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Oxytocin receptor
Oxytocin receptor
Oxytocin receptor
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OXTR
Identifiers
AliasesOXTR, OT-R, oxytocin receptor
External IDsOMIM: 167055; MGI: 109147; HomoloGene: 20255; GeneCards: OXTR; OMA:OXTR - orthologs
Orthologs
SpeciesHumanMouse
Entrez

5021

18430

Ensembl

ENSG00000180914

ENSMUSG00000049112

UniProt

P30559

P97926

RefSeq (mRNA)

NM_000916

NM_001081147

RefSeq (protein)

NP_000907
NP_001341582
NP_001341583
NP_001341584
NP_001341585

NP_001074616

Location (UCSC)n/aChr 6: 112.45 – 112.47 Mb
PubMed search[2][3]
Wikidata
View/Edit HumanView/Edit Mouse

The oxytocin receptor, also known as OXTR, is a protein which functions as receptor for the hormone and neurotransmitter oxytocin.[4][5] In humans, the oxytocin receptor is encoded by the OXTR gene[6][7] which has been localized to human chromosome 3p25.[8]

Evolutionary tree of the oxytocin, vasotocin, mesotocin and isotocin receptors and their ligands. From Koechbach et al.[9]

Function and location

[edit]

The OXTR protein belongs to the G-protein coupled receptor family, specifically Gq,[4] and acts as a receptor for oxytocin. Its activity is mediated by G proteins that activate several different second messenger systems.[10][11]

Oxytocin receptors are expressed by the myoepithelial cells of the mammary gland, and in both the myometrium and endometrium of the uterus at the end of pregnancy. The oxytocin-oxytocin receptor system plays an important role as an inducer of uterine contractions during parturition and of milk ejection.

OXTR is also associated with the central nervous system. The gene is believed to play a major role in social, cognitive, and emotional behavior.[12] A decrease in OXTR expression by methylation of the OXTR gene is associated with callous and unemotional traits in adolescence, rigid thinking in anorexia nervosa, problems with facial and emotional recognition, and difficulties in the affect regulation. A reduction in this gene is believed to lead to prenatal stress, postnatal depression, and social anxiety.[12] Further research must be gathered before concluding these findings, however strong evidence is pointing in this direction. Studies on OXTR methylation—which downregulates oxytocin mechanisms—suggest this process is associated with increased gray matter density in the amygdala, implicating OXTR regulation in stress and parasympathetic regulation.[13]

In some mammals, oxytocin receptors are also found in the kidney and heart.

Mesolimbic dopamine pathways

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The oxytocinergic circuit projecting from the paraventricular hypothalamic nucleus (PVN) innervates the ventral tegmental area (VTA) dopaminergic neurons that project to the nucleus accumbens, i.e., the mesolimbic pathway.[14] Activation of the PVN→VTA projection by oxytocin affects sexual, social, and addictive behavior via this link to the mesolimbic pathway;[14] specifically, oxytocin exerts a prosexual and prosocial effect in this region.[14]

Polymorphism

[edit]

The receptors for oxytocin (OXTR) have genetic differences with varied effects on individual behavior. The polymorphism (rs53576) occurs on the third intron of OXTR in three types: GG, AG, AA. The GG allele is connected with oxytocin levels in people [citation needed]. A-allele carrier individuals are associated with more sensitivity to stress, fewer social skills, and more mental health issues than the GG-carriers.[15][qualify evidence]

In a study looking at empathy and stress, individuals with the allele GG scored higher than A-carrier individuals in a "Reading the Mind in the Eyes" test. GG carriers, with their naturally higher levels of oxytocin, were better able to distinguish between emotions.[citation needed] A-allele carriers responded with more stress to stressful situations than GG-allele carriers.[16][further explanation needed] A-allele carriers had lower scores on psychological resources, like optimism, mastery, and self-esteem, than GG individuals when measured with factor analysis for depressive symptomology and psychological resources, along with the Beck Depression Inventory. A-allele carriers had higher depressive symptomology and lower psychological resources than GG individuals.[15][qualify evidence] A-allele individuals scored lower in human sociality than GG people on a Tridimensional Personality Questionnaire. AA individuals had the lowest amygdala activation while processing emotionally salient information and those with GG had the highest activity when tested using BOLD during an fMRI.[17] On the other hand, variations at the CD38 rs3796863 and OXTR rs53576 loci were not associated with psychosocial characteristics of adolescents assessed with the Strengths and Difficulties Questionnaire (SDQ); in studies with a similar design, authors recommend replication with larger samples and greater power to detect small effects, especially in age–sex subgroups of adolescents.[18]

The frequency of the A allele varies among ethnic groups, being significantly more common among East Asians than Europeans.[19][quantify][additional citation(s) needed]

Some evidence suggests an association between OXTR gene polymorphism, IQ, and autism spectrum disorder (ASD).[20] Studies have done research focusing on variants in the third intron of the gene, a region that is strongly correlated with personality traits and ASD. OXTR knockout mice have shown abnormal behaviors such as social impairments and aggressiveness. These abnormalities can be reduced with oxytocin or oxytocin agonist administration. Overall, the study suggests that rare variants are considerably more abundant in individuals with ASD compared to that of a normal individual, however further research with larger sample sizes must be completed before concluding any information.[21]

Ligands

[edit]

Several selective ligands for the oxytocin receptor have recently been developed, but close similarity between the oxytocin and related vasopressin receptors make it difficult to achieve high selectivity with peptide derivatives.[22][23] However the search for a druggable, non-peptide template has led to several potent, highly selective, orally bioavailable oxytocin antagonists.[24] Oxytocin receptor agonists have also been developed.[25][26]

Agonists

[edit]
Peptide
Non-peptide

Antagonists

[edit]
Peptide
Non-peptide

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Oxytocin receptor

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from Grokipedia
The oxytocin receptor (OXTR) is a seven-transmembrane (GPCR) encoded by the OXTR gene on human chromosome 3p25.3, which selectively binds the oxytocin to mediate a wide array of physiological and behavioral processes. 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 form, stabilized by interactions involving polar residues and a conserved magnesium ion coordination site. Upon binding, OXTR activates intracellular signaling cascades primarily through Gαq/11 or Gαi proteins, leading to activation, calcium mobilization, and downstream pathways such as MAPK/ERK and PI3K-AKT, which underpin its diverse effects. OXTR is expressed in a tissue- and region-specific manner, with high levels in the , mammary glands, and myoepithelial cells for reproductive functions, as well as in regions including the , hippocampus, , paraventricular nucleus, and , where it influences neural circuits. Peripherally, it is found in the heart, vascular , , and immune cells, contributing to cardioprotection, modulation, and . Expression levels are dynamically regulated by factors such as estrogens, stress, developmental stage, and epigenetic modifications like at CpG sites, with notable increases during or . Genetic variations, including single nucleotide polymorphisms like rs53576 and rs2254298, have been associated with individual differences in , anxiety, and susceptibility to disorders such as autism spectrum conditions, although these associations do not appear to be mediated by differences in circulating oxytocin concentrations. In terms of physiological roles, OXTR is essential for uterine contraction during labor and milk ejection during , processes that can be pharmacologically targeted with agonists like oxytocin for induction or antagonists like atosiban for preterm labor prevention. Centrally, it modulates social bonding, trust, empathy, and pair bonding by enhancing and dendritic remodeling in limbic areas, while also exerting effects and facilitating fear extinction through interactions with the hypothalamic-pituitary-adrenal axis. Dysregulation of OXTR signaling has implications for psychiatric conditions, including depression, , and , 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 and functional neurological conditions.

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. It spans approximately 17 kilobases (kb) of genomic DNA and consists of four exons interrupted by three introns. 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. The OXTR gene encodes a protein of 389 that undergoes post-translational processing to form the mature receptor. The promoter region lies upstream of 1, with transcription initiating at sites 618 and 621 base pairs before the ; it features a TATA-like motif approximately 30 base pairs upstream of the transcription start site and an SP-1 about 65 base pairs upstream, along with other potential regulatory elements such as AP-1, AP-2, and GATA-1 sites. 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. The (cDNA) for the human OXTR was first cloned in 1992 from a library derived from term myometrial , enabling initial characterization of the receptor's sequence and expression. The full genomic structure, including intron-exon boundaries, was subsequently elucidated in 1994 through isolation and sequencing of genomic clones. Evolutionarily, the OXTR 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. This timeline underscores the system's conservation across vertebrates, with OXTR orthologs present in diverse species from to mammals.

Protein structure

The oxytocin receptor (OXTR) is a class A G-protein-coupled receptor (GPCR) encoded by the OXTR gene on human chromosome 3p25. It exhibits the canonical topology of this receptor family, comprising seven transmembrane α-helices (TM1–TM7) that form a helical bundle embedded in the , flanked by three extracellular loops (ECL1–ECL3) and three intracellular loops (ICL1–ICL3). The protein features an extracellular N-terminal domain, which extends into the and contains potential sites, and an intracellular C-terminal tail that interacts with the membrane and intracellular components. The mature human OXTR polypeptide consists of 389 with a core molecular weight of approximately 43 kDa, which can increase due to post-translational modifications such as N-linked at three sites (Asn8, Asn15, and Asn26) in the N-terminal domain. Key structural elements contribute to the stability and function of OXTR. A conserved 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. 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. These features are typical of class A GPCRs and have been preserved across species, underscoring their evolutionary importance. 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. 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. 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.

Expression patterns

Peripheral expression

The oxytocin receptor (OXTR) exhibits high levels of expression in peripheral reproductive tissues, particularly the and of the , where it plays a key role in facilitating labor contractions. During , OXTR expression in the human undergoes significant upregulation, with receptor concentrations increasing by more than 100-fold from early 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 . 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.

Central nervous system expression

The oxytocin receptor (OXTR) exhibits a heterogeneous expression pattern across the , with particularly dense localization in key limbic and structures that underpin social, emotional, and reward-related neural circuits. High levels of OXTR mRNA and binding sites are observed in the , notably within the paraventricular nucleus (PVN) and (SON), where the receptor facilitates local oxytocin signaling and modulates neuroendocrine responses. Similarly, dense expression occurs in the central nucleus of the , involved in fear and anxiety processing; the hippocampus, supporting memory formation and synaptic plasticity; and the , a core component of the . These regional distributions have been consistently mapped in models using 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 , which contributes to executive control and decision-making; the (VTA), where it influences dopaminergic reward pathways; and the , particularly the accessory regions that process social pheromones. In contrast, OXTR density remains sparse in the , with limited binding observed primarily in the molecular layer of 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 and hippocampus across the lifespan, with ontogenetic peaks in and adulthood. At the subcellular level, OXTR is predominantly localized to postsynaptic membranes on neuronal somata and dendrites, where it couples to proteins to regulate intracellular calcium and modulate excitatory and inhibitory synaptic transmission. Evidence also indicates of OXTR along certain projections, such as those from VTA neurons to 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 (PET) imaging studies from the 2010s have identified sex differences in OXTR binding within the , particularly in the , where densities vary by sex and correlate with traits in a region-specific manner. For instance, rodents often exhibit lower binding in the central amygdala compared to males, though physiological states like can dynamically alter these patterns.

Mechanism of action

Signaling pathways

The oxytocin receptor (OXTR), a , primarily couples to /11 proteins upon activation by oxytocin, leading to the stimulation of C-β (PLC-β). This activation results in the hydrolysis of (PIP2) into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 binds to IP3 receptors (IP3R) on the , inducing calcium (Ca²⁺) release into the , while DAG remains membrane-bound to facilitate further signaling. The intracellular Ca²⁺ concentration ([Ca²⁺]ᵢ) can be conceptually represented as: [\ceCa2+]i=[\ceCa2+]basal+IP3-induced release via IP3R channels[\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. 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. OXTR can also couple to Gi/o proteins, inhibiting adenylyl cyclase and contributing to signal diversity in specific tissues. Additionally, β-arrestin recruitment follows receptor phosphorylation by G protein-coupled receptor kinases, promoting desensitization and internalization to terminate signaling and prevent overstimulation. Downstream effects of the primary pathway include activation of (PKC) by DAG and Ca²⁺, which target proteins to modulate cellular responses such as contraction and . The pathway also engages (MAPK)/extracellular signal-regulated kinase (ERK) cascades, leading to ERK that influences proliferation, differentiation, and . 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.

Interaction with mesolimbic dopamine pathways

The oxytocin receptor (OXTR) is co-expressed with neurons in the (VTA) and on both and glutamate neurons in the (NAc), key nodes of the . This co-localization enables oxytocin to modulate transmission directly. Specifically, oxytocin binding to OXTR excites VTA neurons while simultaneously inhibiting local interneurons, resulting in net and enhanced release into the NAc. As part of broader 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. This interaction heightens sensitivity to social stimuli by boosting -mediated reinforcement in these neurons. Behaviorally, OXTR modulation of mesolimbic facilitates pair bonding and the rewarding aspects of social interactions in monogamous , where oxytocin enhances partner preference through increased signaling. Similarly, oxytocin reduces cocaine-seeking in self-administration reinstatement models in rats, underscoring its role in attenuating drug-related reward cues via pathways. Studies from 2015 to 2024 demonstrate that OXTR mice, particularly those lacking receptors on neurons, exhibit blunted release in response to , impairing social reward processing.

Genetic variations

Polymorphisms

The oxytocin receptor gene (OXTR) harbors numerous single 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 3p25.3, and often form blocks that can influence binding and regulatory elements. For instance, certain s alter binding sites for , potentially modulating OXTR expression levels in a tissue-specific manner. Among the most studied SNPs are rs53576 (G/A transition in 3) and rs2254298 (G/A in the third ). The rs53576 variant has been extensively investigated for its role in ; the GG genotype is associated with higher levels of , as measured by behavioral tasks like empathic accuracy and self-report scales. However, meta-analyses have shown mixed results, with some OXTR SNPs, including rs53576, failing to consistently replicate associations with social behaviors across populations. In contrast, the A allele of rs53576 is linked to reduced OXTR receptor expression, partly through increased of CpG islands that affects gene transcription and mRNA stability. Notably, reliable studies have found no significant correlation between rs53576 genotypes (GG, AG, or AA) and plasma or serum oxytocin concentrations. Direct measurements indicate that behavioral differences associated with this polymorphism, such as variations in empathy, are not explained by differences in circulating oxytocin levels and likely arise from central mechanisms involving receptor density, function, or signaling rather than peripheral hormone concentrations. The rs2254298 SNP similarly impacts OXTR function, with the A showing associations with altered social processing. Recent research from 2024 indicates that the rs2254298 A is more prevalent in individuals with symptoms, including increased severity of breathlessness and , suggesting a role in respiratory via oxytocin pathways. Functional studies further reveal that this variant may influence corticostriatal connectivity differences, as observed in resting-state functional MRI, where A carriers exhibit variations in striatal network integration potentially tied to reward and circuits. 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. Histone modifications further fine-tune OXTR expression, with of 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 , facilitating affiliative behaviors. This modification contrasts with deacetylation states induced by stress, highlighting the plasticity of structure in regulating oxytocin-mediated social motivation. 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 or , leads to higher 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 in embedding early experiences into enduring neurobiological traits. OXTR methylation exhibits sex-specific differences, with females often displaying higher levels at certain and promoter sites compared to males, potentially reflecting dimorphic roles in reproductive and social behaviors. Certain polymorphisms may briefly influence susceptibility to these changes at specific sites, though epigenetic dynamics predominate. In preclinical models, these alterations prove reversible; treatment with (HDAC) inhibitors, such as , restores at OXTR promoters, thereby enhancing expression and rescuing social deficits in stressed .

Ligands

Endogenous ligand

The endogenous for the oxytocin receptor (OXTR) is oxytocin, a cyclic nonapeptide composed of nine with the sequence Cys¹-Tyr²-Ile³-Gln⁴-Asn⁵-Cys⁶-Pro⁷-Leu⁸-Gly⁹-NH₂, where a bridge forms between Cys¹ and Cys⁶. Oxytocin is synthesized as a larger precursor protein in magnocellular neurons of the paraventricular and supraoptic nuclei in the , processed into the mature peptide, and transported via axons to the for storage and release into the systemic circulation. Oxytocin binds to OXTR with high affinity, typically exhibiting a (K_d) of approximately 1 nM, which enables sensitive detection and activation of the receptor. This binding specificity distinguishes oxytocin from the related peptide arginine , 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. The release of oxytocin is regulated in a pulsatile manner, with surges triggered by physiological stimuli such as during labor or nipple stimulation during , leading to progressively larger and more frequent pulses that facilitate coordinated responses like milk ejection and labor progression. In plasma, oxytocin has a short of about 3-5 minutes, primarily due to rapid enzymatic degradation by oxytocinase and clearance by the kidneys and liver. Oxytocin serves a dual role as a peripheral , influencing reproductive and cardiovascular functions upon systemic release, and as a central neuromodulator, modulating neural circuits when released within the from hypothalamic projections. 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 .

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. Carbetocin, a synthetic analog of oxytocin, acts as a potent OXTR with a Ki 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 in calcium mobilization pathways. Compared to oxytocin, carbetocin shows a slightly reduced maximal response (about 50% lower in Gq activation) but maintains strong activity. Non-peptide agonists offer advantages in selectivity and potential for . WAY-267464 is a selective non-peptide OXTR with a Ki of 58.4 nM at OXTR and negligible affinity for receptors, acting as a with an EC50 of 24 nM in calcium release assays. However, it displays some off-target antagonism at V1a receptors (Ki 12.5 nM), limiting its selectivity profile. Recent advancements include LIT-001, a non-peptide full OXTR 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 Ki of 11 nM for OXTR binding, with selectivity over V2 receptors (Ki ≈50 nM, ) and V1a (Ki >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. Peptide agonists like oxytocin and face challenges with oral due to enzymatic degradation and poor gastrointestinal absorption, often below 1% for oxytocin. Intranasal delivery circumvents these issues, allowing effects; for instance, 24 IU doses of oxytocin elevate plasma levels within 20 minutes and facilitate uptake via olfactory pathways. Non-peptide agonists like LIT-001 show promise for improved , including better penetration without relying solely on intranasal routes.

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 of the receptor, preventing activation. The receptor's binding , as revealed by crystallographic studies, accommodates antagonists with an enlarged extracellular exposure compared to -bound states, facilitating their design for therapeutic applications. Some antagonists, such as L-371,257 and atosiban, exhibit inverse properties by reducing constitutive receptor activity in the absence of . Atosiban, a peptidic oxytocin receptor derived from oxytocin, acts competitively at the receptor with high potency, inhibiting oxytocin-induced calcium mobilization in myometrial cells ( ≈ 5 nM). It has been developed and approved for the management of preterm labor by suppressing 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 and . L-368,899 is a selective, orally active non-peptide with an 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 , 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 in alleviating OXTR hyperactivity in such contexts.

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. 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. In lactation, OXTR activation in the is essential for the milk ejection reflex. Suckling stimulates oxytocin release from the , which binds to OXTR on myoepithelial cells surrounding the alveoli, causing their contraction and the subsequent ejection of into the ducts. This process ensures efficient milk transfer to the offspring. OXTR mice show severe deficits in this reflex, resulting in inadequate ejection and poor pup survival despite normal production. Beyond these core functions, OXTR contributes to ovarian follicle development and male reproductive processes. In the ovary, OXTR expression in granulosa and cells of preovulatory follicles supports follicular maturation and , with exogenous oxytocin influencing follicle growth and luteal function in animal models. In males, OXTR in the reproductive tract, including the testis and , promotes transport through contractions of , enhancing and .

Social and emotional behaviors

The oxytocin receptor (OXTR) plays a pivotal role in mediating prosocial behaviors, including enhanced trust, , and pair bonding, through its activation by oxytocin in social contexts. Genetic factors, including variations in the OXTR , contribute to differences in these behaviors. 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 in naturalistic interactions and biases toward the eyes of faces displaying emotional expressions, particularly , thereby facilitating social cue processing. Oxytocin receptors are expressed in key brain regions such as the and , which support these social attentional mechanisms. However, the effects of intranasal oxytocin on social and emotional behaviors are highly context-dependent. While it frequently promotes prosocial behaviors, such as enhanced empathy and attention to social cues, in certain situational contexts it can lead to antisocial outcomes, including increased envy and schadenfreude (gloating) or heightened aggression toward out-groups. Regarding emotional regulation, OXTR activation attenuates amygdala responses to fearful stimuli, reducing the neural processing of threat and thereby dampening and anxiety. Oxytocin signaling via OXTR in the central 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 release, promoting resilience to psychological stressors. Sex differences in OXTR-mediated effects are evident in emotion recognition tasks, where oxytocin enhances accuracy more robustly in . 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 . Recent studies from 2023 to 2025 have linked OXTR genetic variants to diminished social reward in , 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 .

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 of 1.28 (95% CI 1.11–1.48) for ASD susceptibility. 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 and emotional processing pathways. In psychiatric conditions, OXTR single nucleotide polymorphisms (SNPs) influence connectivity and symptom severity. For , recent 2023 studies demonstrate that OXTR SNPs, such as rs2254298, alter functional connectivity in reward and social 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 is linked to elevated depressive symptoms under 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 , as of 2024 research identifies OXTR polymorphisms, particularly the rs2254298 A-allele, as associated with symptoms, including higher rates of and breathlessness, likely through effects on respiratory control mechanisms. Epigenetic alterations further link OXTR to trauma-related disorders. In (PTSD), hypermethylation of the OXTR promoter leads to epigenetic silencing and approximately 30% lower OXTR expression in peripheral blood cells, correlating with heightened reactivity and impaired fear extinction.

Therapeutic applications

Oxytocin, administered as a or intravenously, is approved for inducing labor and managing postpartum hemorrhage by stimulating through activation of the oxytocin receptor (OXTR). In clinical practice, intranasal oxytocin facilitates cervical ripening and labor augmentation in cases of prolonged delivery, while intravenous forms are standard for controlling after . Atosiban, an OXTR , is approved for intravenous use as a agent to inhibit preterm labor contractions, prolonging pregnancy by up to seven days in women with imminent delivery before 34 weeks gestation. , a long-acting OXTR analog of oxytocin, is utilized postpartum to prevent excessive following cesarean sections, offering sustained uterine tone with a longer duration of action compared to native oxytocin. Experimental applications of OXTR-targeted therapies focus on neuropsychiatric conditions. Intranasal oxytocin, a synthetic form of the hormone administered via nasal spray to potentially elevate central nervous system levels, is primarily used in research to study and potentially treat social, emotional, and behavioral conditions, including autism spectrum disorder, anxiety, depression, PTSD, and stress-related disorders. Key effects include modulation of social cognition (e.g., enhanced empathy, attention to social cues), reduced stress/anxiety responses, and context-dependent behavioral changes (prosocial or sometimes antisocial). It is not widely approved for clinical use beyond investigational settings. Intranasal oxytocin has been investigated for alleviating social deficits in autism spectrum disorder, with Phase II trials showing mixed efficacy in improving and interaction; a 2021 meta-analysis of randomized controlled trials indicated modest benefits in repetitive behaviors but inconsistent overall symptom reduction. OXTR agonists, including oxytocin itself, are under evaluation as adjuncts for , where clinical trials demonstrate potential in enhancing social bonding and reducing stress reactivity when combined with antidepressants like , though larger studies are needed to confirm sustained effects. Preliminary research indicates potential benefits in specific sleep-related contexts. In patients with obstructive sleep apnea (OSA), intranasal oxytocin has been shown to reduce the duration of obstructive events and associated oxygen desaturations and bradycardias while increasing respiratory rate. It may improve sleep quality by enhancing positive couple interactions and closeness in cosleeping partners, with stronger effects in women. In some patients with hypothalamic syndrome, long-term intranasal oxytocin administration improved sleep quality. Animal studies suggest minimal or no significant impact of intranasal administration on sleep-wake patterns. The evidence for these sleep-related effects is preliminary, derived from small studies and trials, and further research is needed to elucidate mechanisms, long-term efficacy, and broader applications. Key challenges in OXTR-targeted therapies include oxytocin's short plasma of 2-4 minutes, which limits its duration of action, and difficulties in achieving penetration due to poor blood-brain barrier crossing, necessitating intranasal delivery for brain-targeted effects while risking peripheral side effects like . OXTR antagonists face similar delivery hurdles in psychiatric applications, such as targeting repetitive behaviors in autism, where selective central modulation remains elusive. In 2023 preclinical studies, selective OXTR agonists like LIT-001 have demonstrated promise in models by enhancing pro-social behaviors and through corticostriatal pathway modulation, reversing deficits in neurodevelopmental paradigms without significant off-target effects.

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