Molecular regulation of the oxytocin receptor in peripheral organs

Estrogen regulates the transcription of guppy isotocin receptors

Estrogen can regulate oxytocin receptor expression, which is mediated through estrogen receptors (ESRs) in mammals, initiating parturition. To further study the reproductive physiological process of ovoviviparous teleosts, guppies (Poecilia reticulata) were employed as the research model in the present study to identify the transcriptional regulation of ESRs on isotocin receptors (itrs). Since guppy embryos develop inside the ovary, in the present study, the levels of itrs in the ovarian stroma of pregnant female guppies treated with estradiol (E2) in vitro were tested. E2 increased only itr2 mRNA levels 3 h post-treatment, with no variation in itr1 mRNA expression levels. In vivo, pregnant guppies were immersed in different concentrations of E2, significantly increasing the relative expression levels of itr1 and itr2 in the ovary. Moreover, based on dual-fluorescence in situ hybridization (ISH), both esrs and itrs mRNAs were localized in the same cells around the embryos in the ovary. To further investigate the regulation of itr transcription by estrogen, a luciferase reporter assay was performed, and the results demonstrated that E2 treatment could induce E2-dependent repression of luciferase activity in cells transfected with ESR1. However, overexpression of ESR2a or ESR2b caused a robust ligand-independent increase in itr2 promoter activity. Deletion analysis of the itr2 promoter indicated that there were novel potential ESR transcription factor-binding sites at -360 bp upstream of the 5' end of the itr2 promoter. Overall, our study provided novel results regarding the ESRs mediating the onset of parturition in ovoviviparous teleosts.

Novel Risk Variants in the Oxytocin Receptor Gene (OXTR) Possibly Linked to and Associated with Familial Type 2 Diabetes

The oxytocin system is well-known for its role in social bonding and reproduction. Recently, the oxytocin system was found to play other metabolic roles such as regulation of food intake, peripheral glucose uptake, and insulin sensitivity. Variants in OXTR gene have been associated with overeating, increased cardiovascular risk, and type 2 diabetes (T2D). We tested 20 microarray-derived single nucleotide polymorphisms in the OXTR gene in 212 Italian families with rich family history for T2D and found four novel and one previously reported variant suggestively significant for linkage and association with the risk of T2D. Our study has shed some light into the genetics of susceptibility to T2D at least in Italian families.

Involvement of oxytocin receptor deficiency in psychiatric disorders and behavioral abnormalities

Oxytocin and its target receptor (oxytocin receptor, OXTR) exert important roles in the regulation of complex social behaviors and cognition. The oxytocin/OXTR system in the brain could activate and transduce several intracellular signaling pathways to affect neuronal functions or responses and then mediate physiological activities. The persistence and outcome of the oxytocin activity in the brain are closely linked to the regulation, state, and expression of OXTR. Increasing evidence has shown that genetic variations, epigenetic modification states, and the expression of OXTR have been implicated in psychiatric disorders characterized by social deficits, especially in autism. Among these variations and modifications, OXTR gene methylation and polymorphism have been found in many patients with psychiatric disorders and have been considered to be associated with those psychiatric disorders, behavioral abnormalities, and individual differences in response to social stimuli or others. Given the significance of these new findings, in this review, we focus on the progress of OXTR's functions, intrinsic mechanisms, and its correlations with psychiatric disorders or deficits in behaviors. We hope that this review can provide a deep insight into the study of OXTR-involved psychiatric disorders.

Socio-behavioral dysfunction in disorders of hypothalamic-pituitary involvement: The potential role of disease-induced oxytocin and vasopressin signaling deficits

Disorders involving hypothalamic and pituitary (HPIT) structures-including craniopharyngioma, Langerhans cell histiocytosis, and intracranial germ cell tumors-can disrupt brain and endocrine function. An area of emerging clinical concern in patients with these disorders is the co-occurring socio-behavioral dysfunction that persists after standard hormone replacement therapy. Although the two neuropeptides most implicated in mammalian social functioning (oxytocin and arginine vasopressin) are of hypothalamic origin, little is known about how disease-induced damage to HPIT structures may disrupt neuropeptide signaling and, in turn, impact patients' socio-behavioral functioning. Here we provide a clinical primer on disorders of HPIT involvement and a review of neuropeptide signaling and socio-behavioral functioning in relevant animal models and patient populations. This collective evidence suggests that neuropeptide signaling disruptions contribute to socio-behavioral deficits experienced by patients with disorders of HPIT involvement. A better understanding of the biological underpinnings of patients' socio-behavioral symptoms is now needed to enable the development of the first targeted pharmacological strategies by which to manage patients' socio-behavioral dysfunction.

Oxytocin infusion rates for maintaining uterine tone during non-elective cesarean section in laboring patients: a randomized, controlled trial

PURPOSE

Oxytocin infusions for uterine tone maintenance are recommended following initial low oxytocin doses during cesarean section. Very limited literature is available on the optimal infusion rates in laboring patients who have been earlier exposed to oxytocin.

METHODS

105 patients, having received oxytocin for induction/augmentation of labor, received oxytocin infusions at rates of 2.5 IU/h (Group 2.5), 5 IU/h (Group 5) or 10 IU/h (Group 10) following 3 IU slow bolus. The primary outcome measure was estimated intraoperative blood loss; secondary outcome measures included uterine tone adequacy, requirements for additional uterotonics, and any side effects. Minor postpartum hemorrhage (PPH) was defined as blood loss > 500 ml and major/severe hemorrhage as blood loss > 1000 ml.

RESULTS

Group 10 had minimum blood loss (311.1 ± 44.9 ml) and uterotonic requirements compared to other groups (p < 0.001). Group 2.5 had maximum blood loss (549.4 ± 74.3 ml) and uterotonic requirements; Group 5 had intermediate values (402.0 ± 49.5 ml). Twenty-six patients in group 2.5 had minor PPH against only one in group 5 and none in group 10 (p < 0.001). No patient in either group had major PPH. The incidence of hypotension was higher in group 10 than in group 2.5 (p = 0.004). Nausea and vomiting were also more frequent in group 10 than in the other two groups.

CONCLUSION

Oxytocin infusions at 5 IU/h and 10 IU/h are more effective in reducing blood loss and preventing PPH than 2.5 IU/h. The dose of 10 IU/h, although the most efficacious, is associated with a high incidence of side effects. Hence, further studies are needed to find out the optimal maintenance infusion rate of oxytocin during cesarean section in laboring patients who have received oxytocin earlier.

Effects of an ω3 fatty acid-biased diet on luteolysis, parturition, and uterine prostanoid synthesis in pregnant mice

The ω3 polyunsaturated fatty acids (PUFAs) are known to have beneficial effects on health and diseases, and hence their intake is encouraged. However, it remains unknown as to how ω3 PUFAs affect female reproduction processes, in which ω6 PUFA-derived prostaglandin (PG) E2 and PGF2α play crucial roles. We therefore compared female reproductive performance between ω3 PUFA-biased linseed oil diet-fed (Lin) mice and ω6 PUFA-biased soybean oil diet-fed (Soy) mice. In Lin mice, the uterine levels of arachidonic acid (AA) and eicosapentaenoic acid (EPA) were 0.42 fold and 16 fold of those in Soy mice, respectively, with the EPA/AA ratio being 0.7 (vs 0.02 in Soy mice). Lin mice showed no alterations in any of the fertility indexes, including luteolysis and parturition. The uterine PG synthesis profiles of Lin mice were similar to those of Soy mice, but the levels of PGF2α and PGE2 were 50% of those in Soy mice, as a result of the increased EPA/AA ratio. PGF3α and PGE3 were undetectable in the uterine tissues of Soy and Lin mice. Interestingly, in Lin mice, 'luteolytic' PGF2α synthesis was considerably maintained even in the ω6 PUFA-reduced condition. These results suggest the existence of an elaborate mechanism securing PGF2α synthesis to a level that is sufficient for triggering luteolysis and parturition, even under ω6 PUFA-reduced conditions.

Oxytocin in Women's Health and Disease

Oxytocin (OT) is a nonapeptide mainly produced in the supraoptic and paraventricular nuclei. OT in the brain and blood has extensive functions in both mental and physical activities. These functions are mediated by OT receptors (OTRs) that are distributed in a broad spectrum of tissues with dramatic sexual dimorphism. In both sexes, OT generally facilitates social cognition and behaviors, facilitates parental behavior and sexual activity and inhibits feeding and pain perception. However, there are significant differences in OT levels and distribution of OTRs in men from women. Thus, many OT functions in men are different from women, particularly in the reproduction. In men, the reproductive functions are relatively simple. In women, the reproductive functions involve menstrual cycle, pregnancy, parturition, lactation, and menopause. These functions make OT regulation of women's health and disease a unique topic of physiological and pathological studies. In menstruation, pre-ovulatory increase in OT secretion in the hypothalamus and the ovary can promote the secretion of gonadotropin-releasing hormone and facilitate ovulation. During pregnancy, increased OT synthesis and preterm release endow OT system the ability to promote maternal behavior and lactation. In parturition, cervix expansion-elicited pulse OT secretion and uterine OT release accelerate the expelling of fetus and reduce postpartum hemorrhage. During lactation, intermittent pulsatile OT secretion is necessary for the milk-ejection reflex and maternal behavior. Disorders in OT secretion can account for maternal depression and hypogalactia. In menopause, the reduction of OT secretion accounts for many menopausal symptoms and diseases. These issues are reviewed in this work.

The Effects of Oxytocin on Appetite Regulation, Food Intake and Metabolism in Humans

The hypothalamic peptide oxytocin and its receptor are involved in a range of physiological processes, including parturition, lactation, cell growth, wound healing, and social behavior. More recently, increasing evidence has established the effects of oxytocin on food intake, energy expenditure, and peripheral metabolism. In this review, we provide a comprehensive description of the central oxytocinergic system in which oxytocin acts to shape eating behavior and metabolism. Next, we discuss the peripheral beneficial effects oxytocin exerts on key metabolic organs, including suppression of visceral adipose tissue inflammation, skeletal muscle regeneration, and bone tissue mineralization. A brief summary of oxytocin actions learned from animal models is presented, showing that weight loss induced by chronic oxytocin treatment is related not only to its anorexigenic effects, but also to the resulting increase in energy expenditure and lipolysis. Following an in-depth discussion on the technical challenges related to endogenous oxytocin measurements in humans, we synthesize data related to the association between endogenous oxytocin levels, weight status, metabolic syndrome, and bone health. We then review clinical trials showing that in humans, acute oxytocin administration reduces food intake, attenuates fMRI activation of food motivation brain areas, and increases activation of self-control brain regions. Further strengthening the role of oxytocin in appetite regulation, we review conditions of hypothalamic insult and certain genetic pathologies associated with oxytocin depletion that present with hyperphagia, extreme weight gain, and poor metabolic profile. Intranasal oxytocin is currently being evaluated in human clinical trials to learn whether oxytocin-based therapeutics can be used to treat obesity and its associated sequela. At the end of this review, we address the fundamental challenges that remain in translating this line of research to clinical care.

The vagus nerve mediates the suppressing effects of peripherally administered oxytocin on methamphetamine self-administration and seeking in rats

The neuropeptide oxytocin has emerged as a promising pharmacotherapy for methamphetamine (METH) addiction, and clinical trials of intranasal oxytocin are underway. However, there is debate as to how peripherally administered oxytocin alters brain signalling to modulate addiction processes. Interestingly, there is evidence for functional interactions between peripheral oxytocin administration and the vagus nerve. Therefore, this study investigated whether the effects of peripherally administered oxytocin require vagal signalling to reduce METH self-administration and reinstatement of METH-seeking behaviours. Male and female Sprague-Dawley rats underwent surgery for jugular catheterisation and either subdiaphragmatic vagotomy (SDV) or a sham operation. Rats were trained to self-administer METH, and the effect of peripherally administered oxytocin on METH intake was assessed. Rats then underwent extinction, and effects of oxytocin were assessed on cue- and METH-induced reinstatement of METH-seeking. Oxytocin treatment robustly attenuated METH intake in both sexes, and SDV entirely prevented the suppressant effect of oxytocin (0.3 mg/kg) on METH intake, and partially prevented the effects of 1 mg/kg oxytocin in both sexes. After extinction, SDV decreased the suppressing effects of oxytocin on cue- and METH-primed reinstatement in males, but not females. SDV was functionally confirmed by measuring food intake following administration of the vagal dependent peptide, cholecyostokin-8. Our data suggest that vagus nerve signalling is required for the inhibitory effects of peripherally administered oxytocin on METH self-administration and reinstatement, and that this vagal dependency is partially mediated by sex and drug withdrawal. This study has implications for the use of oxytocin as a therapy for METH use disorder for both sexes.

Plasma Oxytocin Concentrations During and After Gestation in Japanese Pregnant Women Affected by Anxiety Disorder and Endometriosis

Background

Oxytocin has a key role in mother-infant bonding, maternal care, social interaction, and stress-related psychiatric disorders. However, the factors determining oxytocin concentrations during and after pregnancy such as medical history related to nursing or parental behavior are unknown. To elucidate these, we analyzed the relationships between oxytocin concentrations during and after pregnancy, and medical history assessed in the Japan Environment and Children's Study (JECS).

Methods

We then selected the pregnant women with a medical history of anxiety disorder and endometriosis as cases and pregnant women without medical history as controls adjusting the cohort for age and parity for a nested case-control study, after which 162 women remained for analysis. We evaluated 162 pregnant women from JECS using answers provided in a questionnaire and by measuring plasma oxytocin concentration by ELISA during the first (T1) and second (T2) trimesters of pregnancy, and after childbirth (T3).

Results

Oxytocin concentration increased in a time dependent manner, consistent with previous reports. There were weak negative correlations between oxytocin concentration at T1 and the mother's age and height, but no correlation with other factors. The mean oxytocin concentrations of pregnant women with a history of an anxiety disorder (n = 7) and endometriosis (n = 13) were significantly lower than those of pregnant women with no such history at T2 and T3.

Conclusion

These results suggest that oxytocin concentrations during and after pregnancy were affected by a past history of anxiety disorder and endometriosis. This is the first study of the relationship between oxytocin concentration and endometriosis. To elucidate the molecular mechanisms, further study is needed.

In vitro contractile responses of human detrusor smooth muscle to oxytocin: does it really have effect?

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate the contractile effects of oxytocin (OT) in human detrusor muscle in in vitro conditions.

MATERIAL AND METHODS

Human detrusor muscle samples were obtained from seven patients that undergone radical cystectomy. Four female Wistar rats' uterine samples were used as control. Contractile responses were tested of carbachol in organ bath. Cumulative concentration response curves were constructed to OT and then the strips were incubated with atosiban (OT antagonist) and a second concentration response curve to OT were constructed.

RESULTS

Carbachol, contracted all human strips for the functionality test whereas OT in any concentrations did not produce significant contraction on all human strips. In only one bladder strip and in a very high concentration slight contraction was recorded. Moreover no contractile response was recorded in any OT concentrations in the presence of atosiban. The rat uterine strips responded to OT in a dose dependent manner. Atosiban, the OT receptor antagonist diminished totally those contractile responses.

CONCLUSION

It is been demonstrated here that there is no contractile response to OT in human detrusor muscle. These findings should be supported by further investigations determining the presence of the OT receptor in human detrusor.

Are We missing out the role of oxytocin in overactive bladder syndrome?

Overactive bladder (OAB) is characterized by the storage symptoms of urgency with or without urgency incontinence. Although there is no clear cause of this idiopathic disease, overall prevalence of OAB symptoms in individuals aged 40 years old is more than 15%. Oxytocin, which is one of the most powerful contracting neuropeptide, was also shown to exhibit high intrinsic contractile activity on detrusor muscle. Oxytocin receptor antagonists that inhibit of bladder activity might offer new insights into the treatment of OAB.

Insulin-Regulated Aminopeptidase in Women with Breast Cancer: A Role beyond the Regulation of Oxytocin and Vasopressin

Simple Summary

Insulin-regulated aminopeptidase (IRAP) is a well-known enzyme involved mainly in the regulation of the peptide hormones, oxytocin and vasopressin. However, this enzyme activity has hardly been analyzed in breast cancer patients. Additionally, the influence of both the hormonal status (pre or postmenopause) and the administration of neoadjuvant chemotherapy have rarely been studied. We show that there is a weak association between IRAP activity and the circulating levels of peptide hormones with variations depending on the hormonal status and the neoadjuvant treatment, and propose a role beyond oxytocin and vasopressin regulation that is related to the local mammary renin-angiotensin system and glucose transportation to the cells.

Abstract

Insulin-regulated aminopeptidase (IRAP) is the only enzyme known to cleave oxytocin and vasopressin; however, it is also the high-affinity binding site for angiotensin IV (AngIV) receptor type 4 (AT4) ligands and it is related to insulin-dependent glucose transporters through the translocation of the glucose transporter type 4 (GLUT4). Previous studies have demonstrated an association between IRAP activity and the number and size of mammary tumors in an animal model of breast cancer (BC). Also, a highly significant increase in IRAP activity has been found in BC tissue from women patients. Here, we found no changes in circulating IRAP in premenopausal (preMP) women, but it increased significantly in postmenopausal (postMP) women not treated with neoadjuvant chemotherapy (NACH). However, in women treated with NACH, IRAP activity increased in both preMP and postMP women. Two years of follow-up indicated lower levels of IRAP activity in untreated preMP women, but a return to control levels in untreated postMP women, while IRAP activity returned to control levels in women treated with NACH. Circulating oxytocin decreased in both preMP and postMP women during the follow-up period. Differences in Oxytocin appeared between preMP and postMP women treated with NACH, but not in women who were not treated with NACH. On the contrary, circulating vasopressin increased in untreated and treated preMP and postMP women, with most of the differences related to the hormonal status as well as the neoadjuvant treatment during the two year follow-up We propose that IRAP is involved in mechanisms related not only to oxytocin and/or vasopressin regulation, but also to the local mammary RAS through AngIV and its role in glucose transportation through the IRAP/GLUT4 system.

Aberrant expression of oxytocin receptor in endometrium and decidua in women who have experienced recurrent implantation failure

OBJECTIVE

To detect the oxytocin receptor (OTR) expression levels in the endometrium and decidua from women who have experienced recurrent implantation failure (RIF) and fertile women.

DESIGN

Laboratory study using human endometrial and decidual samples.

SETTINGS

University-affiliated hospital.

PATIENT(S)

Six patients with RIF and six fertile women were recruited for endometrial sampling on day 20-24 of the menstrual cycle. Decidual tissues were collected from women who had a history of RIF and experienced a spontaneous abortion at 6-8 weeks of gestation (n = 8) and women with healthy pregnancies that terminated for nonmedical reasons (n = 8).

INTERVENTION

None.

MAIN OUTCOME MEASURE(S)

OTR expression in the endometrial and decidual tissues was detected with the use of real-time quantitative polymerase chain reaction and Western blotting.

RESULT(S)

OTR protein and mRNA were significantly increased in the endometria of RIF patients. In the decidua, OTR protein was significantly up-regulated in the RIF group, whereas mRNA was significantly decreased in this group.

CONCLUSION(S)

Women who experienced RIF presented with an aberrant expression pattern of OTR in the endometria and decidua.

Oxytocin in the Male Reproductive Tract; The Therapeutic Potential of Oxytocin-Agonists and-Antagonists

In this review, the role of oxytocin and oxytocin-like agents (acting via the oxytocin receptor and belonging to the oxytocin-family) in the male reproductive tract is considered. Previous research (dating back over 60 years) is revised and connected with recently found aspects of the role oxytocin plays in male reproductive health. The local expression of oxytocin and its receptor in the male reproductive tract of different species is summarized. Colocalization and possible crosstalk to other agents and receptors and their resulting effects are discussed. The role of the newly reported oxytocin focused signaling pathways in the male reproductive tract, other than mediating contractility, is critically examined. The structure and effect of the most promising oxytocin-agonists and -antagonists are reviewed for their potential in treating male disorders with origins in the male reproductive tract such as prostate diseases and ejaculatory disorders.

Oxytocin reduces adipose tissue inflammation in obese mice

BACKGROUND

Obesity and adipose tissue expansion is characterized by a chronic state of systemic inflammation that contributes to disease. The neuropeptide, oxytocin, working through its receptor has been shown to attenuate inflammation in sepsis, wound healing, and cardiovascular disease. The current study examined the effects of chronic oxytocin infusions on adipose tissue inflammation in a murine model of obesity, the leptin receptor-deficient (db/db) mouse.

METHODS

The effect of obesity on oxytocin receptor protein and mRNA expression in adipose tissue was evaluated by Western blotting and real-time polymerase chain reaction. Mice were implanted with osmotic minipumps filled with oxytocin or vehicle for 8 weeks. At study endpoint adipose tissue inflammation was assessed by measurement of cytokine and adipokine mRNA tissue levels, adipocyte size and macrophage infiltration via histopathology, and plasma levels of adiponectin and serum amyloid A as markers of systemic inflammation.

RESULTS

The expression of adipose tissue oxytocin receptor was increased in obese db/db mice compared to lean controls. In adipose tissue oxytocin infusion reduced adipocyte size, macrophage infiltration, IL-6 and TNFα mRNA expression, and increased the expression of the anti-inflammatory adipokine, adiponectin. In plasma, oxytocin infusion reduced the level of serum amyloid A, a marker of systemic inflammation, and increased circulating adiponectin.

CONCLUSIONS

In an animal model of obesity and diabetes chronic oxytocin treatment led to a reduction in visceral adipose tissue inflammation and plasma markers of systemic inflammation, which may play a role in disease progression.

Oxytocin mediated cardioprotection is independent of coronary endothelial function in rats

The cardioprotective effect of oxytocin (OT) has been well established. However, there are no related studies on the role of endothelia in oxytocin-induced cardioprotection. Endothelial dysfunction (ED) model was established by injection of 0.01 % Triton X-100 in the isolated rat heart. Oxytocin pretreatment was conducted at the end of stabilization for 40 min, followed by 30 min global ischemia and 60 min reperfusion to induce I/R injury. Coronary perfusion pressure, hemodynamics and arrhythmia severity scores were measured respectively. High-sensitivity cardiac troponin T (hs-cTnT) was evaluated by enzyme-linked immunosorbent assay. Infarct size was detected by triphenyltetrazolium chloride staining. The morphological changes in coronary endothelium were observed by scanning electron microscopy. Injection of 0.01 % Triton X-100 caused significant reduction of CPP induced by histamine and endothelium removal from scanning electron microscopy, but SNP had no significant effect. Oxytocin pretreatment showed significant recovery in LVDP, ±dp/dt_max, RPP and SI after reperfusion (P <  0.05). Additionally, I/R injury led to a rise of arrhythmia severity score, hs-cTnT and infarct size. No significant differences between ED-OT-I/R and OT-I/R groups were found in arrhythmia severity score, hs-cTnT, and infarct size (P >  0.05). I/R injury exacerbated the decrease in CPP and worsened the migration, deformation, and fracture of coronary endothelium, while oxytocin reversed these injuries. Despite the presence of endothelial damages, oxytocin partially alleviated I/R- and Triton-induced endothelial damages. The cardioprotective effects of oxytocin are independent of endothelial function in alleviating I/R injury and I/R-induced coronary endothelial dysfunction.

Anandamide regulates oxytocin/oxytocin receptor system in human placenta at term

Oxytocin plays a pivotal role in the regulation of human parturition, however its role and modulation in the placenta is not fully understood. Non-labour cesarean section placentas were cultured with the endocannabinoid anandamide. We observed an increase in placental oxytocin receptor expression and oxytocin release. We postulate anandamide as a relevant modulator of oxytocin system in the placenta at term.

Autism spectrum disorder: Trends in research exploring etiopathogenesis

Autism spectrum disorder is a neurodevelopmental condition in which affected individuals have difficulties while interacting and communicating socially, and repetitive behaviors. It has a multifactorial etiology. Various risk factors, including genetic and environmental influences, have been explored while trying to understand its causation. As older evidence was suggestive of a high heritability, a majority of research focused on finding the underlying genetic causes of autism. Due to these efforts, there have been advances in the knowledge of some of the genetic factors associated with autism. But a recent trend also shows an increasing interest in exploration of various potential environmental triggers. These efforts have brought us closer to understanding the elusive disorder more so than ever before. The current review discusses the recent trends in research exploring the etiopathogenesis of autism spectrum disorder.

Design of Oxytocin Analogs

The neurohypophyseal hormone oxytocin (OT) and related modulators of the oxytocin receptor (OTR) have been the subject of intensive research for nearly seven decades. Despite having rather poor drug-like properties, OT is used as a treatment for labor induction, postpartum hemorrhage, and lactation support. The potential use of OT in the treatment of central nervous system (CNS)-related diseases has recently renewed interest in the pharmacology of OT. Oxytocin is one of the most extensively studied cyclic peptides and since the elucidation of its structure in 1953 thousands of peptidic OT analogs with antagonistic and agonistic properties have been synthesized and biologically evaluated. Among them are atosiban, a mixed oxytocin receptor (OTR)/vasopressin 1a receptor (V_1aR) antagonist used as a tocolytic agent approved (in certain countries), and carbetocin, a longer acting OTR agonist on the market for the treatment of postpartum hemorrhage. Many other OT analogs with improved pharmacological properties (e.g., barusiban, Antag III) have been identified. These peptides have been tested in clinical trials and/or used as pharmacological tools. In this chapter, the modifications of the OT molecule that led to the discovery of these compounds are reviewed.

The Oxytocin Receptor: From Intracellular Signaling to Behavior

The many facets of the oxytocin (OXT) system of the brain and periphery elicited nearly 25,000 publications since 1930 (see FIGURE 1 , as listed in PubMed), which revealed central roles for OXT and its receptor (OXTR) in reproduction, and social and emotional behaviors in animal and human studies focusing on mental and physical health and disease. In this review, we discuss the mechanisms of OXT expression and release, expression and binding of the OXTR in brain and periphery, OXTR-coupled signaling cascades, and their involvement in behavioral outcomes to assemble a comprehensive picture of the central and peripheral OXT system. Traditionally known for its role in milk let-down and uterine contraction during labor, OXT also has implications in physiological, and also behavioral, aspects of reproduction, such as sexual and maternal behaviors and pair bonding, but also anxiety, trust, sociability, food intake, or even drug abuse. The many facets of OXT are, on a molecular basis, brought about by a single receptor. The OXTR, a 7-transmembrane G protein-coupled receptor capable of binding to either Gαior Gαqproteins, activates a set of signaling cascades, such as the MAPK, PKC, PLC, or CaMK pathways, which converge on transcription factors like CREB or MEF-2. The cellular response to OXT includes regulation of neurite outgrowth, cellular viability, and increased survival. OXTergic projections in the brain represent anxiety and stress-regulating circuits connecting the paraventricular nucleus of the hypothalamus, amygdala, bed nucleus of the stria terminalis, or the medial prefrontal cortex. Which OXT-induced patterns finally alter the behavior of an animal or a human being is still poorly understood, and studying those OXTR-coupled signaling cascades is one initial step toward a better understanding of the molecular background of those behavioral effects.

Oxytocin and Gynecomastia: Correlation or Causality?

Oxytocin has been administered to patients with autism spectrum disorder (ASD) in order to improve social skills, communication, and manage repetitive behaviors in the context of research trials. The majority of the studies focus on acute administration; thus, the effectiveness and potential side effects of chronic administration remain unknown. The main goal of this case report is to highlight the importance of the safety parameters for the chronic use of intranasal oxytocin administration. In a single case conducted in our outpatient clinic, one adolescent (15 years old) received intranasal oxytocin (24 IU) twice per day, in accordance with the recommended doses for this age group that varies from 8 - 25 IU twice per day. After three weeks of treatment, the patient presented with gynecomastia. While it is not certain that the gynecomastia was oxytocin-induced, this case highlights the importance of developing optimal regimens for chronic oxytocin administration, with a particular focus on safety parameters.

Genetic characterization of the oxytocin-neurophysin I gene (OXT) and its regulatory regions analysis in domestic Old and New World camelids

Oxytocin is a neurohypophysial peptide linked to a wide range of biological functions, including milk ejection, temperament and reproduction. Aims of the present study were a) the characterization of the OXT (Oxytocin-neurophysin I) gene and its regulatory regions in Old and New world camelids; b) the investigation of the genetic diversity and the discovery of markers potentially affecting the gene regulation. On average, the gene extends over 814 bp, ranging between 825 bp in dromedary, 811 bp in Bactrian and 810 bp in llama and alpaca. Such difference in size is due to a duplication event of 21 bp in dromedary. The main regulatory elements, including the composite hormone response elements (CHREs), were identified in the promoter, whereas the presence of mature microRNAs binding sequences in the 3'UTR improves the knowledge on the factors putatively involved in the OXT gene regulation, although their specific biological effect needs to be still elucidated. The sequencing of genomic DNA allowed the identification of 17 intraspecific polymorphisms and 69 nucleotide differences among the four species. One of these (MF464535:g.622C>G) is responsible, in alpaca, for the loss of a consensus sequence for the transcription factor SP1. Furthermore, the same SNP falls within a CpG island and it creates a new methylation site, thus opening future possibilities of investigation to verify the influence of the novel allelic variant in the OXT gene regulation. A PCR-RFLP method was setup for the genotyping and the frequency of the allele C was 0.93 in a population of 71 alpacas. The obtained data clarify the structure of OXT gene in domestic camelids and add knowledge to the genetic variability of a genomic region, which has received little investigation so far. These findings open the opportunity for new investigations, including association studies with productive and reproductive traits.

Oxytocin and Naltrexone Successfully Treat Hypothalamic Obesity in a Boy Post-Craniopharyngioma Resection

CONTEXT

Hypothalamic obesity, a treatment-resistant condition common to survivors of craniopharyngioma (CP), is strongly associated with a poor quality of life in this population. Oxytocin (OT), a hypothalamic neuropeptide, has been shown to play a role in the regulation of energy balance and to have anorexigenic effects in animal studies. Naltrexone (NAL), an opiate antagonist, has been shown to deter hedonic eating and to potentiate OT's effects.

DESIGN

In this parent-observed study, we tested the administration of intranasal OT for 10 weeks (phase 1), followed by a combination of intranasal OT and NAL for 38 weeks (phase 2) in a 13-year-old male with confirmed hypothalamic obesity and hyperphagia post-CP resection. Treatment resulted in 1) reduction in body mass index (BMI) z score from 1.77 to 1.49 over 10 weeks during phase 1; 2) reduction in BMI z score from 1.49 to 0.82 over 38 weeks during phase 2; 3) reduced hyperphagia during phases 1 and 2; 4) continued hedonic high-carbohydrate food-seeking in the absence of hunger during phases 1 and 2; and 5) sustained weight reduction during decreased parental monitoring and free access to unlocked food in the home during the last 10 weeks of phase 2.

CONCLUSION

This successful intervention of CP-related hypothalamic obesity and hyperphagia by OT alone and in combination with NAL is promising for conducting future studies of this treatment-recalcitrant form of obesity.

A possible direct action of oxytocin on spermatogenesis and steroidogenesis in pre-pubertal mouse

The aim of this study was to evaluate the effects of in vivo and in vitro treatments of oxytocin (OT) on the testis of pre-pubertal mice. The OT treatment produced significant changes in the spermatogenic and steroidogenic activity by increasing expression of OT-receptor in the testis of pre-pubertal mice. Treatment with OT showed increased proliferation of germ cells as indicated by increased number of spermatocytes and round spermatids. Dose-dependent increase in expression of PCNA, Bcl-2 and AR proteins was observed in the testis of OT-treated mice as compared with the control and further supports the role of OT in germ cell proliferation and survival. The pre-pubertal mice treated with increasing dose of OT showed significant increase in testosterone synthesis due to dose-dependent stimulatory effects on 3β-HSD activity and increased expression of STAR, LH-receptor (LH-R) and gonadotrophin-releasing hormone receptor (GnRH-R) proteins in the testis. The in vitro study has confirmed in vivo finding showing direct action of OT on testicular steroidogenesis. Thus, OT stimulates testicular spermatogenesis and steroidogenesis by directly acting on testis in mice.

Regulation of angiogenic behaviors by oxytocin receptor through Gli1-indcued transcription of HIF-1α in human umbilical vein endothelial cells

Angiogenesis is a dynamic hypoxia-stimulated process playing a key role in tissue growth and repair under various pathophysiological circumstances. Abnormal angiogenesis contributes to the pathogenesis of many human diseases. Oxytocin receptor is a classical G-protein-coupled receptor expressed on endothelial cells. The present study was aimed to investigate how oxytocin receptor regulated the angiogenic behaviors of human umbilical vein endothelial cells (HUVECs). We found that oxytocin at 0.1μM significantly increased cell proliferation, upregulated the mRNA and protein expression of CD31 and vWF (two important endothelial markers), and enhanced the tuber formation capacity in HUVECs. However, oxytocin receptor inhibitor atosiban at 10μM significantly suppressed these angiogenic properties of HUVECs. Additionally, hypoxia-inducible factor-1α (HIF-1α) inhibitor PX-478 at 20μM also remarkably inhibited the angiogenic properties of HUVECs. We further found that atosiban at 10μM significantly repressed the promoter activity of HIF-1α and reduced the mRNA and protein expression of HIF-1α in HUVECs. Moreover, pharmacological inhibition of HIF-1α by PX-478 at 20μM abolished oxytocin-enhanced angiogenic properties of HUVECs. Finally, transcription factor Gli1 inhibitor GANT-58 at 5μM significantly abolished oxytocin-induced mRNA and protein expression of HIF-1α, while the nuclear abundance of Gli1 was significantly reduced by atosiban at 10μM, but was increased by oxytocin at 0.1μM in HUVECs. GANT-58 at 5μM also significantly abolished oxytocin-enhanced angiogenic properties of HUVECs. Altogether, these discoveries suggested that oxytocin receptor signaling promoted the angiogenic behaviors of HUVECs via Gli1-indcued transcription of HIF-1α. We provided novel molecular insights into endothelial cell-mediated angiogenesis.

Approaches Mediating Oxytocin Regulation of the Immune System

The hypothalamic neuroendocrine system is mainly composed of the neural structures regulating hormone secretion from the pituitary gland and has been considered as the higher regulatory center of the immune system. Recently, the hypothalamo-neurohypophysial system (HNS) emerged as an important component of neuroendocrine–immune network, wherein the oxytocin (OT)-secreting system (OSS) plays an essential role. The OSS, consisting of OT neurons in the supraoptic nucleus, paraventricular nucleus, their several accessory nuclei and associated structures, can integrate neural, endocrine, metabolic, and immune information and plays a pivotal role in the development and functions of the immune system. The OSS can promote the development of thymus and bone marrow, perform immune surveillance, strengthen immune defense, and maintain immune homeostasis. Correspondingly, OT can inhibit inflammation, exert antibiotic-like effect, promote wound healing and regeneration, and suppress stress-associated immune disorders. In this process, the OSS can release OT to act on immune system directly by activating OT receptors or through modulating activities of other hypothalamic–pituitary–immune axes and autonomic nervous system indirectly. However, our understandings of the role of the OSS in neuroendocrine regulation of immune system are largely incomplete, particularly its relationship with other hypothalamic–pituitary–immune axes and the vasopressin-secreting system that coexists with the OSS in the HNS. In addition, it remains unclear about the relationship between the OSS and peripherally produced OT in immune regulation, particularly intrathymic OT that is known to elicit central immunological self-tolerance of T-cells to hypophysial hormones. In this work, we provide a brief review of current knowledge of the features of OSS regulation of the immune system and of potential approaches that mediate OSS coordination of the activities of entire neuroendocrine–immune network.

The ventromedial hypothalamus oxytocin induces locomotor behavior regulated by estrogen

Our previous studies demonstrated that excitation of neurons in the rat ventromedial hypothalamus (VMH) induced locomotor activity. An oxytocin receptor (Oxtr) exists in the VMH and plays a role in regulating sexual behavior. However, the role of Oxtr in the VMH in locomotor activity is not clear. In this study we examined the roles of oxytocin in the VMH in running behavior, and also investigated the involvement of estrogen in this behavioral change. Microinjection of oxytocin into the VMH induced a dose-dependent increase in the running behavior in male rats. The oxytocin-induced running activity was inhibited by simultaneous injection of Oxtr-antagonist, (d(CH2)5(1), Try(Me)(2), Orn(8))-oxytocin. Oxytocin injection also induced running behavior in ovariectomized (OVX) female rats. Pretreatment of the OVX rats with estrogen augmented the oxytocin-induced running activity twofold, and increased the Oxtr mRNA in the VMH threefold. During the estrus cycle locomotor activity spontaneously increased in the dark period of proestrus. The Oxtr mRNA was up-regulated in the proestrus afternoon. Blockade of oxytocin neurotransmission by its antagonist before the onset of the dark period of proestrus decreased the following nocturnal locomotor activity. These findings demonstrate that Oxtr in the VMH is involved in the induction of running behavior and that estrogen facilitates this effect by means of Oxtr up-regulation, suggesting the involvement of oxytocin in the locomotor activity of proestrus female rats.

Generation of Oxtr cDNA(HA)-Ires-Cre Mice for Gene Expression in an Oxytocin Receptor Specific Manner

The neurohypophysial hormone oxytocin (OXT) and its receptor (OXTR) have critical roles in the regulation of pro-social behaviors, including social recognition, pair bonding, parental behavior, and stress-related responses. Supporting this hypothesis, a portion of patients suffering from autism spectrum disorder have mutations, such as single nucleotide polymorphisms, or epigenetic modifications in their OXTR gene. We previously reported that OXTR-deficient mice exhibit pervasive social deficits, indicating the critical role of OXTR in social behaviors. In the present study, we generated Oxtr cDNA(HA)-Ires-Cre knock-in mice, expressing both OXTR and Cre recombinase under the control of the endogenous Oxtr promoter. Knock-in cassette of Oxtr cDNA(HA)-Ires-Cre consisted of Oxtr cDNA tagged with the hemagglutinin epitope at the 3' end (Oxtr cDNA(HA)), internal ribosomal entry site (Ires), and Cre. Cre was expressed in the uterus, mammary gland, kidney, and brain of Oxtr cDNA(HA)-Ires-Cre knock-in mice. Furthermore, the distribution of Cre in the brain was similar to that observed in Oxtr-Venus fluorescent protein expressing mice (Oxtr-Venus), another animal model previously generated by our group. Social behavior of Oxtr cDNA(HA)-Ires-Cre knock-in mice was similar to that of wild-type animals. We demonstrated that this construct is expressed in OXTR-expressing neurons specifically after an infection with the recombinant adeno-associated virus carrying the flip-excision switch vector. Using this system, we showed the transport of the wheat-germ agglutinin tracing molecule from the OXTR-expressing neurons to the innervated neurons in knock-in mice. This study might contribute to the monosynaptic analysis of neuronal circuits and to the optogenetic analysis of neurons expressing OXTR.

Maternal adversities during pregnancy and cord blood oxytocin receptor (OXTR) DNA methylation

The aim of this study was to investigate whether maternal adversities and cortisol levels during pregnancy predict cord blood DNA methylation of the oxytocin receptor (OXTR). We collected cord blood of 39 babies born to mothers participating in a cross-sectional study (N = 100) conducted in Basel, Switzerland (2007-10). Mothers completed the Inventory of Life Events (second trimester: T2), the Edinburgh Postnatal Depression Scale (EPDS, third trimester: T3), the Trier Inventory of Chronic Stress (TICS-K, 1-3 weeks postpartum) and provided saliva samples (T2, T3) for maternal cortisol profiles, as computed by the area under the curve with respect to ground (AUCg) or increase (AUCi) for the cortisol awakening response (CAR) and for diurnal cortisol profiles (DAY). OXTR DNA methylation was quantified using Sequenom EpiTYPER. The number of stressful life events (P = 0.032), EPDS score (P = 0.007) and cortisol AUCgs at T2 (CAR: P = 0.020; DAY: P = 0.024) were negatively associated with OXTR DNA methylation. Our findings suggest that distinct prenatal adversities predict decreased DNA methylation in a gene that is relevant for childbirth, maternal behavior and wellbeing of mother and offspring. If a reduced OXTR methylation increases OXTR expression, our findings could suggest an epigenetic adaptation to an adverse early environment.

Intranasal Oxytocin: Myths and Delusions

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

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.

Oxytocin and vasopressin: linking pituitary neuropeptides and their receptors to social neurocircuits

Oxytocin and vasopressin are pituitary neuropeptides that have been shown to affect social processes in mammals. There is growing interest in these molecules and their receptors as potential precipitants of, and/or treatments for, social deficits in neurodevelopmental disorders, including autism spectrum disorder. Numerous behavioral-genetic studies suggest that there is an association between these peptides and individual social abilities; however, an explanatory model that links hormonal activity at the receptor level to complex human behavior remains elusive. The following review summarizes the known associations between the oxytocin and vasopressin neuropeptide systems and social neurocircuits in the brain. Following a micro- to macro- level trajectory, current literature on the synthesis and secretion of these peptides, and the structure, function and distribution of their respective receptors is first surveyed. Next, current models regarding the mechanism of action of these peptides on microcircuitry and other neurotransmitter systems are discussed. Functional neuroimaging evidence on the acute effects of exogenous administration of these peptides on brain activity is then reviewed. Overall, a model in which the local neuromodulatory effects of pituitary neuropeptides on brainstem and basal forebrain regions strengthen signaling within social neurocircuits proves appealing. However, these findings are derived from animal models; more research is needed to clarify the relevance of these mechanisms to human behavior and treatment of social deficits in neuropsychiatric disorders.

Myometrial contractility influences oxytocin receptor (OXTR) expression in term trophoblast cells obtained from the maternal surface of the human placenta

Background

Oxytocin (OXT) acts through its specific receptor (OXTR) and increased density of OXTR and/or augmented sensitivity to OXT were postulated as prerequisites of normal onset of labor. Expression of OXTR in the placental term trophoblast cells has not yet been analyzed in the context of contractile activity of the uterus. Here we examine comparatively OXT contents in the placental tissue adjacent to the uterine wall and expressions of OXTR in this tissue and corresponding isolated placental trophoblast cells.

Methods

Twenty eight placentae after normal labors at term (group I, N = 14) and after cesarean sections performed without uterine contractile activity (group II, N = 14) have been collected. Tissue excised from the maternal surface of examined placenta was used for OXT concentration measurement, cytotrophoblast cell cultures preparation and immunohistochemistry of OXTR. Concentration of OXT was estimated in the tissue homogenates by an enzyme immunoassay with colorimetric detection. Cytotrophoblast cells were isolated using Kliman’s method based on trypsin, DNase, and a 5–70 % Percoll gradient centrifugation. The cultures were incubated for 5 days in normoxia. Both placental specimens and terminated cytotrophoblast cultures were fixed and embedded in paraffin before being immunostained for OXTR. Using light microscopy with computed morphometry for quantitative analysis, OXTR expressions were estimated in calibrated areas of the paraffin sections.

Results

There were not significant differences between the groups in respect to the mean OXT concentration. However, in both groups the median value of OXT concentration was significantly (p < 0.05) higher in the tissue obtained from the peripheral regions of the maternal surface of the placenta, compared to the samples from the central region of this surface. In placental tissue the mean expression of OXTR in group I was significantly (p < 0.05) increased by approximately 3.2-fold and 3.45-fold (the samples collected from central and peripheral regions, respectively) compared to the values obtained in group II.

In the isolated primary trophoblast cultures the differences were even more evident (p < 0.02) and the mean change in OXTR expression in group I comprised approximately 6.9-fold increase and 6.5-fold increase (the samples collected from central and peripheral regions, respectively) compared to the values obtained in group II.

Conclusions

Upregulation of OXTR within placental trophoblast cells localized close or adherent to uterine wall may play a crucial role in labor with efficient contractile activity (vaginal delivery). Further studies may disclose if this local OXT/OXTR signaling is utilized in the third stage of labor to elicit placental detachment or contribute in a more versatile way throughout the labor period.

Oxytocin-induced membrane hyperpolarization in pain-sensitive dorsal root ganglia neurons mediated by Ca(2+)/nNOS/NO/KATP pathway

Oxytocin (OT) plays an important role in pain modulation and antinociception in the central nervous system. However, little is known about its peripheral effects. This study was conducted to investigate the effect of OT on the electrical properties of neurons in the dorsal root ganglia (DRG) and the underlying mechanisms. DRG neurons from adult rats were acutely dissociated and cultured. Intracellular Ca(2+) was determined by fluorescent microscopy using an indicator dye. The electrical properties of DRG neurons were tested by patch-clamp recording. The oxytocin receptor (OTR) and neuronal nitric oxide synthase (nNOS) on DRG neurons were assessed with immunofluorescence assays. OTR co-localized with nNOS in most of Isolectin B4 (IB4)-binding cultured DRG neurons in rats. OT decreased the excitability, increased the outward current, and evoked the membrane hyperpolarization in cultured DRG neurons. Sodium nitroprusside (SNP), the donor of nitric oxide (NO), exerted similar effects as OT on the membrane potential of cultured DRG neurons. OT increased the production of NO in DRGs and cultured DRG neurons. Pre-treatment of the OTR antagonist atosiban or the selective nNOS inhibitor N-Propyl-l-arginine (NPLA) significantly attenuated the hyperpolarization effect evoked by OT. OT produced a concentration-dependent increase in intracellular Ca(2+) in DRG neurons that responds to capsaicin, which can be attenuated by atosiban, but not by NPLA. OT-evoked membrane hyperpolarization and increase of outward current were distinctly attenuated by glibenclamide, a blocker of ATP-sensitive K(+) (KATP) channel. OT might be an endogenous antinociceptive agent and the peripheral antinociceptive effects of OT are mediated by activation of the Ca(2+)/nNOS/NO/KATP pathway in DRG neurons.

Beyond labor: the role of natural and synthetic oxytocin in the transition to motherhood

Emerging research raises questions that synthetic oxytocin during childbirth may alter the endogenous oxytocin system and influence maternal stress, mood, and behavior. Endogenous oxytocin is a key component in the transition to motherhood, affecting molecular pathways that buffer stress reactivity, support positive mood, and regulate healthy mothering behaviors (including lactation). Synthetic oxytocin is widely used throughout labor and postpartum care in modern birth. Yet research on the implications beyond labor of maternal exposure to perinatal synthetic oxytocin is rare. In this article, we review oxytocin-related biologic pathways and behaviors associated with the transition to motherhood and evidence supporting the need for further research on potential effects of intrapartum oxytocin beyond labor. We include a primer on oxytocin at the molecular level.

Epigenetics and autism

This review identifies mechanisms for altering DNA-histone interactions of cell chromatin to upregulate or downregulate gene expression that could serve as epigenetic targets for therapeutic interventions in autism. DNA methyltransferases (DNMTs) can phosphorylate histone H3 at T6. Aided by protein kinase C β 1, the DNMT lysine-specific demethylase-1 prevents demethylation of H3 at K4. During androgen-receptor-(AR-) dependent gene activation, this sequence may produce AR-dependent gene overactivation which may partly explain the male predominance of autism. AR-dependent gene overactivation in conjunction with a DNMT mechanism for methylating oxytocin receptors could produce high arousal inputs to the amygdala resulting in aberrant socialization, a prime characteristic of autism. Dysregulation of histone methyltransferases and histone deacetylases (HDACs) associated with low activity of methyl CpG binding protein-2 at cytosine-guanine sites in genes may reduce the capacity for condensing chromatin and silencing genes in frontal cortex, a site characterized by decreased cortical interconnectivity in autistic subjects. HDAC1 inhibition can overactivate mRNA transcription, a putative mechanism for the increased number of cerebral cortical columns and local frontal cortex hyperactivity in autistic individuals. These epigenetic mechanisms underlying male predominance, aberrant social interaction, and low functioning frontal cortex may be novel targets for autism prevention and treatment strategies.

Nonsocial functions of hypothalamic oxytocin

Oxytocin (OXT) is a hypothalamic neuropeptide composed of nine amino acids. The functions of OXT cover a variety of social and nonsocial activity/behaviors. Therapeutic effects of OXT on aberrant social behaviors are attracting more attention, such as social memory, attachment, sexual behavior, maternal behavior, aggression, pair bonding, and trust. The nonsocial behaviors/functions of brain OXT have also received renewed attention, which covers brain development, reproduction, sex, endocrine, immune regulation, learning and memory, pain perception, energy balance, and almost all the functions of peripheral organ systems. Coordinating with brain OXT, locally produced OXT also involves the central and peripheral actions of OXT. Disorders in OXT secretion and functions can cause a series of aberrant social behaviors, such as depression, autism, and schizophrenia as well as disturbance of nonsocial behaviors/functions, such as anorexia, obesity, lactation failure, osteoporosis, diabetes, and carcinogenesis. As more and more OXT functions are identified, it is essential to provide a general view of OXT functions in order to explore the therapeutic potentials of OXT. In this review, we will focus on roles of hypothalamic OXT on central and peripheral nonsocial functions.

A brief history of oxytocin and its role in modulating psychostimulant effects

Over the past century, the polypeptide oxytocin has played an important role in medicine with major highlights including the identification of its involvement in parturition and the milk let-down reflex. Oxytocin is now implicated in an extensive range of psychological phenomena including reward and memory processes and has been investigated as a treatment for several psychiatric disorders including addiction, anxiety, autism, and schizophrenia. In this review, we first provide an historical overview of oxytocin and describe key aspects of its physiological activity. We then outline some pharmacological limitations in this field of research before highlighting the role of oxytocin in a wide range of behavioral and neuronal processes. Finally, we review evidence for a modulatory role of oxytocin with regard to psychostimulant effects. Key findings suggest that oxytocin attenuates a broad number of cocaine and methamphetamine induced behaviors and associated neuronal activity in rodents. Evidence also outlines a role for oxytocin in the prosocial effects of 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) in both rodents and humans. Clinical trials should now investigate the effectiveness of oxytocin as a novel intervention for psychostimulant addiction and should aim to determine its specific role in the therapeutic properties of MDMA that are currently being investigated.

DNA methylation of specific CpG sites in the promoter region regulates the transcription of the mouse oxytocin receptor

Oxytocin is a peptide hormone, well known for its role in labor and suckling, and most recently for its involvement in mammalian social behavior. All central and peripheral actions of oxytocin are mediated through the oxytocin receptor, which is the product of a single gene. Transcription of the oxytocin receptor is subject to regulation by gonadal steroid hormones, and is profoundly elevated in the uterus and mammary glands during parturition. DNA methylation is a major epigenetic mechanism that regulates gene transcription, and has been linked to reduced expression of the oxytocin receptor in individuals with autism. Here, we hypothesized that transcription of the mouse oxytocin receptor is regulated by DNA methylation of specific sites in its promoter, in a tissue-specific manner. Hypothalamus-derived GT1-7, and mammary-derived 4T1 murine cell lines displayed negative correlations between oxytocin receptor transcription and methylation of the gene promoter, and demethylation caused a significant enhancement of oxytocin receptor transcription in 4T1 cells. Using a reporter gene assay, we showed that methylation of specific sites in the gene promoter, including an estrogen response element, significantly inhibits transcription. Furthermore, methylation of the oxytocin receptor promoter was found to be differentially correlated with oxytocin receptor expression in mammary glands and the uterus of virgin and post-partum mice, suggesting that it plays a distinct role in oxytocin receptor transcription among tissues and under different physiological conditions. Together, these results support the hypothesis that the expression of the mouse oxytocin receptor gene is epigenetically regulated by DNA methylation of its promoter.

Association between oxytocin receptor gene polymorphisms and self-rated 'empathic concern' in schizophrenia

The nonapeptide oxytocin (OXT) and its receptor (OXTR) have been implicated in social cognition, empathy, emotion and stress regulation in humans. Previous studies reported associations between OXT and OXTR genetic polymorphisms and risk for disorders characterized by impaired socio-emotional functioning, such as schizophrenia and autism. Here we investigate the influence of two single nucleotide polymorphisms (SNPs) within the OXTR gene on a measure of socio-emotional functioning in schizophrenic patients. OXTR SNPs that were previously investigated in other studies were genotyped in 145 patients diagnosed with schizophrenia according to DSM-IV and 145 healthy controls matched for age and gender. The Interpersonal Reactivity Index (IRI) was used to assess cognitive ('perspective taking'), affective ('empathic concern') and self-related ('personal distress') dimensions of empathy. No group differences in genotype frequencies were observed. MANCOVA revealed a significant main (F [1,282] = 10.464; p<0.01) and interaction effect (genotype by diagnosis: F [1,282] = 4.329; p<0.05) of OXTR SNP rs2254298(A>GG) with 'empathic concern'. Within the schizophrenia group, linear regression analysis determined OXTR rs2254298 genotype, PANSS negative and general symptom score, and age of disease onset as being significantly associated with 'empathic concern'. OXTR rs2254298 significantly impacted PANSS general psychopathology scores. No associations were found for OXTR rs53576, IRI 'perspective taking' or 'personal distress' ratings. Our preliminary findings support hypotheses about an involvement of OXTR rs2254298 in emotional empathy in schizophrenic and healthy individuals, warranting independent replication.

Molecules and mating: positive selection and reproductive behaviour in primates

Sexual reproduction is generally thought to be more costly than asexual reproduction. However, it does have the advantage of accelerating rates of adaptation through processes such as recombination and positive selection. Comparative studies of the human and nonhuman primate genomes have demonstrated that positive selection has played an important role in the evolutionary history of humans and other primates. To date, many dozens of genes, thought to be affected by positive selection, have been identified. In this chapter, we will focus on genes that are associated with mating behaviours and reproductive processes, concentrating on genes that are most likely to enhance reproductive success and that also show evidence of positive selection. The genes encode phenotypic features that potentially influence mate choice decisions or impact the evolution and function of genes involved in the perception and regulation of, and the response to, phenotypic signals. We will also consider genes that influence precopulatory behavioural traits in humans and nonhuman primates, such as social bonding and aggression. The evolution of post-copulatory strategies such as sperm competition and selective abortion may also evolve in the presence of intense competition and these adaptations will also be considered. Although behaviour may not be solely determined by genes, the evidence suggests that the genes discussed in this chapter have some influence on human and nonhuman primate behaviour and that positive selection on these genes results in some degree of population differentiation and diversity.

Prosocial effects of oxytocin and clinical evidence for its therapeutic potential

There has been unprecedented interest in the prosocial effects of the neuropeptide oxytocin in humans over the last decade. A range of studies has demonstrated correlations between basal oxytocin levels and the strength of social and bonding behaviors both in healthy individuals and in those suffering from psychiatric disorders. Mounting evidence suggests associations between polymorphisms in the oxytocin receptor gene and prosocial behaviors and there may also be important epigenetic effects. Many studies have now reported a plethora of prosocial effects of intranasal application of oxytocin, including the domains of trust, generosity, socially reinforced learning, and emotional empathy. The main focus of this review will be to summarize human preclinical work and particularly the rapidly growing number of clinical studies which have identified important links between oxytocin and a wide range of psychiatric disorders, and have now started to directly assess its therapeutic potential.

Expression and activation of the oxytocin receptor in airway smooth muscle cells: Regulation by TNFalpha and IL-13

Background

During pregnancy asthma may remain stable, improve or worsen. The factors underlying the deleterious effect of pregnancy on asthma remain unknown. Oxytocin is a neurohypophyseal protein that regulates a number of central and peripheral responses such as uterine contractions and milk ejection. Additional evidence suggests that oxytocin regulates inflammatory processes in other tissues given the ubiquitous expression of the oxytocin receptor. The purpose of this study was to define the role of oxytocin in modulating human airway smooth muscle (HASMCs) function in the presence and absence of IL-13 and TNFα, cytokines known to be important in asthma.

Method

Expression of oxytocin receptor in cultured HASMCs was performed by real time PCR and flow cytomery assays. Responses to oxytocin was assessed by fluorimetry to detect calcium signals while isolated tracheal rings and precision cut lung slices (PCLS) were used to measure contractile responses. Finally, ELISA was used to compare oxytocin levels in the bronchoalveloar lavage (BAL) samples from healthy subjects and those with asthma.

Results

PCR analysis demonstrates that OXTR is expressed in HASMCs under basal conditions and that both interleukin (IL)-13 and tumor necrosis factor (TNFα) stimulate a time-dependent increase in OXTR expression at 6 and 18 hr. Additionally, oxytocin increases cytosolic calcium levels in fura-2-loaded HASMCs that were enhanced in cells treated for 24 hr with IL-13. Interestingly, TNFα had little effect on oxytocin-induced calcium response despite increasing receptor expression. Using isolated murine tracheal rings and PCLS, oxytocin also promoted force generation and airway narrowing. Further, oxytocin levels are detectable in bronchoalveolar lavage (BAL) fluid derived from healthy subjects as well as from those with asthma.

Conclusion

Taken together, we show that cytokines modulate the expression of functional oxytocin receptors in HASMCs suggesting a potential role for inflammation-induced changes in oxytocin receptor signaling in the regulation of airway hyper-responsiveness in asthma.