Toward understanding how early-life social experiences alter oxytocin- and vasopressin-regulated social behaviors

Effects of pre-reproductive maternal enrichment on maternal care, offspring's play behavior and oxytocinergic neurons

Potentiating social, cognitive, and sensorimotor stimulations the Environmental Enrichment (EE) increases levels of novelty and complexity experienced by individuals. Growing evidence demonstrates that parental EE experience, even occurring in the pre-reproductive phase, affects behavioral and neural developmental trajectories of the offspring. To discover how the accumulation of early maternal complex experiences may inform and shape the social behavior of the following generation, we examined the effects of pre-reproductive enrichment of dams (post-natal days 21-72) on the play performances of their male and female adolescent offspring. Furthermore, we examined the effects of pre-reproductive enrichment on maternal behavior (during post-partum days 1-10) and male intruder aggression (on post-partum day 11). Since oxytocin modulates maternal care, social bonding, and agonistic behavior, the number of oxytocinergic neurons of the paraventricular (PVN) and supraoptic (SON) nuclei was examined in both dams and offspring. Results revealed that enriched females exhibited higher levels of pup-oriented behaviors, especially Crouching, and initiated pup-retrieval more quickly than standard females after the maternal aggression test. Such behavioral peculiarities were accompanied by increased levels of oxytocinergic neurons in PVN and SON. Moreover, pre-reproductive maternal EE cross-generationally influenced the offspring according to sex. Indeed, male pups born to enriched females exhibited a reduced play fighting associated with a higher number of oxytocinergic neurons in SON in comparison to male pups born to standard-housed females. In conclusion, pre-reproductive EE to the mothers affects their maternal care and has a cross-generational impact on the social behavior of their offspring that do not directly experiences EE. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

The role of trauma in the hormonal interplay of cortisol, testosterone, and oxytocin in adolescent aggression

Although numerous studies have examined the neuroendocrinology of aggression, the findings are mixed and focused on cortisol and testosterone. We argue that past findings remain inconclusive partly because the key roles of oxytocin and trauma have not been systematically integrated yet. Oxytocin is associated with social behavior and interacts with cortisol and testosterone, whereas trauma is a crucial risk factor of aggression that strongly affects hormonal activity. In this review, we investigate the role of trauma in the hormonal interplay of cortisol, testosterone, and oxytocin in aggression during adolescence. We first discuss how these hormones interact with each other and how trauma influences these interactions and then we propose a model that highlights the role of trauma in the hormonal interplay in aggression. We suggest that the timing of trauma has a distinct effect on hormonal activity and it should be integrated into any comprehensive model. Current trauma is linked to different levels of oxytocin, cortisol, testosterone, and testosterone/cortisol ratio than childhood trauma, but this distinction is also influenced by gender and type of aggression. We conclude that in order to better understand the neuroendocrinology of aggression, it is crucial to incorporate the investigation of oxytocin and trauma in future research.

Adversity impacting on oxytocin and behaviour: timing matters

The endogenous oxytocin system plays a vital role in facilitating parturition, lactation and social interaction in humans and other mammals. It also impacts on a number of important endocrine, immune and neurotransmitter systems. A well-regulated oxytocin system has been proposed to increase resilience, and therefore reduce the likelihood of an individual developing mental illness or substance dependence. This review discusses the adverse external influences that can modulate oxytocin receptor and protein levels and impact on substance use and mental health. The paper highlights the impact of adversity such as poor maternal care, parental substance use and child abuse or neglect. We review clinical and preclinical data on the impact of adversity on the basis of the time of exposure from infancy and early childhood, to adolescence, adulthood to older age. Previous research suggests that dysregulation of the endogenous oxytocin system may be implicated in determining susceptibility to stress, anxiety, addiction and mental health conditions. The impact of external influence seems to be strongest in specific time periods where the system shows experience-based development or natural fluctuations in oxytocin levels. Interventions that target the oxytocin system during or soon after exposure to adversity may prove protective.

Prenatal bisphenol A (BPA) exposure alters the transcriptome of the neonate rat amygdala in a sex-specific manner: a CLARITY-BPA consortium study

Bisphenol A (BPA) is a widely recognized endocrine disruptor prevalent in many household items. Because experimental and epidemiological data suggest links between prenatal BPA exposure and altered affective behaviors in children, even at levels below the current US FDA No Observed Adverse Effect Level (NOAEL) of 5mg/kg body weight (bw)/day, there is concern that early life exposure may alter neurodevelopment. The current study was conducted as part of the CLARITY-BPA (Consortium Linking Academic and Regulatory Insights on BPA Toxicity) program and examined the full amygdalar transcriptome on postnatal day (PND) 1, with the hypothesis that prenatal BPA exposure would alter the expression of genes and pathways fundamental to sex-specific affective behaviors. NCTR Sprague-Dawley dams were gavaged from gestational day 6 until parturition with BPA (2.5, 25, 250, 2500, or 25000μg/kg bw/day), a reference estrogen (0.05 or 0.5μg ethinyl estradiol (EE₂)/kg bw/day), or vehicle. PND 1 amygdalae were microdissected and gene expression was assessed with qRT-PCR (all exposure groups) and RNAseq (vehicle, 25 and 250μg BPA, and 0.5μg EE₂ groups only). Our results demonstrate that that prenatal BPA exposure can disrupt the transcriptome of the neonate amygdala, at doses below the FDA NOAEL, in a sex-specific manner and indicate that the female amygdala may be more sensitive to BPA exposure during fetal development. We also provide additional evidence that developmental BPA exposure can interfere with estrogen, oxytocin, and vasopressin signaling pathways in the developing brain and alter signaling pathways critical for synaptic organization and transmission.

History of child maltreatment and telomere length in immune cell subsets: Associations with stress- and attachment-related hormones

Experiencing maltreatment during childhood can have long-lasting consequences for both mental and physical health. Immune cell telomere length (TL) shortening might be one link between child maltreatment (CM) experiences and adverse health outcomes later in life. While the stress hormone cortisol has been associated with TL attrition, the attachment-related hormone oxytocin may promote resilience. In 15 mothers with and 15 age- and body mass index-matched mothers without CM, we assessed TL in peripheral blood mononuclear cells and selected immune cell subsets (monocytes, naive, and memory cytotoxic T cells) by quantitative fluorescence in situ hybridization, as well as peripheral cortisol and oxytocin levels. Memory cytotoxic T cells showed significantly shorter TL in association with CM, whereas TL in monocytes and naive cytotoxic T cells did not significantly differ between the two groups. Across both groups, cortisol was negatively associated with TL, while oxytocin was positively associated with TL in memory cytotoxic T cells. These results indicate that long-lived memory cytotoxic T cells are most affected by the increased biological stress state associated with CM. Keeping in mind the correlational and preliminary nature of the results, the data suggest that cortisol may have a damaging and oxytocin a protective function on TL.

Increased vasopressin expression in the BNST accompanies paternally induced territoriality in male and female California mouse offspring

While developmental consequences of parental investment on species-typical social behaviors has been extensively characterized in same-sex parent-offspring interactions, the impact of opposite-sex relationships is less clear. In the bi-parental California mouse (Peromyscus californicus), paternal retrieval behavior induces territorial aggression and the expression of arginine vasopressin (AVP) in adult male offspring. Although similar patterns of territorially emerge among females, the sexually dimorphic AVP system has not been considered since it is generally thought to regulate male-typical behavior. However, we recently demonstrated that male and female P. californicus offspring experience increases in plasma testosterone following paternal retrieval. Since AVP expression is androgen-dependent during development, we postulate that increases in AVP expression may accompany territoriality in female, as well as male offspring. To explore this aim, adult P. californicus offspring that received either high or low levels of paternal care (retrievals) during early development were tested for territoriality and immunohistochemical analysis of AVP within the bed nucleus of the stria terminalis (BNST), paraventricular nucleus (PVN), and supraoptic nucleus (SON). Consistent with previous studies, high care offspring were more aggressive than low care offspring. Moreover, high care offspring had significantly more AVP immunoreactive (AVP-ir) cells within the BNST than low care offspring. This pattern was observed within female as well as male offspring, suggesting an equally salient role for paternal care on female offspring physiology. Regardless of early social experience, sex differences in AVP persisted in the BNST, with males having greater expression than females.

Effects of social deprivation on social and depressive-like behaviors and the numbers of oxytocin expressing neurons in rats

Social isolation is a known stressor that negatively impacts the well-being of social species. In rodents, social deprivation experienced either before or after weaning profoundly impacts adult behavioral and neuroendocrine profiles. This study compared the effects of post-natal and post-weaning social deprivation on behavioral profiles and hypothalamic oxytocin (OT) neurons. Male and female Sprague-Dawley rats were assigned to two post-natal groups, maternally separated (MS) or non-MS. MS pups were separated from their mothers for 4h daily during post-natal days 2-21 while non-MS litters remained undisturbed. Animals were then weaned and assigned to single or group housing conditions (SH/GH). Social behaviors were evaluated two weeks later and at 2-3 months of age, depressive-like behavioral profiles were assessed using the forced swim and sucrose preference tests. Animals were euthanized, and hypothalamic OT neurons were quantified. Post-weaning isolation significantly impacted behavioral profiles, with SH animals displaying more social behaviors than GH animals. SH animals also exhibited more immobility behavior in the forced swim test and a decreased sucrose preference. Effects of sex and MS were relatively limited. Correlation analyses revealed an inverse relationship between the display of antagonistic social behaviors and the numbers of OT cells in the anterior parvicellular division of the paraventricular nucleus (PVNap). There were no correlations between numbers of OT neurons and prosocial or depressive-like behaviors. Our results demonstrate a rapid and persistent disruption of behaviors in SH animals and suggest that some of these effects may be associated with numbers of OT neurons in the PVNap.

Hippocampal BDNF overexpression or microR124a silencing reduces anxiety- and autism-like behaviors in rats

MicroRNA124a (miR124a) has emerged recently as a key player for multiple neuropsychiatric disorders including depression, anxiety, alcoholism, and cocaine addiction. Although we have previously reported that miR124a and its target the brain-derived neutrophic factor (BDNF) play an important role in autism-like behaviors, the molecular and behavioral dysfunctions remain unknown. The aim of this study was to understand the effects of sustained decreases in miR124a and increases of BDNF in the dentate gyrus (DG) on neonatal isolation-induced anxiety-and autism like behaviors in rats. Here we report that lentiviral-mediated silencing of miR124a in the adult DG attenuated neonatal isolation-induced anxiety-like behavior in the elevated plus maze (EPM) and open-field (OF) tests. Also, miR124a silencing decreased autism-like phenotype in the marble burying test (MBT), self-grooming (SG), and social interaction tests. Pearson's correlations demonstrated that high levels of BDNF, a direct target of miR124a, were negatively correlated with miR124a expression. Interestingly, viral-mediated BDNF overexpression in the DG also reversed the neonatal isolation-induced anxiety-and autism like phenotypes. Collectively, these findings suggest that miR124a, through its target BDNF, may influence neonatal isolation-induced anxiety-and autism like behaviors. In conclusion, these results do support the hypothesis that miR124a in discrete hippocampal areas contributes to anxiety- and autism-like behaviors and may be involved in the neuroadaptations underlying the development of autism spectrum disorders as a persistent and lasting condition, and therefore provide a clearer mechanistic framework for understanding the physiopathology of such psychiatric illnesses.

Experiencing neonatal maternal separation increased pain sensitivity in adult male mice: Involvement of oxytocinergic system

Early-life stress adversely affects the development of the brain, and alters a variety of behaviors such as pain in later life. In present study, we investigated how early-life stress (maternal separation or MS) can affect the nociceptive response later in life. We particularly focused on the role of oxytocin (OT) in regulating nociception in previously exposed (MS during early postnatal development) mice that were subjected to acute stress (restraint stress or RS). Further, we evaluated whether such modulation of pain sensation in MS mice are regulated by shared mechanisms of the OTergic and opioidergic systems. To do this, we assessed the underlying systems mediating the nociceptive response by administrating different antagonists (for both opioid and OTergic systems) under the different experimental conditions (control vs MS, and control plus RS vs MS plus RS). Our results showed that MS increased pain sensitivity in both tail-flick and hot-plate tests while after administration of OT (1μg/μl/mouse, i.c.v) pain threshold was increased. Atosiban, an OT antagonist (10μg/μl/mouse, i.c.v) abolished the effects of OT. While acute RS increased the pain threshold in control (and not MS) mice, treating MS mice with OT normalized the pain response to RS. This latter effect was reversed by atosiban and/or naltrexone, an opioid antagonist (0.5μg/μl/mouse, i.c.v) suggesting that OT enhances the effect of endogenous opioids. OTergic system is involved in mediating the nociception under acute stress in mice subjected to early-life stress and OTergic and opioidergic systems interact to modulate pain sensitivity in MS mice.

Social Interactions and Indirect Genetic Effects on Complex Juvenile and Adult Traits

Most animal species are social in one form or another, yet many studies in rodent model systems use either individually housed animals or ignore potential confounds caused by group housing. While such social interaction effects on developmental and behavioral traits are well established, the genetic basis of social interactions has not been researched in as much detail. Specifically, the effects of genetic variation in social partners on the phenotype of a focal individual have mostly been studied at the phenotypic level. Such indirect genetic effects (IGEs), where the genotype of one individual influences the phenotype of a second individual, can have important evolutionary and medically relevant consequences. In this chapter, we give a brief outline of social interaction effects, and how systems genetics approaches using recombinant inbred populations can be used to investigate indirect genetic effects specifically, including maternal genetic effects. We discuss experimental designs for the study of IGEs and show how indirect genetic loci can be identified that underlie social interaction effects, their mechanisms, and consequences for trait variation in focal individuals.

Oxytocin Signaling in the Early Life of Mammals: Link to Neurodevelopmental Disorders Associated with ASD

Oxytocin plays a role in various functions including endocrine and immune functions but also parent-infant bonding and social interactions. It might be considered as a main neuropeptide involved in mediating the regulation of adaptive interactions between an individual and his/her environment. Recently, a critical role of oxytocin in early life has been revealed in sensory processing and multi-modal integration that are essential for normal postnatal neurodevelopment. An early alteration in the oxytocin-system may disturb its maturation and may have short-term and long-term pathological consequences such as autism spectrum disorders. Here, we will synthesize the existing literature on the development of the oxytocin system and its role in the early postnatal life of mammals (from birth to weaning) in a normal or pathological context. Oxytocin is required in critical windows of time that play a pivotal role and that should be considered for therapeutical interventions.

Effects of chronic oxytocin on attention to dynamic facial expressions in infant macaques

Studies in a variety of species have reported enhanced prosocial effects after an acute administration of the neuromodulating hormone, oxytocin (OT). Although the exact mechanisms underlying these effects are not fully understood, there is broad interest in developing OT into a treatment for social deficits. Only a few studies, however, have examined the effects of OT if given repeatedly during early development, the period when early intervention is likely to have the greatest benefits for reversing the progression towards social impairment. Those studies, exclusively in rodents, report mixed results. Some have shown enhancement of prosocial behavior, including increased social exploration, but others have shown anti-social effects, including increased aggression. In the present study, infant rhesus macaques were treated with a high-frequency (3× per week) or low-frequency (1× per week) dose of intranasal oxytocin (IN-OT) or placebo (IN-saline) between two and six months of age, after which their reactions to dynamic facial expressions (neutral, lipsmacking and threats) were measured. Results showed that IN-OT, compared to placebo, increased the time monkeys spent viewing the expression videos, but selectively reduced attention to the eyes in neutral faces in a dose dependent manner. The mechanism for this non-prosocial effect may be that repeated IN-OT administration down-regulates the expression of OT receptors in brain regions important for regulating social attention. Consequently, our results raise questions about the efficacy of implementing chronic IN-OT as a pharmacotherapy for the treatment of social deficits, particularly if given early in development. More work is needed, not only to identify optimal treatment schedules, but also to understand how IN-OT exerts its influences on the brain and behavior.

DNA methylation-based variation between human populations

Several studies have proved that DNA methylation affects regulation of gene expression and development. Epigenome-wide studies have reported variation in methylation patterns between populations, including Caucasians, non-Caucasians (Blacks), Hispanics, Arabs, and numerous populations of the African continent. Not only has DNA methylation differences shown to impact externally visible characteristics, but is also a potential biomarker for underlying racial health disparities between human populations. Ethnicity-related methylation differences set their mark during early embryonic development. Genetic variations, such as single-nucleotide polymorphisms and environmental factors, such as age, dietary folate, socioeconomic status, and smoking, impacts DNA methylation levels, which reciprocally impacts expression of phenotypes. Studies show that it is necessary to address these external influences when attempting to differentiate between populations since the relative impacts of these factors on the human methylome remain uncertain. The present review summarises several reported attempts to establish the contribution of differential DNA methylation to natural human variation, and shows that DNA methylation could represent new opportunities for risk stratification and prevention of several diseases amongst populations world-wide. Variation of methylation patterns between human populations is an exciting prospect which inspires further valuable research to apply the concept in routine medical and forensic casework. However, trans-generational inheritance needs to be quantified to decipher the proportion of variation contributed by DNA methylation. The future holds thorough evaluation of the epigenome to understand quantification, heritability, and the effect of DNA methylation on phenotypes. In addition, methylation profiling of the same ethnic groups across geographical locations will shed light on conserved methylation differences in populations.

Suboptimal bonding impairs hormonal, epigenetic and neuronal development in preterm infants, but these impairments can be reversed

This review aimed to raise awareness of the consequences of suboptimal bonding caused by prematurity. In addition to hypoxia-ischaemia, infection and malnutrition, suboptimal bonding is one of the many unnatural stimuli that preterm infants are exposed to, compromising their physiological development. However, the physiological consequences of suboptimal bonding are less frequently addressed in the literature than those of other threatening unnatural stimuli.

CONCLUSION

This review found that suboptimal bonding significantly impaired hormonal, epigenetic and neuronal development, but these impairments could be reversed by bonding interventions. This suggests that neonatal intensive care units should focus more on interventions that optimise bonding.

Assembling the Puzzle: Pathways of Oxytocin Signaling in the Brain

Oxytocin (OT) is a neuropeptide, which can be seen to be one of the molecules of the decade due to its profound prosocial effects in nonvertebrate and vertebrate species, including humans. Although OT can be detected in various physiological fluids (blood, saliva, urine, cerebrospinal fluid) and brain tissue, it is unclear whether peripheral and central OT releases match and synergize. Moreover, the pathways of OT delivery to brain regions involved in specific behaviors are far from clear. Here, we discuss the evolutionarily and ontogenetically determined pathways of OT delivery and OT signaling, which orchestrate activity of the mesolimbic social decision-making network. Furthermore, we speculate that both the alteration in OT delivery and OT receptor expression may cause behavioral abnormalities in patients afflicted with psychosocial diseases.

Natural variation in maternal care and cross-tissue patterns of oxytocin receptor gene methylation in rats

This article is part of a Special Issue "Parental Care". Since the first report of maternal care effects on DNA methylation in rats, epigenetic modifications of the genome in response to life experience have become the subject of intense focus across many disciplines. Oxytocin receptor expression varies in response to early experience, and both oxytocin signaling and methylation status of the oxytocin receptor gene (Oxtr) in blood have been related to disordered social behavior. It is unknown whether Oxtr DNA methylation varies in response to early life experience, and whether currently employed peripheral measures of Oxtr methylation reflect variation in the brain. We examined the effects of early life rearing experience via natural variation in maternal licking and grooming during the first week of life on behavior, physiology, gene expression, and epigenetic regulation of Oxtr across blood and brain tissues (mononucleocytes, hippocampus, striatum, and hypothalamus). Rats reared by "high" licking-grooming (HL) and "low" licking-grooming (LL) rat dams exhibited differences across study outcomes: LL offspring were more active in behavioral arenas, exhibited lower body mass in adulthood, and showed reduced corticosterone responsivity to a stressor. Oxtr DNA methylation was significantly lower at multiple CpGs in the blood of LL versus HL males, but no differences were found in the brain. Across groups, Oxtr transcript levels in the hypothalamus were associated with reduced corticosterone secretion in response to stress, congruent with the role of oxytocin signaling in this region. Methylation of specific CpGs at a high or low level was consistent across tissues, especially within the brain. However, individual variation in DNA methylation relative to these global patterns was not consistent across tissues. These results suggest that blood Oxtr DNA methylation may reflect early experience of maternal care, and that Oxtr methylation across tissues is highly concordant for specific CpGs, but that inferences across tissues are not supported for individual variation in Oxtr methylation.

The oxytocin system promotes resilience to the effects of neonatal isolation on adult social attachment in female prairie voles

Genes and social experiences interact to create variation in social behavior and vulnerability to develop disorders of the social domain. Socially monogamous prairie voles display remarkable diversity in neuropeptide receptor systems and social behavior. Here, we examine the interaction of early-life adversity and brain oxytocin receptor (OTR) density on adult social attachment in female prairie voles. First, pups were isolated for 3 h per day, or unmanipulated, from postnatal day 1-14. Adult subjects were tested on the partner preference (PP) test to assess social attachment and OTR density in the brain was quantified. Neonatal social isolation impaired female PP formation, without affecting OTR density. Accumbal OTR density was, however, positively correlated with the percent of time spent huddling with the partner in neonatally isolated females. Females with high accumbal OTR binding were resilient to neonatal isolation. These results are consistent with the hypothesis that parental nurturing shapes neural systems underlying social relationships by enhancing striatal OTR signaling. Thus, we next determined whether early touch, mimicking parental licking and grooming, stimulates hypothalamic OT neuron activity. Tactile stimulation induced immediate-early gene activity in OT neurons in neonates. Finally, we investigated whether pharmacologically potentiating OT release using a melanocortin 3/4 agonist, melanotan-II (10 mg kg(-1) subcutaneously), would mitigate the social isolation-induced impairments in attachment behavior. Neonatal melanotan-II administration buffered against the effects of early isolation on partner preference formation. Thus, variation in accumbal OTR density and early OT release induced by parental nurturing may moderate susceptibility to early adverse experiences, including neglect.

Stress and the social brain: behavioural effects and neurobiological mechanisms

Stress often affects our social lives. When undergoing high-level or persistent stress, individuals frequently retract from social interactions and become irritable and hostile. Predisposition to antisocial behaviours - including social detachment and violence - is also modulated by early life adversity; however, the effects of early life stress depend on the timing of exposure and genetic factors. Research in animals and humans has revealed some of the structural, functional and molecular changes in the brain that underlie the effects of stress on social behaviour. Findings in this emerging field will have implications both for the clinic and for society.

Exposure to synthetic oxytocin during delivery and its effect on psychomotor development

The main objective is to examine the influence of oxytocin administration during delivery on psychomotor development at age five years. This was a retrospective cohort study involving two groups: children of mothers exposed vs. not exposed to oxytocin during labor. Of the 7,465 newborns registered in our maternity service during 2006 we randomly selected an initial sample of 400 children. Of these, 146 children were assessed using the motor scale of the Battelle Developmental Inventory. Other predictor variables that could potentially act as confounders and/or interact with the main relationship were also examined. The data were subjected to bivariate analysis, estimates of measures of strength of association, stratified analysis and multivariate binary logistic regression. The results indicate that exposure to synthetic oxytocin during delivery is an independent risk factor for a delay in gross and fine motor development. This was the case after controlling for the variables duration of labor and sex of the newborn, none of which modified the effect of oxytocin on gross and fine motor development. However, sex of the newborn were shown to be confounding gross motor development. In light of these results, and with the aim of preventing possible psychomotor alterations, further studies are now needed to analyze the effect that the oxytocin dose and the duration of perfusion may have on children's subsequent development.

The influence of early life sexual abuse on oxytocin concentrations and premenstrual symptomatology in women with a menstrually related mood disorder

Oxytocin (OT), associated with affiliation and social bonding, social salience, and stress/pain regulation, may play a role in the pathophysiology of stress-related disorders, including menstrually-related mood disorders (MRMD's). Adverse impacts of early life sexual abuse (ESA) on adult attachment, affective regulation, and pain sensitivity suggest ESA-related OT dysregulation in MRMD pathophysiology. We investigated the influence of ESA on plasma OT, and the relationship of OT to the clinical phenomenology of MRMD's. Compared to MRMD women without ESA (n=40), those with ESA (n=20) displayed significantly greater OT [5.39pg/mL (SD, 2.4) vs. 4.36pg/mL (SD, 1.1); t (58)=-2.26, p=0.03]. In women with ESA, OT was significantly, inversely correlated with premenstrual psychological and somatic symptoms (r's=-0.45 to -0.64, p's<0.05). The relationship between OT and premenstrual symptomatology was uniformly low and non-significant in women without ESA. In women with ESA, OT may positively modulate MRMD symptomatology.

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

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

The many faces of oxytocin: implications for psychiatry

Oxytocin is known as the 'love hormone' due its role in promoting mother-child and pair bonding. More recent research indicates that oxytocin may have broader pro-social effects on behavior and cognition, which points towards oxytocin's potential as an agent to help improve social cognition and functioning in psychiatric disorders such as schizophrenia and autism. However, new research on oxytocin has also uncovered a 'darker side', including oxytocin's possible role in social out-grouping and envy. Instead of a simple view of oxytocin as 'good' or 'bad', a more accurate depiction of oxytocin's role in social processing likely involves the presence of moderating factors. We review moderation effects in oxytocin and their implications for psychiatry. One implication is that, across diagnostic categories, oxytocin administration may have positive effects for patients with social cognitive deficits but negative effects for patients with social cognitive bias. We conclude that future intervention studies should use methods such as signal detection to measure both deficit and bias parameters of social cognition and to evaluate potential individual and contextual moderators both within and between psychiatric diagnoses in order to determine for whom oxytocin treatment may be beneficial and for whom it may actually be harmful.

Epigenetic regulation of Newborns' imprinted genes related to gestational growth: patterning by parental race/ethnicity and maternal socioeconomic status

BACKGROUND

Children born to parents with lower income and education are at risk for obesity and later-life risk of common chronic diseases, and epigenetics has been hypothesised to link these associations. However, epigenetic targets are unknown. We focus on a cluster of well-characterised genomically imprinted genes because their monoallelic expression is regulated by DNA methylation at differentially methylated regions (DMRs), are critical in fetal growth, and DNA methylation patterns at birth have been associated with increased risk of birth weight extremes and overweight status or obesity in early childhood.

METHODS

We measured DNA methylation at DMRs regulating genomically imprinted domains (IGF2/H19, DLK1/MEG3, NNAT and PLAGL1) using umbilical cord blood leucocytes from 619 infants recruited in Durham, North Carolina in 2010-2011. We examined differences in DNA methylation levels by race/ethnicity of both parents, and the role that maternal socioeconomic status (SES) may play in the association between race/ethnic epigenetic differences.

RESULTS

Unadjusted race/ethnic differences only were evident for DMRs regulating MEG3 and IGF2; race/ethnic differences persisted in IGF2/H19 and NNAT after accounting for income and education.

CONCLUSIONS

Results suggest that parental factors may not only influence DNA methylation, but also do so in ways that vary by DMR. Findings support the hypothesis that epigenetics may link the observed lower SES during the prenatal period and poor outcomes such as low birth weight; lower birth weight has previously been associated with adult-onset chronic diseases and conditions that include cardiovascular diseases, diabetes, obesity and some cancers.

Vasopressin, but not oxytocin, increases empathic concern among individuals who received higher levels of paternal warmth: A randomized controlled trial

BACKGROUND

Empathy improves our ability to communicate in social interactions and motivates prosocial behavior. The neuropeptides arginine vasopressin and oxytocin play key roles in socioemotional processes such as pair bonding and parental care, which suggests that they may be involved in empathic processing.

METHODS

We investigated how vasopressin and oxytocin affect empathic responding in a randomized, double-blind, placebo controlled, between-subjects study design. We also examined the moderating role of parental warmth, as reported in the early family environment, on empathic responding following vasopressin, oxytocin, or placebo administration.

RESULTS

Among participants who reported higher levels of paternal warmth (but not maternal warmth), vasopressin (vs. placebo and oxytocin) increased ratings of empathic concern after viewing distressing and uplifting videos. No main or interaction effects were found for individuals who received oxytocin.

CONCLUSIONS

Vasopressin has a role in enhancing empathy among individuals who received higher levels of paternal warmth.

TRIAL REGISTRATION

NCT01680718.

How postnatal insults may program development: studies in animal models

During the postnatal period, the nervous system is modified and shaped by experience, in order to adjust it to the particular environment in which the animal will live. This plasticity, one of the most remarkable characteristics of the nervous system, promotes adaptive changes, but it also makes brain more vulnerable to insults. This chapter will focus on the effects of interventions during the postnatal development in animal models of neonatal handling (usually up to 15 min of handling) and maternal separation (usually at least for 3 h). Sex-specific changes and effects of prepubertal stress such as social isolation later on in life were also considered. These interventions during development induce long-lasting traces in the pups' nervous system, which will be reflected in changes in neuroendocrine functions, including the hypothalamus-pituitary-adrenal and hypothalamus-pituitary-gonadal axes; anxiety and cognitive performance; and feeding, sexual, and social behavior. These enduring changes may be adaptive or maladaptive, depending on the environment in which the animal will live. The challenge researchers facing now is to determine how to reverse the deleterious effects that may result from early-life stress exposure.

Early social environment affects the endogenous oxytocin system: a review and future directions

Endogenous oxytocin plays an important role in a wide range of human functions including birth, milk ejection during lactation, and facilitation of social interaction. There is increasing evidence that both variations in the oxytocin receptor (OXTR) and concentrations of oxytocin are associated with differences in these functions. The causes for the differences that have been observed in tonic and stimulated oxytocin release remain unclear. Previous reviews have suggested that across the life course, these differences may be due to individual factors, e.g., genetic variation (of the OXTR), age or sex, or be the result of early environmental influences, such as social experiences, stress, or trauma partly by inducing epigenetic changes. This review has three aims. First, we briefly discuss the endogenous oxytocin system, including physiology, development, individual differences, and function. Second, current models describing the relationship between the early life environment and the development of the oxytocin system in humans and animals are discussed. Finally, we describe research designs that can be used to investigate the effects of the early environment on the oxytocin system, identifying specific areas of research that need further attention.

Stress, social behavior, and resilience: insights from rodents

The neurobiology of stress and the neurobiology of social behavior are deeply intertwined. The social environment interacts with stress on almost every front: social interactions can be potent stressors; they can buffer the response to an external stressor; and social behavior often changes in response to stressful life experience. This review explores mechanistic and behavioral links between stress, anxiety, resilience, and social behavior in rodents, with particular attention to different social contexts. We consider variation between several different rodent species and make connections to research on humans and non-human primates.

Developmental perspectives on oxytocin and vasopressin

The related neuropeptides oxytocin and vasopressin are involved in species-typical behavior, including social recognition behavior, maternal behavior, social bonding, communication, and aggression. A wealth of evidence from animal models demonstrates significant modulation of adult social behavior by both of these neuropeptides and their receptors. Over the last decade, there has been a flood of studies in humans also implicating a role for these neuropeptides in human social behavior. Despite popular assumptions that oxytocin is a molecule of social bonding in the infant brain, less mechanistic research emphasis has been placed on the potential role of these neuropeptides in the developmental emergence of the neural substrates of behavior. This review summarizes what is known and assumed about the developmental influence of these neuropeptides and outlines the important unanswered questions and testable hypotheses. There is tremendous translational need to understand the functions of these neuropeptides in mammalian experience-dependent development of the social brain. The activity of oxytocin and vasopressin during development should inform our understanding of individual, sex, and species differences in social behavior later in life.

Peripartum depression and anxiety as an integrative cross domain target for psychiatric preventative measures

Exposure to high levels of early life stress has been identified as a potent risk factor for neurodevelopmental delays in infants, behavioral problems and autism in children, but also for several psychiatric illnesses in adulthood, such as depression, anxiety, autism, and posttraumatic stress disorder. Despite having robust adverse effects on both mother and infant, the pathophysiology of peripartum depression and anxiety are poorly understood. The objective of this review is to highlight the advantages of using an integrated approach addressing several behavioral domains in both animal and clinical studies of peripartum depression and anxiety. It is postulated that a greater focus on integrated cross domain studies will lead to advances in treatments and preventative measures for several disorders associated with peripartum depression and anxiety.

Autism, oxytocin and interoception

Autism is a pervasive developmental disorder characterized by profound social and verbal communication deficits, stereotypical motor behaviors, restricted interests, and cognitive abnormalities. Autism affects approximately 1% of children in developing countries. Given this prevalence, identifying risk factors and therapeutic interventions are pressing objectives—objectives that rest on neurobiologically grounded and psychologically informed theories about the underlying pathophysiology. In this article, we review the evidence that autism could result from a dysfunctional oxytocin system early in life. As a mediator of successful procreation, not only in the reproductive system, but also in the brain, oxytocin plays a crucial role in sculpting socio-sexual behavior. Formulated within a (Bayesian) predictive coding framework, we propose that oxytocin encodes the saliency or precision of interoceptive signals and enables the neuronal plasticity necessary for acquiring a generative model of the emotional and social 'self.' An aberrant oxytocin system in infancy could therefore help explain the marked deficits in language and social communication—as well as the sensory, autonomic, motor, behavioral, and cognitive abnormalities—seen in autism.

[The role of genotype in the intergenerational transmission of experiences of childhood adversity]

The prevalence of childhood abuse and maltreatment is estimated to lie at about 15% in the overall German population. Previous research suggested that about one third of all individuals who had experienced childhood adversity subsequently maltreated their own children or responded insensitively to their children's needs. Empirical studies imply that interindividual differences in the responsiveness to childhood adversity can partially be explained by gene-environment interactions. This article discusses the potential interplay of genes and environment in the context of transmitting maltreating behavior and (in)sensitive parenting against the background of current challenges in genetic research. Selected studies on gene × environment interactions are presented and relevant gene polymorphisms are identified. Overall, previous studies reported interactions between polymorphisms of the serotonergic, dopaminergic, oxytocin-related, and arginine vasopressin-related systems and childhood experiences of care and abuse in the prediction of social behaviors during mother-child interactions. The results indicate a differential susceptibility toward both negative and positive environments which is dependent on genetic characteristics. Future research should thus investigate the effects of children's presumed risk gene variants toward negative as well as positive parenting. This could contribute to a deeper understanding of the underlying mechanisms of the intergenerational transmission of abusive and beneficial parenting behavior and help to avoid false stigmatizations.

Modification of female and male social behaviors in estrogen receptor beta knockout mice by neonatal maternal separation

Maternal separation (MS) is an animal model mimicking the effects of early life stress on the development of emotional and social behaviors. Recent studies revealed that MS stress increased social anxiety levels in female mice and reduced peri-pubertal aggression in male mice. Estrogen receptor (ER) β plays a pivotal role in the regulation of stress responses and anxiety-related and social behaviors. Behavioral studies using ERβ knockout (βERKO) mice reported increased social investigation and decreased social anxiety in βERKO females, and elevated aggression levels in βERKO males compared to wild-type (WT) mice. In the present study, using βERKO and WT mice, we examined whether ERβ contributes to MS effects on anxiety and social behaviors. βERKO and WT mice were separated from their dam daily (4 h) from postnatal day 1–14 and control groups were left undisturbed. First, MS and ERβ gene deletion individually increased anxiety-related behaviors in the open field test, but only in female mice. Anxiety levels were not further modified in βERKO female mice subjected to MS stress. Second, βERKO female mice showed higher levels of social investigation compared with WT in the social investigation test and long-term social preference test. However, MS greatly reduced social investigation duration and elevated number of stretched approaches in WT and βERKO females in the social investigation test, suggesting elevated levels of social anxiety in both genotypes. Third, peri-pubertal and adult βERKO male mice were more aggressive than WT mice as indicated by heightened aggression duration. On the other hand, MS significantly decreased aggression duration in both genotypes, but only in peri-pubertal male mice. Altogether, these results suggest that βERKO mice are sensitive to the adverse effects of MS stress on subsequent female and male social behaviors, which could then have overrode the ERβ effects on female social anxiety and male aggression.

Early involvement in friendships predicts later plasma concentrations of oxytocin and vasopressin in juvenile rhesus macaques (Macaca mulatta)

The neuropeptides oxytocin (OT) and arginine vasopressin (AVP) are involved in social bonding in attachment relationships, but their role in friendship is poorly understood. We investigated whether rhesus macaques' (Macaca mulatta) friendships at age one predicted plasma OT and AVP at two later time points. Subjects were 54 rhesus macaques at the California National Primate Research Center (CNPRC). Blood was drawn during a brief capture-and-release in the home cage, and plasma assayed for OT and AVP using an enzyme immunoassay (EIA). Separate linear mixed models for each sex tested the effects of dominance rank, age, sampling time point, housing condition, parturition status, two blood draw timing measures, and five friendship types: proximity friendships, play friendships, reciprocal friendships (a preference for a peer that also preferred the subject), multiplex friendships (friendships displayed in more than one behavioral domain), and total number of friendships. Females' number of reciprocal and play friendships at age one significantly predicted later OT; additionally, these two friendship types interacted with rank, such that high-ranking females with the fewest friendships had the highest OT concentrations. Friendship did not predict later OT levels in males, however proximity, play, reciprocal, and total number of friendships predicted males' plasma AVP. Play and total number of friendships also tended to predict AVP in females. Our results show that peripheral measures of neuroendocrine functioning in juvenile rhesus monkeys are influenced by early involvement in friendships. Friendships have an especially strong impact on an individual's psychosocial development, and our data suggest OT and AVP as potential underlying mechanisms. Moreover, sex differences in the functioning of the OT and AVP systems, and their relation to friendship, may have important clinical implications for the use of OT as a therapeutic, as well as informing the social context in which it is administered.

Sociosexual and communication deficits after traumatic injury to the developing murine brain

Despite the life-long implications of social and communication dysfunction after pediatric traumatic brain injury, there is a poor understanding of these deficits in terms of their developmental trajectory and underlying mechanisms. In a well-characterized murine model of pediatric brain injury, we recently demonstrated that pronounced deficits in social interactions emerge across maturation to adulthood after injury at postnatal day (p) 21, approximating a toddler-aged child. Extending these findings, we here hypothesized that these social deficits are dependent upon brain maturation at the time of injury, and coincide with abnormal sociosexual behaviors and communication. Age-dependent vulnerability of the developing brain to social deficits was addressed by comparing behavioral and neuroanatomical outcomes in mice injured at either a pediatric age (p21) or during adolescence (p35). Sociosexual behaviors including social investigation and mounting were evaluated in a resident-intruder paradigm at adulthood. These outcomes were complemented by assays of urine scent marking and ultrasonic vocalizations as indices of social communication. We provide evidence of sociosexual deficits after brain injury at p21, which manifest as reduced mounting behavior and scent marking towards an unfamiliar female at adulthood. In contrast, with the exception of the loss of social recognition in a three-chamber social approach task, mice that received TBI at adolescence were remarkably resilient to social deficits at adulthood. Increased emission of ultrasonic vocalizations (USVs) as well as preferential emission of high frequency USVs after injury was dependent upon both the stimulus and prior social experience. Contrary to the hypothesis that changes in white matter volume may underlie social dysfunction, injury at both p21 and p35 resulted in a similar degree of atrophy of the corpus callosum by adulthood. However, loss of hippocampal tissue was greater after p21 compared to p35 injury, suggesting that a longer period of lesion progression or differences in the kinetics of secondary pathogenesis after p21 injury may contribute to observed behavioral differences. Together, these findings indicate vulnerability of the developing brain to social dysfunction, and suggest that a younger age-at-insult results in poorer social and sociosexual outcomes.

Neonatal handling: an overview of the positive and negative effects

As one of the first rodent models designed to investigate the effects of early-life experiences, the neonatal handling paradigm has helped us better understand how subtle changes in the infant environment can powerfully drive neurodevelopment of the immature brain in typical or atypical trajectories. Here, we review data from more than 50 years demonstrating the compelling effects of neonatal handling on behavior, physiology, and neural function across the lifespan. Moreover, we present data that challenge the classical view of neonatal handling as an animal model that results only in positive/beneficial outcomes. Indeed, the overall goal of this review is to offer the suggestion that the effects of early-life experiences-including neonatal handling-are nuanced rather than unidirectional. Both beneficial and negative outcomes may occur, depending on the parameters of testing, sex of the subject, and neurobehavioral system analyzed.

Transgenerational effects of social stress on social behavior, corticosterone, oxytocin, and prolactin in rats

Social stressors such as depressed maternal care and family conflict are robust challenges which can have long-term physiological and behavioral effects on offspring and future generations. The current study investigates the transgenerational effects of an ethologically relevant chronic social stress on the behavior and endocrinology of juvenile and adult rats. Exposure to chronic social stress during lactation impairs maternal care in F0 lactating dams and the maternal care of the F1 offspring of those stressed F0 dams. The overall hypothesis was that the male and female F2 offspring of stressed F1 dams would display decreased social behavior as both juveniles and adults and that these behavioral effects would be accompanied by changes in plasma corticosterone, prolactin, and oxytocin. Both the female and male F2 offspring of dams exposed to chronic social stress displayed decreased social behavior as juveniles and adults, and these behavioral effects were accompanied by decreases in basal concentrations of corticosterone in both sexes, as well as elevated juvenile oxytocin and decreased adult prolactin in the female offspring. The data support the conclusion that social stress has transgenerational effects on the social behavior of the female and male offspring which are mediated by changes in the hypothalamic-pituitary-adrenal axis and hypothalamic-pituitary-gonadal axis. Social stress models are valuable resources in the study of the transgenerational effects of stress on the behavioral endocrinology of disorders such as depression, anxiety, autism, and other disorders involving disrupted social behavior.

Oxytocin and autism: a systematic review of randomized controlled trials

OBJECTIVE

Little is known about the effectiveness of pharmacological interventions on autism spectrum disorder (ASD). This is a systematic review of the randomized controlled trials (RCTs) of oxytocin interventions in autism, made from January 1990 to September 2013.

METHOD

A search of computerized databases was supplemented by manual search in the bibliographies of key publications. The methodological quality of the studies included in the review was evaluated independently by two researchers, according to a set of formal criteria. Discrepancies in scoring were resolved through discussion.

RESULTS

The review yielded seven RCTs, including 101 subjects with ASD (males=95) and 8 males with Fragile X syndrome. The main categories of target symptoms tested in the studies were repetitive behaviors, eye gaze, and emotion recognition. The studies had a medium to high risk of bias. Most studies had small samples (median=15). All the studies but one reported statistically significant between-group differences on at least one outcome variable. Most findings were characterized by medium effect size. Only one study had evidence that the improvement in emotion recognition was maintained after 6 weeks of treatment with intranasal oxytocin. Overall, oxytocin was well tolerated and side effects, when present, were generally rated as mild; however, restlessness, increased irritability, and increased energy occurred more often under oxytocin.

CONCLUSIONS

RCTs of oxytocin interventions in autism yielded potentially promising findings in measures of emotion recognition and eye gaze, which are impaired early in the course of the ASD condition and might disrupt social skills learning in developing children. There is a need for larger, more methodologically rigorous RCTs in this area. Future studies should be better powered to estimate outcomes with medium to low effect size, and should try to enroll female participants, who were rarely considered in previous studies. Risk of bias should be minimized. Human long-term administration studies are necessary before clinical recommendations can be made.

Personality is tightly coupled to vasopressin-oxytocin neuron activity in a gregarious finch

Nonapeptides of the vasopressin-oxytocin family modulate social processes differentially in relation to sex, species, behavioral phenotype, and human personality. However, the mechanistic bases for these differences are not well understood, in part because multidimensional personality structures remain to be described for common laboratory animals. Based upon principal components (PC) analysis of extensive behavioral measures in social and nonsocial contexts, we now describe three complex dimensions of phenotype (“personality”) for the zebra finch, a species that exhibits a human-like social organization that is based upon biparental nuclear families embedded within larger social groups. These dimensions can be characterized as Social competence/dominance, Gregariousness, and Anxiety. We further demonstrate that the phasic Fos responses of nonapeptide neurons in the paraventricular nucleus of the hypothalamus and medial bed nucleus of the stria terminalis are significantly predicted by personality, sex, social context, and their interactions. Furthermore, the behavioral PCs are each associated with a distinct suite of neural PCs that incorporate both peptide cell numbers and their phasic Fos responses, indicating that personality is reflected in complex patterns of neuromodulation arising from multiple peptide cell groups. These findings provide novel insights into the mechanisms underlying sex- and phenotype-specific modulation of behavior, and should be broadly relevant, given that vasopressin-oxytocin systems are strongly conserved across vertebrates.

Oxytocin's role in anxiety: a critical appraisal

A growing literature suggests that the oxytocin (OT) system may play a role in human anxiety states, anxiety-related traits, and moreover, that this system may be a target for the development of novel anxiolytic treatments. However, studies of OT's acute and chronic effects on various aspects of anxiety have produced mixed results. In this forward-looking review, we discuss the myriad phenomena to which the term "anxiety" is applied in the OT literature and the problem this presents developing a coherent picture of OT's role in anxiety. We then survey several different fields of research that support the role of the OT system in human anxiety, including evolutionary perspectives, translational and neuroimaging research, genetic studies, and clinical trials of intranasal OT. As an outgrowth of this data, we propose a "bowtie" model of OT's role at the interface of social attachment and anxiety. We next direct attention to understudied brain regions and neural circuits which may be important to study in OT experiments in humans anxiety disorders. Finally, we conclude by proposing questions and priorities for studying both the clinical potential of OT in anxiety, as well as mechanisms that may underlie this potential. Crucially, these priorities include targeted proof-of-concept clinical trials of IN OT in certain anxiety disorders, including investigations of individual moderators of OT's anxiolytic effects (i.e. sex, genetic factors, and early experience). This article is part of a Special Issue entitled Oxytocin and Social Behav.

Neonatal paternal deprivation impairs social recognition and alters levels of oxytocin and estrogen receptor α mRNA expression in the MeA and NAcc, and serum oxytocin in mandarin voles

Paternal care is necessary for the healthy development of social behavior in monogamous rodents and social recognition underpins social behavior in these animals. The effects of paternal care on the development of social recognition and underlying neuroendocrine mechanisms, especially the involvement of oxytocin and estrogen pathways, remain poorly understood. We investigated the effects of paternal deprivation (PD: father was removed from neonatal pups and mother alone raised the offspring) on social recognition in mandarin voles (Microtus mandarinus), a socially monogamous rodent. Paternal deprivation was found to inhibit the development of social recognition in female and male offspring according to a habituation-dishabituation paradigm. Paternal deprivation resulted in increased inactivity and reduced investigation during new encounters with other animals. Paternal deprivation reduced oxytocin receptor (OTR) and estrogen receptor α (ERα) mRNA expression in the medial amygdala and nucleus accumbens. Paternal deprivation reduced serum oxytocin (OT) concentration in females, but had no effect on males. Our results provide substantial evidence that paternal deprivation inhibits the development of social recognition in female and male mandarin voles and alters social behavior later in life. This is possibly the result of altered expression of central OTR and ERα and serum OT levels caused by paternal deprivation.

Natural variation in maternal care shapes adult social behavior in rats

Features of the early postnatal environment profoundly shape later physical and behavioral phenotypes. The amount of licking/grooming that rat dams direct towards their offspring has durable consequences, including behavioral and physiological dimensions of stress reactivity, cognition, and reproductive behavior. We examined how natural variation in maternal care alters social behavior in adult offspring and how this relates to anxiety behavior and oxytocin receptor density. Male and female offspring of mothers who received high levels of licking spent significantly more time in social contact with unfamiliar individuals than did offspring whose dams provided less grooming. Reduced anxiety behavior was associated with greater social interaction. No differences in oxytocin receptor binding assessed by (125) I-OVTA autoradiography were detected between groups. The present investigation characterizes a novel impact of maternal care on adult social interaction behavior, replicates anxiety behavior differences, and illustrates connections between social behavior and anxiety in adulthood across maternal treatment groups.

Individual differences underlying susceptibility to addiction: Role for the endogenous oxytocin system

Recent research shows that the effects of oxytocin are more diverse than initially thought and that in some cases oxytocin can directly influence the response to drugs and alcohol. Large individual differences in basal oxytocin levels and reactivity of the oxytocin system exist. This paper will review the literature to explore how individual differences in the oxytocin system arise and examine the hypothesis that this may mediate some of the individual differences in susceptibility to addiction and relapse. Differences in the oxytocin system can be based on individual factors, e.g. genetic variation especially in the oxytocin receptor, age or gender, or be the result of early environmental influences such as social experiences, stress or trauma. The paper addresses the factors that cause individual differences in the oxytocin system and the environmental factors that have been identified to induce long-term changes in the developing oxytocin system during different life phases. Individual differences in the oxytocin system can influence effects of drugs and alcohol directly or indirectly. The oxytocin system has bidirectional interactions with the stress-axis, autonomic nervous system, neurotransmitter systems (e.g. dopamine, serotonin and GABA/glutamate) and the immune system. These systems are all important, even vital, in different phases of addiction. It is suggested that early life adversity can change the development of the oxytocin system and the way it modulates other systems. This in turn could minimise the negative feedback loops that would normally exist. Individuals may show only minor differences in behaviour and function unless subsequent stressors or drug use challenges the system. It is postulated that at that time individual differences in oxytocin levels, reactivity of the system or interactions with other systems can influence general resilience, drug effects and the susceptibility to develop problematic drug and alcohol use.