Structure and expression of a human oxytocin receptor

Associations between genetic variations in oxytocin pathway genes and hippocampal volume: Insights from the UK Biobank

The role of oxytocin-related genes in social-cognitive function has been previously established, but structural brain mechanisms underlying this link remain poorly understood. Utilizing a substantial dataset from the UK Biobank (N ≈ 30,000), this research determined associations between variations in ten single nucleotide polymorphisms (SNPs) within three oxytocin pathway genes (i.e., the oxytocin/neurophysin I prepropetide gene, the cluster of differentiation 38 glycoprotein gene, the oxytocin receptor gene) and whole-brain gray matter volume. Carriers of the AA or AG genotypes of the oxytocin receptor gene rs237851 SNP exhibited significantly larger hippocampal volume than carriers of the GG genotype. These results support the link between variations in the oxytocin receptor gene and hippocampal structure, with possible impact on social-cognitive function such as social recognition memory.

Structure and function of neurohypophysial hormones

Vasopressin (VP) and oxytocin (OXT) are neuropeptides that are synthesized in the hypothalamus and stored in/secreted from the neurohypophysis. Although VP and OXT were initially characterized as osmoregulatory and reproductive hormones, respectively, these peptides exert versatile actions not only in peripheral organs but also in the central nervous system via multiple G protein-coupled receptors. Orthologous peptides and receptors have been identified in various animal phyla, reflecting an ancient origin of this hormone family. The aim of this review is to provide basic information on this hormone family and to propose matters to be addressed in future studies. In the earlier sections of this review, we summarize the historical aspect of VP/OXT research as well as the basic features of hormonal peptides and corresponding receptors. The latter sections describe VP/OXT family peptides and their receptors in nonmammalian species, including invertebrates, to introduce the evolutionary aspect of this hormone family. By integrating knowledge from both general and comparative endocrinology perspectives, we highlight current and future research trends about the VP/OXT system.

Oxytocin pathway gene variation and corticostriatal resting-state functional connectivity

Genetic variations in single nucleotide polymorphisms (SNPs) within oxytocin pathway genes have been linked to social behavior and neurodevelopmental conditions. However, the neurobiological mechanisms underlying these associations remain elusive. In this study, we investigated the relationship between variations of 10 SNPs in oxytocin pathway genes and resting-state functional connectivity among 55 independent components using a large sample from the UK Biobank (N ≈ 30,000). Our findings revealed that individuals with the GG genotype at rs4813627 within the oxytocin structural gene (OXT) exhibited weaker resting-state functional connectivity in the corticostriatal circuit compared to those with the GA/AA genotypes. Empirical evidence has linked the GG genotype at OXT rs4813627 with a behavioral tendency of insensitivity to others. These results inform the neural mechanisms by which oxytocin-related genetic factors can influence social behavior.

Oxytocin/Oxytocin Receptor Signalling in the Gastrointestinal System: Mechanisms and Therapeutic Potential

The neuropeptide hormone oxytocin (OT) is involved in various physiological and pathological processes via the oxytocin receptor (OTR). While OT is most widely known as a reproductive system hormone and a nervous system neurotransmitter, the OT/OTR system has gradually gained much attention for its role in the gastrointestinal (GI) system, such as the GI motility, secretion, and bowel inflammatory reactions. Its importance in GI cancers has also been reported in the past few decades. The promising clinical observations have revealed OT's anti-nociceptive effect, protective effect over gut injury, and the potential of using microbiota to naturally increase endogenous OT levels, which shed a light on the management of GI disorders with lower side effects. However, no current comprehensive review is available on the actions of OT/OTR in the GI tract. This review aims to present the lesser-known role of the OT/OTR system in the GI tract, and the most recent findings are discussed regarding the distribution and functional role of OTR signalling in regulating (patho)physiological functions of the GI tract. Special emphasis is placed on its therapeutic potential for clinical management of GI disorders, such as GI pain, inflammatory bowel disease (IBD), and irritable bowel syndrome (IBS). The recent characterisation of the OTR's crystal structure has advanced research for designing and identifying new OTR-specific molecules. Future in-depth basic and clinical research is needed to further elucidate the involvement and detailed mechanism of OT/OTR in GI disorders, and the development of OTR-specific ligands.

Role of oxytocin in bone

Oxytocin (OT) is a posterior pituitary hormone that, in addition to its role in regulating childbirth and lactation, also exerts direct regulatory effects on the skeleton through peripheral OT and oxytocin receptor (OTR). Bone marrow mesenchymal stem cells (BMSCs), osteoblasts (OB), osteoclasts (OC), chondrocytes, and adipocytes all express OT and OTR. OT upregulates RUNX2, BMP2, ALP, and OCN, thereby enhancing the activity of BMSCs and promoting their differentiation towards OB rather than adipocytes. OT also directly regulates OPG/RANKL to inhibit adipocyte generation, increase the expression of SOX9 and COMP, and enhance chondrocyte differentiation. OB can secrete OT, exerting influence on the surrounding environment through autocrine and paracrine mechanisms. OT directly increases OC formation through the NκB/MAP kinase signaling pathway, inhibits osteoclast proliferation by triggering cytoplasmic Ca2+ release and nitric oxide synthesis, and has a dual regulatory effect on OCs. Under the stimulation of estrogen, OB synthesizes OT, amplifying the biological effects of estrogen and OT. Mediated by estrogen, the OT/OTR forms a feedforward loop with OB. Apart from estrogen, OT also interacts with arginine vasopressin (AVP), prostaglandins (PGE2), leptin, and adiponectin to regulate bone metabolism. This review summarizes recent research on the regulation of bone metabolism by OT and OTR, aiming to provide insights into their clinical applications and further research.

Oxytocin and corticotropin-releasing hormone exaggerate nucleus tractus solitarii neuronal and synaptic activity following chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) in rodents mimics the hypoxia-induced elevation of blood pressure seen in individuals experiencing episodic breathing. The brainstem nucleus tractus solitarii (nTS) is the first site of visceral sensory afferent integration, and thus is critical for cardiorespiratory homeostasis and its adaptation during a variety of stressors. In addition, the paraventricular nucleus of the hypothalamus (PVN), in part through its nTS projections that contain oxytocin (OT) and/or corticotropin-releasing hormone (CRH), contributes to cardiorespiratory regulation. Within the nTS, these PVN-derived neuropeptides alter nTS activity and the cardiorespiratory response to hypoxia. Nevertheless, their contribution to nTS activity after CIH is not fully understood. We hypothesized that OT and CRH would increase nTS activity to a greater extent following CIH, and co-activation of OT+CRH receptors would further magnify nTS activity. Our data show that compared to their normoxic controls, 10 days' CIH exaggerated nTS discharge, excitatory synaptic currents and Ca2+ influx in response to CRH, which were further enhanced by the addition of OT. CIH increased the tonic functional contribution of CRH receptors, which occurred with elevation of mRNA and protein. Together, our data demonstrate that intermittent hypoxia exaggerates the expression and function of neuropeptides on nTS activity. KEY POINTS: Episodic breathing and chronic intermittent hypoxia (CIH) are associated with autonomic dysregulation, including elevated sympathetic nervous system activity. Altered nucleus tractus solitarii (nTS) activity contributes to this response. Neurons originating in the paraventricular nucleus (PVN), including those containing oxytocin (OT) and corticotropin-releasing hormone (CRH), project to the nTS, and modulate the cardiorespiratory system. Their role in CIH is unknown. In this study, we focused on OT and CRH individually and together on nTS activity from rats exposed to either CIH or normoxia control. We show that after CIH, CRH alone and with OT increased to a greater extent overall nTS discharge, neuronal calcium influx, synaptic transmission to second-order nTS neurons, and OT and CRH receptor expression. These results provide insights into the underlying circuits and mechanisms contributing to autonomic dysfunction during periods of episodic breathing.

Appetite- and Weight-Regulating Neuroendocrine Circuitry in Hypothalamic Obesity

Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.

The role of intraamygdaloid oxytocin in spatial learning and avoidance learning

The goal of the present study is to investigate the role of intraamygdaloid oxytocin in learning-related mechanisms. Oxytocin is a neuropeptide which is involved in social bonding, trust, emotional responses and various social behaviors. By conducting passive avoidance and Morris water maze tests on male Wistar rats, the role of intraamygdaloid oxytocin in memory performance and learning was investigated. Oxytocin doses of 10 ng and 100 ng were injected into the central nucleus of the amygdala. Our results showed that 10 ng oxytocin significantly reduced the time required to locate the platform during the Morris water maze test while significantly increasing the latency time in the passive avoidance test. However, the 100 ng oxytocin experiment failed to produce a significant effect in either of the tests. Wistar rats pretreated with 20 ng oxytocin receptor antagonist (L-2540) were administered 10 ng of oxytocin into the central nucleus of the amygdala and were also subjected to the aforementioned tests to highlight the role of oxytocin receptors in spatial- and avoidance learning. Results suggest that oxytocin supports memory processing during both the passive avoidance and the Morris water maze tests. Oxytocin antagonists can however block the effects of oxytocin in both tests. The results substantiate that oxytocin uses oxytocin receptors to enhance memory and learning performance.

Cloning and deorphanization of three inotocin (insect oxytocin/vasopressin-like) receptors and their ligand from the tick Ixodes scapularis

Many insects produce the cyclic neuropeptide inotocin (CLITNCPRGamide), which is the insect orthologue of the mammalian neuropeptides oxytocin and vasopressin. These insects also have one inotocin G protein-coupled receptor (GPCR), which is the orthologue of the mammalian oxytocin and vasopressin receptors. The tick Ixodes scapularis belongs to the subphylum Chelicerata, an arthropod taxon different from insects, to which also spiders, scorpions, and mites belong. I. scapularis is an ectoparasite and a health risk for humans, because it transfers pathogenic microorganisms to its human host during a blood meal, thereby causing serious neurological diseases, among them Lyme disease and tick-borne encephalitis (TBE). By annotating the genomic sequence of I. scapularis, we previously found one presumed tick inotocin preprohormone gene and, in contrast to insects, three genes coding for presumed inotocin GPCRs. We now find that these GPCR genes cluster on one genomic contig, suggesting that they originated by recent gene duplications. Closely located on the same contig are also four adipokinetic hormone/corazonin-related peptide (ACP) GPCR genes, and one crustacean cardioactive peptide (CCAP) GPCR gene, suggesting evolutionary relationships. These evolutionary relationships are confirmed by phylogenetic tree analyses of their gene products. We also cloned the tick inotocin preprohormone, which has a structural organization closely resembling mammalian oxytocin and vasopressin preprohormones, including the presence of a conserved neurophysin sequence, having seven cystine bridges. This neurophysin sequence has two cystine-knot domains, but in contrast to mammalian neurophysins, the tick neurophysin contains a canonical prohormone convertase cleavage signal and a peptide C-terminal amidation sequence (GKR), suggesting cleavage into two biologically active cystine-knot peptides. This cleavage/amidation sequence occurs in neurophysins from most hard tick species, but not in other chelicerates. Mature tick inotocin is different from insect inotocin and has the sequence CFITNCPPGamide. Finally, we cloned and stably expressed the three tick inotocin receptors in Chinese Hamster Ovary cells and found that each of them was activated by nanomolar concentrations of tick inotocin (EC50 for ITR1 = 1.6 × 10-8 M; EC50 for ITR2 = 5.8 × 10-9 M; EC50 for ITR3 = 9.3 × 10-9 M), thereby establishing that they are genuine tick inotocin receptors.

A Putative Role of Vasopressin/Oxytocin-Type Neuropeptide in Osmoregulation and Feeding Inhibition of Apostichopus japonicus

Vasopressin/oxytocin (VP/OT)-type neuropeptide is an ancient neurophysin-associated neuropeptide and has been intensively studied to be involved in multiple physiological processes in protostomian and deuterostome vertebrates. However, little is known about the functions of VP/OT-type neuropeptide in deuterostome invertebrates especially in echinoderms. Here, we firstly report VP/OT-type neuropeptide signaling in an important economic species, Apostichopus japonicus, which is widely cultured in Asia, with high nutritional and medicinal values. Molecular characterization analysis of holotocin and its precursor revealed the highly conserved features of VP/OT family. The candidate receptor for holotocin (AjHOR) was confirmed to be able to activate the signaling via cAMP-PKA and possible Ca2+-PKC pathway, and further activated the downstream ERK1/2 cascade. Holotocin precursor expression profile showed that they were mainly concentrated in circumoral nerve ring. Furthermore, in vitro pharmacological experiments demonstrated that holotocin caused contractile responses in preparations from A. japonicus. And in vivo functional studies indicated that short-term injection of holotocin resulted in body bloat and long-term injection resulted in reduced body mass, suggesting potential roles of holotocin in osmoregulation and feeding co-inhibition with holotocin-CCK. Our findings provided a comprehensive description of AjHOR-holotocin signaling, revealed ancient roles of holotocin in osmoregulation and feeding inhibition by controlling muscle contractions.

Biosynthesis and Function of VIP and Oxytocin: Mechanisms of C-terminal Amidation, Oxytocin Secretion and Transport

In this review, we provide the status of research on vasoactive intestinal peptide (VIP) and oxytocin, typical C-terminal α-amidated peptide hormones, including their precursor protein structures, processing and C-terminal α-amidation, and the recently identified mechanisms of regulation of oxytocin secretion and its transportation through the blood brain barrier. More than half of neural and endocrine peptides, such as VIP and oxytocin, have the α-amide structure at their C-terminus, which is essential for biological activities. We have studied the synthesis and function of C-terminal α-amidated peptides, including VIP and oxytocin, since the 1980s. Human VIP mRNA encoded not only VIP but also another related C-terminal α-amidated peptide, PHM-27 (peptide having amino-terminal histidine, carboxy-terminal methionine amide, and 27 amino acid residues). The human VIP/PHM-27 gene is composed of 7 exons and regulated synergistically by cyclic AMP and protein kinase C pathways. VIP has an essential role in glycemic control using transgenic mouse technology. The peptide C-terminal α-amidation proceeded through a 2-step mechanism catalyzed by 2 different enzymes encoded in a single mRNA. In the oxytocin secretion from the hypothalamus/the posterior pituitary, the CD38-cyclic ADP-ribose signal system, which was first established in the insulin secretion from pancreatic β cells of the islets of Langerhans, was found to be essential. A possible mechanism involving RAGE (receptor for advanced glycation end-products) of the oxytocin transportation from the blood stream into the brain through the blood-brain barrier has also been suggested.

Endogenous oxytocin levels in children with autism: Associations with cortisol levels and oxytocin receptor gene methylation

Alterations in the brain's oxytocinergic system have been suggested to play an important role in the pathophysiology of autism spectrum disorder (ASD), but insights from pediatric populations are sparse. Here, salivary oxytocin was examined in the morning (AM) and afternoon (PM) in school-aged children with (n = 80) and without (n = 40) ASD (boys/girls 4/1), and also characterizations of DNA methylation (DNAm) of the oxytocin receptor gene (OXTR) were obtained. Further, cortisol levels were assessed to examine links between the oxytocinergic system and hypothalamic-pituitary-adrenal (HPA) axis signaling. Children with ASD displayed altered (diminished) oxytocin levels in the morning, but not in the afternoon, after a mildly stress-inducing social interaction session. Notably, in the control group, higher oxytocin levels at AM were associated with lower stress-induced cortisol at PM, likely reflective of a protective stress-regulatory mechanism for buffering HPA stress activity. In children with ASD, on the other hand, a significant rise in oxytocin levels from the morning to the afternoon was associated with a higher stress-induced cortisol release in the afternoon, likely reflective of a more reactive stress regulatory release of oxytocin for reactively coping with heightened HPA activity. Regarding epigenetic modifications, no overall pattern of OXTR hypo- or hypermethylation was evident in ASD. In control children, a notable association between OXTR methylation and levels of cortisol at PM was evident, likely indicative of a compensatory downregulation of OXTR methylation (higher oxytocin receptor expression) in children with heightened HPA axis activity. Together, these observations bear important insights into altered oxytocinergic signaling in ASD, which may aid in establishing relevant biomarkers for diagnostic and/or treatment evaluation purposes targeting the oxytocinergic system in ASD.

Oxytocin excites dorsal raphe serotonin neurons and bidirectionally gates their glutamate synapses

Oxytocin (OXT) modulates wide spectrum of social and emotional behaviors via modulation of numerous neurotransmitter systems, including serotonin (5-HT). However, how OXT controls the function of dorsal raphe nucleus (DRN) 5-HT neurons remains unknown. Here, we reveal that OXT excites and alters the firing pattern of 5-HT neurons via activation of postsynaptic OXT receptors (OXTRs). In addition, OXT induces cell-type-specific depression and potentiation of DRN glutamate synapses by two retrograde lipid messengers, 2-arachidonoylglycerol (2-AG) and arachidonic acid (AA), respectively. Neuronal mapping demonstrates that OXT preferentially potentiates glutamate synapses of 5-HT neurons projecting to medial prefrontal cortex (mPFC) and depresses glutamatergic inputs to 5-HT neurons projecting to lateral habenula (LHb) and central amygdala (CeA). Thus, by engaging distinct retrograde lipid messengers, OXT exerts a target-specific gating of glutamate synapses on the DRN. As such, our data uncovers the neuronal mechanisms by which OXT modulates the function of DRN 5-HT neurons.

The Role of Oxytocin in Domestic Animal’s Maternal Care: Parturition, Bonding, and Lactation

Oxytocin (OXT) is one of the essential hormones in the birth process; however, estradiol, prolactin, cortisol, relaxin, connexin, and prostaglandin are also present. In addition to parturition, the functions in which OXT is also involved in mammals include the induction of maternal behavior, including imprinting and maternal care, social cognition, and affiliative behavior, which can affect allo-parental care. The present article aimed to analyze the role of OXT and the neurophysiologic regulation of this hormone during parturition, how it can promote or impair maternal behavior and bonding, and its importance in lactation in domestic animals.

Oxytocin preprotein and oxytocin receptor mRNA expression is altered in semen samples with abnormal semen parameters

RESEARCH QUESTION

Are oxytocin preprotein and the oxytocin receptor expressed in human spermatozoa and is their mRNA expression different between normal semen samples and samples with at least one abnormal parameter?

DESIGN

An in-vitro prospective study of 175 semen samples from Greek men, according to World Health Organization criteria, 2010. mRNA expression levels were compared between different categories of semen samples, classified according to their concentration, total number, motility and morphology. Immunohistochemistry was used to detect oxytocin preprotein and its receptor on spermatozoa smears.

RESULTS

Compared with normal samples (normal motility and normal concentration), samples with at least one abnormal sperm parameter had statistically significantly lower oxytocin preprotein mRNA expression (P = 0.019) and higher oxytocin receptor mRNA expression levels (P < 0.001). Oligozoospermic samples had statistically significantly higher oxytocin preprotein mRNA expression levels (P = 0.002) and lower oxytocin receptor mRNA expression levels (P = 0.047). Asthenozoospermic samples had statistically significantly lower oxytocin preprotein mRNA expression levels (P < 0.001). Teratozoospermic samples had statistically significantly lower oxytocin preprotein mRNA expression levels (P = 0.049) and higher oxytocin receptor mRNA expression levels (P < 0.001). Oxytocin preprotein mRNA expression was positively associated with total progressive motility (P < 0.001) and negatively associated with the percentage of immotile spermatozoa (P = 0.001). Oxytocin receptor mRNA expression was negatively associated with the percentage of normal forms (P < 0.001).

CONCLUSION

Oxytocin preprotein and oxytocin receptor mRNA expression in spermatozoa could be used as a novel and unbiased diagnostic tool for male infertility.

Structures of the arginine-vasopressin and oxytocin receptor signaling complexes

Arginine-vasopressin (AVP) and oxytocin (OT) are neurohypophysial hormones which share a high sequence and structure homology. These are two cyclic C-terminally amidated nonapeptides with different residues at position 3 and 8. In mammals, AVP and OT exert their multiple biological functions through a specific G protein-coupled receptor family: four receptors are identified, the V1a, V1b, V2 receptors (V1aR, V1bR and V2R) and the OT receptor (OTR). The chemical structure of AVP and OT was elucidated in the early 1950s. Thanks to X-ray crystallography and cryo-electron microscopy, it took however 70 additional years to determine the three-dimensional structures of the OTR and the V2R in complex with their natural agonist ligands and with different signaling partners, G proteins and β-arrestins. Today, the comparison of the different AVP/OT receptor structures gives structural insights into their orthosteric ligand binding pocket, their molecular mechanisms of activation, and their interfaces with canonical Gs, Gq and β-arrestin proteins. It also paves the way to future rational drug design and therapeutic compound development. Indeed, agonist, antagonist, biased agonist, or pharmacological chaperone analogues of AVP and OT are promising candidates to regulate different physiological functions and treat several pathologies.

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.

Peripartum effects of synthetic oxytocin: The good, the bad, and the unknown

The first clinical applications of oxytocin (OT) were in obstetrics as a hormone to start and speed up labor and to control postpartum hemorrhage. Discoveries in the 1960s and 1970s revealed that the effects of OT are not limited to its peripheral actions around birth and milk ejection. Indeed, OT also acts as a neuromodulator in the brain affecting fear memory, social attachment, and other forms of social behaviors. The peripheral and central effects of OT have been separately subject to extensive scrutiny. However, the effects of peripheral OT-particularly in the form of administration of synthetic OT (synOT) around birth-on the central nervous system are surprisingly understudied. Here, we provide a narrative review of the current evidence, suggest putative mechanisms of synOT action, and provide new directions and hypotheses for future studies to bridge the gaps between neuroscience, obstetrics, and psychiatry.

Polygenic Risk Score Improves Cataract Prediction in East Asian Population

Cataracts, characterized by crystalline lens opacities in human eyes, is the leading cause of blindness globally. Due to its multifactorial complexity, the molecular mechanisms remain poorly understood. Larger cohorts of genome-wide association studies (GWAS) are needed to investigate cataracts’ genetic basis. In this study, a GWAS was performed on the largest Han population to date, analyzing a total of 7079 patients and 13,256 controls from the Taiwan Biobank (TWB) 2.0 cohort. Two cataract-associated SNPs with an adjustment of p < 1 × 10−7 in the older groups and nine SNPs with an adjustment of p < 1 × 10−6 in the younger group were identified. Except for the reported AGMO in animal models, most variations, including rs74774546 in GJA1 and rs237885 in OXTR, were not identified before this study. Furthermore, a polygenic risk score (PRS) was created for the young and old populations to identify high-risk cataract individuals, with areas under the receiver operating curve (AUROCs) of 0.829 and 0.785, respectively, after covariate adjustments. Younger individuals had 17.45 times the risk while older people had 10.97 times the risk when comparing individuals in the highest and lowest PRS quantiles. Validation analysis on an independent TWB1.0 cohort revealed AUROCs of 0.744 and 0.659.

Oxytocin: Narrative Expert Review of Current Perspectives on the Relationship with Other Neurotransmitters and the Impact on the Main Psychiatric Disorders

Is a cyclic neuropeptide produced primarily in the hypothalamus and plays an important neuromodulatory role for other neurotransmitter systems, with an impact on behavior, response to danger, stress, and complex social interactions, such as pair bonding and child care. This narrative expert review examines the literature on oxytocin as a brain hormone. We focused on oxytocin structure, distribution, genetics, and the oxytocin receptor system, as well as the relationship of oxytocin with other neurotransmitters and the resulting impacts on the main psychiatric disorders. Oxytocin levels have been correlated over time with mental illness, with numerous studies focusing on oxytocin and the pathophysiology of the main psychiatric disorders, such as autism, schizophrenia, personality disorders, mood, and eating disorders. We highlight the role oxytocin plays in improving symptoms such as anxiety, depression, and social behavior, as the literature suggests. Risk factors and causes for psychiatric disorders range from genetic to environmental and social factors. Oxytocin could impact the latter, being linked with other neurotransmitter systems that are responsible for integrating different situations during the development phases of individuals. Also, these systems have an important role in how the body responds to stressors or bonding with others, helping with the creation of social support groups that could speed up recovery in many situations. Oxytocin has the potential to become a key therapeutic agent for future treatment and prevention strategies concerning the main psychiatric disorders.

Circulating Isotocin, not Angiotensin II, is the Major Dipsogenic Hormone in Eels

Angiotensin II (AngII) is generally known as the most important dipsogenic hormone throughout vertebrates, while two other neurohypophysial hormones, vasopressin and oxytocin, are not dipsogenic in mammals. In this study, we found that systemic isotocin, but not vasotocin, is the potent dipsogenic hormone in eels. When injected intra-arterially into conscious eels, isotocin, vasotocin and AngII equally increased ventral aortic pressure dose-dependently at 0.03-1.0 nmol/kg, but only isotocin induced copious drinking. The dipsogenic effect was dose-dependent and occurred significantly at as low as 0.1 nmol/kg. By contrast, a sustained inhibition of drinking occurred after AngII, probably due to baroreflexogenic inhibition. No such inhibition was observed after isotocin despite similar concurrent hypertension. The baroreceptor may exist distal to the gill circulation because the vasopressor effect occurred at both ventral and dorsal aorta after AngII but only at ventral aorta after isotocin. By contrast, intra-cerebroventricular (i.c.v.) injection of isotocin had no effect on drinking or blood pressure, but AngII increased drinking and aortic pressure dose-dependently at 0.03-0.3 nmol/eel. Lesioning of the area postrema (AP), a sensory circumventricular organ, abolished drinking induced by peripheral isotocin, but not i.c.v. AngII. Collectively, isotocin seems to be a major circulating hormone that induces swallowing through its action on the AP, while AngII may be an intrinsic brain peptide that induces drinking through its action on a different circumventricular site, possibly a recently identified blood-brain barrier-deficient structure in the antero-ventral third ventricle of eels, as shown in birds and mammals.

Regulation of oxytocin receptor gene expression in obsessive-compulsive disorder: a possible role for the microbiota-host epigenetic axis

BACKGROUND

Obsessive-compulsive disorder (OCD) is a prevalent and severe clinical condition. Robust evidence suggests a gene-environment interplay in its etiopathogenesis, yet the underlying molecular clues remain only partially understood. In order to further deepen our understanding of OCD, it is essential to ascertain how genes interact with environmental risk factors, a cross-talk that is thought to be mediated by epigenetic mechanisms. The human microbiota may be a key player, because bacterial metabolites can act as epigenetic modulators. We analyzed, in the blood and saliva of OCD subjects and healthy controls, the transcriptional regulation of the oxytocin receptor gene and, in saliva, also the different levels of major phyla. We also investigated the same molecular mechanisms in specific brain regions of socially isolated rats showing stereotyped behaviors reminiscent of OCD as well as short chain fatty acid levels in the feces of rats.

RESULTS

Higher levels of oxytocin receptor gene DNA methylation, inversely correlated with gene expression, were observed in the blood as well as saliva of OCD subjects when compared to controls. Moreover, Actinobacteria also resulted higher in OCD and directly correlated with oxytocin receptor gene epigenetic alterations. The same pattern of changes was present in the prefrontal cortex of socially-isolated rats, where also altered levels of fecal butyrate were observed at the beginning of the isolation procedure.

CONCLUSIONS

This is the first demonstration of an interplay between microbiota modulation and epigenetic regulation of gene expression in OCD, opening new avenues for the understanding of disease trajectories and for the development of new therapeutic strategies.

Associations between alcohol use and peripheral, genetic, and epigenetic markers of oxytocin in a general sample of young and older adults

INTRODUCTION

Human and nonhuman animal research suggests that greater oxytocin (OT) activity is protective against harmful substance use. Most research on this topic is preclinical, with few studies evaluating the association between substance use and individual differences in the human OT system. The present study sought to fill this gap by evaluating the relationship between alcohol use and multiple biological measures of OT activity in an overall low to moderate-drinking sample.

METHOD

As part of a larger study, generally healthy young (n = 51) and older (n = 53) adults self-reported whether they regularly used alcohol and how much alcohol they consumed per week. Participants also provided blood samples from which peripheral OT, and in an age-heterogeneous subset of participants (n = 56) variation in the oxytocin receptor gene (the OXTR rs53576 polymorphism) and OXTR DNA methylation levels (at cytosine-guanine dinucleotide sites -860, -924, -934), were obtained.

RESULTS

A-allele carriers of the OXTR rs53579 polymorphism were less likely to regularly consume alcohol. Among regular alcohol consumers, number of alcoholic drinks per week was positively associated with peripheral OT in regression models excluding observations of high influence (postdiagnostic models). Number of alcoholic drinks per week was consistently negatively associated with OXTR DNA methylation at site -860; and with OXTR DNA methylation at site -924 in postdiagnostic models.

CONCLUSIONS

The significant associations between alcohol use and individual differences in OT activity support the involvement of the OT system in alcohol use, which most likely reflect the role of OT when alcohol use is under control of its rewarding properties and/or the acute impacts of alcohol on the OT system. Additional research with markers of OT activity and alcohol use, particularly longitudinal, is needed to clarify the bidirectional effects of OT and alcohol use in moderate to harmful drinking and dependence.

Conformational selection of vasopressin upon V1a receptor binding

The neuropeptide vasopressin (VP) and its three G protein-coupled receptors (V_1aR, V_1bR and V₂R) are of high interest in a wide array of drug discovery programs. V_1aR is of particular importance due to its cardiovascular functions and diverse roles in the central nervous system. The structure–activity relationships underpinning ligand-receptor interactions remain however largely unclear, hindering rational drug design. This is not least due to the high structural flexibility of VP in its free as well as receptor-bound states. In this work, we developed a novel approach to reveal features of conformational selectivity upon VP-V_1aR complex formation. We employed virtual screening strategies to probe VP’s conformational space for transiently adopted structures that favor binding to V_1aR. To this end, we dissected the VP conformational space into three sub-ensembles, each containing distinct structural sets for VP’s three-residue C-terminal tail. We validated the computational results with experimental nuclear magnetic resonance (NMR) data and docked each sub-ensemble to V_1aR. We observed that the conformation of VP’s three-residue tail significantly modulated the complex dissociation constants. Solvent-exposed and proline trans-configured VP tail conformations bound to the receptor with three-fold enhanced affinities compared to compacted or cis-configured conformations. The solvent-exposed and more flexible structures facilitated unique interaction patterns between VP and V_1aR transmembrane helices 3, 4, and 6 which led to high binding energies. The presented “virtual conformational space screening” approach, integrated with NMR spectroscopy, thus enabled identification and characterization of a conformational selection-type complex formation mechanism that confers novel perspectives on targeting the VP-V_1aR interactions at the level of the encounter complex – an aspect that opens novel research avenues for understanding the functionality of the evolutionary selected conformational properties of VP, as well as guidance for ligand design strategies to provide more potent and selective VP analogues.

Labour induction in twin pregnancies

Medically-indicated deliveries are common in twin pregnancies given the increased risk of various obstetric complications in twin compared to singleton pregnancies, mainly hypertensive disorders of pregnancy and foetal growth restriction. Due to the unique characteristics of twin pregnancies, the success rates and safety of labour induction may be different than in singleton pregnancies. However, while there are abundant data regarding induction of labour in singleton pregnancies, the efficacy and safety of labour induction in twin pregnancies have been far less studied. In the current manuscript we summarize available data on various aspects of labour induction in twin pregnancies including incidence, success rate, prognostic factors, safety and methods for labour induction in twins. This information may assist healthcare providers in counselling patients with twin pregnancies when labour induction is indicated.

Oxytocin: A citation network analysis of 10 000 papers

Our understanding of the oxytocin system has been built over the last 70 years by the work of hundreds of scientists, reported in thousands of papers. Here, we construct a map to that literature, using citation network analysis in conjunction with bibliometrics. The map identifies ten major 'clusters' of papers on oxytocin that differ in their particular research focus and that densely cite papers from the same cluster. We identify highly cited papers within each cluster and in each decade, not because citations are a good indicator of quality, but as a guide to recognising what questions were of wide interest at particular times. The clusters differ in their temporal profiles and bibliometric features; here, we attempt to understand the origins of these differences.

Oxytocin receptor polymorphism influences characterization of harm avoidance by moderating susceptibility to affectionless control parenting

INTRODUCTION

Oxytocin receptor (OXTR) gene polymorphism reportedly moderates effects of negative environments during childhood on mental function and behavior such as depressive symptoms and externalizing problems. This study examined OXTR gene polymorphism effects on personality traits in healthy participants, considering interaction effects of polymorphism with affectionless control (AC) parenting which is one of the dysfunctional and pathogenic parenting styles.

METHODS

For 496 Japanese volunteers, personality was evaluated using the Temperament and Character Inventory. The Parental Bonding Instrument, which has subscales of care and protection, was used to assess perceived parental rearing. AC parenting was defined as low care and high protection. A/G polymorphism of the OXTR gene (rs53576) was detected using TaqMan SNP Genotyping Assay.

RESULTS

Two-way analysis of covariance revealed significant interaction effects between the genotype and the number of AC parents on scores of harm avoidance, with no significant main effect of genotype on any personality. Post-hoc analysis revealed that the harm avoidance scores were increased in a stepwise manner with respect to the increase of the number of AC parents in the A allele carriers. No similar association was observed in the A allele noncarriers.

CONCLUSION

The results of this study suggest that OXTR polymorphism influences characterization of harm avoidance by moderating susceptibility to AC parenting.

A randomized controlled trial of intranasal oxytocin in Phelan-McDermid syndrome

Background

Phelan-McDermid syndrome (PMS) is a rare neurodevelopmental disorder caused by haploinsufficiency of the SHANK3 gene and characterized by global developmental delays, deficits in speech and motor function, and autism spectrum disorder (ASD). Monogenic causes of ASD such as PMS are well suited to investigations with novel therapeutics, as interventions can be targeted based on established genetic etiology. While preclinical studies have demonstrated that the neuropeptide oxytocin can reverse electrophysiological, attentional, and social recognition memory deficits in Shank3-deficient rats, there have been no trials in individuals with PMS. The purpose of this study is to assess the efficacy and safety of intranasal oxytocin as a treatment for the core symptoms of ASD in a cohort of children with PMS.

Methods

Eighteen children aged 5–17 with PMS were enrolled. Participants were randomized to receive intranasal oxytocin or placebo (intranasal saline) and underwent treatment during a 12-week double-blind, parallel group phase, followed by a 12-week open-label extension phase during which all participants received oxytocin. Efficacy was assessed using the primary outcome of the Aberrant Behavior Checklist-Social Withdrawal (ABC-SW) subscale as well as a number of secondary outcome measures related to the core symptoms of ASD. Safety was monitored throughout the study period.

Results

There was no statistically significant improvement with oxytocin as compared to placebo on the ABC-SW (Mann–Whitney U = 50, p = 0.055), or on any secondary outcome measures, during either the double-blind or open-label phases. Oxytocin was generally well tolerated, and there were no serious adverse events.

Limitations

The small sample size, potential challenges with drug administration, and expectancy bias due to relying on parent reported outcome measures may all contribute to limitations in interpreting results.

Conclusion

Our results suggest that intranasal oxytocin is not efficacious in improving the core symptoms of ASD in children with PMS.

Trial registration NCT02710084.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13229-021-00459-1.

Antenatal breastmilk expression for women with diabetes in pregnancy - a feasibility study

Background

Mothers with diabetes are less likely to achieve successful breastfeeding. Antenatal breastmilk expression (ABE) may facilitate earlier breastfeeding, but feasibility of introducing ABE and its acceptance among Scandinavian women have previously not been investigated.

Methods

This observational trial was conducted between the 1 January 2019 and the 12 March 2020 in Tromsø, Norway. We aimed to determine the feasibility of ABE in terms of practicality and acceptability among women with medically (metformin or insulin) treated diabetes. Women were invited to participate during antenatal visits from 32 weeks gestation. Participants received instruction and started ABE from gestation week 37 + 0. Participants, and their infants, were followed until 6–8 weeks after birth. We collected data on breastfeeding rates, infant hypoglycemia, transfer to the neonatal unit, and the women’s overall experience and satisfaction with antenatal breastmilk expression.

Results

Twenty-eight of 34 (82%) invited women consented to participate. All started ABE from week 37 + 0, and continued until hospital admission. No women reported any discomfort or side effects. Labor was induced at 38 weeks gestation. Twenty-four women brought harvested colostrum to the maternity ward, which was given to their infants during the first 24 h of life. Breastfeeding rates at discharge were 24/28 (86%) and 21/27 (78%) at 6–8 weeks after delivery. Seven (25%) infants were transferred to the neonatal unit; four because of hypoglycemia. Maternal satisfaction assessed 6–8 weeks after delivery revealed that all participants felt positive about the ABE, but one woman would not recommend it to other pregnant women.

Conclusions

Implementing a structured ABE guideline for women with medically treated diabetes was feasible. The intervention was associated with high level of satisfaction among study participants. No obvious side effects were observed, and breastfeeding rates at discharge and 6–8 weeks after delivery were higher than in comparable studies.

Trial registration

The study was registered at the research study registry at the University Hospital of North Norway (Nr 2018/7181).

Oxytocin receptor induces mammary tumorigenesis through prolactin/p-STAT5 pathway

Oxytocin receptor (OXTR) is involved in social behaviors, thermoregulation, and milk ejection, yet little is known about its role in breast cancer. To investigate the role of OXTR in mammary gland development and tumorigenesis, a transgenic mouse model of OXTR overexpression (⁺⁺Oxtr) was used. Overexpression of OXTR-induced progressive mammary hyperplasia, unexpected milk production, and tumorigenesis in females. OXTR-induced mammary tumors showed ERBB2 upregulation and mixed histological subtypes with predomination of papillary and medullary carcinomas. OXTR overexpression led to an activation of prolactin (PRL)/p-STAT5 pathway and created a microenvironment that promotes mammary-specific tumorigenesis. PRL inhibitor bromocriptine (Br) could mitigate OXTR-driven mammary tumor growth. The study demonstrates Oxtr is an oncogene and a potential drug target for HER2-type breast cancer.

Human Chorionic Gonadotropin Modulates the Transcriptome of the Myometrium and Cervix in Late Gestation

Human chorionic gonadotropin (hCG) is a critical hormone for the establishment and maintenance of pregnancy. hCG administration prevents the onset of preterm labor in mice; yet, the transcriptomic changes associated with this tocolytic effect that take place in the myometrium and cervix have not been elucidated. Herein, we implemented both discovery and targeted approaches to investigate the transcriptome of the myometrium and cervix after hCG administration. Pregnant mice were intraperitoneally injected with 10 IU of hCG on 13.0, 15.0, and 17.0 days post coitum, and the myometrium and cervix were collected. RNA sequencing was performed to determine differentially expressed genes, enriched biological processes, and impacted KEGG pathways. Multiplex qRT-PCR was performed to investigate the expression of targeted contractility- and inflammation-associated transcripts. hCG administration caused the differential expression of 720 genes in the myometrium. Among the downregulated genes, enriched biological processes were primarily associated with regulation of transcription. hCG administration downregulated key contractility genes, Gja1 and Oxtr, but upregulated the prostaglandin-related genes Ptgfr and Ptgs2 and altered the expression of inflammation-related genes in the myometrium. In the cervix, hCG administration caused differential expression of 3348 genes that were related to inflammation and host defense, among others. The downregulation of key contractility genes and upregulation of prostaglandin-related genes were also observed in the cervix. Thus, hCG exerts tocolytic and immunomodulatory effects in late gestation by altering biological processes in the myometrium and cervix, which should be taken into account when considering hCG as a potential treatment to prevent the premature onset of labor.

The Biology of Vasopressin

Vasopressins are evolutionarily conserved peptide hormones. Mammalian vasopressin functions systemically as an antidiuretic and regulator of blood and cardiac flow essential for adapting to terrestrial environments. Moreover, vasopressin acts centrally as a neurohormone involved in social and parental behavior and stress response. Vasopressin synthesis in several cell types, storage in intracellular vesicles, and release in response to physiological stimuli are highly regulated and mediated by three distinct G protein coupled receptors. Other receptors may bind or cross-bind vasopressin. Vasopressin is regulated spatially and temporally through transcriptional and post-transcriptional mechanisms, sex, tissue, and cell-specific receptor expression. Anomalies of vasopressin signaling have been observed in polycystic kidney disease, chronic heart failure, and neuropsychiatric conditions. Growing knowledge of the central biological roles of vasopressin has enabled pharmacological advances to treat these conditions by targeting defective systemic or central pathways utilizing specific agonists and antagonists.

Development of Magnetic Nanobeads Modified by Artificial Fluorescent Peptides for the Highly Sensitive and Selective Analysis of Oxytocin

We describe two novel fluorescent peptides (compounds 1 and 2) targeting oxytocin with a boron-dipyrromethenyl group as the fluorophore bound to an artificial peptide based on the oxytocin receptor, and their application for the analysis of oxytocin levels in human serum using nanometer-sized magnetic beads modified by fluorescent peptides (FMB-1 and FMB-2). Under the optimized experimental protocols, FMB-1 and FMB-2 emitted low levels of fluorescence but emitted much higher levels of fluorescence when associated with oxytocin. The detection limit of oxytocin by FMB-2 was 0.4 pM, which is approximately 37.5 times higher than that of conventional methods, such as ELISA. Using these fluorescent sensors, oxytocin was specifically detected over a wide linear range with high sensitivity, good reusability, stability, precision, and reproducibility. This fluorescent sensor-based detection system thus enabled the measurement of oxytocin levels in human serum, which has widespread applications for oxytocin assays across varied research fields.

Oxytocin Receptor Signaling in Vascular Function and Stroke

The oxytocin receptor (OXTR) is a G protein-coupled receptor with a diverse repertoire of intracellular signaling pathways, which are activated in response to binding oxytocin (OXT) and a similar nonapeptide, vasopressin. This review summarizes the cell and molecular biology of the OXTR and its downstream signaling cascades, particularly focusing on the vasoactive functions of OXTR signaling in humans and animal models, as well as the clinical applications of OXTR targeting cerebrovascular accidents.

Oxytocin receptor gene polymorphism (rs53576) and digit ratio associates with aggression: comparison in seven ethnic groups

Background

The specific role of the oxytocin receptor (OXTR) gene polymorphisms in emotional support seeking, related to social norms and culturally normative behavior, has been discussed in several studies. Evidence on the association between aggression and OXTR polymorphisms has also been reported. The goal of the current study was to analyze the effect of the OXTR rs53576 polymorphism, prenatal testosterone effect (second-to-fourth digit ratio, or 2D:4D), and culture on aggression assessed with the Buss-Perry Aggression Questionnaire (BPAQ).

Methods

The data were collected in Russia and Tanzania and included seven ethnic groups of European, Asian, and African origin. The total sample included 1705 adults (837 males, 868 females). All the subjects were evaluated with the BPAQ. As a measure of prenatal androgenization, the second and fourth digits were measured directly from hand, and the digit ratios were calculated. All the participants provided buccal samples, from which genomic DNA was extracted, and the OXTR gene rs53576 polymorphism was genotyped. Statistical analysis was performed using SPSS version 23.0; the alpha level for all analyses was set at 0.05.

Results

The ethnic group factor was the most significant predictor of ratings on BPAQ (medium effect size for physical aggression, anger and hostility scales, and low for verbal aggression). To study the effect of sex, the OXTR polymorphism, and prenatal androgenization, we conducted the z-score transformation for BPAQ scales and 2D:4D for each ethnic group and pooled these data into new z-score variables. According to the GLM analysis after leveling the effects of culture (z-transformation), all four scales of BPAQ demonstrated association with sex (main effects), with men scoring higher on physical and verbal aggression and women scoring higher on anger and hostility. Anger and hostility scales were also associated with OXTR polymorphism and 2D:4D of the right hand. The lowest levels of anger and hostility were observed in individuals with the AA genotype, especially in men.

Conclusions

Our data suggest that both oxytocin (OXTR gene polymorphism) and fetal testosterone (2D:4D) may significantly affect emotional (anger) and cognitive (hostility) aggression in humans, given the leveling the role of culture.

What's Love Got to do with it: Role of oxytocin in trauma, attachment and resilience

Oxytocin (OT) is a neurohypophysial hormone and neuropeptide produced by the hypothalamus and released by the pituitary gland. It has multiple physiological roles including stimulation of parturition and lactation, and promotion of pro-adaptive social behaviors necessary for mammalian survival. OT interacts with one receptor subtype: the OT receptor (OTR) which, upon stimulation, triggers different intracellular signal transduction cascades to mediate its physiological actions. Preclinical studies show that OT regulates social behaviors such as pair bonding, recognition and social interaction. It also coordinates the activation of the hypothalamic-pituitary-adrenal (HPA) axis and the release of corticotrophin-releasing hormone. Further evidence suggests that OT plays an important role in regulating caloric intake and metabolism, and in maintaining electrolyte and cardiovascular homeostasis. OT is also involved in attenuating the neurophysiological and neurochemical effects of trauma on the brain and body by facilitating both physical attachment such as wound healing, and psychological/social attachment, thereby increasing resilience to subsequent traumatic events. Clinical trials have reported that intranasal administration of OT provides therapeutic benefits for patients diagnosed with traumatic stress-related diseases such as major depressive disorders and post-traumatic stress disorder. OT's therapeutic benefits may result from context-dependent interactions with key neural pathways (social, cognitive, and reward), neurotransmitters (dopamine, norepinephrine, serotonin, and endogenous opioids), and biomarkers (adrenocorticotropic hormone, cortisol, and dehydroepiandrosterone sulfate), that lead to a decrease in stress -associated behaviors, and facilitate post-traumatic growth, ultimately leading to increased resilience, through improved social cohesion and attachment. OT induced-augmentation of physical and cognitive resilience may play a significant role in both the prevention of, and improved clinical outcomes for, traumatic stress-related disorders following either acute or enduring traumatic experiences.

Gestational and Hormonal Effects on Magnesium Sulfate's Ability to Inhibit Mouse Uterine Contractility

Magnesium sulfate is used as a tocolytic, but clinical efficacy has been seriously questioned. Our objective was to use controlled ex vivo conditions and known pregnancy stages, to investigate how 2 key factors, hormones and gestation, affect magnesium's tocolytic ability. We hypothesized that these factors could underlie the varying clinical findings around magnesium's efficacy. Myometrial strips were obtained from nonpregnant (n = 10), mid-pregnant (n = 12), and term-pregnant (n = 11) mouse uterus. The strips were mounted in organ baths superfused with oxygenated physiological saline at pH 7.4 and 37 °C. The effect of different concentrations of MgSO₄ (2-20 mM) was examined on spontaneous and oxytocin-induced (0.5-1 nM) contractions. Contractile properties (amplitude, frequency, and area under the curve) were measured before and after application of magnesium. Magnesium sulfate had a dose-dependent inhibitory effect on both spontaneous and oxytocin-induced contractions but was less effective in the presence of oxytocin. In spontaneous contractions, magnesium was more potent as gestation progressed (P < .0001). In the presence of oxytocin, however, there were no significant gestational differences in its effects on contraction. The rapid onset and reversal of magnesium's effects suggest an extracellular action on calcium entry. Taken together, we conclude that magnesium's actions are influenced by both gestational state and hormones, such that, at least in mice, it is least effective in early gestation with oxytocin present and most effective at term in the absence of oxytocin. That magnesium is least effective preterm and oxytocin decreases its effectiveness throughout gestation, may explain its disappointing clinical effects as a tocolytic.

Vasopressin & Oxytocin in Control of the Cardiovascular System: An Updated Review

Since the discovery of vasopressin (VP) and oxytocin (OT) in 1953, considerable knowledge has been gathered about their roles in cardiovascular homeostasis. Unraveling VP vasoconstrictor properties and V1a receptors in blood vessels generated powerful hemostatic drugs and drugs effective in the treatment of certain forms of circulatory collapse (shock). Recognition of the key role of VP in water balance via renal V2 receptors gave birth to aquaretic drugs found to be useful in advanced stages of congestive heart failure. There are still unexplored actions of VP and OT on the cardiovascular system, both at the periphery and in the brain that may open new venues in treatment of cardiovascular diseases. After a brief overview on VP, OT and their peripheral action on the cardiovascular system, this review focuses on newly discovered hypothalamic mechanisms involved in neurogenic control of the circulation in stress and disease.

Oxytocin modulates responsibility attribution and hypothetical Resource allocation during cooperation

Reasonable responsibility attribution and resource allocation in intragroup contexts benefit the evolution of group cooperation. Oxytocin (OT) has been shown to promote prosocial behavior; however, it remains unclear whether OT affects responsibility attribution and hypothetical resource allocation. In the present study, participants were intranasally administered OT or placebo (PLC) before a response task with a partner. The participant could win a certain amount of money depending on the group's performance, which was determined by the faster player. The contribution was manipulated to be similar in the first phase, while the participants could individually contribute more in the second phase. Our results show that both groups attributed more credit to the player who performed better in a trial. Moreover, reward magnitude only enhanced effort-based attribution in the OT group. Although both groups proposed to distribute money based on individual efforts, the PLC group increased their effort-based allocation when they contributed more, regardless of the fact that the money was eventually equally distributed. Our study demonstrates that OT modulates responsibility attribution and hypothetical resource allocation in different manners, suggesting that OT has different effects on a participant's perception of individual contribution and fairness when allocating a reward during social cooperation in a real effort task.

Role of Oxytocin/Vasopressin-Like Peptide and Its Receptor in Vitellogenesis of Mud Crab

Oxytocin (OT)/vasopressin (VP) signaling system is important to the regulation of metabolism, osmoregulation, social behaviours, learning, and memory, while the regulatory mechanism on ovarian development is still unclear in invertebrates. In this study, Spot/vp-like and its receptor (Spot/vpr-like) were identified in the mud crab Scylla paramamosain. Spot/vp-like transcripts were mainly expressed in the nervous tissues, midgut, gill, hepatopancreas, and ovary, while Spot/vpr-like were widespread in various tissues including the hepatopancreas, ovary, and hemocytes. In situ hybridisation revealed that Spot/vp-like mRNA was mainly detected in 6–9th clusters in the cerebral ganglion, and oocytes and follicular cells in the ovary, while Spot/vpr-like was found to localise in F-cells in the hepatopancreas and oocytes in the ovary. In vitro experiment showed that the mRNA expression level of Spvg in the hepatopancreas, Spvgr in the ovary, and 17β-estradiol (E₂) content in culture medium were significantly declined with the administration of synthetic SpOT/VP-like peptide. Besides, after the injection of SpOT/VP-like peptide, it led to the significantly reduced expression of Spvg in the hepatopancreas and subduced E₂ content in the haemolymph in the crabs. In brief, SpOT/VP signaling system might inhibit vitellogenesis through neuroendocrine and autocrine/paracrine modes, which may be realised by inhibiting the release of E₂.

Characterization of Oxytocin Receptor Expression Within Various Neuronal Populations of the Mouse Dorsal Hippocampus

Oxytocin, acting through the oxytocin receptor (Oxtr) in the periphery, is best known for its roles in regulating parturition and lactation. However, it is also now known to possess a number of important social functions within the central nervous system, including social preference, memory and aggression, that vary to different degrees in different species. The Oxtr is found in both excitatory and inhibitory neurons within the brain and research is focusing on how, for example, activation of the receptor in interneurons can enhance the signal-to-noise of neuronal transmission. It is important to understand which neurons in the mouse dorsal hippocampus might be activated during memory formation. Therefore, we examined the colocalization of transcripts in over 5,000 neurons for Oxtr with those for nine different markers often found in interneurons using hairpin chain reaction in situ hybridization on hippocampal sections. Most pyramidal cell neurons of CA2 and many in the CA3 express Oxtr. Outside of those excitatory neurons, over 90% of Oxtr-expressing neurons co-express glutamic acid decarboxylase-1 (Gad-1) with progressively decreasing numbers of co-expressing cholecystokinin, somatostatin, parvalbumin, neuronal nitric oxide synthase, the serotonin 3a receptor, the vesicular glutamate transporter 3, calbindin 2 (calretinin), and vasoactive intestinal polypeptide neurons. Distributions were analyzed within hippocampal layers and regions as well. These findings indicate that Oxtr activation will modulate the activity of ~30% of the Gad-1 interneurons and the majority of the diverse population of those, mostly, interneuron types specifically examined in the mouse hippocampus.

A Nonpeptide Oxytocin Receptor Agonist for a Durable Relief of Inflammatory Pain

Oxytocin possesses several physiological and social functions, among which an important analgesic effect. For this purpose, oxytocin binds mainly to its unique receptor, both in the central nervous system and in the peripheral nociceptive terminal axon in the skin. However, despite its interesting analgesic properties and its current use in clinics to facilitate labor, oxytocin is not used in pain treatment. Indeed, it is rapidly metabolized, with a half-life in the blood circulation estimated at five minutes and in cerebrospinal fluid around twenty minutes in humans and rats. Moreover, oxytocin itself suffers from several additional drawbacks: a lack of specificity, an extremely poor oral absorption and distribution, and finally, a lack of patentability. Recently, a first non-peptide full agonist of oxytocin receptor (LIT-001) of low molecular weight has been synthesized with reported beneficial effect for social interactions after peripheral administration. In the present study, we report that a single intraperitoneal administration of LIT-001 in a rat model induces a long-lasting reduction in inflammatory pain-induced hyperalgesia symptoms, paving the way to an original drug development strategy for pain treatment.

Functional Hierarchy of Uterotonics Required for Successful Parturition in Mice

Parturition is an essential process in placental mammals for giving birth to offspring. However, the molecular machineries of parturition are not fully understood. We investigated whether oxytocin plays a crucial role in the progress of parturition in cooperation with the prostaglandin F2α (PGF2α) receptor. We first examined alterations in the expression of uterine contraction-associated genes in uteri of oxytocin receptor-deficient mice (Oxtr-/-) during parturition. We found that induction of cyclooxygenase (COX)-2 and connexin 43 expression was impaired in Oxtr-/-, whereas that of PGF2α receptor expression was not. We next generated mice with double knockout of genes for the oxytocin receptor/oxytocin and PGF2α receptor (Oxtr-/-;Ptgfr-/- and Oxt-/-;Ptgfr-/-) and evaluated their parturition with Oxtr-/-, Oxt-/-, Ptgfr-/-, and wild-type mice. In Oxtr-/-;Ptgfr-/- and Oxt-/-;Ptgfr-/-, pregnancy rates were similar to those of other genotypes. However, normal parturition was not observed in Oxtr-/-;Ptgfr-/- or Oxt-/-;Ptgfr-/- because of persistent progesterone from the corpus luteum, as observed in Ptgfr-/-. We administered RU486, a progesterone antagonist, to Ptgfr-/-, Oxtr-/-;Ptgfr-/-, and Oxt-/-;Ptgfr-/- on gestation day 19. These mice were able to deliver a living first pup and the parturition onset was similar to that in Ptgfr-/-. Meanwhile, unlike Ptgfr-/-, ∼75% of Oxtr-/-;Ptgfr-/- and Oxt-/-;Ptgfr-/- administered RU486 remained in labor at 24 hours after the onset of parturition. All of the pups that experienced prolonged labor died. We thus revealed that the oxytocin receptor is an upstream regulator of COX-2 and connexin 43 in the uterus during parturition and that both oxytocin/oxytocin receptor and PGF2α receptor are major components for successful parturition.

Influence of oxytocin receptor single nucleotide sequence variants on contractility of human myometrium: an in vitro functional study

Background

Oxytocin receptor (OXTR) gene variants have been shown to affect the prevalence of preterm birth, mode of delivery and oxytocin (OXT) requirements for labor induction and augmentation. We hypothesized that this might be associated with different myometrium responses to oxytocin. Our aim was to investigate the influence of a selection of eight OXTR gene single nucleotide variants on oxytocin-induced stimulation of human myometrium contractility in vitro.

Methods

Human myometrium biopsies were collected during elective cesarean sections at term, if patients had given informed consent. Myometrial strips were submerged under tension in an organ bath and allowed to contract; the remaining material was stored at − 80 °C for further determination of relevant genetics and mRNA level. The area under the curve (AUC) of all contractions taking place in the absence of OXT and of those occurring upon OXT addition (for 30 min each) was measured. OXT stimulation, defined as the ratio between AUC measurements after OXT addition and those in the absence of OXT was calculated for each strip. TaqMan™ Assays were used to detect the allele distribution of the eight OXTR variants and to determine the relative amounts of OXTR-mRNA in the samples. For each variant, oxytocin stimulation of contractility was compared between samples homozygous for the reference allele (reference group) and samples with at least one variant allele (variant group) by linear regression.

Results

Sixty samples were included in the present study. For rs1042778, rs11706648, rs4686301, rs53576, rs237895, and rs237902, OXT stimulation was similar in the reference and in the variant groups. However, the values of OXT stimulation differed significantly between the reference and the variant groups for rs4686302 (3.1 vs. 4.1 times; p = 0.022) and rs237888 (3.2 vs. 5.5 times; p = 0.001). No significant differences between the levels of OXTR-mRNA in the various reference and corresponding variant groups were detected.

Conclusions

Patients with variant alleles of rs237888 and/or rs4686302 may be more sensitive to oxytocin stimulation, explaining why these sequence variants have been associated with lower cesarean section prevalence and premature birth, respectively.

Circulating Oxytocin Is Genetically Determined and Associated With Obesity and Impaired Glucose Tolerance

CONTEXT

Despite the emerging evidence on the role of oxytocin (OXT) in metabolic diseases, there is a lack of well-powered studies addressing the relationship of circulating OXT with obesity and diabetes.

OBJECTIVES AND DESIGN

Here, we measured OXT in a study cohort (n = 721; 396 women, 325 men; mean age ± SD, 47.7 ± 15.2 years) with subphenotypes related to obesity, including anthropometric traits such as body mass index [BMI (mean ± SD), 26.8 ± 4.6 kg/m2], waist-to-hip ratio (WHR; 0.88 ± 0.09), blood parameters (glucose, 5.32 ± 0.50 mmol/L; insulin, 5.3 ± 3.3 µU/mL), and oral glucose tolerance test to clarify the association with OXT. We also tested in a genome-wide association study (GWAS) whether the interindividual variation in OXT serum levels might be explained by genetic variation.

RESULTS

The OXT concentration was increased in subjects with elevated BMI and positively correlated with WHR, waist circumference, and triglyceride levels. The OXT concentration in subjects with BMI <25 kg/m2 was significantly lower (n = 256; 78.6 pg/mL) than in subjects with a BMI between 25 and 30 kg/m2 (n = 314; 98.5 pg/mL, P = 6 × 10-6) and with BMI >30 kg/m2 (n = 137; 106.4 pg/mL, P = 8 × 10-6). OXT levels were also positively correlated with plasma glucose and insulin and were elevated in subjects with impaired glucose tolerance (P = 4.6 × 10-3). Heritability of OXT was estimated at 12.8%. In a GWAS, two hits in linkage disequilibrium close (19 kb) to the OXT reached genome-wide significant association (top-hit rs12625893, P = 3.1 × 10-8, explained variance 3%).

CONCLUSIONS

Our data show that OXT is genetically affected by a variant near OXT and is associated with obesity and impaired glucose tolerance.

Arginine vasotocin (AVT)/mesotocin (MT) receptors in chickens: Evidence for the possible involvement of AVT-AVPR1 signaling in the regulation of oviposition and pituitary prolactin expression

Two structurally related peptides, arginine vasotocin (AVT) and mesotocin (MT), are reported to regulate many physiological processes, such as anti-diuresis and oviposition in birds, and their actions are likely mediated by four AVT/MT receptors (AVPR1A, AVPR1B, MTR and AVPR2b), which are orthologous/paralogous to human AVPR1A, AVPR1B, OXTR and AVPR2 respectively. However, our knowledge regarding the functions of these avian AVT/MT receptors has been limited. Here, we examined the functionality and expression of these receptors in chickens and investigated the roles of AVT in the anterior pituitary. Our results showed that 1) AVPR1A, AVPR1B and AVPR2b could be preferentially activated by AVT, monitored by cell-based luciferase reporter assays and/or Western blot, indicating that they are AVT-specific receptors (AVPR1A; AVPR1B) or AVT-preferring receptor (AVPR2b) functionally coupled to intracellular calcium, MAPK/ERK and cAMP/PKA signaling pathways. In contrast, MTR could be activated by AVT and MT with similar potencies, indicating that MTR is a receptor common for both peptides; 2) Using qPCR, differential expression of the four receptors was found in chicken tissues including the oviduct and anterior pituitary. In particular, only AVPR1A is abundantly expressed in the uterus, suggesting its involvement in mediating AVT-induced oviposition. 3) In cultured chick pituitary cells, AVT could stimulate ACTH and PRL expression and secretion, an action likely mediated by AVPR1B and/or AVPR1A abundantly expressed in anterior pituitary. Collectively, our data helps to elucidate the roles of AVT/MT in birds, such as the 'oxytocic action' of AVT, which induces uterine muscle contraction during oviposition.

Attenuation of Oxytocin and Serotonin 2A Receptor Signaling through Novel Heteroreceptor Formation

The oxytocin receptor (OTR) and the 5-hydroxytryptamine 2A receptor (5-HTR_2A) are expressed in similar brain regions modulating central pathways critical for social and cognition-related behaviors. Signaling crosstalk between their endogenous ligands, oxytocin (OT) and serotonin (5-hydroxytryptamine, 5-HT), highlights the complex interplay between these two neurotransmitter systems and may be indicative of the formation of heteroreceptor complexes with subsequent downstream signaling changes. In this study, we assess the possible formation of OTR-5HTR_2A heteromers in living cells and the functional downstream consequences of this receptor-receptor interaction. First, we demonstrated the existence of a physical interaction between the OTR and 5-HTR_2A in vitro, using a flow cytometry-based FRET approach and confocal microscopy. Furthermore, we investigated the formation of this specific heteroreceptor complex ex vivo in the brain sections using the Proximity Ligation Assay (PLA). The OTR-5HTR_2A heteroreceptor complexes were identified in limbic regions (including hippocampus, cingulate cortex, and nucleus accumbens), key regions associated with cognition and social-related behaviors. Next, functional cellular-based assays to assess the OTR-5HTR_2A downstream signaling crosstalk showed a reduction in potency and efficacy of OT and OTR synthetic agonists, carbetocin and WAY267464, on OTR-mediated Gαq signaling. Similarly, the activation of 5-HTR_2A by the endogenous agonist, 5-HT, also revealed attenuation in Gαq-mediated signaling. Finally, altered receptor trafficking within the cell was demonstrated, indicative of cotrafficking of the OTR/5-HTR_2A pair. Overall, these results constitute a novel mechanism of specific interaction between the OT and 5-HT neurotransmitters via OTR-5HTR_2A heteroreceptor formation and provide potential new therapeutic strategies in the treatment of social and cognition-related diseases.

Oxytocin: Potential to mitigate cardiovascular risk

Cardiovascular disease (CVD) remains the leading cause of death worldwide, despite multiple treatment options. In addition to elevated lipid levels, oxidative stress and inflammation are key factors driving atherogenesis and CVD. New strategies are required to mitigate risk and most urgently for statin-intolerant patients. The neuropeptide hormone oxytocin, synthesized in the brain hypothalamus, is worthy of consideration as a CVD ancillary treatment because it moderates factors directly linked to atherosclerotic CVD such as inflammation, weight gain, food intake and insulin resistance. Though initially studied for its contribution to parturition and lactation, oxytocin participates in social attachment and bonding, associative learning, memory and stress responses. Oxytocin has shown promise in animal models of atherosclerosis and in some human studies as well. A number of properties of oxytocin make it a candidate CVD treatment. Oxytocin not only lowers fat mass and cytokine levels, but also improves glucose tolerance, lowers blood pressure and relieves anxiety. Further, it has an important role in communication in the gut-brain axis that makes it a promising treatment for obesity and type 2 diabetes. Oxytocin acts through its receptor which is a class I G-protein-coupled receptor present in cells of the vascular system including the heart and arteries. While oxytocin is not used for heart disease at present, residual CVD risk remains in a substantial portion of patients despite multidrug regimens, leaving open the possibility of using the endogenous nonapeptide as an adjunct therapy. This review discusses the possible role for oxytocin in human CVD prevention and treatment.