The Role of Oxytocin in Social Buffering: What Do Primate Studies Add?

Stay social, stay young: a bioanthropological outlook on the processes linking sociality and ageing

In modern human societies, social interactions and pro-social behaviours are associated with better individual and collective health, reduced mortality, and increased longevity. Conversely, social isolation is a predictor of shorter lifespan. The biological processes through which sociality affects the ageing process, as well as healthspan and lifespan, are still poorly understood. Unveiling the physiological, neurological, genomic, epigenomic, and evolutionary mechanisms underlying the association between sociality and longevity may open new perspectives to understand how lifespan is determined in a broader socio/evolutionary outlook. Here we summarize evidence showing how social dynamics can shape the evolution of life history traits through physiological and genetic processes directly or indirectly related to ageing and lifespan. We start by reviewing theories of ageing that incorporate social interactions into their model. Then, we address the link between sociality and lifespan from two separate points of view: (i) considering evidences from comparative evolutionary biology and bioanthropology that demonstrates how sociality contributes to natural variation in lifespan over the course of human evolution and among different human groups in both pre-industrial and post-industrial society, and (ii) discussing the main physiological, neurological, genetic, and epigenetic molecular processes at the interface between sociality and ageing. We highlight that the exposure to chronic social stressors deregulates neurophysiological and immunological pathways and promotes accelerated ageing and thereby reducing lifespan. In conclusion, we describe how sociality and social dynamics are intimately embedded in human biology, influencing healthy ageing and lifespan, and we highlight the need to foster interdisciplinary approaches including social sciences, biological anthropology, human ecology, physiology, and genetics.

More allogrooming is followed by higher physiological stress in wild female baboons

Social bonds increase fitness in a range of mammals. One pathway by which social bonds may increase fitness is by reducing the exposure to physiological stress, i.e. glucocorticoid (GC) hormones, that can be detrimental to health and survival. This is achieved through downregulating hypothalamic-pituitary-adrenal (HPA)-axis activity. Indeed, long-term measures of social (grooming) bonds are often negatively correlated with HPA-axis activity. However, the proximate role of physical touch through allogrooming remains an open question in the sociality-health-fitness debate. Demonstrating the potential anxiolytic benefits of grooming in the wild is hindered by methodological limitations. Here, we match accelerometer-identified grooming in wild female chacma baboons (Papio ursinus) to non-invasive faecal GC metabolite concentrations (fGCs). Consistent with previous work, we found a negative (but statistically non-significant) overall relationship between individual averaged fGCs and grooming rates. However, when time-matching grooming to fGCs, we found that both more giving and receiving grooming were followed by higher fGCs. This upregulation of HPA-axis activity suggests that maintaining social bonds (and its ultimate fitness benefits) may come at a shorter-term physiological cost. This finding sheds new light on a ubiquitous social behaviour typically considered 'relaxing' and suggests that sociopositive contact can trigger physiological stress.

Physiological and behavioral contagion/buffering effects of chronic unpredictable stress in a socially enriched environment: A preliminary study

Rodents are sensitive to the emotional state of conspecifics. While the presence of affiliative social partners mitigates the physiological response to stressors (buffering), the partners of stressed individuals show behavioral and endocrine changes indicating that stress parameters can be transmitted across the group members (contagion). In this study, we investigated the social contagion/buffering phenomena in behavior and neuroendocrine mechanisms after exposure to chronic stress, in groups of rats living in the PhenoWorld (PhW). Three groups were tested (8 stressed rats, 8 unstressed rats, and a mixed group with 4 and 4) and these were analyzed under 4 conditions: stressed (pure stress group, n = 8), unstressed (naive control group, n = 8), stressed from mixed group (stressed companion group, n = 8), unstressed from mixed group (unstressed companion group, n = 8. While naive control animals remained undisturbed, pure stress group animals were all exposed to stress. Half of the animals under the mixed-treatment condition were exposed to stress (stressed companion group) and cohabitated with their unstressed partners (unstressed companion group). We confirmed the well-established chronic unpredictable stress (CUS) effects in physiological, behavioral, and neuroendocrine endpoints; body weight gain, open arm entries and time in EPM, and oxytocin receptor expression levels in the amygdala decreased by stress exposure, whereas adrenal weight was increased by stress. Furthermore, we found that playing, rearing and solitary resting behaviors decreased, whereas huddling behavior increased by CUS. In addition, we detected significant increases (stress-buffering) in body weight gain and huddling behaviors between pure stress and stress companion animals, and significant stress contagion effects in emotional behavior and oxytocin receptor expression levels between naive control and control companion groups. Hence, we demonstrate buffering and contagion effects were evident in physiological parameters, emotional behaviors, and social home-cage behaviors of rats and we suggest a possible mediation of these effects by oxytocin neurotransmission. In conclusion, the results herein suggest that the stress status of animals living in the same housing environment influences the behavior of the group.

An AAV-CRISPR/Cas9 strategy for gene editing across divergent rodent species: Targeting neural oxytocin receptors as a proof of concept

A major issue in neuroscience is the poor translatability of research results from preclinical studies in animals to clinical outcomes. Comparative neuroscience can overcome this barrier by studying multiple species to differentiate between species-specific and general mechanisms of neural circuit functioning. Targeted manipulation of neural circuits often depends on genetic dissection, and use of this technique has been restricted to only a few model species, limiting its application in comparative research. However, ongoing advances in genomics make genetic dissection attainable in a growing number of species. To demonstrate the potential of comparative gene editing approaches, we developed a viral-mediated CRISPR/Cas9 strategy that is predicted to target the oxytocin receptor (Oxtr) gene in >80 rodent species. This strategy specifically reduced OXTR levels in all evaluated species (n = 6) without causing gross neuronal toxicity. Thus, we show that CRISPR/Cas9-based tools can function in multiple species simultaneously. Thereby, we hope to encourage comparative gene editing and improve the translatability of neuroscientific research.

Similar behavioral but different endocrine responses to conspecific interactions in hand-raised wolves and dogs

Domestication has altered dogs' conspecific social organization compared to their closest, non-domesticated relatives, gray wolves. Wolves live in packs whose survival depends on coordinated behavior, but dogs rely less on conspecifics, which predicts greater cohesiveness in wolf than dog packs. Endocrine correlates such as oxytocin and glucocorticoids modulate group cohesion resulting in species-specific differences in social interactions. We found that although wolves' and dogs' observable behavioral reactions to a territorial threat and separation from the pack were similar, hormonal responses differed. Wolves' but not dogs' oxytocin and glucocorticoid concentrations correlated positively with territorial behaviors and only wolves showed increased glucocorticoid concentrations after separation from their pack. Together, results suggest stronger emotional activation to threats to group integrity in wolves than dogs, in line with their socio-ecology.

The moderating role of social support on workplace violence and stress among psychiatric nurses

Exposure to violent acts is considered one of the major stressful events psychiatric nurses are exposed to. Social support has been found to reduce nurses' stress and alleviate their experience of workplace violence; however, no accounts are available on whether social support moderates the relationship between workplace violence and stress. Therefore, the aim of this study was to examine the moderating role of social support on workplace violence and stress among psychiatric nurses. A cross-sectional descriptive and predictive design was utilized. A total of 195 psychiatric nurses were recruited from two governmental mental health hospitals. The results showed that psychiatric nurses were frequently exposed to violence, both verbally and physically, whether during their entire career or within the past 12 months. Verbal violence was more common among participants than physical abuse. Male nurses and nurses working mix-shift were more likely to experience violent acts. Regression analysis showed that only workplace violence and social support predicted psychiatric nurses' stress. On the other hand, social support did not moderate the relationship between workplace violence and stress. Further research is needed to investigate whether similar findings will conform with the results of this study. Meanwhile, healthcare institutions need to implement strategies to reduce or prevent nurses' exposure to workplace violence and lower their stress levels. Mobilizing and activating social support resources at work are considered other avenues to reduce stress experienced by psychiatric nurses.

Oxytocin modulation in the medial prefrontal cortex of pair-exposed rats during fear conditioning

INTRODUCTION

Social buffering is the phenomenon, in which stress and fear reactions caused by exposure to stressful stimuli when animals are exposed to homogeneous relationships are attenuated. Social buffering reduces fear memory behavior such as escape, avoidance, and freezing behavior in rodents due to social existence. Here, we aimed to determine alterations of fear behavior and neural activity in the medial prefrontal cortex (mPFC) in response to the presence of another rat in fear-exposed conditions and to confirm the role of oxytocin in mPFC in regulating social buffering.

METHODS

We performed a passive avoidance test and determined positive c-Fos expression in single- and pair-exposed rats. Anisomycin (a protein synthesis inhibitor) and oxytocin receptor regulators (carbetocin; agonist and atosiban; antagonist) were microinjected into the mPFC to clarify the role of oxytocin in the mPFC.

RESULTS

While single-exposed rats showed a significant increase in both freezing and passive avoidance behaviors compared to control rats, pair-exposed rats showed significantly less fear behavior compared to single-exposed rats. The c-Fos expression in the prelimbic (PL) mPFC was significantly increased in pair-exposed rats compared to that in control and single-exposed rats. The pair-exposed effect was blocked by anisomycin injections into the PL mPFC of pair-exposed rats. Furthermore, when a carbetocin was injected into the PL mPFC in single-exposed rats, fear behavior was decreased, and these changes were blocked by atosiban.

DISCUSSION

Our findings suggest that reduction of fear-related behavior induced by acute pair-exposure is mediated by oxytocin receptors in the PL mPFC. Pair exposure with conspecifics during fear-inducing situations helps coping with fear by significantly increasing the role of oxytocin in the PL mPFC.

Social Support and Longevity: Meta-Analysis-Based Evidence and Psychobiological Mechanisms

Over the past 60 years, evidence has accumulated on the fundamental role of supportive social relationships in individual health and longevity. This paper first summarizes the results of 23 meta-analyses published between 1994 and 2021, which include 1,187 longitudinal and cross-sectional studies with more than 1,458 million participants. The effect sizes reported in these meta-analyses are highly consistent with regard to the predicted link between social support and reduced disease and mortality; the meta-analyses also highlight various theoretical and methodological issues concerning the multi-dimensionality of the social support concept and its measurements, and the need to control potential confounding and moderator variables. This is followed by an analysis of the experimental evidence from laboratory studies on psychobiological mechanisms that may explain the effect of social support on health and longevity. The stress-buffering hypothesis is examined and extended to incorporate recent findings on the inhibitory effect of social support figures (e.g., the face of loved ones) on fear learning and defensive reactions alongside evidence on the effect of social support on brain networks that down-regulate the autonomic nervous system, HPA axis, and immune system. Finally, the paper discusses the findings in the context of three emerging research areas that are helping to advance and consolidate the relevance of social factors for human health and longevity: (a) convergent evidence on the effects of social support and adversity in other social mammals, (b) longitudinal studies on the impact of social support and adversity across each stage of the human lifespan, and (c) studies that extend the social support framework from individual to community and societal levels, drawing implications for large-scale intervention policies to promote the culture of social support.

Pharmacological Treatment for Social Cognition: Current Evidence

Cognitive impairment is currently considered a core feature of schizophrenia (SZ) and is gaining attention as a fundamental therapeutic target. Standard treatment for SZ involves the use of antipsychotics that are successfully used to control positive symptoms and disorganized behaviour. However, it is still unclear whether they are effective on social cognition (SC) impairment. Furthermore, different medications are currently being studied to improve SC in patients with SZ. A literature search on this topic was conducted using the PubMed database. All kinds of publications (i.e., reviews, original contributions and case reports) written in English and published in the last 15 years were included. The aim of our literature review is to draw a picture of the current state of the pharmacological treatment of SC impairment in SZ.

The role of oxytocin and vasopressin dysfunction in cognitive impairment and mental disorders

Oxytocin (OXT) and arginine-vasopressin (AVP) are structurally homologous peptide hormones synthesized in the hypothalamus. Nowadays, the role of OXT and AVP in the regulation of social behaviour and emotions is generally known. However, recent researches indicate that peptides also participate in cognitive functioning. This review presents the evidence that the OXT/AVP systems are involved in the formation of social, working, spatial and episodic memory, mediated by such brain structures as the hippocampal CA2 and CA3 regions, amygdala and prefrontal cortex. Some data have demonstrated that the OXT receptor's polymorphisms are associated with impaired memory in humans, and OXT knockout in mice is connected with memory deficit. Additionally, OXT and AVP are involved in mental disorders' progression. Stress-induced imbalance of the OXT/AVP systems leads to an increased risk of various mental disorders, including depression, schizophrenia, and autism. At the same time, cognitive deficits are observed in stress and mental disorders, and perhaps peptide hormones play a part in this. The final part of the review describes possible therapeutic strategies for the use of OXT and AVP for treatment of various mental disorders.

Lactating Coquerel's sifaka (Propithecus coquereli) exhibit reduced stress responses in comparison to males and nonlactating females

Cortisol is a glucocorticoid hormone that plays a principal role in metabolic function and stress responses in wild primates. Stressors are ubiquitous in environments and elicit a variety of physiological and behavioral responses. While stress responses are adaptive in the short-term, they can have negative effects when experienced over longer durations. As a physiological stressor, the process of lactation is an energetically expensive activity for mammals. Milk production increases water loss and increased hydration demands are amplified in mammalian species inhabiting xeric habitats, including lemur species living in northwestern Madagascar-the region for this research work. Here, sifakas give birth during the dry season (May-October) and wean infants during the subsequent wet season (November-April). The author collected fecal samples during the 24 weeks following infant births in 10 groups of Coquerel's sifaka in Ankarafantsika Park, Madagascar. The author analyzed the samples by comparing the first 12-week time block to the second 12-week time block, which corresponded to the dry and the beginning of the wet seasons, respectively. Analyses were based on 375 samples collected over two birth seasons (2010 and 2011). A linear mixed model determined the relationships between reproductive class and temporal cortisol variation. The three reproductive classes had significantly different cortisol concentrations. Lactating females had lower cortisol than adult males and nonlactating females in all weeks postnatal. Males had significantly higher cortisol in weeks 13-24 relative to weeks 1-12. Examining seasonal changes in cortisol concentrations demonstrates how lemurs respond physiologically to the energetic constraints of lactation during the critical life history stage of infant development.

Role of oxytocin in the control of stress and food intake

Oxytocin neurones in the hypothalamus are activated by stressful stimuli and food intake. The oxytocin receptor is located in various brain regions, including the sensory information-processing cerebral cortex; the cognitive information-processing prefrontal cortex; reward-related regions such as the ventral tegmental areas, nucleus accumbens and raphe nucleus; stress-related areas such as the amygdala, hippocampus, ventrolateral part of the ventromedial hypothalamus and ventrolateral periaqueductal gray; homeostasis-controlling hypothalamus; and the dorsal motor complex controlling intestinal functions. Oxytocin affects behavioural and neuroendocrine stress responses and terminates food intake by acting on the metabolic or nutritional homeostasis system, modulating emotional processing, reducing reward values of food intake, and facilitating sensory and cognitive processing via multiple brain regions. Oxytocin also plays a role in interactive actions between stress and food intake and contributes to adaptive active coping behaviours.

In the face of stress: Interpreting individual differences in stress-induced facial expressions

Stress is an inevitable part of life that can profoundly impact social and emotional functioning, contributing to the development of psychiatric disease. One key component of emotion and social processing is facial expressions, which humans can readily detect and react to even without conscious awareness. Facial expressions have been the focus of philosophic and scientific interest for centuries. Historically, facial expressions have been relegated to peripheral indices of fixed emotion states. More recently, affective neuroscience has undergone a conceptual revolution, resulting in novel interpretations of these muscle movements. Here, we review the role of facial expressions according to the leading affective neuroscience theories, including constructed emotion and social-motivation accounts. We specifically highlight recent data (Mayo et al, 2018) demonstrating the way in which stress shapes facial expressions and how this is influenced by individual factors. In particular, we focus on the consequence of genetic variation within the endocannabinoid system, a neuromodulatory system implicated in stress and emotion, and its impact on stress-induced facial muscle activity. In a re-analysis of this dataset, we highlight how gender may also influence these processes, conceptualized as variation in the "fight-or-flight" or "tend-and-befriend" behavioral responses to stress. We speculate on how these interpretations may contribute to a broader understanding of facial expressions, discuss the potential use of facial expressions as a trans-diagnostic marker of psychiatric disease, and suggest future work necessary to resolve outstanding questions.

Oxytocin modulates mate-guarding behavior in marmoset monkeys

In socially-monogamous species, intolerance of interactions between a pairmate and a sexual rival (i.e., mate-guarding) promotes the preservation of long-lasting partnerships. One promising neurobiological candidate for the regulation of mate-guarding behavior in monogamous primates is the oxytocin (OT) system, given its established role in both the development of monogamous bonds and the behavioral processes that facilitate the preservation of those bonds. In this study, male and female marmosets were exposed to a same-sex intruder in their home environment during conditions when their pairmate was present and absent, and across three treatment conditions (OT receptor agonist; saline control; OT receptor antagonist). Saline-treated marmosets spent significantly more time in proximity to the intruder, relative to the empty pairmate enclosure, when their pairmate was absent. However, when marmosets received OT they spent less time in proximity to the intruder, indicating that OT may reduce interest in a same-sex stranger in a territorial context. When their pairmate was present, saline-treated marmosets spent equal time in proximity to both intruder and pairmate; yet when they received OT they spent significantly more time in proximity to the intruder, indicating that OT may increase interest in a same-sex stranger in a mate-guarding context. While OT treatment did not directly influence the expression of aggression, OT system manipulations impacted the expression of selective social interest during an intruder challenge, suggesting that OT may enhance adaptive responses to social challenges. Moreover, these findings add to the converging evidence that the OT system regulates behavioral processes that underlie the preservation of established relationships.

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.