Iron deficiency anemia and affective response in rhesus monkey infants

Innovation, Inhibition and Flexibility in Rhesus Macaques (Macaca mulatta)

Innovation is a key component of behavioral flexibility. When individuals are presented with novel problems, their ability to behave flexibly often relies upon their exploratory tendencies, motivational states and intrinsic traits. Studies of repeated innovation pose additional benefits to understand mechanisms of behavioral flexibility, including measuring persistence, exploration and inhibitory control when learned solutions are blocked. The multi-access box (MAB) paradigm tests repeated innovation without prior training and minimal habituation. We tested fifty adult captive female rhesus macaques (Macaca mulatta) with a MAB to evaluate the role of individual traits on repeated innovation and explore the relationship between inhibitory responses and innovation. We found that exploratory diversity positively predicted repeated innovation, as has been reported for previous studies. We also found that traits such as age and personality influenced innovation, where younger individuals and those that scored high on nervousness had higher innovation scores. However, we did not find any relationship between inhibitory responses and innovation. Our study provides the first assessment of repeated innovation in rhesus macaques using a MAB design and highlights the importance of individual traits for repeated innovation in this species.

Repeatability of measures of behavioral organization over two years in captive infant rhesus macaques, Macaca mulatta

Individual differences of infant temperament have been associated with future health outcomes that provide explanatory power beyond adult personality. Despite the importance of such a metric, our developmental understanding of personality-like traits is poor. Therefore, we examined whether young primates show consistency in personality traits throughout development. We replicated a Biobehavioral Assessment (BBA) at three time periods: 3-4 months, 1 year, and 2 years of age in 47 rhesus macaque (Macaca mulatta) subjects from large mixed-sex outdoor social housing units at the California National Primate Research Center. We report results for tests focused on responses and adaptation to the temporary separation and relocation, responses to a threatening stimulus, and ratings of overall temperament. We found consistently repeatable associations in measures of Emotionality; these associations were stronger in males, but also present in females, and broadly consistent between Years 1 and 2. We also explored whether behavioral responses to this experimental relocation might be influenced by their experience being relocated for other reasons (i.e., hospitalizations) as individuals' responses might be influenced by similar experiences to the BBA procedure. Only locomotion, during one of the assessments, was associated with past hospitalization events. Overall, repeatability in Emotionality-associated behaviors was evident across the 2 years, in both sexes. We did, however, find evidence of the emergence of sex differences via differentiated expression of behavioral responses during the BBA. We emphasize that there is likely contextual nuance in the use of these BBA factor-associated behaviors. Further research is required to determine whether and how shifts occur in underlying factor structure and the expression of associated behaviors.

An analysis of risk factors for spontaneously occurring type 2 diabetes mellitus in rhesus macaques (Macaca mulatta)

BACKGROUND

Type 2 Diabetes Mellitus (T2D) is a chronic disease with a high prevalence worldwide. Human literature suggests factors beyond well-known risk factors (e.g., age, body mass index) for T2D: cytomegalovirus serostatus, season of birth, maternal age, birth weight, and depression. Nothing is known, however, about whether these variables are influential in primate models of T2D.

METHODS

Using a retrospective methodology, we identified 22 cases of spontaneously occurring T2D among rhesus monkeys at our facility. A control sample of n = 1199 was identified.

RESULTS

Animals born to mothers that were ≤5.5 years of age, and animals that showed heightened Activity and Emotionality in response to brief separation in infancy, had a greater risk for development of T2D in adulthood.

CONCLUSIONS

Knowledge of additional risk factors for T2D could help colony managers better identify at-risk animals and enable diabetes researchers to select animals that might be more responsive to their manipulations.

Rhesus infant nervous temperament predicts peri-adolescent central amygdala metabolism & behavioral inhibition measured by a machine-learning approach

Anxiety disorders affect millions of people worldwide and impair health, happiness, and productivity on a massive scale. Developmental research points to a connection between early-life behavioral inhibition and the eventual development of these disorders. Our group has previously shown that measures of behavioral inhibition in young rhesus monkeys (Macaca mulatta) predict anxiety-like behavior later in life. In recent years, clinical and basic researchers have implicated the central extended amygdala (EAc)-a neuroanatomical concept that includes the central nucleus of the amygdala (Ce) and the bed nucleus of the stria terminalis (BST)-as a key neural substrate for the expression of anxious and inhibited behavior. An improved understanding of how early-life behavioral inhibition relates to an increased lifetime risk of anxiety disorders-and how this relationship is mediated by alterations in the EAc-could lead to improved treatments and preventive strategies. In this study, we explored the relationships between infant behavioral inhibition and peri-adolescent defensive behavior and brain metabolism in 18 female rhesus monkeys. We coupled a mildly threatening behavioral assay with concurrent multimodal neuroimaging, and related those findings to various measures of infant temperament. To score the behavioral assay, we developed and validated UC-Freeze, a semi-automated machine-learning (ML) tool that uses unsupervised clustering to quantify freezing. Consistent with previous work, we found that heightened Ce metabolism predicted elevated defensive behavior (i.e., more freezing) in the presence of an unfamiliar human intruder. Although we found no link between infant-inhibited temperament and peri-adolescent EAc metabolism or defensive behavior, we did identify infant nervous temperament as a significant predictor of peri-adolescent defensive behavior. Our findings suggest a connection between infant nervous temperament and the eventual development of anxiety and depressive disorders. Moreover, our approach highlights the potential for ML tools to augment existing behavioral neuroscience methods.

Brain Iron Homeostasis and Mental Disorders

Iron plays an essential role in various physiological processes. A disruption in iron homeostasis can lead to severe consequences, including impaired neurodevelopment, neurodegenerative disorders, stroke, and cancer. Interestingly, the link between mental health disorders and iron homeostasis has not received significant attention. Therefore, our understanding of iron metabolism in the context of psychological diseases is incomplete. In this review, we aim to discuss the pathologies and potential mechanisms that relate to iron homeostasis in associated mental disorders. We propose the hypothesis that maintaining brain iron homeostasis can support neuronal physiological functions by impacting key enzymatic activities during neurotransmission, redox balance, and myelination. In conclusion, our review highlights the importance of investigating the relationship between trace element nutrition and the pathological process of mental disorders, focusing on iron. This nutritional perspective can offer valuable insights for the clinical treatment of mental disorders.

Early-life behavioral features are associated with chronic emesis in rhesus macaques (Macaca mulatta)

Chronic emesis (CE) is a poorly understood condition in human and nonhuman primates that negatively impacts the quality of life. Early identification of risk factors for the development of CE is likely to improve the ability to manage CE cases successfully and is, therefore, desirable. Using a case-control study, we reviewed the necropsy records of the California National Primate Research Center and identified 24 animals with recorded CE, defined as five or more incidents of emesis in 1 month. A group of 89 healthy rhesus macaques (Macaca mulatta), comparable in age and percent time housed indoors, was similarly identified. Next, we investigated the association between the occurrence of CE during later stages of life after infancy and the behavioral temperament scores attained in infancy, age, sex, birth location, rearing condition, history of self-injurious behavior (SIB), and the number of lifetime sedation events. Our analysis revealed that CE was associated with degrees of temperament constructs obtained in infancy (data was available for n = 113), such as Confidence (odds ratio (OR) = 0.45, 95% CI: 0.18, 1.08, p = 0.07), Gentleness (OR = 0.47, 95% CI: 0.23, 0.96, p = 0.03), Nervousness (OR = 2.04, 95% CI: 0.98, 4.23, p = 0.05), and Vigilance (OR = 0.36, 95% CI: 015, 0.87, p = 0.02), suggesting that CE is linked to behavioral phenomenon measured in early life, long before it becomes a medical concern. Our data suggest that CE was positively correlated with a history of SIB (OR 4.26, 95% CI: 0.98, 18.47, p = 0.04). Accurate prediction of CE can then assist behavioral and colony management professionals in making informed decisions regarding the care of animals at risk of developing CE. Moreover, the novel information we reported here could have valuable implications in human medicine, where gastrointestinal distress is a common complaint affecting a person's quality of life.

Variation in infant rhesus monkeys' (Macaca mulatta) neutrophil-to-lymphocyte ratio is associated with environmental conditions, emotionality, and cortisol concentrations, and predicts disease-related outcomes

The neutrophil-to-lymphocyte ratio (NLR) is a predictor of morbidity for a variety of medical conditions, but little is known about how variation in NLR arises. We examined variation in this measure in a sample of 4577 infant rhesus monkeys (54.8 % female), who participated in the BioBehavioral Assessment program at the California National Primate Research Center at 3-4 months of age. Lower values for NLR were seen for animals reared indoors, for animals that were raised to be free of specific pathogens, and for males. In addition lower NLR was associated with higher stress values of cortisol and with greater emotionality in response to an acute stressor. Finally, lower NLR in infancy was associated with greater risk for developing airways hyperresponsiveness (a hallmark of asthma); with display of diarrhea up to 3.97 years later; and with greater viral load when infected with the simian immunodeficiency virus at a mean of 6.1 years of age. Infant NLR was a better predictor of viral load than was a contemporaneously obtained measure of NLR. Infant and adult values of NLR were only modestly correlated; one reason may be that the infant measure was obtained during stressful conditions and the adult measure was obtained under baseline conditions. We propose that NLR is an integrated outcome measure reflecting organization and interaction of stress-response and immune systems. As such, assessment of NLR under conditions of stress may be a particularly useful marker of individual differences in morbidity, especially for conditions in which stress plays an important role, as in asthma, diarrhea/colitis, and AIDS.

Variation in the serotonin transporter genotype is associated with maternal restraint and rejection of infants: A nonhuman primate (Macaca mulatta) model

Studies show that maternal behaviors are mediated by the bivariate serotonin transporter (5-HTT) genotype, although the findings are mixed, with some studies showing that mothers with the s allele exhibit increased maternal sensitivity, while other studies show that mothers with the s allele show decreased maternal sensitivity. Nonhuman primate studies offer increased control over extraneous variables and may contribute to a better understanding of the effects of the 5-HTT genotype on maternal sensitivity. This study assesses the influence of 5-HTT genotype variation on maternal sensitivity in parenting in 125 rhesus macaque mothers (Macaca mulatta) during the first three-months of their infants' lives, an age well before typical infants undergo weaning. Mothers were genotyped for the 5-HTT genotype and maternal behaviors were collected, including neglectfulness, sensitivity, and premature rejections during undisturbed social interactions. Results showed that mothers homozygous for the s allele rejected their infants the most and restrained their infants the least, an indication that mothers with the s allele are more likely to neglect their infants' psychological and physical needs. These findings suggest that, at an age when an infant's needs are based on warmth, security, and protection, mothers with an s allele exhibit less sensitive maternal behaviors. High rates of rejections and low rates of restraints are behaviors that typically characterize premature weaning and are inappropriate for their infant's young age. This study is an important step in understanding the etiology of variability in maternal warmth and care, and further suggests that maternal 5-HTT genotype should be examined in studies assessing genetic influences on variation in maternal sensitivity, and ultimately, mother-infant attachment quality.

Determination of dexamethasone dose for cortisol suppression in adult common marmosets (Callithrix jacchus)

We conducted a dose-response study of dexamethasone to investigate an optimal dexamethasone suppression test for common marmosets. Twelve marmosets received 0.1, 0.5, or 1.0 mg/kg dexamethasone. Doses of 0.5 and 1.0 mg/kg both suppressed endogenous cortisol for at least 18 h with greater individual variability in the lower 0.5 mg/kg dose.

The relationship of maternal rank, 5-HTTLPR genotype, and MAOA-LPR genotype to temperament in infant rhesus monkeys (Macaca mulatta)

Temperament is a construct whose manifestations are quantifiable from an early age, and whose origins have been proposed as "biological." Our goal was to determine whether maternal rank and infant genotype are associated with five measures of temperament in 3- to 4-month old rhesus monkeys (Macaca mulatta), all of whom were born and reared by their mothers in large, outdoor, half-acre cages. Maternal rank was defined as the proportion of animals outranked by each female, and the two genes of interest to us were monoamine oxidase and serotonin transporter, both of which are polymorphic in their promoter regions (MAOA-LPR and 5-HTTLPR, respectively), with one allele of each gene considered a "plasticity" allele, conferring increased sensitivity to environmental events. Our large sample size (n = 2014-3140) enabled us to examine the effects of individual genotypes rather than combining genotypes as is often done. Rank was positively associated with Confident temperament, but only for animals with the 5-repeat allele for MAOA-LPR. Rank had no other effect on temperament. In contrast, genotype had many different effects, with 5-HTTLPR associated with behavioral inhibition, and MAOA-LPR associated with ratings-based measures of temperament. We also examined the joint effect of the two genotypes and found some evidence for a dose-response: animals with the plasticity alleles for both genes were more likely to be behaviorally inhibited. Our results suggest phenotypic differences between animals possessing alleles for MAOA-LPR that show functional equivalence based on in vitro tests, and our data for 5-HTTLPR revealed differences between short/short homozygotes and long/short heterozygotes, strongly suggesting that combining genotypes for statistical analysis should be avoided if possible. Our analysis also provides evidence of sex differences in temperament, and, to our knowledge, the only evidence of differences in temperament based on specific pathogen-free status. We suggest several directions for future research.

Adverse biobehavioral effects in infants resulting from pregnant rhesus macaques' exposure to wildfire smoke

As wildfires across the world increase in number, size, and intensity, exposure to wildfire smoke (WFS) is a growing health problem. To date, however, little is known for any species on what might be the behavioral or physiological consequences of prenatal exposure to WFS. Here we show that infant rhesus monkeys exposed to WFS in the first third of gestation (n = 52) from the Camp Fire (California, November, 2018) show greater inflammation, blunted cortisol, more passive behavior, and memory impairment compared to animals conceived after smoke had dissipated (n = 37). Parallel analyses, performed on a historical control cohort (n = 2490), did not support the alternative hypothesis that conception timing alone could explain the results. We conclude that WFS may have a teratogenic effect on the developing fetus and speculate on mechanisms by which WFS might affect neural development.

Little is known about the consequences of prenatal exposure to wildfire smoke on biobehavioural outcomes. Here, the authors show that infant rhesus monkeys exposed early in gestation to wildfire smoke from the 2018 Camp Fire in California show more inflammation, blunted cortisol and altered behaviour outcomes compared to non-exposed animals.

Inheritance of hormonal stress response and temperament in infant rhesus macaques (Macaca Mulatta): Nonadditive and sex-specific effects

OBJECTIVE

Early life interindividual variation in hypothalamic-pituitary-adrenal (HPA) reactivity to stress is predictive of later life psychological and physical well-being, including the development of many pathological syndromes that are often sex-biased. A complex and interactive set of environmental and genetic causes for such variation has been implicated by previous studies, though little attention has been paid to nonadditive effects (e.g. dominance, X-linked) or sex-specific genetic effects.

METHOD

We used a large pedigreed sample of captive 3-4 months old infant rhesus macaques (N = 2,661, 54% female) to fit univariate and multivariate linear mixed quantitative genetic models for four longitudinal blood cortisol samples and three reliable ratings of infant temperament (nervousness, gentleness, confidence) during a mother-infant separation protocol.

RESULTS

Each trait had a moderate narrow-sense heritability (h², 0.26-0.46), but dominance effects caused the first two cortisol samples to have much larger broad-sense heritabilities (H², 0.57 and 0.77). We found no evidence for X-linked variance or common maternal environment variance. There was a sex difference in heritability of the first cortisol sample (h_f² < h_m²), suggesting differing genetic architecture of perception of maternal separation and relocation during infancy. Otherwise, genetic covariance matrices for the sexes were very similar. Genetic correlations between cortisol levels and temperament were weak (< |0.4|) but stronger than residual or phenotypic correlations.

CONCLUSIONS

HPA reactivity and temperament had a primarily additive genetic basis in infant macaques, but there were important complexities to the genetic architecture of including genetic dominance and sex differences in heritability at this early life stage. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Iron Deficiency-Induced Changes in the Hippocampus, Corpus Striatum, and Monoamines Levels That Lead to Anxiety, Depression, Sleep Disorders, and Psychotic Disorders

Iron deficiency anemia caused by severe iron deficiency in infancy is associated with poor health and severe neurological impairment such as mental, motor, social, emotional, neurophysiological, and neurocognitive dysfunction. The behavioral effects of iron deficiency can present themselves in infancy, but they are also found in adulthood. Some behaviors can start in childhood but persist throughout adulthood.

The behaviors that are particularly often seen in infants and children include wariness and hesitance, lack of positive affect, and diminished social engagement. The affected behaviors in adults include anxiety, depression, higher complex cogitative tasks, and other psychological disorders.

The mechanisms of how iron deficiency affects behavior include affecting the hippocampus, the corpus striatum, and certain neurotransmitters. The hippocampus is a brain region that is essential for memory, learning, and other purposes. The hippocampus is very sensitive to lack of Iron during early development. The corpus striatum dispatches dopamine-rich projects to the prefrontal cortex, and it is involved in controlling executive activities such as planning, inhibitory control, sustained attention, working memory, regulation of emotion, memory storage and retrieval, motivation, and reward. Iron deficiency has been known to cause changes in behavioral and developmental aspects by affecting neurotransmitters such as serotonin, noradrenaline, and dopamine.

Iron deficiency causes behavior changes that can present in infancy and, even if corrected postnatally, it can have long-lasting effects well into adulthood.

Temperament Predicts the Quality of Social Interactions in Captive Female Rhesus Macaques (Macaca mulatta)

Previous reports suggest that female macaques with greater similarity in emotionality and nervous temperament, as evaluated in a well-established BioBehavioral Assessment (BBA) at the California National Primate Research Center, were more likely to form successful pairs. We tested whether the same measures can also predict the quality of social interactions among 20 female rhesus macaque pairs. We correlated the pairs' emotionality and nervous temperament scores obtained in infancy and the levels of behaviors recorded systematically during the pairing process years later. Supporting previous findings, partners with similar emotionality scores were more affiliative, and pairs with similar nervous temperament expressed less dominance/submissive behavior. Exploratorily, we found that pairs that were better at processing social information (part of BBA) were also more anxious. Such animals should be prioritized to be introduced in rooms that house calmer, less aggressive animals and provide opportunities for hiding to alleviate their anxiety. Indeed, positive social experiences not only promote animal welfare, but also reduce stress related confounds and unexplained data variability. Therefore, by incorporating the animals' temperament into the pair configuration process we increase the likelihood of forming high-quality pairs, both in terms of welfare and the research of which they are a part.

Knowledge of Biobehavioral Organization Can Facilitate Better Science: A Review of the BioBehavioral Assessment Program at the California National Primate Research Center

Animals vary on intrinsic characteristics such as temperament and stress responsiveness, and this information can be useful to experimentalists for identifying more homogeneous subsets of animals that show consistency in risk for a particular research outcome. Such information can also be useful for balancing experimental groups, ensuring animals within an experiment have similar characteristics. In this review, we describe the BioBehavioral Assessment Program at the California National Primate Research Center, which, since its inception in 2001, has been providing quantitative information on intrinsic characteristics to scientists for subject selection and balancing, and to colony management staff for management purposes. We describe the program and review studies relating to asthma, autism, behavioral inhibition, etc., where the BBA Program was used to select animals. We also review our work, showing that factors such as rearing, ketamine exposure, and prenatal experience can affect biobehavioral organization in ways that some investigators might want to control for in their studies. Attention to intrinsic characteristics of subject populations is consistent with the growing interest in precision medicine and can lead to a reduction in animal numbers, savings in time and money for investigators, and reduced distress for the animals.

Biobehavioral organization shapes the immune epigenome in infant rhesus Macaques (Macaca mulatta)

How individuals respond to and cope with stress is linked with their health and well-being. It is presumed that early stress responsiveness helps shape the health of the developing organism, but the relationship between stress responsiveness and early immune function during development is not well-known. We hypothesized that stress responsiveness may shape epigenetic regulation of immune genes in infancy. We investigated whether aspects of behavioral responsiveness and hypothalamic-pituitary adrenal stress-response were associated with epigenome-wide immune cell DNA methylation patterns in 154 infant rhesus monkeys (3-4 months old). Infants' behavioral and physiological responses were collected during a standardized biobehavioral assessment, which included temporary relocation and separation from their mother and social group. Genome-wide DNA methylation was quantified using restricted representation bisulfite sequencing (RRBS) from blood DNA collected 2-hours post-separation. Epigenome-wide analyses were conducted using simple regression, multiple regression controlling for immune cell counts, and permutation regression, all corrected for false discovery rate. Across the variables analyzed, there were 20,368 unique sites (in 9,040 genes) at which methylation was significantly associated with at least one behavioral responsiveness or cortisol measure across the three analyses. There were significant associations in 442 genes in the Immune System Process ontology category, and 94 genes in the Inflammation mediated by chemokine and cytokine signaling gene pathway. Out of 35 candidate genes that were selected for further investigation, there were 13 genes with at least one site at which methylation was significantly associated with behavioral responsiveness or cortisol, including two intron sites in the glucocorticoid receptor gene, at which methylation was negatively correlated with emotional behavior the day following the social separation (Day 2 Emotionality; β = -0.39, q < 0.001) and cortisol response following a relocation stressor (Sample 1; β = -0.33, q < 0.001). We conclude that biobehavioral stress responsiveness may correlate with the developing epigenome, and that DNA methylation of immune cells may be a mechanism by which patterns of stress response affect health and immune functioning.

Stress-induced plasma cortisol concentrations in infancy are associated with later parenting behaviors in female rhesus macaques (Macaca mulatta)

Few studies have longitudinally assessed the relationship between infant stress reactivity and future parenting style. Studies show that stress-induced plasma cortisol concentrations are stable over development and that they can be utilized as a marker for stress reactivity. This study investigates the relationship between stress-induced plasma cortisol concentrations in infancy and later parenting behavior in a translational nonhuman primate model. We hypothesized that higher stress-induced cortisol levels in infancy would predict impairments in maternal behaviors in adulthood. Subjects were rhesus macaque females (N = 122; Macaca mulatta), assessed as infants and again as mothers. At 3-4 months of age, subjects underwent a standardized BioBehavioral Assessment during which blood samples were obtained and they were assessed for behaviorally inhibition. Approximately 7 years later, subjects were observed as they interacted with their own offspring for four 300-s sessions. Typical rhesus monkey mother-offspring behaviors were recorded, including approaches and leaves and maternal cradling. Results showed that subjects' stress-induced cortisol concentrations and whether they exhibited behavioral inhibition as infants predicted later maternal behavior, with high cortisol concentrations and behavioral inhibition predicting high rates of offspring approaches and leaves and low rates of maternal cradling. Results also showed that higher stress-induced cortisol concentrations in infancy predicted higher scores on the Brown Index, an indication that the subjects' offspring, rather than the subject themselves, initiated changes in proximity. Taken together, these results suggest that individuals that exhibit higher stress-induced cortisol concentrations and behavioral inhibition at 3-4 months of age are at risk for engaging in less sensitive parenting behaviors as adults. To the extent that these findings generalize to humans, they suggest an important link between stress-induced cortisol concentrations and behavioral inhibition in infancy and behavior later in life, such that early-life stress reactivity can serve as a marker for later parenting behavior.

Structural differences in the hippocampus and amygdala of behaviorally inhibited macaque monkeys

Behavioral inhibition is a temperamental disposition to react warily when confronted by unfamiliar people, objects, or events. Behaviorally inhibited children are at greater risk of developing anxiety disorders later in life. Previous studies reported that individuals with a history of childhood behavioral inhibition exhibit abnormal activity in the hippocampus and amygdala. However, few studies have investigated the structural differences that may underlie these functional abnormalities. In this exploratory study, we evaluated rhesus monkeys exhibiting a phenotype consistent with human behavioral inhibition. We performed quantitative neuroanatomical analyses that cannot be performed in humans including estimates of the volume and neuron number of distinct hippocampal regions and amygdala nuclei in behaviorally inhibited and control rhesus monkeys. Behaviorally inhibited monkeys had larger volumes of the rostral third of the hippocampal field CA3, smaller volumes of the rostral third of CA2, and smaller volumes of the accessory basal nucleus of the amygdala. Furthermore, behaviorally inhibited monkeys had fewer neurons in the rostral third of CA2. These structural differences may contribute to the functional abnormalities in the hippocampus and amygdala of behaviorally inhibited individuals. These structural findings in monkeys are consistent with a reduced modulation of amygdala activity via prefrontal cortex projections to the accessory basal nucleus. Given the putative roles of the amygdala in affective processing, CA3 in associative learning and CA2 in social memory, increased amygdala and CA3 activity, and diminished CA2 structure and function, may be associated with increased social anxiety and the heritability of behavioral inhibition. The findings from this exploratory study compel follow-up investigations with larger sample sizes and additional analyses to provide greater insight and more definitive answers regarding the neurobiological bases of behavioral inhibition.

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.

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.

Lipid metabolism is associated with temperament, corticosteroid, and hematological measures in infant rhesus monkeys ( Macaca mulatta)

Individuals can differ in how their behavioral and physiological systems are organized. The fact that these individual differences persist across life suggests they are supported by physical structures that may co-vary. Here, we explored three datasets associated with health and behavioral outcomes, which were obtained from infant rhesus monkeys during standardized assessment of biobehavioral organization. Variation in biobehavioral measures was related to variation in molecular pathways, as assessed by metabolomics. Plasma from infant male rhesus monkeys ( Macaca mulatta) ( n=52) was subjected to metabolite profiling. Principal component analyses identified multiple factors that explained 60%-80% of the variance in the metabolite measures. Correlational and regression analyses of corticosteroid, hematological, and temperament measures revealed significant relationships with indicators of lipid metabolism. Significant relationships were found for cortisol responses to stress and adrenocorticotropin (ACTH) stimulation, indicators of innate immunity (monocytes and natural killer (NK) cells), hemoglobin/hematocrit, and three measures of temperament. It will be important to replicate this first-of-a-kind study to determine whether the relationship between measures of biobehavioral organization and lipid metabolism are a general result, or one that is specific to early development.

Teeth as Potential New Tools to Measure Early-Life Adversity and Subsequent Mental Health Risk: An Interdisciplinary Review and Conceptual Model

Early-life adversity affects nearly half of all youths in the United States and is a known risk factor for psychiatric disorders across the life course. One strategy to prevent mental illness may be to target interventions toward children who are exposed to adversity, particularly during sensitive periods when these adversities may have even more enduring effects. However, a major obstacle impeding progress in this area is the lack of tools to reliably and validly measure the existence and timing of early-life adversity. In this review, we summarize empirical work across dentistry, anthropology, and archaeology on human tooth development and discuss how teeth preserve a time-resolved record of our life experiences. Specifically, we articulate how teeth have been examined in these fields as biological fossils in which the history of an individual's early-life experiences is permanently imprinted; this area of research is related to, but distinct from, studies of oral health. We then integrate these insights with knowledge about the role of psychosocial adversity in shaping psychopathology risk to present a working conceptual model, which proposes that teeth may be an understudied yet suggestive new tool to identify individuals at risk for mental health problems following early-life psychosocial stress exposure. We end by presenting a research agenda and discussion of future directions for rigorously testing this possibility and with a call to action for interdisciplinary research to meet the urgent need for new biomarkers of adversity and psychiatric outcomes.

Animal Models of Normal and Disturbed Iron and Copper Metabolism

Research on the interplay between iron and copper metabolism in humans began to flourish in the mid-20th century, and diseases associated with dysregulated homeostasis of these essential trace minerals are common even today. Iron deficiency is the most frequent cause of anemia worldwide, leading to significant morbidity, particularly in developing countries. Iron overload is also quite common, usually being the result of genetic mutations which lead to inappropriate expression of the iron-regulatory hormone hepcidin. Perturbations of copper homeostasis in humans have also been described, including rare genetic conditions which lead to severe copper deficiency (Menkes disease) or copper overload (Wilson disease). Historically, the common laboratory rat (Rattus norvegicus) was the most frequently utilized species to model human physiology and pathophysiology. Recently, however, the development of genetic-engineering technology combined with the worldwide availability of numerous genetically homogenous (i.e., inbred) mouse strains shifted most research on iron and copper metabolism to laboratory mice. This created new opportunities to understand the function of individual genes in the context of a living animal, but thoughtful consideration of whether mice are the most appropriate models of human pathophysiology was not necessarily involved. Given this background, this review is intended to provide a guide for future research on iron- and copper-related disorders in humans. Generation of complementary experimental models in rats, swine, and other mammals is now facile given the advent of newer genetic technologies, thus providing the opportunity to accelerate the identification of pathogenic mechanisms and expedite the development of new treatments to mitigate these important human disorders.

Arginine vasopressin in cerebrospinal fluid is a marker of sociality in nonhuman primates

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by core social impairments. ASD remains poorly understood because of the difficulty in studying disease biology directly in patients and the reliance on mouse models that lack clinically relevant, complex social cognition abilities. We use ethological observations in rhesus macaques to identify male monkeys with naturally occurring low sociality. These monkeys showed differences in specific neuropeptide and kinase signaling pathways compared to socially competent male monkeys. Using a discovery and replication design, we identified arginine vasopressin (AVP) in cerebrospinal fluid (CSF) as a key marker of group differences in monkey sociality; we replicated these findings in an independent monkey cohort. We also confirmed in an additional monkey cohort that AVP concentration in CSF is a stable trait-like measure. Next, we showed in a small pediatric cohort that CSF AVP concentrations were lower in male children with ASD compared to age-matched male children without ASD (but with other medical conditions). We demonstrated that CSF AVP concentration was sufficient to accurately distinguish ASD cases from medical controls. These data suggest that AVP and its signaling pathway warrant consideration in future research studies investigating new targets for diagnostics and drug development in ASD.

Behavioral effects of postnatal ketamine exposure in rhesus macaque infants are dependent on MAOA-LPR genotype

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist widely used in pediatric anesthetic and therapeutic practices and veterinary medicine. Previous evidence suggests that exposure to ketamine during sensitive periods of development results in neural apoptosis and atypical behavior. Since monoamine neurotransmitters play important roles in prenatal and early postnatal neural development, and since previous work suggests ketamine can inhibit monoamine transporters, we hypothesized that there would be behavioral consequences of prenatal and early postnatal exposure to ketamine moderated by genotype of the promoter in the monoamine oxidase-A (MAOA) gene. From a large sample of animals (N = 408), we compared groups of rhesus monkeys that had experienced a single exposure to ketamine during prenatal development, an exposure during prenatal development and one postnatal exposure, a postnatal exposure with no prenatal exposure, and no exposures. Animals were classified by putative activity levels for the MAOA genotype and were tested between 3 and 4 months of age on a battery of behavioral tests. Results suggested that animals exposed to ketamine postnatally, at a dose typically used for sedative effects that also had the low-activity variant of MAOA performed poorly on a visual memory test compared to animals with the high-activity variant of the MAOA gene.

Social stability influences the association between adrenal responsiveness and hair cortisol concentrations in rhesus macaques

Hair cortisol concentrations are increasingly being used in both humans and nonhuman animals as a biomarker of chronic stress. However, many details regarding how hair cortisol concentrations relate to the dynamic activity and regulation of the HPA axis are still unknown. The current study explores 1) how the regulation of the HPA axis in infancy relates to hair cortisol concentrations (HCC) in infancy 2) whether this relationship persists into adulthood under conditions of social stability, and 3) how social instability impacts these relationships. All subjects were rhesus monkeys housed in large social groups at the California National Primate Research Center, and all had participated in a 25-hr. long BioBehavioral Assessment (BBA) at 3-4 months of age when four plasma samples were taken to assess HPA regulation, in particular cortisol responses to 1) 2-hour social separation and relocation, 2) sustained challenge, 3) dexamethasone and 4) ACTH administration. In Study 1, hair samples were collected at the end of the BBA testing from 25 infant rhesus monkeys from 2 different stable social groups. In Study 2, hair samples were obtained at three timepoints from 108 adults from 3 different stable social groups (1 in the Spring/Summer and 2 in the Fall/Winter) to examine the temporal stability of the relationship between HCC and HPA axis regulation. In Study 3, subjects included 31 infants and 33 adults from a single social group experiencing social instability following the same procedures as in Studies 1 and 2. Generalized linear models were used to determine if infants' HPA axis activity and regulation predicted HCC in infancy (Study 1), in adulthood with animals living in stable social conditions (Study 2) or in animals living in an unstable social group (Study 3). Results indicated that for both infants and adults living in stable social groups, HCC are associated with the adrenal response to ACTH in infancy. Samples collected in the winter also had higher HCC than those collected in summer. In the unstable social group, adult hair cortisol levels were higher than in the stable social groups. Additionally, there were no consistent relationships between HCC and infant HPA axis regulation among adults or infants living in a group experiencing social instability. These results suggest that the aspects of the HPA axis that drive HCC may differ depending on context. Under stable, non-stressed conditions there seems to be a trait-like association between adrenal responsivity and HCC in infancy and adulthood. However, this association may be reduced or eliminated under conditions of social stress.

Personality, environmental stressors, and diarrhea in Rhesus macaques: An interactionist perspective

Previous research has repeatedly shown both personality and psychological stress to predict gastrointestinal disorders and chronic diarrhea in humans. The goal of the present research was to evaluate the role of personality, as well as psychological stressors (i.e., housing relocations and rearing environment), in predicting chronic diarrhea in captive Rhesus macaques, with particular attention to how personality regulated the impact of such stressors. Subjects were 1,930 R. macaques at the California National Primate Research Center reared in a variety of environments. All subjects took part in an extensive personality evaluation at approximately 90-120 days of age. Data were analyzed using generalized linear models to determine how personality, rearing condition, housing relocations, and personality by environment interactions, predicted both diarrhea risk (an animal's risk for having diarrhea at least once) and chronic diarrhea (how many repeated bouts of diarrhea an animal had after their initial bout). Much like the human literature, we found that certain personality types (i.e., nervous, gentle, vigilant, and not confident) were more likely to have chronic diarrhea, and that certain stressful environments (i.e., repeated housing relocations) increased diarrhea risk. We further found multiple interactions between personality and environment, supporting the "interactionist" perspective on personality and health. We conclude that while certain stressful environments increase risk for chronic diarrhea, the relative impact of these stressors is highly dependent on an animal's personality.

Coping style and cortisol levels in infancy predict hair cortisol following new group formation in captive rhesus macaques (Macaca mulatta)

Social instability in primate groups has been used as a model to understand how social stress affects human populations. While it is well established that individual cercopithecines have different temperaments or personalities, little is known about how temperament mediates the experience of social instability in large, naturalistic groups. Here, we report findings from a study tracking a newly formed group of captive rhesus macaques (Macaca mulatta). We examine whether inter-individual differences in temperament during infancy affect physiological responses to new group formation years later, measured through hair cortisol 9 months after the group was formed. Our results show that early life measures of temperament characteristics predict later-life hypothalamic-pituitary-adrenal activity following new group formation, though not always in the directions we predicted. Individuals with higher blood cortisol concentrations in response to a novel stressor and lower blood cortisol concentrations following a Dexamethasone Suppression Test in infancy had lower hair cortisol values following new group formation later in life. Individuals characterized in infancy as more emotional or more active exhibited lower hair cortisol profiles 9 months after group formation. We suggest that these two temperament characteristics, emotionality and activity, may represent two different mechanisms leading to low hair cortisol values. That is, the physiological measure of low hair cortisol may have two different meanings depending on temperament characteristics of the individual. Our results demonstrate that temperament and physiological responsiveness measures in infancy can predict individual responses to a new group formation years later.

Naturally Occurring Nonhuman Primate Models of Psychosocial Processes

Human research into psychological processes such as anxiety, depression, or loneliness typically involves accruing cases in which the phenomenon of interest is naturally occurring, and then comparing such a sample with control cases. In contrast, animal research designed to model similar processes to test mechanistic hypotheses typically involves inducing the phenomenon of interest via some exogenously (i.e., human) administered procedure. In the present review, the author proposes that naturally occurring animal models can complement induced models in understanding complex psychological phenomena. Advantages and disadvantages of naturally occurring versus induced models are described, and detailed examples of three naturally occurring models-for loneliness and health, behavioral inhibition and asthma, and social functioning and autism-are described, along with a formal program (the BioBehavioral Assessment program) at the California National Primate Research Center, that is designed to quantify variation in biobehavioral processes in infant rhesus macaques to facilitate development of naturally occurring models. It is argued that, because of the similarity in complex behavioral and psychological processes between macaques and humans, naturally occurring primate models provide a bridge between human studies and induced primate models and have the potential to identify new models for translational research.

Adiposity and weight gain during pregnancy associate independently with behavior of infant rhesus monkeys (Macaca mulatta)

Growing evidence identifies maternal adiposity as a potentially modifiable risk factor for adverse neurodevelopment. This retrospective cohort analysis examined whether maternal prepregnancy adiposity and gestational weight gain were associated with behavioral outcomes in 173 rhesus macaque infants at the California National Primate Research Center. Dams conceived indoors, had uncomplicated pregnancies, delivered vaginally, and reared infants indoors. Infants underwent standardized biobehavioral analysis at 90-120 days of age from 3/2001-5/2015. Offspring of mothers with greater baseline adiposity or gestational weight gain exhibited a pattern of poor adaptability characterized by greater emotionality as the assessments proceeded, blunted affective response to a human intruder challenge, and reduced interest in novel stimuli which is associated with poorer social functioning later in life. They also had lower cortisol levels following dexamethasone suppression, perhaps a response to cortisol excess during gestation. These results amplify growing public health concerns implicating maternal adiposity in impaired fetal neurobehavioral programming.

Biomarkers of Nutrition for Development (BOND)-Iron Review

This is the fifth in the series of reviews developed as part of the Biomarkers of Nutrition for Development (BOND) program. The BOND Iron Expert Panel (I-EP) reviewed the extant knowledge regarding iron biology, public health implications, and the relative usefulness of currently available biomarkers of iron status from deficiency to overload. Approaches to assessing intake, including bioavailability, are also covered. The report also covers technical and laboratory considerations for the use of available biomarkers of iron status, and concludes with a description of research priorities along with a brief discussion of new biomarkers with potential for use across the spectrum of activities related to the study of iron in human health.The I-EP concluded that current iron biomarkers are reliable for accurately assessing many aspects of iron nutrition. However, a clear distinction is made between the relative strengths of biomarkers to assess hematological consequences of iron deficiency versus other putative functional outcomes, particularly the relationship between maternal and fetal iron status during pregnancy, birth outcomes, and infant cognitive, motor and emotional development. The I-EP also highlighted the importance of considering the confounding effects of inflammation and infection on the interpretation of iron biomarker results, as well as the impact of life stage. Finally, alternative approaches to the evaluation of the risk for nutritional iron overload at the population level are presented, because the currently designated upper limits for the biomarker generally employed (serum ferritin) may not differentiate between true iron overload and the effects of subclinical inflammation.

In vivo study of paraspinal muscle weakness using botulinum toxin in one primate model

BACKGROUND

It has been generally speculated that paraspinal muscle weakness is related to the spinal degeneration including intervertebral disc failure. The purpose of this study was to investigate the effects of paraspinal muscle weakness induced by the botulinum toxin type-A on the lumbar spine and behavior pattern in an in-vivo primate model which has an upright locomotion similar to that of humans.

METHODS

Botox injections into paraspinal muscle of one cynomolgus monkey were conducted biweekly up to 19 weeks at L2-L3, L3-L4 and L4-L5. MRIs were performed for measurement of muscle cross-sectional areas and behavioral data were collected using a high-resolution portable digital video camera.

FINDINGS

The cross-sectional areas of the paraspinal muscles at L2-L3, L3-L4 and L4-L5 decreased by 8%, 12% and 8% at 21 weeks after the Botox injection, respectively. Intervertebral disc thickness at L2-L3, L3-L4 and L4-L5 decreased by 6%, 8% and 5% at 21 weeks after initial Botox injection, respectively. After the Botox injections, locomotion and movement activity of the monkey was decreased. The duration of sitting increased from 21% to a maximum of 97% at 9 weeks after the Botox injection, while stance time decreased from 9% to a minimum of 1% at 11 weeks post Botox injection.

INTERPRETATION

The findings of this study revealed that paraspinal muscle atrophy affects intervertebral disc morphology and locomotion activity of a primate and may lead to an onset of intervertebral disc degeneration.

Cognitive performance of juvenile monkeys after chronic fluoxetine treatment

Potential long term effects on brain development are a concern when drugs are used to treat depression and anxiety in childhood. In this study, male juvenile rhesus monkeys (three-four years of age) were dosed with fluoxetine or vehicle (N=16/group) for two years. Histomorphometric examination of cortical dendritic spines conducted after euthanasia at one year postdosing (N=8/group) suggested a trend toward greater dendritic spine synapse density in prefrontal cortex of the fluoxetine-treated monkeys. During dosing, subjects were trained for automated cognitive testing, and evaluated with a test of sustained attention. After dosing was discontinued, sustained attention, recognition memory and cognitive flexibility were evaluated. Sustained attention was affected by fluoxetine, both during and after dosing, as indexed by omission errors. Response accuracy was not affected by fluoxetine in post-dosing recognition memory and cognitive flexibility tests, but formerly fluoxetine-treated monkeys compared to vehicle controls had more missed trial initiations and choices during testing. Drug treatment also interacted with genetic and environmental variables: MAOA genotype (high- and low transcription rate polymorphisms) and testing location (upper or lower tier of cages). Altered development of top-down cortical regulation of effortful attention may be relevant to this pattern of cognitive test performance after juvenile fluoxetine treatment.

Maternal rearing environment impacts autonomic nervous system activity

While it is now well known that social deprivation during early development permanently perturbs affective responding, accumulating evidence suggests that less severe restriction of the early social environment may also have deleterious effects. In the present report, we evaluate the affective responding of rhesus macaque (Macaca mulatta) infants raised by their mothers in restricted social environments or by their mothers in large social groups by indexing autonomic nervous system activity. Following a 25-hr evaluation of biobehavioral organization, electrocardiogram, and an index of respiration were recorded for 10 min. This allowed for an evaluation of both heart rate and respiratory sinus arrhythmia (RSA), an index of parasympathetic activity, during a challenging situation. Three- to four-month-old infants raised in restricted social environments had significantly higher heart rates and lower RSA as compared to infants raised in unrestricted social environments, consistent with a more potent stress response to the procedure. These results are consistent with mounting evidence that the environment in which individuals are raised has important consequences for affective processing.

The well-being of laboratory non-human primates

The well-being of non-human primates in captivity is of joint concern to scientists, veterinarians, colony managers, caretakers, and researchers working with non-human primates in biomedical research. With increased regulatory, accreditation, and research focus on optimizing the use of social housing for laboratory primates, as well as the advent of techniques to assess indices of chronic stress and related measures of well-being, there is no better time to present the most current advances in the field of non-human primate behavioral management. The collective body of research presented here was inspired in part by a 2014 symposium entitled, "Chronic Hormones and Demographic Variables: Center-Wide Studies on Non-Human Primate Well-Being" held at the American Society of Primatologists' 37th Annual Meeting in Decatur, GA. By aiming to target readership with scientific and/or management oversight of captive primate behavioral management programs, this special issue provides badly-needed guidance for implementing social housing programs in a research environment and leverages collaboration across multiple facilities to address key components of behavioral management, explore refinements in how well-being can be measured, and identify the interrelationships between varying indices. Am. J. Primatol. 79:e22520, 2017. © 2016 Wiley Periodicals, Inc.

Early Predictors of Impaired Social Functioning in Male Rhesus Macaques (Macaca mulatta)

Autism spectrum disorder (ASD) is characterized by social cognition impairments but its basic disease mechanisms remain poorly understood. Progress has been impeded by the absence of animal models that manifest behavioral phenotypes relevant to ASD. Rhesus monkeys are an ideal model organism to address this barrier to progress. Like humans, rhesus monkeys are highly social, possess complex social cognition abilities, and exhibit pronounced individual differences in social functioning. Moreover, we have previously shown that Low-Social (LS) vs. High-Social (HS) adult male monkeys exhibit lower social motivation and poorer social skills. It is not known, however, when these social deficits first emerge. The goals of this study were to test whether juvenile LS and HS monkeys differed as infants in their ability to process social information, and whether infant social abilities predicted later social classification (i.e., LS vs. HS), in order to facilitate earlier identification of monkeys at risk for poor social outcomes. Social classification was determined for N = 25 LS and N = 25 HS male monkeys that were 1-4 years of age. As part of a colony-wide assessment, these monkeys had previously undergone, as infants, tests of face recognition memory and the ability to respond appropriately to conspecific social signals. Monkeys later identified as LS vs. HS showed impairments in recognizing familiar vs. novel faces and in the species-typical adaptive ability to gaze avert to scenes of conspecific aggression. Additionally, multivariate logistic regression using infant social ability measures perfectly predicted later social classification of all N = 50 monkeys. These findings suggest that an early capacity to process important social information may account for differences in rhesus monkeys' motivation and competence to establish and maintain social relationships later in life. Further development of this model will facilitate identification of novel biological targets for intervention to improve social outcomes in at-risk young monkeys.

Biobehavioral consequences of prenatal exposure to a matrilineal overthrow and relocation in captive infant rhesus (Macaca mulatta) monkeys

There is a general consensus that perinatal experiences help to shape infant behavior; however, relatively little is known about the effects of prenatal experience on postnatal phenotype in non-human primates. The current study sought to take advantage of a naturally occurring incident in a captive population of rhesus monkeys. Following a matrilineal overthrow in an outdoor field cage, pregnant female rhesus macaques were relocated from outdoor to indoor housing. Using data collected from the California National Primate Research Center's Biobehavioral Assessment Program, we assessed infants born to mothers that were in their first or second trimester of pregnancy during the overthrow and relocation, and compared their data with that of animals from two control groups born in the same year: indoor mother raised infants and field cage reared infants. Our results suggest that the experience of an overthrow and relocation during the first trimester elevated postnatal emotional responsiveness, while the same experience in the second trimester resulted in modified HPA axis regulation, elevated glucocorticoid output following maternal separation, and lower hematocrit levels compared to control groups. These data add to a growing body of literature that prenatal experiences represent a significant contribution to postnatal phenotypic variability. Findings such as ours have implications for studies in captive management and the management of captive rhesus monkey populations. Am. J. Primatol. 78:895-903, 2016. © 2016 Wiley Periodicals, Inc.

Sleep disturbance as detected by actigraphy in pre-pubertal juvenile monkeys receiving therapeutic doses of fluoxetine

Sleep disturbance is a reported side effect of antidepressant drugs in children. Using a nonhuman primate model of childhood selective serotonin reuptake inhibitor (SSRI) therapy, sleep was studied quantitatively with actigraphy. Two 48-h sessions were recorded in the home cage environment of juvenile male rhesus monkeys at two and three years of age, after one and two years of treatment with a therapeutic dose of the SSRI fluoxetine, and compared to vehicle treated controls. A third session was conducted one year after discontinuation of treatment at four years of age. During treatment, the fluoxetine group demonstrated sleep fragmentation as indexed by a greater number of rest-activity transitions compared to controls. In addition fluoxetine led to more inactivity during the day as indexed by longer duration of rest periods and the reduced activity during these periods. The fluoxetine effect on sleep fragmentation, but not on daytime rest, was modified by the monkey's genotype for polymorphisms of monoamine oxidase A (MAOA), an enzyme that metabolizes serotonin. After treatment, the fluoxetine effect on nighttime rest-activity transitions persisted, but daytime activity was not affected. The demonstration in this nonhuman primate model of sleep disturbance in connection with fluoxetine treatment and specific genetic polymorphisms, and in the absence of diagnosed psychopathology, can help inform use of this drug in children.

Effect of Indoor Compared with Outdoor Location during Gestation on the Incidence of Diarrhea in Indoor-Reared Rhesus Macaques (Macaca mulatta)

Behavior and health, including the incidence of chronic idiopathic diarrhea, can vary widely among NHP reared indoors. We hypothesized that factors during gestation account for some of the variability in chronic diarrhea risk that cannot be explained by postnatal environment, genes, or known physiologic deficits. We hypothesized that, among macaques reared indoors postnatally, outdoor housing during gestation (when the dam engaged with a large, species-typical social group) would be protective against diarrhea as compared with gestation experienced in an indoor setting. We also hypothesized that exposure to routine husbandry and veterinary care in utero would increase diarrhea rates in offspring. We built models to test the influence of specific events during pregnancy as well as their interactions with anxiety-related genotype as a way of understanding gene×environment interaction on the development of diarrhea in indoor-reared rhesus macaques. Although previous reports have suggested that rearing by the mother in an indoor environment is preferable to nursery rearing, we found that whether gestation occurred indoors (in single or pair housing) or outdoors (in a large social group) better explained the variability in diarrhea rate in our study population of indoor-reared macaques. Furthermore, the diarrhea incidence was associated with nervous temperament and serotonin transporter promoter genotype. Several significant interactions indicated that some of these effects were specific to subsets of animals. Our results demonstrate that the prenatal environment can have unexpected lasting health consequences.

Do "birds of a feather flock together" or do "opposites attract"? Behavioral responses and temperament predict success in pairings of rhesus monkeys in a laboratory setting

The growing recognition that social needs of primates in captivity must be addressed can present challenges to staff at primate facilities charged with implementing pair-housing solutions for animals. Unfortunately, there are few published papers that identify individual characteristics that might facilitate the social pairing process, and those that have looked at pre-pairing measures of behavior have produced mixed results. Using a database of n = 340 isosexual pairing attempts, we report that measures associated with responses to a standardized infant assessment protocol (the BioBehavioral Assessment program) predict success in pairing attempts that occurred years later. Behavioral responses to a brief separation and relocation, to a human intruder challenge, as well as ratings of temperament, were obtained from rhesus monkeys at 3-4 months of age. Logistic regression was used to identify potential predictors of success when animals were paired up to 10 years after the behavioral assessments. Among females, success was higher when members of a pair were more similar (i.e., a smaller difference scores) in patterns of emotional responding (Emotionality, Nervous temperament) during the infant assessments. In contrast, among males, success was higher when the pair had lower mean values for Gentle and Nervous temperament scores; when the members were younger; when pairs had a greater weight difference; and when they came from the same rearing background. Together, our results suggest that broad measures reflecting patterns of emotionality in response to challenge, which can be assessed in infancy (but which remain relatively stable throughout life) can be usefully employed to increase the likelihood of success in pairing attempts. Am. J. Primatol. 79:e22464, 2017. © 2015 Wiley Periodicals, Inc.

Developmental consequences of behavioral inhibition: a model in rhesus monkeys (Macaca mulatta)

In children, behavioral inhibition is characterized by a disposition to withdraw in the presence of strangers and novel situations. Later in life, behavioral inhibition can result in an increased risk for anxiety and depression and a decrease in social behavior. We selected rhesus monkeys that, during infancy, showed evidence of behavioral inhibition in response to separation, and contrasted them with non-inhibited peers. To understand the development of behavioral inhibition at juvenile age, we collected behavioral data in response to relocation; in response to a human intruder challenge; and in naturalistic outdoor field corrals. At 4 years of age (young adulthood), we again collected behavioral data in the outdoor field corrals to understand the adult social consequences of behavioral inhibition. We also included sex, dominance rank, and number of available kin in our analyses. Finally, to understand the consistency in behavior in behaviorally inhibited animals, we conducted exploratory analyses contrasting behaviorally inhibited animals that showed high vs. low durations of non-social behaviors as adults. At juvenile age, behaviorally inhibited animals continued to show behavioral differences in the novel testing room and during the human intruder challenge, generally showing evidence of greater anxiety and emotionality compared to non-inhibited controls. In their outdoor corrals, behaviorally inhibited juveniles spent more time alone and less time in proximity and grooming with mother and other adult females. In young adulthood, we found that behavioral inhibition was not related to time spent alone. We did find that duration of time alone in adulthood was related to time alone exhibited as juveniles; sex, dominance rank, or the number of kin were not influential in adult non-social duration, either as main effects or as moderators. Finally, exploratory analyses revealed that behaviorally inhibited females that were more sociable (less time spent alone) as adults had spent more time grooming as juveniles, suggesting that high-quality social interaction at a young age might mitigate the social consequences of behavioral inhibition. Overall, we believe that the many similarities with the human data that we found suggest that this monkey model of naturally occurring behavioral inhibition can be valuable for understanding social development.

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.

Neonatal exposure to sevoflurane may not cause learning and memory deficits and behavioral abnormality in the childhood of Cynomolgus monkeys

Results of animal studies have raised a significant concern that commonly used general anesthetics may induce neurotoxicity in children. It may be difficult to resolve this concern with human studies because randomizing children only for testing anesthetic toxicity may not be feasible. We randomized 6-day old male Cynomolgus monkeys to receive or not to receive sevoflurane anesthesia at surgical plane for 5 h. Sevoflurane is the most commonly used general anesthetic in children in the U.S.A. Here, we showed that sevoflurane anesthesia did not affect the behavior evaluated by holding cage method when the monkeys were 3 and 7 months old. However, there was an age-dependent decrease in the frequency of stress events and environmental exploration behavior during the test. Sevoflurane also did not affect the learning and memory of the monkeys when they were assessed from the age of 7 months. Finally, sevoflurane did not affect the expression of multiple neuron-specific proteins in the hippocampus and cerebral cortex of 10-month old monkeys after all behavioral and cognitive tests were completed. These results suggest that exposure of neonatal monkey to sevoflurane may not affect cognition, behavior and neuronal structures in childhood, indicating the safety of sevoflurane anesthesia in children.

Fetal iron deficiency and genotype influence emotionality in infant rhesus monkeys

BACKGROUND

Anemia during the third trimester of fetal development affects one-third of the pregnancies in the United States and has been associated with postnatal behavioral outcomes. This study examines how fetal iron deficiency (ID) interacts with the fetal monoamine oxidase A (MAOA) genotype. MAOA metabolizes monoamine neurotransmitters. MAOA polymorphisms in humans affect temperament and modify the influence of early adverse environments on later behavior.

OBJECTIVE

The aim of the study was to advance translation of developmental ID research in animal models by taking into account genetic factors that influence outcomes in human populations.

METHODS

Male infant rhesus monkeys 3-4 mo old born to mothers fed an ID (10 ppm iron) diet were compared with controls (100 ppm iron). Infant monkeys with high- or low-transcription rate MAOA polymorphisms were equally distributed between diet groups. Behavioral responses to a series of structured experiences were recorded during a 25-h separation of the infants from their mothers.

RESULTS

Infant monkeys with low-transcription MAOA polymorphisms more clearly demonstrated the following ID effects suggested in earlier studies: a 4% smaller head circumference, a 39% lower cortisol response to social separation, a 129% longer engagement with novel visual stimuli, and 33% lesser withdrawal in response to a human intruder. The high MAOA genotype ID monkeys demonstrated other ID effects: less withdrawal and emotionality after social separation and lower "fearful" ratings.

CONCLUSION

MAOA × ID interactions support the role of monoamine neurotransmitters in prenatal ID effects in rhesus monkeys and the potential involvement of common human polymorphisms in determining the pattern of neurobehavioral effects produced by inadequate prenatal nutrition.

Cortisol in mother's milk across lactation reflects maternal life history and predicts infant temperament

In monkeys, high cortisol and changes in cortisol levels in mother’s milk are associated with more nervous and less confident infants. Sons are more sensitive than are daughters to changes in cortisol in mother’s milk across lactation. Females that are earlier in their reproductive career tend to have higher cortisol in their milk. Mothers may be “programming” behaviorally cautious offspring that prioritize growth through cortisol signaling.

The maternal environment exerts important influences on offspring mass/growth, metabolism, reproduction, neurobiology, immune function, and behavior among birds, insects, reptiles, fish, and mammals. For mammals, mother’s milk is an important physiological pathway for nutrient transfer and glucocorticoid signaling that potentially influences offspring growth and behavioral phenotype. Glucocorticoids in mother’s milk have been associated with offspring behavioral phenotype in several mammals, but studies have been handicapped by not simultaneously evaluating milk energy density and yield. This is problematic as milk glucocorticoids and nutrients likely have simultaneous effects on offspring phenotype. We investigated mother’s milk and infant temperament and growth in a cohort of rhesus macaque (Macaca mulatta) mother–infant dyads at the California National Primate Research Center (N = 108). Glucocorticoids in mother’s milk, independent of available milk energy, predicted a more Nervous, less Confident temperament in both sons and daughters. We additionally found sex differences in the windows of sensitivity and the magnitude of sensitivity to maternal-origin glucocorticoids. Lower parity mothers produced milk with higher cortisol concentrations. Lastly, higher cortisol concentrations in milk were associated with greater infant weight gain across time. Taken together, these results suggest that mothers with fewer somatic resources, even in captivity, may be “programming” through cortisol signaling, behaviorally cautious offspring that prioritize growth. Glucocorticoids ingested through milk may importantly contribute to the assimilation of available milk energy, development of temperament, and orchestrate, in part, the allocation of maternal milk energy between growth and behavioral phenotype.

Depressive-like behavioral response of adult male rhesus monkeys during routine animal husbandry procedure

Social isolation is a major risk factor for the development of depressive illness; yet, no practical nonhuman primate model is available for studying processes involved in this effect. In a first study, we noted that adult male rhesus monkeys housed individually indoors occasionally exhibited a hunched, depressive-like posture. Therefore, Study 2 investigated the occurrence of a hunched posture by adult males brought from outdoor social groups to indoor individual housing. We also scored two other behaviors—lying on the substrate and day time sleeping—that convey an impression of depression. During the first week of observation following individual housing, 18 of 26 adult males exhibited the hunched posture and 21 of 26 displayed at least one depressive-like behavior. Over 2 weeks, 23 of 26 males showed depressive-like behavior during a total of only 20 min observation. Further, the behavior during the first week was positively related to the level of initial response to a maternal separation procedure experienced in infancy. In Study 3, more than half of 23 adult males of a new sample displayed depressive-like behavior during 10 min of observation each of Weeks 7–14 of individual housing. The surprisingly high frequency of depressive-like behavior in Studies 2 and 3 may have been due to recording behavior via camera with no human in the room to elicit competing responses. These results suggest that a common animal husbandry procedure might provide a practical means for examining effects of social isolation on depression-related endpoints in a nonhuman primate. The findings also suggest that trait-like differences in emotional responsiveness during separation in infancy may predict differences in responsiveness during social isolation in adulthood.

Developmental plasticity of red blood cell homeostasis

Most human physiologic set points like body temperature are tightly regulated and show little variation between healthy individuals. Red blood cell (RBC) characteristics such as hematocrit and mean cell volume are stable within individuals but can vary by 20% from one healthy person to the next. The mechanisms for the majority of this inter-individual variation are unknown and do not appear to involve common genetic variation. Here, we show that environmental conditions present during development, namely in utero iron availability, can exert long-term influence on a set point related to the RBC life cycle. In a controlled study of rhesus monkeys and a retrospective study of humans, we use a mathematical model of in vivo RBC population dynamics to show that in utero iron deficiency is associated with a lowered threshold for RBC clearance and turnover. This in utero effect is plastic, persisting at least 2 years after birth and after the cessation of iron deficiency. Our study reports a rare instance of developmental plasticity in the human hematologic system and also shows how mathematical modeling can be used to identify cellular mechanisms involved in the adaptive control of homeostatic set points.

Alterations of selected iron management parameters and activity in food-restricted female Wistar rats (animal anorexia models)

AIMS

The aim of this study was to assess the influence of food-restricted diets (anorexia models) on iron management and activity of rats.

MATERIALS AND METHODS

48 rats were divided into 6 groups: 1 control (K) and 5 testing groups (K/2, GI, GII, GIII, GIV). K was fed ad libitum. K/2 received half the portion of the diet of K. The other groups received 100% of the diet eaten by K, but with different models of food restriction: GI-1 day on, 1 day starvation; GII-2 days on, 2 days starvation; GIII-3 days on, 3 days starvation; and GIV-4 days on, 4 days starvation. As a result, all testing groups ate half of the diet consumed by the control group. The concentrations of iron in selected tissues, ferritin, and selected iron management parameters in blood were examined, as well as the animals' activities associated with food craving.

RESULTS

The animal anorexia models used in this study had a significant influence on the blood concentrations of hemoglobin (p < 0.01), hematocrit (p < 0.05), RBC (p < 0.05), iron levels in liver (p < 0.05), kidney (p < 0.001), and heart (p < 0.05), the serum ferritin concentration (p < 0.001) and the rats activity (p < 0.001); whereas there was no influence on the other parameters. Generally, the statistically negative effects of starvation models on iron management parameters and activity of animals were observed. However, these effects were dependent on the model of anorexia more than on the quantity of food intake.

CONCLUSIONS

The negative effect of food deprivation on iron deficiency and rat activities were observed in all groups; however, the strongest effect was noticed in those animals subject to chronic starvation. Acute deprivations caused the reduction of activity in the rats, however, chronic starvation caused an increase in the activity of the first phase of the experiment, followed by a decline in the subsequent phase. It is possible that stress and frustration as well as depression may be caused by insufficient food intake, and as a result, by iron deficiency in a diet similar to human anorexia. However, more animal/human comparison studies are necessary.

Signaling context modulates social function of silent bared-teeth displays in rhesus macaques (Macaca mulatta)

The signaling context has been found to change the meaning of the silent bared-teeth display (SBT) in pigtail macaques (Macaca nemestrina) such that the SBT in apparently peaceful contexts communicates subordination, a long-term pattern of behavior, whereas in conflict contexts it communicates immediate submission (PNAS, 104: 1581-1586). However, the context dependent nature of the SBT has not yet been explored in other species. We investigated SBT usage with respect to grooming, severe aggression, and signaler-receiver sex, rank difference, and body size in seven captive groups of rhesus macaques. Peaceful SBTs were given most often to male receivers by male and female signalers whereas conflict SBTs were given to both male and female receivers primarily by female signalers. Male signalers rarely gave SBTs (peaceful or conflict) to female receivers. Unlike pigtail macaques, peaceful SBTs in rhesus were often accompanied by withdrawal behavior (referred to as peaceful SBT-leave), which influenced grooming, but not aggression, at the dyadic level. Severe aggression was less frequent among dyads using peaceful SBTs (regardless of withdrawal behavior) than those using conflict SBTs. In contrast, grooming was more frequent among dyads using peaceful SBT-stay signals than those using peaceful SBT-leave signals or conflict SBTs. In total, our results indicate that peaceful SBTs are a functionally different signal from conflict SBTs in rhesus macaques.