Chronic enhancement of brain oxytocin levels causes enduring anti-aggressive and pro-social explorative behavioral effects in male rats

Fear, love, and the origins of canid domestication: An oxytocin hypothesis

The process of dog domestication likely involved at least two functional stages. The initial stage occurred when subpopulations of wolves became synanthropes, benefiting from life nearby or in human environments. The second phase was characterized by the evolution of novel forms of interspecific cooperation and social relationships between humans and dogs. Here, we discuss possible roles of the oxytocin system across these functional stages of domestication. We hypothesize that in early domestication, oxytocin played important roles in attenuating fear and stress associated with human contact. In later domestication, we hypothesize that oxytocin's most critical functions were those associated with affiliative social behavior, social engagement, and cooperation with humans. We outline possible neurobiological changes associated with these processes and present a Siberian fox model of canid domestication in which these predictions can be tested. Lastly, we identify limitations of current studies on the neuroendocrinology of domestication and discuss challenges and opportunities for future research.

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We propose various roles for oxytocin across canid domestication.

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In early domestication, oxytocin primarily regulated fear and anxiety toward humans.

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In late domestication, oxytocin facilitated interspecific social bonds and cooperation.

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Comparative neurobiology is critical for understanding oxytocin's roles in domestication.

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Experimentally domesticated Siberian foxes provide a powerful model for these studies.

HIV-1 Tat and morphine decrease murine inter-male social interactions and associated oxytocin levels in the prefrontal cortex, amygdala, and hypothalamic paraventricular nucleus

Many persons infected with HIV-1 (PWH) and opioid-dependent individuals experience deficits in sociability that interfere with daily living. Sociability is regulated by the prefrontal cortico-hippocampal-amygdalar circuit. Within this circuit HIV-1 trans-activator of transcription (HIV-1 Tat) and opioids can increase dendritic pathology and alter neuronal firing. Changes in sociability are also associated with dysregulation of hypothalamic neuropeptides such as oxytocin or corticotropin releasing factor (CRF) in the prefrontal cortico-hippocampal-amygdalar circuit. Accordingly, we hypothesized that the interaction of HIV-1 Tat and morphine would impair inter-male social interactions and disrupt oxytocin and CRF within the PFC and associated circuitry. Male mice were exposed to HIV-1 Tat for 8 weeks and administered saline or escalating doses of morphine twice daily (s.c.) during the last 2 weeks of HIV-1 Tat exposure. Tat attenuated aggressive interactions with an unknown intruder, whereas morphine decreased both non-aggressive and aggressive social interactions in the resident-intruder test. However, there was no effect of Tat or morphine on non-reciprocal interactions in the social interaction and novelty tests. Tat, but not morphine, decreased oxytocin levels in the PFC and amygdala, whereas both Tat and morphine decreased the percentage of oxytocin-immunoreactive neurons in the hypothalamic paraventricular nucleus (PVN). In Tat(+) or morphine-exposed mice, regional levels of CRF and oxytocin correlated with alterations in behavior in the social interaction and novelty tests. Overall, decreased expression of oxytocin in the prefrontal cortico-hippocampal-amygdalar circuit is associated with morphine- and HIV-Tat-induced deficits in social behavior.

Oxytocin in Schizophrenia: Pathophysiology and Implications for Future Treatment

Schizophrenia is a form of mental disorder that is behaviorally characterized by abnormal behavior, such as social function deficits or other behaviors that are disconnected from reality. Dysregulation of oxytocin may play a role in regulating the expression of schizophrenia. Given oxytocin’s role in social cognition and behavior, a variety of studies have examined the potential clinical benefits of oxytocin in improving the psychopathology of patients with schizophrenia. In this review, we highlight the evidence for the role of endogenous oxytocin in schizophrenia, from animal models to human studies. We further discuss the potential of oxytocin as a therapeutic agent for schizophrenia and its implication in future treatment.

Reconstruction of the Hypothalamo-Neurohypophysial System and Functional Dissection of Magnocellular Oxytocin Neurons in the Brain

The hypothalamo-neurohypophysial system (HNS), comprising hypothalamic magnocellular neuroendocrine cells (MNCs) and the neurohypophysis, plays a pivotal role in regulating reproduction and fluid homeostasis by releasing oxytocin and vasopressin into the bloodstream. However, its structure and contribution to the central actions of oxytocin and vasopressin remain incompletely understood. Using viral tracing and whole-brain imaging, we reconstruct the three-dimensional architecture of the HNS and observe collaterals of MNCs within the brain. By dual viral tracing, we further uncover that subsets of MNCs collaterally project to multiple extrahypothalamic regions. Selective activation of magnocellular oxytocin neurons promote peripheral oxytocin release and facilitate central oxytocin-mediated social interactions, whereas inhibition of these neurons elicit opposing effects. Our work reveals the previously unrecognized complexity of the HNS and provides structural and functional evidence for MNCs in coordinating both peripheral and central oxytocin-mediated actions, which will shed light on the mechanistic understanding of oxytocin-related psychiatric diseases.

Wireless Optogenetic Stimulation of Oxytocin Neurons in a Semi-natural Setup Dynamically Elevates Both Pro-social and Agonistic Behaviors

Complex behavioral phenotyping techniques are becoming more prevalent in the field of behavioral neuroscience, and thus methods for manipulating neuronal activity must be adapted to fit into such paradigms. Here, we present a head-mounted, magnetically activated device for wireless optogenetic manipulation that is compact, simple to construct, and suitable for use in group-living mice in an enriched semi-natural arena over several days. Using this device, we demonstrate that repeated activation of oxytocin neurons in male mice can have different effects on pro-social and agonistic behaviors, depending on the social context. Our findings support the social salience hypothesis of oxytocin and emphasize the importance of the environment in the study of social neuromodulators. Our wireless optogenetic device can be easily adapted for use in a variety of behavioral paradigms, which are normally hindered by tethered light delivery or a limited environment.

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A small, wireless device is used for optogenetic activation in a complex environment

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PVN oxytocin neurons were activated repeatedly over 2 days in a group setting

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Repeated activation in a group setting elicited both pro-social and agonistic behavior

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Findings support the social salience hypothesis of oxytocin neuro-modulation

Empathy as a Concept from Bench to Bedside: A Translational Challenge

Empathy is a multidimensional paradigm, and there currently is a lack of scientific consensus in its definition. In this paper, we review the possibility of compromising data during behavioral neuroscience experiments, including but not limited to those who study empathy. The experimental protocols can affect, and be affected by, empathy and related processes at multiple levels. We discuss several points to help researchers develop a successful translational pathway for behavioral research on empathy. Despite varying in their focus with no widely accepted model, current rodent models on empathy have provided sound translational explanations for many neuropsychiatric proof-of-concepts to date. Research has shown that empathy can be influenced by many parameters, some of which are to be reviewed in this paper. We emphasize the future importance of consistency in modeling proof of concept; efforts to create a multidisciplinary group which would include both bench scientists and clinicians with expertise in neuropsychiatry, and the consideration of empathy as an independent variable in animal behavioral experimental designs which is not the mainstream practice at present.

Chronic oxytocin administration as a tool for investigation and treatment: A cross-disciplinary systematic review

Oxytocin (OT) subserves various physiological, behavioral, and cognitive processes. This paired with the ability to administer OT with minimal and inconsistent side effects has spurred research to explore its therapeutic potential. Findings from single-dose studies indicate that OT administration may be beneficial, at least under certain circumstances. The state of the field, however, is less clear regarding effects from chronic OT administration, which more closely resembles long-term treatment. To address this gap, this review synthesizes existing findings on the use of chronic OT administration in animal and human work. In addition to detailing the effects of chronic OT administration across different functional domains, this review highlights factors that have contributed to mixed findings. Based on this review, a basic framework of interrelated regulatory functions sensitive to chronic OT administration is offered. The paper also identifies future research directions across different contexts, populations, and outcomes, specifically calling for more systematic and standardized research on chronic OT administration in humans to supplement and expand what is currently known from preclinical work.

Intranasal oxytocin reduces reactive aggression in men but not in women: A computational approach

Aggression is an important behaviour that concerns individual survival and large-scale social stability. It comprises a variety of psychological subcomponents and is modulated by different biological factors. Two factors in particular, gender and oxytocin, appear to play a robust role in aggressive behaviour. However, whether these two factors interact to impact aggressive behaviour is not currently known. The current study investigated the modulating effect of gender on the relationship between oxytocin and aggression and characterized its underlying mechanisms by combining behavioural economic, pharmacological, and computational approaches. Specifically, we employed a double-blind, randomized, placebo-controlled, between-subjects design, in which one hundred participants (50 men and 50 women) completed a norm-training version of the multi-round one-shot ultimatum game (UG) after intranasal oxytocin or placebo administration. Rejection rates in the UG were adopted as an indicator of reactive aggression. The results indicated that oxytocin compared with placebo administration decreased aggression among men but not among women. Further analyses suggested that this decrease in aggression was a result of changes in men's sensitivity to provocation and positive affect, rather than norm adaptation rates or concerns about the cost of aggression. These findings highlight the role of gender in the relationship between oxytocin and reactive aggression and reveal its underlying psychological and computational mechanisms.

Social status in mouse social hierarchies is associated with variation in oxytocin and vasopressin 1a receptor densities

The neuropeptides oxytocin and vasopressin and their receptors have established roles in the regulation of mammalian social behavior including parental care, sex, affiliation and pair-bonding, but less is known regarding their relationship to social dominance and subordination within social hierarchies. We have previously demonstrated that male mice can form stable linear dominance hierarchies with individuals occupying one of three classes of social status: alpha, subdominant, subordinate. Alpha males exhibit high levels of aggression and rarely receive aggression. Subdominant males exhibit aggression towards subordinate males but also receive aggression from more dominant individuals. Subordinate males rarely exhibit aggression and receive aggression from more dominant males. Here, we examined whether variation in social status was associated with levels of oxytocin (OTR) and vasopressin 1a (V1aR) receptor binding in socially relevant brain regions. We found that socially dominant males had significantly higher OTR binding in the nucleus accumbens core than subordinate animals. Alpha males also had higher OTR binding in the anterior olfactory nucleus, posterior part of the cortical amygdala and rostral lateral septum compared to more subordinate individuals. Conversely, alpha males had lower V1aR binding in the rostral lateral septum and lateral preoptic area compared to subordinates. These observed relationships have two potential explanations. Preexisting individual differences in the patterns of OTR and V1aR binding may underlie behavioral differences that promote or inhibit the acquisition of social status. More likely, the differential social environments experienced by dominant and subordinate animals may shift receptor expression, potentially facilitating the expression of adaptive social behaviors.

Complementary Neural Circuits for Divergent Effects of Oxytocin: Social Approach Versus Social Anxiety

Oxytocin (OT) is widely known for promoting social interactions, but there is growing appreciation that it can sometimes induce avoidance of social contexts. The social salience hypothesis posed an innovative solution to these apparently opposing actions by proposing that OT enhances the salience of both positive and negative social interactions. The mesolimbic dopamine system was put forth as a likely system to evaluate social salience owing to its well-described role in motivation. Evidence from several sources supports the premise that OT acting within the nucleus accumbens and ventral tegmental area facilitates social reward and approach behavior. However, in aversive social contexts, additional pathways play critical roles in mediating the effects of OT. Recent data indicate that OT acts in the bed nucleus of the stria terminalis to induce avoidance of potentially dangerous social contexts. Here, we review evidence for neural circuits mediating the effects of OT in appetitive and aversive social contexts. Specifically, we propose that distinct but potentially overlapping circuits mediate OT-dependent social approach or social avoidance. We conclude that a broader and more inclusive consideration of neural circuits of social approach and avoidance is needed as the field continues to evaluate the potential of OT-based therapeutics.

Oxytocin and vasopressin inhibit hyper-aggressive behaviour in socially isolated mice

Despite the high prevalence of aggression across a wide range of disorders, there is a severe lack of pharmacological treatments. Recent rodent studies have shown both centrally and peripherally administered oxytocin is effective in reducing territorial aggression, an adaptive form of aggression not reflective of pathological hyper-aggression. The current study tested i.p. administered oxytocin and vasopressin in a model of non-territorial hyper-aggression and examined the involvement of oxytocin receptors (OXTR) and vasopressin V1a receptors (V1aR). Male Swiss mice (N = 160) were either socially isolated or group housed for 6 weeks prior to the commencement of testing; wherein two unfamiliar weight and condition matched mice were placed into a neutral context for 10 min. Socially isolated mice exhibited heightened aggression that was powerfully and dose-dependently inhibited by oxytocin and vasopressin and that was accompanied by dose-dependent increases in close social contact (huddling) and grooming. These anti-aggressive effects of oxytocin were blocked by pre-treatment with a higher dose of selective V1aR antagonist SR49059 (20 mg/kg i.p.), but not a lower dose of SR49059 (5 mg/kg i.p.) or selective OXTR antagonist L-368,899 (10 mg/kg i.p.). This is consistent with a growing number of studies linking a range of effects of exogenous oxytocin to actions at the V1a receptor. Interestingly, the highest dose of the OXTR agonist TGOT (10 mg/kg) also reduced isolation-induced aggression. These results suggest that while activation of the V1a receptor appears critical for the anti-aggressive effects of oxytocin, activation of the oxytocin receptor cannot be excluded. This article is part of the Special Issue entitled 'Current status of the neurobiology of aggression and impulsivity.'

Oxytocin attenuates phencyclidine hyperactivity and increases social interaction and nucleus accumben dopamine release in rats

The pituitary neuropeptide oxytocin promotes social behavior, and is a potential adjunct therapy for social deficits in schizophrenia and autism. Oxytocin may mediate pro-social effects by modulating monoamine release in limbic and cortical areas, which was investigated herein using in vivo microdialysis, after establishing a dose that did not produce accompanying sedative or thermoregulatory effects that could concomitantly influence behavior. The effects of oxytocin (0.03-0.3 mg/kg subcutaneous) on locomotor activity, core body temperature, and social behavior (social interaction and ultrasonic vocalizations) were examined in adult male Lister-hooded rats, using selective antagonists to determine the role of oxytocin and vasopressin V_1a receptors. Dopamine and serotonin efflux in the prefrontal cortex and nucleus accumbens of conscious rats were assessed using microdialysis. 0.3 mg/kg oxytocin modestly reduced activity and caused hypothermia but only the latter was attenuated by the V_1a receptor antagonist, SR49059 (1 mg/kg intraperitoneal). Oxytocin at 0.1 mg/kg, which did not alter activity and had little effect on temperature, significantly attenuated phencyclidine-induced hyperactivity and increased social interaction between unfamiliar rats without altering the number or pattern of ultrasonic vocalizations. In the same rats, oxytocin (0.1 mg/kg) selectively elevated dopamine overflow in the nucleus accumbens, but not prefrontal cortex, without influencing serotonin efflux. Systemic oxytocin administration attenuated phencyclidine-induced hyperactivity and increased pro-social behavior without decreasing core body temperature and selectively enhanced nucleus accumbens dopamine release, consistent with activation of mesocorticolimbic circuits regulating associative/reward behavior being involved. This highlights the therapeutic potential of oxytocin to treat social behavioral deficits seen in psychiatric disorders such as schizophrenia.

Aggressive behavior and stress response after oxytocin administration in male Norway rats selected for different attitudes to humans

Oxytocin (OXT) is known to influence on social behaviors, including intermale aggression and hypothalamic-pituitary-adrenal (HPA) axis activity. However, there are no data on the effects of oxytocin on intermale aggression and HPA axis activity in rats selected for elimination and enhancement of aggressiveness towards humans. The aim of this study is to elucidate the role of oxytocin in expression of aggressive behavior and stress response in Norway rats selected for elimination (tame) and enhancement (aggressive) of an aggressive-defensive reaction to humans. Oxytocin was administered to males via nasal applications once or for 5 days (daily). Resident-intruder test showed that in aggressive males, single oxytocin administration caused an increase in the latent period of aggressive interactions and a decrease in the percentage of direct aggression time (not including the time of lateral threat postures) as compared to the control aggressive rats administered with saline. After a 5-day oxytocin administration, aggressive animals demonstrated shorter time of aggressive interactions compared to the control rats. Resident-intruder test revealed no significant changes in behavior of tame rats after single oxytocin administration, while multiple administration caused an increase in aggressive behavior in tame rats. Oxytocin applications caused an elevation of corticosterone level after restriction in aggressive males, but did not affect expression of Crh, Crh1 and Crhr2 genes in hypothalamus in either tame or aggressive rats. The data obtained indicate significant role of oxytocinergic system in the behavior formed in the process of selection by reaction to humans.

Role of oxytocin in parental behaviour

Both animal and human studies have provided conclusive evidence that oxytocin (OXT) acts in the brain (eg, medial preoptic area, ventral tegmental area, nucleus accumbens) to promote parental behaviour under different reproductive and physiological conditions. OXT appears to accelerate and strengthen the neural process that makes newborns attractive or rewarding. Furthermore, OXT reduces stress/anxiety and might improve mood and well being, resulting in indirect benefits for parents. However, OXT also plays a role in the development of species reproductive and social strategies, making some species or individuals more prone to display caring activities in nonreproductive contexts. There are important differences in the development of the OXT system and its regulation by gonadal hormones that can make individuals or species very different. Those intra- and interspecific differences in the OXT system have been associated with differences in parental behaviour. For example, differences in OXT levels in body fluids and genetic variants for the OXT and OXT receptor genes have been associated with variability in parental mood and behaviour in humans. Thus, OXT has received much attention as a potential therapeutic agent for affective, emotional and behavioural problems. Despite many preliminary studies indicating promising findings, several unknown aspects of the OXT system remain to be addressed before we can achieve a complete understanding of its function in the brain. The enormous interest that this area of study has attracted in the last decade will likely continually contribute to advancing our understanding of the role of OXT in parental behaviour and other behavioural and physiological functions.

Oxytocin and Aggression

The neuropeptide oxytocin (OT) has a solid reputation as a facilitator of social interactions such as parental and pair bonding, trust, and empathy. The many results supporting a pro-social role of OT have generated the hypothesis that impairments in the endogenous OT system may lead to antisocial behavior, most notably social withdrawal or pathological aggression. If this is indeed the case, administration of exogenous OT could be the "serenic" treatment that psychiatrists have for decades been searching for.In the present review, we list and discuss the evidence for an endogenous "hypo-oxytocinergic state" underlying aggressive and antisocial behavior, derived from both animal and human studies. We furthermore examine the reported effects of synthetic OT administration on aggression in rodents and humans.Although the scientific findings listed in this review support, in broad lines, the link between a down-regulated or impaired OT system activity and increased aggression, the anti-aggressive effects of synthetic OT are less straightforward and require further research. The rather complex picture that emerges adds to the ongoing debate questioning the unidirectional pro-social role of OT, as well as the strength of the effects of intranasal OT administration in humans.

Involvement of GABAA receptors in the regulation of social preference and emotional behaviors by oxytocin in the central amygdala of female mandarin voles

The central nucleus of the amygdala (CeA) is the main output of the amygdala and plays an important role in behavioral and neuroendocrine responses to stress. Receptors for the neuropeptide oxytocin (OT) and GABA_A are found in high concentration in the CeA. The mechanisms underlying regulation of CeA OT in emotional and social behavior remain unclear. In this study we evaluated the effects of intra-CeA OT administration of different doses (0.1, 1 and 10ng/side), OT receptor antagonist (OTR-A) (1, 10 and 100ng/side) and OT plus OTR-A on social and emotional behavior using a social preference paradigm, open field test and elevated plus maze test in female monogamous mandarin voles (Microtus mandarinus). We then examined whether different doses of the GABA_A receptor antagonist bicuculline (5, 10 and 100ng/side) affected the behavioral changes induced by intra-CeA microinjection of OT (1ng/side). We found that administration of OT to the CeA increased social preference, central area investigation times in the open field test, and visits, transitions and time spent in the open arms in the elevated plus maze test; all responses were dose-dependent. Administration of OT plus OTR-A to the CeA produced no effects. Administration of bicuculline in combination with OT to the CeA decreased social preference, central area investigation times in the open field test, and visits, transitions and time spent in the open arms of the elevated plus maze test. These data suggest that OT in the CeA facilitates sociality and reduces levels of anxiety by interacting with local GABA_A receptors.

Increased aggression and lack of maternal behavior in Dio3-deficient mice are associated with abnormalities in oxytocin and vasopressin systems

Thyroid hormones regulate many aspects of brain development and function, and alterations in the levels of thyroid hormone action lead to abnormal anxiety- and depression-like behaviors. A complement of factors in the brain function independently of circulating levels of hormone to strictly controlled local thyroid hormone signaling. A critical factor is the type 3 deiodinase (DIO3), which is located in neurons and protects the brain from excessive thyroid hormone. Here, we examined whether a local increase in brain thyroid hormone action secondary to DIO3 deficiency is of consequence for social behaviors. Although we did not observe alterations in sociability, Dio3-/- mice of both sexes exhibited a significant increase in aggression-related behaviors and mild deficits in olfactory function. In addition, 85% of Dio3-/- dams manifested no pup-retrieval behavior and increased aggression toward the newborns. The abnormal social behaviors of Dio3-/- mice were associated with sexually dimorphic alterations in the physiology of oxytocin (OXT) and arginine vasopressin (AVP), 2 neuropeptides with important roles in determining social interactions. These alterations included low adult serum levels of OXT and AVP, and an abnormal expression of Oxt, Avp and their receptors in the neonatal and adult hypothalamus. Our results demonstrate that DIO3 is essential for normal aggression and maternal behaviors, and indicate that abnormal local regulation of thyroid hormone action in the brain may contribute to the social deficits associated with neurodevelopmental disorders.

Chronic hindbrain administration of oxytocin is sufficient to elicit weight loss in diet-induced obese rats

Oxytocin (OT) administration elicits weight loss in diet-induced obese (DIO) rodents, nonhuman primates, and humans by reducing energy intake and increasing energy expenditure. Although the neurocircuitry underlying these effects remains uncertain, OT neurons in the paraventricular nucleus are positioned to control both energy intake and sympathetic nervous system outflow to interscapular brown adipose tissue (BAT) through projections to the hindbrain nucleus of the solitary tract and spinal cord. The current work was undertaken to examine whether central OT increases BAT thermogenesis, whether this effect involves hindbrain OT receptors (OTRs), and whether such effects are associated with sustained weight loss following chronic administration. To assess OT-elicited changes in BAT thermogenesis, we measured the effects of intracerebroventricular administration of OT on interscapular BAT temperature in rats and mice. Because fourth ventricular (4V) infusion targets hindbrain OTRs, whereas third ventricular (3V) administration targets both forebrain and hindbrain OTRs, we compared responses to OT following chronic 3V infusion in DIO rats and mice and chronic 4V infusion in DIO rats. We report that chronic 4V infusion of OT into two distinct rat models recapitulates the effects of 3V OT to ameliorate DIO by reducing fat mass. While reduced food intake contributes to this effect, our finding that 4V OT also increases BAT thermogenesis suggests that increased energy expenditure may contribute as well. Collectively, these findings support the hypothesis that, in DIO rats, OT action in the hindbrain evokes sustained weight loss by reducing energy intake and increasing BAT thermogenesis.

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.

Fibroblast growth factor 2 alters the oxytocin receptor in a developmental model of anxiety-like behavior in male rat pups

We aimed to determine the short-term effects of early-life stress in the form of maternal separation (MS) on anxiety-like behavior in male rat pups. In order to assess anxiety, we measured 40kHz separation-induced ultrasonic vocalizations (USV) on postnatal day (PND) 11. We further aimed to evaluate the potential involvement of two neurochemical systems known to regulate social and anxiety-like behaviors throughout life: oxytocin (OT) and fibroblast growth factor 2 (FGF2). For these purposes, we tested the effects of neonatal administration (on PND1) of an acute dose of FGF2 on USV and its potential interaction with MS. In addition, we validated the anxiolytic effects of OT and measured oxytocin receptor (OTR) gene expression, binding and epigenetic regulation via histone acetylation. Our results show that MS potentiated USV while acute administration of OT and FGF2 attenuated them. Further, we found that both FGF2 and MS increased OTR gene expression and the association of acH3K14 with the OTR promoter in the bed nucleus of the stria terminalis (BNST). Comparable changes, though not as pronounced, were also found for the central amygdala (CeA). Our findings suggest that FGF2 may exert its anxiolytic effects in male MS rats by a compensatory increase in the acetylation of the OTR promoter to overcome reduced OT levels in the BNST.

Rigorous tests of gene-environment interactions in a lab study of the oxytocin receptor gene (OXTR), alcohol exposure, and aggression

Naturalistic studies of gene-environment interactions (G X E) have been plagued by several limitations, including difficulty isolating specific environmental risk factors from other correlated aspects of the environment, gene-environment correlation (rGE ), and the use of a single genetic variant to represent the influence of a gene. We present results from 235 Finnish young men in two lab studies of aggression and alcohol challenge that attempt to redress these limitations of the extant G X E literature. Specifically, we use a latent variable modeling approach in an attempt to more fully account for genetic variation across the oxytocin receptor gene (OXTR) and to robustly test its main effects on aggression and its interaction with alcohol exposure. We also modeled aggression as a latent variable comprising various indices, including the average and maximum levels of aggression, the earliest trial on which aggression was expressed, and the proportion of trials on which the minimum and maximum levels of aggression were expressed. The best fitting model for the genetic variation across OXTR included six factors derived from an exploratory factor analysis, roughly corresponding to six haplotype blocks. Aggression levels were higher on trials in which participants were administered alcohol, won, or were provoked. There was a significant main effect of OXTR on aggression across studies after controlling for covariates. The interaction of OXTR and alcohol was also significant across studies, such that OXTR had stronger effects on aggression in the alcohol administration condition. © 2015 Wiley Periodicals, Inc.

Antisocial behavior and polymorphisms in the oxytocin receptor gene: findings in two independent samples

The quantitative genetic contribution to antisocial behavior is well established, but few, if any, genetic variants are established as risk factors. Emerging evidence suggests that the neuropeptide oxytocin (OXT) may modulate interpersonal aggression. We here investigated whether single-nucleotide polymorphisms (SNPs) in the OXT receptor gene (OXTR) are associated with the expression of antisocial behavior. A discovery sample, including both sexes, was drawn from the Child and Adolescent Twin Study in Sweden (CATSS; n=2372), and a sample from the Twin Study of Child and Adolescent Development (TCHAD; n=1232) was used for replication. Eight SNPs in OXTR, selected on previous associations with social and antisocial behavior, were genotyped in the participants of CATSS. Significant polymorphisms were subsequently genotyped in TCHAD for replication. Participants completed self-assessment questionnaires-Life History of Aggression (LHA; available only in CATSS), and Self-Reported Delinquency (SRD; available in both samples)-designed to capture antisocial behavior as continuous traits. In the discovery sample, the rs7632287 AA genotype was associated with higher frequency of antisocial behavior in boys, and this was then replicated in the second sample. In particular, overt aggression (directly targeting another individual) was strongly associated with this genotype in boys (P=6.2 × 10(-7) in the discovery sample). Meta-analysis of the results for antisocial behavior from both samples yielded P=2.5 × 10(-5). Furthermore, an association between rs4564970 and LHA (P=0.00013) survived correction in the discovery sample, but there was no association with the SRD in the replication sample. We conclude that the rs7632287 and rs4564970 polymorphisms in OXTR may independently influence antisocial behavior in adolescent boys. Further replication of our results will be crucial to understanding how aberrant social behavior arises, and would support the OXT receptor as one potential target in the treatment of aggressive antisocial behavior.

Plasma Oxytocin and Arginine-Vasopressin Levels in Children with Autism Spectrum Disorder in China: Associations with Symptoms

Autism spectrum disorder (ASD) is defined by impairments of social interaction and the presence of obsessive behaviors. The "twin" nonapeptides oxytocin (OXT) and arginine-vasopressin (AVP) are known to play regulatory roles in social behaviors. However, the plasma levels and behavioral relevance of OXT and AVP in children with ASD have seldom been investigated. It is also unknown whether their mothers have abnormal plasma peptide levels. Here, using well-established methods of neuropeptide measurement and a relatively large sample size, we determined the plasma levels of the two neuropeptides in 85 normal children, 84 children with ASD, and 31 mothers from each group of children. As expected, children with ASD had lower plasma OXT levels than gender-matched controls (P = 0.028). No such difference was found for plasma AVP concentrations. Correlation analysis showed that ASD children with higher plasma OXT concentrations tended to have less impairment of verbal communication (Rho = -0.22, P = 0.076), while those with higher plasma AVP levels tended to have lower levels of repetitive use of objects (Rho = -0.231, P = 0.079). Unlike the findings in children, maternal plasma OXT levels showed no group difference. However, plasma AVP levels in the mothers of ASD children tended to be lower than in the mothers of normal children (P = 0.072). In conclusion, our results suggest that the OXT system is dysregulated in children with ASD, and that OXT and AVP levels in plasma seem to be associated with specific autistic symptoms. The plasma levels of OXT or AVP in mothers and their ASD children did not seem to change in the same direction.

A Review of Oxytocin's Effects on the Positive, Negative, and Cognitive Domains of Schizophrenia

Schizophrenia is a disabling, heterogeneous disorder with clinical features that can be parsed into three domains: positive symptoms, negative symptoms, and cognitive deficits. Current antipsychotic drugs produce fairly robust clinical benefit against positive symptoms but typically have minimal therapeutic effects on negative symptoms and cognitive deficits. Oxytocin (OT) is a nonapeptide that, in addition to its role as a hormone regulating peripheral reproductive-relevant functions, acts as a neurotransmitter in the brain. Several lines of preclinical and clinical research suggest that the OT system may play a role in regulating the expression of schizophrenia spectrum disorders and that targeting the central OT system may yield novel treatments to address these symptoms. In this review, we summarize the extant preclinical and clinical evidence relevant to the role of OT in schizophrenia with particular emphasis on its putative therapeutic effects on each of the three above-mentioned clinical domains.

Oxytocin, Vasopressin, and the Motivational Forces that Drive Social Behaviors

The motivation to engage in social behaviors is influenced by past experience and internal state, but also depends on the behavior of other animals. Across species, the oxytocin (Oxt) and vasopressin (Avp) systems have consistently been linked to the modulation of motivated social behaviors. However, how they interact with other systems, such as the mesolimbic dopamine system, remains understudied. Further, while the neurobiological mechanisms that regulate prosocial/cooperative behaviors have been extensively examined, far less is understood about competitive behaviors, particularly in females. In this chapter, we highlight the specific contributions of Oxt and Avp to several cooperative and competitive behaviors and discuss their relevance to the concept of social motivation across species, including humans. Further, we discuss the implications for neuropsychiatric diseases and suggest future areas of investigation.

Translational and therapeutic potential of oxytocin as an anti-obesity strategy: Insights from rodents, nonhuman primates and humans

The fact that more than 78 million adults in the US are considered overweight or obese highlights the need to develop new, effective strategies to treat obesity and its associated complications, including type 2 diabetes, kidney disease and cardiovascular disease. While the neurohypophyseal peptide oxytocin (OT) is well recognized for its peripheral effects to stimulate uterine contraction during parturition and milk ejection during lactation, release of OT within the brain is implicated in prosocial behaviors and in the regulation of energy balance. Previous findings indicate that chronic administration of OT decreases food intake and weight gain or elicits weight loss in diet-induced obese (DIO) mice and rats. Furthermore, chronic systemic treatment with OT largely reproduces the effects of central administration to reduce weight gain in DIO and genetically obese rodents at doses that do not appear to result in tolerance. These findings have now been recently extended to more translational models of obesity showing that chronic subcutaneous or intranasal OT treatment is sufficient to elicit body weight loss in DIO nonhuman primates and pre-diabetic obese humans. This review assesses the potential use of OT as a therapeutic strategy for treatment of obesity in rodents, nonhuman primates, and humans, and identifies potential mechanisms that mediate this effect.

Acute and repeated intranasal oxytocin administration exerts anti-aggressive and pro-affiliative effects in male rats

Socio-emotional deficits and impulsive/aggressive outbursts are prevalent symptoms of many neuropsychiatric disorders, and intranasal administration of oxytocin (OXT) is emerging as a putative novel therapeutic approach to curb these problems. Recently, we demonstrated potent anti-aggressive and pro-social effects of intracerebroventricular (icv) OXT administration in male rats. The present study tested whether similar behavioral effects are induced when OXT is delivered intranasally. Heart-rate and blood-pressure responses were telemetrically monitored to investigate whether peripheral physiological effects were provoked after intranasal OXT administration. Intranasal OXT administration in resident animals reduced offensive aggression and increased social exploration toward an unfamiliar male intruder. Using a partner-preference test, intranasal OXT also strengthened the bonding between the male resident and its female partner. No changes in cardiovascular (re)activity were found, indicating an absence of direct peripheral physiological effects after intranasal OXT treatment. In conclusion, although the precise route and mechanisms of nose-to-brain transport/communication remain to be elucidated, our data demonstrated intranasal OXT to be an effective application method for suppressing intermale aggression and enhancing social affiliation.

Chronic oxytocin administration inhibits food intake, increases energy expenditure, and produces weight loss in fructose-fed obese rhesus monkeys

Despite compelling evidence that oxytocin (OT) is effective in reducing body weight (BW) in diet-induced obese (DIO) rodents, studies of the effects of OT in humans and rhesus monkeys have primarily focused on noningestive behaviors. The goal of this study was to translate findings in DIO rodents to a preclinical translational model of DIO. We tested the hypothesis that increased OT signaling would reduce BW in DIO rhesus monkeys by inhibiting food intake and increasing energy expenditure (EE). Male DIO rhesus monkeys from the California National Primate Research Center were adapted to a 12-h fast and maintained on chow and a daily 15% fructose-sweetened beverage. Monkeys received 2× daily subcutaneous vehicle injections over 1 wk. We subsequently identified doses of OT (0.2 and 0.4 mg/kg) that reduced food intake and BW in the absence of nausea or diarrhea. Chronic administration of OT for 4 wk (0.2 mg/kg for 2 wk; 0.4 mg/kg for 2 wk) reduced BW relative to vehicle by 3.3 ± 0.4% (≈0.6 kg; P < 0.05). Moreover, the low dose of OT suppressed 12-h chow intake by 26 ± 7% (P < 0.05). The higher dose of OT reduced 12-h chow intake by 27 ± 5% (P < 0.05) and 8-h fructose-sweetened beverage intake by 18 ± 8% (P < 0.05). OT increased EE during the dark cycle by 14 ± 3% (P < 0.05) and was associated with elevations of free fatty acids and glycerol and reductions in triglycerides suggesting increased lipolysis. Together, these data suggest that OT reduces BW in DIO rhesus monkeys through decreased food intake as well as increased EE and lipolysis.