Estrogens Exacerbate Nociceptive Pain via Up-Regulation of TRPV1 and ANO1 in Trigeminal Primary Neurons of Female Rats

Anoctamin 1, a multi-modal player in pain and itch

Anoctamin 1 (ANO1/TMEM16A) encodes a Ca2+-activated Cl- channel. Among ANO1's many physiological functions, it plays a significant role in mediating nociception and itch. ANO1 is activated by intracellular Ca2+ and depolarization. Additionally, ANO1 is activated by heat above 44 °C, suggesting heat as another activation stimulus. ANO1 is highly expressed in nociceptors, indicating a role in nociception. Conditional Ano1 ablation in dorsal root ganglion (DRG) neurons results in a reduction in acute thermal pain, as well as thermal and mechanical allodynia or hyperalgesia evoked by inflammation or nerve injury. Pharmacological interventions also lead to a reduction in nocifensive behaviors. ANO1 is functionally linked to the bradykinin receptor and TRPV1. Bradykinin stimulates ANO1 via IP3-mediated Ca2+ release from intracellular stores, whereas TRPV1 stimulates ANO1 via a combination of Ca2+ influx and release. Nerve injury causes upregulation of ANO1 expression in DRG neurons, which is blocked by ANO1 antagonists. Due to its role in nociception, strong and specific ANO1 antagonists have been developed. ANO1 is also expressed in pruritoceptors, mediating Mas-related G protein-coupled receptors (Mrgprs)-dependent itch. The activation of ANO1 leads to chloride efflux and depolarization due to high intracellular chloride concentrations, causing pain and itch. Thus, ANO1 could be a potential target for the development of new drugs treating pain and itch.

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.

The Influence of Sex Steroid Hormone Fluctuations on Capsaicin-Induced Pain and TRPV1 Expression

Sexual dimorphism among mammals includes variations in the pain threshold. These differences are influenced by hormonal fluctuations in females during the estrous and menstrual cycles of rodents and humans, respectively. These physiological conditions display various phases, including proestrus and diestrus in rodents and follicular and luteal phases in humans, distinctly characterized by varying estrogen levels. In this study, we evaluated the capsaicin responses in male and female mice at different estrous cycle phases, using two murine acute pain models. Our findings indicate that the capsaicin-induced pain threshold was lower in the proestrus phase than in the other three phases in both pain assays. We also found that male mice exhibited a higher pain threshold than females in the proestrus phase, although it was similar to females in the other cycle phases. We also assessed the mRNA and protein levels of TRPV1 in the dorsal root and trigeminal ganglia of mice. Our results showed higher TRPV1 protein levels during proestrus compared to diestrus and male mice. Unexpectedly, we observed that the diestrus phase was associated with higher TRPV1 mRNA levels than those in both proestrus and male mice. These results underscore the hormonal influence on TRPV1 expression regulation and highlight the role of sex steroids in capsaicin-induced pain.

Function and Regulation of the Calcium-Activated Chloride Channel Anoctamin 1 (TMEM16A)

Various human tissues express the calcium-activated chloride channel Anoctamin 1 (ANO1), also known as TMEM16A. ANO1 allows the passive chloride flux that controls different physiological functions ranging from muscle contraction, fluid and hormone secretion, gastrointestinal motility, and electrical excitability. Overexpression of ANO1 is associated with pathological conditions such as hypertension and cancer. The molecular cloning of ANO1 has led to a surge in structural, functional, and physiological studies of the channel in several tissues. ANO1 is a homodimer channel harboring two pores - one in each monomer - that work independently. Each pore is activated by voltage-dependent binding of two intracellular calcium ions to a high-affinity-binding site. In addition, the binding of phosphatidylinositol 4,5-bisphosphate to sites scattered throughout the cytosolic side of the protein aids the calcium activation process. Furthermore, many pharmacological studies have established ANO1 as a target of promising compounds that could treat several illnesses. This chapter describes our current understanding of the physiological roles of ANO1 and its regulation under physiological conditions as well as new pharmacological compounds with potential therapeutic applications.

Ovariectomy induces hyperalgesia accompanied by upregulated estrogen receptor α and protein kinase B in the rat spinal cord

Hormone supplementation is one of the common therapies for menopause-related disorders. Among different tools, the ovariectomy (OVX) rodents are widely accepted as an appropriate menopausal pain model. Our previous study has showed that OVX produces a significant pain facilitation in both acute pain and tonic pain, however, the underlying mechanisms remain unclear. In this study, we examined the effects of OVX treatment and estradiol (E2) supplementation on formalin-induced nociceptive responses, and explored the associated spinal mechanisms. Female Sprague-Dawley rats underwent bilateral OVX, and E2 supplementation was given subcutaneously from the 5th week after surgery (30 μg/day for 7 days). Our results showed that formalin-induced nociceptive behaviors did not differ between diestrus and proestrus stages of the estrous in intact rats. However, OVX exacerbated formalin-evoked inflammatory pain, especially in the late phase at 4-5 weeks but not 2 weeks post-surgery. E2 supplementation significantly reversed the OVX-triggered hyperalgesia. Double immunofluorescence staining revealed that both ERα and ERβ in the spinal dorsal horn were co-labeled with the neuronal markers, but not with markers of astrocytes or microglia. The spinal ERα (but not ERβ) expression significantly increased in the OVX group, which was reversed by E2 supplementation. Moreover, the OVX individuals showed an increased protein kinase B (AKT) level in lumbar spinal cord, and E2 supplementation diminished the AKT expression in OVX rats. Finally, intrathecal injection Wortmannin, an inhibitor for AKT signaling, effectively reduced the nociceptive behaviors in the late phase and the number of c-fos positive cells. Together, our findings indicate that E2 supplementation alleviates the OVX-induced hyperalgesia, which might be involved in spinal ERα and AKT mechanisms.

Sexually Dimorphic Pattern of Pain Mitigation Following Prophylactic Regenerative Peripheral Nerve Interface (RPNI) in a Rat Neuroma Model

BACKGROUND

Treating neuroma pain is a clinical challenge. Identification of sex-specific nociceptive pathways allows a more individualized pain management. The Regenerative Peripheral Nerve Interface (RPNI) consists of a neurotized autologous free muscle using a severed peripheral nerve to provide physiological targets for the regenerating axons.

OBJECTIVE

To evaluate prophylactic RPNI to prevent neuroma pain in male and female rats.

METHODS

F344 rats of each sex were assigned to neuroma, prophylactic RPNI, or sham groups. Neuromas and RPNIs were created in both male and female rats. Weekly pain assessments including neuroma site pain and mechanical, cold, and thermal allodynia were performed for 8 weeks. Immunohistochemistry was used to evaluate macrophage infiltration and microglial expansion in the corresponding dorsal root ganglia and spinal cord segments.

RESULTS

Prophylactic RPNI prevented neuroma pain in both sexes; however, female rats displayed delayed pain attenuation when compared with males. Cold allodynia and thermal allodynia were attenuated exclusively in males. Macrophage infiltration was mitigated in males, whereas females showed a reduced number of spinal cord microglia.

CONCLUSION

Prophylactic RPNI can prevent neuroma site pain in both sexes. However, attenuation of both cold allodynia and thermal allodynia occurred in males exclusively, potentially because of their sexually dimorphic effect on pathological changes of the central nervous system.

THC, CBD, and Anxiety: A review of recent findings on the anxiolytic and anxiogenic effects of cannabis' primary cannabinoids

Purpose of review

In the context of ongoing decriminalization and legalization of cannabis, a better understanding of how THC and CBD impact anxiety is critical to elucidate the risks of recreational cannabis use as well as to establish the therapeutic potential of cannabis products for anxiety-related applications.

Recent findings

Recent literature supports anxiogenic effects of THC administration, which may be attenuated among regular cannabis users. Data regarding anxiolytic effects of CBD administration are mixed. Most newer studies contradict earlier findings in reporting no effects of CBD on anxiety in healthy participants, whereas inconsistent results have been reported among individuals with anxiety disorders, substance use disorders, and other clinical populations.

Summary

Future research is needed to reconcile heterogenous findings, explore sex differences in the effects of THC and CBD on anxiety, as well as to assess how effects change with extended exposure, the impact of different CBD doses, and interactions between THC, CBD, and other cannabis compounds.

Sex-related differences in oxaliplatin-induced changes in the expression of transient receptor potential channels and their contribution to cold hypersensitivity

Transient receptor potential (TRP) channels are involved in the development of oxaliplatin-induced neuropathic pain, a frequent and debilitating side effect of cancer therapy. Here we explored whether oxaliplatin-induced changes in the expression of TRP channels, as well as the development of pain-related behaviours, differed between male and female animals. Adult rats were injected with oxaliplatin or saline and mechanical and cold allodynia were evaluated using Von Frey and Choi Tests. The mRNA levels of TRPV1, TRPM8 and TRPA1 were assessed in lumbar ganglia and spinal cord by using real time RT-PCR. Oxaliplatin administration induced mechanical and cold hypersensitivity and allodynia in both sexes, with more severe responses to cold stimulation detected in females. Oxaliplatin also induced a significant increase in the expression of TRPV1, TRPM8 and TRPA1 in lumbar dorsal root ganglia. Interestingly, while TRPV1 and TRPA1 upregulation showed no sex difference, the increase in TRPM8 mRNA levels was more pronounced in female ganglia, correlating with the increased sensitivity to innocuous cold stimuli observed in females. TRPV1 and TRPM8 were also found to be upregulated in the spinal cord of animals of both sexes. Our results reveal previously undescribed changes in the expression of TRP channels occurring in peripheral ganglia and spinal cord of both male and female oxaliplatin-treated animals, with some of these changes exhibiting sex-related differences that could underlie the development of sex-specific patterns of pain-related behaviours.

Estrogen modulation of the pronociceptive effects of serotonin on female rat trigeminal sensory neurons is timing dependent and dosage dependent and requires estrogen receptor alpha

ABSTRACT

The role of the major estrogen estradiol (E2) on orofacial pain conditions remains controversial with studies reporting both a pronociceptive and antinociceptive role of E2. E2 modulation of peripheral serotonergic activity may be one mechanism underlying the female prevalence of orofacial pain disorders. We recently reported that female rats in proestrus and estrus exhibit greater serotonin (5HT)-evoked orofacial nocifensive behaviors compared with diestrus and male rats. Further coexpression of 5HT 2A receptor mRNA in nociceptive trigeminal sensory neurons that express transient receptor potential vanilloid 1 ion channels contributes to pain sensitization. E2 may exacerbate orofacial pain through 5HT-sensitive trigeminal nociceptors, but whether low or high E2 contributes to orofacial pain and by what mechanism remains unclear. We hypothesized that steady-state exposure to a proestrus level of E2 exacerbates 5HT-evoked orofacial nocifensive behaviors in female rats, explored the transcriptome of E2-treated female rats, and determined which E2 receptor contributes to sensitization of female trigeminal sensory neurons. We report that a diestrus level of E2 is protective against 5HT-evoked orofacial pain behaviors, which increase with increasing E2 concentrations, and that E2 differentially alters several pain genes in the trigeminal ganglia. Furthermore, E2 receptors coexpressed with 5HT 2A and transient receptor potential vanilloid 1 and enhanced capsaicin-evoked signaling in the trigeminal ganglia through estrogen receptor α. Overall, our data indicate that low, but not high, physiological levels of E2 protect against orofacial pain, and we provide evidence that estrogen receptor α receptor activation, but not others, contributes to sensitization of nociceptive signaling in trigeminal sensory neurons.

Estrogen rapid effects: a window of opportunity for the aging brain?

Estrogen produces several beneficial effects in healthy neurological tissues and exhibits cardioprotective effects. Hormone therapy has been widely used to treat menopausal estrogen deficiency for more than 80 years. Despite high initial expectations of cardioprotective effects, there has been substantial distrust following important randomized clinical trials, such as the Women's Health Initiative. Subsequently, the timing of treatment in relation to the onset of menopause came under consideration and led to the proposal of the timing hypothesis, that early initial treatment is important, and benefits are lost as the timing since menopause becomes prolonged. Subsequent analyses of the Women's Health Initiative data, together with more recent data from randomized and observational trials, consistently show reductions in coronary heart disease and mortality in younger menopausal women. Regarding cognitive function, the timing hypothesis is consistent with observations from basic and animal studies. There is some clinical evidence to support the benefits of hormonal therapy in this context, though skepticism remains due to the paucity of clinical trials of substantial length in younger menopausal women. It is likely that the effects of estrogens on cognitive performance are due to rapid mechanisms, including mechanisms that influence Ca2+ homeostasis dynamics, provide protection in a hostile environment and reduce inflammatory signals from neural tissues. In the future, inflammatory profiles accounting for early signs of pathological inflammation might help identify the 'window of opportunity' to use estrogen therapy for successful cognitive protection.

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.

Prevalence of trigeminal neuralgia in multiple sclerosis: A systematic review and meta-analysis

BACKGROUND

The prevalence of Trigeminal Neuralgia (TN) in patients diagnosed with multiple sclerosis (MS) is insufficiently understood and controversially reported. This study focused on providing a better understanding of the prevalence of TN in MS patients.

METHOD

We systematically searched PubMed, Scopus, EMBASE, Web of Science, and Google Scholar to identify studies published from January 1, 1990, to December 30, 2020. We included studies reporting the TN prevalence among MS patients and exclude case reports/series and editorial studies, review studies, and non-English written articles. We used pooled prevalence estimates to determine the TN prevalence among MS patients.

RESULTS

Pooled overall TN prevalence among 19 studies and 30,348 MS patients was estimated as 3.4% (95% CI: 1.5%-5.9%) with a high level of heterogeneity among studies (I2=98.92%; p<0.001). The pooled prevalence of TN in male and female patients across 9 surveys was 2.4% (95% CI: 0.5%-5.4%) and 3.8% (95% CI: 0.8%-8.7%), respectively. No heterogeneity between the two groups was observed (p = 0.558). A meta-regression was performed to explore the source of the heterogeneity. None of the candidate covariates, including the year of a study publication, the sample size, the average age of patients, and the disease duration, were significant in the model.

CONCLUSION

Our results showed that TN is a common problem among patients with MS, predominantly male patients. Future studies should target the general prevalence of pain in MS patients.

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

Sex differences in the nervous system have gained recent academic interest. While the prominent differences are observed in mood and anxiety disorders, growing number of evidences also suggest sex difference in pain perception. This review focuses on estrogen as the key molecule underlying such difference, because estrogen plays many functions in the nervous system, including modulation of transient receptor potential vanilloid 1 (TRPV1) and P2X purinoceptor 3 (P2X3), two important nociceptive receptors. Estrogen was shown in various studies to up-regulate TRPV1 expression through two distinct pathways, resulting in pro-nociceptive effect. However, estrogen alleviated pain in other studies, by down-regulating nerve growth factor (NGF)-activated pathways and TRPV1. Estrogen may also attenuate nociception by inhibiting P2X3 receptors and ATP-signaling. Understanding the mechanism underlying the pro- and anti-nociceptive effect of estrogen might be crucial to understand pathophysiology of the burning mouth syndrome (BMS), a common chronic orofacial pain disorder in menopausal women. The involvement of TRPV1 is strongly suspected because of burning sensation. Reduced estrogen level of the BMS patient might have caused increased activity of P2X3 receptors. Interestingly, the increased expression of TRPV1 and P2X3 in oral mucosa of BMS patients was reported. The combinational impact of differential modulation of TRPV1/P2X3 during menopause might be an important contributing factor of etiology of BMS. Understanding the estrogen-dependent regulation of nociceptive receptors may provide a valuable insight toward the peripheral mechanism of sex-difference in pain perception.

Gut feelings: the microbiota-gut-brain axis on steroids

The intricate connection between central and enteric nervous systems is well established with emerging evidence linking gut microbiota function as a significant new contributor to gut-brain axis signaling. Several microbial signals contribute to altered gut-brain communications, with steroids representing an important biological class that impacts central and enteric nervous system function. Neuroactive steroids contribute pathologically to neurological disorders, including dementia and depression, by modulating the activity of neuroreceptors. However, limited information is available on the influence of neuroactive steroids on the enteric nervous system and gastrointestinal function. In this review, we outline how steroids can modulate enteric nervous system function by focusing on their influence on different receptors that are present in the intestine in health and disease. We also highlight the potential role of the gut microbiota in modulating neuroactive steroid signaling along the gut-brain axis.

Effect of menstrual cycle and female hormones on TRP and TREK channels in modifying thermosensitivity and physiological functions in women

Thermoregulation is crucial for human survival at various ambient temperatures. Transient receptor potential (TRP) and TWIK-related K⁺ (TREK) channels expressed in sensory neurons play a role in peripheral thermosensitivity for temperature detection. In addition, these channels have various physiological roles in the skeletal, nervous, immune, vascular, digestive, and urinary systems. In women, the female hormones estradiol (E2) and progesterone (P4), which fluctuate during the menstrual cycle, affect various physiological functions, such as thermoregulation in hot and cold environments. The present review describes the effect of female hormones on TRP and TREK channels and related physiological functions. The P4 decreased thermosensitivity via TRPV1. E2 facilitates temporomandibular joint disease (TRPV1), breast cancer (TRPM8), and calcium absorption in the digestive system (TRPV5 and TRPV6), inhibits the facilitation of vasoconstriction (TRPM3), nerve inflammation (TRPM4), sweetness sensitivity (TRPM5), and menstrual disorders (TRPC1), and prevents insulin resistance (TRPC5) via each channel. P4 inhibits vasoconstriction (TRPM3), sweetness sensitivity (TRPM5), ciliary motility in the lungs (TRPV4), menstrual disorder (TRPC1), and immunity (TRPC3), and facilitates breast cancer (TRPV6) via each channel as indicated. The effects of female hormones on TREK channels and physiological functions are still under investigation. In summary, female hormones influence physiological functions via some TRP channels; however, the literature is not comprehensive and future studies are needed, especially those related to thermoregulation in women.

IL-23/IL-17A/TRPV1 axis produces mechanical pain via macrophage-sensory neuron crosstalk in female mice

Although sex dimorphism is increasingly recognized as an important factor in pain, female-specific pain signaling is not well studied. Here we report that administration of IL-23 produces mechanical pain (mechanical allodynia) in female but not male mice, and chemotherapy-induced mechanical pain is selectively impaired in female mice lacking Il23 or Il23r. IL-23-induced pain is promoted by estrogen but suppressed by androgen, suggesting an involvement of sex hormones. IL-23 requires C-fiber nociceptors and TRPV1 to produce pain but does not directly activate nociceptor neurons. Notably, IL-23 requires IL-17A release from macrophages to evoke mechanical pain in females. Low-dose IL-17A directly activates nociceptors and induces mechanical pain only in females. Finally, deletion of estrogen receptor subunit α (ERα) in TRPV1⁺ nociceptors abolishes IL-23- and IL-17-induced pain in females. These findings demonstrate that the IL-23/IL-17A/TRPV1 axis regulates female-specific mechanical pain via neuro-immune interactions. Our study also reveals sex dimorphism at both immune and neuronal levels.

Estrogen exacerbates the nociceptive effects of peripheral serotonin on rat trigeminal sensory neurons

Orofacial pain disorders involving trigeminal sensory neurons disproportionately affect women and can be modulated by hormones, especially estrogen (E2). Proinflammatory mediators, like serotonin (5HT), can act on sensory neurons expressing the transient receptor potential vanilloid 1 (TRPV1) ion channel, resulting in peripheral sensitization. We previously reported peripheral 5HT evokes greater pain behaviors in the hindpaw of female rats during proestrus and estrus, stages when E2 fluctuates. It is unknown if this interaction is comparable in the trigeminal system. We hypothesized that E2 exacerbates 5HT-evoked nocifensive pain behaviors and pain signaling in female trigeminal sensory neurons. We report 5HT-evoked nocifensive behaviors are significantly higher during estrus and proestrus, which is attenuated by blocking the 5HT2A receptor. The comparable dose of 5HT was not nociceptive in males unless capsaicin was also administered. When administered with capsaicin, a lower dose of 5HT evoked trigeminal pain behaviors in females during proestrus. Further, basal 5HT content in the vibrissal pad was higher in cycling females compared to males. Ex vivo, E2 enhanced 5HT-potentiated CGRP release from trigeminal neurons, which was not significantly reduced by blocking the 5HT2A receptor. Our data indicates that estrogen fluctuation influences the pronociceptive effects of 5HT on trigeminal sensory neurons.

17β-Estradiol Exacerbated Experimental Occlusal Interference-Induced Chronic Masseter Hyperalgesia by Increasing the Neuronal Excitability and TRPV1 Function of Trigeminal Ganglion in Ovariectomized Rats

Pain symptoms in temporomandibular disorders (TMD) predominantly affect reproductive women, suggesting that estrogen regulates pain perception. However, how estrogen contributes to chronic TMD pain remains largely unclear. In the present study, we performed behavioral tests, electrophysiology, Western blot and immunofluorescence to investigate the role and underlying mechanisms of estrogen in dental experimental occlusal interference (EOI)-induced chronic masseter mechanical hyperalgesia in rats. We found that long-term 17β-estradiol (E2) replacement exacerbated EOI-induced masseter hyperalgesia in a dose-dependent manner in ovariectomized (OVX) rats. Whole-cell patch-clamp recordings demonstrated that E2 (100 nM) treatment enhanced the excitability of isolated trigeminal ganglion (TG) neurons in OVX and OVX EOI rats, and EOI increased the functional expression of transient receptor potential vanilloid-1 (TRPV1). In addition, E2 replacement upregulated the protein expression of TRPV1 in EOI-treated OVX rats. Importantly, intraganglionic administration of the TRPV1 antagonist AMG-9810 strongly attenuated the facilitatory effect of E2 on EOI-induced masseter mechanical sensitivity. These results demonstrate that E2 exacerbated EOI-induced chronic masseter mechanical hyperalgesia by increasing TG neuronal excitability and TRPV1 function. Our study helps to elucidate the E2 actions in chronic myogenic TMD pain and may provide new therapeutic targets for relieving estrogen-sensitive pain.

Genistein reverses the effect of 17β-estradiol on exacerbating experimental occlusal interference-induced chronic masseter hyperalgesia in ovariectomised rats

BACKGROUND

Oro-facial pain is more prevalent in women than in men, and oestrogen may underlie this sex difference. Genistein reversed the potentiation of 17β-estradiol (E2) on glutamate-induced acute masseter nociceptive behaviour, but its role in dental experimental occlusal interference (EOI)-induced chronic masseter hyperalgesia remains unclear.

OBJECTIVE

This study aimed to investigate sex differences, and to explore the role and underlying mechanisms of genistein in E2-potentiated EOI-induced chronic masseter hyperalgesia in rats.

METHODS

Female and male rats were prepared to compare the sex differences of masseter hyperalgesia induced by EOI using a 0.4-mm-thick metal crown. Female rats were ovariectomised (OVX) and treated with E2 and genistein, followed by EOI. The head withdrawal threshold (HWT) was examined to assess masseter sensitivity. The protein expression of transient receptor potential vanilloid-1 (TRPV1) in the trigeminal ganglion (TG) was detected using western blotting. Immunofluorescence staining was used to reveal the colocalisation of oestrogen receptors (ERs) with TRPV1 and the percentage of TRPV1-positive neurons in the TG.

RESULTS

To some extent, female rats displayed enhanced sensitivity to EOI-induced chronic masseter hyperalgesia compared with males. Female rats showed the lowest HWT in the pro-oestrus phase. Pre-treatment with genistein antagonised E2 potentiation in EOI-induced masseter hyperalgesia and blocked the effect of E2 by downregulating TRPV1 protein expression and the percentage of TRPV1-positive neurons in the TG.

CONCLUSION

Female rats showed greater masseter hyperalgesia than males under EOI. Genistein antagonised the facilitation of EOI-induced chronic masseter hyperalgesia by E2 probably through inhibiting TRPV1 in the TG.

Estrogen receptors in pain modulation: cellular signaling

Sensory perception and emotional disorders are disproportionally represented in men and women and are thus thought to be modulated by different sex hormones in various conditions. Among the most important hormones perceived to affect sensory processing and transduction is estrogen. Numerous previous researchers have endeavored to demonstrate that estrogen is capable of modulating the activity of sensory neurons in peripheral and central sites in female, male, or castrated animals. However, the underlying mechanisms of its modulation of neuronal activity are somewhat unclear. In the present review, we discuss the possible cellular and molecular mechanisms involved in the modulation of nociception by estrogen.

Sex-Bias in Irritable Bowel Syndrome: Linking Steroids to the Gut-Brain Axis

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is more common in females. Despite its high global incidence, the disease mechanism is still unclear and therapeutic options remain limited. The sexual dimorphism in IBS incidence suggests that sex steroids play a role in disease onset and symptoms severity. This review considers sex steroids and their involvement in IBS symptoms and the underlying disease mechanisms. Estrogens and androgens play important regulatory roles in IBS symptomology, including visceral sensitivity, gut motility and psychological conditions, possibly through modulating the gut-brain axis. Steroids are regulators of hypothalamic-pituitary-adrenal activity and autonomic nervous system function. They also modulate gut microbiota and enteric nervous systems, impacting serotonin and mast cell signaling. Sex steroids also facilitate bidirectional cross-talk between the microbiota and host following bacterial transformation and recycling of steroids by the intestine. The sex-specific interplay between sex steroids and the host provides neuroendocrinology insight into the pathophysiology, epigenetics and treatment of IBS patients.

Sex differences in neuro(auto)immunity and chronic sciatic nerve pain

Chronic pain occurs with greater frequency in women, with a parallel sexually dimorphic trend reported in sufferers of many autoimmune diseases. There is a need to continue examining neuro-immune-endocrine crosstalk in the context of sexual dimorphisms in chronic pain. Several phenomena in particular need to be further explored. In patients, autoantibodies to neural antigens have been associated with sensory pathway hyper-excitability, and the role of self-antigens released by damaged nerves remains to be defined. In addition, specific immune cells release pro-nociceptive cytokines that directly influence neural firing, while T lymphocytes activated by specific antigens secrete factors that either support nerve repair or exacerbate the damage. Modulating specific immune cell populations could therefore be a means to promote nerve recovery, with sex-specific outcomes. Understanding biological sex differences that maintain, or fail to maintain, neuroimmune homeostasis may inform the selection of sex-specific treatment regimens, improving chronic pain management by rebalancing neuroimmune feedback. Given the significance of interactions between nerves and immune cells in the generation and maintenance of neuropathic pain, this review focuses on sex differences and possible links with persistent autoimmune activity using sciatica as an example.

TRPV1-Estradiol Stereospecific Relationship Underlies Cell Survival in Oxidative Cell Death

17β-estradiol is a neuronal survival factor against oxidative stress that triggers its protective effect even in the absence of classical estrogen receptors. The polymodal transient receptor potential vanilloid subtype 1 (TRPV1) channel has been proposed as a steroid receptor implied in tissue protection against oxidative damage. We show here that TRPV1 is sufficient condition for 17β-estradiol to enhance metabolic performance in injured cells. Specifically, in TRPV1 expressing cells, the application of 17β-estradiol within the first 3 h avoided H₂O₂-dependent mitochondrial depolarization and the activation of caspase 3/7 protecting against the irreversible damage triggered by H₂O₂. Furthermore, 17β-estradiol potentiates TRPV1 single channel activity associated with an increased open probability. This effect was not observed after the application of 17α-estradiol. We explored the TRPV1-Estrogen relationship also in primary culture of hippocampal-derived neurons and observed that 17β-estradiol cell protection against H₂O₂-induced damage was independent of estrogen receptors pathway activation, membrane started and stereospecific. These results support the role of TRPV1 as a 17β-estradiol-activated ionotropic membrane receptor coupling with mitochondrial function and cell survival.

Steroids and TRP Channels: A Close Relationship

Transient receptor potential (TRP) channels are remarkable transmembrane protein complexes that are essential for the physiology of the tissues in which they are expressed. They function as non-selective cation channels allowing for the signal transduction of several chemical, physical and thermal stimuli and modifying cell function. These channels play pivotal roles in the nervous and reproductive systems, kidney, pancreas, lung, bone, intestine, among others. TRP channels are finely modulated by different mechanisms: regulation of their function and/or by control of their expression or cellular/subcellular localization. These mechanisms are subject to being affected by several endogenously-produced compounds, some of which are of a lipidic nature such as steroids. Fascinatingly, steroids and TRP channels closely interplay to modulate several physiological events. Certain TRP channels are affected by the typical genomic long-term effects of steroids but others are also targets for non-genomic actions of some steroids that act as direct ligands of these receptors, as will be reviewed here.

Effect of chronic pretreatment with 17β-estradiol and/or progesterone on the nociceptive response to uterine cervical distension in a rat model

It is widely known that visceral pain is more prevalent in women than in men, and this phenomenon is interpreted as a consequence of the gonadal hormone modulation of pain perception and transduction. Uterine cervical distension might cause obstetric and gynecologic pain with clinical relevance to visceral pain. In this study, we focused on the roles of 17β-estradiol and progesterone in visceral nociception with the use of a rat model of uterine cervical distension. Female ovariectomized rats were injected with 17β-estradiol (E₂) or progesterone (P₄) for 21 days, after which visceral pain-induced spinal c-fos expression and visceromotor reflex changes were compared between ovariectomized and hormone-substituted groups. We found that uterine cervical distension induced a drastic increase in spinal c-fos expression and visceromotor reflex activity, and ovariectomy inhibited the increase in c-fos expression induced by visceral pain; this inhibition was reversed by estrogen but not progesterone replacement. This study demonstrates that estrogen is involved in uterine cervical nociception, while progesterone plays less of a significant role.

The Duration of Nerve Block from Local Anesthetic Formulations in Male and Female Rats

PURPOSE

It is unknown whether there are sex differences in response to free or encapsulated local anesthetics.

METHODS

We examined nerve block duration and toxicity following peripheral nerve blockade in male and female rats. We studied the local anesthetic bupivacaine (free or encapsulated) as well as tetrodotoxin, which acts on a different site of the same voltage-gated channel.

RESULTS

Sensory nerve blockade was 158.5 [139-190] minutes (median [interquartile range]) (males) compared to 173 [134-171] minutes (females) (p = 0.702) following bupivacaine injection, N = 8 male, 8 female. Motor nerve blockade was 157 [141-171] minutes (males) compared to 172 [146-320] minutes (females) (p = 0.2786). Micellar bupivacaine (N = 8 male, 8 female) resulted in sensory nerve blockade of 266 [227-320] minutes (males) compared to 285 [239-344] minutes (females) (p = 0.6427). Motor nerve blockade was 264 [251-264] minutes (males) compared to 287 [262-287] minutes (females) (p = 0.3823). Liposomal bupivacaine (N = 8 male, 8 female) resulted in sensory nerve blockade of 240 [207-277] minutes (males) compared to 289 [204-348] minutes (females) (p = 0.1654). Motor nerve blockade was 266 [237-372] minutes (males) compared to 317 [251-356] minutes (females) (p = 0.6671). Following tetrodotoxin injection (N = 12 male,12 female) sensory nerve blockade was 54.8 [5-117] minutes (males) compared to 54 [14-71] minutes (females) (p = 0.6422). Motor nerve blockade was 72 [40-112] minutes (males) compared to 64 [32-143] minutes (females) (p = 0.971).

CONCLUSIONS

We found no statistically significant sex differences associated with the formulations tested. In both sexes, durations of nerve block were similar between micellar and liposomal bupivacaine formulations, despite the micellar formulation containing less drug.

Depolarization of pacemaker potentials by caffeic acid phenethyl ester in interstitial cells of Cajal from the murine small intestine

Interstitial cells of Cajal (ICCs) are pacemaker cells in the gastrointestinal (GI) tract and generate pacemaker potentials. In this study, we investigated the effects of caffeic acid phenethyl ester (CAPE) on the pacemaker potentials of ICCs from the mouse small or large intestine. Using the whole-cell patch-clamp configuration, we found that CAPE depolarized the pacemaker potentials of cultured ICCs from the murine small intestine in a dose-dependent manner. The estrogen receptor (ER) β antagonist PHTPP completely inhibited CAPE-induced depolarization, but the ERα antagonist BHPI did not. Intracellular GDP-β-S and pretreatment with Ca²⁺-free solution or thapsigargin also blocked CAPE-induced depolarization. To investigate the mechanisms of CAPE-mediated depolarization of ICCs, we used the nonselective cation channel (NSCC) inhibitor flufenamic acid, the Cl^- channel blocker, mitogen-activated protein kinase (MAPK) inhibitors PD98059, SB203580, or SP600125, and PI3 kinase inhibitor LY294002. All inhibitors blocked the CAPE-induced pacemaker potential depolarization of ICCs. These results suggest that CAPE induces pacemaker potential depolarization through ERβ in a G protein, NSCC, Cl^- channel, MAPK- and PI3 kinase dependent manner via intracellular and extracellular Ca²⁺ regulation in the murine small intestine. CAPE may therefore modulate GI motility by acting on ICCs in the murine small intestine.

Influence of androgenic blockade with flutamide on pain behaviour and expression of the genes that encode the NaV1.7 and NaV1.8 voltage-dependent sodium channels in a rat model of postoperative pain

Background

Experimental studies suggest that testosterone reduces the nociceptive response after inflammatory and neuropathic stimuli, however the underlying mechanisms have not been fully elucidated. The aims of this study were to evaluate the effect of peripheral blockade of testosterone on pain behaviour and on expression levels of the genes that encode the NaV1.7 and NaV1.8 channels, in dorsal root ganglia in an acute postoperative pain model, as well as the influence of androgen blockade on the expression of these genes.

Methods

Postoperative pain was induced by a plantar incision and the study group received flutamide to block testosterone receptor. The animals were submitted to behavioural evaluation preoperatively, 2 h after incision, and on the 1st, 2nd, 3rd and 7th postoperative days. Von Frey test was used to evaluate paw withdrawal threshold after mechanical stimuli and the guarding pain test to assess spontaneous pain. The expression of the genes encoding the sodium channels at the dorsal root ganglia was determined by real time quantitative polymerase chain reaction.

Results

Animals treated with flutamide presented lower paw withdrawal threshold at the 1st, 2nd, 3rd, and 7th postoperative days. The guarding pain test showed significant decrease in the flutamide group at 2 h and on the 3rd and 7th postoperative days. No difference was detected between the study and control groups for the gene expression.

Conclusions

Our data suggest an antinociceptive effect of androgens following plantar incision. The expression of genes that encode voltage-gated sodium channels was not influenced by androgen blockade.

Emerging Perspectives on Pain Management by Modulation of TRP Channels and ANO1

Receptor-type ion channels are critical for detection of noxious stimuli in primary sensory neurons. Transient receptor potential (TRP) channels mediate pain sensations and promote a variety of neuronal signals that elicit secondary neural functions (such as calcitonin gene-related peptide [CGRP] secretion), which are important for physiological functions throughout the body. In this review, we focus on the involvement of TRP channels in sensing acute pain, inflammatory pain, headache, migraine, pain due to fungal infections, and osteo-inflammation. Furthermore, action potentials mediated via interactions between TRP channels and the chloride channel, anoctamin 1 (ANO1), can also generate strong pain sensations in primary sensory neurons. Thus, we also discuss mechanisms that enhance neuronal excitation and are dependent on ANO1, and consider modulation of pain sensation from the perspective of both cation and anion dynamics.

Signs of chronic itch in the mouse imiquimod model of psoriasiform dermatitis: sex differences and roles of TRPV1 and TRPA1

Plaque psoriasis is a chronic inflammatory skin disease that affects a substantial proportion of the world population. This disorder is characterized by scaly, thick skin, intense ongoing itch, and itch from light touch (such as clothing contacting skin, called “alloknesis”). Imiquimod is a topical treatment for basal cell carcinomas and warts that has been used to create a mouse model of plaque psoriasis. Imiquimod-treated male, but not female, wildtype B6 mice showed significant increases in spontaneous scratching, while both sexes exhibited increased alloknesis, indicative of chronic itch. TRPV1 and TRPA1 knockout (KO) mice all exhibited numeric increases in spontaneous scratching which were significant for TRPV1KO mice and TRPA1KO males. Female TRPV1KO and TRPA1KO mice exhibited imiquimod-induced increases in alloknesis scores that did not significantly differ from wildtypes, while alloknesis scores in imiquimod-treated male TRPV1KO and TRPA1KO mice were significantly lower compared with wildtypes, suggesting that these ion channels are necessary for the development of alloknesis in males but not females in this model. Curiously, none of the groups exhibited any significant overall change in chloroquine-evoked scratching following imiquimod treatment, indicating that hyperknesis does not develop in this mouse model. Overall, the data indicate that there are sex differences in this mouse model of psoriasis, and that TRPV1 and TRPA1 ion channels have a small role in promoting the development of itch sensitization. This contrasts with the far greater role these channels play in the manifestation of skin changes in psoriatic dermatitis.

Ion Channels Involved in Tooth Pain

The tooth has an unusual sensory system that converts external stimuli predominantly into pain, yet its sensory afferents in teeth demonstrate cytochemical properties of non-nociceptive neurons. This review summarizes the recent knowledge underlying this paradoxical nociception, with a focus on the ion channels involved in tooth pain. The expression of temperature-sensitive ion channels has been extensively investigated because thermal stimulation often evokes tooth pain. However, temperature-sensitive ion channels cannot explain the sudden intense tooth pain evoked by innocuous temperatures or light air puffs, leading to the hydrodynamic theory emphasizing the microfluidic movement within the dentinal tubules for detection by mechanosensitive ion channels. Several mechanosensitive ion channels expressed in dental sensory systems have been suggested as key players in the hydrodynamic theory, and TRPM7, which is abundant in the odontoblasts, and recently discovered PIEZO receptors are promising candidates. Several ligand-gated ion channels and voltage-gated ion channels expressed in dental primary afferent neurons have been discussed in relation to their potential contribution to tooth pain. In addition, in recent years, there has been growing interest in the potential sensory role of odontoblasts; thus, the expression of ion channels in odontoblasts and their potential relation to tooth pain is also reviewed.

History of Estrogen: Its Purification, Structure, Synthesis, Biologic Actions, and Clinical Implications

This mini-review summarizes key points from the Clark Sawin Memorial Lecture on the History of Estrogen delivered at Endo 2018 and focuses on the rationales and motivation leading to various discoveries and their clinical applications. During the classical period of antiquity, incisive clinical observations uncovered important findings; however, extensive anatomical dissections to solidify proof were generally lacking. Initiation of the experimental approach followed later, influenced by Claude Bernard's treatise "An Introduction to the Study of Experimental Medicine." With this approach, investigators began to explore the function of the ovaries and their "internal secretions" and, after intensive investigations for several years, purified various estrogens. Clinical therapies for hot flashes, osteoporosis, and dysmenorrhea were quickly developed and, later, methods of hormonal contraception. Sophisticated biochemical methods revealed the mechanisms of estrogen synthesis through the enzyme aromatase and, after discovery of the estrogen receptors, their specific biologic actions. Molecular techniques facilitated understanding of the specific transcriptional and translational events requiring estrogen. This body of knowledge led to methods to prevent and treat hormone-dependent neoplasms as well as a variety of other estrogen-related conditions. More recently, the role of estrogen in men was uncovered by prismatic examples of estrogen deficiency in male patients and by knockout of the estrogen receptor and aromatase in animals. As studies became more extensive, the effects of estrogen on nearly every organ were described. We conclude that the history of estrogen illustrates the role of intellectual reasoning, motivation, and serendipity in advancing knowledge about this important sex steroid.

Chronic 17β-estradiol pretreatment has pronociceptive effect on behavioral and morphological changes induced by orofacial formalin in ovariectomized rats

Background

The prevalence of craniofacial pain disorders show sexual dimorphism with generally more common appearance in women suggesting the influence of estradiol, but the exact cause remains unknown. The common point in the pathogenesis of these disorders is the activation of trigeminal system. One of the animal experimental models of trigeminal activation is the orofacial formalin test, in which we investigated the effect of chronic 17β-estradiol pretreatment on the trigeminal pain-related behavior and activation of trigeminal second-order neurons at the level of spinal trigeminal nucleus pars caudalis (TNC).

Methods

Female Sprague Dawley rats were ovariectomized and silicone capsules were implanted subcutaneously containing cholesterol in the OVX group and 17β-estradiol and cholesterol in 1:1 ratio in the OVX+E₂ group. We determined 17β-estradiol levels in serum after the implantation of capsules. Three weeks after operation, 50 µL of physiological saline or 1.5% of formalin solution was injected subcutaneously into the right whisker pad of rats. The time spent on rubbing directed to the injected area and c-Fos immunoreactivity in TNC was measured as the formalin-induced pain-related behavior, and as the marker of pain-related neuronal activation, respectively.

Results

The chronic 17β-estradiol pretreatment mimics the plasma levels of estrogen occurring in the proestrus phase and significantly increased the formalin-induced pain-related behavior and neuronal activation in TNC.

Conclusion

Our results demonstrate that the chronic 17β-estradiol treatment has strong pronociceptive effect on orofacial formalin-induced inflammatory pain suggesting modulatory action of estradiol on head pain through estrogen receptors, which are present in the trigeminal system.

TRP Channels as Potential Targets for Sex-Related Differences in Migraine Pain

Chronic pain is one of the most debilitating human diseases and represents a social and economic burden for our society. Great efforts are being made to understand the molecular and cellular mechanisms underlying the pathophysiology of pain transduction. It is particularly noteworthy that some types of chronic pain, such as migraine, display a remarkable sex dimorphism, being up to three times more prevalent in women than in men. This gender prevalence in migraine appears to be related to sex differences arising from both gonadal and genetic factors. Indeed, the functionality of the somatosensory, immune, and endothelial systems seems modulated by sex hormones, as well as by X-linked genes differentially expressed during development. Here, we review the current data on the modulation of the somatosensory system functionality by gonadal hormones. Although this is still an area that requires intense investigation, there is evidence suggesting a direct regulation of nociceptor activity by sex hormones at the transcriptional, translational, and functional levels. Data are being accumulated on the effect of sex hormones on TRP channels such as TRPV1 that make pivotal contributions to nociceptor excitability and sensitization in migraine and other chronic pain syndromes. These data suggest that modulation of TRP channels' expression and/or activity by gonadal hormones provide novel pathways for drug intervention that may be useful for targeting the sex dimorphism observed in migraine.

Sex-dependent difference in the association between frequency of spicy food consumption and risk of hypertension in Chinese adults

PURPOSE

The aim of our study was to explore the association between frequency of spicy food consumption and risk of hypertension in Chinese adults.

METHODS

Data were extracted from the 2009 wave of the China Health and Nutrition Survey, consisting of 9273 apparently healthy adults. Height, weight, and blood pressure (BP) were measured and diet was assessed with three consecutive 24-h recalls in combination with a weighed food inventory. Frequency of spicy food consumption and degree of pungency in spicy food consumption were self-reported. Hypertension was defined as systolic BP (SBP) ≥ 140 mmHg and/or diastolic BP (DBP) ≥ 90 mmHg, or having known hypertension. Multilevel mixed-effects models were constructed to estimate changes in SBP and DBP levels as well as risk of hypertension.

RESULTS

Higher frequency of spicy food consumption was significantly associated with lower SBP and DBP levels and lower risk of hypertension in female participants after adjustment for potential confounders (all P trend < 0.05) and cluster effects at different levels (individual, community, and province). Compared with female participants who did not eat spicy food, the adjusted odds ratios of hypertension were 0.740 (95% CI 0.569, 0.963; P = 0.025) in female participants who consumed usually, and 0.760 (95% CI 0.624, 0.925; P = 0.006) in female participants who ate spicy food with moderate pungency. There was no significant association of spicy food consumption with hypertension in male participants.

CONCLUSIONS

Frequency of spicy food consumption was inversely associated with risk of hypertension in female, but not male adults.

Estrogen Modulates Corneal Nociception and Maintains Corneal Homeostasis in Rat Eye

PURPOSE

To evaluate the role of estrogen in corneal nociception, its influence on lacrimal secretion, and development of dry eye.

METHODS

Ovariectomy was performed in normal healthy female rats (OVX). Estrogen replacement was performed in a population of these rats (OVX+E). Tests for dry eye and corneal sensitivity were performed and compared with rats in proestrus (PRO) as controls. Gene expression of neuropeptides such as substance P, calcitonin gene receptor-like protein (CGRP), estrogen receptor α, TRPV1, and TRPM8 was evaluated in the cornea and trigeminal ganglion. Expression of substance P and CGRP in the cornea was also examined by immunohistochemistry. The response of the cornea to capsaicin and menthol was evaluated to identify the activity of receptors TRPV1 and TRPM8, respectively.

RESULTS

There was a significant decrease in tear formation (4.2 ± 0.6 mm/min vs. 6.6 ± 0.42 mm/min), corneal sensitivity (2.2 ± 0.17 cm vs. 6 ± 0 cm), and increase in fluorescein staining in corneas after ovariectomy compared with controls. There was a significant decrease in gene expression of CGRP, substance P, TRPV1, and TRPM8 in the ovarioectomized cornea. A significant decrease in tear formation (3.17 ± 0.30 mm/min vs. 7.17 ± 0.87 mm/min) and eye wipe response (10.5 ± 1.99 wipes vs. 18.33 ± 1.05 wipes) after treatment with menthol and capsaicin in OVX rats was observed. Estrogen replacement significantly enhanced tear formation (4.02 ± 0.6 mm/min vs. 6.7 ± 0.80 mm/min), corneal sensitivity (2.2 ± 0.17 cm vs. 3.2 ± 0.17 cm), and response to capsaicin (10.5 ± 1.99 eye wipes vs. 24.5 ± 0.92 wipes) and menthol (3.17 ± 0.30 mm/min vs. 6.5 ± 0.22 mm/min) and increased expression of neuropeptides, TRPV1 and TRPM8.

CONCLUSIONS

This study demonstrates the role of estrogen in corneal nociception and its deficiency as a cause of dry eye.

Females have stronger neurogenic response than males after non-specific nasal challenge in patients with seasonal allergic rhinitis

Epidemiological studies show female predominance in the prevalence of non- allergic rhinitis (NAR) and local allergic rhinitis (LAR). Experimental studies show female patients with allergic rhinitis (AR) demonstrate higher levels of sensitivity to irritants and airway hyperresponsiveness than males. Bronchial asthma shows female predominance in post-puberty patients, and gender interaction with severe asthma endotypes. Fibromyalgia, chronic fatigue syndrome, migraine and chronic cough, syndromes, which are commonly related to neurokinin substance P (SP) in the literature, also show strong female predominance. Studies have demonstrated that sex hormones, primarily oestrogens, affect mast cell activation. Mast cell proteases can amplify neurogenic inflammatory responses including the release of SP. Based on human epidemiological data and animal experimental data we hypothesized that female patients have different interaction between mast cell activation and neurogenic inflammation, i.e. substance P release, resulting in a different nasal symptom profile. To test the hypothesis we performed allergen and non-specific nasal challenges in patients with seasonal allergic rhinitis (SAR) out of season and looked for gender differences in subjective and objective responses. The interaction between subjective and objective reactivity was evaluated through the comparison of subjective symptom scores, concentrations of neurokinin substance P (SP) and cellular markers in nasal lavages after low doses of nasal allergen challenges. Female allergic subjects tended to have higher substance P (SP) concentrations both before and after non-specific challenges. The difference between post-allergen and post - hypertonic saline (HTS) challenge was highly significant in female patients (p = 0.001), while insignificant in male subjects (p = 0.14). Female patients had significantly stronger burning sensation after HTS challenge than male. These data indicate difference in the interaction between inflammatory cells and the neurogenic response, which is gender- related, and which may affect symptom profiles after challenges. Different regulation of neurogenic inflammation in females may have impact on symptoms and endotyping in respiratory disorders, not only in allergic rhinitis, but also asthma, chronic rhinosinusitis and irritant -induced cough.

Sex-Dependent Effects of Cannabis and Cannabinoids: A Translational Perspective

Recent policy changes have led to significant increases in the use of cannabis for both medical and recreational purposes. Although men are more likely to endorse past month cannabis use and are more frequently diagnosed with Cannabis Use Disorder relative to women, a growing proportion of medical cannabis users are reported to be women. The increased popularity of cannabis for medical purposes and the narrowing gap in prevalence of use between men and women raises questions regarding sex-dependent effects related to therapeutic efficacy and negative health effects of cannabis and cannabinoids. The objective of this review is to provide a translational perspective on the sex-dependent effects of cannabis and cannabinoids by synthesizing findings from preclinical and clinical studies focused on sex comparisons of their therapeutic potential and abuse liability, two specific areas that are of significant public health relevance. Hormonal and pharmacological mechanisms that may underlie sex differences in the effects of cannabis and cannabinoids are highlighted.

Daily Fluctuations of Progesterone and Testosterone Are Associated With Fibromyalgia Pain Severity

The purpose of this longitudinal blood sampling study was to examine relationships between sex hormones and fibromyalgia pain. Eight women meeting case definition criteria for fibromyalgia provided venous blood samples and reported their fibromyalgia pain severity over 25 consecutive days. All women exhibited normal menstrual cycles and were not taking oral contraceptives. Cortisol, and the sex hormones estradiol, progesterone, and testosterone, were assayed from serum. A linear mixed model was used to determine if fluctuations of sex hormones were associated with changes in pain severity. In the entire sample, day to day changes in progesterone (P = .002) as well as testosterone (P = .015) were significantly and inversely correlated with pain severity. There was no relationship between estradiol and pain (P = .551) or cortisol and pain (P = .633). These results suggest that progesterone and testosterone play a protective role in fibromyalgia pain severity. Sex and other hormones may serve to increase as well as decrease fibromyalgia pain severity.

PERSPECTIVE

Sex hormones fluctuate normally in women with fibromyalgia, but may still contribute to pain severity.

Gender aspects of CGRP in migraine

Background

Migraine is two to three times more prevalent in women than in men, but the mechanisms involved in this gender disparity are still poorly understood. In this respect, calcitonin gene-related peptide (CGRP) plays a key role in migraine pathophysiology and, more recently, the functional interactions between ovarian steroid hormones, CGRP and the trigeminovascular system have been recognized and studied in more detail.

Aims

To provide an overview of CGRP studies that have addressed gender differences utilizing animal and human migraine preclinical research models to highlight how the female trigeminovascular system responds differently in the presence of varying ovarian steroid hormones.

Conclusions

Gender differences are evident in migraine. Several studies indicate that fluctuations of ovarian steroid hormone (mainly estrogen) levels modulate CGRP in the trigeminovascular system during different reproductive milestones. Such interactions need to be considered when conducting future animal and human experiments, since these differences may contribute to the development of gender-specific therapies.