Estrogen-dependent regulation of transient receptor potential vanilloid 1 (TRPV1) and P2X purinoceptor 3 (P2X3): Implication in burning mouth syndrome

Therapeutic targeting of P2X receptors for orofacial pain

P2X receptors (P2XRs), membrane ion channels activated by extracellular adenosine 5' -triphosphate (ATP), play a pivotal role in nociception by directly promoting pain signaling. Currently, antagonists targeting P2XRs have taken effect in alleviating various pain. The therapeutic potential of the P2X receptor family has become a central focus. Consequently, numerous research groups and pharmaceutical companies are actively engaged in developing novel P2XR antagonists. Furthermore, an increasing number of clinical trials on P2XR antagonists have obtained encouraging results. This review provides an overview of the structural characteristics and cellular localization of P2XRs, their molecular mechanisms and signaling pathways implicated in orofacial pain. Additionally, it explores the development of P2XR antagonists and their therapeutic application for managing orofacial pain. In conclusion, this review highlights the promising role of P2XRs as therapeutic targets for orofacial pain treatment.

Estrogen-Mediated Neural Mechanisms of Sex Differences in Burning Mouth Syndrome

BACKGROUND/OBJECTIVES

Burning mouth syndrome (BMS) is a chronic pain disorder of the oral cavity in the absence of organic disease and is prevalent among menopausal women. Estrogen may be involved in the formation of nerves involved in pain.

METHODS

This paper presents an inferred mechanism for the relationship between estrogen and BMS based on a synthesis and interpretation of findings from a selection of published studies.

RESULTS

Estrogen influences the formation of neural circuits in BMS by dividing the complex pain circuit into the following three components: the peripheral pain circuit, brain network pain circuit, and memorized pain circuit.

CONCLUSIONS

The development of BMS may be influenced by the formation of neural circuits by sex hormones.

Studies on Burning Mouth Syndrome in the Past 20 Years: A Bibliometric and Visualised Analysis

OBJECTIVE

Burning mouth syndrome (BMS) is a common oral pain disorder characterised by a burning sensation without any oral mucosal lesions. The etiopathogenesis of BMS remains unclear. A number of psychogenic and molecular mechanisms have been proposed to explain BMS; however, no bibliometric analyses have compiled the knowledge of BMS. Thus, this study aimed to explore the BMS research hotspots and trends from a bibliometric analysis perspective.

METHODS

A comprehensive search related to BMS publications within the Web of Science Core Collection database was conducted. CiteSpace and VOSviewer software were used to analyse the bibliometric characteristics of the BMS research from January 2003 to September 2023, visualising the country distribution; author and co-cited authors; journals and co-cited journals; references and co-cited references; keyword cluster analysis; and timelines. We also reviewed related articles to provide references for integrating research frameworks.

RESULTS

A total of 1080 BMS articles were published in 466 journals, with 34121 citations from 1447 institutions in 75 countries. The USA has made significant contributions to this field, with Nihon University (Japan) and the Mayo Clinic (USA) publishing the most articles. Toyofuku Akira is the most active author. Oral Diseases is regarded as the most productive journal. The top 3 co-citation clusters were cytokines, chronic pain, and therapy. According to the keyword burst analysis, the strongest keywords include stomatodynia, symptoms, and anxiety.

CONCLUSION

Over the last 2 decades, the number of BMS publications has gradually and significantly increased worldwide. In recent years, research in the field of BMS has focused on studying the cellular and molecular underpinnings. A bibliometric analysis helps develop a better understanding of the pathogenesis of BMS and innovate more targeted therapeutic interventions in this field.

Short-Term Dietary Caffeine Intake for Alleviating Symptoms of Burning Mouth Syndrome: A Randomised Controlled Comparison With Alpha-Lipoic Acid

OBJECTIVE

This study investigates whether daily supplementation of 120-150 mg of caffeine can relieve symptoms of Burning Mouth Syndrome (BMS) compared to alpha-lipoic acid (ALA) and a control group.

METHODS

In this randomised controlled trial, 118 BMS patients were divided into three groups: caffeine, ALA, and control. The caffeine group received 120-150 mg of caffeine daily, the ALA group received 200 mg of ALA three times daily, and the control group received no interventions. Symptom relief was assessed over 2 weeks using the Visual Analog Scale (VAS), with subgroup analyses based on symptom subtypes, disease duration, symptom sites, and characteristics.

RESULTS

The VAS of BMS patients in the caffeine and ALA groups exhibited significant reductions (p < 0.0005). The caffeine group exhibited a 65.1% symptom relief rate compared to 46.5% in the ALA group and 12.5% in the control group. Significant differences in symptom relief were noted between the caffeine and control groups (p < 0.0005) and between the ALA and control groups (p = 0.0032). No significant difference was observed between the caffeine and ALA groups (p = 0.084). Type I BMS patients in the caffeine group showed greater symptom relief than those in the ALA group (p = 0.026).

CONCLUSIONS

Both caffeine and ALA effectively treated BMS, with caffeine showing higher efficacy in Type I patients. Treatments were well-tolerated with minimal adverse effects, suggesting caffeine and ALA as promising treatments for BMS, warranting further research on their long-term effects and mechanisms of action. [The study was registered on ClinicalTrials.gov (Identification No. NCT06195137).].

Capsaicin (But Not Other Vanillins) Enhances Estrogen Binding to Its Receptor: Implications for Power Sports and Cancers

Capsaicin (CAP), the pain-inducing compound in chili peppers, exerts its effects mainly through the transient receptor potential vanilloid channel 1 (TRPV1), which mediates pain perception and some metabolic functions. CAP has also been demonstrated to improve performance in power sports (but not endurance sports) and does so mainly for females. CAP may also have anti-cancer effects. Many mechanisms have been explored to explain these phenomena, particularly the effects of TRPV1 activation for calcium influx, glucose transporter (GLUT) upregulation and inhibition of insulin (INS) production, but two important ones seem to have been missed. We demonstrate here that CAP binds to both INS and to the estrogen receptor (ESR1), enhancing estradiol binding. Other TRPV1 agonists, such as vanillin, vanillic acid and acetaminophen, have either no effect or inhibit estrogen binding. Notably, TRPV1, ESR1 and INS share significant regions of homology that may aid in identifying the CAP-binding site on the ESR1. Because activation of the estrogen receptor upregulates GLUT expression and thereby glucose transport, we propose that the observed enhancement of performance in power sports, particularly among women, may result, in part, from CAP enhancement of ESR1 function and prevent INS degradation. Chronic exposure to CAP, however, may result in downregulation and internalization of ESR1, as well as TRPV1 stimulation of glucagon-like peptide 1 (GLP-1) expression, both of which downregulate GLUT expression, thereby starving cancer cells of glucose. The binding of capsaicin to the ESR1 may also enhance ESR1 antagonists such as tamoxifen, benefiting some cancer patients.

Burning mouth syndrome - known and unknown

The aim of this literature review was to provide a brief perspective over the scientific research of the condition known as burning mouth syndrome. Information from review articles, original studies, and dissertations was gathered using keywords describing etiological factors, clinical, laboratory findings and treatment protocols. We compiled information on potential etiological factors, symptoms, and potential treatments from the fifty-three included studies on dental and general health issues in patients complaining of burning sensations in their mouths. Despite the numerous attempts by dental and medical professionals to diagnose and treat mouth burning, the etiology and pathogenesis of this disorder remain rather unclear. In most cases, it is concluded that further research is needed with the inclusion of more patients, administering a long-term therapy, and monitoring the results.

Amitriptyline effectiveness in burning mouth syndrome: An in-depth case series analysis

OBJECTIVES

To assess the effectiveness of amitriptyline (AMT), and to identify the determinants of the treatment's effectiveness in patients diagnosed with burning mouth syndrome (BMS).

BACKGROUND

Treatment of BMS is challenging and no established treatment protocol is available. AMT may be an important treatment option, cout not all patients benefit from this drug. Studies assessing factors related to treatment response are valuable in improving decision-making.

MATERIALS AND METHODS

This case series study examined the medical records of all patients diagnosed with BMS at an oral medicine unit in a university hospital from 2008 to 2022. The patients were divided into responders to AMT and non-responders to AMT. Data on demographic information, comorbidities, medications, types of symptoms and oral subsites affected were collected. Descriptive and bivariate analyses were conducted to assess the association between the independent variables and the outcome, using the Chi-squared test (P < .05).

RESULTS

Three hundred and fourty-nine patients reported a burning mouth sensation, 50 of them (14.3%) being diagnosed with primary BMS. Of these, 35 were treated with AMT, and 26 (74.2%) responded significantly to AMT. All males responded to AMT, whereas only 67.9% of females responded. The mean dose of AMT among responders was 29.8 ± 12.3 mg, with most patients achieving a response with 25 mg (61.5% of patients), followed by 50 mg (23%). The concomitant use of an anticonvulsant resulted in non-response.

CONCLUSIONS

AMT may be effective in BMS management for most patients.

The Role of the Gut Microbiota in Individuals with Irritable Bowel Syndrome: A Scoping Review

Irritable bowel syndrome (IBS) represents the most prevalent disorder of brain-gut interaction, affecting approximately 10% of the global population. The objective of this study was to examine the mechanisms by which the gut microbiota contributes to the development of IBS. To this end, a review of articles that examined the gut microbiota of IBS patients was conducted. A search was conducted using PubMed and J-STAGE for articles published over the past five years that relate to the gut microbiota in patients with IBS. Individuals diagnosed with IBS display a reduction in alpha diversity and a decline in butyrate-producing bacteria, which collectively indicate a state of dysbiosis within their gut microbiota. Butyrate plays a dual role in the body, acting as a source of nutrition for the intestinal epithelium while also regulating the expression of dopamine transporters and D2 receptors in the central nervous system through epigenetic mechanisms. These characteristics may be linked to dysfunction of the central dopamine D2 pathway and play a role in the formation of various symptoms in IBS.

Sexual hormones changes in burning mouth syndrome: A systematic review

BACKGROUND

Burning mouth syndrome (BMS) is a chronic pain condition affecting the oral cavity. This condition mostly affects peri- or postmenopausal women; for this reason, sexual hormonal changes have been implicated in BMS pathogenesis.

METHODS

A systematic review was performed in MEDLINE/PubMed, Scopus, Web of Science, Cochrane Library and EMBASE without restriction for language or year. Eligibility criteria were controlled studies addressing the PICO question: (P) patients with BMS; (I) detection of the sex hormones; (C) patients without BMS; (O) changes on sexual hormones as a risk factor for BMS severity. Risk of bias was performed with Newcastle-Ottawa Quality Assessment Scale.

RESULTS

Four studies were included. Salivary levels were evaluated in three studies and serum blood was used in one. Three studies analysed oestradiol and/or dehydroepiandrosterone (DHEA), two assessed progesterone and one evaluated follicle-stimulating hormone (FSH). Oestradiol results were contradictory, with two studies reporting lower levels in BMS patients compared to controls and one finding the opposite. DHEA was statistically lower in the BMS group in one study. Progesterone showed opposite results in two studies, although none with statistical significance. FSH was statistically higher in the BMS group compared to controls. Correlation of hormones with quality of life was performed in three studies and there was no significant correlation with self-perceived symptoms severity.

CONCLUSION

Sexual hormones can be altered in BMS, especially oestradiol. Despite these changes, we did not find correlation between hormone fluctuation and BMS symptoms intensity affecting quality of life. These findings suggested the need for further investigation on hormonal alterations, which may be a promising target on BMS management.

The influence of sex on neuroimmune communication, pain, and physiology

With the National Institutes of Health's mandate to consider sex as a biological variable (SABV), there has been a significant increase of studies utilizing both sexes. Historically, we have known that biological sex and hormones influence immunological processes and now studies focusing on interactions between the immune, endocrine, and nervous systems are revealing sex differences that influence pain behavior and various molecular and biochemical processes. Neuroendocrine-immune interactions represent a key integrative discipline that will reveal critical processes in each field as it pertains to novel mechanisms in sex differences and necessary therapeutics. Here we appraise preclinical and clinical literature to discuss these interactions and key pathways that drive cell- and sex-specific differences in immunity, pain, and physiology.

Increased Purinergic Signaling in Human Dental Pulps With Inflammatory Pain is Sex-Dependent

An enhanced understanding of neurotransmitter systems contributing to pain transmission aids in drug development, while the identification of biological variables like age and sex helps in the development of personalized pain management and effective clinical trial design. This study identified enhanced expression of purinergic signaling components specifically in painful inflammation, with levels increased more in women as compared to men. Inflammatory dental pain is common and potentially debilitating; as inflammation of the dental pulp can occur with or without pain, it provides a powerful model to examine distinct pain pathways in humans. In control tissues, P2X3 and P2X2 receptors colocalized with PGP9.5-positive nerves. Expression of the ecto-nucleotidase NTPDase1 (CD39) increased with exposure to extracellular adenosine triphosphate (ATP), implying CD39 acted as a marker for sustained elevation of extracellular ATP. Both immunohistochemistry and immunoblots showed P2X2, P2X3, and CD39 increased in symptomatic pulpitis, suggesting receptors and the ATP agonist were elevated in patients with increased pain. The increased expression of P2X3 and CD39 was more frequently observed in women than men. In summary, this study identifies CD39 as a marker for chronic elevation of extracellular ATP in fixed human tissue. It supports a role for increased purinergic signaling in humans with inflammatory dental pain and suggests the contribution of purines shows sexual dimorphism. This highlights the potential for P2X antagonists to treat pain in humans and stresses the need to consider sex in clinical trials that target pain and purinergic pathways. PERSPECTIVE: This article demonstrates an elevation of ATP-marker CD39 and of ATP receptors P2X2 and P2X3 with inflammatory pain and suggests the rise is greater in women. This highlights the potential for P2X antagonists to treat pain and stresses the consideration of sexual dimorphism in studies of purines and pain.

Gender differences in pain perception among burning mouth syndrome patients: a cross-sectional study of 242 men and 242 women

Several orofacial painful conditions are influenced by gender-related factors, but no studies are available with regard to Burning Mouth Syndrome (BMS). The present study aimed at investigating gender differences among BMS patients and their influence on pain perception. 242 BMS males (BMSm) and 242 BMS females (BMSf) matched for age were consecutively enrolled. Sociodemographic and clinical characteristics were recorded and the numeric rating scale (NRS), the Total Pain Rating Index (T-PRI), the Hamilton rating scale for anxiety and depression (HAM-A, HAM-D), the Pittsburgh sleep quality index (PSQI) and the Epworth sleepiness scale (ESS) were administered. The BMSm presented statistically significant higher levels of education and rate of employment compared to the BMSf (p-values: 0.001**). Moreover, the BMSm were greater consumers of alcohol and had a higher BMI than the BMSf (p-values: < 0.001**, 0.034*). With respect to systemic comorbidities, cardiovascular diseases were statistically more prevalent among the BMSm, while hypothyroidism was more frequent in the BMSf (p-vales: < 0.001**). No differences were noted between the two groups in terms of oral symptoms and in the median scores of NRS, T-PRI, HAM-A, HAM-D, PSQI and ESS. Interestingly, the multivariate regression analysis revealed that, while anxiety, high BMI, poor sleep and high level of T-PRI were correlated to the intensity of pain (NRS) in both groups, low education was additional predictor of pain in BMSf. Further, depression, alcohol and intensity of pain were factors positively associated to the quality of pain (T-PRI) in the BMSm, whereas low education, non-married status and NRS were correlated to the T-PRI, in the BMSf. Surprisingly, smoking was inversely correlated to the intensity of pain and quality of pain respectively in BMSf and BMSm. Sociodemographic and risk factors were found to differently influence pain perception in BMSm and BMSf. Therefore, clinicians should take into account gender differences in the assessment of BMS patients to better tailor the overall pain management.

Purinergic P2X3 receptors in the carotid body as new therapeutic targets for controlling heart failure

Heart failure is associated with multiple mechanisms, including sympatho-excitation, and is one of the leading causes of death worldwide. Enhanced carotid body chemoreflex function is strongly related to excessive sympathetic nerve activity and sleep-disordered breathing in heart failure. How to reduce the excitability of the carotid body is still scientifically challenging. Both clinical and experimental evidence have suggested that targeting purinergic receptors is of great potential to combat heart failure. In a recent study, Lataro et al. (Lataro et al. in Nat Commun 14:1725, 5) demonstrated that targeting purinergic P2X3 receptors in the carotid body attenuates the progression of heart failure. Using a series of molecular, biochemical, and functional assays, the authors observed that the carotid body generates spontaneous, episodic burst discharges coincident with the onset of disordered breathing in male rats with heart failure, which was generated by ligating the left anterior descending coronary artery. Moreover, P2X3 receptor expression was found to be upregulated in the petrosal ganglion chemoreceptive neurons of rats with heart failure. Of particular note, treatment with a P2X3 antagonist rescued pathological breathing disturbances, abolished episodic discharges, reinstated autonomic balance, attenuated cardiac dysfunction, and reduced the immune cell response and plasma cytokine levels in those rats.

Thermal escape box: A cost-benefit evaluation paradigm for investigating thermosensation and thermal pain

Thermosensation, the ability to detect and estimate temperature, is an evolutionarily conserved process that is essential for survival. Thermosensing is impaired in various pain syndromes, resulting in thermal allodynia, the perception of an innocuous temperature as painful, or thermal hyperalgesia, an exacerbated perception of a painful thermal stimulus. Several behavioral assays exist to study thermosensation and thermal pain in rodents, however, most rely on reflexive withdrawal responses or the subjective quantification of spontaneous nocifensive behaviors. Here, we created a new apparatus, the thermal escape box, which can be attached to temperature-controlled plates and used to assess temperature-dependent effort-based decision-making. The apparatus consists of a light chamber with an opening that fits around temperature-controlled plates, and a small entryway into a dark chamber. A mouse must choose to stay in a brightly lit aversive area or traverse the plates to escape to the enclosed dark chamber. We quantified escape latencies of adult C57Bl/6 mice at different plate temperatures from video recordings and found they were significantly longer at 5 °C, 18 °C, and 52 °C, compared to 30 °C, a mouse's preferred ambient temperature. Differences in escape latencies were abolished in male Trpm8-/- mice and in male Trpv1-/- animals. Finally, we show that chronic constriction injury procedures or oxaliplatin treatement significantly increased escape latencies at cold temperatures compared to controls, the later of which was prevented by the analgesic meloxicam. This demonstrates the utility of this assay in detecting cold pain. Collectively, our study has identified a new and effective tool that uses cost-benefit valuations to study thermosensation and thermal pain.

Oral mucosal diseases and psychosocial factors: progress in related neurobiological mechanisms

The aetiology of oral mucosal diseases, such as recurrent aphthous ulcer (RAU), oral lichen planus (OLP) and burning mouth syndrome (BMS), involves many factors, and it remains difficult for clinicians to effectively relieve disease symptoms and formulate coping strategies. With the rapid development of psychology, the role of mental and psychological factors in RAU, OLP and BMS has gradually attracted researchers attention, but the specific mechanism has not been completely determined. This narrative review describes the potential neurobiological mechanism of oral mucosal diseases and detailed psychological factors after introducing relevant research into psychological factors and oral mucosal diseases. Future research strategies and innovations needed to understand and treat oral mucosal diseases and psychological factors, as well as how to prevent oral mucosal diseases by regulation of the neuroendocrine system, are also discussed.

Gender-based research underscores sex differences in biological processes, clinical disorders and pharmacological interventions

Earlier research has presumed that the male and female biology is similar in most organs except the reproductive system, leading to major misconceptions in research interpretations and clinical implications, with serious disorders being overlooked or misdiagnosed. Careful research has now identified sex differences in the cardiovascular, renal, endocrine, gastrointestinal, immune, nervous, and musculoskeletal systems. Also, several cardiovascular, immunological, and neurological disorders have shown differences in prevalence and severity between males and females. Genetic variations in the sex chromosomes have been implicated in several disorders at young age and before puberty. The levels of the gonadal hormones estrogen, progesterone and testosterone and their receptors play a role in the sex differences between adult males and premenopausal women. Hormonal deficiencies and cell senescence have been implicated in differences between postmenopausal and premenopausal women. Specifically, cardiovascular disorders are more common in adult men vs premenopausal women, but the trend is reversed with age with the incidence being greater in postmenopausal women than age-matched men. Gender-specific disorders in females such as polycystic ovary syndrome, hypertension-in-pregnancy and gestational diabetes have attained further research recognition. Other gender-related research areas include menopausal hormone therapy, the "Estrogen Paradox" in pulmonary arterial hypertension being more predominant but less severe in young females, and how testosterone may cause deleterious effects in the kidney while having vasodilator effects in the coronary circulation. This has prompted the National Institutes of Health (NIH) initiative to consider sex as a biological variable in research. The NIH and other funding agencies have provided resources to establish state-of-the-art centers for women health and sex differences in biology and disease in several academic institutions. Scientific societies and journals have taken similar steps to organize specialized conferences and publish special issues on gender-based research. These combined efforts should promote research to enhance our understanding of the sex differences in biological systems beyond just the reproductive system, and provide better guidance and pharmacological tools for the management of various clinical disorders in a gender-specific manner.

An Unusual Case of Burning Mouth Syndrome in an Adult Male: A Case Report

Burning mouth syndrome (BMS) is a rare disorder primarily affecting the oral mucosa and characterized by a chronic burning sensation without specific oral mucosal lesions. This paper presents a case of a 54-year-old adult male patient who complained of chronic burning mouth pain. The clinical diagnosis was made after excluding various differentials, including oral candidiasis, hairy oral leukoplakia, gastroesophageal reflux disease, oral lichen planus, local infective processes, and nutritional deficiencies. Physical examination did not reveal specific signs or lesions related to BMS; however, considering the patient's signs, symptoms, and the exclusion of other possibilities, a possible diagnosis of BMS was considered. The patient was evaluated in an outpatient setting, and management was conducted in this setting to reduce patient costs. This presentation is considered rare, as the disorder predominantly affects postmenopausal females, and most proposed theories behind its pathophysiology revolve around estrogen-mediated modulation of pain receptors. Currently, diagnostic and management criteria for BMS may vary and continue to evolve. The management of this patient focuses on patient education and routine follow-up. This case report presents the management of this particular case, along with a review of other proposed management options.

Physiology of the tongue with emphasis on taste transduction

The tongue is a complex multifunctional organ that interacts and senses both interoceptively and exteroceptively. Although it is easily visible to almost all of us, it is relatively understudied and what is in the literature is often contradictory or is not comprehensively reported. The tongue is both a motor and a sensory organ: motor in that it is required for speech and mastication, and sensory in that it receives information to be relayed to the central nervous system pertaining to the safety and quality of the contents of the oral cavity. Additionally, the tongue and its taste apparatus form part of an innate immune surveillance system. For example, loss or alteration in taste perception can be an early indication of infection as became evident during the present global SARS-CoV-2 pandemic. Here, we particularly emphasize the latest updates in the mechanisms of taste perception, taste bud formation and adult taste bud renewal, and the presence and effects of hormones on taste perception, review the understudied lingual immune system with specific reference to SARS-CoV-2, discuss nascent work on tongue microbiome, as well as address the effect of systemic disease on tongue structure and function, especially in relation to taste.

Role of ATP in migraine mechanisms: focus on P2X3 receptors

Migraine is a major health burden worldwide with complex pathophysiology and multifarious underlying mechanisms. One poorly understood issue concerns the early steps in the generation of migraine pain. To elucidate the basic process of migraine pain further, it seems useful to consider key molecular players that may operate synergistically to evoke headache. While the neuropeptide CGRP is an important contributor, we propose that extracellular ATP (that generally plays a powerful nociceptive role) is also a major component of migraine headache, acting in concert with CGRP to stimulate trigeminal nociceptive neurons. The aim of the present focused review is to highlight the role of ATP activating its P2X3 membrane receptors selectively expressed by sensory neurons including their nerve fiber terminals in the meninges. Specifically, we present data on the homeostasis of ATP and related purines in the trigeminovascular system and in the CNS; the basic properties of ATP signalling at peripheral and central nerve terminals; the characteristics of P2X3 and related receptors in trigeminal neurons; the critical speed and persistence of P2X3 receptor activity; their cohabitation at the so-called meningeal neuro-immune synapse; the identity of certain endogenous agents cooperating with ATP to induce neuronal sensitization in the trigeminal sensory system; the role of P2X3 receptors in familial type migraine; the current state of P2X3 receptor antagonists and their pharmacological perspectives in migraine. It is proposed that the unique kinetic properties of P2X3 receptors activated by ATP offer an interesting translational value to stimulate future studies for innovative treatments of migraine pain.

Estrogen metabolites increase nociceptor hyperactivity in a mouse model of uterine pain

Pain emanating from the female reproductive tract is notoriously difficult to be treated and the prevalence of transient pelvic pain has been placed as high as 70-80% in women surveyed. Although sex hormones, especially estrogen, are thought to underlie enhanced pain perception in females, the underlying molecular and cellular mechanisms are not completely understood. Here we show that the pain-initiating TRPA1 channel is required for pain-related behaviors in a mouse model of estrogen-induced uterine pain in ovariectomized female mice. Surprisingly, 2- and 4-hydroxylated estrogen metabolites (HEMs) in the estrogen hydroxylation pathway, but not estrone, estradiol and 16-HEMs, directly increase nociceptor hyperactivity through TRPA1 and TRPV1 channels, and picomolar concentrations of 2- and 4-hydroxylation estrone (OHE1) can sensitize TRPA1 channel function. Moreover, both TRPA1 and TRPV1 are expressed in uterine-innervating primary nociceptors and their expressions are increased in the estrogen-induced uterine pain model. Importantly, pretreatment of 2- or 4-OHE1 recapitulates estrogen-induced uterine pain-like behaviors and intraplantar injections of 2- and 4-OHE1 directly produce a TRPA1-dependent mechanical hypersensitivity. Our findings demonstrate that TRPA1 is critically involved in estrogen-induced uterine pain-like behaviors, which may provide a potential drug target for treating female reproductive tract pain.