Gestational cortisol and social play shape development of marmosets' HPA functioning and behavioral responses to stressors

Associations between fecal glucocorticoid levels and social bonds vary with relatedness in juvenile rhesus macaques

Strong social bonds in gregarious adult animals have been associated with lower levels of glucocorticoids. However, similar research is lacking for juvenile primates. We examined relationships between social bonds and mean concentrations of fecal glucocorticoid metabolites (fGCMs) in 44 free-ranging juvenile rhesus macaques (Macaca mulatta) on Cayo Santiago, Puerto Rico. We measured frequencies of affiliative behavior (grooming, play, approaches and proximity) with other same-sex, same-aged juveniles (peers) and the total number of affiliative peer relationships. We found a positive relationship between fGCMs and grooming frequencies. Females that spent more time in proximity to peers also had higher fGCMs. In contrast, among juveniles with more closely related peers, those with more affiliative peers or more frequent play bouts had lower fGCMs. However, strong peer bonds in most juveniles did not appear to be associated with reduced glucocorticoid levels. fGCMs were higher for females than males, but were unassociated with physical activity, aggression, or peer seeking tendencies. We propose that the establishment and navigation of some peer bonds at this life stage may involve increased metabolic demand.

Glucocorticoids and behavior in non-human primates: A meta-analytic approach to unveil potential coping mechanisms

Glucocorticoids (GCs) mediate responses to energetic and psychosocial challenges and are associated with behavioral adjustments that form part of an adaptive vertebrate stress response. GCs and behavior can indirectly influence each other, leading to either an intensification or attenuation of stress responses. Exploring these GC-behavior relationships may offer insights into the beneficial aspects of behavior and help identify coping mechanisms that potentially enhance individual fitness. We conducted a systematic review of the relationship between GCs and several behavioral traits, as described in the literature on captive and wild primates, and evaluated the effect of different categorical factors on these relationships using a meta-analytic approach. According to the type of behavior, we grouped statistical measures into affiliative, agonistic, anxiety-like, and foraging domains which were further differentiated into behavioral subgroups. We also categorized measures based on setting, method, sex and age of individuals, and sample matrix involved in each primary study. Overall, we found that some affiliative and foraging behaviors are associated with lower GC levels, while agonistic and anxiety-like behaviors are linked to higher GC levels. Specifically, non-sexual affiliation and energetically inexpensive activities were negatively related to GCs. In contrast, inter- and intragroup aggression, noncommunicative and self-directed behaviors, and energetically expensive activities were positively related to GCs. By demonstrating how certain social, ecological and intrinsic factors affect the GC-behavior relationships, our study helps elucidate the contexts that may alleviate or intensify the stress responses in non-human primates.

Nuancing 'Emotional' Social Play: Does Play Behaviour Always Underlie a Positive Emotional State?

This review focuses on social play, a complex behaviour that is often difficult to categorize. Although play has been typically associated with positive emotional states, a thorough examination of the literature indicates that it may relate to different emotional systems, from attachment to conflict. Play oscillates between competition and cooperation, and includes a spectrum in between; thus, quantitatively identifying and demonstrating the emotional nature of play remains challenging. We considered examples from human and non-human animal studies and explored the emotional and neuro-hormonal systems involved in play. We assessed ethological data possibly indicating the emotional states underlying play, and we focused on the cooperative and competitive elements of play. We investigated the relationship between play and affiliative/aggressive behaviours, the communicative meaning of play signals (especially primate play faces), and the motor and possibly emotional contagion function of rapid motor mimicry during play. From all the literature on play, this review selects and combines studies in an innovative way to present the methods (e.g., play indices and social network analysis), tools (e.g., sequential analysis and facial coding software), and evidence indicative of the emotional states underlying play, which is much more complex than previously thought.

Effects of social environments on male primate HPG and HPA axis developmental programming

Developmental plasticity is particularly important for humans and other primates because of our extended period of growth and maturation, during which our phenotypes adaptively respond to environmental cues. The hypothalamus-pituitary-gonadal (HPG) and hypothalamus-pituitary-adrenal (HPA) axes are likely to be principal targets of developmental "programming" given their roles in coordinating fitness-relevant aspects of the phenotype, including sexual development, adult reproductive and social strategies, and internal responses to the external environment. In social animals, including humans, the social environment is believed to be an important source of cues to which these axes may adaptively respond. The effects of early social environments on the HPA axis have been widely studied in humans, and to some extent, in other primates, but there are still major gaps in knowledge specifically relating to males. There has also been relatively little research examining the role that social environments play in developmental programming of the HPG axis or the HPA/HPG interface, and what does exist disproportionately focuses on females. These topics are likely understudied in males in part due to the difficulty of identifying developmental milestones in males relative to females and the general quiescence of the HPG axis prior to maturation. However, there are clear indicators that early life social environments matter for both sexes. In this review, we examine what is known about the impact of social environments on HPG and HPA axis programming during male development in humans and nonhuman primates, including the role that epigenetic mechanisms may play in this programming. We conclude by highlighting important next steps in this research area.

Antibiotic-induced gut dysbiosis elicits gut-brain axis relevant multi-omic signatures and behavioral and neuroendocrine changes in a nonhuman primate model

Emerging evidence indicates that antibiotic-induced dysbiosis can play an etiological role in the pathogenesis of neuropsychiatric disorders. However, most of this evidence comes from rodent models. The objective of this study was to evaluate if antibiotic-induced gut dysbiosis can elicit changes in gut metabolites and behavior indicative of gut-brain axis disruption in common marmosets (Callithrix jacchus) - a nonhuman primate model often used to study sociability and stress. We were able to successfully induce dysbiosis in marmosets using a custom antibiotic cocktail (vancomycin, enrofloxacin and neomycin) administered orally for 28 days. This gut dysbiosis altered gut metabolite profiles, behavior, and stress reactivity. Increase in gut Fusobacterium spp. post-antibiotic administration was a novel dysbiotic response and has not been observed in any rodent or human studies to date. There were significant changes in concentrations of several gut metabolites which are either neurotransmitters (e.g., GABA and serotonin) or have been found to be moderators of gut-brain axis communication in rodent models (e.g., short-chain fatty acids and bile acids). There was an increase in affiliative behavior and sociability in antibiotic-administered marmosets, which might be a coping mechanism in response to gut dysbiosis-induced stress. Increase in urinary cortisol levels after multiple stressors provides more definitive proof that this model of dysbiosis may cause disrupted communication between gut and brain in common marmosets. This study is a first attempt to establish common marmosets as a novel model to study the impact of severe gut dysbiosis on gut-brain axis cross-talk and behavior.

Bundling the haystack to find the needle: Challenges and opportunities in modeling risk and resilience following early life stress

Various forms of early life adversity (ELA) have been linked with increased risk for negative health outcomes, including neuropsychiatric disorders. Understanding how the complex interplay between types, timing, duration, and severity of ELA, together with individual differences in genetic, socio-cultural, and physiological differences can mediate risk and resilience has proven difficult in population based studies. Use of animal models provides a powerful toolset to isolate key variables underlying risk for altered neural and behavioral maturational trajectories. However, a lack of clarity regarding the unique features of differing forms of adversity, lab differences in the implementation and reporting of methods, and the ability compare across labs and types of ELA has led to some confusion. Here, we highlight the diversity of approaches available, current challenges, and a possible ways forward to increase clarity and drive more meaningful and fruitful implementation and comparison of these approaches.

Effect of Morphine Administration on Social andNon-Social Play Behaviour in Calves

Simple Summary

Play can be used as an indicator of welfare in animals, because animals play more when all their basic needs are met. Opioids have a modulatory effect on social play behaviour in rodents and primates, however little is known regarding the central mechanisms involved in play behaviour in ruminants. In ruminants, we need to know more about what factors influence play behaviour, to determine which elements of play may more accurately be used as indicators of positive welfare. Therefore, the objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. In an arena test, morphine administration increased the performance of social play events but had no effect on locomotor play in calves. Similar to research in rodents and primates, morphine administration appears to increase social but not non-social elements of play in calves, suggesting that increased social play may be more indicative of a positive affective state.

Abstract

The objective of this study was to evaluate the effect of morphine on social and non-social play behaviour in calves. Twelve calves experienced four treatments in a cross over 2 × 2 factorial design: Calves received an intravenous injection of morphine or saline 10 min prior to being tested individually or in pairs in an arena for 20 min. Play behaviour was continuously recorded in the arena test. Lying times were recorded in the home pen. Cortisol concentrations were measured before and after testing. In the arena test, calves given morphine tended to perform more social play events than calves given saline, however, morphine administration had no effect on locomotor play. Calves given morphine spent less time lying than calves given saline during the first 4 h after returning to the home pen. Cortisol concentrations were suppressed in calves given morphine. Administration of morphine appeared to increase social play but had no effect on locomotor play in calves. This study highlights the importance of investigating different aspects of play behaviour in animals as some may be more indicative of a positive affective state than others. More studies investigating the effects of morphine on play are needed to confirm the results found in this study.

Oxytocin regulates reunion affiliation with a pairmate following social separation in marmosets

While separation from significant social partners produces a host of neurobiological and behavioral perturbations, including behavioral distress and increased glucocorticoid production, positive social interactions upon reunion are critical for the reestablishment of normative relationship dynamics and the attenuation of the biobehavioral stress response. The hormone oxytocin has critical and pervasive roles in reproductive and behavioral processes across the lifespan, and plays a particularly prominent role in social bonding. In this study, we examined the extent that oxytocin modulates interactions with a pairmate following separation challenges that varied in both social context (isolation; separation) and duration (long; short), in marmosets. We demonstrated that the impact of pharmacological manipulations of the oxytocin system on the expression of affiliation upon reunion depended on both the context and duration of the separation challenge. Specifically, marmosets treated with an oxytocin antagonist spent less time in proximity with their pairmate upon reunion following a long-separation challenge. During the short-separation challenge, marmosets engaged in more social gaze when separated with an opposite-sex stranger, but not when separated with their mate. Furthermore, marmosets that received the most social gaze from opposite-sex strangers spent the most time in proximity with their long-term mate upon reunion. We also showed that marmosets treated with an OT agonist received increased levels of gaze from opposite-sex strangers, but not from their mate. Overall, these results suggest that marmosets are sensitive to the nature of the social interactions during separation, and subsequently alter their expression of affiliation upon reunion with their long-term mate. These findings further implicate oxytocin as a bond-enhancing molecule that regulates the reestablishment of normative levels of affiliation with a mate following separation, and add to the emerging literature that suggests the OT system underlies critical behavioral processes that contribute to the preservation of long-lasting social bonds.

Impact of prenatal stress on mother-infant dyadic behavior during the still-face paradigm

BACKGROUND

Mother-infant interaction provides important training for the infant's ability to cope with stress and the development of resilience. Prenatal stress (PS) and its impact on the offspring's development have long been a focus of stress research, with studies highlighting both harmful and beneficial effects. The aim of the current study was to examine the possible influence of both psychological stress and hypothalamic-pituitary-adrenal (HPA) axis activity during pregnancy with mother-child dyadic behavior following stress exposure.

METHODS

The behavior of 164 mother-infant dyads during the still-face situation was filmed at six months postpartum and coded into three dyadic patterns: 1) both positive, 2) infant protesting-mother positive, and 3) infant protesting-mother negative. PS exposure was assessed prenatally according to psychological measures (i.e., psychopathological, perceived and psychosocial PS; n = 164) and HPA axis activity measures (maternal salivary cortisol, i.e., cortisol decline and area under the curve with respect to ground (AUCg); n = 134).

RESULTS

Mother-infant dyads in both the high- and low-stress groups showed decreasing positive and increasing negative dyadic behavior in the reunion episode, which is associated with the well-known "still-face" and "carry-over" effect. Furthermore, mother-infant dyads with higher psychosocial PS exhibited significantly more positive dyadic behavior than the low psychosocial PS group in the first play episode, but not in the reunion episode. Similarly, mother-infant dyads with high HPA axis activity (i.e. high AUCg) but steeper diurnal cortisol decline (i.e. cortisol decline) displayed significantly less negative behavior in the reunion episode than dyads with low HPA axis activity. No significant results were found for psychopathological stress and perceived stress.

CONCLUSIONS

The results suggest a beneficial effect of higher psychosocial PS and higher prenatal maternal HPA axis activity in late gestation, which is in line with "stress inoculation" theories.

Peripubertal Stress With Social Support Promotes Resilience in the Face of Aging

The peripubertal period of development is a sensitive window, during which adverse experiences can increase the risk for presentation of cognitive and affective dysfunction throughout the lifespan, especially in women. However, such experiences in the context of a supportive social environment can actually ameliorate this risk, suggesting that resilience can be programmed in early life. Affective disorders and cognitive deficits commonly emerge during aging, with many women reporting increased difficulty with prefrontal cortex (PFC)-dependent executive functions. We have developed a mouse model to examine the interaction between peripubertal experience and age-related changes in cognition and stress regulation. Female mice were exposed to peripubertal chronic stress, during which they were either individually housed or housed with social interaction. One year after this stress experience, mice were examined in tasks to access their cognitive ability and flexibility in stress reactive measures. In a test of spatial memory acquisition and reversal learning where aged females normally display a decreased performance, the females that had experienced stress with social interaction a year earlier showed improved performance in reversal learning, a measure of cognitive flexibility. Because peripuberty is a time of major PFC maturation, we performed transcriptomic and biochemical analysis of the aged PFC, in which long-term changes in microRNA expression and in myelin proteins were found. These data suggest that stress in the context of social support experienced over the pubertal window can promote epigenetic reprogramming in the brain to increase the resilience to age-related cognitive decline in females.

Early-life Social Adversity and Developmental Processes in Nonhuman Primates

Most primate species produce offspring that are altricial and highly dependent upon caregivers. As a consequence, a host of developmental trajectories can be dramatically altered by variation in early experiences. We review the impact of early social experiences (in both experimental models and natural contexts) on developmental profiles in three species of nonhuman primates: marmosets, squirrel monkeys, and macaques. Graded exposure to early-life social adversity (ELSA) produces short- to long-term effects on multiple developmental outcomes, including affect, social behavior, cognitive and attentional processes, and in the neural substrates that underlie these sociobehavioral traits.

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.

Environmental insults in early life and submissiveness later in life in mouse models

Dominant and subordinate dispositions are not only determined genetically but also nurtured by environmental stimuli during neuroendocrine development. However, the relationship between early life environment and dominance behavior remains elusive. Using the IntelliCage-based competition task for group-housed mice, we have previously described two cases in which environmental insults during the developmental period altered the outcome of dominance behavior later in life. First, mice that were repeatedly isolated from their mother and their littermates (early deprivation; ED), and second, mice perinatally exposed to an environmental pollutant, dioxin, both exhibited subordinate phenotypes, defined by decreased occupancy of limited resource sites under highly competitive circumstances. Similar alterations found in the cortex and limbic area of these two models are suggestive of the presence of neural systems shared across generalized dominance behavior.