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Oxytocin receptor

The oxytocin receptor (OXTR) is a seven-transmembrane G protein-coupled receptor (GPCR) encoded by the OXTR gene on human chromosome 3p25.3, which selectively binds the neuropeptide hormone oxytocin to mediate a wide array of physiological and behavioral processes.^[1] As a member of the rhodopsin-like GPCR family, OXTR features a characteristic helical bundle structure with a relatively large, solvent-exposed ligand-binding pocket that accommodates oxytocin's cyclic peptide form, stabilized by interactions involving polar residues and a conserved magnesium ion coordination site.^[2] Upon binding, OXTR activates intracellular signaling cascades primarily through Gαq/11 or Gαi proteins, leading to phospholipase C activation, calcium mobilization, and downstream pathways such as MAPK/ERK and PI3K-AKT, which underpin its diverse effects.^[1]^[3] OXTR is expressed in a tissue- and region-specific manner, with high levels in the uterus, mammary glands, and myoepithelial cells for reproductive functions, as well as in central nervous system regions including the amygdala, hippocampus, prefrontal cortex, paraventricular nucleus, and supraoptic nucleus, where it influences neural circuits.^[1] Peripherally, it is found in the heart, vascular endothelium, bone, and immune cells, contributing to cardioprotection, inflammation modulation, and bone metabolism.^[3] Expression levels are dynamically regulated by factors such as estrogens, stress, developmental stage, and epigenetic modifications like DNA methylation at CpG sites, with notable increases during lactation or pregnancy.^[1] Genetic variations, including single nucleotide polymorphisms like rs53576 and rs2254298, have been associated with individual differences in social cognition, anxiety, and susceptibility to disorders such as autism spectrum conditions.^[1] In terms of physiological roles, OXTR is essential for uterine smooth muscle contraction during labor and milk ejection during lactation, processes that can be pharmacologically targeted with agonists like oxytocin for induction or antagonists like atosiban for preterm labor prevention.^[3] Centrally, it modulates social bonding, trust, empathy, and pair bonding by enhancing synaptic plasticity and dendritic remodeling in limbic areas, while also exerting anxiolytic effects and facilitating fear extinction through interactions with the hypothalamic-pituitary-adrenal axis.^[1] Dysregulation of OXTR signaling has implications for psychiatric conditions, including depression, schizophrenia, and social anxiety, prompting ongoing research, including 2025 clinical trials for conditions like Prader-Willi syndrome, into intranasal oxytocin as a therapeutic agent to normalize receptor function in affected brain circuits. As of 2025, emerging research highlights circadian influences on OXTR efficacy, novel analogues for psychiatric treatments, and expanded genetic associations with disorders like panic and functional neurological conditions.^[1]^[4]^[5]^[6]^[7]

Gene and structure

Gene location and organization

The OXTR gene, which encodes the oxytocin receptor, is located on the short arm of human chromosome 3 at the cytogenetic band 3p25.3.^[8] It spans approximately 17 kilobases (kb) of genomic DNA and consists of four exons interrupted by three introns.^[9] The first two exons are untranslated and contain 5'-noncoding sequences, while exons 3 and 4 encode the full-length protein; a notably large third intron of about 12 kb separates the coding sequence after the region corresponding to the sixth transmembrane domain.^[9] The OXTR gene encodes a protein of 389 amino acids that undergoes post-translational processing to form the mature receptor.^[10] The promoter region lies upstream of exon 1, with transcription initiating at sites 618 and 621 base pairs before the start codon; it features a TATA-like motif approximately 30 base pairs upstream of the transcription start site and an SP-1 binding site about 65 base pairs upstream, along with other potential regulatory elements such as AP-1, AP-2, and GATA-1 sites.^[9] Additionally, a CpG island extends from 140 base pairs upstream to 2338 base pairs downstream of the transcription start site, influencing epigenetic regulation of expression.^[11] The complementary DNA (cDNA) for the human OXTR was first cloned in 1992 from a library derived from term myometrial messenger RNA, enabling initial characterization of the receptor's sequence and expression.^[12] The full genomic structure, including intron-exon boundaries, was subsequently elucidated in 1994 through isolation and sequencing of genomic clones.^[9] Evolutionarily, the OXTR gene traces its origins to early vertebrates, reflecting the ancient roots of the oxytocin signaling system. A 2024 phylogenetic analysis indicates that OXTR belongs to the 64% of pathway genes classified as "modern," having arisen in jawless vertebrates approximately 540 million years ago, while 18% of pathway components are far older, predating multicellular life.^[13] This timeline underscores the system's conservation across vertebrates, with OXTR orthologs present in diverse species from fish to mammals.^[13]

Protein structure

The oxytocin receptor (OXTR) is a class A G-protein-coupled receptor (GPCR) encoded by the OXTR gene on human chromosome 3p25.^[10] It exhibits the canonical topology of this receptor family, comprising seven transmembrane α-helices (TM1–TM7) that form a helical bundle embedded in the cell membrane, flanked by three extracellular loops (ECL1–ECL3) and three intracellular loops (ICL1–ICL3).^[14] The protein features an extracellular N-terminal domain, which extends into the extracellular space and contains potential glycosylation sites, and an intracellular C-terminal tail that interacts with the membrane and intracellular components.^[15] The mature human OXTR polypeptide consists of 389 amino acids with a core molecular weight of approximately 43 kDa, which can increase due to post-translational modifications such as N-linked glycosylation at three sites (Asn8, Asn15, and Asn26) in the N-terminal domain.^[16]^[17] Key structural elements contribute to the stability and function of OXTR. A conserved disulfide bond between Cys112 in ECL1 (position 3.25 in Ballesteros-Weinstein numbering) and Cys187 in ECL2 anchors the extracellular loops, maintaining the integrity of the ligand-binding region.^[18] Additionally, the receptor includes the conserved DRY motif (Asp136–Arg137–Tyr138) at the cytoplasmic end of TM3, which plays a role in stabilizing the inactive conformation of the GPCR.^[19] These features are typical of class A GPCRs and have been preserved across species, underscoring their evolutionary importance.^[15] Insights into the three-dimensional structure of OXTR have evolved from early homology models based on the 2001 bovine rhodopsin crystal structure to more precise determinations using modern techniques.^[15] High-resolution cryo-electron microscopy (cryo-EM) structures, such as the 3.2 Å active-state model from 2022, reveal the orthosteric binding pocket formed primarily by residues in TM helices 2, 3, 5, 6, and 7, along with contributions from the ECLs.^[14] This pocket accommodates peptide ligands in a deep, enclosed space, with polar interactions on one side and hydrophobic contacts on the other, highlighting the receptor's specificity for nonapeptide hormones.^[20]

Expression patterns

Peripheral expression

The oxytocin receptor (OXTR) exhibits high levels of expression in peripheral reproductive tissues, particularly the myometrium and endometrium of the uterus, where it plays a key role in facilitating labor contractions. During pregnancy, OXTR expression in the human uterus undergoes significant upregulation, with receptor concentrations increasing by more than 100-fold from early gestation to term, as quantified through binding assays and mRNA analyses. This dramatic rise is essential for the heightened uterine sensitivity to oxytocin that drives parturition. Similarly, in the mammary glands, OXTR is prominently expressed in myoepithelial cells surrounding the alveoli, enabling oxytocin-mediated contraction for milk ejection during lactation. Moderate OXTR expression is observed in several other peripheral organs, including the kidney, heart, vascular tissues, bone, and immune cells. In the kidney, particularly in the collecting ducts of rodents, OXTR facilitates water reabsorption through interactions that enhance aquaporin-2 trafficking, though this effect is more pronounced in species like rats compared to humans, where oxytocin primarily acts via vasopressin V2 receptor cross-reactivity. In the heart, OXTR is localized to cardiac myocytes, contributing to cardiovascular regulation, while in vascular endothelium, the receptor is present on endothelial cells, influencing vasorelaxation and angiogenesis. In bone, OXTR is expressed in osteoblasts and osteoclasts, supporting bone remodeling and metabolism. In immune cells such as T-lymphocytes and dendritic cells, it modulates inflammation and immune responses. Developmental regulation of OXTR is evident in reproductive tissues, with estrogen and progesterone driving upregulation during pregnancy, and species-specific differences, such as elevated renal expression in rodents, highlighting variations in peripheral physiology across mammals.^[21]^[22]

Central nervous system expression

The oxytocin receptor (OXTR) exhibits a heterogeneous expression pattern across the central nervous system, with particularly dense localization in key limbic and hypothalamic structures that underpin social, emotional, and reward-related neural circuits. High levels of OXTR mRNA and binding sites are observed in the hypothalamus, notably within the paraventricular nucleus (PVN) and supraoptic nucleus (SON), where the receptor facilitates local oxytocin signaling and modulates neuroendocrine responses. Similarly, dense expression occurs in the central nucleus of the amygdala, involved in fear and anxiety processing; the hippocampus, supporting memory formation and synaptic plasticity; and the nucleus accumbens, a core component of the reward system. These regional distributions have been consistently mapped in rodent models using in situ hybridization and receptor autoradiography, highlighting the receptor's role in integrating sensory and motivational inputs. Moderate OXTR expression is noted in several cortical and subcortical areas, including the prefrontal cortex, which contributes to executive control and decision-making; the ventral tegmental area (VTA), where it influences dopaminergic reward pathways; and the olfactory bulb, particularly the accessory regions that process social pheromones. In contrast, OXTR density remains sparse in the cerebellum, with limited binding observed primarily in the molecular layer of rodents and modest increases noted in human cerebellar cortex during adulthood, though overall levels are low compared to forebrain structures. Human postmortem studies using RNA sequencing further confirm elevated OXTR transcripts in subcortical regions like the striatum and hippocampus across the lifespan, with ontogenetic peaks in adolescence and adulthood. At the subcellular level, OXTR is predominantly localized to postsynaptic membranes on neuronal somata and dendrites, where it couples to Gq/11 proteins to regulate intracellular calcium and modulate excitatory and inhibitory synaptic transmission. Evidence also indicates axonal transport of OXTR along certain projections, such as those from VTA neurons to forebrain targets, enabling receptor delivery to distal sites for localized signaling. This postsynaptic emphasis underscores the receptor's neuromodulatory influence on circuit dynamics rather than direct presynaptic release control. Autoradiography and emerging positron emission tomography (PET) imaging studies from the 2010s have identified sex differences in OXTR binding within the central nervous system, particularly in the amygdala, where densities vary by sex and correlate with social behavior traits in a region-specific manner. For instance, female rodents often exhibit lower binding in the central amygdala compared to males, though physiological states like lactation can dynamically alter these patterns.

Mechanism of action

Signaling pathways

The oxytocin receptor (OXTR), a G protein-coupled receptor, primarily couples to Gq/11 proteins upon activation by oxytocin, leading to the stimulation of phospholipase C-β (PLC-β).^[15] This activation results in the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG).^[15] IP3 binds to IP3 receptors (IP3R) on the endoplasmic reticulum, inducing calcium (Ca²⁺) release into the cytosol, while DAG remains membrane-bound to facilitate further signaling.^[15] The intracellular Ca²⁺ concentration ([Ca²⁺]ᵢ) can be conceptually represented as:

[\ce{Ca^{2+}}]_i = [\ce{Ca^{2+}}]_{\text{basal}} + \text{IP3-induced release via IP3R channels}

This Ca²⁺ mobilization is dose-dependent, occurring at low nanomolar concentrations of oxytocin.^[23] In certain cellular contexts, OXTR exhibits secondary coupling to Gs proteins, which activates adenylyl cyclase and elevates cyclic AMP (cAMP) levels, often indirectly through prostaglandin E2 intermediates.^[24] OXTR can also couple to Gi/o proteins, inhibiting adenylyl cyclase and contributing to signal diversity in specific tissues.^[17] Additionally, β-arrestin recruitment follows receptor phosphorylation by G protein-coupled receptor kinases, promoting desensitization and internalization to terminate signaling and prevent overstimulation.^[17] Downstream effects of the primary pathway include activation of protein kinase C (PKC) by DAG and Ca²⁺, which phosphorylates target proteins to modulate cellular responses such as contraction and gene expression.^[15] The pathway also engages mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) cascades, leading to ERK phosphorylation that influences proliferation, differentiation, and synaptic plasticity.^[17] Recent studies highlight how genetic variants in the OXTR gene can alter these dynamics, including variant-induced changes in Ca²⁺ desensitization, potentially affecting signaling efficiency and duration.^[24]

Interaction with mesolimbic dopamine pathways

The oxytocin receptor (OXTR) is co-expressed with dopamine neurons in the ventral tegmental area (VTA) and on both dopamine and glutamate neurons in the nucleus accumbens (NAc), key nodes of the mesolimbic pathway. This co-localization enables oxytocin to modulate dopamine transmission directly. Specifically, oxytocin binding to OXTR excites VTA dopamine neurons while simultaneously inhibiting local GABAergic interneurons, resulting in net disinhibition and enhanced dopamine release into the NAc.^[25] As part of broader central nervous system expression, OXTR in the NAc facilitates integration with reward circuits. Within mesolimbic circuits, OXTR activation preferentially occurs in D1 dopamine receptor-expressing medium spiny neurons of the NAc, amplifying D1 signaling and promoting the direct pathway for reward processing.^[26] This interaction heightens sensitivity to social stimuli by boosting dopamine-mediated reinforcement in these neurons.^[27] Behaviorally, OXTR modulation of mesolimbic dopamine facilitates pair bonding and the rewarding aspects of social interactions in monogamous rodents, where oxytocin enhances partner preference through increased dopamine signaling. Similarly, oxytocin reduces cocaine-seeking behavior in self-administration reinstatement models in rats, underscoring its role in attenuating drug-related reward cues via dopamine pathways. Studies from 2015 to 2024 demonstrate that OXTR knockout mice, particularly those lacking receptors on dopamine neurons, exhibit blunted dopamine release in response to social cues, impairing social reward processing.^[28]

Genetic variations

Polymorphisms

The oxytocin receptor gene (OXTR) harbors numerous single nucleotide polymorphisms (SNPs), with over 100 variants identified across its sequence in human populations. These SNPs are distributed throughout the gene, which spans approximately 17 kb on chromosome 3p25.3, and often form haplotype blocks that can influence transcription factor binding and regulatory elements.^[29] For instance, certain haplotypes alter binding sites for transcription factors, potentially modulating OXTR expression levels in a tissue-specific manner.^[30] Among the most studied SNPs are rs53576 (G/A transition in intron 3) and rs2254298 (G/A in the third intron).^[31] The rs53576 variant has been extensively investigated for its role in social cognition; the GG genotype is associated with higher levels of empathy, as measured by behavioral tasks like empathic accuracy and self-report scales.^[32] However, meta-analyses have shown mixed results, with some OXTR SNPs, including rs53576, failing to consistently replicate associations with social behaviors across populations.^[33] In contrast, the A allele of rs53576 is linked to reduced OXTR receptor expression, partly through increased methylation of CpG islands that affects gene transcription and mRNA stability.^[34] The rs2254298 SNP similarly impacts OXTR function, with the A allele showing associations with altered social processing. Recent research from 2024 indicates that the rs2254298 A allele is more prevalent in individuals with obstructive sleep apnea symptoms, including increased severity of breathlessness and snoring, suggesting a role in respiratory regulation via oxytocin pathways.^[35] Functional studies further reveal that this variant may influence corticostriatal connectivity differences, as observed in resting-state functional MRI, where A allele carriers exhibit variations in striatal network integration potentially tied to reward and motivation circuits.^[36] These polymorphisms highlight how sequence variations in OXTR can fine-tune receptor density and signaling, contributing to individual differences in behavioral phenotypes.

Epigenetic regulation

The epigenetic regulation of the oxytocin receptor (OXTR) gene encompasses dynamic modifications such as DNA methylation and histone acetylation that modulate its expression in response to environmental cues, particularly during development. These changes allow the OXTR to adapt to social and stress-related experiences without altering the underlying DNA sequence, influencing oxytocin signaling in the brain and periphery. Promoter methylation at specific CpG sites in the OXTR gene, especially within the MT2 region, is a key mechanism affected by early life stress. Hypermethylation in this region, observed in both human cohorts and animal models exposed to adverse early experiences like low parental care, significantly reduces OXTR mRNA expression by repressing transcriptional activity. For instance, in prairie voles subjected to early life stress, increased methylation at sites such as -901, -924, and -934 correlates with diminished receptor levels, contributing to altered stress responses. This hypermethylation has been linked to heightened amygdala activity, as evidenced by greater BOLD responses to emotional stimuli in individuals with elevated OXTR methylation, potentially exacerbating emotional dysregulation.^[37]^[38] Histone modifications further fine-tune OXTR expression, with acetylation of histone H3 at promoter regions promoting transcriptional activation in contexts of social bonding. In prairie voles forming pair bonds, enhanced H3 acetylation at the OXTR promoter accompanies increased receptor mRNA and protein levels in the nucleus accumbens, facilitating affiliative behaviors. This modification contrasts with deacetylation states induced by stress, highlighting the plasticity of chromatin structure in regulating oxytocin-mediated social motivation.^[39] Environmental factors, notably childhood adversity, persistently elevate OXTR methylation as shown in 2023 longitudinal analyses of human cohorts. These studies reveal that cumulative early trauma, such as abuse or neglect, leads to higher methylation across multiple OXTR CpG sites in peripheral blood, correlating with long-term deficits in social functioning and stress resilience. Such patterns underscore the role of epigenetics in embedding early experiences into enduring neurobiological traits.^[40] OXTR methylation exhibits sex-specific differences, with females often displaying higher levels at certain intron and promoter sites compared to males, potentially reflecting dimorphic roles in reproductive and social behaviors. Certain polymorphisms may briefly influence susceptibility to these methylation changes at specific sites, though epigenetic dynamics predominate. In preclinical models, these methylation alterations prove reversible; treatment with histone deacetylase (HDAC) inhibitors, such as sodium butyrate, restores acetylation at OXTR promoters, thereby enhancing expression and rescuing social deficits in stressed rodents.^[41]

Ligands

Endogenous ligand

The endogenous ligand for the oxytocin receptor (OXTR) is oxytocin, a cyclic nonapeptide composed of nine amino acids with the sequence Cys¹-Tyr²-Ile³-Gln⁴-Asn⁵-Cys⁶-Pro⁷-Leu⁸-Gly⁹-NH₂, where a disulfide bridge forms between Cys¹ and Cys⁶.^[42] Oxytocin is synthesized as a larger precursor protein in magnocellular neurons of the paraventricular and supraoptic nuclei in the hypothalamus, processed into the mature peptide, and transported via axons to the posterior pituitary for storage and release into the systemic circulation.^[43] Oxytocin binds to OXTR with high affinity, typically exhibiting a dissociation constant (K_d) of approximately 1 nM, which enables sensitive detection and activation of the receptor.^[23] This binding specificity distinguishes oxytocin from the related peptide arginine vasopressin, primarily due to the Ile³ and Leu⁸ residues in oxytocin, which differ from Phe³ and Arg⁸ in vasopressin and confer a roughly 400-fold lower affinity for vasopressin receptors such as V2R.^[44]^[14] The release of oxytocin is regulated in a pulsatile manner, with surges triggered by physiological stimuli such as uterine contractions during labor or nipple stimulation during nursing, leading to progressively larger and more frequent pulses that facilitate coordinated responses like milk ejection and labor progression.^[45] In plasma, oxytocin has a short half-life of about 3-5 minutes, primarily due to rapid enzymatic degradation by oxytocinase and clearance by the kidneys and liver.^[46] Oxytocin serves a dual role as a peripheral hormone, influencing reproductive and cardiovascular functions upon systemic release, and as a central neuromodulator, modulating neural circuits when released within the brain from hypothalamic projections.^[47] Recent evolutionary analyses highlight the co-evolution of oxytocin and its receptor, with the signaling pathway incorporating modern genes primarily during the emergence of vertebrates, underscoring adaptations that support social and reproductive behaviors across species.^[13]

Agonists

Agonists of the oxytocin receptor (OXTR) are compounds that bind to and activate the receptor, mimicking the effects of the endogenous ligand oxytocin. In mammals, oxytocin itself serves as the primary agonist, while synthetic variants have been developed to enhance stability, selectivity, or delivery. Natural variants such as mesotocin, the oxytocin homolog in non-mammalian tetrapods like birds and reptiles, can also activate OXTR-like receptors but are not prominent in mammalian systems.^[48] Carbetocin, a synthetic peptide analog of oxytocin, acts as a potent OXTR agonist with a K_i of 7.24 nM in rat uterine membrane preparations and an EC₅₀ of approximately 48 nM in functional contraction assays, demonstrating its efficacy as a partial agonist in calcium mobilization pathways. Compared to oxytocin, carbetocin shows a slightly reduced maximal response (about 50% lower in Gq activation) but maintains strong uterotonic activity.^[49]^[50]^[51] Non-peptide agonists offer advantages in selectivity and potential for oral administration. WAY-267464 is a selective non-peptide OXTR agonist with a K_i of 58.4 nM at human OXTR and negligible affinity for vasopressin receptors, acting as a partial agonist with an EC₅₀ of 24 nM in calcium release assays. However, it displays some off-target antagonism at vasopressin V1a receptors (K_i 12.5 nM), limiting its selectivity profile.^[52]^[53]^[54] Recent advancements include LIT-001, a non-peptide full OXTR agonist developed in 2018 and further studied as of 2023 for pro-social effects. It demonstrates an EC₅₀ of 5.3 nM in calcium mobilization assays and a K_i of 11 nM for OXTR binding, with selectivity over vasopressin V2 receptors (K_i ≈50 nM, partial agonist) and V1a (K_i >500 nM). LIT-001 penetrates the blood-brain barrier effectively upon intraperitoneal administration, achieving brain exposure levels supporting behavioral effects at 10 mg/kg doses.^[54]^[55] Peptide agonists like oxytocin and carbetocin face challenges with oral bioavailability due to enzymatic degradation and poor gastrointestinal absorption, often below 1% for oxytocin. Intranasal delivery circumvents these issues, allowing central nervous system effects; for instance, 24 IU doses of oxytocin elevate plasma levels within 20 minutes and facilitate brain uptake via olfactory pathways. Non-peptide agonists like LIT-001 show promise for improved pharmacokinetics, including better brain penetration without relying solely on intranasal routes.^[56]^[57]^[54]

Antagonists

Oxytocin receptor antagonists are compounds that inhibit the binding of oxytocin to its receptor, thereby blocking downstream signaling pathways. These agents are primarily competitive inhibitors that occupy the orthosteric binding pocket of the receptor, preventing agonist activation. The receptor's binding pocket, as revealed by crystallographic studies, accommodates antagonists with an enlarged extracellular exposure compared to agonist-bound states, facilitating their design for therapeutic applications. Some antagonists, such as L-371,257 and atosiban, exhibit inverse agonistic properties by reducing constitutive receptor activity in the absence of ligand. Atosiban, a peptidic oxytocin receptor antagonist derived from oxytocin, acts competitively at the receptor with high potency, inhibiting oxytocin-induced calcium mobilization in myometrial cells (IC50 ≈ 5 nM). It has been developed and approved for the management of preterm labor by suppressing uterine contractions mediated by oxytocin signaling. Atosiban demonstrates selectivity for the oxytocin receptor over vasopressin receptors, though it retains some affinity for V1a receptors. Non-peptidic antagonists offer advantages in oral bioavailability and pharmacokinetics. L-368,899 is a selective, orally active non-peptide antagonist with an IC50 of 8.9 nM at the oxytocin receptor in rat uterus membranes, showing over 40-fold selectivity against the vasopressin V1a receptor. Similarly, retosiban (GSK221149A), another orally bioavailable non-peptide antagonist, binds with subnanomolar affinity (Ki = 0.65 nM for human oxytocin receptor) and has been investigated in preclinical models for its ability to inhibit oxytocin-mediated uterine contractility without significant off-target effects on vasopressin receptors. In recent research, oxytocin receptor antagonists have shown potential in modulating behaviors associated with neurodevelopmental disorders. For instance, administration of atosiban in a valproic acid-induced autism model in female rats significantly reduced autistic-like behaviors, including repetitive actions and social deficits, suggesting a role for receptor blockade in alleviating OXTR hyperactivity in such contexts.^[58]

Physiological roles

Reproductive functions

The oxytocin receptor (OXTR) plays a critical role in parturition by mediating uterine contractions necessary for labor. In the myometrium, OXTR expression is dramatically upregulated toward the end of gestation, increasing receptor density up to 200-fold in the uterus, which enhances sensitivity to oxytocin and facilitates coordinated contractions.^[59]^[60] This upregulation is driven by rising estrogen levels and prepares the uterus for the oxytocin surge during delivery, enabling effective expulsion of the fetus. OXTR knockout mice demonstrate normal parturition, including timing and delivery, without apparent complications.^[61] In lactation, OXTR activation in the mammary gland is essential for the milk ejection reflex. Suckling stimulates oxytocin release from the posterior pituitary, which binds to OXTR on myoepithelial cells surrounding the alveoli, causing their contraction and the subsequent ejection of milk into the ducts.^[62]^[63] This process ensures efficient milk transfer to the offspring. OXTR knockout mice show severe deficits in this reflex, resulting in inadequate milk ejection and poor pup survival despite normal milk production.^[61]^[64] Beyond these core functions, OXTR contributes to ovarian follicle development and male reproductive processes. In the ovary, OXTR expression in granulosa and theca cells of preovulatory follicles supports follicular maturation and ovulation, with exogenous oxytocin influencing follicle growth and luteal function in animal models.^[65]^[66] In males, OXTR in the reproductive tract, including the testis and epididymis, promotes sperm transport through contractions of smooth muscle, enhancing ejaculation and fertility.^[67]^[68]^[69] The oxytocin receptor (OXTR) plays a pivotal role in mediating prosocial behaviors, including enhanced trust, empathy, and pair bonding, through its activation by oxytocin in social contexts. Genetic factors, including variations in the OXTR gene, contribute to individual differences in these behaviors.^[1] Intranasal administration of oxytocin, which targets central OXTR, promotes prosocial gaze patterns by increasing attention to the eye region during social tasks. For instance, a single dose of intranasal oxytocin enhances eye contact in naturalistic interactions and biases gaze toward the eyes of faces displaying emotional expressions, particularly fear, thereby facilitating social cue processing.^[70]^[71] Oxytocin receptors are expressed in key brain regions such as the amygdala and nucleus accumbens, which support these social attentional mechanisms.^[1] Regarding emotional regulation, OXTR activation attenuates amygdala responses to fearful stimuli, reducing the neural processing of threat and thereby dampening fear and anxiety.^[72]^[73] Oxytocin signaling via OXTR in the central amygdala modulates defensive behaviors, shifting from high-fear states to more adaptive responses. Additionally, OXTR influences stress modulation by inhibiting hypothalamic-pituitary-adrenal (HPA) axis activation; central oxytocin administration selectively reduces stress-induced cortisol release, promoting resilience to psychological stressors.^[74]^[75] Sex differences in OXTR-mediated effects are evident in emotion recognition tasks, where oxytocin enhances accuracy more robustly in females. Women with higher endogenous oxytocin levels perceive emotional faces as happier, and intranasal oxytocin amplifies this bias, potentially due to greater OXTR sensitivity in female neural circuits for affective processing.^[76]^[77] Recent studies from 2023 to 2025 have linked OXTR genetic variants to diminished social reward processing in schizophrenia, with polymorphisms associated with reduced motivation for social interactions and negative symptoms. These findings suggest that OXTR dysfunction contributes to impaired social reward valuation, exacerbating deficits in affective social engagement.^[78]^[79]

Clinical significance

Associated disorders

Dysfunction in the oxytocin receptor (OXTR) has been implicated in several neurodevelopmental and psychiatric disorders, particularly through genetic variations and epigenetic modifications that alter receptor expression and signaling. In autism spectrum disorder (ASD), the rs2254298 A-allele of the OXTR gene is associated with increased risk, with meta-analyses indicating an odds ratio of 1.28 (95% CI 1.11–1.48) for ASD susceptibility.^[80] Reduced OXTR expression, often due to promoter hypermethylation, correlates with social deficits characteristic of ASD, as evidenced by 20% lower OXTR mRNA levels in the temporal cortex of affected individuals compared to controls. These polymorphisms contribute to risk by modulating social cognition and emotional processing pathways. In psychiatric conditions, OXTR single nucleotide polymorphisms (SNPs) influence brain connectivity and symptom severity. For schizophrenia, recent 2023 studies demonstrate that OXTR SNPs, such as rs2254298, alter functional connectivity in reward and social brain networks, potentially exacerbating social withdrawal and cognitive impairments. Similarly, OXTR variants heighten stress sensitivity, increasing vulnerability to depression and anxiety; for instance, the rs53576 AA genotype is linked to elevated depressive symptoms under psychosocial stress, with interactions between OXTR polymorphisms and environmental stressors amplifying HPA axis dysregulation. Beyond psychiatric disorders, OXTR dysfunction associates with obstetric and respiratory conditions. Low OXTR expression or function, often mediated by polymorphisms like rs4686302, contributes to preterm labor by impairing myometrial contractility regulation, increasing delivery risk before 37 weeks gestation. In sleep apnea, as of 2024 research identifies OXTR polymorphisms, particularly the rs2254298 A-allele, as associated with obstructive sleep apnea symptoms, including higher rates of snoring and breathlessness, likely through effects on respiratory control mechanisms.^[81] Epigenetic alterations further link OXTR to trauma-related disorders. In post-traumatic stress disorder (PTSD), hypermethylation of the OXTR promoter leads to epigenetic silencing and approximately 30% lower OXTR expression in peripheral blood cells, correlating with heightened amygdala reactivity and impaired fear extinction.

Therapeutic applications

Oxytocin, administered as a nasal spray or intravenously, is approved for inducing labor and managing postpartum hemorrhage by stimulating uterine contractions through activation of the oxytocin receptor (OXTR).^[82] In clinical practice, intranasal oxytocin facilitates cervical ripening and labor augmentation in cases of prolonged delivery, while intravenous forms are standard for controlling bleeding after childbirth.^[83] Atosiban, an OXTR antagonist, is approved for intravenous use as a tocolytic agent to inhibit preterm labor contractions, prolonging pregnancy by up to seven days in women with imminent delivery before 34 weeks gestation.^[84] Carbetocin, a long-acting OXTR agonist analog of oxytocin, is utilized postpartum to prevent excessive bleeding following cesarean sections, offering sustained uterine tone with a longer duration of action compared to native oxytocin.^[85] Experimental applications of OXTR-targeted therapies focus on neuropsychiatric conditions. Intranasal oxytocin has been investigated for alleviating social deficits in autism spectrum disorder, with Phase II trials showing mixed efficacy in improving social cognition and interaction; a 2021 meta-analysis of randomized controlled trials indicated modest benefits in repetitive behaviors but inconsistent overall symptom reduction.^[86] OXTR agonists, including oxytocin itself, are under evaluation as adjuncts for major depressive disorder, where clinical trials demonstrate potential in enhancing social bonding and reducing stress reactivity when combined with antidepressants like escitalopram, though larger studies are needed to confirm sustained antidepressant effects.^[87] Key challenges in OXTR-targeted therapies include oxytocin's short plasma half-life of 2-4 minutes, which limits its duration of action, and difficulties in achieving central nervous system penetration due to poor blood-brain barrier crossing, necessitating intranasal delivery for brain-targeted effects while risking peripheral side effects like hypotension.^[88] OXTR antagonists face similar delivery hurdles in psychiatric applications, such as targeting repetitive behaviors in autism, where selective central modulation remains elusive.^[89] In 2023 preclinical studies, selective OXTR agonists like LIT-001 have demonstrated promise in schizophrenia models by enhancing pro-social behaviors and cognition through corticostriatal pathway modulation, reversing deficits in neurodevelopmental rodent paradigms without significant off-target effects.^[90]

References

[1]
The Oxytocin Receptor: From Intracellular Signaling to Behavior | Physiological Reviews | American Physiological Society
Below is a merged summary of the Oxytocin Receptor (OXTR) that consolidates all information from the provided segments into a single, comprehensive response. To maximize detail and clarity, I’ve organized key information into a dense, tabular format where appropriate (e.g., for expression patterns and signaling pathways) and provided a narrative summary for other sections. All unique details from each segment are retained, with redundancies minimized.
[2]
Crystal structure of the human oxytocin receptor | Science Advances
The peptide hormone oxytocin modulates socioemotional behavior and sexual reproduction via the centrally expressed oxytocin receptor (OTR) across several ...
[3]
An overview of the oxytocin-oxytocin receptor signaling network - PMC
Sep 14, 2016 · OXT-OXTR signaling has been associated with various biological functions. However, its role in uterine contraction and labor induction was the ...
[4]
5021 - Gene ResultOXTR oxytocin receptor [ (human)] - NCBI
Sep 9, 2025 · ... OXTR on chromosome 3p25. Results of genetic expression analyses in human hippocampal tissue showed a twofold difference in messenger RNA ...
[5]
Structural organization of the human oxytocin receptor gene - PubMed
Dec 23, 1994 · 2 of the human chromosome. The gene spans approximately 17 kilobases and contains 3 introns and 4 exons. Exons 1 and 2 correspond to the 5'-non- ...
[6]
OXTR - Oxytocin receptor - Homo sapiens (Human) - UniProt
Apr 3, 2007 · Amino acids. 389 (go to sequence). Protein existence. Evidence at ... Length. C9JQC4, C9JQC4_HUMAN, OXTR, 43. C9JN09, C9JN09_HUMAN, OXTR, 92 ...
[7]
DNA Methylation of the Human Oxytocin Receptor Gene Promoter ...
In the human oxytocin receptor (OTR) gene, there is a CpG island from 140 bp upstream to 2338 bp downstream of the transcription start site (TSS).
[8]
Structure and expression of a human oxytocin receptor - Nature
Apr 9, 1992 · We report here the structure and expression of the human oxytocin receptor complementary DNA isolated by expression cloning. ... Kimura, T.
[9]
An evolutionary timeline of the oxytocin signaling pathway - Nature
Apr 17, 2024 · The most intensively studied genes in the OT signaling pathway in both humans and non-human animals are the primary OT genes OXTR, encoding for ...
[10]
Structural basis for the activation and ligand recognition of ... - Nature
Jul 18, 2022 · Here we report the single-particle cryo-electron microscopy structure of the active oxytocin receptor (OTR) in complex with its cognate ligand oxytocin.
[11]
The Oxytocin Receptor System: Structure, Function, and Regulation
Apr 1, 2001 · [Modified from Inoue et al. (254).] In the OT receptor gene of ... Structural organization of the human oxytocin receptor gene. J Biol ...
[12]
Oxytocin Receptor - an overview | ScienceDirect Topics
The human oxytocin receptor has 389 amino acids and a core molecular mass of approximately 40 to 45 kDa that can be increased by glycosylation. The oxytocin ...
[13]
Oxytocin Receptor Signaling in Vascular Function and Stroke
Oxytocin receptor is considered a Class A GPCR with respect to its interaction with β-arrestins, meaning that it maintains a strong connection with β-arrestin ...Abstract · The Oxytocin Receptor · The OXTR as a Therapeutic... · Conclusion
[14]
Crystal structure of the human oxytocin receptor - bioRxiv
Feb 21, 2020 · Our structure reveals insights into the detailed interactions between the G-protein coupled receptor (GPCR) and an OTR-selective antagonist.
[15]
The DRY motif as a molecular switch of the human oxytocin receptor
The human oxytocin receptor is known to exhibit promiscuous activity by coupling to both Galpha(q) and Galpha(i) G proteins to activate distinct signaling ...Missing: disulfide bond
[16]
Crystal structure of the human oxytocin receptor - PMC
Overall, OTR displays the canonical GPCR topology consisting of a seven-transmembrane helical bundle (helices I to VII), two ICLs and three extracellular loops ...
[17]
Dual Oxytocin Receptor-G Protein Signaling in the Autoregulation of ...
Oct 6, 2023 · This switch of OT neuronal activity is largely determined by the switch of signaling pathways downstream to Gq and Gi/o proteins that couple to ...
[18]
Oxytocin receptor behavioral effects and cell types in the bed ...
... Oxtr was confined primarily to D1 medium spiny neurons and interneurons. While some BNST neurons have electrophysiological properties (inward rectification in ...
[19]
Interaction Between Oxytocin and Dopamine Signaling - MDPI
Dopamine receptors, for instance, have been demonstrated in oxytocin neurons, and dopamine signaling influences oxytocin release [21,22]. Conversely, oxytocin ...
[20]
Gating of social reward by oxytocin in the ventral tegmental area
Sep 29, 2017 · Homozygous OXTr DA knockout (KO) mice exhibited no social CPP ... This increases DA release in the NAc, which reinforces the social interaction.
[21]
Roles of the Oxytocin Receptor (OXTR) in Human Diseases - PMC
Feb 15, 2023 · The oxytocin receptor (OXTR), encoded by the OXTR gene, is responsible for the signal transduction after binding its ligand, oxytocin.
[22]
Functional genetic variants can mediate their regulatory effects ...
Aug 2, 2019 · In this study, we provide direct evidence that functional variants can alter transcription factor binding.
[23]
Does the oxytocin receptor polymorphism (rs2254298) confer ...
Apr 17, 2012 · It is suggested that polymorphic variation at the oxytocin receptor gene (rs2254298) is associated with sociability, amygdala volume and differential risk for ...
[24]
Oxytocin receptor genetic variation relates to empathy and stress ...
OXTR rs53576 polymorphism relates to behavioral and self-report measures of empathy. (A) Individuals with the GG genotype perform better on an empathic accuracy ...
[25]
Oxytocin Genes (OXTR) & SNPs: Are You High or Low in it?
Feb 7, 2023 · People with GG had lower rates of autism. People with GG had less ... greater risk for Autism [3]. ~48% of the population has CT, ~36 ...
[26]
Randomized clinical trial shows no substantial modulation of ...
Jul 23, 2021 · There is evidence that the A allele of rs53576 is linked to increased methylation levels of CpG-islands of the OXTR and reduces the OXTR gene ...
[27]
Oxytocin Receptor Polymorphism Is Associated With Sleep Apnea ...
Nov 26, 2024 · The OXTR rs2254298 A allele is more frequent in those with OSA symptoms, particularly breathlessness and snoring, and lower subjective sleep ...
[28]
Oxytocin pathway gene variation and corticostriatal resting-state ...
OXT rs4813627 GG carriers showed weaker corticostriatal connectivity compared to allele A carriers (GG/AA genotypes). Abstract. Genetic variations in single ...
[29]
An epigenetic rheostat of experience: DNA methylation of OXTR as ...
Many gene promoters have dense regions of CpGs called CpG islands, and DNA methylation of CpG islands is associated with decreased transcription of the gene [17] ...
[30]
Epigenetic regulation of the oxytocin receptor gene - Frontiers
CpG islands often span the promoter region of genes and are associated with active gene expression (Saxonov et al., 2006). These stretches of DNA have a higher ...
[31]
Epigenetic Regulation of Motivated Behaviors by Histone ...
Histone deacetylase inhibitors can correct some of the pathologies linked to motivated behaviors including substance abuse, feeding and social attachments.
[32]
The DNA methylation landscape of the human oxytocin receptor ...
Jul 21, 2023 · We focused on regulatory regions of the OXTR gene: A CpG island comprising 188 CpG sites [11, 21] and 21 CpG sites at a potential enhancer ...
[33]
Associations among oxytocin receptor gene (OXTR) DNA ... - Nature
Aug 7, 2017 · The goal of this study was to examine the association of ELA with oxytocin receptor gene (OXTR) methylation among young adults.
[34]
REVIEW: Oxytocin: Crossing the Bridge between Basic Science and ...
The central actions of oxytocin are mediated via oxytocin receptors (OTRs) distributed widely in the brain in a remarkably species‐specific fashion. Areas ...
[35]
Physiology, Posterior Pituitary - StatPearls - NCBI Bookshelf - NIH
Apr 24, 2023 · The posterior pituitary gland secretes ... hypothalamus, while oxytocin is synthesized in the paraventricular nuclei of the hypothalamus.
[36]
Predicting oxytocin binding dynamics in receptor genetic variants ...
Feb 8, 2025 · This model provides key insights into how genetic variants influence OXT dose responses and offers a framework for tailoring OXT dosing to patient-specific ...
[37]
Maternal plasma levels of oxytocin during physiological childbirth
Aug 9, 2019 · We found that blood oxytocin levels gradually rise in pregnancy and become even higher during labour, when pulses of oxytocin become progressively bigger and ...
[38]
The Oxytocin System and Implications for Oxytocin Deficiency in ...
Pulsatile peripheral release of OXT has been demonstrated in women during labor ... plasma OXT half-life is about 3 to 5 minutes (385). A recent study sampled ...
[39]
Oxytocin - an overview | ScienceDirect Topics
Oxytocin is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus and is released into the periphery via the posterior pituitary (Figure ...
[40]
Mesotocin - an overview | ScienceDirect Topics
Mesotocin is a neuropeptide hormone that serves as the oxytocin-like hormone in nonmammalian tetrapods, including lungfishes, amphibians, reptiles, and birds, ...
[41]
Carbetocin - OEL Fastrac with ADE - Affygility Solutions
$$899.00Carbetocin is a cyclic peptide analogue of oxytocin and is an oxytocin agonist (EC50 0.7 nM). Its action is similar to that of oxytocin, in that it causes ...
[42]
Oxytocin receptor binding and uterotonic activity of carbetocin and ...
These results indicate that carbetocin is a partial agonist/antagonist to the oxytocin receptor while the two metabolites carbetocin metabolite I and carbetocin ...
[43]
Carbetocin is a Functional Selective Gq Agonist That Does Not ...
In addition, compared to oxytocin, carbetocin displays a five‐fold right‐shifted EC50 value and a 50% reduction in the maximal OXTR/Gq activation value, ...
[44]
WAY 267464 dihydrochloride | Oxytocin Receptors - Tocris Bioscience
$$45 deliveryWAY 267464 dihydrochloride is a potent, selective non-peptide oxytocin receptor (OTR) agonist (K i = 58.4 nM at human OTR). Exhibits anxiolytic-like effects.Missing: synthetic | Show results with:synthetic
[45]
Receptor and behavioral pharmacology of WAY-267464 ... - PubMed
In this study, we report the receptor and behavioral pharmacology of WAY-267464, a first generation small-molecule OTR agonist.Missing: carbetocin | Show results with:carbetocin
[46]
https://academic.oup.com/edrv/article/46/4/518/8030228
[47]
Pro-social and pro-cognitive effects of LIT-001, a novel oxytocin ...
Since oxytocin (OXT) is known to play a role in social functions and modulates cognitive processes, we investigated the effects of a novel, nonpeptide, ...
[48]
Hybrid peptide-small molecule oxytocin analogs are potent and ...
Feb 1, 2018 · OT is administered intravenously and intranasally rather than orally, in part because its low passive permeability causes low oral ...
[49]
Intranasal administration of oxytocin: Behavioral and clinical effects ...
After intranasal administration of 24 I.U of OT (∼48 μg) blood levels of OT start rising from about 7.5 to about 15 pg/ml X 103 within less than 20 min in male ...
[50]
The Role of Oxytocin and the Effect of Stress During Childbirth
Oct 27, 2021 · Nonetheless, it has been shown that the number of uterine oxytocin receptors increases up to 200-fold towards the end of gestation (5, 27), ...
[51]
Labor and Inflammation Increase the Expression of Oxytocin ...
Using real-time RT-PCR, we found that the expression of OXTR mRNA in postlabor primary amnion epithelial cells was 16-fold higher than in prelabor cells (P < 0 ...
[52]
Social Deficits, Normal Parturition in Oxytocin Receptor-Deficient Mice
Oxtr-/- mice were viable and had no obvious deficits in fertility or reproductive behavior. Oxtr-/- dams exhibited normal parturition but demonstrated defects ...
[53]
Oxytocin modulates the onset of murine parturition by competing ...
To better define the roles of OT during pregnancy, we evaluated OT action and OT receptor regulation in wild-type and OT-deficient knockout (KO) mice.
[54]
The physiological basis of breastfeeding - Infant and Young ... - NCBI
The oxytocin reflex makes the breast milk flow along the ducts, and the action of the baby's tongue presses the milk from the ducts into the baby's mouth. When ...
[55]
Oxytocin and neuroscience of lactation: Insights from the molecular ...
This reflex is triggered by the infant's suckling of the nipple, which activates central oxytocin (OT) neurons in the paraventricular (PVH) and supraoptic (SON) ...
[56]
Milk Ejection - an overview | ScienceDirect Topics
Milk ejection is essential for lactation, as shown by the observation that mice genetically deficient in oxytocin have a severe lactation deficit (472,515). The ...<|control11|><|separator|>
[57]
Effects of oxytocin on follicular development and duration of the ...
Holstein heifers were used to study effects of exogenous administration of oxytocin on luteal function and ovarian follicular development.
[58]
Changes in oxytocin receptor in bovine preovulatory follicles ...
These results suggest the direct action of oxytocin on both theca and granulosa cells of bovine periovulatory follicles through binding to its receptor.
[59]
Oxytocin in the Male Reproductive Tract - PubMed Central - NIH
OT was found to increase fluid flow and number of spermatozoa in the rete testis of rams (70, 105) and accelerated the arrival of first sperm into the ...
[60]
Oxytocin—its role in male reproduction and new potential ...
Exogenous administration of OT has, in some cases, been shown to increase the numbers of ejaculated sperm, possibly by stimulating contractions of the ...
[61]
Seasonal Expression of Oxytocin and Oxytocin Receptor in the ...
Nov 30, 2017 · In the testis and epididymis, OT promotes sperm transport and maturation by increasing tubules contraction. In the rat testis, for example, lack ...
[62]
Oxytocin - StatPearls - NCBI Bookshelf - NIH
Feb 15, 2025 · Oxytocin is FDA-approved for use in the antepartum and postpartum periods to facilitate labor and control postpartum hemorrhage.
[63]
Oxytocin (intravenous route, intramuscular route) - Side effects & uses
Mar 31, 2025 · Oxytocin is a hormone used to help start or continue labor and to control bleeding after delivery. It is also sometimes used to help milk secretion in breast- ...
[64]
An oxytocin receptor antagonist (atosiban) in the treatment of ...
Conclusions: In this trial the treatment of patients in preterm labor with atosiban resulted in prolongation of pregnancy for up to 7 days for those at a ...
[65]
Carbetocin: Uses, Interactions, Mechanism of Action - DrugBank
Carbetocin binds to oxytocin receptors present on the smooth musculature of the uterus, resulting in rhythmic contractions of the uterus.
[66]
Intranasal oxytocin in the treatment of autism spectrum disorders
The current meta-analysis aims to assess the crucial question of oxytocin's efficacy in the treatment of ASD. We performed a systematic literature search, ...
[67]
Oxytocin and Major Depressive Disorder - PubMed Central - NIH
The most promising indications from studies to date include the role of OXT in social behaviour, stress-attenuation and interactions with the serotonergic ...
[68]
Peripheral Administration of a Long-Acting Peptide Oxytocin ...
Oxytocin (OT) modulates the expression of social and emotional behaviors and consequently has been proposed as a pharmacologic treatment of psychiatric ...
[69]
Helping oxytocin deliver: considerations in the development of ...
These shortcomings include a brief plasma half-life and poor oral bioavailability due to their degradation by plasma and gastric proteases, as well as limited ...
[70]
Pro-social and pro-cognitive effects of LIT-001, a novel oxytocin ...
In the present study, we investigated whether social and cognitive impairments could be alleviated with the novel, nonpeptide, selective OXTR agonist - LIT-001.