, NRXN3 is involved in the development of depression induced by maternal separation, and the specific mechanism involves the NRXN3-NLGN1 complex, which can mediate synaptic plasticity and increase susceptibility todepression.

The evolving neurobiology of early-life stress

Because early-life stress is common and constitutes a strong risk factor for cognitive and mental health disorders, it has been the focus of a multitude of studies in humans and experimental models. Yet, we have an incomplete understanding of what is perceived as stressful by the developing brain, what aspects of stress influence brain maturation, what developmental ages are particularly vulnerable to stress, which molecules mediate the effects of stress on brain operations, and how transient stressful experiences can lead to enduring emotional and cognitive dysfunctions. Here, we discuss these themes, highlight the challenges and progress in resolving them, and propose new concepts and avenues for future research.

Female rats exposed to early life scarcity-adversity are resilient to later life changes in maternal behavior

In both humans and rodents, maternal care is disturbed by exposure to environmental adversity, including low resource conditions (i.e., poverty, scarcity). Maternal adversity is associated with compromised quality of mother-infant attachment and increased adverse caregiving patterns such as abuse, maltreatment and/or neglect, which disrupt behavioral development in the female offspring. Importantly, maternal behavior is thought to be an intergenerational behavior, meaning that the quality of maternal care a female experiences during early life is thought to influence the quality of care she will display towards her own offspring when she becomes a mother. Here, we tested this idea by employing a rodent model of postpartum environmental adversity based on creating an impoverished nesting environment during postpartum days (PD) 2-9, which disrupts mother-infant interactions and is thought to upregulate hypothalamic-pituitary-adrenal (HPA)-axis function in the pups. We examined the impact of this form of early life adversity on pup stress hormone (i.e., corticosterone- CORT) levels by collecting trunk blood and later life maternal behavior by conducting maternal behavior observations and maternal motivation tests (e.g., T-Maze, pup retrieval, pup-associated conditioned place preference) in the first filial (F1) generation. We report no impact of early life scarcity-adversity/adverse caregiving on pup CORT levels or later life naturalistic or motivated maternal behaviors. In sum, we show that female rat pups who experienced adverse caregiving during early life showed resilience towards developing negative caregiving patterns, as they did not perpetuate the same aberrant maternal behavior that they received from their mothers.

Infant Maltreatment Induces Early Alterations in Adrenal Glands and Stress Response in Juvenile Rat Offspring

Chronic stressors, such as infant maltreatment during early development, can have long-lasting effects on an individual's health and stress-coping abilities across the lifespan. In this study, we applied the scarcity-adversity model (SAM) to Wistar rats from postnatal days (PND) 8 to 12 to evaluate the impact of scarcity condition on adrenal glands morphology and stress response in juvenile offspring (PND 21-35) of both sexes. Our results demonstrate that SAM exposure leads to significant alterations in the adrenal glands of offspring. Notably, the cortex-to-medulla ratio was reduced in SAM pups starting at PND 28. Morphological analysis of the adrenal cortex revealed an increased thickness of the undifferentiated zone, suggesting enhanced cell proliferation, alongside a transient reduction in the thickness of the zona fasciculata, where glucocorticoid-synthesizing cells are located. Additionally, we observed a reduction in the cytoplasmic diameter of zona fasciculata cells, coupled with an increase in the thickness of blood capillaries in this region in SAM offspring of both sexes. An increase in BrdU + cells in the cortex at PND 28 was observed in male SAM pups, but not in females. Endocrine assessments revealed a marked increase in corticosterone levels following stress induced by movement restriction in juvenile SAM offspring of both sexes. In conclusion, our findings underscore the significant impact of early-life stress on adrenal gland morphology and stress responsiveness, with potential long-term consequences for health and stress-coping mechanisms in offspring.

Unraveling sex differences in maternal and paternal care impacts on social behaviors and neurobiological responses to early-life adversity

Early-life stress (ELS) affects the development of prosocial behaviors and social-cognitive function, often leading to structural brain changes and increased psychosocial disorders. Recent studies suggest that mother- and father-child relationships independently influence social development in a sex-specific manner, but the effects of impaired father-child relationships are often overlooked. This review examines preclinical rodent studies to explore how parental neglect impacts neuroplasticity and social behaviors in offspring. We highlight that disruptions in maternal interactions may affect male pups more in uniparental rodents, while impaired paternal interactions in biparental rodents tend to impact female pups more. Due to limited research, the separate effects of maternal and paternal neglect on brain development and social behaviors in biparental species remain unclear. Addressing these gaps could clarify the sex-specific mechanisms underlying social and neurobiological deficits following parental neglect.

Stress and parental behaviors

In nearly all mammalian species, newborn pups are weak and vulnerable, relying heavily on care and protection from parents for survival. Thus, developmentally hardwired neural circuits are in place to ensure the timely expression of parental behaviors. Furthermore, several neurochemical systems, including estrogen, oxytocin, and dopamine, facilitate the emergence and expression of parental behaviors. However, stress can adversely affect these systems, impairing parental behaviors. In this review, we will summarize our current knowledge regarding the impact of stress on pup-directed behavior circuits that lead to infant neglect, abuse, and, in extreme cases, killing. We will discuss various stressors that influence parental behaviors at different life stages and how stress induces changes in the neurochemical systems that support parental care, ultimately leading to its poor performance.

FAAH Inhibition Reverses Depressive-like Behavior and Sex-Specific Neuroinflammatory Alterations Induced by Early Life Stress

Early life stress (ELS) increases predisposition to major depressive disorder (MDD), with neuroinflammation playing a crucial role. This study investigated the long-term effects of the fatty acid amide hydrolase (FAAH) inhibitor URB597 on ELS-induced depressive-like behavior and messenger RNA (mRNA) of pro-inflammatory cytokines in the medial prefrontal cortex (mPFC) and CA1 regions. We also assessed whether these gene expression alterations were present at the onset of URB597 treatment during late adolescence. ELS induced a depressive-like phenotype in adult male and female rats, which was reversed by URB597. In the mPFC, ELS downregulated nuclear factor kappa B1 (nfκb1) in both sexes, while URB597 normalized this expression exclusively in males. In females, ELS downregulated interleukin (il) 6 and tumor necrosis factor alpha (tnfα) but upregulated il1β and corticotropin-releasing factor (crf); URB597 normalized il6, il1β, and crf. In the CA1, ELS downregulated il1β and tnfα in males and upregulated il1β expression in females, which was reversed by URB597. Some of these effects began in late adolescence, including mPFC-nfκb1 expression in both sexes, mPFC-il6 and mPFC-il1β in females, CA1-il1β and CA1-tnfα in males, and CA1-il1β in females. These findings highlight URB597 as a therapeutic approach for reversing ELS-induced depressive-like behavior by associating with changes in the gene expression of neuroinflammatory cytokines, with notable sex differences.

Enduring memory consequences of early-life stress / adversity: Structural, synaptic, molecular and epigenetic mechanisms

Adverse early life experiences are strongly associated with reduced cognitive function throughout life. The link is strong in many human studies, but these do not enable assigning causality, and the limited access to the live human brain can impede establishing the mechanisms by which early-life adversity (ELA) may induce cognitive problems. In experimental models, artificially imposed chronic ELA/stress results in deficits in hippocampus dependent memory as well as increased vulnerability to the deleterious effects of adult stress on memory. This causal relation of ELA and life-long memory impairments provides a framework to probe the mechanisms by which ELA may lead to human cognitive problems. Here we focus on the consequences of a one-week exposure to adversity during early postnatal life in the rodent, the spectrum of the ensuing memory deficits, and the mechanisms responsible. We highlight molecular, cellular and circuit mechanisms using convergent trans-disciplinary approaches aiming to enable translation of the discoveries in experimental models to the clinic.

Looking Back to Move Forward: Research in Stress, Behavior, and Immune Function

BACKGROUND

From the original studies investigating the effects of adrenal gland secretion to modern high-throughput multidimensional analyses, stress research has been a topic of scientific interest spanning just over a century.

SUMMARY

The objective of this review was to provide historical context for influential discoveries, surprising findings, and preclinical models in stress-related neuroimmune research. Furthermore, we summarize this work and present a current understanding of the stress pathways and their effects on the immune system and behavior. We focus on recent work demonstrating stress-induced immune changes within the brain and highlight studies investigating stress effects on microglia. Lastly, we conclude with potential areas for future investigation concerning microglia heterogeneity, bone marrow niches, and sex differences.

KEY MESSAGES

Stress is a phenomenon that ties together not only the central and peripheral nervous system, but the immune system as well. The cumulative effects of stress can enhance or suppress immune function, based on the intensity and duration of the stressor. These stress-induced immune alterations are associated with neurobiological changes, including structural remodeling of neurons and decreased neurogenesis, and these contribute to the development of behavioral and cognitive deficits. As such, research in this field has revealed important insights into neuroimmune communication as well as molecular and cellular mediators of complex behaviors relevant to psychiatric disorders.

Leveraging the science of early life predictability to inform policies promoting child health

Addressing the tremendous burden of early-life adversity requires constructive dialogues between scientists and policy makers to improve population health. Whereas dialogues focused on several aspects of early-life adversity have been initiated, discussion of an underrecognized form of adversity that has been observed across multiple contexts and cultures is only now emerging. Here we provide evidence for "why unpredictability?", including: 1. Evidence that exposures to unpredictability affect child neurodevelopment, with influences that persist into adulthood. 2. The existence of a translational non-human animal model of exposure to early life unpredictability that can be capitalized upon to causally probe neurobiological mechanisms. 3. Evidence that patterns of signals in the early environment promote brain maturation across species. 4. The uneven distribution of unpredictability across demographic populations that illuminates a possible focal point for enhancing health equity. We then outline the potential of unpredictability in terms of the "what"; that is, how might the concept of unpredictability be leveraged to inform policy? We emphasize the importance of interdisciplinary and community partnerships to the success of this work and describe our community-engaged research project. Finally, we highlight opportunities for the science of unpredictability to inform policies in areas such as screening, immigration, criminal justice, education, childcare, child welfare, employment, healthcare and housing.

Neural correlates of learning and memory are altered by early-life stress

The ability to learn and remember, which is fundamental for behavioral adaptation, is susceptible to stressful experiences during the early postnatal period, such as abnormal levels of maternal care. The exact mechanisms underlying these effects still remain elusive. This study examined whether early life stress (ELS) alters memory and brain activation patterns in male mice. Therefore, we examined the expression of the immediate early genes (IEGs) c-Fos and Arc in the dentate gyrus (DG) and basolateral amygdala (BLA) after training and memory retrieval in a fear conditioning task. Furthermore, we examined the potential of RU38486 (RU486), a glucocorticoid receptor antagonist, to mitigate ELS-induced memory deficits by blocking stress signalling during adolescence. Arc::dVenus reporter mice, which allow investigating experience-dependent expression of the immediate early gene Arc also at more remote time points, were exposed to ELS by housing dams and offspring with limited bedding and nesting material (LBN) between postnatal days (PND) 2-9 and trained in a fear conditioning task at adult age. We found that ELS reduced both fear acquisition and contextual memory retrieval. RU486 did not prevent these effects. ELS reduced the number of Arc::dVenus+ cells in DG and BLA after training, while the number of c-Fos+ cells were left unaffected. After memory retrieval, ELS decreased c-Fos+ cells in the ventral DG and BLA. ELS also altered the colocalization of c-Fos+ cells with Arc::dVenus+ cells in the ventral DG, possibly indicating impaired engram allocation in the ventral DG after memory retrieval. In conclusion, this study shows that ELS alters neuronal activation patterns after fear acquisition and retrieval, which may provide mechanistic insights into enduring impact of ELS on the processing of fear memories, possibly via changes in cell (co-) activation and engram cell allocation.

Early life adversities, psychopathologies and novel pharmacological strategies

Exposure to adversities during early life stages (early life adversities - ELA), ranging from pregnancy to adolescence, represents a major risk factor for the vulnerability to mental disorders. Hence, it is important to understand the molecular and functional underpinning of such relationship, in order to develop strategies aimed at reducing the psychopathologic burden associated with ELA, which may eventually lead to a significant improvement in clinical practice. In this review, we will initially recapitulate clinical and preclinical evidence supporting the link between ELA and psychopathology and we will primarily discuss the main biological mechanisms that have been described as potential mediators of the effects of ELA on the psychopathologic risk, including the role for genetic factors as well as sex differences. The knowledge emerging from these studies may be instrumental for the development of novel therapeutic strategies aimed not only at correcting the deficits that emerge from ELA exposure, but also in preventing the manifestation of a full-blown psychopathologic condition. With this respect, we will specifically focus on adolescence as a key time frame for disease onset as well as for early therapeutic intervention. We believe that incorporating clinical and preclinical research data in the context of early life adversities can be instrumental to elucidate the mechanisms contributing to the risk for psychopathology or that may promote resilience. This will ultimately allow the identification of 'at risk' individuals who may benefit from specific forms of interventions that, by interfering with disease trajectories, could result in more benign clinical outcomes.

Integrating developmental neuroscience with community-engaged approaches to address mental health outcomes for housing-insecure youth: Implications for research, practice, and policy

One in three children in the United States is exposed to insecure housing conditions, including unaffordable, inconsistent, and unsafe housing. These exposures have detrimental impacts on youth mental health. Delineating the neurobehavioral pathways linking exposure to housing insecurity with children's mental health has the potential to inform interventions and policy. However, in approaching this work, carefully considering the lived experiences of youth and families is essential to translating scientific discovery to improve health outcomes in an equitable and representative way. In the current paper, we provide an introduction to the range of stressful experiences that children may face when exposed to insecure housing conditions. Next, we highlight findings from the early-life stress literature regarding the potential neurobehavioral consequences of insecure housing, focusing on how unpredictability is associated with the neural circuitry supporting cognitive and emotional development. We then delineate how community-engaged research (CEnR) approaches have been leveraged to understand the effects of housing insecurity on mental health, and we propose future research directions that integrate developmental neuroscience research and CEnR approaches to maximize the impact of this work. We conclude by outlining practice and policy recommendations that aim to improve the mental health of children exposed to insecure housing.

Sublethal effects of early-life exposure to common and emerging contaminants in birds

The plight of wild birds is becoming critical due to exposure to environmental contaminants. Although laboratory studies have provided insights into the developmental effects of chemical exposures, less is known about the adverse effects of environmental chemicals in developing wild birds. Early life stages are critical windows during which long-term organization of physiological, behavioral, and neurological systems can occur. Thus, contaminant exposure at early life stages can directly influence survival and reproductive success, with consequences for population stability and resilience in wild species. This review synthesizes existing knowledge regarding both short- and long-term effects of early-life exposure to widespread contaminants in birds. We focus especially on wild birds and on contaminants of concern within the Gulf of Mexico as an example of a habitat under anthropogenic stress from exposure to a complex mixture of chemicals and changing land uses that exacerbate existing vulnerabilities of wildlife in this region. Chemical contaminants for discussion in this review are based on avian mortality records from the Wildlife Health Information Sharing Partnership (WHISPers) database and on additional review of the literature regarding avian contaminants of concern for the northern Gulf of Mexico, and include oil and associated polycyclic aromatic hydrocarbons, dioxin and dioxin-like compounds, flame retardants, pesticides, heavy metals, and plastics. We provide an overview of effects in bird species at both the pre-hatching and post-hatching early life stages, discuss differences in sensitivities by route of exposure, life stage, and life history, and provide recommendations for future research. We find that additional research is needed on altricial species, post-hatching early-life exposure, long-term effects, and on ecologically relevant contaminant concentrations and routes of exposure. Given the increasing frequency and intensity of anthropogenic stressors encountered by wild animals, understanding both lethal and sublethal impacts of contaminants on the health of individuals and populations will be critical to inform restoration, management, and mitigation efforts.

Early-Life Resource Scarcity in Mice Does Not Alter Adult Corticosterone or Preovulatory Luteinizing Hormone Surge Responses to Acute Psychosocial Stress

Early-life stressors can affect reproductive development and change responses to adult stress. We tested if resource scarcity in the form of limited bedding and nesting (LBN) from postnatal days (PND) 4 to 11 delayed sexual maturation in male and female mice and/or altered the response to an acute, layered, psychosocial stress (ALPS) in adulthood. Contrary to the hypotheses, age and mass at puberty were unaffected by the present application of LBN. Under basal conditions and after ALPS, corticosterone concentrations in males, diestrous females, and proestrous females reared in standard (STD) or LBN environments were similar. ALPS disrupts the luteinizing hormone (LH) surge in most mice when applied on the morning of proestrus; this effect was not changed by resource scarcity. In this study, the paucity of effects in the offspring may relate to a milder response of CBA dams to the paradigm. While LBN dams exited the nest more often and their offspring were smaller than STD-reared offspring on PND11, dam corticosterone concentrations were similar on PND11. To test if ALPS disrupts the LH surge by blunting the increase in excitatory GABAergic input to gonadotropin-releasing hormone (GnRH) neurons on the afternoon of proestrus, we conducted whole-cell voltage-clamp recordings. The frequency of GABAergic postsynaptic currents in GnRH neurons was not altered by LBN, ALPS, or their interaction. It remains possible that ALPS acts at afferents of GnRH neurons, changes response of GnRH neurons to input, and/or alters pituitary responsiveness to GnRH and that a more pronounced resource scarcity would affect the parameters studied.

Individual longitudinal changes in DNA-methylome identify signatures of early-life adversity and correlate with later outcome

Adverse early-life experiences (ELA) affect a majority of the world's children. Whereas the enduring impact of ELA on cognitive and emotional health is established, there are no tools to predict vulnerability to ELA consequences in an individual child. Epigenetic markers including peripheral-cell DNA-methylation profiles may encode ELA and provide predictive outcome markers, yet the interindividual variance of the human genome and rapid changes in DNA methylation in childhood pose significant challenges. Hoping to mitigate these challenges we examined the relation of several ELA dimensions to DNA methylation changes and outcome using a within-subject longitudinal design and a high methylation-change threshold. DNA methylation was analyzed in buccal swab/saliva samples collected twice (neonatally and at 12 months) in 110 infants. We identified CpGs differentially methylated across time for each child and determined whether they associated with ELA indicators and executive function at age 5. We assessed sex differences and derived a sex-dependent 'impact score' based on sites that most contributed to methylation changes. Changes in methylation between two samples of an individual child reflected age-related trends and correlated with executive function years later. Among tested ELA dimensions and life factors including income to needs ratios, maternal sensitivity, body mass index and infant sex, unpredictability of parental and household signals was the strongest predictor of executive function. In girls, high early-life unpredictability interacted with methylation changes to presage executive function. Thus, longitudinal, within-subject changes in methylation profiles may provide a signature of ELA and a potential predictive marker of individual outcome.

Early-life stress impairs acquisition and retrieval of fear memories: sex-effects, corticosterone modulation, and partial prevention by targeting glucocorticoid receptors at adolescent age

The early postnatal period is a sensitive time window that is characterized by several neurodevelopmental processes that define neuronal architecture and function later in life. Here, we examined in young adult mice, using an auditory fear conditioning paradigm, whether stress during the early postnatal period 1) impacts fear acquisition and memory consolidation in male and female mice; 2) alters the fear responsiveness to corticosterone and 3) whether effects of early-life stress (ELS) can be prevented by treating mice with a glucocorticoid (GR) antagonist at adolescence. Male and female mice were exposed to a limited nesting and bedding model of ELS from postnatal day (PND) 2-9 and injected i.p with RU38486 (RU486) at adolescent age (PND 28-30). At two months of age, mice were trained in the fear conditioning (FC) paradigm (with and without post training administration of corticosterone - CORT) and freezing behavior during fear acquisition and contextual and auditory memory retrieval was scored. We observed that ELS impaired fear acquisition specifically in male mice and reduced both contextual and auditory memory retrieval in male and female mice. Acute post-training administration of CORT increased freezing levels during auditory memory retrieval in female mice but reduced freezing levels during the tone presentation in particular in control males. Treatment with RU486 prevented ELS-effects in acquisition in male mice and in females during auditory memory retrieval. In conclusion, this study highlights the long-lasting consequences of early-life stress on fear memory processing and further illustrates 1) the potential of a glucocorticoid antagonist intervention during adolescence to mitigate these effects and 2) the partial modulation of the auditory retrieval upon post training administration of CORT, with all these effects being sex-dependent.

Analysis of hippocampal synaptic function in a rodent model of early life stress

Background

Early life stress (ELS) is an important risk factor in the aetiology of depression. Developmental glucocorticoid exposure impacts multiple brain regions with the hippocampus being particularly vulnerable. Hippocampal mediated behaviours are dependent upon the ability of neurones to undergo long-term potentiation (LTP), an N-methyl-D-aspartate receptor (NMDAR) mediated process. In this study we investigated the effect of ELS upon hippocampal NMDAR function.

Methods

Hooded Long-Evans rat pups (n=82) were either undisturbed or maternally separated for 180 minutes per day (MS180) between post-natal day (PND) 1 and PND14. Model validation consisted of sucrose preference (n=18) and novelty supressed feeding (NSFT, n=34) tests alongside assessment of corticosterone (CORT) and paraventricular nucleus (PVN) cFos reactivity to stress and hippocampal neurogenesis (all n=18). AMPA/NMDA ratios (n=19), miniEPSC currents (n=19) and LTP (n=15) were assessed in whole-cell patch clamp experiments in CA1 pyramidal neurones.

Results

MS180 animals showed increased feeding latency in the NSFT alongside increased overall CORT in the restraint stress experiment and increased PVN cFos expression in males but no changes in neurogenesis or sucrose preference. MS180 was associated with a lower AMPA/NMDA ratio with no change in miniEPSC amplitude or area. There was no difference in short- or long-term potentiation between MS180 and control animals nor were there any changes during the induction protocol.

Conclusions

The MS180 model showed a behavioural phenotype consistent with previous work. MS180 animals showed increased NMDAR function with preliminary evidence suggesting that this was not concurrent with an increase in LTP.

Limited bedding and nesting increases ethanol drinking in female rats

Prenatal opioid exposure (POE) and postnatal adverse experiences are early life adversities (ELA) that often co-occur and increase problematic alcohol (EtOH) drinking during adolescence. We investigated the relationship between POE, postnatal adversity, and adolescent EtOH drinking in rats. We also sought to determine whether ELAs affect alpha-adrenoceptor density in the brain because the noradrenergic system is involved in problematic alcohol drinking and its treatment. We hypothesized that the combination of POE and postnatal adversity will increase alcohol drinking in rats compared to rats with exposure to either adversity alone or to control. We also predicted that POE and postnatal adversity would increase α1-adrenoceptor density and decrease α2-adrenoceptor density in brain to confer a stress-responsive phenotype. Pregnant rats received morphine (15 mg/kg/day) or saline via subcutaneous minipumps from gestational day 9 until birth. Limited bedding and nesting (LBN) procedures were introduced from postnatal day (PD) 3-11 to mimic early life adversity-scarcity. Offspring rats (PD 31-33) were given opportunities to drink EtOH (20 %, v/v) using intermittent-access, two-bottle choice (with water) procedures. Rats given access to EtOH were assigned into sub-groups that were injected with either yohimbine (1 mg/kg, ip) or vehicle (2 % DMSO, ip) 30 min prior to each EtOH access session to determine the effects of α2-adrenoceptor inhibition on alcohol drinking. We harvested cortices, brainstems, and hypothalami from EtOH-naïve littermates on either PD 30 or PD 70 and conducted radioligand receptor binding assays to quantify α1- and α2-adrenoceptor densities. Contrary to our hypothesis, only LBN alone increased EtOH intake in female adolescent rats compared to female rats with POE. Neither POE nor LBN affected α1- or α2-adrenoceptor densities in the cortex, brainstem, or hypothalamus of early- or late-aged adolescent rats. These results suggest a complex interaction between ELA type and sex on alcohol drinking.

Epigenetic mechanisms linking early-life adversities and mental health

Early-life adversities, whether prenatal or postnatal exposure, have been linked to adverse mental health outcomes later in life increasing the risk of several psychiatric disorders. Research on its neurobiological consequences demonstrated an association between exposure to adversities and persistent alterations in the structure, function, and connectivity of the brain. Consistent evidence supports the idea that regulation of gene expression through epigenetic mechanisms are involved in embedding the impact of early-life experiences in the genome and mediate between social environments and later behavioral phenotypes. In addition, studies from rodent models and humans suggest that these experiences and the acquired risk factors can be transmitted through epigenetic mechanisms to offspring and the following generations potentially contributing to a cycle of disease or disease risk. However, one of the important aspects of epigenetic mechanisms, unlike genetic sequences that are fixed and unchangeable, is that although the epigenetic markings are long-lasting, they are nevertheless potentially reversible. In this review, we summarize our current understanding of the epigenetic mechanisms involved in the mental health consequences derived from early-life exposure to malnutrition, maltreatment and poverty, adversities with huge and pervasive impact on mental health. We also discuss the evidence about transgenerational epigenetic inheritance in mammals and experimental data suggesting that suitable social and pharmacological interventions could reverse adverse epigenetic modifications induced by early-life negative social experiences. In this regard, these studies must be accompanied by efforts to determine the causes that promote these adversities and that result in health inequity in the population.

Long-term effects of Preweaning environmental impoverishment on neurobehavioral and neurocognitive outcomes in Sprague Dawley rats: An early environmental stress model

Developmental stress, including low socioeconomic status (SES), can induce dysregulation of the hypothalamic-pituitary-adrenal axis and result in long-term changes in stress reactivity. Children in lower SES conditions often experience more stress than those in other SES groups. There are multiple model systems of early environmental stress (EES), one of which is reduced cage bedding. Here we tested the effects of both prenatal and lactational EES in rats on a range of long-term behavioral and cognitive outcomes. There were persistent reductions in body weight in the EES rats in both sexes. The behavioral results showed no effects on learning and memory using tests of spatial learning or cognitive flexibility in the Morris water maze, egocentric learning in the Cincinnati water maze, or working memory in the radial-arm maze. There were no effects on basic open-field activity, elevated zero-maze, or forced swim test, but EES rats had reduced time in the dark side of the light/dark test. When rats were drug challenged in the open-field with d-amphetamine or MK-801, there were no differential responses to d-amphetamine, but the EES group under responded compared with the drug-induced hyperactivity in the control group in both males and females. The objective was to establish a developmental stress model that induced cognitive deficits and to the extent that this method did not cause such effects it was not the model we sought. However, the data showed several long-term effects of EES, including the reduced response to the irreversible NMDA antagonist MK-801. This effect merits further investigation.

Heterogenous effect of early adulthood stress on cognitive aging and synaptic function in the dentate gyrus

Cognitive aging widely varies among individuals due to different stress experiences throughout the lifespan and vulnerability of neurocognitive mechanisms. To understand the heterogeneity of cognitive aging, we investigated the effect of early adulthood stress (EAS) on three different hippocampus-dependent memory tasks: the novel object recognition test (assessing recognition memory: RM), the paired association test (assessing episodic-like memory: EM), and trace fear conditioning (assessing trace memory: TM). Two-month-old rats were exposed to chronic mild stress for 6 weeks and underwent behavioral testing either 2 weeks or 20 months later. The results show that stress and aging impaired different types of memory tasks to varying degrees. RM is affected by combined effect of stress and aging. EM became less precise in EAS animals. TM, especially the contextual memory, showed impairment in aging although EAS attenuated the aging effect, perhaps due to its engagement in emotional memory systems. To further explore the neural underpinnings of these multi-faceted effects, we measured long-term potentiation (LTP), neural density, and synaptic density in the dentate gyrus (DG). Both stress and aging reduced LTP. Additionally, the synaptic density per neuron showed a further reduction in the stress aged group. In summary, EAS modulates different forms of memory functions perhaps due to their substantial or partial dependence on the functional integrity of the hippocampus. The current results suggest that lasting alterations in hippocampal circuits following EAS could potentially generate remote effects on individual variability in cognitive aging, as demonstrated by performance in multiple types of memory.

Annual Research Review: The power of predictability - patterns of signals in early life shape neurodevelopment and mental health trajectories

The global burden of early life adversity (ELA) is profound. The World Health Organization has estimated that ELA accounts for almost 30% of all psychiatric cases. Yet, our ability to identify which individuals exposed to ELA will develop mental illness remains poor and there is a critical need to identify underlying pathways and mechanisms. This review proposes unpredictability as an understudied aspect of ELA that is tractable and presents a conceptual model that includes biologically plausible mechanistic pathways by which unpredictability impacts the developing brain. The model is supported by a synthesis of published and new data illustrating the significant impacts of patterns of signals on child development. We begin with an overview of the existing unpredictability literature, which has focused primarily on longer patterns of unpredictability (e.g. years, months, and days). We then describe our work testing the impact of patterns of parental signals on a moment-to-moment timescale, providing evidence that patterns of these signals during sensitive windows of development influence neurocircuit formation across species and thus may be an evolutionarily conserved process that shapes the developing brain. Next, attention is drawn to emerging themes which provide a framework for future directions of research including the evaluation of functions, such as effortful control, that may be particularly vulnerable to unpredictability, sensitive periods, sex differences, cross-cultural investigations, addressing causality, and unpredictability as a pathway by which other forms of ELA impact development. Finally, we provide suggestions for prevention and intervention, including the introduction of a screening instrument for the identification of children exposed to unpredictable experiences.

Age-dependent effects of acute stress on the behavior, blood parameters, immunity, and enteric nerves of mice

The impact of stress on mental and digestive health has been extensively studied, with chronic stress being associated with various disorders. However, age-related differences in the response to acute stress, both behaviorally and physiologically, remain poorly understood. Therefore, this study aimed to develop a model to detect transient stress in mice of different ages. The stressor employed in our experiments was a restraint stress procedure, where mice were subjected to brief periods of immobilization to induce an acute stress response. Male C3H/HeN mice aged 3, 6, 12, and 30 weeks were subjected to acute restrain stress (ARS) by being placed in a 50 ml conical centrifuge tube for 15 min. Subsequently, their behavior, organ tissues, hematological parameters, cortisol concentration, and immune responses were assessed. Following ARS, the increased in time and entries into the center by the 12-week-old mice following stress. In comparison to mice of other ages, those aged 6 weeks demonstrated notable elevations in erythrocytes, platelets, hemoglobin, and hematocrit, all of which were influenced by the time-dependent changes and the recovery process of ARS. Blood corticosterone levels were substantially elevated in all age groups after ARS. Furthermore, ARS induced a notable increase in leukocytes, basophils, residential macrophages, and CD4+ T cells in all age groups except for 3-week-old mice. However, the number of monocyte-derived macrophages and CD8+ T cells did not change significantly. Additionally, mice aged 3 and 6 weeks demonstrated an increase in GFAP+ cells following ARS, whereas NeuN+ cells decreased across all ages. These results suggest that ARS has varying effects on the behavior, cortisol concentration, and quantity of blood cells as well as hepatic immune cells in mice of different ages. These age-dependent responses shed light on the complex interplay between stress and physiological systems and contribute to the broader understanding of stress-related diseases.

DNA methylation signatures of early-life adversity are exposure-dependent in wild baboons

The early-life environment can profoundly shape the trajectory of an animal's life, even years or decades later. One mechanism proposed to contribute to these early-life effects is DNA methylation. However, the frequency and functional importance of DNA methylation in shaping early-life effects on adult outcomes is poorly understood, especially in natural populations. Here, we integrate prospectively collected data on fitness-associated variation in the early environment with DNA methylation estimates at 477,270 CpG sites in 256 wild baboons. We find highly heterogeneous relationships between the early-life environment and DNA methylation in adulthood: aspects of the environment linked to resource limitation (e.g., low-quality habitat, early-life drought) are associated with many more CpG sites than other types of environmental stressors (e.g., low maternal social status). Sites associated with early resource limitation are enriched in gene bodies and putative enhancers, suggesting they are functionally relevant. Indeed, by deploying a baboon-specific, massively parallel reporter assay, we show that a subset of windows containing these sites are capable of regulatory activity, and that, for 88% of early drought-associated sites in these regulatory windows, enhancer activity is DNA methylation-dependent. Together, our results support the idea that DNA methylation patterns contain a persistent signature of the early-life environment. However, they also indicate that not all environmental exposures leave an equivalent mark and suggest that socioenvironmental variation at the time of sampling is more likely to be functionally important. Thus, multiple mechanisms must converge to explain early-life effects on fitness-related traits.

Adverse effects of early-life stress: focus on the rodent neuroendocrine system

Early-life stress is associated with a high prevalence of mental illnesses such as post-traumatic stress disorders, attention-deficit/hyperactivity disorder, schizophrenia, and anxiety or depressive behavior, which constitute major public health problems. In the early stages of brain development after birth, events such as synaptogenesis, neuron maturation, and glial differentiation occur in a highly orchestrated manner, and external stress can cause adverse long-term effects throughout life. Our body utilizes multifaceted mechanisms, including neuroendocrine and neurotransmitter signaling pathways, to appropriately process external stress. Newborn individuals first exposed to early-life stress deploy neurogenesis as a stress-defense mechanism; however, in adulthood, early-life stress induces apoptosis of mature neurons, activation of immune responses, and reduction of neurotrophic factors, leading to anxiety, depression, and cognitive and memory dysfunction. This process involves the hypothalamus-pituitary-adrenal axis and neurotransmitters secreted by the central nervous system, including norepinephrine, dopamine, and serotonin. The rodent early-life stress model is generally used to experimentally assess the effects of stress during neurodevelopment. This paper reviews the use of the early-life stress model and stress response mechanisms of the body and discusses the experimental results regarding how early-life stress mediates stress-related pathways at a high vulnerability of psychiatric disorder in adulthood.

Early life adversity reduces affiliative behavior with a stressed cagemate and leads to sex-specific alterations in corticosterone responses in adult mice

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both groups of mice 20 or 90 min after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

SYK-623, a δ Opioid Receptor Inverse Agonist, Mitigates Chronic Stress-Induced Behavioral Abnormalities and Disrupted Neurogenesis

The δ opioid receptor (DOR) inverse agonist has been demonstrated to improve learning and memory impairment in mice subjected to restraint stress. Here, we investigated the effects of SYK-623, a new DOR inverse agonist, on behavioral, immunohistochemical, and biochemical abnormalities in a mouse model of imipramine treatment-resistant depression. Male ddY mice received daily treatment of adrenocorticotropic hormone (ACTH) combined with chronic mild stress exposure (ACMS). SYK-623, imipramine, or the vehicle was administered once daily before ACMS. After three weeks, ACMS mice showed impaired learning and memory in the Y-maze test and increased immobility time in the forced swim test. SYK-623, but not imipramine, significantly suppressed behavioral abnormalities caused by ACMS. Based on the fluorescent immunohistochemical analysis of the hippocampus, ACMS induced a reduction in astrocytes and newborn neurons, similar to the reported findings observed in the postmortem brains of depressed patients. In addition, the number of parvalbumin-positive GABA neurons, which play a crucial role in neurogenesis, was reduced in the hippocampus, and western blot analysis showed decreased glutamic acid decarboxylase protein levels. These changes, except for the decrease in astrocytes, were suppressed by SYK-623. Thus, SYK-623 mitigates behavioral abnormalities and disturbed neurogenesis caused by chronic stress.

Early life stress modulates the genetic influence on brain structure and cognitive function in children

The enduring influence of early life stress (ELS) on brain and cognitive development has been widely acknowledged, yet the precise mechanisms underlying this association remain elusive. We hypothesize that ELS might disrupt the genome-wide influence on brain morphology and connectivity development, consequently exerting a detrimental impact on children's cognitive ability. We analyzed the multimodal data of DNA genotypes, brain imaging (structural and diffusion MRI), and neurocognitive battery (NIH Toolbox) of 4276 children (ages 9-10 years, European ancestry) from the Adolescent Brain Cognitive Development (ABCD) study. The genome-wide influence on cognitive function was estimated using the polygenic score (GPS). By using brain morphometry and tractography, we identified the brain correlates of the cognition GPSs. Statistical analyses revealed relationships for the gene-brain-cognition pathway. The brain structural variance significantly mediated the genetic influence on cognition (indirect effect = 0.016, PFDR < 0.001). Of note, this gene-brain relationship was significantly modulated by abuse, resulting in diminished cognitive capacity (Index of Moderated Mediation = -0.007; 95 % CI = -0.012 ∼ -0.002). Our results support a novel gene-brain-cognition model likely elucidating the long-lasting negative impact of ELS on children's cognitive development.

Chronic Stress in Early Development and Effects on Traumatic Brain Injury Outcome

In recent years, significant advances have been made in the study of mild traumatic brain injury (mTBI). Complete recovery from mTBI normally requires days to weeks, yet a subset of the population suffers from symptoms for weeks to months after injury. The risk factors for these prolonged symptoms have not yet been fully understood. In this chapter, we address one proposed risk factor, early life stress (ELS) and its influence on mTBI recovery. To study the effects of ELS on mTBI recovery, accepted animal models of ELS, including maternal separation, limited bedding and nesting, and chronic unpredictable stress, have been implemented. Combining these ELS models with standardized mTBI models, such as fluid percussion injury or controlled cortical impact, has allowed for a deeper understanding of the neuronal, hormonal, and cognitive changes that occur after mTBI following ELS. These preclinical findings are being used to understand how adverse childhood experiences may predispose a subset of individuals to poorer recovery after mTBI.

Within-subject changes in methylome profile identify individual signatures of early-life adversity, with a potential to predict neuropsychiatric outcome

Background

Adverse early-life experiences (ELA), including poverty, trauma and neglect, affect a majority of the world's children. Whereas the impact of ELA on cognitive and emotional health throughout the lifespan is well-established, it is not clear how distinct types of ELA influence child development, and there are no tools to predict for an individual child their vulnerability or resilience to the consequences of ELAs. Epigenetic markers including DNA-methylation profiles of peripheral cells may encode ELA and provide a predictive outcome marker. However, the rapid dynamic changes in DNA methylation in childhood and the inter-individual variance of the human genome pose barriers to identifying profiles predicting outcomes of ELA exposure. Here, we examined the relation of several dimensions of ELA to changes of DNA methylation, using a longitudinal within-subject design and a high threshold for methylation changes in the hope of mitigating the above challenges.

Methods

We analyzed DNA methylation in buccal swab samples collected twice for each of 110 infants: neonatally and at 12 months. We identified CpGs differentially methylated across time, calculated methylation changes for each child, and determined whether several indicators of ELA associated with changes of DNA methylation for individual infants. We then correlated select dimensions of ELA with methylation changes as well as with measures of executive function at age 5 years. We examined for sex differences, and derived a sex-dependent 'impact score' based on sites that most contributed to the methylation changes.

Findings

Setting a high threshold for methylation changes, we discovered that changes in methylation between two samples of an individual child reflected age-related trends towards augmented methylation, and also correlated with executive function years later. Among the tested factors and ELA dimensions, including income to needs ratios, maternal sensitivity, body mass index and sex, unpredictability of parental and household signals was the strongest predictor of executive function. In girls, an interaction was observed between a measure of high early-life unpredictability and methylation changes, in presaging executive function.

Interpretation

These findings establish longitudinal, within-subject changes in methylation profiles as a signature of some types of ELA in an individual child. Notably, such changes are detectable beyond the age-associated DNA methylation dynamics. Future studies are required to determine if the methylation profile changes identified here provide a predictive marker of vulnerabilities to poorer cognitive and emotional outcomes.

Potential resilience treatments for orangutans (Pongo spp.): Lessons from a scoping review of interventions in humans and other animals

Wild orangutans (Pongo spp.) rescued from human-wildlife conflict must be adequately rehabilitated before being returned to the wild. It is essential that released orangutans are able to cope with stressful challenges such as food scarcity, navigating unfamiliar environments, and regaining independence from human support. Although practical skills are taught to orangutans in rehabilitation centres, post-release survival rates are low. Psychological resilience, or the ability to 'bounce back' from stress, may be a key missing piece of the puzzle. However, there is very little knowledge about species-appropriate interventions which could help captive orangutans increase resilience to stress. This scoping review summarises and critically analyses existing human and non-human animal resilience literature and provides suggestions for the development of interventions for orangutans in rehabilitation. Three scientific databases were searched in 2021 and 2023, resulting in 63 human studies and 266 non-human animal studies. The first section brings together human resilience interventions, identifying common themes and assessing the applicability of human interventions to orangutans in rehabilitation. The second section groups animal interventions into categories of direct stress, separation stress, environmental conditions, social stress, and exercise. In each category, interventions are critically analysed to evaluate their potential for orangutans in rehabilitation. The results show that mild and manageable forms of intervention have the greatest potential benefit with the least amount of risk. The study concludes by emphasising the need for further investigation and experimentation, to develop appropriate interventions and measure their effect on the post-release survival rate of orangutans.

Early life stress lastingly alters the function and AMPA-receptor composition of glutamatergic synapses in the hippocampus of male mice

Early postnatal life is a sensitive period of development that shapes brain structure and function later in life. Exposure to stress during this critical time window can alter brain development and may enhance the susceptibility to psychopathology and neurodegenerative disorders later in life. The developmental effects of early life stress (ELS) on synaptic function are not fully understood, but could provide mechanistic insights into how ELS modifies later brain function and disease risk. We here assessed the effects of ELS on synaptic function and composition in the hippocampus of male mice. Mice were subjected to ELS by housing dams and pups with limited bedding and nesting material from postnatal days (P) 2-9. Synaptic strength was measured in terms of miniature excitatory postsynaptic currents (mEPSCs) in the hippocampal dentate gyrus at three different developmental stages: the early postnatal phase (P9), preadolescence (P21, at weaning) and adulthood at 3 months of age (3MO). Hippocampal synaptosome fractions were isolated from P9 and 3MO tissue and analyzed for protein content to assess postsynaptic composition. Finally, dendritic spine density was assessed in the DG at 3MO. At P9, ELS increased mEPSC frequency and amplitude. In parallel, synaptic composition was altered as PSD-95, GluA3 and GluN2B content were significantly decreased. The increased mEPSC frequency was sustained up to 3MO, at which age, GluA3 content was significantly increased. No differences were found in dendritic spine density. These findings highlight how ELS affects the development of hippocampal synapses, which could provide valuable insight into mechanisms how ELS alters brain function later in life.

Characterizing experiential elements of early-life stress to inform resilience: Buffering effects of controllability and predictability and the importance of their timing

Key theoretical frameworks have proposed that examining the impact of exposure to specific dimensions of stress at specific developmental periods is likely to yield important insight into processes of risk and resilience. Utilizing a sample of N = 549 young adults who provided a detailed retrospective history of their lifetime exposure to numerous dimensions of traumatic stress and ratings of their current trauma-related symptomatology via completion of an online survey, here we test whether an individual's perception of their lifetime stress as either controllable or predictable buffered the impact of exposure on trauma-related symptomatology assessed in adulthood. Further, we tested whether this moderation effect differed when evaluated in the context of early childhood, middle childhood, adolescence, and young adulthood stress. Consistent with hypotheses, results highlight both stressor controllability and stressor predictability as buffering the impact of traumatic stress exposure on trauma-related symptomatology and suggest that the potency of this buffering effect varies across unique developmental periods. Leveraging dimensional ratings of lifetime stress exposure to probe heterogeneity in outcomes following stress - and, critically, considering interactions between dimensions of exposure and the developmental period when stress occurred - is likely to yield increased understanding of risk and resilience following traumatic stress.

Neonatal Maternal Separation Induces Sexual Dimorphism in Brain Development: The Influence on Amino Acid Levels and Cognitive Disorders

Repeated maternal separation (MS) is a useful experimental model in rodents for studying the long-term influence of early-life stress on brain neurophysiology. In our work, we assessed the effect of repeated MS (postnatal day (PND)1-21, 180 min/day) on the postnatal development of rat brain regions involved in memory using proton magnetic resonance spectroscopy (1HMRS) for tissue volume and the level of amino acids such as glutamate, aspartate, glutamine, glycine and gamma-aminobutyric acid (GABA) in the hippocampus. We assessed whether these effects are sex dependent. We also use novel object recognition (NOR) task to examine the effect of MS on memory and the effect of ethanol on it. Finally, we attempted to ameliorate postnatal stress-induced memory deficits by using VU-29, a positive allosteric modulator (PAM) of the metabotropic glutamate type 5 (mGlu5) receptor. In males, we noted deficits in the levels of glutamate, glycine and glutamine and increases in GABA in the hippocampus. In addition, the values of perirhinal cortex, prefrontal cortex and insular cortex and CA3 were decreased in these animals. MS females, in contrast, demonstrated significant increase in glutamate levels and decrease in GABA levels in the hippocampus. Here, the CA1 values alone were increased. VU-29 administration ameliorated these cognitive deficits. Thus, MS stress disturbs amino acids levels mainly in the hippocampus of adult male rats, and enhancement of glutamate neurotransmission reversed recognition memory deficits in these animals.

The Interaction between Psychological Stress and Iron Status on Early-Life Neurodevelopmental Outcomes

This review presents evidence from animal and human studies demonstrating the possible connection and significant impact of poor iron status and psychological distress on neurocognitive development during pregnancy and the neonatal period, with implications for long-term cognition. Stress and iron deficiency are independently prevalent and thus are frequently comorbid. While iron deficiency and early-life stress independently contribute to long-term neurodevelopmental alterations, their combined effects remain underexplored. Psychological stress responses may engage similar pathways as infectious stress, which alters fundamental iron metabolism processes and cause functional tissue-level iron deficiency. Psychological stress, analogous to but to a lesser degree than infectious stress, activates the hypothalamic-pituitary-adrenocortical (HPA) axis and increases proinflammatory cytokines. Chronic or severe stress is associated with dysregulated HPA axis functioning and a proinflammatory state. This dysregulation may disrupt iron absorption and utilization, likely mediated by the IL-6 activation of hepcidin, a molecule that impedes iron absorption and redistributes total body iron. This narrative review highlights suggestive studies investigating the relationship between psychological stress and iron status and outlines hypothesized mechanistic pathways connecting psychological stress exposure and iron metabolism. We examine findings regarding the overlapping impacts of early stress exposure to iron deficiency and children's neurocognitive development. We propose that studying the influence of psychological stress on iron metabolism is crucial for comprehending neurocognitive development in children exposed to prenatal and early postnatal stressors and for children at risk of early iron insufficiency. We recommend future directions for dual-exposure studies exploring iron as a potential mediating pathway between early stress and offspring neurodevelopment, offering opportunities for targeted interventions.

Loss of spines in the prelimbic cortex is detrimental to working memory in mice with early-life adversity

Adverse experiences in early life can shape neuronal structures and synaptic function in multiple brain regions, leading to deficits of distinct cognitive functions later in life. Focusing on the pyramidal cells of the prelimbic cortex (PrL), a main subregion of the medial prefrontal cortex, the impact of early-life adversity (ELA) was investigated in a well-established animal model generated by changing the rearing environment during postnatal days 2 to 9 (P2-P9), a sensitive developmental period. ELA has enduring detrimental impacts on the dendritic spines of PrL pyramidal cells, which is most apparent in a spatially circumscribed region. Specifically, ELA affects both thin and mushroom-type spines, and ELA-provoked loss of spines is observed on selective dendritic segments of PrL pyramidal cells in layers II-III and V-VI. Reduced postsynaptic puncta represented by postsynaptic density protein-95 (PSD-95), but not synaptophysin-labelled presynaptic puncta, in ELA mice supports the selective loss of spines in the PrL. Correlation analysis indicates that loss of spines and postsynaptic puncta in the PrL contributes to the poor spatial working memory of ELA mice, and thin spines may play a major role in working memory performance. To further understand whether loss of spines affects glutamatergic transmission, AMPA- and NMDA-receptor-mediated synaptic currents (EPSCs) were recorded in a group of Thy1-expressing PrL pyramidal cells. ELA mice exhibited a depressed glutamatergic transmission, which is accompanied with a decreased expression of GluR1 and NR1 subunits in the PrL. Finally, upregulating the activation of Thy1-expressing PrL pyramidal cells via excitatory DREADDs can efficiently improve the working memory performance of ELA mice in a T-maze-based task, indicating the potential of a chemogenetic approach in restoring ELA-provoked memory deficits.

Individual differences in T1w/T2w ratio development during childhood

Myelination is a key developmental process that promotes rapid and efficient information transfer. Myelin also stabilizes existing brain networks and thus may constrain neuroplasticity, defined here as the brain's potential to change in response to experiences rather than the canonical definition as the process of change. Characterizing individual differences in neuroplasticity may shed light on mechanisms by which early experiences shape learning, brain and body development, and response to interventions. The T1-weighted/T2-weighted (T1w/T2w) MRI signal ratio is a proxy measure of cortical microstructure and thus neuroplasticity. Here, in pre-registered analyses, we investigated individual differences in T1w/T2w ratios in children (ages 4-10, n = 157). T1w/T2w ratios were positively associated with age within early-developing sensorimotor and attention regions. We also tested whether socioeconomic status, cognition (crystallized knowledge or fluid reasoning), and biological age (as measured with molar eruption) were related to T1w/T2w signal but found no significant effects. Associations among T1w/T2w ratios, early experiences, and cognition may emerge later in adolescence and may not be strong enough to detect in moderate sample sizes.

Early life adversity reduces affiliative behavior towards a distressed cagemate and leads to sex-specific alterations in corticosterone responses

Experiencing early life adversity (ELA) alters stress physiology and increases the risk for developing psychiatric disorders. The social environment can influence dynamics of stress responding and buffer and/or transfer stress across individuals. Yet, the impact of ELA on sensitivity to the stress of others and social behavior following stress is unknown. Here, to test the impact of ELA on social and physiological responses to stress, circulating blood corticosterone (CORT) and social behaviors were assessed in adult male and female mice reared under limited bedding and nesting (LBN) or control conditions. To induce stress, one cagemate of a pair-housed cage underwent a footshock paradigm and was then returned to their unshocked partner. CORT was measured in both mice 20 or 90 minutes after stress exposure, and social behaviors were recorded and analyzed. ELA rearing influenced the CORT response to stress in a sex-specific manner. In males, both control and ELA-reared mice exhibited similar stress transfer to unshocked cagemates and similar CORT dynamics. In contrast, ELA females showed a heightened stress transfer to unshocked cagemates, and sustained elevation of CORT relative to controls, indicating enhanced stress contagion and a failure to terminate the stress response. Behaviorally, ELA females displayed decreased allogrooming and increased investigative behaviors, while ELA males showed reduced huddling. Together, these findings demonstrate that ELA influenced HPA axis dynamics, social stress contagion and social behavior. Further research is needed to unravel the underlying mechanisms and long-term consequences of ELA on stress systems and their impact on behavioral outcomes.

How can early life adversity still exert an effect decades later? A question of timing, tissues and mechanisms

Exposure to any number of stressors during the first 1000 days from conception to age 2 years is important in shaping an individual's life trajectory of health and disease. Despite the expanding range of stressors as well as later-life phenotypes and outcomes, the underlying molecular mechanisms remain unclear. Our previous data strongly suggests that early-life exposure to a stressor reduces the capacity of the immune system to generate subsequent generations of naïve cells, while others have shown that, early life stress impairs the capacity of neuronal stem cells to proliferate as they age. This leads us to the "stem cell hypothesis" whereby exposure to adversity during a sensitive period acts through a common mechanism in all the cell types by programming the tissue resident progenitor cells. Furthermore, we review the mechanistic differences observed in fully differentiated cells and suggest that early life adversity (ELA) may alter mitochondria in stem cells. This may consequently alter the destiny of these cells, producing the lifelong "supply" of functionally altered fully differentiated cells.

DNA methylation signatures of early life adversity are exposure-dependent in wild baboons

The early life environment can profoundly shape the trajectory of an animal's life, even years or decades later. One mechanism proposed to contribute to these early life effects is DNA methylation. However, the frequency and functional importance of DNA methylation in shaping early life effects on adult outcomes is poorly understood, especially in natural populations. Here, we integrate prospectively collected data on fitness-associated variation in the early environment with DNA methylation estimates at 477,270 CpG sites in 256 wild baboons. We find highly heterogeneous relationships between the early life environment and DNA methylation in adulthood: aspects of the environment linked to resource limitation (e.g., low-quality habitat, early life drought) are associated with many more CpG sites than other types of environmental stressors (e.g., low maternal social status). Sites associated with early resource limitation are enriched in gene bodies and putative enhancers, suggesting they are functionally relevant. Indeed, by deploying a baboon-specific, massively parallel reporter assay, we show that a subset of windows containing these sites are capable of regulatory activity, and that, for 88% of early drought-associated sites in these regulatory windows, enhancer activity is DNA methylation-dependent. Together, our results support the idea that DNA methylation patterns contain a persistent signature of the early life environment. However, they also indicate that not all environmental exposures leave an equivalent mark and suggest that socioenvironmental variation at the time of sampling is more likely to be functionally important. Thus, multiple mechanisms must converge to explain early life effects on fitness-related traits.

Early life adversity as a risk factor for cognitive impairment and Alzheimer's disease

Neurological conditions, including cognitive impairment and Alzheimer's disease (AD), impose a huge burden on society, affecting millions of people globally. In addition to genetic factors, recent studies indicate that environmental and experiential factors may contribute to the pathogenesis of these diseases. Early life adversity (ELA) has a profound impact on brain function and health later in life. In rodent models, exposure to ELA results in specific cognitive deficits and aggravated AD pathology. Extensive concerns have been raised regarding the higher risk of developing cognitive impairments in people with a history of ELA. In this review, we scrutinize findings from human and animal studies focusing on the connection of ELA with cognitive impairment and AD. These discoveries suggest that ELA, especially at early postnatal stages, increases susceptibility to cognitive impairment and AD later in life. In terms of mechanisms, ELA could lead to dysregulation of the hypothalamus-pituitary-adrenal axis, altered gut microbiome, persistent inflammation, oligodendrocyte dysfunction, hypomyelination, and aberrant adult hippocampal neurogenesis. Crosstalks among these events may synergistically contribute to cognitive impairment later in life. Additionally, we discuss several interventions that may alleviate adverse consequences of ELA. Further investigation into this crucial area will help improve ELA management and reduce the burden of related neurological conditions.

Early life adversity impaired dorsal striatal synaptic transmission and behavioral adaptability to appropriate action selection in a sex-dependent manner

Early life adversity (ELA) is a major health burden in the United States, with 62% of adults reporting at least one adverse childhood experience. These experiences during critical stages of brain development can perturb the development of neural circuits that mediate sensory cue processing and behavioral regulation. Recent studies have reported that ELA impaired the maturation of dendritic spines on neurons in the dorsolateral striatum (DLS) but not in the dorsomedial striatum (DMS). The DMS and DLS are part of two distinct corticostriatal circuits that have been extensively implicated in behavioral flexibility by regulating and integrating action selection with the reward value of those actions. To date, no studies have investigated the multifaceted effects of ELA on aspects of behavioral flexibility that require alternating between different action selection strategies or higher-order cognitive processes, and the underlying synaptic transmission in corticostriatal circuitries. To address this, we employed whole-cell patch-clamp electrophysiology to assess the effects of ELA on synaptic transmission in the DMS and DLS. We also investigated the effects of ELA on the ability to update action control in response to outcome devaluation in an instrumental learning paradigm and reversal of action-outcome contingency in a water T-maze paradigm. At the circuit level, ELA decreased corticostriatal glutamate transmission in male but not in female mice. Interestingly, in DMS, glutamate transmission is decreased in male ELA mice, but increased in female ELA mice. ELA impaired the ability to update action control in response to reward devaluation in a context that promotes goal-directedness in male mice and induced deficits in reversal learning. Overall, our findings demonstrate the sex- and region-dependent effects of ELA on behavioral flexibility and underlying corticostriatal glutamate transmission. By establishing a link between ELA and circuit mechanisms underlying behavioral flexibility, our findings will begin to identify novel molecular mechanisms that can represent strategies for treating behavioral inflexibility in individuals who experienced early life traumatic incidents.

Association of Stress With Cognitive Function Among Older Black and White US Adults

Importance

Perceived stress can have long-term physiological and psychological consequences and has shown to be a modifiable risk factor for Alzheimer disease and related dementias.

Objective

To investigate the association between perceived stress and cognitive impairment in a large cohort study of Black and White participants aged 45 years or older.

Design, Setting, and Participants

The Reasons for Geographic and Racial Differences in Stroke (REGARDS) study is a national population-based cohort of 30 239 Black and White participants aged 45 years or older, sampled from the US population. Participants were recruited from 2003 to 2007, with ongoing annual follow-up. Data were collected by telephone, self-administered questionnaires, and an in-home examination. Statistical analysis was performed from May 2021 to March 2022.

Exposures

Perceived stress was measured using the 4-item version of the Cohen Perceived Stress Scale. It was assessed at the baseline visit and during 1 follow-up visit.

Main Outcomes and Measures

Cognitive function was assessed with the Six-Item Screener (SIS); participants with a score below 5 were considered to have cognitive impairment. Incident cognitive impairment was defined as a shift from intact cognition (SIS score >4) at the first assessment to impaired cognition (SIS score ≤4) at the latest available assessment.

Results

The final analytical sample included 24 448 participants (14 646 women [59.9%]; median age, 64 years [range, 45-98 years]; 10 177 Black participants [41.6%] and 14 271 White participants [58.4%]). A total of 5589 participants (22.9%) reported elevated levels of stress. Elevated levels of perceived stress (dichotomized as low stress vs elevated stress) were associated with 1.37 times higher odds of poor cognition after adjustment for sociodemographic variables, cardiovascular risk factors, and depression (adjusted odds ratio [AOR], 1.37; 95% CI, 1.22-1.53). The association of the change in the Perceived Stress Scale score with incident cognitive impairment was significant in both the unadjusted model (OR, 1.62; 95% CI, 1.46-1.80) and after adjustment for sociodemographic variables, cardiovascular risk factors, and depression (AOR, 1.39; 95% CI, 1.22-1.58). There was no interaction with age, race, and sex.

Conclusions and Relevance

This study suggests that there is an independent association between perceived stress and both prevalent and incident cognitive impairment. The findings suggest the need for regular screening and targeted interventions for stress among older adults.

The times they are a-changin': a proposal on how brain flexibility goes beyond the obvious to include the concepts of "upward" and "downward" to neuroplasticity

Since the brain was found to be somehow flexible, plastic, researchers worldwide have been trying to comprehend its fundamentals to better understand the brain itself, make predictions, disentangle the neurobiology of brain diseases, and finally propose up-to-date treatments. Neuroplasticity is simple as a concept, but extremely complex when it comes to its mechanisms. This review aims to bring to light an aspect about neuroplasticity that is often not given enough attention as it should, the fact that the brain's ability to change would include its ability to disconnect synapses. So, neuronal shrinkage, decrease in spine density or dendritic complexity should be included within the concept of neuroplasticity as part of its mechanisms, not as an impairment of it. To that end, we extensively describe a variety of studies involving topics such as neurodevelopment, aging, stress, memory and homeostatic plasticity to highlight how the weakening and disconnection of synapses organically permeate the brain in so many ways as a good practice of its intrinsic physiology. Therefore, we propose to break down neuroplasticity into two sub-concepts, "upward neuroplasticity" for changes related to synaptic construction and "downward neuroplasticity" for changes related to synaptic deconstruction. With these sub-concepts, neuroplasticity could be better understood from a bigger landscape as a vector in which both directions could be taken for the brain to flexibly adapt to certain demands. Such a paradigm shift would allow a better understanding of the concept of neuroplasticity to avoid any data interpretation bias, once it makes clear that there is no morality with regard to the organic and physiological changes that involve dynamic biological systems as seen in the brain.

Pinostrobin alleviates chronic restraint stress‑induced cognitive impairment by modulating oxidative stress and the function of astrocytes in the hippocampus of rats

Chronic stress has been recognized to induce the alterations of neuronal and glial cells in the hippocampus, and is thus implicated in cognitive dysfunction. There is increasing evidence to indicate that natural compounds capable of exerting neuroprotective and antioxidant activities, may function as potential therapeutic agents for cognitive impairment. The present study examined the neuroprotective effects of pinostrobin from Boesenbergia rotunda (L.) against chronic restraint stress (CRS)-induced cognitive impairment associated with the alterations of oxidative stress, neuronal density and glial fibrillary acidic protein (GFAP) of astrocytes in the hippocampus. For this purpose, male Wistar rats were administered once daily with pinostrobin (20 and 40 mg/kg, per os) prior to exposure to CRS (6 h/day) for 21 days. The cognitive behaviors, the concentration of malondialdehyde, and the activities of superoxide dismutase and catalase were determined. Histologically, the alterations in astrocytic GFAP and excitatory amino acid transporter 2 (EAAT2) in the hippocampus were examined. The results revealed that pinostrobin potentially attenuated cognitive impairment in the Y-maze and in novel object recognition tests, with a reduction in oxidative stress. Furthermore, pinostrobin effectively increased neuronal density, as well as the immunoreactivities of GFAP and EAAT2 in the hippocampus. Taken together, these findings indicate that treatment with pinostrobin alleviates chronic stress-induced cognitive impairment by exerting antioxidant effects, reducing neuronal cell damage, and improving the function of astrocytic GFAP and EAAT2. Thus, pinostrobin may have potential for use as a neuroprotective agent to protect against chronic stress-induced brain dysfunction and cognitive deficits.

Biochemical mechanisms in pathogenesis of infantile epileptic spasm syndrome

The molecular mechanisms leading to infantile epileptic spasm syndrome (IESS) remain obscure. The only common factor seems to be that the spasms are restricted to a limited period of infancy, during a certain maturational state. Here the current literature regarding the biochemical mechanisms of brain maturation in IESS is reviewed, and various hypotheses of the pathophysiology are put together. They include: (1) imbalance of inhibitory (NGF, IGF-1, ACTH, GABA) and excitatory factors (glutamate, nitrites) which distinguishes the different etiological subgroups, (2) abnormality of the hypothalamic pituitary adrenal (HPA) axis linking insults and early life stress, (3) inflammation (4) yet poorly known genetic and epigenetic factors, and (5) glucocorticoid and vigabatrin action on brain development, pinpointing at molecular targets of the pathophysiology from another angle. An altered maturational process may explain why so many, seemingly independent etiological factors lead to the same clinical syndrome and frequently to developmental delay. Understanding these factors can provide ideas for novel therapies.

Maternal High Fat Diet Anticipates the AD-like Phenotype in 3xTg-AD Mice by Epigenetic Dysregulation of Aβ Metabolism

Maternal overnutrition has been reported to affect brain plasticity of the offspring by altering gene expression, regulating both synaptic plasticity and adult neurogenesis. However, whether perinatal metabolic stress may influence the accumulation of misfolded proteins and the development of neurodegeneration remains to be clarified. We investigated the impact of maternal high fat diet (HFD) in an experimental model of Alzheimer's disease (AD). The 3xTg-AD mice born to overfed mothers showed an impairment of synaptic plasticity and cognitive deficits earlier than controls. Maternal HFD also altered the expression of genes regulating amyloid-β-protein (Aβ) metabolism (i.e., Bace1, Ern1, Ide and Nicastrin) and enhanced Aβ deposition in the hippocampus. Finally, we found an epigenetic derangement and an aberrant recruitment of transcription factors NF-kB and STAT3 and chromatin remodeler HDAC2 on the regulatory sequences of the same genes. Collectively, our data indicate that early life metabolic stress worsens the AD phenotype via epigenetic alteration of genes regulating Aβ synthesis and clearance.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

Early life stress impairs synaptic pruning in the developing hippocampus

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.