Interplay between social experiences and the genome: epigenetic consequences for behavior

A roadmap for social determinants of health and biological nursing research in the National Institute of Nursing Research 2022-2026 Strategic Plan: Optimizing health and advancing health equity using antiracist framing

BACKGROUND

Health equity is essential for improving the well-being of all individuals and groups, and research remains a critical element for understanding barriers to health equity. While considering how to best support research that acknowledges current health challenges, it is crucial to understand the role of social justice frameworks within health equity research and the contributions of minoritized researchers. Additionally, there should be an increased understanding of the influence of social determinants of health on biological mechanisms.

PURPOSE

Biological health equity research seeks to understand and address health disparities among historically excluded populations.

DISCUSSION

While there are examples of studies in this area led by minoritized researchers, some individuals and groups remain understudied due to underfunding. Research within minoritized populations must be prioritized to authentically achieve health equity. Furthermore, there should be increased funding from National Institutes of Health to support minoritized researchers working in this area.

Towards a three-level neo-Tinbergenian approach to object play: Structure, causes and consequences of a behavioral puzzle

My main goal in this paper is to propose a reformulation of foundational models in behavioral research, including Tinbergen's (1963) well-known four levels of analysis (namely, ontogenetic, mechanistic, functional, and evolutionary questions) and Mayr's (1961) dichotomy between proximate and ultimate causations. After critically evaluating these influential but problematic models, I present a three-level neo-Tinbergenian approach to behavior that considers the triadic integration of behavioral causes, structure, and consequences along a single temporal continuum. I then argue that object-directed play is a good candidate behavior to apply this new paradigm by presenting significant examples of the combined analysis of at least two of these three levels. Finally, I show how stone handling, a form of culturally-transmitted object play in macaques, is perfectly amenable to this unified three-level explanatory framework. My proposed approach fits recent theoretical and empirical advances in behavioral biology, has a heuristic value, and may provide numerous benefits to a range of behavioral scientists.

Current Marital Status and Epigenetic Clocks Among Older Adults in the United States: Evidence From the Health and Retirement Study

Objectives: This study examines how current marital status is associated with epigenetic aging. Methods: Data from the 2016 Health and Retirement Study were used to examine marital status differences in the four epigenetic clocks, that is, GrimAge, DunedinPoAm, PhenoAge, and Zhang (N = 3765). Weighted ordinary least square regression models were estimated separately for men and women. Results: Remarried, cohabiting, divorced/separated and widowed older adults showed greater epigenetic aging than the continuously married similarly among men and women. Distinct sex difference was observed among the never married. While never-married women exhibited greater epigenetic aging than their continuously married counterparts, older men in lifelong singlehood showed comparable epigenetic aging to their continuously married peers. Discussion: The findings speak to the importance of marital context for epigenetic aging in later life and the biological risk associated with lifelong singlehood for older women in the US.

Leveling with Tinbergen: Four levels simplified to causes and consequences

In 1963, Niko Tinbergen published his foundational manuscript identifying the four questions we ask in animal behavior-how does the behavior emerge across the lifespan (development); how does it work (mechanism); how and why did it evolve (evolution); and why is it adaptive (function). Tinbergen clarified that these 'levels of analysis' are complementary, not competing, thereby avoiding many fruitless scientific debates. However, the relationships among the four levels was never established. Here, we propose 'leveling' Tinbergen's questions to a single temporal timescale divided into causes (encompassing mechanism, development, and evolution) and consequences (encompassing function). Scientific advances now seamlessly link evolution, development, and mechanism into a continuum of 'causes'. The cause-consequence distinction separates the processes that precede (and lead to) a behavior, from the processes that come after (and result from) a behavior. Even for past behaviors, the functional outcomes are (historical) consequences of the causes that preceded them.

Neural and Molecular Mechanisms of Biological Embedding of Social Interactions

Animals operate in complex environments, and salient social information is encoded in the nervous system and then processed to initiate adaptive behavior. This encoding involves biological embedding, the process by which social experience affects the brain to influence future behavior. Biological embedding is an important conceptual framework for understanding social decision-making in the brain, as it encompasses multiple levels of organization that regulate how information is encoded and used to modify behavior. The framework we emphasize here is that social stimuli provoke short-term changes in neural activity that lead to changes in gene expression on longer timescales. This process, simplified-neurons are for today and genes are for tomorrow-enables the assessment of the valence of a social interaction, an appropriate and rapid response, and subsequent modification of neural circuitry to change future behavioral inclinations in anticipation of environmental changes. We review recent research on the neural and molecular basis of biological embedding in the context of social interactions, with a special focus on the honeybee.

Insects Provide Unique Systems to Investigate How Early-Life Experience Alters the Brain and Behavior

Early-life experiences have strong and long-lasting consequences for behavior in a surprising diversity of animals. Determining which environmental inputs cause behavioral change, how this information becomes neurobiologically encoded, and the functional consequences of these changes remain fundamental puzzles relevant to diverse fields from evolutionary biology to the health sciences. Here we explore how insects provide unique opportunities for comparative study of developmental behavioral plasticity. Insects have sophisticated behavior and cognitive abilities, and they are frequently studied in their natural environments, which provides an ecological and adaptive perspective that is often more limited in lab-based vertebrate models. A range of cues, from relatively simple cues like temperature to complex social information, influence insect behavior. This variety provides experimentally tractable opportunities to study diverse neural plasticity mechanisms. Insects also have a wide range of neurodevelopmental trajectories while sharing many developmental plasticity mechanisms with vertebrates. In addition, some insects retain only subsets of their juvenile neuronal population in adulthood, narrowing the targets for detailed study of cellular plasticity mechanisms. Insects and vertebrates share many of the same knowledge gaps pertaining to developmental behavioral plasticity. Combined with the extensive study of insect behavior under natural conditions and their experimental tractability, insect systems may be uniquely qualified to address some of the biggest unanswered questions in this field.

Social defeat stress in adult mice causes alterations in gene expression, alternative splicing, and the epigenetic landscape of H3K4me3 in the prefrontal cortex: An impact of early-life stress

Chronic stress is the leading risk factor of a broad range of severe psychopathologies. Nonetheless, the molecular mechanisms triggering these pathological processes are not well understood. In our study, we investigated the effects of 15-day social defeat stress (SDS) on the genome-wide landscape of trimethylation at the 4th lysine residue of histone H3 (H3K4me3) and on the transcriptome in the prefrontal cortex of mice that were reared normally (group SDS) or subjected to maternal separation early in life (group MS+SDS). The mice with the history of stress early in life showed increased susceptibility to SDS in adulthood and demonstrated long-lasting genome-wide alterations in gene expression and splicing as well as in the H3K4me3 epigenetic landscape in the prefrontal cortex. Thus, the high-throughput techniques applied here allowed us to simultaneously detect, for the first time, genome-wide epigenetic and transcriptional changes in the murine prefrontal cortex that are associated with both chronic SDS and increased susceptibility to this stressor.

Positive Feedback between Behavioral and Hormonal Dynamics Leads to Differentiation of Life-History Tactics

AbstractCompetitive interaction among individuals of a single population may result in the differentiation of two or more distinct life-history tactics. For example, although they exhibit unimodal size distribution, male juveniles of salmonids differentiate into those going down to the ocean to grow and returning to the natal stream after several years to reproduce (migratory tactic) and those staying in the stream and reproducing for multiple years (resident tactic). In this study, we developed a simple mathematical model for the positive feedback between hormonal and behavioral dynamics, with the expectation of establishing multiple discrete clusters of hormone levels leading to differentiation of life-history tactics. The assumptions were that probability of winning in fighting depends both on the body size and hormone level of the two contestants. An individual with a higher hormone level would be more likely to win the competition, which further enhanced hormone production, forming a positive feedback loop between hormone level and fighting ability. If the positive feedback was strong but not excessive, discrete clusters of hormone levels emerged from a continuous distribution. In contrast, no clear clustering structure appeared in the distribution of hormone levels if the probability of winning in fighting was controlled by the body size.

Whole Genome 5'-Methylcytosine Level Quantification in Cirrhotic HCV-Infected Egyptian Patients with and without Hepatocellular Carcinoma

DNA methylation is an epigenetic mechanism used by cells to control gene expression. DNA methylation is a commonly used epigenetic signaling tool that can hold genes in the “off” position. Chronic infection with hepatitis C virus (HCV) is considered a major risk for chronic liver impairment. It is the most common leading cause of HCC. The present work is aimed at studying whole genome 5′-methylcytosine levels in cirrhotic HCV-infected Egyptian patients. In the present study, 120 Egyptian adults were included. They were divided into two groups: group І (40 apparently healthy control subjects) and group ІІ (80 HCV-infected patients). Furthermore, group II was subdivided into 2 subgroups according to the presence of HCC in HCV-infected subjects. To all studied subjects, the level of 5-mC% was measured in peripheral blood. In the present study, the median of 5′-methylcytosine% in the control group (group I) was 2.5, in the HCV group (group IIa) was 2.45, and in the HCC group (group II b) was 2.25. A stepwise decrease in 5′-methylcytosine% from the control (group I) toward HCC (group IIb) was observed, taking into consideration that the stepwise global hypomethylation was not statistically significant (p = 0.811). There was a negative correlation between ALT and 5′-methylcytosine% (p = −0.029). From this study, we can conclude that global DNA 5′-methylcytosine% does not differ in HCV-infected cirrhotic patients and HCC patients when compared to normal controls. Consecutively, we had concluded that there is no impact of 5′-methylcytosine% on the development of liver cirrhosis or HCC. Moreover, the negative correlation between 5′-methylcytosine% and serum ALT level denotes a trend of decrease in 5′-methylcytosine% with more liver damage.

Maternal Deprivation and Sex Alter Central Levels of Neurotrophins and Inflammatory Cytokines in Rats Exposed to Palatable Food in Adolescence

Maternal deprivation (MD) in rodents is used to simulate human-infant early life stress, which leads to neural, hormonal, and behavioral alterations. Palatable food (PF) can reduce the stress response, and individuals use it as a self-applied stress relief method. Thus, the present study aimed to evaluate the effect of the association between MD in the early life (P1-P10) and PF consumption (condensed milk, P21-P44) in the central neuroplasticity (BDNF/NGF levels) and central neuroinflammatory parameters (TNF-α, IL-6, and IL-10 levels) in male and female Wistar rats in the adolescence. In addition, weight-related parameters (weight gain, Lee Index, and relative adipose tissue weight) were evaluated. PF exposure increased relative adipose tissue weight; however, it did not lead to a change in animals' body weight. MD reduced hypothalamic BDNF and NGF levels, and hippocampal TNF-α levels in male and female rats. Animals of both sexes that received PF, exhibited reduced hypothalamic NGF levels. Neuroinflammatory marker evaluations showed that male rats were more susceptible to the interventions than female rats, since MD reduced their cortical IL-10 levels and PF increased their IL-6 levels. Differences in the Lee index, central BDNF, TNF-α, and IL-6levels were observed between sexes. Male animals per se presented greater Lee index. Female rats had higher BDNF and IL-6 levels in the hippocampus and hypothalamus and higher hypothalamic TNF-α levels than those observed in males. In conclusion, there were more noticeable effects of MD than PF on the variables measured in this study. Sex effect was identified as an important factor and influenced most of the neurochemical measures in this study. In this way, we suggest including both female and male animals in researches to improve the quality of translational studies.

Genome-wide effects of social status on DNA methylation in the brain of a cichlid fish, Astatotilapia burtoni

BACKGROUND

Successful social behavior requires real-time integration of information about the environment, internal physiology, and past experience. The molecular substrates of this integration are poorly understood, but likely modulate neural plasticity and gene regulation. In the cichlid fish species Astatotilapia burtoni, male social status can shift rapidly depending on the environment, causing fast behavioral modifications and a cascade of changes in gene transcription, the brain, and the reproductive system. These changes can be permanent but are also reversible, implying the involvement of a robust but flexible mechanism that regulates plasticity based on internal and external conditions. One candidate mechanism is DNA methylation, which has been linked to social behavior in many species, including A. burtoni. But, the extent of its effects after A. burtoni social change were previously unknown.

RESULTS

We performed the first genome-wide search for DNA methylation patterns associated with social status in the brains of male A. burtoni, identifying hundreds of Differentially Methylated genomic Regions (DMRs) in dominant versus non-dominant fish. Most DMRs were inside genes supporting neural development, synapse function, and other processes relevant to neural plasticity, and DMRs could affect gene expression in multiple ways. DMR genes were more likely to be transcription factors, have a duplicate elsewhere in the genome, have an anti-sense lncRNA, and have more splice variants than other genes. Dozens of genes had multiple DMRs that were often seemingly positioned to regulate specific splice variants.

CONCLUSIONS

Our results revealed genome-wide effects of A. burtoni social status on DNA methylation in the brain and strongly suggest a role for methylation in modulating plasticity across multiple biological levels. They also suggest many novel hypotheses to address in mechanistic follow-up studies, and will be a rich resource for identifying the relationships between behavioral, neural, and transcriptional plasticity in the context of social status.

Future Directions for Personality Research: Contributing New Insights to the Understanding of Animal Behavior

As part of the European Conference on Behavioral Biology 2018, we organized a symposium entitled, "Animal personality: providing new insights into behavior?" The aims of this symposium were to address current research in the personality field, spanning both behavioral ecology and psychology, to highlight the future directions for this research, and to consider whether differential approaches to studying behavior contribute something new to the understanding of animal behavior. In this paper, we discuss the study of endocrinology and ontogeny in understanding how behavioral variation is generated and maintained, despite selection pressures assumed to reduce this variation. We consider the potential mechanisms that could link certain traits to fitness outcomes through longevity and cognition. We also address the role of individual differences in stress coping, mortality, and health risk, and how the study of these relationships could be applied to improve animal welfare. From the insights provided by these topics, we assert that studying individual differences through the lens of personality has provided new directions in behavioral research, and we encourage further research in these directions, across this interdisciplinary field.

Epigenetic Regulation of the Social Brain

Social behavior, a highly adaptive and crucial component of mammalian life, is regulated by particularly sensitive regulatory brain mechanisms. Substantial evidence implicates classical epigenetic mechanisms including histone modifications, DNA methylation, and nucleosome remodeling as well as nonclassical mechanisms mediated by noncoding RNA in the regulation of social behavior. These mechanisms collectively form the 'epigenetic network' that orchestrates genomic integration of salient and transient social experiences. Consequently, its dysregulation has been linked to behavioral deficits and psychopathologies. This review focuses on the role of the epigenetic network in regulating the enduring effects of social experiences during early-life, adolescence, and adulthood. We discuss research in animal models, primarily rodents, and associations between dysregulation of epigenetic mechanisms and human psychopathologies, specifically autism spectrum disorder (ASD) and schizophrenia.

Does the Stress of Laboratory Life and Experimentation on Animals Adversely Affect Research Data? A Critical Review

Recurrent acute and/or chronic stress can affect all vertebrate species, and can have serious consequences. It is increasingly and widely appreciated that laboratory animals experience significant and repeated stress, which is unavoidable and is caused by many aspects of laboratory life, such as captivity, transport, noise, handling, restraint and other procedures, as well as the experimental procedures applied to them. Such stress is difficult to mitigate, and lack of significant desensitisation/habituation can result in considerable psychological and physiological welfare problems, which are mediated by the activation of various neuroendocrine networks that have numerous and pervasive effects. Psychological damage can be reflected in stereotypical behaviours, including repetitive pacing and circling, and even self-harm. Physical consequences include adverse effects on immune function, inflammatory responses, metabolism, and disease susceptibility and progression. Further, some of these effects are epigenetic, and are therefore potentially transgenerational: the biology of animals whose parents/grandparents were wild-caught and/or have experienced chronic stress in laboratories could be altered, as compared to free-living individuals. It is argued that these effects must have consequences for the reliability of experimental data and their extrapolation to humans, and this may not be recognised sufficiently among those who use animals in experiments.

Sex-specific epigenetic mediators between early life social disadvantage and adulthood BMI

AIM

The objective of this study was to identify potential epigenetic mediating pathways linking early life social disadvantage (ELSD) to adulthood BMI.

METHODS

Sex-specific epigenome-wide two-stage mediation analyses were conducted in blood and adipose tissue, and mediation estimates were obtained using cross-product mediation analysis. Pathway analyses were conducted using GREAT software (Bejerano Lab, CA, USA).

RESULTS

Candidate mediation CpG sites were identified in adipose tissue, but not blood, and were sex-specific. Significant mediation sites in females included CpG loci in genes: PKHG1, BCAR3, ADAM5P, PIEZO1, FGFRL1, FASN and DPP9, among others. Pathway analyses revealed evidence of enrichment for processes associated with TFG-β signaling and immunologic signatures. In males, significant mediation loci included sites in MAP3K5 and RPTOR, which have previously been associated with adipogenesis, inflammation and insulin resistance.

CONCLUSION

Our findings provide supportive evidence for the mediating role of epigenetic mechanisms in the effect of early life social disadvantage on adulthood BMI.

Does childhood trauma influence offspring's birth characteristics?

Background

: A recent epigenetic hypothesis postulates that 'a sex-specific male-line transgenerational effect exists in humans', which can be triggered by childhood trauma during 'the slow growth period' just before puberty. The evidence is based on a few rather small epidemiological studies. We examine what response childhood trauma predicts, if any, in the birth size and prematurity risk of almost 800 000 offspring.

Methods

Children of parity 1, 2 or 3, born 1976-2002 in Sweden, for whom we could trace both parents and all four grandparents, constituted generation 3 (G3, n = 764 569). Around 5% of their parents, G2, suffered parental (G1) death during their own childhood. The association of such trauma in G2 with G3 prematurity and birthweight was analysed, while controlling for confounders in G1 and G2. We examined whether the slow growth period was extra sensitive to parental loss.

Results

Parental (G1) death during (G2) childhood predicts premature birth and lower birthweight in the offspring generation (G3). This response is dependent on G2 gender, G2 age at exposure and G3 parity, but not G3 gender.

Conclusions

The results are compatible with the Pembrey-Bygren hypothesis that trauma exposure during boys' slow growth period may trigger a transgenerational response; age at trauma exposure among girls seems less important, suggesting a different set of pathways for any transgenerational response. Finally, parental death during childhood was not important for the reproduction of social inequalities in birthweight and premature birth.

Advancing behavioural genomics by considering timescale

Animal behavioural traits often covary with gene expression, pointing towards a genomic constraint on organismal responses to environmental cues. This pattern highlights a gap in our understanding of the time course of environmentally responsive gene expression, and moreover, how these dynamics are regulated. Advances in behavioural genomics explore how gene expression dynamics are correlated with behavioural traits that range from stable to highly labile. We consider the idea that certain genomic regulatory mechanisms may predict the timescale of an environmental effect on behaviour. This temporally minded approach could inform both organismal and evolutionary questions ranging from the remediation of early life social trauma to understanding the evolution of trait plasticity.

Early-life adversity and long-term neurobehavioral outcomes: epigenome as a bridge?

Accumulating evidence suggests that adversities at critical periods in early life, both pre- and postnatal, can lead to neuroendocrine perturbations, including hypothalamic-pituitary-adrenal axis dysregulation and inflammation persisting up to adulthood. This process, commonly referred to as biological embedding, may cause abnormal cognitive and behavioral functioning, including impaired learning, memory, and depressive- and anxiety-like behaviors, as well as neuropsychiatric outcomes in later life. Currently, the regulation of gene activity by epigenetic mechanisms is suggested to be a key player in mediating the link between adverse early-life events and adult neurobehavioral outcomes. Role of particular genes, including those encoding glucocorticoid receptor, brain-derived neurotrophic factor, as well as arginine vasopressin and corticotropin-releasing factor, has been demonstrated in triggering early adversity-associated pathological conditions. This review is focused on the results from human studies highlighting the causal role of epigenetic mechanisms in mediating the link between the adversity during early development, from prenatal stages through infancy, and adult neuropsychiatric outcomes. The modulation of epigenetic pathways involved in biological embedding may provide promising direction toward novel therapeutic strategies against neurological and cognitive dysfunctions in adult life.

Relationship of Genetic Variants With Procedural Pain, Anxiety, and Distress in Children

OBJECTIVE

This study used a candidate gene approach to examine genomic variation associated with pain, anxiety, and distress in children undergoing a medical procedure.

STUDY DESIGN

Children aged 4-10 years having an IV catheter insertion were recruited from three Midwestern children's hospitals. Self-report measures of pain, anxiety, and distress were obtained as well as an observed measure of distress. Samples were collected from children and biological parents for analysis of genomic variation. Genotyped variants had known or suspected association with phenotypes of interest. Analyses included child-only association and family-based transmission disequilibrium tests.

RESULTS

Genotype and phenotype data were available from 828 children and 376 family trios. Children were 50% male, had a mean age of 7.2 years, and were 84% White/non-Hispanic. In family-based analysis, one single-nucleotide polymorphism (SNP; rs1143629, interleukin ( IL1B) 1β) was associated with observed child distress at Bonferroni-corrected levels of significance ( p = .00013), while two approached significance for association with high state anxiety (rs6330 Nerve Growth Factor, Beta Subunit, [ NGFB]) and high trait anxiety (rs6265 brain-derived neurotrophic factor [ BDNF]). In the child-only analysis, multiple SNPs showed nominal evidence of relationships with phenotypes of interest. rs6265 BDNF and rs2941026 cholecystokinin B receptor had possible relationships with trait anxiety in child-only and family-based analyses.

CONCLUSIONS

Exploring genomic variation furthers our understanding of pain, anxiety, and distress and facilitates genomic screening to identify children at high risk of procedural pain, anxiety, and distress. Combined with clinical observations and knowledge, such explorations could help guide tailoring of interventions to limit procedure-related distress and identify genes and pathways of interest for future genotype-phenotype studies.

Neonatal Maternal Separation Alters, in a Sex-Specific Manner, the Expression of TRH, of TRH-Degrading Ectoenzyme in the Rat Hypothalamus, and the Response of the Thyroid Axis to Starvation

Hypothalamic-pituitary-thyroid (HPT) axis activity is important for energy homeostasis, and is modified by stress. Maternal separation (MS) alters the stress response and predisposes to metabolic disturbances in the adult. We therefore studied the effect of MS on adult HPT axis activity. Wistar male and female pups were separated from their mothers 3 h/d during postnatal day (PND)2-PND21 (MS), or left nonhandled (NH). Open field and elevated plus maze tests revealed increased locomotion in MS males and anxiety-like behavior in MS females. At PND90, MS females had increased body weight gain, Trh expression in the hypothalamic paraventricular nucleus, and white adipose tissue mass. MS males had increased expression of TRH-degrading enzyme in tanycytes, reduced TSH and T3, and enhanced corticosterone serum concentrations. MS stimulated brown adipose tissue deiodinase 2 activity in either sex. Forty-eight hours of fasting (PND60) augmented serum corticosterone levels similarly in MS or NH females but more in MS than in NH male rats. MS reduced the fasting-induced drop in hypothalamic paraventricular nucleus-Trh expression of males but not of females and abolished the fasting-induced increase in Trh expression in both sexes. Fasting reduced serum concentrations of TSH, T4, and T3, less in MS than in NH males, whereas in females, TSH decreased in MS but not in NH rats, but T4 and T3 decreased similarly in NH and MS rats. In conclusion, MS produced long-term changes in the activity of the HPT axis that were sex specific; response to fasting was partially blunted in males, which could affect their adaptive response to negative energy balance.

In tribute to Bob Blanchard: Divergent behavioral phenotypes of 16p11.2 deletion mice reared in same-genotype versus mixed-genotype cages

Mouse models offer indispensable heuristic tools for studying genetic and environmental causes of neuropsychiatric disorders, including autism. Development of useful animal models of complex human behaviors depends not only on extensive knowledge of the human disease, but also on a deep understanding of animal behavior and ethology. Robert and Caroline Blanchard pioneered a number of elegant social paradigms in rodents. Their early work led to systematic delineations of rodent naturalist defensive behaviors,which were proven to be highly useful models of human psychiatric disorders, including fear and anxiety. Their work using the Visible Burrow System to study social stress in rats represented an unprecedented approach to study biological mechanisms of depression. In recent years, their extensive knowledge of mouse behavior and ethology enabled them to quickly become leading figures in the field of behavioral genetics of autism. To commemorate Robert Blanchard's influences on animal models of human psychiatric disorders, here we describe a study conceptualized and led by Mu Yang who was trained as a graduate student in the Blanchard laboratory in the early 2000s. This investigation focuses on social housing in a genetic mouse model of 16p11.2 deletion syndrome. Heterozygous deletions and duplications of a segment containing about 29 genes on human chromosome 16 appear in approximately 0.5–1% of all cases of autism. 16p11.2 deletion syndrome is also associated with intellectual disabilities and speech impairments. Our previous studies showed that a mouse model of 16p11.2 deletion syndrome exhibited deficits in vocalizations and novel object recognition, as compared to wildtype littermate control cagemates. In the spirit of Bob Blanchard's careful attention to the role of social dominance in rodent behaviors, we became interested in the question of whether behavioral outcomes of a mutation differ when mutants are housed in mixed genotype cages, versus housing only mutants together in one group cage, and only wildtype littermates together in another group cage after weaning. 16p11.2 deletion presented a particularly good model organism to investigate this question, because the heterozygotes are smaller than their wildtype littermates, and may therefore become subordinate to their larger cagemates.Wildtype and heterozygotes were housed with cagemates of the same genotype (same-genotype cage) or with cagemates of the opposite genotype (mixed-genotype cage). Current results replicated social vocalization and object recognition deficits that we previously found in heterozygotes living in mixed-genotype cages. In contrast, heterozygotes that lived in same-genotype cages emitted normal numbers of vocalizations during male–female interactions, and displayed normal novel object recognition, indicating that the deletion per se was not sufficient to cause cognitive or social deficits. Social approach, same-sex social interaction, anxiety-related behavior, depression-related behavior, and open field exploration were not different between genotypes, and were not affected by housing in mixed versus in same-genotype cages. These findings suggest that elements of the home cage social environment could interact with genotype to impact aspects of disease phenotypes. Current findings are discussed as potentially reflecting behavioral deficits resulted from social stress, as inspired by a seminal paper by Bob and Caroline Blanchard [1].

The Intergenerational Impact of Genetic and Psychological Factors on Blood Pressure (InterGEN) Study: Design and Methods for Complex DNA Analysis

The Intergenerational Impact of Genetic and Psychological Factors on Blood Pressure (InterGEN) study aims to delineate the independent and interaction effects of genomic (genetic and epigenetic) and psychological-environmental (maternally perceived racial discrimination, mental health, and parenting behavior) factors on blood pressure (BP) among African American mother-child dyads over time. The purpose of this article is to describe the two-step genetic and epigenetic approach that will be executed to explore Gene × Environment interactions on BP using a longitudinal cohort design. Procedure for the single collection of DNA at Time 1 includes the use of the Oragene 500-format saliva sample collection tube, which provides enough DNA for both the Illumina Multi-Ethnic Genotyping and 850K EPIC methylation analyses. BP readings, height, weight, percentage of body fat, and percentage of body water will be measured on all participants every 6 months for 2 years for a total of 4 time points. Genomic data analyses to be completed include multivariate modeling, assessment of population admixture and structure, and extended analyses including Bonferroni correction, false discovery rate methods, Monte Carlo approach, EIGENSTRAT methods, and so on, to determine relationships among both main and interaction effects of genetic, epigenetic, and psychological environmental factors on BP.

DNA methylation, early life environment, and health outcomes

Epigenetics, and especially DNA methylation, have recently become provocative biological explanations for early-life environmental effects on later health. Despite the large increase in papers on the topic over the last few years, many questions remain with regards to the biological feasibility of this mechanism and the strength of the evidence to date. In this review, we examine the literature on early-life effects on epigenetic patterns, with special emphasis on social environmental influences. First, we review the basic biology of epigenetic modification of DNA and debate the role of early-life stressful, protective, and positive environments on gene-specific, system-specific, and whole-genome epigenetic patterns later in life. Second, we compare the epigenetic literatures of both humans and other animals and review the research linking epigenetic patterns to health in order to complete the mechanistic pathway. Third, we discuss physical environmental and social environmental effects, which have to date, generally not been jointly considered. Finally, we close with a discussion of the current state of the area's research, its future direction, and its potential use in pediatric health.

Early-life experience affects honey bee aggression and resilience to immune challenge

Early-life social experiences cause lasting changes in behavior and health for a variety of animals including humans, but it is not well understood how social information ''gets under the skin'' resulting in these effects. Adult honey bees (Apis mellifera) exhibit socially coordinated collective nest defense, providing a model for social modulation of aggressive behavior. Here we report for the first time that a honey bee's early-life social environment has lasting effects on individual aggression: bees that experienced high-aggression environments during pre-adult stages showed increased aggression when they reached adulthood relative to siblings that experienced low-aggression environments, even though all bees were kept in a common environment during adulthood. Unlike other animals including humans however, high-aggression honey bees were more, rather than less, resilient to immune challenge, assessed as neonicotinoid pesticide susceptibility. Moreover, aggression was negatively correlated with ectoparasitic mite presence. In honey bees, early-life social experience has broad effects, but increased aggression is decoupled from negative health outcomes. Because honey bees and humans share aspects of their physiological response to aggressive social encounters, our findings represent a step towards identifying ways to improve individual resiliency. Pre-adult social experience may be crucial to the health of the ecologically threatened honey bee.

Bisphenol A Interaction With Brain Development and Functions

Brain development is an organized, but constantly adaptive, process in which genetic and epigenetic signals allow neurons to differentiate, to migrate, and to develop correct connections. Gender specific prenatal sex hormone milieu participates in the dimorphic development of many neuronal networks. Environmental cues may interfere with these developmental programs, producing adverse outcomes. Bisphenol A (BPA), an estrogenic/antiandrogenic endocrine disruptor widely diffused in the environment, produces adverse effects at levels below the acceptable daily intake. This review analyzes the recent literature on the consequences of perinatal exposure to BPA environmental doses on the development of a dimorphic brain. The BPA interference with the development and function of the neuroendocrine hypothalamus and of the nuclei controlling energy balance, and with the hippocampal memory processing is also discussed. The detrimental action of BPA appears complex, involving different hormonal and epigenetic pathways activated, often in a dimorphic way, within clearcut susceptibility windows. To date, discrepancies in experimental approaches and in related outcomes make unfeasible to translate the available information into clear dose-response models for human risk assessment. Evaluation of BPA brain levels in relation to the appearance of adverse effects in future basic studies will certainly give better definition of the warning threshold for human health.

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism influences the association of the methylome with maternal anxiety and neonatal brain volumes

Early life environments interact with genotype to determine stable phenotypic outcomes. Here we examined the influence of a variant in the brain-derived neurotropic factor (BDNF) gene (Val66Met), which underlies synaptic plasticity throughout the central nervous system, on the degree to which antenatal maternal anxiety associated with neonatal DNA methylation. We also examined the association between neonatal DNA methylation and brain substructure volume, as a function of BDNF genotype. Infant, but not maternal, BDNF genotype dramatically influences the association of antenatal anxiety on the epigenome at birth as well as that between the epigenome and neonatal brain structure. There was a greater impact of antenatal maternal anxiety on the DNA methylation of infants with the methionine (Met)/Met compared to both Met/valine (Val) and Val/Val genotypes. There were significantly more cytosine–phosphate–guanine sites where methylation levels covaried with right amygdala volume among Met/Met compared with both Met/Val and Val/Val carriers. In contrast, more cytosine–phosphate–guanine sites covaried with left hippocampus volume in Val/Val infants compared with infants of the Met/Val or Met/Met genotype. Thus, antenatal Maternal Anxiety × BDNF Val66Met Polymorphism interactions at the level of the epigenome are reflected differently in the structure of the amygdala and the hippocampus. These findings suggest that BDNF genotype regulates the sensitivity of the methylome to early environment and that differential susceptibility to specific environmental conditions may be both tissue and function specific.

Neuroendocrine regulation of maternal behavior

The expression of maternal behavior in mammals is regulated by the developmental and experiential events over a female's lifetime. In this review the relationships between the endocrine and neural systems that play key roles in these developmental and experiential processes that affect both the establishment and maintenance of maternal care are presented. The involvement of the hormones estrogen, progesterone, and lactogens are discussed in the context of ligand, receptor, and gene activity in rodents and to a lesser extent in higher mammals. The roles of neuroendocrine factors, including oxytocin, vasopressin, classical neurotransmitters, and other neural gene products that regulate aspects of maternal care are set forth, and the interactions of hormones with central nervous system mediators of maternal behavior are discussed. The impact of prior developmental factors, including epigenetic events, and maternal experience on subsequent maternal care are assessed over the course of the female's lifespan. It is proposed that common neuroendocrine mechanisms underlie the regulation of maternal care in mammals.

Hormonal modulation of catecholaminergic neurotransmission in a prenatal stress model

Our laboratory has a long-standing interest in the effects of prenatal stress (PS) on various neurotransmitter pathways and the morphology of the developing brain as well as in behavioural aspects of the offspring. Employing a commonly used PS paradigm in which the dams were subjected to restraint stress during the last week of gestation, we observed that several of these pathways were altered in the offspring brain. In this chapter, we will summarize and discuss the results obtained with the main catecholaminergic pathways, namely dopamine (DA) and norepinephrine (NE). In our hands, PS produces an increase in dopamine D2-type receptors in limbic areas, a decreased DA release after amphetamine stimulation in prefrontal cortex (PFC) and an increase in NE release in the same area of the adult offspring brain. In addition, DA uptake is altered at prepubertal stages that persist through adulthood. However, the expression of the step-limiting enzyme of the DA synthesis, tyrosine hydroxylase (TH), is only impaired at early stages of development after PS in the neuronal bodies. At the nuclear regulation level, dopaminergic transcription factors Nurr1 and Ptx3 showed a high vulnerability to PS showing changes along the lifespan. It was striking to observe that many impairments observed in most of these pathways differed depending on whether they were tested before or after puberty indicating a particular sensitivity of the systems to variations in gonadal hormones peaks. In fact, we observed that PS induced long-term effects on the male offspring reproductive system and spermatogenesis development, particularly by inducing a long-term imbalance of circulating sexual hormone levels. Our findings suggest that PS exerts long-term effects on various neurotransmitter pathways altering the normal connectivity between brain areas. Since the developing forebrain was shown to be influenced by androgen exposure, and PS was shown to disrupt prenatal testosterone surges, our results suggest that prenatal insults might be affecting the organizational role of androgens during brain development and differentially modulating their activational role during pubertal brain maturation.

Epigenetic programming by early-life stress: Evidence from human populations

BACKGROUND

A substantial body of experimental and epidemiological evidence has been accumulated suggesting that stressful events in early life including acute perinatal stress, maternal deprivation or separation, and variation in maternal care may lead to neuroendocrine perturbations thereby affecting reproductive performance, cognitive functions, and stress responses as well as the risk for infectious, cardio-metabolic and psychiatric diseases in later life.

RESULTS

Findings from recent studies based on both genome-wide and candidate gene approaches highlighted the importance of mechanisms that are involved in epigenetic regulation of gene expression, such as DNA methylation, histone modifications, and non-coding RNAs, in the long-term effects of exposure to stress in early life.

CONCLUSIONS

This review is focused on the findings from human studies indicating the role of epigenetic mechanisms in the causal link between early-life stress and later-life health outcomes.

Parents and early life environment affect behavioral development of laying hen chickens

Severe feather pecking (SFP) in commercial laying hens is a maladaptive behavior which is associated with anxiety traits. Many experimental studies have shown that stress in the parents can affect anxiety in the offspring, but until now these effects have been neglected in addressing the problem of SFP in commercially kept laying hens. We therefore studied whether parental stock (PS) affected the development of SFP and anxiety in their offspring. We used flocks from a brown and white genetic hybrid because genetic background can affect SFP and anxiety. As SFP can also be influenced by housing conditions on the rearing farm, we included effects of housing system and litter availability in the analysis. Forty-seven rearing flocks, originating from ten PS flocks were followed. Behavioral and physiological parameters related to anxiety and SFP were studied in the PS at 40 weeks of age and in the rearing flocks at one, five, ten and fifteen weeks of age. We found that PS had an effect on SFP at one week of age and on anxiety at one and five weeks of age. In the white hybrid, but not in the brown hybrid, high levels of maternal corticosterone, maternal feather damage and maternal whole-blood serotonin levels showed positive relations with offsprings' SFP at one week and offsprings' anxiety at one and five weeks of age. Disruption and limitation of litter supply at an early age on the rearing farms increased SFP, feather damage and fearfulness. These effects were most prominent in the brown hybrid. It appeared that hens from a brown hybrid are more affected by environmental conditions, while hens from a white hybrid were more strongly affected by parental effects. These results are important for designing measures to prevent the development of SFP, which may require a different approach in brown and white flocks.

Brain region-specific methylation in the promoter of the murine oxytocin receptor gene is involved in its expression regulation

Oxytocin is a nine amino acid neuropeptide that is known to play a critical role in fetal expulsion and breast-feeding, and has been recently implicated in mammalian social behavior. The actions of both central and peripheral oxytocin are mediated through the oxytocin receptor (Oxtr), which is encoded by a single gene. In contrast to the highly conserved expression of oxytocin in specific hypothalamic nuclei, the expression of its receptor in the brain is highly diverse among different mammalian species or even within individuals of the same species. The diversity in the pattern of brain Oxtr expression among mammals is thought to contribute to the broad range of social systems and organizations. Yet, the mechanisms underlying this diversity are poorly understood. DNA methylation is a major epigenetic mechanism that regulates gene transcription, and has been linked to reduced expression levels of the Oxtr in individuals with autism. Here we hypothesize that DNA methylation is involved in the expression regulation of Oxtr in the mouse brain. By combining bisulfite DNA conversion and Next-Generation Sequencing we found that specific CpG sites are differentially methylated between distinct brain regions expressing different levels of Oxtr mRNA. Some of these CpG sites are located within putative binding sites of transcription factors known to regulate Oxtr expression, including estrogen receptor α (ERα) and SP1. Specifically, methylation of the SP1 site was found to positively correlate with Oxtr expression. Furthermore, we revealed that the methylation levels of these sites in the various brain regions predict the relationship between ERα and Oxtr mRNA levels. Collectively, our results suggest that brain region-specific expression of the mouse Oxtr gene is epigenetically regulated by DNA methylation of its promoter.

Prenatal transport stress, postnatal maternal behavior, and offspring sex differentially affect seizure susceptibility in young rats

Epilepsy is a heterogeneous and chronic neurological condition of undefined etiology in the majority of cases. Similarly, the pathogenesis of the unprovoked seizures that lead to epilepsy is not known. We are interested in the factors that modify inherent seizure susceptibility, with a particular focus on those occurring during the prenatal and early postnatal periods. Female Sprague-Dawley rats were bred in-house or transported during pregnancy at one of two gestational days (G9 or G16). The effects of transport stress, maternal behavior, and offspring sex were then examined in terms of how they were related to provoked seizure susceptibility to kainic acid (KA) or a model of febrile convulsions (FCs) on postnatal day 14 (P14). We also examined the pattern of neuronal activation in the hippocampus and amygdala as indicated by the density of FosB protein immunoreactivity (FosB-ir). Results demonstrated only a small and inconsistent effect of transport alone, suggesting that the groups differed slightly prior to experimental manipulations. However, the influence of maternal behaviors such as licking and grooming (LG), arched back nursing (ABN), and dam-off time (DO) exerted a much stronger effect on the offspring. Dams designated as high LG gave birth to smaller litters, had pups that weighed less, had greater seizure susceptibility and severity, and had more FosB-ir neurons predominantly in the ventral hippocampus and the medial subnucleus of the amygdala (MeA). We also found a sex-dependent effect such that P14 males were smaller than their female littermates and had a greater seizure susceptibility and severity. Taken together, these results suggest an impact of prenatal and postnatal factors, as well as sex, on seizure susceptibility in young animals.

Permanent and plastic epigenesis in neuroendocrine systems

The emerging area of neuroepigenetics has been linked to numerous mental health illnesses. Importantly, a large portion of what we know about early gene×environment interactions comes from examining epigenetic modifications of neuroendocrine systems. This review will highlight how neuroepigenetic mechanisms during brain development program lasting differences in neuroendocrine systems and how other neuroepigenetic processes remain plastic, even within the adult brain. As epigenetic mechanisms can either be stable or plastic, elucidating the mechanisms involved in reversing these processes could aid in understanding how to reverse pathological epigenetic programming.

Prenatal and gestational cocaine exposure: Effects on the oxytocin system and social behavior with implications for addiction

Drug abuse during pregnancy is a major public health concern, with negative consequences throughout development. Prenatal cocaine exposure (PCE) in rats produces social behavior deficits with corresponding changes in neuroendocrine and monoaminergic signaling. The relevance of parental care in social behavior maturity cannot be ignored, and gestational exposure to cocaine severely disrupts parental care, thus impacting the early environment of the offspring. Oxytocin (Oxt) is critical in regulating social behaviors and central levels are disrupted following acute and chronic cocaine (CC) treatment in postpartum rat dams, coincident with deficits in maternal care. We will discuss studies aimed to determine the relative contribution of PCE and CC-induced deficits in maternal care to social behaviors and Oxt signaling across development. PCE results in decreased social (including parental) behaviors in adolescence and adulthood. PCE is also associated with increased aggression in adults. Rearing by CC-exposed mothers synergistically increases the behavioral effects of PCE. Rearing by CC-exposed mothers, but not PCE, disrupts Oxt levels and mRNA in regions relevant to social behavior, but does not affect receptors in postpartum adult offspring. Preliminary work indicates that PCE/CC rearing has dynamic effects on Oxt levels and receptors in neonatal rat pups, suggesting very early regulation of Oxt signaling. This work highlights how the interactive role of Oxt signaling and behavioral context throughout development can be derailed by drug abuse during pregnancy. The relevance of disrupted Oxt to intergenerational transmission of addiction is briefly discussed.

Cryptic confounding compounds: A brief consideration of the influences of anthropogenic contaminants on courtship and mating behavior

Contaminants, like pesticides, polychlorinated biphenyls (PCBs), dioxins and metals, are persistent and ubiquitous and are known to threaten the environment. Traditionally, scientists have considered the direct physiological risks that these contaminants pose. However, scientists have just begun to integrate ethology and toxicology to investigate the effects that contaminants have on behavior. This review considers the potential for contaminant effects on mating behavior. Here we assess the growing body of research concerning disruptions in sexual differentiation, courtship, sexual receptivity, arousal, and mating. We discuss the implications of these disruptions on conservation efforts and highlight the importance of recognizing the potential for environmental stressors to affect behavioral experimentation. More specifically, we consider the negative implications for anthropogenic contaminants to affect the immediate behavior of animals, and their potential to have cascading and/or long-term effects on the behavioral ecology and evolution of populations. Overall, we aim to raise awareness of the confounding influence that contaminants can have, and promote caution when interpreting results where the potential for cryptic affects are possible.

The effects of bisphenol A on emotional behavior depend upon the timing of exposure, age and gender in mice

Experimental evidence suggests that endocrine-disrupting chemicals (EDCs) can permanently disrupt the development of sexually dimorphic behaviors and the structure of sexually dimorphic areas of the brain. EDC exposure has different effects depending on diverse factors, such as the timing and dose of the exposure, the maternal environment and the individual's age and sex. Among EDCs, bisphenol A (BPA) is one of the most studied because of its extensive use, which ranges from dentistry to food/drink packaging. In the present study, we aimed to investigate the behavioral effects of developmental exposure to a low dose of BPA with respect to the timing of the exposure, maternal environment, sex and age at testing. Starting from the last week of pregnancy to the first postpartum week, dams spontaneously drank either corn oil (control group) or a solution containing BPA (10 μg/kg bw/day). At birth, the litters were cross-fostered to different dams to differentiate among the effects of pre- and postnatal exposure. Pre- and postnatally exposed offspring underwent three diverse experimental paradigms for anxiety-related behaviors: as juveniles, a novelty test and at adulthood, both the free exploratory open field and elevated plus maze tests. At both testing ages, pre- and postnatally exposed females showed evidence of increased anxiety and were less prone to explore a novel environment relative to the control females, showing a behavioral profile more similar to control males than females. In this study, the direction of the behavioral changes was affected similarly by the pre- and postnatal exposures, resulting in a disruption of these sexually dimorphic behaviors, although with a greater effect associated with postnatal exposure primarily in females. Our findings indicate that non-reproductive, sexually dimorphic behaviors are sensitive to endocrine disruption during critical developmental periods-particularly the highly critical early neonatal stage. Combined with previous research, our study provides further evidence of the potential risks that even low doses of EDCs may pose to humans, with fetuses and infants being highly vulnerable.

Sexual differentiation of the brain in man and animals: of relevance to Klinefelter syndrome?

The developing brain is highly sensitive to the organizing effects of steroids of gonadal origin in a process referred to as sexual differentiation. Early hormone effects prime the brain for adult sensitivity to the appropriate hormonal milieu, maximizing reproductive fitness via coordinated physiology and behavior. Animal models, in particular rodents, have provided insight into general principles and the cellular and molecular mechanisms of brain differentiation. Cellular endpoints influenced by steroids in the developing brain include neurogenesis, migration, apoptosis, dendritic growth, and synaptic patterning. Important roles for prostaglandins, endocanabinoids, and epigenetics are among the many cellular mediators of hormonal organization. Transference of general principles of brain sexual differentiation to humans relies on observations of individuals with genetic anomalies that either increase or decrease hormone exposure and sensitivity. The physiology and behavior of individuals with XXY (Klinefelter syndrome) has not been considered in the context of sexual differentiation of the brain, most likely due to the delay in diagnoses and highly variable presentation. The behavioral phenotype and impairments in the domains of speech and language that are characteristic of individuals with XXY is consistent with the reduced androgen production associated with the syndrome. Hormone replacement appears effective in restoring some deficits and impact may be further improved by increased understanding of the hormonally mediated sexual differentiation of the brain.

Neonatal pain in very preterm infants: long-term effects on brain, neurodevelopment and pain reactivity

Effects of early life psychosocial adversity have received a great deal of attention, such as maternal separation in experimental animal models and abuse/neglect in young humans. More recently, long-term effects of the physical stress of repetitive procedural pain have begun to be addressed in infants hospitalized in neonatal intensive care. Preterm infants are more sensitive to pain and stress, which cannot be distinguished in neonates. The focus of this review is clinical studies of long-term effects of repeated procedural pain-related stress in the neonatal intensive care unit (NICU) in relation to brain development, neurodevelopment, programming of stress systems, and later pain sensitivity in infants born very preterm (24-32 weeks' gestational age). Neonatal pain exposure has been quantified as the number of invasive and/or skin-breaking procedures during hospitalization in the NICU. Emerging studies provide convincing clinical evidence for an adverse impact of neonatal pain/stress in infants at a time of physiological immaturity, rapidly developing brain microstructure and networks, as well as programming of the hypothalamic-pituitary-adrenal axis. Currently it appears that early pain/stress may influence the developing brain and thereby neurodevelopment and stress-sensitive behaviors, particularly in the most immature neonates. However, there is no evidence for greater prevalence of pain syndromes compared to children and adults born healthy at full term. In addressing associations between pain/stress and outcomes, careful consideration of confounding clinical factors related to prematurity is essential. The need for pain management for humanitarian care is widely advocated. Non-pharmacological interventions to help parents reduce their infant's stress may be brain-protective.