Deficiency of female sex hormones augments PGE2 and CGRP levels within midbrain periaqueductal gray

CGRP as a potential mediator for the sexually dimorphic responses to traumatic brain injury

BACKGROUND

The outcomes of traumatic brain injury (TBI) exhibit variance contingent upon biological sex. Although female sex hormones exert neuroprotective effects, the administration of estrogen and progesterone has not yielded conclusive results. Hence, it is conceivable that additional mediators, distinct from female sex hormones, merit consideration due to their potential differential impact on TBI outcomes. Calcitonin gene-related peptide (CGRP) exhibits sexually dimorphic expression and demonstrates neuroprotective effects in acute brain injuries. In this study, we aimed to examine sex-based variations in TBI structural and functional outcomes with respect to CGRP expression.

METHODS

Male and female Sprague Dawley rats were exposed to controlled cortical impact to induce severe TBI, followed by interventions with and without CGRP inhibition. In the acute phase of TBI, the study centered on elucidating the influence of CGRP on oxidative stress, nuclear factor erythroid 2-related factor 2 (Nrf2) and endothelial nitric oxide synthase (eNOS) signaling in the peri-impact tissue. Subsequently, during the chronic phase of TBI, the investigation expanded to evaluate CGRP expression in relation to lesion volume, microvascular dysfunction, and white matter injury, as well as working and spatial memory, anxiety-like, and depression-like behaviors in subjects of both sexes.

RESULTS

Female rats exhibited elevated levels of CGRP in the peri-impact brain tissue during both baseline conditions and in the acute and chronic phases of TBI, in comparison to age-matched male counterparts. Enhanced CGRP levels in specific brain sub-regions among female rats correlated with superior structural and functional outcomes following TBI compared to their male counterparts. CGRP inhibition induced heightened oxidative stress and a reduction in the expression of Nrf2 and eNOS in both male and female rats, with the observed alteration being more pronounced in females than in males.

CONCLUSIONS

This study marks the inaugural identification of CGRP as a downstream mediator contributing to the sexually dimorphic response observed in TBI outcomes.

Sex Hormones and Calcitonin Gene-Related Peptide in Women With Migraine: A Cross-sectional, Matched Cohort Study

BACKGROUND AND OBJECTIVES

Sex hormones may modulate calcitonin gene-related peptide (CGRP) release in the trigeminovascular system. We studied CGRP concentrations in plasma and tear fluid in female participants with episodic migraine (EM) and a regular menstrual cycle (RMC), female participants with EM and combined oral contraception (COC), and female participants with EM in the postmenopause. For control, we analyzed 3 corresponding groups of age-matched female participants without EM.

METHODS

Participants with an RMC had 2 visits: during menstruation on menstrual cycle day 2 ± 2 and in the periovulatory period on day 13 ± 2. Participants with COC were examined at day 4 ± 2 of the hormone-free interval (HFI) and between days 7 and 14 of hormone intake (HI). Postmenopausal participants were assessed once at a random time point. Plasma and tear fluid samples were collected at each visit for determination of CGRP levels with an ELISA.

RESULTS

A total of 180 female participants (n = 30 per group) completed the study. Participants with migraine and an RMC showed statistically significantly higher CGRP concentrations in plasma and tear fluid during menstruation compared with female participants without migraine (plasma: 5.95 pg/mL [IQR 4.37-10.44] vs 4.61 pg/mL [IQR 2.83-6.92], p = 0.020 [Mann-Whitney U test]; tear fluid: 1.20 ng/mL [IQR 0.36-2.52] vs 0.4 ng/mL [IQR 0.14-1.22], p = 0.005 [Mann-Whitney U test]). In contrast, female participants with COC and in the postmenopause had similar CGRP levels in the migraine and the control groups. In migraine participants with an RMC, tear fluid but not plasma CGRP concentrations during menstruation were statistically significantly higher compared with migraine participants under COC (p = 0.015 vs HFI and p = 0.029 vs HI, Mann-Whitney U test).

DISCUSSION

Different sex hormone profiles may influence CGRP concentrations in people, with current or past capacity to menstruate, with migraine. Measurement of CGRP in tear fluid was feasible and warrants further investigation.

Monoclonal anti-CGRP antibodies in post-menopausal women: a real-life study

INTRODUCTION

Migraine usually ameliorates after menopause. However, 10-29% of women still experience migraine attacks after menopause, especially if menopause is surgical. The use of monoclonal antibodies against the calcitonin gene-related peptide (CGRP) is changing the landscape of migraine treatment. This study aims to explore the effectiveness and safety of anti-CGRP monoclonal antibodies in women in menopause.

METHODS

Women affected by either migraine or chronic migraine and treated with an anti-CGRP monoclonal antibody for up to 1 year. Visits were scheduled every 3 months.

RESULTS

Women in menopause displayed a similar response compared to women of childbearing age. Among women in menopause, the women experiencing surgical menopause seemed to exhibit a similar response compared to the ones experiencing physiological menopause. Erenumab and galcanezumab displayed similar effectiveness in women in menopause. No serious adverse events were registered.

DISCUSSION

The effectiveness of anti-CGRP monoclonal antibodies is almost the same between women in menopause and women of childbearing age, without appreciable differences between the different antibodies.

Gradually shifting clinical phenomics in migraine spectrum: a cross-sectional, multicenter study of 5438 patients

Background

The aim of the study was to investigate whether MwoA and MwA are different manifestations of a single disease, distinct clinical entities, or located at two poles of a spectrum.

Methods

In this cross-sectional study, 5438 patients from 10 hospitals in China were included: 4651 were diagnosed with migraine without aura (MwoA) and 787 with migraine with aura (MwA). We used a validated standardized electronic survey to collect multidimensional data on headache characteristics and evaluated the similarities and differences between migraine subtypes. To distinguish migraine subtypes, we employed correlational analysis, factor analysis of mixed data (FAMD), and decision tree analysis.

Results

Compared to MwA, MwoA had more severe headaches, predominantly affected females, were more easily produced by external factors, and were more likely to have accompanying symptoms and premonitory neck stiffness. Patients with MwA are heterogeneous, according to correlation analysis; FAMD divided the subjects into three clear clusters. The majority of the differences between MwoA and MwA were likewise seen when typical aura with migraine headache (AWM) and typical aura with non-migraine headache (AWNM) were compared. Furthermore, decision trees analysis revealed that the chaotic MwA data reduced the decision tree’s accuracy in distinguishing MwoA from MwA, which was significantly increased by splitting MwA into AWM and AWNM.

Conclusions

The clinical phenomics of headache phenotype varies gradually from MwoA to AWM and AWNM, and AWM is a mid-state between MwoA and AWNM. We tend to regard migraine as a spectrum disorder, and speculate that different migraine subtypes have different “predominant regions” that generate attacks.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01461-5.

Role of Estrogens in Menstrual Migraine

Migraine is a major neurological disorder affecting one in nine adults worldwide with a significant impact on health care and socioeconomic systems. Migraine is more prevalent in women than in men, with 17% of all women meeting the diagnostic criteria for migraine. In women, the frequency of migraine attacks shows variations over the menstrual cycle and pregnancy, and the use of combined hormonal contraception (CHC) or hormone replacement therapy (HRT) can unveil or modify migraine disease. In the general population, 18–25% of female migraineurs display a menstrual association of their headache. Here we present an overview on the evidence supporting the role of reproductive hormones, in particular estrogens, in the pathophysiology of migraine. We also analyze the efficacy and safety of prescribing exogenous estrogens as a potential treatment for menstrual-related migraine. Finally, we point to controversial issues and future research areas in the field of reproductive hormones and migraine.

Sex Differences of Periaqueductal Grey Matter Functional Connectivity in Migraine

The existence of “sex phenotype” in migraine is a long-standing scientific question. Fluctuations of female sex hormones contribute to migraine attacks, and women also have enhanced brain activity during emotional processing and their functional brain networks seem to be more vulnerable to migraine-induced disruption compared to men. Periaqueductal grey matter (PAG) is a core region of pain processing and modulation networks with possible sex-related implications in migraine. In our study, sex differences of PAG functional resting-state connectivity were investigated in the interictal state in 32 episodic migraines without aura patients (16 women and 16 men). A significant main effect of sex was detected in PAG connectivity with postcentral, precentral, and inferior parietal gyri, and further differences were found between right PAG and visual areas (superior occipital gyrus, calcarine, and cuneus), supplementary motor area, and mid-cingulum connectivity. In all cases, PAG functional connectivity was stronger in female migraineurs compared to males. However, higher average pain intensity of migraine attacks correlated with stronger connectivity of PAG and middle temporal, superior occipital, and parietal gyri in male migraineurs compared to females. Migraine-related disability is also associated with PAG connectivity but without sex differences. Our results indicate that sex differences in PAG connectivity with brain regions involved in sensory and emotional aspects of pain might contribute to the “sex-phenotype” in migraine. The stronger functional connectivity between PAG and pain processing areas may be a sign of increased excitability of pain pathways even in resting-state in females compared to male migraineurs, which could contribute to female vulnerability for migraine. However, pain intensity experienced by male migraineurs correlated with increased connectivity between PAG and regions involved in the subjective experience of pain and pain-related unpleasantness. The demonstrated sex differences of PAG functional connectivity may support the notion that the female and male brain is differently affected by migraine.

Sigma-1 receptors and progesterone metabolizing enzymes in nociceptive sensory neurons of the female rat trigeminal ganglia: A neural substrate for the antinociceptive actions of progesterone

Orofacial pain disorders are predominately experienced by women. Progesterone, a major ovarian hormone, is neuroprotective and antinociceptive. We recently reported that progesterone attenuates estrogen-exacerbated orofacial pain behaviors, yet it remains unclear what anatomical substrate underlies progesterone's activity in the trigeminal system. Progesterone has been reported to exert protective effects through actions at intracellular progesterone receptors (iPR), membrane-progesterone receptors (mPR), or sigma 1 receptors (Sig-1R). Of these, the iPR and Sig-1R have been reported to have a role in pain. Progesterone can also have antinociceptive effects through its metabolite, allopregnanolone. Two enzymes, 5α-reductase and 3α-hydroxysteroid dehydrogenase (3α-HSD), are required for the metabolism of progesterone to allopregnanolone. Both progesterone and allopregnanolone rapidly attenuate pain sensitivity, implicating action of either progesterone at Sig-1R and/or conversion to allopregnanolone which targets GABAA receptors. In the present study, we investigated whether Sig-1 Rs are expressed in nociceptors within the trigeminal ganglia of cycling female rats and whether the two enzymes required for progesterone metabolism to allopregnanolone, 5α-reductase and 3α-hydroxysteroid dehydrogenase, are also present. Adult female rats from each stage of the estrous cycle were rapidly decapitated and the trigeminal ganglia collected. Trigeminal ganglia were processed by either fluorescent immunochemistry or western blotting to for visualization and quantification of Sig-1R, 5α-reductase, and 3α-hydroxysteroid dehydrogenase. Here we report that Sig-1Rs and both enzymes involved in progesterone metabolism are highly expressed in a variety of nociceptive sensory neuron populations in the female rat trigeminal ganglia at similar levels across the four stages of the estrous cycle. These data indicate that trigeminal sensory neurons are an anatomical substrate for the reported antinociceptive activity of progesterone via Sig-1R and/or conversion to allopregnanolone.

Differential Synovial CGRP/RAMP1 Expression in Men and Women With Knee Osteoarthritis

Background

Female patients with osteoarthritis report more severe knee pain compared to men. However, the mechanism underlying sex differences in pain remains unclear. We previously found that calcitonin gene-related peptide (CGRP) was expressed in synovial tissue and that this localization may play a role in pain associated with knee osteoarthritis (KOA). Several animal studies have shown that the expression of CGRP and its receptor (receptor activity modifying protein 1, RAMP1) differs by sex. Here, we investigated synovial CGRP and RAMP1 expression in male and female patients with KOA.

Methods

Synovial tissue (ST) was harvested from male and female subjects (n=30 each) with radiographically confirmed unilateral Kellgren/Lawrence grade 3-4 KOA during total knee arthroplasty. Patients’ subjective pain severity was scored on a 0 to 10 cm visual analog scale (VAS). We compared the expression of CGRP and RAMP1 in ST from men and women and examined the correlation between mRNA levels of CGRP and RAMP1 and pain severity.

Results

Synovial expression of CGRP and RAMP1 was significantly elevated in women compared to men (CGRP, P=0.017; RAMP1, P=0.028). While CGRP expression was positively correlated with pain severity in females (ρ=0.443, P=0.014), no correlation was observed in men (ρ=-0.021, P=0.913). RAMP1 expression was not correlated with pain severity in either men or women (male, ρ=-0.114, P=0.939; female, ρ=-0.047, P=0.807).

Conclusion

CGRP and RAMP1 expression levels differ between men and women. Differential CGRP levels may suggest the presence of different pain mechanisms in men and women with KOA.

Gender-related differences in migraine

Migraine is considered mostly a woman’s complaint, even if it affects also men. Epidemiological data show a higher incidence of the disease in women, starting from puberty throughout life. The sex-related differences of migraine hold clinical relevance too. The frequency, duration, and disability of attacks tend to be higher in women. Because of this, probably, they also consult specialists more frequently and take more prescription drugs than men. Different mechanisms have been evaluated to explain these differences. Hormonal milieu and its modulation of neuronal and vascular reactivity is probably one of the most important aspects. Estrogens and progesterone regulate a host of biological functions through two mechanisms: nongenomic and genomic. They influence several neuromediators and neurotransmitters, and they may cause functional and structural differences in several brain regions, involved in migraine pathogenesis. In addition to their central action, sex hormones exert rapid modulation of vascular tone. The resulting specific sex phenotype should be considered during clinical management and experimental studies.

Menstrual Headache in Women with Chronic Migraine Treated with Erenumab: An Observational Case Series

BACKGROUND

We aimed to assess the differences between menstrual and non-menstrual headache in women with chronic migraine treated with erenumab.

METHODS

We included fertile women from a single center. Patients were defined as responders to erenumab if reporting a ≥50% decrease in monthly headache days, as compared to pre-treatment for more than half of the treatment period. Premenstrual days were defined as the two days preceding menstruation, while menstrual days were defined as the first three days of menstruation.

RESULTS

We included 18 women (11 erenumab responders and 7 erenumab non-responders) contributing to a total of 103 menstrual cycles and 2926 days. The proportion of headache days was higher in menstrual than in premenstrual and non-menstrual days in erenumab responders (34.4% vs. 14.8% vs. 16.3%, respectively; p < 0.001) and in erenumab non-responders (71.4% vs. 53.6% vs. 48.3%, respectively; p < 0.001). Headache days with ≥2 acute medications were higher in menstrual than in premenstrual or non-menstrual headache days in erenumab non-responders (p = 0.002) but not in erenumab responders (p = 0.620).

CONCLUSIONS

Our data suggest that migraine is more frequent during than outside menstrual days even in women treated with erenumab.

Mal de Debarquement Syndrome: A Matter of Loops?

Introduction: Mal de Debarquement Syndrome (MdDS) is a poorly understood neurological disorder affecting mostly perimenopausal women. MdDS has been hypothesized to be a maladaptation of the vestibulo-ocular reflex, a neuroplasticity disorder, and a consequence of neurochemical imbalances and hormonal changes. Our hypothesis considers elements from these theories, but presents a novel approach based on the analysis of functional loops, according to Systems and Control Theory.

Hypothesis: MdDS is characterized by a persistent sensation of self-motion, usually occurring after sea travels. We assume the existence of a neuronal mechanism acting as an oscillator, i.e., an adaptive internal model, that may be able to cancel a sinusoidal disturbance of posture experienced aboard, due to wave motion. Thereafter, we identify this mechanism as a multi-loop neural network that spans between vestibular nuclei and the flocculonodular lobe of the cerebellum. We demonstrate that this loop system has a tendency to oscillate, which increases with increasing strength of neuronal connections. Therefore, we hypothesize that synaptic plasticity, specifically long-term potentiation, may play a role in making these oscillations poorly damped. Finally, we assume that the neuromodulator Calcitonin Gene-Related Peptide, which is modulated in perimenopausal women, exacerbates this process thus rendering the transition irreversible and consequently leading to MdDS.

Conclusion and Validation: The concept of an oscillator that becomes noxiously permanent can be used as a model for MdDS, given a high correlation between patients with MdDS and sea travels involving undulating passive motion, and an alleviation of symptoms when patients are re-exposed to similar passive motion. The mechanism could be further investigated utilizing posturography tests to evaluate if subjective perception of motion matches with objective postural instability. Neurochemical imbalances that would render individuals more susceptible to developing MdDS could be investigated through hormonal profile screening. Alterations in the connections between vestibular nuclei and cerebellum, notably GABAergic fibers, could be explored by neuroimaging techniques as well as transcranial magnetic stimulation. If our hypothesis were tested and verified, optimal targets for MdDS treatment could be found within both the neural networks and biochemical factors that are deemed to play a fundamental role in loop functioning and synaptic plasticity.

Estrogen receptors α, β and GPER in the CNS and trigeminal system - molecular and functional aspects

BACKGROUND

Migraine occurs 2-3 times more often in females than in males and is in many females associated with the onset of menstruation. The steroid hormone, 17β-estradiol (estrogen, E2), exerts its effects by binding and activating several estrogen receptors (ERs). Calcitonin gene-related peptide (CGRP) has a strong position in migraine pathophysiology, and interaction with CGRP has resulted in several successful drugs for acute and prophylactic treatment of migraine, effective in all age groups and in both sexes.

METHODS

Immunohistochemistry was used for detection and localization of proteins, release of CGRP and PACAP investigated by ELISA and myography/perfusion arteriography was performed on rat and human arterial segments.

RESULTS

ERα was found throughout the whole brain, and in several migraine related structures. ERβ was mainly found in the hippocampus and the cerebellum. In trigeminal ganglion (TG), ERα was found in the nuclei of neurons; these neurons expressed CGRP or the CGRP receptor in the cytoplasm. G-protein ER (GPER) was observed in the cell membrane and cytoplasm in most TG neurons. We compared TG from males and females, and females expressed more ER receptors. For neuropeptide release, the only observable difference was a baseline CGRP release being higher in the pro-estrous state as compared to estrous state. In the middle cerebral artery (MCA), we observed similar dilatory ER-responses between males and females, except for vasodilatory ERβ which we observed only in female arteries.

CONCLUSION

These data reveal significant differences in ER receptor expression between male and female rats. This contrasts to CGRP and PACAP release where we did not observe discernable difference between the sexes. Together, this points to a hypothesis where estrogen could have a modulatory role on the trigeminal neuron function in general rather than on the acute CGRP release mechanisms and vasomotor responses.

Effects of estrogen and progesterone on the neurogenic inflammatory neuropeptides: implications for gender differences in migraine

Neurogenic inflammation including calcitonin gene-related peptide (CGRP) and substance-P (SP) release plays a pivotal role in migraine pathogenesis. Prevalence of migraine is ~ 3 folds higher in women than in men, but its underlying mechanisms remained unclear. We investigated the effects of female sex hormones estrogen and progesterone on CGRP and SP in in-vivo and ex-vivo in rats of both sexes. For in-vivo experiments, male, female and ovariectomized rats were separated into four groups (n = 7) as control, estrogen, progesterone and estrogen + progesterone, respectively. Groups received daily intraperitoneal vehicle, 17β-estradiol, progesterone and 17β-estradiol + progesterone for 5 days, respectively. For ex-vivo experiments in both sexes, isolated trigeminal ganglia and hemiskull preparations were divided into four groups (n = 6 or 8), respectively, as in-vivo groups, and administered the same test substances. CGRP and SP contents in plasma and superfusates were determined using ELISA. In in-vivo experiments, 17β-estradiol decreased CGRP levels in males and SP levels in ovariectomized rats. Progesterone increased both CGRP and SP levels in females. Their combination decreased both CGRP and SP levels in males, and only SP levels in ovariectomized rats. In ex-vivo experiments, 17β-estradiol reduced CGRP release in males and SP release in females in trigeminal ganglia. While progesterone increased CGRP release in trigeminal ganglia, it reduced SP release from hemiskulls in both sexes. Their combination restored progesterone-mediated changes in neuropeptides releases in both trigeminal ganglia and hemiskulls in both sexes. Estrogen alleviates neurogenic inflammation through modulation of CGRP and SP release. Progesterone has dual effects on these neuropeptides in different sites associated with migraine pain.

Dysregulation of prostaglandine E2 and BDNF signaling mediated by estrogenic dysfunction induces primary hippocampal neuronal cell death after single and repeated paraquat treatment

Paraquat (PQ) produces hippocampal neuronal cell death and cognitive dysfunctions after unique and continued exposure, but the mechanisms are not understood. Primary hippocampal wildtype or βAPP-Tau silenced cells were co-treated with PQ with or without E2, N-acetylcysteine (NAC), NS-398 (cyclooxygenase-2 inhibitor), MF63 (PGES-1 inhibitor) and/or recombinant brain-derived neurotrophic factor (BDNF) during one- and fourteen-days to studied PQ effect on prostaglandin E2 (PGE2) and BDNF signaling and their involvement in hyperphosphorylated Tau (pTau) and amyloid-beta (Aβ) protein formation, and oxidative stress generation, that lead to neuronal cell loss through estrogenic disruption, as a possible mechanism of cognitive dysfunctions produced by PQ. Our results indicate that PQ overexpressed cyclooxygenase-2 that leads to an increase of PGE2 and alters the expression of EP1-3 receptor subtypes. PQ induced also a decrease of proBDNF and mature BDNF levels and altered P75^NTR and tropomyosin receptor kinase B (TrkB) expression. PQ induced PGE2 and BDNF signaling dysfunction, mediated through estrogenic disruption, leading to Aβ and pTau proteins synthesis, oxidative stress generation and finally to cell death. Our research provides relevant information to explain PQ hippocampal neurotoxic effects, indicating a probable explanation of the cognitive dysfunction observed and suggests new therapeutic strategies to protect against PQ toxic effects.

Is There Any MRI Pattern That Discriminates Female From Male Migraine Patients?

There has been accumulating evidence on sex disparity in incidence, prevalence, symptomology, and burden of migraine. Several neuroimaging studies on migraine patients attempted to unravel the mechanisms of the disease, yet very few of them examined the sex-related differences. Here, we will first discuss some of the reported neuroimaging patterns that discriminate females from males in migraine. We will then re-examine the salient neuroimaging findings in migraine and discuss them in relation to sex-related influences. Finally, we will discuss some of the intriguing recent data suggesting the presence of sex-specific traits in migraineurs. These findings may have potential implications for future neuroimaging studies to identify underlying correlating patterns in the brain to (1) explain the neural basis for higher prevalence of migraine in women, and (2) better understand migraine-specific changes during different stages of life in both men and women.

Association between the levels of prostaglandin E2 in tears and severity of dry eye

AIM

To investigate the relationship between the levels of prostaglandin E2 (PGE2) in tears and dry eye disease severity based on both clinical symptoms and signs.

METHODS

Tear samples were collected from 36 non-Sjögren syndrome dry eye patients (10 males and 26 females, mean age 50.11±11.17y). All participants completed the Ocular Surface Disease Index (OSDI) questionnaire and underwent a detailed ophthalmic examination including, tear film breakup time (TBUT), ocular surface fluorescein staining, Schirmer I test, and meibomian gland assessment. The level of PGE2 in tears was measured using enzyme-linked immunosorbent assay (ELISA). The independent associations between tear PGE2 levels and other variables including demographics, OSDI scores, TBUT, Schirmer scores, ocular surface staining scores, and stage of meibomian gland dysfunction (MGD) were evaluated using linear regression analysis.

RESULTS

The mean PGE2 level in tears of dry eye patients was 537.85±234.02 pg/mL. The tear PGE2 levels significantly positively correlated with OSDI scores (R=0.608, P<0.001), however, they did not significantly associate with TBUT (R=0.153, P=0.373), Schirmer scores (R=-0.098, P=0.570), ocular surface staining scores (R=0.282, P=0.095), and stage of MGD (R=-0.107, P=0.535). Male sex was significantly negatively correlated with tear PGE2 levels.

CONCLUSION

The levels of PGE2 in tears are positively correlated with dry eye symptoms. However, no significant association was found between tear PGE2 levels and the results of other common dry eye diagnostic tests.

A new theory on GABA and Calcitonin Gene-Related Peptide involvement in Mal de Debarquement Syndrome predisposition factors and pathophysiology

INTRODUCTION

Mal de Debarquement Syndrome (MdDS) is a condition characterized by a sensation of motion in the absence of a stimulus, which presents with two subtypes depending on the onset: Motion-Triggered, and Spontaneous or Non-Motion Triggered. MdDS predominantly affects women around 40-50 years of age and a high number of patients report associated disorders, such as migraine and depression. The pathophysiology of MdDS is unclear, as is whether there are predisposing factors that make individuals more vulnerable to developing the condition. Hormonal changes in women similarly to what observed in migraineous patients, as well as depression disorder, have been examined as potential key factors for developing MdDS. Studies on migraine and depression have revealed correlations with hormonal fluctuations in females as well as aberrant levels of some key neurotransmitters such as Gamma-Aminobutyric Acid (GABA) and inflammatory neuropeptides like Calcitonin Gene-Related Peptide (CGRP). Consequently, this manuscript aims to propose a new hypothesis on the predisposing factors for MdDS and a new concept that could contribute to the understanding of its pathophysiology.

NEW HYPOTHESIS

Recent findings have demonstrated a role for hormonal influences in MdDS patients, similar to previous observations in patients with depression and migraine. We hypothesize the involvement of gonadal hormones and aberrant neurotransmitter levels, including the GABAergic and serotonergic systems, in MdDS pathophysiology. Our theory is that certain individuals are more vulnerable to develop MdDS during specific gonadal hormonal phases. Furthermore, we hypothesize that it may be possible to identify these individuals by measurement of an existing imbalance of these neurotransmitters or inflammatory neuropeptides like CGRP.

FURTHER EVALUATION OF THE HYPOTHESIS

According to one theory, MdDS is considered as a maladaptation of the Vestibular Ocular Reflex (VOR) and velocity storage. When considering this theory, it is essential to highlight that the brainstem nuclei involved in the VOR and the velocity storage include GABA_b sensitive neurons, which appear to produce inhibitory control of velocity storage. Responses of these GABA_b sensitive neurons are also modulated by CGRP. Thus an alteration of the GABAergic network by imbalances of inhibitory neurotransmitters or CGRP could influence signal integration in the velocity storage system and therefore be directly involved in MdDS pathophysiology.

CONSEQUENCE OF THE HYPOTHESIS AND FUTURE STUDIES

A hormonal and neurotransmitter imbalance may act to predispose individuals in developing MdDS. Future studies should focus on the hormonal influences on neurotransmitters (e.g. GABA) and on the trial of CGRP antagonist drugs for the treatment of MdDS patients.

Menstrual migraine: a review of current and developing pharmacotherapies for women

INTRODUCTION

Migraine is one of the most common neurological disorders in the general population. It affects 18% of women and 6% of men. In more than 50% of women migraineurs the occurrence of migraine attacks correlates strongly with the perimenstrual period. Menstrual migraine is highly debilitating, less responsive to therapy, and attacks are longer than those not correlated with menses. Menstrual migraine requires accurate evaluation and targeted therapy, that we aim to recommend in this review.

AREAS COVERED

This review of the literature provides an overview of currently available pharmacological therapies (especially with triptans, anti-inflammatory drugs, hormonal strategies) and drugs in development (in particular those acting on calcitonin gene-related peptide) for the treatment of acute migraine attacks and the prophylaxis of menstrual migraine. The studies reviewed here were retrieved from the Medline database as of June 2017.

EXPERT OPINION

The treatment of menstrual migraine is highly complex. Accurate evaluation of its characteristics is prerequisite to selecting appropriate therapy. An integrated approach involving neurologists and gynecologists is essential for patient management and for continuous updating on new therapies under development.

Chronic Pelvic Pain: Assessment, Evaluation, and Objectivation

Chronic Pelvic Pain (CPP) and Chronic Pelvic Pain Syndrome (CPPS) have a significant impact on men and women of reproductive and nonreproductive age, with a considerable burden on overall quality of life (QoL) and on psychological, functional, and behavioural status. Moreover, diagnostic and therapeutic difficulties are remarkable features in many patients. Therefore evaluation, assessment and objectivation tools are often necessary to properly address each patient and consequently his/her clinical needs. Here we review the different tools for pain assessment, evaluation, and objectivation; specific features regarding CPP/CPPS will be highlighted. Also, recent findings disclosed with neuroimaging investigations will be reviewed as they provide new insights into CPP/CPPS pathophysiology and may serve as a tool for CPP assessment and objectivation.

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.

Antinociceptive effects of dexmedetomidine via spinal substance P and CGRP

The aim of this study was to examine the role played by substance P and calcitonin gene-related peptide (CGRP) within the dorsal horn of the spinal cord in engagement of antinociception evoked by dexmedetomidine (DEX). Paw withdrawal threshold (PWT) to mechanical stimulation was determined after chronic intrathecal infusion of DEX and enzyme-linked immunosorbent assay (ELISA) was employed to examine the levels of spinal substance P and CGRP. Our results show that PWT was significantly increased by intrathecal administration of DEX in rats (P < 0.05 vs. vehicle control, n = 20 in each group). Also, intrathecal infusion of DEX significantly decreased the concentrations of substance P and CGRP as compared with vehicle control (P < 0.05 DEX vs. vehicle control, n = 20 in each group). Blocking α₂-adrenoreceptors (α₂-AR) blunted the decreases of substance P and CGRP levels and the enhancement of PWT evoked by DEX. Additionally, a linear relationship was observed between PWT and the levels of spinal substance P (r = 0.87; P < 0.005) and CGRP (r = 0.85; P < 0.005). Moreover, blocking individual substance P and CGRP receptors amplified PWT without altering substance P and CGRP levels. Thus, DEX plays a role in stimulating α₂-AR receptors, which thereby decreases substance P and CGRP levels within the dorsal horn. This contributes to DEX-evoked antinociception.

Blocking mammalian target of rapamycin alleviates bladder hyperactivity and pain in rats with cystitis

BACKGROUND

Bladder disorders associated with interstitial cystitis are frequently characterized by increased contractility and pain. The purposes of this study were to examine (1) the effects of blocking mammalian target of rapamycin (mTOR) on the exaggerated bladder activity and pain evoked by cystitis and (2) the underlying mechanisms responsible for the role of mTOR in regulating cystic sensory activity.

RESULTS

The expression of p-mTOR, mTOR-mediated phosphorylation of p70 ribosomal S6 protein kinase 1 (p-S6K1), 4 E-binding protein 4 (p-4 E-BP1), as well as phosphatidylinositide 3-kinase (p-PI3K) pathway were amplified in cyclophosphamide rats as compared with control rats. Blocking mTOR by intrathecal infusion of rapamycin attenuated bladder hyperactivity and pain. In addition, blocking PI3K signal pathway attenuated activities of mTOR, which was accompanied with decreasing bladder hyperactivity and pain. Inhibition of either mTOR or PI3K blunted the enhanced spinal substance P and calcitonin gene-related peptide in cyclophosphamide rats.

CONCLUSIONS

The data for the first time revealed specific signaling pathways leading to cyclophosphamide-induced bladder hyperactivity and pain, including the activation of mTOR and PI3K. Inhibition of these pathways alleviates cystic pain. Targeting one or more of these signaling molecules may present new opportunities for treatment and management of overactive bladder and pain often observed in cystitis.

Blocking mammalian target of rapamycin (mTOR) improves neuropathic pain evoked by spinal cord injury

Spinal cord injury (SCI) is an extremely serious type of physical trauma observed in clinics. Neuropathic pain resulting from SCI has a lasting and significant impact on most aspects of daily life. Thus, a better understanding of the molecular pathways responsible for the cause of neuropathic pain observed in SCI is important to develop effective therapeutic agents and treatment strategies. Mammalian target of rapamycin (mTOR) is a serine/threonine protein kinase that is well known for its critical roles in regulating protein synthesis and growth. Furthermore, compelling evidence supports the notion that widespread dysregulation of mTOR and its downstream pathways are involved in neuropathic pain. Thus, in this study we specifically examined the underlying mechanisms by which mTOR and its signaling pathways are involved in SCI-evoked neuropathic pain in a rat model. Overall, we demonstrated that SCI increased the protein expression of p-mTOR, and mTORmediated- phosphorylation of 4E–binding protein 4 (4E-BP1) and p70 ribosomal S6 protein kinase 1 (S6K1) in the superficial dorsal horn of the spinal cord. Also, we showed that blocking spinal mTOR by intrathecal injection of rapamycin significantly inhibited pain responses induced by mechanical and thermal stimulation. In addition, blocking spinal phosphatidylinositide 3-kinase (p-PI3K) pathway significantly attenuated activities of p-mTOR pathways as well as mechanical and thermal hyperalgesia in SCI rats. Moreover, blocking mTOR and PI3K decreased the enhanced levels of substance P and calcitonin gene-related peptide (CGRP) in the dorsal horn of SCI rats. We revealed specific signaling pathways leading to SCI-evoked neuropathic pain, including the activation of PI3K, mTOR and its downstream signaling pathways. Targeting one or more of these signaling molecules may present new opportunities for treatment and management of neuropathic pain often observed in patients with SCI.

Prostaglandin E2-mediated upregulation of neuroexcitation and persistent tetrodotoxin-resistant Na(+) currents in Ah-type trigeminal ganglion neurons isolated from adult female rats

Prostaglandin-E2 (PGE2) is a very important inflammatory mediator and PGE2-mediated neuroexcitation in sex-specific distribution of Ah-type trigeminal ganglion neurons (TGNs) isolated from adult female rats is not fully addressed. The whole-cell patch-clamp experiment was performed to verify the effects of PGE2, forskolin, and GPR30-selective agonist (G-1) on action potential (AP) and tetrodotoxin-resistant (TTX-R) Na(+) currents in identified Ah-type TGNs. The results showed that the firing frequency was increased in Ah- and C-types by PGE2, which was simulated by forskolin and inhibited by Rp-cyclic adenosine monophosphate (cAMP), while G-1 mimicked this effect only in Ah-types, which was abolished by GPR30-selective antagonist (G-15). Although the amplitude of AP was increased in Ah- and C-types, increased maximal upstroke velocity was confirmed only in Ah-types, suggesting distinct alternations in current density and/or voltage-dependent property of Na(+) channels. With 1.0 μM PGE2, TTX-R Na(+) currents were upregulated without changing the current-voltage relationship and voltage-dependent activation in C-types, however, the TTX-R Na(+) current was augmented in Ah-types, peaked voltage and the voltage-dependent activation were both shifted toward hyperpolarized direction with faster slope. Intriguingly, the low-threshold persistent TTX-R component was activated from -60 mV and increased almost double at -30 mV compared with ∼30-40% increment of TTX-R component being activated at ∼-10 mV. Additionally, the change in TTX-R component of Ah-types was equivalent well with that in C-type TGNs. Taken these data together, we conclude that PGE2 modulates the neuroexcitation via cAMP-mediated upregulation of TTX-R Na(+) currents in both cell-types with hormone-dependent feature, especially persistent TTX-R Na(+) currents in sex-specific distribution of myelinated Ah-type TGNs.

Blocking proteinase-activated receptor 2 alleviated neuropathic pain evoked by spinal cord injury

Spinal cord injury (SCI) is an extremely serious type of physical trauma observed in clinics. Especially, neuropathic pain resulting from SCI has a lasting and significant impact on most aspects of daily life. Thus, a better understanding of the molecular pathways responsible for the cause of neuropathic pain observed in SCI is important to develop effectively therapeutic agents and treatment strategies. Proteinase-activated receptors (PARs) are a family member of G-protein-coupled receptors and are activated by a proteolytic mechanism. One of its subtypes PAR2 has been reported to be engaged in mechanical and thermal hyperalgesia. Thus, in this study we specifically examined the underlying mechanisms responsible for SCI evoked-neuropathic pain in a rat model. Overall, we demonstrated that SCI increases PAR2 and its downstream pathways TRPV1 and TRPA1 expression in the superficial dorsal horn of the spinal cord. Also, we showed that blocking spinal PAR2 by intrathecal injection of FSLLRY-NH2 significantly inhibits neuropathic pain responses induced by mechanical and thermal stimulation whereas FSLLRY-NH2 decreases the protein expression of TRPV1 and TRPA1 as well as the levels of substance P and calcitonin gene-related peptide. Results of this study have important implications, i.e. targeting one or more of these signaling molecules involved in activation of PAR2 and TRPV1/TRPA1 evoked by SCI may present new opportunities for treatment and management of neuropathic pain often observed in patients with SCI.