Clearance studies of oxytocin in humans using radioimmunoassay measurements of the hormone in plasma and urine

A fit-for-purpose validation of a commercial radioimmunoassay for measurement of human peripheral oxytocin

Oxytocin (OT) is a peptide hormone synthesized in the hypothalamus and released into systemic circulation or other areas of the brain. Its physiological roles include action as a hormone with stimulation of uterine contractions and that as a neuromodulator with involvement in social behaviors and regulation of mood. Its small size and low levels within biological matrices make it challenging to accurately measure. The goal of this study was to demonstrate the specificity of the antibody, sensitivity, and reproducibility of the Phoenix Pharmaceuticals (PP) OT radioimmunoassay (RIA) for use in human urine, serum, and saliva. Specificity of the antibody was assessed by high pressure liquid chromatography with ultraviolet (HPLC-UV) separation and assay of the fractions. Immunoreactivity was evaluated using the percent OT bound, and the fraction retention times were compared to the retention time of an intact OT standard to determine which fractions contained OT in the extracted samples. Reproducibility was assessed by running replicates of pools of each biomatrix over several assays. Sensitivity was assessed by repeated measurement of physiologically relevant low-concentration specimens. In all tested specimens the greatest reactivity in assay corresponded to the same fraction(s) as the OT standard. Only minimal reactivity was found in the other fractions, suggesting that in an unfractionated sample the antibody reacts mostly with intact OT. Reproducibility was acceptable for all specimens and the coefficient of variation (CV) ranged from 3.72 to 8.04% and 5.89-12.8%, for intra and inter-assay, respectively. The limits of quantitation (LOQ) were sufficient for measurement of normal values in urine (0.643 & 1.43 pg/mL), serum (1.90 pg/mL), and saliva pools (0.485 & 4.42 pg/mL). In conclusion, the PP OT RIA is specific and sensitive enough for reproducible measurement of intact OT in human peripheral biological matrices.

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.

Advances in human oxytocin measurement: challenges and proposed solutions

Oxytocin, a neuropeptide known for its role in reproduction and socioemotional processes, may hold promise as a therapeutic agent in treating social impairments in patient populations. However, research has yet to uncover precisely how to manipulate this system for clinical benefit. Moreover, inconsistent use of standardized and validated oxytocin measurement methodologies-including the design and study of hormone secretion and biochemical assays-present unresolved challenges. Human studies measuring peripheral (i.e., in plasma, saliva, or urine) or central (i.e., in cerebrospinal fluid) oxytocin concentrations have involved very diverse methods, including the use of different assay techniques, further compounding this problem. In the present review, we describe the scientific value in measuring human endogenous oxytocin concentrations, common issues in biochemical analysis and study design that researchers face when doing so, and our recommendations for improving studies using valid and reliable methodologies.

Oxytocin reactivity to a lab-based stressor predicts support seeking after stress in daily life: Implications for the Tend-and-Befriend theory

Social relationships play an important role in mental and physical health, particularly during times of stress. However, little is known about the biological mechanisms underlying the tendency to seek support following stress. The Tend-and-Befriend theory suggests that oxytocin (OT) may enhance the desire for social contact in response to stress. Yet, no studies in humans have provided empirical support for the connection between stress-induced changes in endogenous OT and increased support seeking after stress. In the present study, 94 participants performed a standardized laboratory stressor and then completed two weeks of daily assessments of support seeking after stress. In line with preregistered hypotheses, stress-induced plasma OT reactivity to the laboratory stressor was associated with more frequent support seeking behaviors following stress in daily life (i.e., outside of the laboratory). Additional results suggested that attachment anxiety (but not avoidance) strengthened this association. Our findings implicate the OT system in affiliative behaviors following stress, providing empirical support for the Tend-and-Befriend theory.

What are oxytocin assays measuring? Epitope mapping, metabolites, and comparisons of wildtype & knockout mouse urine

Oxytocin has become a popular analyte in behavioral endocrinology in recent years, due in part to its roles in social behavior, stress physiology, and cognition. Urine samples have the advantage of being non-invasive and minimally disruptive to collect, allowing for oxytocin measurements even in some wild populations. However, methods for urinary oxytocin immunoassay have not been sufficiently optimized and rigorously assessed for their potential limitations. Using samples from oxytocin knockout (KO) and wildtype (WT) mice, we find evidence of considerable interference in unextracted urine samples, with similar distributions of measured oxytocin in both genotypes. Importantly, although this interference can be reduced by a reversed-phase solid-phase extraction (SPE), this common approach is not sufficient for eliminating false-positive signal on three immunoassay kits. To better understand the source of the observed interference, we conducted epitope mapping of the Arbor Assays antibody and assessed its cross-reactivity with known, biologically active fragments of oxytocin. We found considerable cross-reactivity (0.5-52% by-molarity) for three fragments of oxytocin that share the core epitope, with more cross-reactivity for longer fragments. Given the presence of some cross-reactivity for even the tripeptide MIF-1, it is likely that many small protein metabolites might be sufficiently similar to the epitope that at high concentrations they interfere with immunoassays. We present a new mixed-mode cation-exchange SPE method that minimizes interference-with knockout samples measuring below the assay's limit of detection-while effectively retaining oxytocin from the urine of wildtype mice. This method demonstrates good parallelism and spike recovery across multiple species (mice, dogs, sifakas, humans). Our results suggest that immunoassays of urine samples may be particularly susceptible to interference, even when using common extraction protocols, but that this interference can be successfully managed using a novel mixed-mode cation exchange extraction. These findings imply that previous conclusions based on urinary oxytocin measurements-especially those involving unextracted samples-may need to be reassessed.

Social anxiety is associated with greater peripheral oxytocin reactivity to psychosocial stress

To date, it has been difficult to establish reliable biomarkers associated with specific forms of psychopathology. Social anxiety, for example, is associated with inconsistent biological responses to psychosocial stress on markers including cortisol and salivary alpha-amylase. Thus, it is critical that studies identify more reliable biomarkers that index patterns associated with social anxiety. Two potential candidates are the neuropeptides oxytocin and vasopressin, which have been implicated in stress responsivity across species. Studies have demonstrated a reliable increase in oxytocin, and a surrogate marker for vasopressin, following engagement in the most widely used lab-based psychosocial stress paradigm: the Trier Social Stress Test (TSST). However, no study has examined whether social anxiety moderates peripheral oxytocin or vasopressin reactivity to psychosocial stress. In 101 young adult participants, dimensionally assessed social anxiety was associated with greater plasma oxytocin, but not vasopressin, reactivity to the TSST. Results were maintained following the inclusion of depression as a covariate. Findings suggest that studying changes in peripheral oxytocin concentrations may be a method of differentiating individuals with higher levels of social anxiety.

Measurement of urinary mesotocin in large-billed crows by enzyme-linked immunosorbent assay

Mesotocin (MT) is an avian homologue of oxytocin (OT). Behavioral pharmacological studies in birds have suggested the involvement of MT in socially affiliative behavior. However, investigations of peripheral MT levels associated with social behavior are lacking because non-invasive methods to measure surrogate plasma MT have yet to be established. This study aimed to measure urinary MT in crows using a commercially available OT enzyme-linked immunosorbent assay kit. Urine samples were collected after intravenous injection of MT and centrifuged to separate urine and fecal components. We found that urinary MT was significantly elevated 15–30 min after MT injection. These results validate our method for the use of urine samples for the measurement of peripheral MT levels in crows.

Neuroendocrine Mechanisms of Social Bonds and Separation Stress in Rodents, Dogs, and Other Species

Mammalian species form unique bonds between mothers and infants. Maternal care, including suckling, is necessary for infant survival, and the mother and, sometimes, the father require a lot of effort in nurturing infants. An infant's probability of survival depends on the extent of the investment of care by the mother. In parallel, mothers must identify their offspring and invest only in those who possess their genes to achieve evolutionary benefits. Therefore, they need to recognize their offspring and show a strong preference for them. For this reason, bond formation between mothers and infants is important. The mother monitors her offspring's physical condition and stays close to them. The offspring also form strong bonds with their mothers. Therefore, a separation between the mother and infant causes severe stress for both parties. Although it was initially thought that such bonds between mother and infant are limited to the same species, we have also observed a similar phenomenon in the human-dog relationship. In this article, we discuss the neuroendocrine mechanisms that underlie bond formation and separation based on findings of neurobiological research in mice and the relationship between humans and dogs.

Being moved by listening to unfamiliar sad music induces reward-related hormonal changes in empathic listeners

Many people enjoy sad music, and the appeal for tragedy is widespread among the consumers of film and literature. The underlying mechanisms of such aesthetic experiences are not well understood. We tested whether pleasure induced by sad, unfamiliar instrumental music is explained with a homeostatic or a reward theory, each of which is associated with opposite patterns of changes in the key hormones. Sixty-two women listened to sad music (or nothing) while serum was collected for subsequent measurement of prolactin (PRL) and oxytocin (OT) and stress marker (cortisol and adrenocorticotropic hormone) concentrations. Two groups of participants were recruited on the basis of low and high trait empathy. In the high empathy group, PRL and OT levels were significantly lower with music compared with no music. And compared to the low empathy group, the high empathy individuals reported an increase of positive mood and higher ratings of being moved with music. None of the stress markers showed any changes across the conditions or the groups. These hormonal changes, inconsistent with the homeostatic theory proposed by Huron, exhibit a pattern expected of general reward. Our findings illuminate how unfamiliar and low arousal music may give rise to pleasurable experiences.

The role of oxytocin signaling in depression and suicidality in returning war veterans

Many war veterans struggle with depression and suicidality, and separation from the military is a time of particularly high risk. Based on research in non-human animals, we hypothesized that reduced oxytocin signaling would mediate symptoms of depression and suicidality in war veterans recently separated from their close comrades. We also hypothesized that veterans with more frequent contact with comrades would have fewer symptoms of depression and suicidality. In this cross-sectional study, male veterans from the Iraq and Afghanistan wars (n = 86) provided blood and urine samples for measurement of peripheral oxytocin (OT) levels, as well as saliva samples for DNA extraction followed by genotyping of oxytocin receptor gene (OXTR) Single Nucleotide Polymorphisms, and CpG-methylation assessment. Participants also completed a series of mental health questionnaires and interviews. Veterans reported feeling very close to their comrades during war, and missing them greatly upon returning home. Neither peripheral OT levels nor OXTR genotypes were related to symptoms of depression or suicidality. On the other hand, methylation at OXTR CpG -924 was negatively correlated with depressive symptomology, after controlling for possible confounds. Veterans who socialized with comrades more frequently had higher levels of urinary, but not plasma OT, as well as less depressive symptomology. Social connectedness was a strong negative predictor of symptoms of both depression and suicidality, eclipsing the predictive power of other variables such as post-deployment social support, the degree to which participants reported missing their comrades, and the frequency with which they socialized with comrades. Our results suggest that veteran mental health is more impacted by lack of social connectedness than by separation from close comrades per se. While there is some evidence that OXTR methylation relates to depressive symptomology, decreased OT signaling does not appear to mediate the relationship between social disconnectedness and depression or suicidality. Sleep quality and anxiety disorders were also significantly associated with mental health symptoms, independent of social connectedness. Our findings suggest that efforts aimed at alleviating the burden of depression and suicidality in returning war veterans should focus on re-integrating veterans into society and establishing a feeling of social connectedness, as well as on treating anxiety disorders and sleep problems.

Validation of a commercial enzyme immunoassay to assess urinary oxytocin in humans

Within the last decade, oxytocin (OT) has attracted a lot of attention in the context of various human social behaviors. Besides its importance in regulating physiological processes in females related to giving birth and lactation, OT is involved in the establishment and maintenance of social relationships, trust and emotion recognition. However, results are not always consistent across studies, which may partly be due to the incomplete validation of methods used to assess OT levels. Carefully validating a method before its use is of crucial importance to ensure that it can be used to accurately, reliably and repeatedly assess OT levels. With this study we evaluated a commercially available Enzyme Immunoassay to assess OT in human urine samples by conducting a careful analytical validation. Results indicate that, with regard to parallelism and immunoreactivity, human urinary OT can be assessed reliably. However, extraction methods need further improvement to optimize measures of accuracy and extraction efficiency, especially in the lower range of the assay system. Tests on OT stability indicate that OT is affected by degradation when stored at 4°C or room temperature. Storing urine samples over longer periods revealed that OT levels are most stable when stored as ethanol extracts at -20°C compared to being stored as samples at -20°C or -80°C. Although some of the validated parameters did not reach the intended quality criteria, this study highlights the importance of such in depth validation procedures and reporting results to make them available to researchers embarking on projects utilizing such methods.

Salivary oxytocin in pigs, cattle, and goats during positive human-animal interactions

Research on oxytocin (OT) has provided crucial insight into the neuroendocrine mechanisms of social behavior and human-animal interactions. Nonetheless, this peptide hormone remains challenging to sample, usually requiring invasive measures in the brain or blood, which limits its use. We conducted an analytical validation of the measurement of OT in the saliva of three common farm animal species: pigs, cattle and goats. We then investigated the biological significance of salivary OT concentrations by using a positive human-animal interaction paradigm. The paradigm varied in terms of human familiarity and included a control condition where the animal was alone in the testing pen. A total of 18 pigs, 18 cattle and 9 goats were subjected to each condition using a within-individual counterbalanced design. Animals were free to choose to interact with the human. Saliva samples were collected immediately before and after the 10-min test, and behavior during the test was analyzed. Oxytocin could be reliably measured by ELISA in the saliva of goats (without extraction), and in the saliva of pigs and cattle after extraction. Salivary OT concentration did not change consistently according to testing condition. However, salivary OT concentration was significantly associated with some behaviors, with different relationships depending on the species. In conclusion, OT can be reliably measured in the saliva of goats and, after extraction, in the saliva of pigs and cattle. The relationships of OT with human-animal interactions and animal behavior were complex and to some extent species-dependent, possibly reflecting the perception of the interaction by the animal.

Improved oxytocin analysis from human serum and urine by orbitrap ESI-LC-HRAM-MS

Native circulating oxytocin (OT) levels in non-pregnant/non-lactating/non-medicated humans are very low (≤ 8 pg/mL). The lower limit of detection (LLOD) of our previous liquid chromatography mass spectrometry (LC-MS) method (10-25 pg/mL) precluded their quantification in serum and urine. Thus, we sought to improve the LC-MS sensitivity of OT measurements in these matrices by hydrophobic tagging and solid phase extraction (SPE). In the former approach, OT was reduced then alkylated with N-alkyl acetamide (C12, C14, C16, and C18) tags or derivatized using sulfonyl chloride-based reagents. In the latter approach, native OT in serum and urine was concentrated by offline SPE using gradient acetonitrile washings after first crashing with acetonitrile. Peak urinary eluate fractions were further concentrated online then analyzed by orbitrap-based LC-MS with electrospray ionization. All hydrophobic OT derivatives had lower sensitivity than native OT. Washing with a water-acetonitrile gradient during SPE improved the LLOD of OT in spiked serum to 2.5 pg/mL, while adding a subsequent online-concentration step improved the LLOD in spiked urine to 1-5 pg/mL and allowed us to detect OT in urine from lactating women. We were unable to improve the sensitivity of OT measurements by hydrophobic tagging or by derivatization using sulfonyl chloride-based reagents. However, we were successful in improving the sensitivity of native OT measurements in serum and urine 2- and 5-fold, respectively, from our previous orbitrap-based LC-MS method. Offline SPE was mandatory for both matrices and a subsequent online-concentration step was required for urine.

Oxytocin increases after affiliative interactions in male Barbary macaques

Mammals living in stable social groups often mitigate the costs of group living through the formation of social bonds and cooperative relationships. The neuropeptide hormone oxytocin (OT) is proposed to promote both bonding and cooperation although only a limited number of studies have investigated this under natural conditions. Our aim was to assess the role of OT in bonding and cooperation in male Barbary macaques (Macaca sylvanus). First, we tested for an effect of affiliation - grooming and triadic male-infant-male interactions - with bond and non-bond partners on urinary OT levels. Second, we tested whether grooming interactions (and thus increased OT levels) increase a male's general propensity to cooperate in polyadic conflicts. We collected >4000 h of behavioral data on 14 adult males and measured OT levels from 139 urine samples collected after affiliation and non-social control periods. Urinary OT levels were higher after grooming with any partner. By contrast, OT levels after male-infant-male interactions with any partner or with bond partners were not different from controls but were higher after interactions with non-bond partners. Previous grooming did not increase the likelihood of males to support others in conflicts. Collectively, our results support research indicating that OT is involved in the regulation of adult affiliative relationships. However, our male-infant-male interaction results contradict previous studies suggesting that it is affiliation with bond rather than non-bond partners that trigger the release of OT. Alternatively, OT levels were elevated prior to male-infant-male interactions thus facilitating interaction between non-bond partners. The lack of an association of grooming and subsequent support speaks against an OT linked increase in the general propensity to cooperate.

The cooperative sex: Sexual interactions among female bonobos are linked to increases in oxytocin, proximity and coalitions

In some species habitual same-sex sexual behavior co-occurs with high levels of intra-sexual alliance formation, suggesting that these behaviors may be linked. We tested for such a link by comparing behavioral and physiological outcomes of sex with unrelated same- and opposite-sex partners in female bonobos (Pan paniscus). We analyzed behavioral outcomes following 971 sexual events involving n = 19 female and n = 8 male adult and sub-adult members of a wild, habituated bonobo community. We additionally collected n = 143 urine samples before and after sexual interactions to non-invasively measure oxytocin (OT), which modulates female sexual behavior and facilitates cooperation in other species. The majority of sexual events (65%) consisted of female same-sex genito-genital rubbing (or GG-rubbing). Female dyads engaged in significantly more sexual interactions than did inter-sexual dyads, and females were more likely to remain within close proximity to their partners following GG-rubbing. Females also exhibited greater increases in urinary OT following GG-rubbing compared with copulations, indicating a physiological basis for increased motivation to cooperate among females. The frequency of coalitionary support among non-kin was positively predicted by the frequency of sexual interactions for female as well opposite-sex dyads, although coalitionary support tended to be more frequent among females. The emergence of habitual same-sex sexual behavior may have been an important step in the evolution of cooperation outside of kinship and pair-bonds in one of our closest phylogenetic relatives.

The Role of Oxytocin in the Dog-Owner Relationship

Simple Summary

A number of studies have shown that when dogs and humans interact with each other in a positive way (for example cuddling) both partners exhibit a surge in oxytocin, a hormone which has been linked to positive emotional states. It is not clear however, if this increase in oxytocin occurs between any dog and human or whether this is more specific to the dog–owner bond. In this study we measured oxytocin levels in dogs and humans before and after they interacted with their closely bonded partner (dog–owner dyads) and with a partner they were familiar with but with whom they did not have a close bond. Based on previous literature we predicted that dogs and owners would show an increase in oxytocin after a positive social interaction, and that this increase would be higher when the dog and owner were interacting with each other than when the interaction occurred with a partner that was just ‘familiar’. In fact, overall we did not find an increase in either, dogs’ or humans’ oxytocin level, although there was a lot of variability in the response. We discuss various reasons why our results are not in line with other studies.

Abstract

Oxytocin (OT) is involved in multiple social bonds, from attachment between parents and offspring to “friendships”. Dogs are an interesting species in which to investigate the link between the oxytocinergic system and social bonds since they establish preferential bonds with their own species but also with humans. Studies have shown that the oxytocinergic system may be involved in the regulation of such inter-specific relationships, with both dogs and their owners showing an increase in OT levels following socio-positive interactions. However, no direct comparison has been made in dogs’ OT reactivity following a social interaction with the owner vs. a familiar (but not bonded) person, so it is unclear whether relationship type mediates OT release during socio-positive interactions or whether the interaction per se is sufficient. Here we investigated OT reactivity in both dogs and owners, following a socio-positive interaction with each other or a familiar partner. Results showed neither the familiarity with the partner, nor the type of interaction affected OT reactivity (as measured in urine) in either dogs or owners. Given the recent mixed results on the role of oxytocin in dog-human interactions, we suggest there is a need for greater standardization of methodologies, an assessment of overall results taking into account ‘publication bias’ issues, and further studies investigating the role of relationship quality and interaction type on OT release.

Analytical validation of an Enzyme Immunoassay for the measurement of urinary oxytocin in dogs and wolves

Assessing changes in oxytocin (OT) levels in response to a variety of social stimuli has become of major interest in the field of behavioral endocrinology. OT is involved in the regulation of various aspects of social behavior such as tolerance, and the formation and maintenance of social bonds but also the regulation of stress. All of these aspects have been identified as potential targets of selection during the domestication process. Therefore, comparing the role of the oxytocinergic system in various aspects of dog and wolf social behavior, might help to understand whether this system was involved in the domestication process. Studies assessing OT levels in dogs and wolves have used invasively collected plasma and serum samples and non-invasively collected urine samples. However, when using an assay system on a new species a careful and complete validation of the method is of crucial importance, and to date no proper validation, to assess urinary OT levels in dogs and wolves, has been reported. We therefore conducted an analytical validation of an Enzyme Immunoassay (EIA) for the measurement of OT in urine of dogs and wolves, using a commercially available EIA. Stability tests revealed that OT levels degrade over time when stored at 4 °C, but are little affected by repeated thawing. In addition, our results indicate that the variance in OT levels is slightly lower when phosphoric acid is added following collection to prevent OT degradation. Long term storage tests revealed that urinary OT levels are least variable when stored as extracts in ethanol at -20 °C, rather than as unextracted urine samples. Validation results were acceptable with regard to parallelism, but values for accuracy and extraction efficiency were not meeting the standard criteria usually applied to steroid EIAs, especially when assessed for the lower range of the assay. The results of this study highlight the importance of an analytical assay validation, since even if validation parameters are not optimal, if published, they allow readers to estimate the relevance of studies using the validated method.

Intranasal administration of oxytocin decreases task-related aggressive responses in healthy young males

Aggression and distrust are often challenging problems in mental health treatment. Converging evidence reveals that oxytocin increases trust in social interactions and decreases fear of social betrayal. However, oxytocin has also been associated with protective behavior and, as such, might increase defensive aggressive reactions. In this randomized double-blind, placebo-controlled study, the effects of intranasal oxytocin (32IU) on task-related aggressive responses were measured using the Point Subtraction Aggression Paradigm (PSAP). Fifty-seven healthy males were enrolled and randomized to oxytocin (N = 30) or placebo (n = 27). Salivary oxytocin, cortisol and testosterone were measured serially prior to the intervention, and then before and after the PSAP, to evaluate the effects of oxytocin administration on hormonal functioning in relation to aggression. In addition, oxytocin was measured in urine collected directly after the experimental task, reflecting the 2 h period after oxytocin or placebo administration. The proportion of aggressive responses to the PSAP was significantly lower in participants receiving oxytocin versus placebo (β= -0.46, P = 0.01). No significant effect of oxytocin was found regarding defensive reactions. Urinary oxytocin was negatively associated with the proportion of aggressive responses to the PSAP in both the oxytocin and the placebo group (β= -0.02, P < 0.01), suggesting that higher levels of urinary oxytocin corresponded with reduced aggressive responding. Our results indicate that oxytocin administration reduces aggressive behavior in healthy young men. Moreover, increased endogenous urinary oxytocin is associated with less aggressive responding. Taken together, these findings suggest that oxytocin signaling has a causal influence on aggressive behavior.

Exploring associations between perinatal depression, anxiety, and urinary oxytocin levels in Latinas

Perinatal depression has been associated with lower oxytocin (OT) levels. However, few studies have explored this topic in relation to Latinas who are at high risk of perinatal depression. The objective of this study was to explore these associations in Latinas. A total of 108 Latinas in the third trimester of pregnancy participated in the study. Depression and urinary OT levels were assessed in pregnancy and 6 weeks postpartum. Nonparametric tests were implemented to test the proposed associations. Results revealed that 28% of the participants had probable depression in pregnancy, and 23% at 6 weeks postpartum. OT levels significantly decreased from prenatal to postpartum in the whole sample; however, participants with probable prenatal depression did not exhibit a significant change in OT levels. Participants who were depressed or anxious at 6 weeks postpartum exhibited persistently higher mean OT levels over time. A distinct pattern of higher levels of OT in depressed Latinas suggests that OT levels may be an important neuroendocrine factor contributing to depressive and anxious symptoms.

Cortisol and oxytocin show independent activity during chimpanzee intergroup conflict

The oxytocinergic system is involved in a range of functions, from attachment and social bonding to aggression and stress responses. Whether oxytocin is released in response to a stressor, shows contradictory results across species and potential contexts-dependent differences. To avoid unintended contextual changes due to experimental procedures, we tested this question non-invasively in wild chimpanzees in an ecologically valid context. We collected endogenous hormonal measures during exposure to a known natural stressor, intergroup conflict. Specifically, we tested for potential synchronous activation patterns between urinary oxytocin and cortisol in male and female chimpanzees during stressor exposure. Oxytocinergic system reactivity during chimpanzee intergroup conflict has already been established in this study population. Thus, we first investigated urinary cortisol levels during border patrol and intergroup encounter days, in comparison to another potential stressor, hunting, and control days. We found higher urinary cortisol levels during intergroup encounter days compared with control and hunting days. We then compared secretion patterns of oxytocin and cortisol in relation to increased levels of out-group contact and hostility ('out-group risk') during intergroup conflict. We found that increased 'out-group risk' was associated with higher cortisol levels, especially when involving direct visual or physical contact with rival groups. Although urinary oxytocin levels were high across intergroup conflict contexts, increasing levels of out-group risk showed no significant variation. Taken together, results indicate independent secretion of oxytocin and cortisol during chimpanzee intergroup conflict, emphasizing that stressor exposure in this context is not the main trigger of oxytocin secretion.

Oxytocin in metabolic homeostasis: implications for obesity and diabetes management

Oxytocin was once understood solely as a neuropeptide with a central role in social bonding, reproduction, parturition, lactation and appetite regulation. Recent evidence indicates that oxytocin enhances glucose uptake and lipid utilization in adipose tissue and skeletal muscle, suggesting that dysfunction of the oxytocin system could underlie the pathogenesis of insulin resistance and dyslipidaemia. Murine studies revealed that deficiencies in oxytocin signalling and oxytocin receptor expression lead to obesity despite normal food intake, motor activity and increased leptin levels. In addition, plasma oxytocin concentration is notably lower in obese individuals with diabetes, which may suggest an involvement of the oxytocin system in the pathogenesis of cardiometabolic disease. More recently, small scale studies demonstrated that intranasal administration of oxytocin was associated with significant weight loss as well as improvements in insulin sensitivity and pancreatic β-cell responsivity in human subjects. The multi-pronged effects of oxytocin signalling on improving peripheral insulin sensitivity, pancreatic function and lipid homeostasis strongly suggest a role for this system as a therapeutic target in obesity and diabetes management. The complexity of obesity aetiology and the pathogenesis of obesity-related metabolic complications underscore the need for a systems approach to better understand the role of oxytocin in metabolic function.

Oxytocin analysis from human serum, urine, and saliva by orbitrap liquid chromatography-mass spectrometry

Oxytocin (OT) is a neurohormone that has gained interest recently due to its emerging role in cognition and social/emotional behaviors, including possibly depression and autism. OT is commonly measured using enzyme- or radio-based immunoassays (RIA, ELISA), which lack specificity or are complicated to perform and involve hazardous radioactive material. We have developed a high resolution accurate-mass (HRAM) liquid chromatography-mass spectrometry (LC-MS) method that separates interferences and selectively and accurately quantitates native OT from human serum, urine, and saliva after solid phase extraction. The doubly protonated OT ion m/z 562.25503 was selected for quantitation due its high signal intensity. With our method lower limit of detection (LLOD) of 5-25 pg/mL, we measured native OT in serum from pregnant women (16-24 pg/mL) and rats (350 pg/mL), and in serum, urine, and saliva from a healthy male after intranasal (IN) OT application of 100 IU and 20 IU and from a healthy post-menopausal female after IN OT application of 100 IU. Peak levels were detected in serum, urine, and saliva 15-30 minutes after each dose then decreased to below detection limits 1-2 hours thereafter. We were unable to detect native OT in serum from non-pregnant/non-lactating/non-medicated women due to levels known to occur below 5 pg/mL. The fast elimination of OT we found is in excellent agreement with the pharmacokinetics of OT in other studies. The effects on the central nervous system occurring after IN OT administration remains to be determined.

Urinary oxytocin levels in relation to post-conflict affiliations in wild male chimpanzees (Pan troglodytes verus)

Many animals living in social groups have evolved behaviors to resolve conflicts between group members, behaviors thought crucial for maintaining stable group life. Several hypotheses, based mainly on observational data, aim to explain how post-conflict (PC) affiliations, such as reconciliation and consolation, resolve conflicts by restoring relationships and/or alleviating anxiety. To examine a potential endocrinological mechanism of PC affiliations, we used an experimental-like procedure to investigate whether the oxytocinergic system is activated during naturally observed reconciliations, receiving bystander PC affiliations and aggressions not followed by PC affiliations in wild male chimpanzees. We compared urinary oxytocin (uOT) levels after reconciliations, receiving bystander PC affiliations or aggressions without affiliations with two control conditions: affiliations without previous aggression and after time periods without social interactions. We furthermore tested the 'valuable relationship' hypothesis of reconciliation, as well as the influence of relationship quality between individuals engaged in each of the three behavioral conditions involving aggression on uOT levels. We found that the probability to reconcile a conflict increased with increasing relationship quality between opponents, thus our results support the 'valuable relationship' hypothesis. However, relationship quality did not influence uOT levels, while behavioral condition had a significant effect on uOT levels. uOT levels after reconciliations, receiving bystander PC affiliations and affiliations not related to conflicts were higher than after aggressions alone and time periods without social interactions. Overall, our results indicate that the oxytocinergic system is activated during affiliative interactions, whether occurring as reconciliation, bystander PC affiliation or affiliation alone. We conclude that the oxytocinergic system, in addition to building and maintaining social relationships, also takes part in repairing them.

How do hypothalamic nonapeptides shape youth's sociality? A systematic review on oxytocin, vasopressin and human socio-emotional development

The hypothalamic nonapeptides oxytocin and vasopressin are important modulators of socio-affective behaviours in a wide variety of animal species, including humans. Nevertheless, there is little research addressing their possible roles on socio-affective dimensions of human behaviour across development, during which considerable behavioural and physiological change occurs. Questions still remain about the extent to which findings from adults may directly apply to earlier phases of human development. In this article, we systematically summarize and discuss all existing studies investigating the developmental association of endogenous levels of hypothalamic neuropeptides oxytocin and vasopressin with human social behaviour or on its disruption in paediatric populations. Evidence is sparse insofar as there are still relatively few developmental studies and limited due to correlational research designs and unreliability of methods currently used for neuropeptide measurements in biological fluids. The findings to date generally converge with adult evidence, but also suggest that important differences between age stages may exist. Further studies focusing these differences may prove critical for informing drug development for socio-affective deficits in paediatric populations.

Oxytocin and Social Bonds: The Role of Oxytocin in Perceptions of Romantic Partners' Bonding Behavior

In this research, we tested hypotheses about the role of oxytocin in adult human bonding. Inspired by revisiting the research on pair bonding in microtine voles that fueled psychologists’ interest in the role of oxytocin in social life, we drew on recent theory from affective and relationship science to identify a well-defined bonding context for human romantic relationships. We then paired these behaviors and subjective psychological responses with a measure of naturally circulating oxytocin. In 129 romantically involved adults whose partner expressed gratitude to them in the lab, greater oxytocin over the prior 24 hr was associated with greater perceptions of the expresser’s responsiveness and gratitude, as well as greater experienced love, but not general affective reward. Moreover, in this one-time conversation, higher oxytocin acted like rose-colored glasses, attenuating the effect of a partner’s behaviorally coded expressive behavior on perceptions of the expresser’s responsiveness. These results justify future research on the role of oxytocin in psychological aspects of growth processes.

Plasma and Urinary Oxytocin Trajectories in Extremely Premature Infants During NICU Hospitalization

Extremely premature infants are at great risk for poor neurodevelopmental outcomes, in part because neurologic structures designed to mature in the womb must now do so in the extrauterine environment. Reliable biomarkers of neurodevelopment are especially critical in this population, as behavioral measures can be unreliable due to immaturity of the premature infant nervous system. Oxytocin (OT) has the potential to be a marker of neurobiological processes that offer infant neuroprotection. However, no studies have measured OT in the plasma and urine of premature infants. The purposes of this study were to describe plasma and urine OT levels of premature infants through 34 weeks corrected gestational age (CGA), determine whether plasma and urine OT are correlated, and explore associations between infant demographics and OT trajectories. Plasma and urine from 37 premature infants, born at gestational ages 25-28 6/7 weeks, were longitudinally collected at 14 days of life, then weekly until 34 weeks CGA. Plasma OT decreased with age, at a rate of 15% per week, and exhibited strong stability within infants. Urine OT was not correlated with plasma OT and did not show a significant trend over time; thus, urine may not be a reliable, noninvasive measurement in this population. Apgar score was the only infant demographic characteristic associated with plasma OT. Given the novelty of this work, replication is needed to confirm these findings, and future research should explore potential mechanisms (e.g., stress, normal maturation, and social experiences) that contribute to declining plasma OT levels in premature infants.

Neuroendocrine control in social relationships in non-human primates: Field based evidence

Primates maintain a variety of social relationships and these can have fitness consequences. Research has established that different types of social relationships are unpinned by different or interacting hormonal systems, for example, the neuropeptide oxytocin influences social bonding, the steroid hormone testosterone influences dominance relationships, and paternal care is characterized by high oxytocin and low testosterone. Although the oxytocinergic system influences social bonding, it can support different types of social bonds in different species, whether pair bonds, parent-offspring bonds or friendships. It seems that selection processes shape social and mating systems and their interactions with neuroendocrine pathways. Within species, there are individual differences in the development of the neuroendocrine system: the social environment individuals are exposed to during ontogeny alters their neuroendocrine and socio-cognitive development, and later, their social interactions as adults. Within individuals, neuroendocrine systems can also have short-term effects, impacting on social interactions, such as those during hunting, intergroup encounters or food sharing, or the likelihood of cooperating, winning or losing. To understand these highly dynamic processes, extending research beyond animals in laboratory settings to wild animals living within their natural social and ecological setting may bring insights that are otherwise unreachable. Field endocrinology with neuropeptides is still emerging. We review the current status of this research, informed by laboratory studies, and identify questions particularly suited to future field studies. We focus on primate social relationships, specifically social bonds (mother-offspring, father-offspring, cooperative breeders, pair bonds and adult platonic friendships), dominance, cooperation and in-group/out-group relationships, and examine evidence with respect to the 'tend and defend' hypothesis.

Oxytocin reactivity during intergroup conflict in wild chimpanzees

Intergroup conflict is evident throughout the history of our species, ubiquitous across human societies, and considered crucial for the evolution of humans' large-scale cooperative nature. Like humans, chimpanzee societies exhibit intragroup coordination and coalitionary support during violent intergroup conflicts. In both species, cooperation among group members is essential for individuals to gain access to benefits from engaging in intergroup conflict. Studies suggest that a contributive mechanism regulating in-group cooperation during intergroup conflicts in humans involves the neuropeptide hormone oxytocin, known to influence trust, coordination, and social cognition, although evidence from natural settings is lacking. Here, applying a noninvasive method, we investigate oxytocinergic system involvement during natural intergroup conflicts in wild chimpanzees. We found that chimpanzees of both sexes had significantly higher urinary oxytocin levels immediately before and during intergroup conflict compared with controls. Also, elevated hormone levels were linked with greater cohesion during intergroup conflicts, rather than with the level of potential threat posed by rival groups, intragroup affiliative social interactions, or coordinated behavior alone. Thus, the oxytocinergic system, potentially engendering cohesion and cooperation when facing an out-group threat, may not be uniquely human but rather a mechanism with evolutionary roots shared by our last common ancestor with chimpanzees, likely expediting fitness gains during intergroup conflict.

A meta-analytic review of the correlation between peripheral oxytocin and cortisol concentrations

The stress dampening effects of exogenous oxytocin in humans have been well documented. However, the relation between endogenous oxytocin and cortisol is poorly understood. We conducted a meta-analysis on the correlation between oxytocin and cortisol levels measured at baseline (k=24, N=739). The effect size for the baseline correlation statistic was small (Pearson r=0.163, p=0.008), with high heterogeneity (I²=67.88%). Moderation analysis revealed that studies where participants anticipated an experimental manipulation evidenced a greater positive correlation compared to those that did not (Pearson r=0.318, p=0.006). A supplementary analysis including additional studies indicated that oxytocin levels in unextracted samples were 60 times higher when using this questionable practice. The findings suggest that the interplay between oxytocin and cortisol is dynamic and sensitive to the anticipation of stress or novelty. Furthermore, extraction of oxytocin appears to be an essential methodological practice.

Oxytocin for preventing postpartum haemorrhage (PPH) in non-facility birth settings

BACKGROUND

Postpartum haemorrhage (PPH) is the single leading cause of maternal mortality worldwide. Most of the deaths associated with PPH occur in resource-poor settings where effective methods of prevention and treatment - such as oxytocin - are not accessible because many births still occur at home, or in community settings, far from a health facility. Likewise, most of the evidence supporting oxytocin effectiveness comes from hospital settings in high-income countries, mainly because of the need of well-organised care for its administration and monitoring. Easier methods for oxytocin administration have been developed for use in resource-poor settings, but as far as we know, its effectiveness has not been assessed in a systematic review.

OBJECTIVES

To assess the effectiveness and safety of oxytocin provided in non-facility birth settings by any way in the third stage of labour to prevent PPH.

SEARCH METHODS

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register, the WHO International Clinical Trials Registry Platform (ICTRP), ClinicalTrials.gov (12 November 2015), and reference lists of retrieved reports.

SELECTION CRITERIA

All published, unpublished or ongoing randomised or quasi-randomised controlled trials comparing the administration of oxytocin with no intervention, or usual/standard care for the management of the third stage of labour in non-facility birth settings were considered for inclusion.Quasi-randomised controlled trials and randomised controlled trials published in abstract form only were eligible for inclusion but none were identified. Cross-over trials were not eligible for inclusion in this review.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility, assessed risk of bias and extracted the data using an agreed data extraction form. Data were checked for accuracy.

MAIN RESULTS

We included one cluster-randomised trial conducted in four rural districts in Ghana that randomised 28 community health officers (CHOs) (serving 2404 potentially eligible pregnant women) to the intervention group and 26 CHOs (serving 3515 potentially eligible pregnant women) to the control group. Overall, the trial had a high risk of bias. CHOs delivered the intervention in the experimental group (injection of 10 IU (international units) of oxytocin in the thigh one minute following birth using a prefilled, auto-disposable syringe). In the control group, CHOs did not provide this prophylactic injection to the women they observed. CHOs had no midwifery skills and did not in any way manage the birth. All other CHO activities (outcome measurement, data collection, and early treatment and referral when necessary) were identical across the control and oxytocin CHOs.Although only one of the nine cases of severe PPH (blood loss greater or equal to 1000 mL) occurred in the oxytocin group, the effect estimate for this outcome was very imprecise and it is uncertain whether the intervention prevents severe PPH (risk ratio (RR) 0.16, 95% confidence interval (CI) 0.02 to 1.30; 1570 women (very low-quality evidence)). Similarly, because of the lack of cases of severe maternal morbidity (e.g. uterine rupture) and maternal deaths, it was not possible to obtain effect estimates for those outcomes (both very low-quality evidence).Oxytocin compared with the control group decreased the incidence of PPH (> 500 mL) in both our unadjusted (RR 0.48, 95% CI 0.28 to 0.81; 1569 women) and adjusted (RR 0.49, 95% CI 0.27 to 0.90; 1174 women (both low-quality evidence)) analyses. There was little or no difference between the oxytocin and control groups on the rates of transfer or referral of the mother to a healthcare facility (RR 0.72, 95% CI 0.34 to 1.56; 1586 women (low-quality evidence)), stillbirths (RR 1.27, 95% CI 0.67 to 2.40; 2006 infants (low-quality evidence)); andearly infant deaths (0 to three days) (RR 1.03, 95% CI 0.35 to 3.07; 1969 infants (low-quality evidence)). There were no cases of needle-stick injury or any other maternal major or minor adverse event or unanticipated harmful event. There were no cases of oxytocin use during labour.There were no data reported for some of this review's secondary outcomes: manual removal of placenta, maternal anaemia, neonatal death within 28 days, neonatal transfer to health facility for advanced care, breastfeeding rates. Similarly, the women's or the provider's satisfaction with the intervention was not reported.

AUTHORS' CONCLUSIONS

It is uncertain if oxytocin administered by CHO in non-facility settings compared with a control group reduces the incidence of severe PPH (>1000 mL), severe maternal morbidity or maternal deaths. However, the intervention probably decreases the incidence of PPH (> 500 mL).The quality of the one trial included in this review was limited because of the risk of attrition and recruitment biases related to limitations in the follow-up of pregnant women in both arms of the trials and some baseline imbalance on the size of babies at birth. Additionally, there was serious imprecision of the effect estimates for most of the primary outcomes mainly because of the size of the trial, very few or no events and CIs around both relative and absolute estimates of effect that include both appreciable benefit and appreciable harm.Although the trial presented data both for primary and secondary outcomes, it seemed to be underpowered to detect differences in the primary outcomes that are the ones more relevant for making judgments about the potential applicability of the intervention in other settings (especially severe PPH).Therefore, taking into account the extreme setting where the intervention was implemented, the limited role of the CHO in the trial and the lack of power for detecting effects on primary (relevant) outcomes, the applicability of the evidence found seems to be rather limited.Further well-executed and adequately-powered randomised controlled trials assessing the effects of using oxytocin in pre-filled injection devices or other new delivery systems (spray-dried ultrafine formulation of oxytocin) on severe PPH are urgently needed. Likewise, other important outcomes like possible adverse events and acceptability of the intervention by mothers and other community stakeholders should also be assessed.

The relationship between central and peripheral oxytocin concentrations: a systematic review and meta-analysis protocol

BACKGROUND

Research examining the effects of oxytocin (OT) interventions on psychiatric, social-behavioral, and social-cognitive outcomes regularly collect peripheral levels of OT as markers of central bioavailability. Such inferences rest on the assumption that central and peripheral levels of OT are directly associated. However, conflicting evidence from coordinated sampling of central and peripheral OT question the validity of this assumption. The purpose of this meta-analysis is to evaluate the correlation between central and peripheral OT, as well as to account for potential heterogeneity in the literature.

METHODS/DESIGN

Studies that report coordinated sampling of central and peripheral OT in humans and animals will be identified. Research investigating concentrations in both basal states and after exogenous administration will be considered. PubMed and Embase databases will be searched, along with citation lists of retrieved articles. Peer-reviewed studies written in English published from 1971 onwards will be included in the meta-analysis. Data will be extracted from eligible studies for a random-effects meta-analysis. For each study, a summary effect size, heterogeneity, risk of bias, publication bias, and the effect of categorical and continuous moderator variables will be determined.

DISCUSSION

This systematic review and meta-analysis will identify and synthesize evidence to determine if there is an association between central and peripheral OT concentrations. If significant associations are observed, evidence would provide a rationale for future research to use peripheral measures as a proxy for central OT concentrations.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015027864.

Intranasal Oxytocin: Myths and Delusions

Despite widespread reports that intranasal application of oxytocin has a variety of behavioral effects, very little of the huge amounts applied intranasally appears to reach the cerebrospinal fluid. However, peripheral concentrations are increased to supraphysiologic levels, with likely effects on diverse targets including the gastrointestinal tract, heart, and reproductive tract. The wish to believe in the effectiveness of intranasal oxytocin appears to be widespread and needs to be guarded against with scepticism and rigor. Preregistering trials, declaring primary and secondary outcomes in advance, specifying the statistical methods to be applied, and making all data openly available should minimize problems of publication bias and questionable post hoc analyses. Effects of intranasal oxytocin also need proper dose-response studies, and such studies need to include control subjects for peripheral effects, by administering oxytocin peripherally and by blocking peripheral actions with antagonists. Reports in the literature of oxytocin measurements include many that have been made with discredited methodology. Claims that peripheral measurements of oxytocin reflect central release are questionable at best.

Inflammatory and Epigenetic Pathways for Perinatal Depression

Depression during the perinatal period is common and can have adverse consequences for women and their children. Yet, the biobehavioral mechanisms underlying perinatal depression are not known. Adverse early life experiences increase the risk for adult depression. One potential mechanism by which this increased risk occurs is epigenetic embedding of inflammatory pathways. The purpose of this article is to propose a conceptual model that explicates the linkage between early life adversity and the risk for maternal depression. The model posits that early life adversity embeds a proinflammatory epigenetic signature (altered DNA methylation) that predisposes vulnerable women to depression during pregnancy and the postpartum period. As proposed, women with a history of early life adversity are more likely to exhibit higher levels of proinflammatory cytokines and lower levels of oxytocin in response to the demands of pregnancy and new motherhood, both of which are associated with the risk for perinatal depression. The model is designed to guide investigations into the biobehavioral basis for perinatal depression, with emphasis upon the impact of early life adversity. Testing this model will provide a better understanding of maternal depressive risk and improve identification of vulnerable women who would benefit from targeted interventions that can reduce the impact of perinatal depression on maternal–infant health.

Strongly bonded family members in common marmosets show synchronized fluctuations in oxytocin

Oxytocin is a key regulator of social bonding and is positively linked to affiliation and prosocial behavior in several mammal species. In chimpanzees, this link is dyad-specific as affiliative interactions only elicit high oxytocin release if they involve strongly bonded individuals. These studies involved isolated dyads and sampling events. Little is known about the role of oxytocin in affiliation and social bonding, and about potential long-term patterns of bonding-related and dyad-specific oxytocin effects within highly affiliative and cooperative social groups. Our aim was to investigate whether bonding-related oxytocin signatures linked to dyadic affiliation are present in family groups of cooperatively breeding marmoset monkeys (Callithrix jacchus) that show high levels of cohesion and cooperation. In 30 dyads from four family groups and one pair, we measured urinary baseline oxytocin over six weeks and analyzed the link to bond strength (mean dyadic affiliation). Strongly bonded dyads showed synchronized longitudinal fluctuations of oxytocin, indicating that dyad-specific oxytocin effects can also be traced in the group context and in an interdependent species. We discuss these results in light of the potential function of differentiated relationships between marmoset dyads other than the breeding pair, and the role of oxytocin as a mediator for social bonding.

The neurochemistry and social flow of singing: bonding and oxytocin

Music is used in healthcare to promote physical and psychological well-being. As clinical applications of music continue to expand, there is a growing need to understand the biological mechanisms by which music influences health. Here we explore the neurochemistry and social flow of group singing. Four participants from a vocal jazz ensemble were conveniently sampled to sing together in two separate performances: pre-composed and improvised. Concentrations of plasma oxytocin and adrenocorticotropic hormone (ACTH) were measured before and after each singing condition to assess levels of social affiliation, engagement and arousal. A validated assessment of flow state was administered after each singing condition to assess participants' absorption in the task. The feasibility of the research methods were assessed and initial neurochemical data was generated on group singing. Mean scores of the flow state scale indicated that participants experienced flow in both the pre-composed (M = 37.06) and improvised singing conditions (M = 34.25), with no significant difference between conditions. ACTH concentrations decreased in both conditions, significantly so in the pre-composed singing condition, which may have contributed to the social flow experience. Mean plasma oxytocin levels increased only in response to improvised singing, with no significant difference between improvised and pre-composed singing conditions observed. The results indicate that group singing reduces stress and arousal, as measured by ACTH, and induces social flow in participants. The effects of pre-composed and improvised group singing on oxytocin are less clear. Higher levels of plasma oxytocin in the improvised condition may perhaps be attributed to the social effects of improvising musically with others. Further research with a larger sample size is warranted.

Social evolution. Oxytocin-gaze positive loop and the coevolution of human-dog bonds

Human-like modes of communication, including mutual gaze, in dogs may have been acquired during domestication with humans. We show that gazing behavior from dogs, but not wolves, increased urinary oxytocin concentrations in owners, which consequently facilitated owners' affiliation and increased oxytocin concentration in dogs. Further, nasally administered oxytocin increased gazing behavior in dogs, which in turn increased urinary oxytocin concentrations in owners. These findings support the existence of an interspecies oxytocin-mediated positive loop facilitated and modulated by gazing, which may have supported the coevolution of human-dog bonding by engaging common modes of communicating social attachment.

Urinary oxytocin positively correlates with performance in facial visual search in unmarried males, without specific reaction to infant face

The neuropeptide oxytocin plays a central role in prosocial and parental behavior in non-human mammals as well as humans. It has been suggested that oxytocin may affect visual processing of infant faces and emotional reaction to infants. Healthy male volunteers (N = 13) were tested for their ability to detect infant or adult faces among adult or infant faces (facial visual search task). Urine samples were collected from all participants before the study to measure the concentration of oxytocin. Urinary oxytocin positively correlated with performance in the facial visual search task. However, task performance and its correlation with oxytocin concentration did not differ between infant faces and adult faces. Our data suggests that endogenous oxytocin is related to facial visual cognition, but does not promote infant-specific responses in unmarried men who are not fathers.

Endogenous peripheral oxytocin measures can give insight into the dynamics of social relationships: a review

The neuropeptide, oxytocin, receives increasing attention due to its role in stress regulation and promoting affiliative social behavior. Research across mammals points to a complex pattern whereby social context and individual differences moderate the central release of oxytocin as well as moderate the effects that exogenous administration of oxytocin has on social behavior. In addition, it is becoming evident that measuring endogenous peripheral oxytocin levels is an informative tool. This is particularly so when oxytocin can be measured from non-invasively collected samples, such as in urine. Although it is still debated as to whether peripheral measures of oxytocin relate to central measures of oxytocin, anatomical and functional evidence indicate a link between the two. We argue that non-invasive measures of peripheral oxytocin hold several research and potential therapeutic advantages. Principally, study subjects can be sampled repeatedly in different social contexts where social history between interaction partners can be taken into account. Several hormones can be measured simultaneously allowing examination of the influence of oxytocin interactions with other hormones on motivational states. Valence of relationships as well as changes in relationship quality over time can be measured through endocrine responses. Also, the approach of identifying natural social contexts that are associated with endogenous oxytocin release offers the potential of behavioral therapy as an addition or alternative to chemical therapy in the field of mental health.

Food sharing is linked to urinary oxytocin levels and bonding in related and unrelated wild chimpanzees

Humans excel in cooperative exchanges between unrelated individuals. Although this trait is fundamental to the success of our species, its evolution and mechanisms are poorly understood. Other social mammals also build long-term cooperative relationships between non-kin, and recent evidence shows that oxytocin, a hormone involved in parent-offspring bonding, is likely to facilitate non-kin as well as kin bonds. In a population of wild chimpanzees, we measured urinary oxytocin levels following a rare cooperative event--food sharing. Subjects showed higher urinary oxytocin levels after single food-sharing events compared with other types of social feeding, irrespective of previous social bond levels. Also, urinary oxytocin levels following food sharing were higher than following grooming, another cooperative behaviour. Therefore, food sharing in chimpanzees may play a key role in social bonding under the influence of oxytocin. We propose that food-sharing events co-opt neurobiological mechanisms evolved to support mother-infant bonding during lactation bouts, and may act as facilitators of bonding and cooperation between unrelated individuals via the oxytocinergic system across social mammals.

Urinary oxytocin and social bonding in related and unrelated wild chimpanzees

Animals that maintain cooperative relationships show gains in longevity and offspring survival. However, little is known about the cognitive or hormonal mechanisms involved in cooperation. Indeed, there is little support for a main hypothesis that non-human animals have the cognitive capacities required for bookkeeping of cooperative exchanges. We tested an alternative hypothesis that cooperative relationships are facilitated by an endocrinological mechanism involving oxytocin, a hormone required for bonding in parental and sexual relationships across mammals. We measured urinary oxytocin after single bouts of grooming in wild chimpanzees. Oxytocin levels were higher after grooming with bond partners compared with non-bond partners or after no grooming, regardless of genetic relatedness or sexual interest. We ruled out other possible confounds, such as grooming duration, grooming direction or sampling regime issues, indicating that changes in oxytocin levels were mediated by social bond strength. Oxytocin, which is thought to act directly on neural reward and social memory systems, is likely to play a key role in keeping track of social interactions with multiple individuals over time. The evolutionary linkage of an ancestral hormonal system with complex social cognition may be the primary mechanism through which long-term cooperative relationships develop between both kin and non-kin in mammals.

The association between oxytocin and social capital

BACKGROUND

Oxytocin is known to be related to social behaviors, including trust. However, few studies have investigated the association between oxytocin levels and social capital. Thus, we tested the hypothesis that endogenous oxytocin levels are positively associated with social capital. We also considered whether the association differed across gender because previous studies have shown differential effects of OT on social behaviors depending on gender.

METHODS

We recruited a convenience sample of 50 women and 31 men in Japan via community sampling from whom we obtained urine sample with which to measure oxytocin levels. Individual-level cognitive social capital (social trust and mutual aid) and structural social capital (community participation) were assessed using a questionnaire. We used multivariate regression, adjusted for covariates (age, number of children, self-rated health, and education), and stratified by gender to consider associations between oxytocin and social capital.

RESULTS

Among women, oxytocin was inversely associated with social trust and mutual aid (p<0.05). However, women participating in only 1 organization in the community showed higher oxytocin than women who participated in either no organizations (p<0.05) or 2 or more organization (i.e. inverse-U shape association). Among men, no association was observed between oxytocin and either form of cognitive and structural social capital.

CONCLUSION

Women who perceived low cognitive social capital showed higher oxytocin levels, while structural social capital showed inverse-U shape association with oxytocin. No association between oxytocin and social capital was found among men. Further study is needed to elucidate why oxytocin was inversely associated with cognitive social capital only among women.

Peripheral oxytocin in female baboons relates to estrous state and maintenance of sexual consortships

The neuro-hypophysial hormone oxytocin (OT) has been implicated in female reproductive and maternal behaviors and in the formation of pair bonds in monogamous species. Here we measure variation in urinary OT concentrations in relation to reproductive biology and socio-sexual behavior in a promiscuously breeding species, the chacma baboon (Papio hamadryas ursinus). Subjects were members of a habituated group of baboons in the Okavango Delta, Botswana. We collected behavioral data and urine samples from n=13 cycling females across their estrous cycles and during and outside short-term, exclusive sexual consortships. Samples were analyzed via enzyme immunoassay (EIA) and we used linear mixed models (LMM) to explore the relationship between peripheral OT and a female's estrous stage and consortship status, her previous reproductive experience and fertility. We also used a Pearson's correlation to examine the relationship between OT concentrations of consorting females and their extent of behavioral coordination with their consort partners. The results of the LMM indicate that only estrous stage had a significant influence on OT levels. Females had higher OT levels during their periovulatory period than during other stages of their estrous cycle. There were no differences in the OT levels between consorting and non-consorting periovulatory females. However, among consorting females, there was a significant positive relationship between urinary OT levels and the maintenance of close proximity between consort partners. Our results suggest that physiological and behavioral changes associated with the initiation and maintenance of short-term inter-sexual relationships in baboons correspond with changes in peripheral OT.