Parental experience is linked with lower vasopressin receptor 1a binding and decreased postpartum androgens in titi monkeys.

Parenting induces many neurological and behavioral changes that enable parents to rear offspring. Vasopressin plays an important role in this process via its effects on cognition, affect, and neuroplasticity, and in some cases, via interactions with decreased parental androgens. Thus far, the role of these hormones has been primarily studied in rodents. To address this gap, we explored vasopressin receptors and androgens in titi monkeys, a pair-bonding and biparental primate species. In Studies 1 and 2, we used receptor autoradiography to correlate arginine vasopressin receptor 1a (AVPR1a) binding in the hippocampus (Study 1, n = 10) and the rest of the forebrain (Study 2, n = 23) with parental status, parental experience, parity, infant carrying, and pair affiliation. We found that parents exhibited lower AVPR1a binding than non-parents throughout most brain regions assessed, with especially strong effects in the hippocampus (ß = -.61), superior colliculus (ß = -.88), lateral septum (ß = -.35), and medial preoptic area (ß = -.29). The other measures of parental experience also tended to be negatively associated with AVPR1a binding across different brain regions. In Study 3 (n = 44), we compared pre- and postpartum urinary androgen levels in parents and non-parents and found that mothers exhibited a sustained androgen decrease across 3-4 months postpartum (relative to 3 months prepartum; ß ranged from -.72 to -.62 for different comparisons). For males, we found that multiparous fathers exhibited decreased androgen levels at 1-2 weeks postpartum (ß = -.25) and at 3-4 months postpartum (ß = -.40) compared to the prepartum, indicating both immediate and long-term reductions with subsequent paternal experience. Together, the results of this study suggest that decreases in AVPR1a binding and circulating androgens are associated with parental behavior and physiology in titi monkeys.

Infant inhibited temperament in primates predicts adult behavior, is heritable, and is associated with anxiety-relevant genetic variation.

An anxious or inhibited temperament (IT) early in life is a major risk factor for the later development of stress-related psychopathology. Starting in infancy, nonhuman primates, like humans, begin to reveal their temperament when exposed to novel situations. Here, in Study 1 we demonstrate this infant IT predicts adult behavior. Specifically, in over 600 monkeys, we found that individuals scored as inhibited during infancy were more likely to refuse treats offered by potentially-threatening human experimenters as adults. In Study 2, using a sample of over 4000 monkeys from a large multi-generational family pedigree, we demonstrate that infant IT is partially heritable. The data revealed infant IT to reflect a co-inherited substrate that manifests across multiple latent variables. Finally, in Study 3 we performed whole-genome sequencing in 106 monkeys to identify IT-associated single-nucleotide variations (SNVs). Results demonstrated a genome-wide significant SNV near CTNNA2, suggesting a molecular target worthy of additional investigation. Moreover, we observed lower p values in genes implicated in human association studies of neuroticism and depression. Together, these data demonstrate the utility of our model of infant inhibited temperament in the rhesus monkey to facilitate discovery of genes that are relevant to the long-term inherited risk to develop anxiety and depressive disorders.

Prenatal Relocation Stress Enhances Resilience Under Challenge in Infant Rhesus Macaques.

The prenatal period is a developmental stage of peak sensitivity, during which environmental exposures can program post-natal developmental outcomes. Prenatal stress, in particular, has often been associated with detrimental neurobehavioral outcomes like mood and anxiety disorders. In the present study, we examined the effects of a stressful prenatal maternal experience (maternal relocation during pregnancy) on the post-partum development of offspring in rhesus macaques. To help isolate the effects of prenatal stress from genetic predispositions and post-natal experience, we compared biologically reared infants (infants raised with their biological mothers) with cross-fostered infants (those raised by non-related females in new social groups). We examined the effects of prenatal relocation stress on measures collected at 3-4 months of age during a standardized biobehavioral assessment. Unexpectedly, we found that prenatal stress resulted in a behavioral pattern consistent with resilience rather than anxiety: prenatal stress was linked with greater activity, lower anxiety, and more interaction with novel objects, as well as higher ratings of temperamental confidence during assessment. These effects were observed in infants reared by biological mothers as well as cross-fostered infants, suggesting that the effects of prenatal stress were not attributable to maternal genetics or post-natal factors. Our surprising results suggest that prenatal relocation stress may confer resilience in infant rhesus monkeys.

Behavioral mimicry predicts social favor in adolescent rhesus macaques (Macaca mulatta).

Non-conscious mimicry is a highly conserved component of animal behavior with multifaceted connections to sociality across taxa. One intriguing consequence of this mimicry in primates is that it promotes positive social feedback from the recipient toward the mimicker. This suggests that mimicry in primates may be an important aspect of positive social interaction, but few studies have tracked the consequences of mimicry in naturally occurring complex social conditions. Here, we designed a novel ethogram to characterize mimicry between conspecifics, to better understand whether mimicry is associated with affiliation between primates in a semi-naturalistic captive setting. In this study, 15 juvenile (aged 2-4 years) rhesus macaques (Macaca mulatta) were observed at the California National Primate Research Center. Frequencies of mimicry defined a priori (e.g. following, postural mimicry) were observed over a course of 12 weeks. In separate observations during the same period, focal social behavior (e.g. aggression, play, affiliation) with group members was also observed. Subjects that exhibited higher degrees of mimicry were not more prosocial, but they received significantly more play overtures from social partners (p < 0.01). Additionally, rates of mimicry were higher in 2- and 3-year-olds than 4-year-olds. These results provide proof of principle in a small sample of monkeys that mimicry is associated with social advantages in a complex, semi-naturalistic setting in primates.

Sequence diversity analyses of an improved rhesus macaque genome enhance its biomedical utility.

The rhesus macaque (Macaca mulatta) is the most widely studied nonhuman primate (NHP) in biomedical research. We present an updated reference genome assembly (Mmul_10, contig N50 = 46 Mbp) that increases the sequence contiguity 120-fold and annotate it using 6.5 million full-length transcripts, thus improving our understanding of gene content, isoform diversity, and repeat organization. With the improved assembly of segmental duplications, we discovered new lineage-specific genes and expanded gene families that are potentially informative in studies of evolution and disease susceptibility. Whole-genome sequencing (WGS) data from 853 rhesus macaques identified 85.7 million single-nucleotide variants (SNVs) and 10.5 million indel variants, including potentially damaging variants in genes associated with human autism and developmental delay, providing a framework for developing noninvasive NHP models of human disease.

Early Social Stress Promotes Inflammation and Disease Risk in Rhesus Monkeys.

Early social stress has potent lifelong health effects. We examined the association of early stress in the attachment relationship (low maternal sensitivity, low MS), lower maternal social hierarchy rank, and greater frequency of group-level social conflict, with biomarkers of inflammatory stress response in plasma (IL-8, MCP-1 and CRP collected two hours after temporary separation from mothers and social groups) and risk for developing a common macaques disease outcome (infectious colitis) in 170 socially-housed rhesus monkeys. We controlled for gene-environment correlations by comparing cross-fostered subjects with infants reared by their biological mothers. Low MS predicted higher levels of pro-inflammatory cytokines and proteins at 3-4 months of age (F(3, 162) = 3.508, p = 0.002, partial eta2 = 0.061) and higher lifetime risk for developing colitis for up to twelve years of age (chi square = 5.919, p = 0.026). Lower maternal social rank (F (3, 162) = 3.789, p = 0.012, partial eta2 = 0.06) and higher rates of social conflict (F (3, 162) = 4.264, p = 0.006, partial eta2 = 0.074) each also predicted greater inflammation in infancy, but not lifetime colitis risk (both p > 0.05). The effects of low MS, lower social rank, and higher social conflict were significant in infants reared by biological mothers and cross-fostered infants, suggesting that our results did not arise from gene-environment correlations, but environmental stressors alone. We conclude that several types of early social stress confer risk for inflammation in infancy, but that stress in the mother-infant relationship may confer the longest-term risk for adverse health outcomes.

Genetic and environmental factors in the intergenerational transmission of maternal care in rhesus macaques: Preliminary findings.

Early life experiences reorganize the brain and behavior of the developing infant, often with lifelong consequences. There is perhaps no more potent developmental influence than the quality of parental care: it is an experience common to all mammals, and its effects have been observed across species. The effects of parental care can be particularly difficult to abolish, as levels of care are often perpetuated across generations. However, genetic relatedness between parents can obscure the true mechanism of transgenerational cycles of parental care, because in intact families, genes, and environment are confounded. We examined the transmission of maternal care quality in biologically reared (n = 21) and cross fostered (n = 6) female rhesus monkeys. Interactions between female infant subjects and their mothers were observed from subjects' birth to 12 weeks of age. Females were then observed 4-5 years later for the quality of care they displayed toward their own newborn offspring. Maternal protectiveness in the first and second generations were correlated in both biologically reared and cross-fostered females. However, other aspects of maternal care, such as aggressiveness and sensitivity, were transmitted differently depending on foster status. These data provide preliminary findings in a small sample that the intergenerational transmission of maternal care may arise from complex genetic and environmental mechanisms in rhesus monkeys.

Paternal line effects of early experiences persist across three generations in rhesus macaques.

The effects of early stress may not be limited to the exposed generation, but are sometimes passed on to subsequent generations. Such non-genetic transgenerational inheritance is a potentially important developmental and evolutionary force. We compared the transgenerational effects of maternal and paternal line early stress on anxiety- and health-related traits in three non-exposed generations (F1, F2 and F3) of semi-naturalistically raised rhesus macaques. As infants, F0 macaques were exposed to nursery rearing (NR) or semi-naturalistic social conditions (CONTROL). Three hundred forty non-exposed F1-F3 descendants were CONTROL reared and physiological and behavioral measures were collected during standardized assessment at 3-4 months of age. Paternal line NR was significantly associated with greater nervousness in F1-F3 and lower immune cell counts in F1-F2. Maternal-line NR effects were not observed. This study suggests that acquired stress-related traits may be "inherited" across generations in primates, through complex social or germ-line mechanisms.

Paternal early experiences influence infant development through non-social mechanisms in Rhesus Macaques.

BACKGROUND: Early experiences influence the developing organism, with lifelong and potentially adaptive consequences. It has recently become clear that the effects of early experiences are not limited to the exposed generation, but can influence physiological and behavioral traits in the next generation. Mechanisms of transgenerational effects of parental early experiences on offspring development are often attributed to prenatal or postnatal parental influence, but recent data suggest that germ-line plasticity may also play a role in the transgenerational effects of early experiences. These non-genetic transgenerational effects are a potentially important developmental and evolutionary force, but the effects of parental experiences on behavior and physiology are not well understood in socially complex primates. In the non-human primate, the rhesus macaque, nursery rearing (NR) is an early life manipulation used for colony management purposes, and involves separating infants from parents early in life. We examined the effects of maternal and paternal early NR on infant rhesus macaque immunity, physiology, and behavior. RESULTS: We theorized that differences in behavior or physiology in the absence of parent-offspring social contact would point to biological and perhaps germ-line, rather than social, mechanisms of effect. Thus, all subjects were themselves NR. Male and female infant rhesus macaques (N= 206) were separated from parents and social groups in the first four days of life to undergo NR. These infants differed only in their degree of NR ancestry - whether their dams or sires were themselves NR. At 3-4 months of age, infants underwent a standardized biobehavioral assessment. Factors describing immunity, plasma cortisol, and emotion regulation were generated from these data using factor analysis. Paternal, but not maternal, NR was associated with greater emotionality and higher plasma cortisol, compared with infants born to CONTROL reared fathers. CONCLUSIONS: These data suggest that macaque biobehavioral makeup is strongly influenced by paternal experiences, and via non-social mechanisms.

Transgenerational effects of variable foraging demand stress in female bonnet macaques.

Stress coping is an important part of mammalian life, influencing somatic and mental health, social integration, and reproductive success. The experience of early psychological stress helps shape lifelong stress coping strategies. Recent studies have shown that the effects of early stress may not be restricted to the affected generation, but may also be transmitted to offspring. Understanding whether early stress influences development in subsequent generations may help us understand somewhat why many stress-related traits and diseases, for which little genetic basis has been discovered, run in families. Experimental early life "variable foraging demand" (VFD) stress has been associated with behavioral hypo-responsiveness to stress in infant and adolescent bonnet macaques. The present study examined the behavioral effects of experimental early VFD stress in adult bonnet macaques, and further investigated whether non-exposed adolescent offspring of VFD macaques were also affected. Thirty female bonnet macaques from four rearing histories were observed for behavioral response during stress: adults which had been VFD reared as infants (n = 11), adults which had been Control reared as infants (n = 9), and foraging demand naïve adolescents whose mothers were VFD (n = 4) or Control reared (n = 6). Subjects were observed for behavioral response during two experimental stressor conditions, including: (1) relocation to a novel environment; and (2) relocation with exposure to a "human intruder" making eye contact. Factor analysis yielded five factors that described categories of behavior across stress conditions. While adult VFD and Control reared females unexpectedly did not differ significantly, non-exposed adolescent offspring of VFD reared mothers displayed significant hypo-responsiveness in all behavioral categories compared with non-exposed adolescent offspring of Control females. We suggest that stress hypo-responsiveness previously observed in adolescent VFD reared animals may abate with age, but is nonetheless observed in the next generation. We conclude that VFD stress affects behavioral development of subsequent generations in non-human primates.

Enhancing genotyping of MAOA-LPR and 5-HTT-LPR in rhesus macaques (Macaca mulatta).

BACKGROUND: Genetic variation in monoamine oxidase A (MAOA) and serotonin transporter (5-HTT)-linked polymorphic regions (LPR) is associated with neuropsychiatric behavior. METHODS: We genotyped 37 macaques using conventional PCR product gel fractionation and by capillary electrophoresis of multiplexed amplicons and compared the data. RESULTS: Genotype concordance was 97% and 95% for MAOA-LPR and 5-HTT-LPR, respectively. Capillary electrophoresis was more sensitive and cost-effective. CONCLUSIONS: Multiplexing MAOA-LPR and 5-HTT-LPR will enhance the genotyping of large sample sets.

DNA methylation as a risk factor in the effects of early life stress.

Epigenetic marks (e.g., DNA 5-methylcytosine [5mC] content or CpG methylation) within specific gene regulatory regions have been demonstrated to play diverse roles in stress adaptation and resulting health trajectories following early adversity. Yet the developmental programming of the vast majority of the epigenome has not yet been characterized, and its role in the impact of early stress largely unknown. In the present study, we investigated the relationships among early life stress, whole-epigenome and candidate stress pathway gene (serotonin transporter, 5-HTT) methylation patterns, and adult behavioral stress adaptation in a non-human primate model. Early in life, experimental variable foraging demand (VFD) stress or control conditions were administered to two groups each of 10 female bonnet macaques (Macaca radiata) and their mothers. As adults (3-13 years of age), these females were assessed for behavioral adaptation to stress across four conditions of increasing intensity. Blood DNA 5-HTT 5mC status was determined using sodium bisulfite pyrosequencing and total 5mC content was determined using ELISA. Neither stress reactivity nor DNA methylation differed based on early life stress. However, we found that both greater 5-HTT and whole-genome 5mC was associated with enhanced behavioral stress reactivity following early life stress, but not control conditions. Therefore, regardless of developmental origin, greater DNA methylation conferred a genomic background of "risk" in the context of early stress. We suggest that this may arise from constrained plasticity in gene expression needed for stress adaptation early in development. This risk may have wider implications for psychological and physical stress adaptation and health.

Serotonin pathway gene-gene and gene-environment interactions influence behavioral stress response in infant rhesus macaques.

A subset of serotonin (5-HT) pathway polymorphisms has been shown to confer risk for psychological dysfunction, particularly in individuals who experience early adversity. Understanding the developmental processes underlying these Gene x Environment interactions will strengthen the search for risk factors for behavioral dysfunction. We investigated the combined influence of two serotonin pathway polymorphisms and species-atypical, and possibly adverse, rearing (nursery rearing [NR]) on two dimensions of behavioral stress response in infant rhesus macaques. We hypothesized that the experience of NR and possession of both "high-risk" genotypes (genotypes that are thought to confer low 5-HT function) would predict the greatest behavioral stress response to maternal/social separation. Using a matched-pair design, the impact of early experience and the serotonin transporter (rh5-HTTLPR) and monoamine oxidase A (rhMAO-A-LPR) promoter polymorphisms on behavioral reactivity of 136 infant rhesus macaques (90-120 days of age) during a 25-hr social separation/relocation procedure was assessed. Each pair included one infant reared with mother in a large, outdoor field enclosure (field rearing) and one infant reared in a nursery (NR). Pairs were matched for putative gene activity of each polymorphism, sex, age, and weight at testing. Behavioral responses in a "human intruder" test were recorded, and activity and emotional reactivity composites were created to detect different aspects of psychological adaptation to stress. Our hypothesis that high-risk groups would be the most reactive to stress was not entirely borne out. Rh5-HTTLPR x rhMAOA-LPR interactions predicted emotional reactivity and tended to predict behavioral activity scores. Carriers of the two "low-risk" alleles exhibited the lowest behavioral activity, as might be predicted, but carriers of both "high-risk" alleles were two of four genotype groups exhibiting the highest observed Emotional Reactivity. Gene x Gene interactions were exacerbated by the experience of nursery rearing, as predicted, however. Finally, we suggest that genetic or environmental factors may mitigate the risk for behavioral dysregulation illustrated in the patterns of behavioral activity and emotional reactivity displayed by infants.

Parental care moderates the influence of MAOA-uVNTR genotype and childhood stressors on trait impulsivity and aggression in adult women.

OBJECTIVES: Adverse childhood experiences are associated with poor mental health outcomes, including vulnerability to mood disorders and/or antisocial behavior. A functional polymorphism in the regulatory region of the monoamine oxidase A gene (monoamine oxidase A untranslated variable nucleotide tandem repeat, MAOA-uVNTR) may moderate the degree of risk conferred by early trauma. Experiential factors may mitigate or exacerbate the effects of trauma on individuals at genetic risk. We examined the association among MAOA-uVNTR genotype, early stress (family death, family separation, parents' divorce, physical and/or sexual abuse), quality of parental care, and disadvantageous outcomes (trait impulsivity/aggression and depression severity) in adult women. METHODS: Diagnostic assessments were completed for 159 female participants. All were either healthy or were diagnosed with major depressive disorder or bipolar disorder. Participants were assessed for lifetime trait aggression and impulsiveness and current severity of depression, and were genotyped for the MAOA-uVNTR polymorphism. Participants rated the level of parental care they experienced, and were asked to report specific childhood stressors and abuse. RESULTS: High perceived parental care mitigated the effect of a childhood stressor on impulsivity scores in low-expressing MAOA-uVNTR allele carriers, but level of perceived care had no effect in the group homozygous for the high-expressing MAOA-uVNTR allele. Gene-environment interactions did not influence depression severity in the mood disorder group, indicating that the effects of parenting we observed in our participants were independent of depression status. CONCLUSION: These results suggest that gene-environment interactions influence not only disadvantageous outcomes, but also sensitivity to features of the environment that could alleviate these outcomes.

Reported childhood abuse is associated with low serotonin transporter binding in vivo in major depressive disorder.

BACKGROUND: Physical or psychological adversity in childhood is associated with a higher risk for depression in adulthood, and with persistent serotonergic abnormalities in humans and in animal models. We hypothesized that reported childhood abuse would be associated with lower brain serotonin transporter (5-HTT) binding potential (BP(P), proportional to the number of available transporters) in adults. We examined healthy volunteers and subjects with major depressive disorder, a sample enriched for childhood abuse. METHODS: Regional brain 5-HTT BP(P) was measured using positron emission tomography (PET) with [(11)C]McN 5652 and a metabolite-corrected arterial input function in 43 healthy volunteers and 23 subjects in a major depressive episode, ten of whom reported a history of sexual and/or physical abuse before age 15, and 13 of whom did not. As only two healthy volunteers reported childhood abuse, primary analyses were restricted to the depressed sample, with healthy controls presented as comparators. RESULTS: Depressed subjects reporting childhood abuse had lower 5-HTT BP(P) than nonabused depressed subjects across all brain regions examined (P = 0.017). The groups did not differ in relevant demographic or clinical variables. Genotype frequencies of a functional polymorphism in the 5-HTT gene promoter (5-HTTLPR) did not differ between the groups. CONCLUSIONS: Reported childhood abuse is associated with lower 5-HTT BP(P) in this sample of subjects with major depression, consistent with other reports that childhood adversity can lower serotonergic function permanently. Lower 5-HTT BP(P) may represent a biological pathway through which early life stress predisposes to the development of subsequent psychiatric illness, including major depressive disorder.

What is an "adverse" environment? Interactions of rearing experiences and MAOA genotype in rhesus monkeys.

BACKGROUND: Studies have been inconsistent in demonstrating that early adversity and specific genotype can be joint risk factors for poor behavioral outcomes. Using a rhesus monkey model, we examined how social context and different forms of early adversity influence whether a specific genotype (polymorphism in the promoter region of monoamine oxidase A [MAOA]) affects display of aggressive, fearful, and anxious behaviors. METHODS: Rhesus monkey infants (n = 473) were exposed to brief social challenge at age 3-4 months. Infants were reared 1) with mothers and up to 150 other animals in large cages; 2) with mothers in smaller social groups; 3) with mother and access to, at most, one other mother-infant pair; and 4) without mother but with access to a same-age peer in a nursery. RESULTS: No effects of genotype were found for infants reared by mothers in large social cages, although several genotype by rearing environment interactions were evident. Animals reared in smaller social groups were more likely to display aggression, which was especially true of animals possessing the low-activity MAOA genotype. In addition, animals with low-activity genotypes that had experienced restricted mother rearing showed more anxious behavior (scratch, yawn). CONCLUSIONS: Among mother-reared animals, broader contextual features, associated with the social environment and experience of the mother, can affect the extent to which genotype contributes to behavioral expression under conditions of challenge. Results also suggest that different forms of early adverse experience can affect the types of responses displayed by animals of different genotypes.

Dimensions of response to novelty are associated with social engagement and aggression in adult male rhesus macaques (Macaca mulatta).

In this study, the authors tested the hypothesis that behavioral response across social and nonsocial, novel and familiar conditions may be guided by the same trait(s) related to impulsivity in adult male rhesus macaques. The authors assessed 23 individuals' behavioral response to a series of nonsocial novel scenarios, as well as aggression and sociality within familiar and novel social contexts. Factor analysis of responses to nonsocial novelty identified two factors: Caution, which reflected latency to engage different novel situations, and Interest in Novelty, which consisted of duration and quality of exploration. Each dimension was associated with different social manifestations. Caution was negatively correlated with social aggression in novel and familiar social circumstances; Interest in Novelty was positively associated with social engagement in familiar, but not novel, social circumstances. The authors conclude that traits influencing impulsive response to novelty contribute to risky and normal social behavior across social contexts.

Serotonin function is associated with behavioral response to a novel conspecific in marmosets.

The function of the central nervous system neurotransmitter serotonin (5-HT) contributes to individual differences in impulsive behavior in humans and nonhuman primates. We investigated the relationship between 5-HT function and behavioral responses to a novel social scenario in marmosets. In the first study, marmosets (n=10) were treated orally with fluoxetine HCl (FLX) or vehicle for two trial periods and exposed to a novel conspecific for a 20-min trial following each treatment. Levels of behavioral inhibition in response to a novel conspecific were quantified. The animals exhibited less inhibition toward the novel conspecific following the 14-day FLX treatment than they did following the vehicle treatment. In the second study we first characterized the parameters of the marmoset peripheral 5-HT system and further assessed the relationship between natural variation in peripheral 5-HT and 5-HIAA levels with behavioral inhibition in response to a novel conspecific (n=14). Individual peripheral 5-HT and 5-HIAA levels were higher in animals that exhibited more inhibition in response toward the stranger. We conclude that serotonergic influences play a role in behavioral response to a novel conspecific in marmosets.