The role of oxytocin in mating and pregnancy

Existential neuroscience: effects of mortality salience on the neurocognitive processing of attractive opposite-sex faces

Being reminded of the inherently finite nature of human existence has been demonstrated to elicit strivings for sexual reproduction and the formation and maintenance of intimate relationships. Recently, it has been proposed that the perception of potential mating partners is influenced by mortality salience. Using functional magnetic resonance imaging, we investigated the neurocognitive processing of attractive opposite-sex faces after priming with death-related words for heterosexual men and women. Significant modulations of behavioral and neural responses were found when participants were requested to decide whether they would like to meet the presented person. Men were more in favor of meeting attractive women after being primed with death-related words compared to a no-prime condition. Increased neural activation could be found under mortality salience in the left anterior insula and the adjacent lateral prefrontal cortex (lPFC) for both men and women. As previously suggested, we believe that the lPFC activation reflects an approach-motivated defense mechanism to overcome concerns that are induced by being reminded of death and dying. Our results provide insight on a neurocognitive level that approach motivation in general, and mating motivation in particular is modulated by mortality salience.

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

An oxytocin-induced facilitation of neural and emotional responses to social touch correlates inversely with autism traits

Social communication through touch and mutual grooming can convey highly salient socio-emotional signals and has been shown to involve the neuropeptide oxytocin (OXT) in several species. Less is known about the modulatory influence of OXT on the neural and emotional responses to human interpersonal touch. The present randomized placebo (PLC)-controlled within-subject pharmaco-functional magnetic resonance imaging (fMRI) study was designed to test the hypothesis that a single intranasal dose of synthetic OXT (24 IU) would facilitate both neural and emotional responses to interpersonal touch in a context- (female vs male touch) and trait- (autistic trait load) specific manner. Specifically, the experimental rationale was to manipulate the reward value of interpersonal touch independent of the intensity and type of actual cutaneous stimulation administered. Thus, 40 heterosexual males believed that they were touched by either a man or a woman, although in fact an identical pattern of touch was always given by the same female experimenter blind to condition type. Our results show that OXT increased the perceived pleasantness of female, but not male touch, and associated neural responses in insula, precuneus, orbitofrontal, and pregenual anterior cingulate cortex. Moreover, the behavioral and neural effects of OXT were negatively correlated with autistic-like traits. Taken together, this is the first study to show that the perceived hedonic value of human heterosexual interpersonal touch is facilitated by OXT in men, but that its behavioral and neural effects in this context are blunted in individuals with autistic traits.

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.

Differential effects of intranasal oxytocin on sexual experiences and partner interactions in couples

Knowledge about the effects of the neuropeptide oxytocin (OXT) on human sexual behaviors and partner interactions remains limited. Based on our previous studies, we hypothesize that OXT should be able to positively influence parameters of sexual function and couple interactions. Employing a naturalistic setting involving 29 healthy heterosexual couples (n=58 participants), we analyzed the acute effects of intranasally administered OXT (24IU) on sexual drive, arousal, orgasm and refractory aspects of sexual behavior together with partner interactions. Data were assessed by psychometric instruments (Acute Sexual Experiences Scale, Arizona Sexual Experience Scale) as well as biomarkers, such as cortisol, α-amylase and heart rate. Intranasal OXT administration did not alter "classical" parameters of sexual function, such as sexual drive, arousal or penile erection and lubrication. However, analysis of variance and a hierarchical linear model (HLM) revealed specific effects related to the orgasmic/post-orgasmic interval as well as parameters of partner interactions. According to HLM analysis, OXT increased the intensity of orgasm, contentment after sexual intercourse and the effect of study participation. According to ANOVA analysis, these effects were more pronounced in men. Men additionally indicated higher levels of sexual satiety after sexual intercourse with OXT administration. Women felt more relaxed and subgroups indicated better abilities to share sexual desires or to empathize with their partners. The effect sizes were small to moderate. Biomarkers indicated moderate psychophysiological activation but were not affected by OXT, gender or method of contraception. Using a naturalistic setting, intranasal OXT administration in couples exerted differential effects on parameters of sexual function and partner interactions. These results warrant further investigations, including subjects with sexual and relationship problems.

Oxytocin enhances brain reward system responses in men viewing the face of their female partner

The biological mechanisms underlying long-term partner bonds in humans are unclear. The evolutionarily conserved neuropeptide oxytocin (OXT) is associated with the formation of partner bonds in some species via interactions with brain dopamine reward systems. However, whether it plays a similar role in humans has as yet not been established. Here, we report the results of a discovery and a replication study, each involving a double-blind, placebo-controlled, within-subject, pharmaco-functional MRI experiment with 20 heterosexual pair-bonded male volunteers. In both experiments, intranasal OXT treatment (24 IU) made subjects perceive their female partner's face as more attractive compared with unfamiliar women but had no effect on the attractiveness of other familiar women. This enhanced positive partner bias was paralleled by an increased response to partner stimuli compared with unfamiliar women in brain reward regions including the ventral tegmental area and the nucleus accumbens (NAcc). In the left NAcc, OXT even augmented the neural response to the partner compared with a familiar woman, indicating that this finding is partner-bond specific rather than due to familiarity. Taken together, our results suggest that OXT could contribute to romantic bonds in men by enhancing their partner's attractiveness and reward value compared with other women.

Ancient neuromodulation by vasopressin/oxytocin-related peptides

Neuropeptidergic signaling is widely adopted by animals for the regulation of physiology and behavior in a rapidly changing environment. The vasopressin/oxytocin neuropeptide family originates from an ancestral peptide precursor in the antecedent of protostomian and deuterostomian animals. In vertebrates, vasopressin and oxytocin have both hormonal effects on peripheral target tissues, such as in the regulation of reproduction and water balance, and neuromodulatory actions in the central nervous system controlling social behavior and cognition. The recent identification of vasopressin/oxytocin-related signaling in C. elegans reveals that this peptidergic system is widespread among nematodes. Genetic analysis of the C. elegans nematocin system denotes vasopressin/oxytocin-like peptides as ancient neuromodulators of neuronal circuits involved in reproductive behavior and associative learning, whereas former invertebrate studies focused on conserved peripheral actions of this peptide family. Nematocin provides neuromodulatory input into the gustatory plasticity circuit as well as into distinct male mating circuits to generate a coherent mating behavior. Molecular interactions are comparable to those underlying vasopressin- and oxytocin-mediated effects in the mammalian brain. Understanding how the vasopressin/oxytocin family fine-tunes neuronal circuits for social behavior, learning and memory poses a major challenge. Functional conservation of these effects in nematodes and most likely in other invertebrates enables the development of future models to help answering this question.

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.

Intranasal administration of oxytocin: behavioral and clinical effects, a review

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The mechanisms behind the effects of IN-applied substances need more attention.

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The mechanisms involved in the brain-distribution of IN-OT are completely unexplored.

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The possibly cascading effects of IN-OT on the intrinsic OT-system require serious investigation.

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IN-OT induces clear and specific changes in neural activation.

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IN-OT is a promising approach to treat certain clinical symptoms.

The intranasal (IN-) administration of substances is attracting attention from scientists as well as pharmaceutical companies. The effects are surprisingly fast and specific. The present review explores our current knowledge about the routes of access to the cranial cavity. ‘Direct-access-pathways’ from the nasal cavity have been described but many additional experiments are needed to answer a variety of open questions regarding anatomy and physiology.

Among the IN-applied substances oxytocin (OT) has an extensive history. Originally applied in women for its physiological effects related to lactation and parturition, over the last decade most studies focused on their behavioral ‘prosocial’ effects: from social relations and ‘trust’ to treatment of ‘autism’.

Only very recently in a microdialysis study in rats and mice, the ‘direct-nose-brain-pathways’ of IN-OT have been investigated directly, implying that we are strongly dependent on results obtained from other IN-applied substances. Especially the possibility that IN-OT activates the ‘intrinsic’ OT-system in the hypothalamus as well needs further clarification.

We conclude that IN-OT administration may be a promising approach to influence human communication but that the existing lack of information about the neural and physiological mechanisms involved is a serious problem for the proper understanding and interpretation of the observed effects.

Neurophysiological mechanisms underlying affiliative social behavior: insights from comparative research

Humans are intensely social animals, and healthy social relationships are vital for proper mental health (see Lim and Young, 2006). By using animal models, the behavior, mental, and physiological processes of humans can be understood at a level that cannot be attained by studying human behavior and the human brain alone. The goals of this review are threefold. First, we define affiliative social behavior and describe the primary relationship types in which affiliative relationships are most readily observed--the mother-infant bond and pair-bonding. Second, we summarize neurophysiological studies that have investigated the role of neurohypophyseal nanopeptides (oxytocin and vasopressin) and the catecholamine dopamine in regulating affiliative social behavior and the implications of said research for our understanding of human social behavior. Finally, we discuss the merits and limitations of the using a comparative approach to enhance our understanding of the mechanisms underlying human affiliative social behavior.

The behavioral, anatomical and pharmacological parallels between social attachment, love and addiction

RATIONALE

Love has long been referred to as an addiction in literature and poetry. Scientists have often made comparisons between social attachment processes and drug addiction, and it has been suggested that the two may share a common neurobiological mechanism. Brain systems that evolved to govern attachments between parents and children and between monogamous partners may be the targets of drugs of abuse and serve as the basis for addiction processes.

OBJECTIVES

Here, we review research on drug addiction in parallel with research on social attachments, including parent-offspring attachments and social bonds between mating partners. This review focuses on the brain regions and neurochemicals with the greatest overlap between addiction and attachment and, in particular, the mesolimbic dopamine (DA) pathway.

RESULTS

Significant overlap exists between these two behavioral processes. In addition to conceptual overlap in symptomatology, there is a strong commonality between the two domains regarding the roles and sites of action of DA, opioids, and corticotropin-releasing factor. The neuropeptides oxytocin and vasopressin are hypothesized to integrate social information into attachment processes that is not present in drug addiction.

CONCLUSIONS

Social attachment may be understood as a behavioral addiction, whereby the subject becomes addicted to another individual and the cues that predict social reward. Understandings from both fields may enlighten future research on addiction and attachment processes.

Simultaneous oxytocin and arg-vasopressin measurements in microdialysates using capillary liquid chromatography-mass spectrometry

Oxytocin (OXT) and arg-vasopressin (AVP) are nonapeptides with many important functions both peripherally and centrally. Intracerebral microdialysis has helped characterize their importance in regulating complex social and emotional processes. Radioiummunoassay is the most commonly used analytical method used for OXT and AVP measurements in microdialysates. These measurements have several well-known issues including single peptide per assay limit, possible cross-reactivity between structurally related peptides, and laborious sample preparation with radioactive materials. Here we demonstrate the use of capillary LC-MS(3) for measuring OXT and AVP simultaneously in dialysates at a 10 min sampling frequency. Microdialysate samples required no preparation and instrumentation was commercially available. Microdialysis probes made with polyacrylonitrile membranes were suitable for high level recovery of the peptides in vitro and in vivo. Responses were linear from 1 to 100 pM. Matrix effect was assessed by standard addition experiments and by comparing signal intensities of OXT and AVP standards made in aCSF or dialysate. It was determined that the online washing step used on this setup was adequate for removing contaminants which interfere with electrospray ionization efficiency. In vivo, both peptides were stimulated by high K(+) (75 mM) aCSF perfusion in the paraventricular nucleus (PVN). Also, a systemic injection of high Na(+) (2M) caused a rapid and transient increase in PVN OXT while AVP increased only after 1.5h. Our findings suggest that capillary LC-MS(3) is a straightforward method for monitoring OXT and AVP simultaneously from complex samples such as dialysates.