Behavioral and pituitary--adrenal responses during a prolonged separation period in infant rhesus macaques

The Development of Stress Reactivity and Regulation in Children and Adolescents

Adversity experienced in early life can have detrimental effects on physical and mental health. One pathway in which these effects occur is through the hypothalamic-pituitary-adrenal (HPA) axis, a key physiological stress-mediating system. In this review, we discuss the theoretical perspectives that guide stress reactivity and regulation research, the anatomy and physiology of the axis, developmental changes in the axis and its regulation, brain systems regulating stress, the role of genetic and epigenetics variation in axis development, sensitive periods in stress system calibration, the social regulation of stress (i.e., social buffering), and emerging research areas in the study of stress physiology and development. Understanding the development of stress reactivity and regulation is crucial for uncovering how early adverse experiences influence mental and physical health.

Caregiver-child proximity as a dimension of early experience

Human infancy and early childhood is both a time of heightened brain plasticity and responsivity to the environment as well as a developmental period of dependency on caregivers for survival, nurturance, and stimulation. Across primate species and human evolutionary history, close contact between infants and caregivers is species-expected. As children develop, caregiver-child proximity patterns change as children become more autonomous. In addition to developmental changes, there is variation in caregiver-child proximity across cultures and families, with potential implications for child functioning. We propose that caregiver-child proximity is an important dimension for understanding early environments, given that interactions between children and their caregivers are a primary source of experience-dependent learning. We review approaches for operationalizing this construct (e.g., touch, physical distance) and highlight studies that illustrate how caregiver-child proximity can be measured. Drawing on the concepts proposed in dimensional models of adversity, we consider how caregiver-child proximity may contribute to our understanding of children's early experiences. Finally, we discuss future directions in caregiver-child proximity research with the goal of understanding the link between early experiences and child adaptive and maladaptive functioning.

Change of pace: How developmental tempo varies to accommodate failed provision of early needs

The interplay of genes and environments (GxE) is a fundamental source of variation in behavioral and developmental outcomes. Although the role of developmental time (T) in the unfolding of such interactions has yet to be fully considered, GxE operates within a temporal frame of reference across multiple timescales and degrees of biological complexity. Here, we consider GxExT interactions to understand adversity-induced developmental acceleration or deceleration whereby environmental conditions hasten or hinder children's development. To date, developmental pace changes have been largely explained through a focus on the individual: for example, how adversity "wears down" aging biological systems or how adversity accelerates or decelerates maturation to optimize reproductive fitness. We broaden such theories by positing shifts in developmental pace in response to the parent-child dyad's capacity or incapacity for meeting children's early, physiological and safety needs. We describe empirical evidence and potential neurobiological mechanisms supporting this new conceptualization of developmental acceleration and deceleration. We conclude with suggestions for future research on the developmental consequences of early adverse exposures.

The Effects of At-Birth Adoption on Atypical Behavior and Anxiety: A Nonhuman Primate Model

OBJECTIVE

Adopted children tend to show an increased risk for a variety of psychopathological outcomes, even when adoption occurs at birth, which some suggest is a result of nonrandom assignment of adoptees and parents. This study uses a nonhuman primate model, in which adoptions were randomly assigned, to investigate the behavioral and physiological outcomes associated with at-birth adoption.

METHOD

Immediately following birth, rhesus monkey infants were randomly assigned to be reared by either their biological mother (n = 113) or by an unrelated, lactating, adoptive mother (n = 34). At 6 months of age, infant behavior and physiology were assessed during a stressful series of mother-infant separations. Four years later, stress-related behaviors were measured following confrontation by an unfamiliar intruder, an ecologically meaningful stressor.

RESULTS

When compared to infants reared by their biological mothers, adopted infants exhibited more behavioral withdrawal and higher plasma adrenocorticotropic hormone (ACTH) concentrations in response to separation. These behavioral differences persisted 4 years later during a stressful intruder challenge, with adoptees exhibiting more behavioral withdrawal, stereotypies, and impulsive approaches of the potentially aggressive intruder.

CONCLUSION

Compared to infants reared by their biological mothers, adopted infants exhibited more behavioral inhibition, impulsivity, and higher ACTH concentrations, even when subjects were randomly assigned to be adopted or to remain with their biological mother. To the extent that these findings generalize to humans, they suggest that the overall risk for psychopathology in adopted individuals persists even after random assignment to adoption conditions.

Maternal regulation of the infant's hypothalamic-pituitary-adrenal axis stress response: Seymour 'Gig' Levine's legacy to neuroendocrinology

Thirty years ago, Seymour 'Gig' Levine published a serendipitous, yet, seminal finding with respect to the regulatory role of maternal presence on the corticosterone stress response of neonatal rats during the developmental period known as the stress hyporesponsive period. At the same time, his group of students also investigated the stress response of infant monkeys with respect to maternal separation, as a means of understanding the stress to the primary caregiver resulting from disruptions of attachment. Gig and his group of students and collaborators, mainly in the USA and the Netherlands, investigated how initial social relationships buffer the stress response of nonhuman primates and rodent infants. His work in rodents involved determining how prolonged deprivation of maternal care disinhibits the stress response of neonates and how maternal behaviours regulate specific aspects of the hypothalamic-pituitary-adrenal axis. Maternal deprivation for 24 hours was useful for determining the importance of nutrition in suppressing the corticosterone stress response, whereas anogenital licking and grooming inhibited stress-induced adrenocortoctrophic hormone release, with the combination of both behaviours preventing the effects of maternal deprivation on the central hypothalamic stress response. Levine's group also studied the consequences of maternal deprivation on basal and stress-induced activity of the hypothalamic-pituitary-adrenal axis in juveniles and the persistent effects of the replacement of maternal behaviours on these parameters. Gig's legacy allowed many groups around the world to use the 24-hour maternal deprivation paradigm as an animal model of vulnerability and resilience to stress-related psychiatric disorders, as well as in studies of the neurobiological underpinnings of disruption of the mother-infant relationship and loss of parental care, a highly prevalent condition in humans. This review pays homage to a great scientist and mentor, whose discoveries paved the way for the understanding of how early social relationsships build resilience or lead to susceptibility to emotional disorders later in life.

Social Buffering of Stress in Development: A Career Perspective

This review provides a broad overview of my research group's work on social buffering in human development in the context of the field. Much of the focus is on social buffering of the hypothalamic-pituitary-adrenocortical (HPA) system, one of the two major arms of the mammalian stress system. This focus reflects the centrality of the HPA system in research on social buffering in the fields of developmental psychobiology and developmental science. However, buffering of the cardiovascular and autonomic nervous system is also discussed. The central developmental question in this area derives from attachment theory, which argues that the infant's experience of stress and arousal regulation in the context of her early attachment relationships is not an immature form of social buffering experienced in adulthood but rather the foundation out of which individual differences in the capacity to gain stress relief from social partners emerges. The emergence of social buffering in infancy, changes in social buffering throughout childhood and adolescence, the influence of early experience on later individual differences in social buffering, and critical gaps in our knowledge are described.

Contributions of Psychophysiology to Research on Adult Attachment: Review and Recommendations

Despite the increasing use of psychophysiological measures to investigate social and interpersonal phenomena, few studies of adult romantic attachment have taken advantage of this approach. In this article I argue for a biologically-specific, theory-based integration of psychophysiological measures into adult attachment research. This approach would help elucidate the normative psychobiological properties of the attachment system, which have received little study in humans. Specifically, it would allow researchers to test targeted hypotheses regarding affect and arousal regulation in attachment relationships. I provide a general introduction to 2 biological systems that hold particular promise for adult attachment research: the parasympathetic branch of the autonomic nervous system and the hypothalamic-pituitary-adrenocortical axis of the endocrine system. I highlight the relevance of these systems for attachment phenomena and review findings from selected social psychophysiological research. I conclude by outlining a tentative theoretical model of the psychobiology of adult attachment and identifying specific directions for future research.

The social buffering of the hypothalamic-pituitary-adrenocortical axis in humans: Developmental and experiential determinants

Social buffering, a subset of social support, is the process through which the availability of a conspecific reduces the activity of stress-mediating neurobiological systems. While its role in coping and resilience is significant, we know little about its developmental history in humans. This brief review presents an integrative developmental account of the social buffering of hypothalamic-pituitary-adrenocortical (HPA) stress reactivity in humans, from infancy to adulthood. During infancy, parents are powerful stress-regulators for children, but child temperament also plays a role and interacts with parenting quality to predict the magnitude of stress responses to fear or pain stimuli. Recent work indicates that parental support remains a potent stress buffer into late childhood, but that it loses its effectiveness as a buffer of the HPA axis by adolescence. Puberty may be the switch that alters the potency of parental buffering. Beginning in middle childhood, friends may serve as stress buffers, particularly when other peers are the source of stress. By adulthood, romantic partners assume this protective role, though studies often reveal sex differences that are currently not well understood. Translational research across species will be critical for developing a mechanistic understanding of social buffering and the processes involved in developmental changes noted in this review.

Reunion behavior after social separation is associated with enhanced HPA recovery in young marmoset monkeys

The relationships that offspring develop with caregivers can exert a powerful influence on behavior and physiology, including the hypothalamic-pituitary-adrenal (HPA) axis. In many mammalian species, offspring-caregiver relationships are largely limited to interactions with mother. Marmoset monkeys receive care in early life from multiple classes of caregivers in addition to the mother, including fathers and siblings. We evaluated whether affiliative social interactions with family members in marmosets were associated with differences in cortisol reactivity to a short-term social separation stressor, and whether these variations in affiliative interactions upon reunion predicted how well marmosets subsequently regulated HPA axis function after cessation of the stressor. Marmosets were separated from the family for 8h at three developmental time points (6-, 12-, and 18-months of age), and interactions of the separated marmoset with the family group were recorded during reunion. Urinary cortisol was measured prior to social separation, every 2h during the separation, and on the morning after separation. Heightened cortisol reactivity during social separation did not predict affiliative social behavior upon reunion but higher rates of grooming and play behavior predicted enhanced HPA regulation. Marmosets with higher rates of grooming and play with family members upon reunion had post-stress cortisol levels closer to preseparation baseline than marmosets with lower rates of affiliative reunion behavior. Combined with previous research showing the early programming effects of social interactions with caregivers, as well as the buffering effect of a close social partner during stress, the current study highlights the high degree of behavioral and HPA adaptability to social stressors across development in marmoset monkeys.

Variation of hair cortisol concentrations among wild populations of two baboon species (Papio anubis, P. hamadryas) and a population of their natural hybrids

Male olive (Papio anubis) and hamadryas (P. hamadryas) baboons have distinctive sociobehavioral and physical characteristics. In the Awash National Park, Ethiopia, a hybrid population at the contact zone between these two species, exhibits heterogeneous sociobehavioral and physical characteristics. The ambiguity of the hybrid social environment and disruption of parental stress genotypes may be sources of physiological stress for hybrids. We examined levels of chronic stress among males of the three populations and tested the prediction that chronic cortisol levels would be higher among the hybrids. Animals were captured, sampled, and released during the wet season, and a hair sample was taken for assay. Cortisol was extracted from 182 hair samples with methanol and quantified by ELISA. We included age, age class, rainfall variation, and species affiliation in models examining variation in hair cortisol levels. Species and age significantly contributed to models explaining variation in hair cortisol. Infant hypercortisolism was observed in all three groups, and a decline in cortisol through juvenile and adolescent stages, with a subsequent rise in adulthood. This rise occurred earliest in hamadryas, corroborating other evidence of the precocious development of hamadryas baboons. As expected, hybrids had significantly elevated hair cortisol compared with olive baboons and hamadryas, irrespective of age, except for very young animals. Infant hypercortisolism was also less pronounced among hybrids. Species differences and age-related differences in cortisol levels suggest a dysregulated cortisol phenotype in hybrids, and possibly reflect some form of hybrid disadvantage. More work will be required to disentangle the effects of genetic factors and the social environment.

Physiological and behavioural responses to weaning conflict in free-ranging primate infants

Weaning, characterized by maternal reduction of resources, is both psychologically and energetically stressful to mammalian offspring. Despite the importance of physiology in this process, previous studies have reported only indirect measures of weaning stress from infants, because of the difficulties of collecting physiological measures from free-ranging mammalian infants. Here we present some of the first data on the relationship between weaning and energetic and psychological stress in infant mammals. We collected data on 47 free-ranging rhesus macaque infants on Cayo Santiago, Puerto Rico, showing that faecal glucocorticoid metabolite (fGCM) concentrations were directly related to the frequency of maternal rejection, with fGCM concentrations increasing as rates of rejection increased. Infants with higher fGCM concentrations also engaged in higher rates of mother following, and mother following was associated with increased time on the nipple, suggesting that infants that experienced greater weaning-related stress increased their efforts to maintain proximity and contact with their mothers. Infants experiencing more frequent rejection uttered more distress vocalizations when being rejected; however, there was no relationship between rates of distress vocalizations and fGCM concentrations, suggesting a disassociation between behavioural and physiological stress responses to weaning. Elevated glucocorticoid concentrations during weaning may function to mobilize energy reserves and prepare the infant for continued maternal rejection and shortage of energetic resources.

Separation at weaning from the family is stressful for naturally group-living, but not solitary-living, male African striped mice Rhabdomys

Early separation from a family is stressful for young mammals, but might be more stressful for group-living than solitary species. Using juvenile males of three African striped mice Rhabdomys taxa that are either group (R. pumilio) or solitary (R. dilectus dilectus and R. d. chakae) living, we predicted greater separation anxiety in R. pumilio than R. dilectus because group-living could reduce anxiety in R. pumilio. Three brothers from each of 10 litters per taxon were randomly assigned soon after natural weaning (25 days) to one of three treatments for 10 days: (1) remained with the family (philopatric); (2) separated from the family by a wire mesh barrier (separated); and (3) isolated from the family (isolated). Males were individually tested in a four-arm maze to assess their anxiety responses and sampled for corticosterone concentrations 20 mins and 10 days later. Compared to R. dilectus males, R. pumilio males showed a greater treatment response to separation: philopatric males used the light arms of the maze less and had higher corticosterone concentrations compared to isolated males, which spent the most time in the light arms and had the lowest corticosterone concentrations overall; separated males showed an intermediate behavioural response, but had similar corticosterone concentrations to philopatric males. Thus, separation from a family group is more stressful in group-living Rhabdomys and this stress response dissipates with time. Philopatry and group-living may be more important for young R. pumilio, whereas dispersal at weaning is an important life history event for solitary R. dilectus.

Behavioral responses to social separation stressor change across development and are dynamically related to HPA activity in marmosets

Psychosocial stressors activate two distinct stress-response systems, a central, behavioral response, and a peripheral, endocrine response. Both behavioral and endocrine responses to stressors are subject to individual and developmental variables, but it is not known whether stressor induced behaviors are stable across development, and how they correspond with changes in the endocrine component of the stress response. We characterized the development and stability of behavioral responses to a mild psychosocial stressor in marmosets (Callithrix geoffroyi), and assessed the degree to which the behavioral and endocrine stress-response systems were co-activated. The behavioral response to stressors was stable within individuals, but only some stressor-induced behaviors changed as the monkeys developed. Overall, there was more variability in the development of behavioral responses compared to stress-induced endocrine profiles found previously [French et al., 2012. Horm Behav 61:196-203]. In young marmosets, only increased alarm calling was correlated with increased cortisol reactivity, and in older marmosets increased cage manipulations and motor activity were associated with poorer post-stressor cortisol regulation. Because these relationships were so few, we conclude that while the behavioral and endocrine systems follow a similar developmental trajectory, each system maintains a level of independence. Furthermore, the relationship between stressor-induced behaviors and HPA activity changes across development.

The social brain: neurobiological basis of affiliative behaviours and psychological well-being

The social brain hypothesis proposes that the demands of the social environment provided the evolutionary pressure that led to the expansion of the primate brain. Consistent with this notion, that functioning in the social world is crucial to our survival, while close supportive relationships are known to enhance well-being, a range of social stressors such as abuse, discrimination and dysfunctional relationships can increase the risk of psychiatric disorders. The centrality of the social world to our everyday lives is further exemplified by the fact that abnormality in social behaviour is a salient feature of a range of neurodevelopmental and psychiatric disorders. This paper aims to provide a selective overview of current knowledge of the neurobiological basis of our ability to form and maintain close personal relationships, and of the benefits these relationships confer on our health. Focusing on neurochemical and neuroendocrine interactions within affective and motivational neural circuits, it highlights the specific importance of cutaneous somatosensation in affiliative behaviours and psychological well-being and reviews evidence, in support of the hypothesis, that a class of cutaneous unmyelinated, low threshold mechanosensitive nerves, named c-tactile afferents, have a direct and specific role in processing affiliative tactile stimuli.

Family relationships and children's stress responses

In this chapter, the theoretical and empirical associations between family relationships and children's responses to stressors are reviewed. Family relationships explored are primarily dyadic, representing the emphasis of past empirical research; these include parent-parent, parent-child, and sibling relationships. However, in recognition of the more complicated and interconnected nature of family relationships, also reviewed are associations between the broader family context and children's stress responses. Multiple measures of stress responses are considered, including both physiological and emotional responses to and recovery from stressful experiences. Overall, the studies reviewed suggest that poor-quality family environments, including those characterized by low emotional support or high conflict, are associated with dysregulated stress responses throughout childhood and adolescence. In contrast, children and adolescents in families with high emotional support or low conflict seem to be protected from developing stress regulatory problems. Limitations in this body of research as well as directions for future research are discussed.

The impact of sexual abuse on female development: lessons from a multigenerational, longitudinal research study

This is a report on the research design and findings of a 23-year longitudinal study of the impact of intrafamilial sexual abuse on female development. The conceptual framework integrated concepts of psychological adjustment with theory regarding how psychobiological factors might impact development. Participants included 6- to 16-year-old females with substantiated sexual abuse and a demographically similar comparison group. A cross-sequential design was used and six assessments have taken place, with participants at median age 11 at the first assessment and median age 25 at the sixth assessment. Mothers of participants took part in the early assessments and offspring took part at the sixth assessment. Results of many analyses, both within circumscribed developmental stages and across development, indicated that sexually abused females (on average) showed deleterious sequelae across a host of biopsychosocial domains including: earlier onsets of puberty, cognitive deficits, depression, dissociative symptoms, maladaptive sexual development, hypothalamic-pituitary-adrenal attenuation, asymmetrical stress responses, high rates of obesity, more major illnesses and healthcare utilization, dropping out of high school, persistent posttraumatic stress disorder, self-mutilation, Diagnostic and Statistical Manual of Mental Disorders diagnoses, physical and sexual revictimization, premature deliveries, teen motherhood, drug and alcohol abuse, and domestic violence. Offspring born to abused mothers were at increased risk for child maltreatment and overall maldevelopment. There was also a pattern of considerable within group variability. Based on this complex network of findings, implications for optimal treatments are elucidated. Translational aspects of extending observational research into clinical practice are discussed in terms that will likely have a sustained impact on several major public health initiatives.

Abuse in childhood and risk of uterine leiomyoma: the role of emotional support in biologic resilience

BACKGROUND

Childhood adversities are associated with adult health. We hypothesize that exposure to physical and sexual abuse in childhood and adolescence will be associated with incidence of clinically symptomatic uterine leiomyomas (fibroids) through influences on health behaviors and reproductive hormone regulation.

METHODS

Participants included 68,505 women enrolled in the Nurses' Health Study II, an ongoing prospective cohort study of premenopausal women from 14 US states aged 25-42 years at enrollment (1989), who completed a retrospective questionnaire on childhood violence exposure (2001). A cumulative indicator of severity and chronicity of child/teen violence exposure was derived using factor analysis. We used a Cox proportional-hazards model to estimate the incidence rate ratios (IRRs) and 95% confidence intervals (CIs).

RESULTS

During the 728,865 woman-years of follow-up (1989-2005), 9823 incident diagnoses of ultrasound- or hysterectomy-confirmed uterine leiomyomas were reported; 65% reported any physical or sexual abuse. A dose-response association between cumulative abuse and fibroid risk was found. Compared with those who reported no abuse, multivariable IRRs for ultrasound or hysterectomy-confirmed uterine leiomyomas were 1.08 (95% CI = 1.03-1.13), 1.17 (1.10-1.24), 1.23 (1.14-1.33), 1.24 (1.10-1.39), and 1.36 (1.18-1.54), for cumulative exposures ranging from mildest to most severe. Increased emotional support in childhood also attenuated associations.

CONCLUSIONS

Severity and chronicity of child/teen sexual and physical abuse was associated with increasing risk of clinically detected fibroids among premenopausal women.

Stressor paradigms in developmental studies: what does and does not work to produce mean increases in salivary cortisol

The stress response system is comprised of an intricate interconnected network that includes the hypothalamic-pituitary-adrenocortical (HPA) axis. The HPA axis maintains the organism's capacity to respond to acute and prolonged stressors and is a focus of research on the sequelae of stress. Human studies of the HPA system have been facilitated enormously by the development of salivary assays which measure cortisol, the steroid end-product of the HPA axis. The use of salivary cortisol is prevalent in child development stress research. However, in order to measure children's acute cortisol reactivity to circumscribed stressors, researchers must put children in stressful situations which produce elevated levels of cortisol. Unfortunately, many studies on the cortisol stress response in children use paradigms that fail to produce mean elevations in cortisol. This paper reviews stressor paradigms used with infants, children, and adolescents to guide researchers in selecting effective stressor tasks. A number of different types of stressor paradigms were examined, including: public speaking, negative emotion, relationship disruption/threatening, novelty, handling, and mild pain paradigms. With development, marked changes are evident in the effectiveness of the same stressor paradigm to provoke elevations in cortisol. Several factors appear to be critical in determining whether a stressor paradigm is successful, including the availability of coping resources and the extent to which, in older children, the task threatens the social self. A consideration of these issues is needed to promote the implementation of more effective stressor paradigms in human developmental psychoendocrine research.

Early experience and the development of stress reactivity and regulation in children

Children who spend early portions of their lives in institutions or those maltreated in their families of origin are at risk for developing emotional and behavioral problems reflecting disorders of emotion and attention regulation. Animal models may help explicate the mechanisms producing these effects. Despite the value of the animal models, many questions remain in using the animal data to guide studies of human development. In 1999, the National Institute of Mental Health in the United States funded a research network to address unresolved issues and enhance translation of basic animal early experience research to application in child research. Professor Seymour Levine was both the inspiration for and an active member of this research network until his death in October of 2007. This review pays tribute to his legacy by outlining the conceptual model which is now guiding our research studies.

Neuroendocrine dysregulation following early social deprivation in children

Human and nonhuman animal studies reveal that early experiences with caregivers shape children's ability to regulate their responses to stress. To understand the effects of early deprivation on the regulation of the hypothalamic-pituitary-adrenal axis following social interactions, we examined urinary cortisol levels in a group of internationally adopted children who had experienced institutional care, and thus, species-atypical attachment relationships, early in life prior to adoption. Cortisol regulation was assessed both basally and following standardized interpersonal interactions between the child and his/her mother and the child and an unfamiliar adult. Postinstitutionalized children showed prolonged elevations in cortisol levels following the mother, but not the stranger, interaction. More severe neglect was associated with the highest basal cortisol levels and the most impaired cortisol regulation following the mother interaction. These results suggest that early social deprivation may contribute to long-term regulatory problems of the stress-responsive system, and that these differences are most evident within the context of ongoing, close interpersonal relationships.

The communicative functions of touch in humans, nonhuman primates, and rats: a review and synthesis of the empirical research

Although touch is one of the most neglected modalities of communication, several lines of research bear on the important communicative functions served by the modality. The authors highlighted the importance of touch by reviewing and synthesizing the literatures pertaining to the communicative functions served by touch among humans, nonhuman primates, and rats. In humans, the authors focused on the role that touch plays in emotional communication, attachment, bonding, compliance, power, intimacy, hedonics, and liking. In nonhuman primates, the authors examined the relations among touch and status, stress, reconciliation, sexual relations, and attachment. In rats, the authors focused on the role that touch plays in emotion, learning and memory, novelty seeking, stress, and attachment. The authors also highlighted the potential phylogenetic and ontogenetic continuities and discussed suggestions for future research.

Dating couples' attachment styles and patterns of cortisol reactivity and recovery in response to a relationship conflict

This study investigated theoretically predicted links between attachment style and a physiological indicator of stress, salivary cortisol levels, in 124 heterosexual dating couples. Cortisol was assessed at 7 points before and after an experimental conflict negotiation task, creating a trajectory of stress reactivity and recovery for each participant. Growth modeling of cortisol data tested hypotheses that (a) insecurely attached individuals show patterns of greater physiological stress reactions to interpersonal conflict than do securely attached individuals and (b) people with insecurely attached partners show patterns of greater stress in reaction to relationship conflict than those with securely attached partners. Hypothesis 1 was supported, but men and women differed in the type of insecure attachment that predicted stress trajectories. Hypothesis 2 was supported for men, but not for women. The discussion emphasizes the role of gender role norms and partner characteristics in understanding connections between adult attachment and patterns of cortisol responses to interpersonal stress.

Early parental loss and salivary cortisol in young adulthood: The moderating role of family environment

Early family life adversity has been linked with negative physical and psychological health consequences in adulthood, possibly due to alterations in neuroendocrine activity. Young adults from families characterized by parental loss (N = 45) and control participants (N = 43) completed self-report measures of prior abuse and family conflict, and performed a stressful speech task designed to elicit neuroendocrine responses. Higher reported abuse and conflict were associated with increased cortisol for the loss group, but were unrelated to cortisol in the control group. Results indicate alterations in neuroendocrine functioning associated with early parental loss, which are moderated by the quality of the family environment.

Transition to child care: associations with infant-mother attachment, infant negative emotion, and cortisol elevations

Seventy 15-month-old infants were studied at home before starting child care, during adaptation (mothers present) and separation (first 9 days without mothers) phases, and 5 months later. Security of infant-mother attachment was assessed before and 3 months after child care began. In the separation phase, salivary cortisol rose over the first 60 min following the mothers' departures to levels that were 75% to 100% higher than at home. Compared with insecure infants, secure infants had markedly lower cortisol levels during the adaptation phase and higher fuss and cry levels during the separation phase, and their fuss and cry levels were significantly correlated with their cortisol levels. Attachments remained secure or became secure if mothers spent more days adapting their children to child care.

Separation as a natural cue to danger in the spotted hyena (Crocuta crocuta)

Spotted hyena biology suggests mothers and infants will exhibit one of two alternative responses to separation: (a) Due to prolonged dependency, infants will act similarly to Old World monkeys, displaying distress and proximity seeking behaviors; or (b) because mother-infant separations are frequent in the wild, infants will exhibit little distress or change in reunion behavior. Hence, reunion behavior following mother-infant separation was compared to control periods in captive hyena (Crocuta crocuta) mothers and infants at two developmental periods. Significant increases (p < or =.05) in distress (i.e., agitated arousal and increased vocalization) and proximity maintenance (i.e., cub and maternal approaches, and maternal monitoring) as well as a trend towards increased sibling aggression following separation were observed. Responsibility for proximity maintenance, assessed by the Hinde Index, adhered to patterns common to primates---with cubs assuming increased responsibility later in development. Findings are discussed in light of hyena ecology and Attachment Theory.

Maternal separation in rats leads to anxiety-like behavior and a blunted ACTH response and altered neurotransmitter levels in response to a subsequent stressor

Adverse early life experiences can have a negative impact on behavior later in life. We subjected rat pups to maternal separation and determined the effect's thereof on adult behavior. We removed rat pups from their mothers for 3 h daily from postnatal days 2 to 14. While controls were reared normally on day 60, the behaviors of the rats were tested using the elevated plus-maze. Some rats were subsequently subjected to restraint stress for a 10-min period. Trunk blood was collected for basal, as well as 15- and 60-min postrestraint stress ACTH determinations. Neurotransmitter levels (noradrenaline (NA), serotonin (5HT), and their metabolites, MHPG and 5HIAA, respectively) were also determined at basal, immediately and 15-min post-restraint stress in the hypothalamus, hippocampus, and frontal cortex in another group of animals. The amount of entries into the arms of the elevated plus-maze was significantly reduced in the separated animals, indicating decreased locomotion. They spent significantly more time in the closed arms of the maze. A significant increase in defecation frequency was noted. These observations suggested anxious behavior. Basal ACTH levels were significantly higher in separated animals. At 15-min post-restraint stress, the ACTH levels were significantly lower than controls, indicating a blunted stress response. A decrease in noradrenaline was noted first in limbic regions and an increase in 5HIAA levels was found in the frontal cortex and hippocampus. We conclude that maternal separation induced abnormal behaviors and stress responses that were associated with altered neurotransmitter levels.

What are the costs of marital conflict and dissolution to children's physical health?

Do parental marital conflict and dissolution influence the risk trajectory of children's physical health risk? This paper reviews evidence addressing this question in the context of understanding how early environmental adversities may trigger a succession of risks that lead to poor health in childhood and greater risk for chronic health problems in adulthood. We first review existing evidence linking marital conflict and dissolution to offspring's physical health outcomes. Next, we provide evidence supporting biopsychosocial pathways that may link marital conflict and dissolution with accelerated health risk trajectories across the lifespan. Specifically, we posit that consequential to the stresses associated with marital conflict and disruption, parenting practices are compromised, leading to offspring deficits in affective, behavioral, and cognitive domains. These deficits, in turn, are hypothesized to increase health risk through poor health behaviors and by altering physiological stress-response systems, including neuroendocrine, cardiovascular, and neurotransmitter functioning. On the basis of the available direct evidence and theoretically plausible pathways, it appears that there is a cost of marital conflict and disruption to children's health; however, more comprehensive investigations are needed to further elucidate this relationship. In the final section, we address limitations in the current literature and identify research that is needed to better evaluate the association between marital conflict and dissolution and children's physical health.

Repeated parental deprivation in the infant common marmoset (Callithrix jacchus, primates) and analysis of its effects on early development

BACKGROUND

We describe a successful demonstration that repeated early deprivation of parental care (ED), as used to study effects of early life stress in rats, can be performed in a primate and that it constitutes an early life stressor.

METHODS

Seven breeding pairs of marmoset monkeys each provided control twins (CON) and twins that were subjected to ED for 30-120 min/day on postnatal days (PND) 2-28. Urine samples were obtained to monitor the acute effect of ED on cortisol and catecholamine levels. Behavior samples were obtained in the home cage to monitor the effects of ED on infant and infant-parent behavior.

RESULTS

Early deprivation of parental care caused acute increases in cortisol, epinephrine, and norepinephrine. At PND 28, basal cortisol was reduced in ED compared with CON infants, and ED infants were smaller than CON infants. Early deprivation infants tended to spend more time in the suckling position than did CON. Early deprivation infants demonstrated more distress vocalization than CON infants, even though the parental care they received in the home cage was similar. Early deprivation infants tended to play less socially than did CON.

CONCLUSIONS

To our knowledge, this is the first demonstration that a repeated early life stressor of the type developed in rats can also be applied to a primate species.

Presence of mother and unfamiliar female alters levels of testosterone, progesterone, cortisol, adrenocorticotropin, and behavior in maturing Guinea pigs

Although the guinea pig is characterized by precocial physical development and minimal active maternal care, studies suggest the presence of the mother can influence neuroendocrine and behavioral activity of offspring even well beyond weaning. Previous results may have been influenced by the procedure of housing weaned subjects with the mother to within 2 days of testing. The present study examined approximately 40-day-old guinea pigs housed apart from the mother for 0 (not rehoused), 2, or 10 days. Rehousing without the mother led to elevations in plasma testosterone (measured in males), progesterone (measured in females), cortisol, and adrenocorticotropin (ACTH) (both measured in males and females). Offspring housed without the mother for 10 days had the highest progesterone, cortisol, and ACTH levels. Testosterone elevations were observed in 2-day-, but not 10-day-, rehoused animals. Regardless of rehousing condition, 60 min isolation in a novel test cage elevated progesterone, cortisol, and ACTH, and reduced testosterone. These effects were all moderated if the subject was tested with the mother or another female. Sexual behavior toward the mother was observed frequently, but only in males housed apart from her prior to testing. Overall, males and females that had been housed apart from the mother interacted with her as they would an unfamiliar female. Our results corroborate previous findings, suggest the effect of housing apart from the mother on male testosterone is transitory, and indicate that continuous housing with the mother past weaning suppresses circulating progesterone in females and cortisol and ACTH in both sexes.

Early deprivation and behavioral and physiological responses to social separation/novelty in the marmoset

Long-term effects of adverse early environment on neurobehavioral development have been reported for rodents and primates. The present study used daily early deprivation (ED), a paradigm developed for rats, for the first time in a nonhuman primate, the common marmoset, and investigated its effects on the behavioral and physiological responses to social separation/novelty (SSN) challenge tests in juveniles. On postnatal days (PNDs) 2-28, infants (n=5 twin pairs) were removed from the parents and placed alone in an isolation chamber for 30-120 min (9 h/week). Parents and control subjects (n=5 twin pairs) were briefly restrained (CON). At Weeks 18-20, behavioral responses of ED and CON juveniles to six 60-min SSN tests in an isolated cage, comprising 45 min alone and 15 min reunion with the father, were measured. Baseline and post-test urine samples were collected for measurement of cortisol. ED subjects exhibited significantly lower basal SSN urinary cortisol than CON, whilst SSN response cortisol values were similar in ED and CON. When alone, ED subjects were significantly less mobile and emitted significantly less contact calls than CON. Following reunion, ED subjects were significantly less in contact with or being carried by the father than CON and demonstrated significantly more tail piloerection. Although they require validation by additional parameters (e.g. cardiovascular), these data strongly suggest that early-life stress alters endocrine and behavioral responsiveness to psychosocial challenge in this primate and in a direction that could model important changes in disorders of human affective state.

Effects of maternal deprivation on adrenal and behavioural responses in rats with anterodorsal thalami nuclei lesions

There is evidence that repeated maternal isolation of neonatal rats may influence both emotional behavior and Hypothalamic-Pituitary Adrenal (HPA) activity. On the other hand the Anterodorsal Thalami Nuclei (ADTN) exerts an inhibitory influence on the hypophyso-adrenal system under basal and stressful conditions. In the present work we investigated whether neonatal maternal deprivation produces long term effects on the ADTN regulation of behavioral patterns (open field test) and on HPA axis activity. Specifically, we sought to determine whether adult female rats with ADTN lesions, previously isolated for 4.5 hours daily during the first 3 weeks of life, react in endocrinologically and behaviourally distinct manner as compared to controls. The examined groups were: non maternally deprived (NMD)/sham lesioned, NMD/lesioned, maternally deprived (MD)/sham lesioned, MD/lesioned with and without the open field test. At 3 months MD/sham lesioned animals showed a marked decrease in ambulation (P < 0.01), and with ADTN lesion, the rearing values were lower (P < 0.01) and grooming higher (P < 0.05) than NMD. This last data would indicate a high emotional index. Regarding the activity of the HPA axis, maternal deprivation induced a significant decrease in plasma ACTH concentration both in sham and lesioned animals (P < 0.001), and plasma Corticosterone (C) increased in sham animals (P < 0.001). This data would indicate a higher sensitivity of the adrenal glands. After the open field test ACTH and C were different between deprived and non-deprived animals depending on the ADTN lesion. Taking into consideration the increase of ACTH levels in sham lesioned MD animals exposed to the test, we could conclude that this new situation was a stressful situation. Finally in the present work, it was very difficult to relate the behavioral parameters with the endocrine data. It is known that depending on the context, corticosteroids may produce opposite effects on emotional behavior via different receptors in the brain.In summary, neonatal maternal deprivation induced alterations of behavioral patterns and affected the ADTN inhibitory influence on ACTH and C secretion.

Effects of separation and novelty on distress vocalizations and cortisol in the common marmoset (Callithrix jacchus)

In socially-bonding species, separation from familiar attachment figures is widely known to stimulate a physiological and behavioral stress response. This study investigated the hormonal and vocal responses of adult common marmosets to separation from familiar group members and to 24 hr of cohabitation with an unfamiliar opposite-sex conspecific. All subjects were removed from their home cages and placed into a novel environment for 20 min. In one group, marmosets were exposed to an unfamiliar, opposite-sex partner in the novel environment and remained paired with this partner for the 24 hr test period. In three other groups, marmosets experienced the novel environment alone and subsequently were returned to their original social- or single-housing condition, or kept separate from their social groups for a 24 h period. Blood samples were collected the day before, and at 30 min, 90 min, and at 24 h after separation. Cortisol responses were differentially affected by the length of separation and the presence of unfamiliar conspecifics. Brief separation followed by the return to the social group had minimal effect on plasma cortisol levels. All marmosets produced high levels of separation calls in the novel environment, but there was no apparent relationship between calling and cortisol levels. The lack of a temporal relationship between the production of distress vocalizations and serum cortisol has previously been noted in squirrel monkey and rhesus monkey infant separation studies; the behavioral and physiological responses to separation appear to be similarly dissociated in the marmoset. Further, the characteristics of a separation environment can differentially affect the hormonal response by adult marmosets without differentially affecting their behavioral response.

Childhood attachment and loss experiences affect adult cardiovascular and cortisol function

OBJECTIVE

This study proposes to test the hypothesis that early loss of a parent, coupled with poor quality family relationships, would result in long-term increased cardiovascular and cortisol reactivity to stress.

METHODS

Subjects included 30 university students who lost one parent before age 16, and 31 control subjects. Blood pressure (BP) was measured continuously during 5-minute baseline and recovery periods, and during each of 2 tasks--viewing a 7-minute video clip depicting the death of a parent, and giving a 3-minute impromptu speech (1-hour rest between tasks). Salivary cortisol samples were collected immediately before each task, and at 5 and 20 minutes posttask. Quality of family relationships (FR) was measured using the Moos Family Environment Scale.

RESULTS

Repeated-measures analysis of covariance revealed significant main effects on BP of both parental loss and FR for both tasks (all p values < .05) such that subjects who lost a parent or reported poor quality FR showed higher BP across all periods. The loss by FR by period interaction was not significant. An FR by period interaction was found for cortisol during the movie, in which poor quality FR subjects showed increased cortisol, whereas all others showed decreases. A loss by period interaction was found for cortisol during the speech, in which cortisol increased in loss subjects and decreased in non-loss subjects.

CONCLUSIONS

These findings indicate that both childhood loss of a parent and poor quality of caretaking are associated with long-term increases in BP and altered neurohormonal responses to stress.

Neuroendocrine correlates of separation stress in the Siberian dwarf hamster (Phodopus sungorus)

Siberian dwarf hamsters form monogamous male-female pair bonds. Disruption of the pair bond results in increases in body mass and behavioral alterations similar to profiles seen in human atypical depression. We examined behavioral and neuroendocrine correlates associated with separation of the male from his mate. Animals were paired (n = 28 pairs) for 3 weeks, then 15 pairs were separated and 13 pairs remained as controls. Behaviors of the males were observed in a novel environment following 3 weeks of pairing and 4 weeks of separation. The 5-min behavioral test monitored exploratory, territorial behavior, and locomotor activity. Separated males showed a significant increase in body mass (p < 0.01). paralleled by an increase in food consumption (p < 0.01). Separated males had decreased seminal vesicle mass (p < 0.05) and testicular mass (p < 0.05). Behavioral analysis revealed that separated males showed no significant differences in grooming, scent-marking, alert on 2 feet, or escape behavior when compared to paired males. Separated males did show significant increases in inactivity (p < 0.05). Plasma cortisol levels were significantly increased in separated animals (p < 0.05), but there were no significant effects on testosterone. Resting levels of plasma norepinephrine and epinephrine were less in separated males, but this was significant only for norepinephrine (p < 0.05). In conclusion, separation stress was accompanied by increased hypothalamic-pituitary-adrenal axis function and decreased peripheral sympathetic nervous system activity and decreased reproductive profiles.

Hypothalamic-pituitary-adrenal responses to brief social separation

Involuntary separation from close social companions is widely held to lead to pathophysiological outcomes. Presumably, the relationship with, or category of, the separated individual determines the nature of the physiological response. Here, experiments examining the consequences of brief involuntary separation on the activity of the stress-responsive hypothalamic-pituitary-adrenal (HPA) system are reviewed. Only those studies designed specifically to assess the effect of the absence of the social partner are considered. Evidence for HPA activation in response to social separation has been obtained in a number of species; yet, many studies find no effect of separation of affiliative partners on HPA activity. The occurrence of an HPA response to separation does not appear to be related to the phylogenetic position or cognitive capacity of the species studied, nor is it a universal response to mother-infant separation. Rather, it is suggested that the pattern of results can be largely understood in the context of attachment. Separation of partners exhibiting signs of emotional attachment leads to an immediate and persistent HPA response, whereas separation of partners that are affiliative, but do not exhibit attachment, has little or no effect on HPA activity.

Response to removal from and return to a social group in adult male rhesus monkeys

The removal of four adult rhesus monkeys from a large social group (n = 85) to peer housing resulted in no significant changes in basal cortisol levels or absolute numbers of T lymphocyte subsets 24 h later. However, the return of these males 1 year later to the same social group resulted in significant increases in cortisol levels (66 +/- 21%) and significant decreases in T-helper (-31.6 +/- 15.8%) and T-suppressor cells (-35.2 +/- 8.7%) 24 h later. Blood samples for immune and cortisol measurements were obtained before and 24 h following both the removal and the return 1 year later. Aggressive and sexual behavioral data were recorded on audiotape for 3.5 h following the reintroduction using an all occurrences of some behaviors sampling technique. Analyses revealed a negative correlation between percent change from baseline in T-helper cells 24 h following the return and the frequency of bites (nonwounding) and chases received during the 3.5 h following the return. The absence of a stress response to separation in adult males is in contrast to the presence of a stress response observed in infants, juveniles, and adult females and possibly is due to sex differences in group attachment in sexually mature males. On the other hand, the return to the social group did induce a psychosocial stress response in the males, and the degrees of the stress, as determined by cortisol and immune cell measures, was related to the agonistic interactions experienced by the individuals.

Behavioral and physiological response of juvenile sooty mangabeys to reunion with their mothers following a year's absence

The return of 6 juvenile mangabey monkeys to their social group following an absence of a year resulted in increased basal cortisol secretion for both the offspring and the mothers and in significant decrements in the absolute number of lymphocyte subsets for the offspring. Six 9-month-old sooty mangabeys were removed from their socially housed mothers, subsequently peer housed, and returned to the maternal social group 1 year later. Offspring showed a significant increase in cortisol levels 24 hr following reunion (48 +/- 6%) and this difference persisted through 1 month, while the mothers showed a significant increase only at the 24-hr sample point (18 +/- 3%). Moreover, the offspring, but not the mothers, showed a significant decrease in lymphocyte subsets which were evident through the 1-month sample point. Behavioral data revealed a significant positive correlation between the percent of total scan samples offspring were with their mothers (proximity, contact, huddle) the day of return and the offspring's percent change from baseline in total T cells 24 hr later, r = 0.84. All mother-offspring pairs with the exception of one exhibited frequent affiliative behaviors toward one another by 6 days following the return. These data demonstrate that the reunion of juvenile mangabeys with their mothers after a year's absence is an acute stressor for the mothers and a relatively longer term stressor for the offspring, and that behavioral interactions which characterize the return of individual subjects to the natal group can predict acute physiological responses.

A longitudinal assessment of CSF monoamine metabolite and plasma cortisol concentrations in young rhesus monkeys

Twenty-two rhesus macaques were studied longitudinally from infancy to early adolescence in order to assess the effects of developmental change, experimental history, gender, and individual variation on the response of the catecholaminergic, serotonergic, and adrenocortical systems to separation-induced stress. Experimental effects were assessed by comparing subjects reared for the first 6 months of life either with their mothers or in peer groups. Developmental changes in response to repeated separation stress were assessed by subjecting the monkeys to four sequential 4-day social separations when they were 6 and 18 months old. At both ages, prior to, and on the last day of the first and fourth separations, cerebrospinal fluid (CSF) was obtained from the cisterna magna to assess monoamine metabolite concentrations, and blood samples were collected to assess plasma cortisol concentrations. Blood samples were also obtained on the first day of each separation at each age. Age-related declines were found in both homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations for all subjects. Social separation consistently increased CSF 3-methoxy-4-hydroxyphenolglycol (MHPG) over baseline levels, but decreased HVA concentrations, whereas 5-HIAA levels increased following the first, but not the fourth separation. Plasma cortisol increased rapidly immediately after separation and remained higher than baseline on day 4 of both the first and fourth separation. Independent of age and experimental condition, peer-rearing increased CSF MHPG and plasma cortisol concentrations. During year 1, peer-rearing also produced diminished CSF 5-HIAA concentrations in female monkeys relative to female mother-reared monkeys, but increased male peer-reared monkeys' concentrations relative to mother-reared males. Interindividual differences were highly stable, with significant correlations both within and between years for each of the three metabolites and cortisol.

First time experiences in infancy: when they appear to be pleasant, do they activate the adrenocortical stress response?

The effect of a positive first-time experience on adrenocortical activity was examined in 48 6- to 13-month-old infants who took part in two sessions of a YMCA-like mother-infant swim class. Experience was manipulated by comparing Novice swimmers with infants who previously had taken a swim class, and by examining responses to first versus second class session. In addition, the effects of temperamental fear of novelty were examined by maternal report prior to the first session. Preswim and Postswim cortisol levels were compared to measures obtained at the same time of day in two comparison groups, one tested at home and one tested in a playroom at the University. The results yielded no evidence of an adrenocortical stress response (elevated cortisol) to the swim sessions for either the Novice or Experienced swimmers. Infant temperamental fearfulness predicted behavioral but not adrenocortical responses during swimming. Postswim cortisol levels were significantly lower than posttest levels in the two baseline comparison groups, and lower postswim cortisol levels were associated with less negative and more positive emotional behavior and engagement of the swimming experience. These results are consistent with the hypothesis that emotions serve as a major pathway influencing adrenocortical activity, and provide no support for the uncertainty hypothesis of adrenocortical activation.

Social separation and reunion affects immune system in juvenile rhesus monkeys

Removal of juvenile rhesus monkeys from their natal social group to indoor individual caging resulted in increased basal cortisol secretion and significant decrements in the frequency of lymphoid subpopulations. Fourteen juvenile rhesus monkeys, which had never been removed from the group, were studied. Baseline immune and cortisol measurements were obtained before seven of the subjects were removed from social housing to standard individual cages. The remaining seven subjects, matched for age, sex, weight, and rank, remained in the social group throughout the study serving as controls. Blood samples were taken 24 hours after removal of the test subjects from the group and at specific intervals thereafter through 11 weeks. At 24 hours after the separation test subjects showed a significant increase in basal cortisol levels (40%) and a significant decrease in several immune parameters, with absolute numbers of total T cells declining 72 +/- 12%. Significant group differences in immune parameters persisted through 11 weeks. Eighteen weeks following removal, the test subjects were returned to the group which produced a cortisol rise in both test and controls at the 24-hour postreturn sample. Although there were no group differences in the frequency of lymphoid subsets 24 hours after return, some test subjects showed marked decrements which were inversely related to cortisol and were predicted by behavioral events. These data demonstrate that the removal of naive juvenile rhesus monkeys from their natal social group to individual indoor caging is a potent psychosocial stressor and that the behavioral interactions which characterize the return of the individual subjects to the natal group may predict physiological response.

Interactions of anxiolytic and antidepressant drugs with hormones of the hypothalamic-pituitary-adrenal axis

Changes in hormones of the hypothalamic-pituitary-adrenal (HPA) axis in patients suffering from anxiety and depressive disorders are reviewed, and the changes that occur when animals are exposed to test situations used preclinically to model anxiety or depression. The effects of exogenous administration of HPA hormones both clinically and in animal tests is discussed and the effects of clinically used anxiolytics and antidepressants on hormones of the HPA axis. The final section discusses stress-induced changes in the CNS.