Oxytocin and Migraine Headache

Oxytocin Receptors on Calvarial Periosteal Innervation: Therapeutic Target for Post-Traumatic Headache?

OBJECTIVE

Following a mild traumatic brain injury (mTBI), the most prevalent and profoundly debilitating occurrence is the emergence of an acute and persistent post-traumatic headache (PTH), for which there are presently no approved treatments. A crucial gap in knowledge exists regarding the consequences of an mTBI, which could serve as a foundation for the development of therapeutic approaches. The activation of trigeminal sensory nerve terminals that innervate the calvarial periosteum (CP)-a densely innervated tissue layer covering the calvarial skull-has been implicated in both migraines and PTHs. We have previously shown that trigeminal oxytocin receptors (OTRs) may provide a therapeutic target for PTHs. This study examined the expression of oxytocin receptors on trigeminal nerves innervating the periosteum and whether these receptors might serve as a therapeutic target for PTHs using a direct application of oxytocin to the periosteum in a rodent model of PTH.

METHODS

We used retrograde tracing and immunohistochemistry to determine if trigeminal ganglion (TG) neurons innervating the periosteum expressed OTRs and/or CGRPs. To model the impact of local inflammation that occurs following an mTBI, we applied chemical inflammatory mediators directly to the CP and assessed for changes in immediate-early gene expression as an indication of neuronal activation. We also determined whether mTBI would lead to expression changes to OTR levels. To determine whether these OTRs could be a viable therapeutic target, we assessed the impact of oxytocin injections into the CP in a mouse model of PTH-induced periorbital allodynia.

RESULTS

The results of these experiments demonstrate the following: (1) the cell bodies of CP afferents reside in the TG and express both OTRs and CGRPs; (2) inflammatory chemical stimulation of the periosteum leads to rapid activation of TG neurons (phospho-ERK (p-ERK) expression), (3) mTBI-induced inflammation increased OTR expression compared to the sham group; and (4) administration of oxytocin into the periosteum on day 2 and day 40 blocked cutaneous allodynia for up to one hour post-administration for both acute and persistence phases in the PTH model-an effect that was preventable by the administration of an OTR antagonist.

CONCLUSION

Taken together, our observations suggest that periosteal trigeminal afferents contribute to post-TBI craniofacial pain, and that periosteum tissue can be used as a potential local target for therapeutics such as oxytocin.

Pharmacological management of migraine: current strategies and future directions

INTRODUCTION

Migraine is a complex neurological disorder that affects a significant portion of the global population. As traditional pharmacological approaches often fall short in alleviating symptoms, the development of innovative therapies has garnered significant interest. This text aims to summarize the current pharmacological options for managing migraine and to explore the potential impact of novel therapies.

AREAS COVERED

We focused on conventional treatments, emerging therapies, and novel compounds in clinical development, including therapies targeting the trigeminovascular system, cannabis-based therapies, hormonal and metabolic therapies, and other options. English peer-reviewed articles were searched in PubMed, Scopus, and ClinicalTrials.gov electronic databases.

EXPERT OPINION

Several novel treatment options for migraine have become available in recent years. Emerging pharmacological therapies targeting the trigeminovascular system, cannabis-based therapies, hormonal and metabolic interventions, and other emerging treatment modalities, may prove to be valuable for the treatment of migraine. Further research, clinical trials, and substantiated evidence are necessary to validate the efficacy, safety, and long-term outcomes of these therapeutic options.

Potential treatment targets for migraine: emerging options and future prospects

Migraine is a leading cause of disability worldwide. Despite the recent approval of several calcitonin gene-related peptide-targeted therapies, many people with migraine do not achieve satisfactory headache improvement with currently available therapies and there continues to be an unmet need for effective and tolerable migraine-specific treatments. Exploring additional targets that have compelling evidence for their involvement in modulating migraine pathways is therefore imperative. Potential new therapies for migraine include pathways involved in nociception, regulation of homoeostasis, modulation of vasodilation, and reward circuits. Animal and human studies show that these targets are expressed in regions of the CNS and peripheral nervous system that are involved in pain processing, indicating that these targets might be regarded as promising for the discovery of new migraine therapies. Future studies will require assessment of whether targets are suitable for therapeutic modulation, including assessment of specificity, affinity, solubility, stability, efficacy, and safety.

How Sex Hormones Affect Migraine: An Interdisciplinary Preclinical Research Panel Review

Sex hormones and migraine are closely interlinked. Women report higher levels of migraine symptoms during periods of sex hormone fluctuation, particularly during puberty, pregnancy, and perimenopause. Ovarian steroids, such as estrogen and progesterone, exert complex effects on the peripheral and central nervous systems, including pain, a variety of special sensory and autonomic functions, and affective processing. A panel of basic scientists, when challenged to explain what was known about how sex hormones affect the nervous system, focused on two hormones: estrogen and oxytocin. Notably, other hormones, such as progesterone, testosterone, and vasopressin, are less well studied but are also highlighted in this review. When discussing what new therapeutic agent might be an alternative to hormone therapy and menopause replacement therapy for migraine treatment, the panel pointed to oxytocin delivered as a nasal spray. Overall, the conclusion was that progress in the preclinical study of hormones on the nervous system has been challenging and slow, that there remain substantial gaps in our understanding of the complex roles sex hormones play in migraine, and that opportunities remain for improved or novel therapeutic agents. Manipulation of sex hormones, perhaps through biochemical modifications where its positive effects are selected for and side effects are minimized, remains a theoretical goal, one that might have an impact on migraine disease and other symptoms of menopause. This review is a call to action for increased interest and funding for preclinical research on sex hormones, their metabolites, and their receptors. Interdisciplinary research, perhaps facilitated by a collaborative communication network or panel, is a possible strategy to achieve this goal.

Involvement of the ipsilateral-to-the-pain anterior-superior hypothalamic subunit in chronic cluster headache

BACKGROUND

Despite hypothalamus has long being considered to be involved in the pathophysiology of cluster headache, the inconsistencies of previous neuroimaging studies and a limited understanding of the hypothalamic areas involved, impede a comprehensive interpretation of its involvement in this condition.

METHODS

We used an automated algorithm to extract hypothalamic subunit volumes from 105 cluster headache patients (57 chronic and 48 episodic) and 59 healthy individuals; after correcting the measures for the respective intracranial volumes, we performed the relevant comparisons employing logist regression models. Only for subunits that emerged as abnormal, we calculated their correlation with the years of illness and the number of headache attacks per day, and the effects of lithium treatment. As a post-hoc approach, using the 7 T resting-state fMRI dataset from the Human Connectome Project, we investigated whether the observed abnormal subunit, comprising the paraventricular nucleus and preoptic area, shows robust functional connectivity with the mesocorticolimbic system, which is known to be modulated by oxytocin neurons in the paraventricular nucleus and that is is abnormal in chronic cluster headache patients.

RESULTS

Patients with chronic (but not episodic) cluster headache, compared to control participants, present an increased volume of the anterior-superior hypothalamic subunit ipsilateral to the pain, which, remarkably, also correlates significantly with the number of daily attacks. The post-hoc approach showed that this hypothalamic area presents robust functional connectivity with the mesocorticolimbic system under physiological conditions. No evidence of the effects of lithium treatment on this abnormal subunit was found.

CONCLUSIONS

We identified the ipsilateral-to-the-pain antero-superior subunit, where the paraventricular nucleus and preoptic area are located, as the key hypothalamic region of the pathophysiology of chronic cluster headache. The significant correlation between the volume of this area and the number of daily attacks crucially reinforces this interpretation. The well-known roles of the paraventricular nucleus in coordinating autonomic and neuroendocrine flow in stress adaptation and modulation of trigeminovascular mechanisms offer important insights into the understanding of the pathophysiology of cluster headache.

Considerations for hormonal therapy in migraine patients: a critical review of current practice

INTRODUCTION

Migraine, a neurovascular headache disorder, is a leading cause of disability worldwide. Within the multifaceted pathophysiology of migraine, hormonal fluctuations play an evident triggering and exacerbating role, pointing toward the need for identification and proper usage of both existing and new hormonal targets in migraine treatment.

AREAS COVERED

With a threefold higher incidence of migraine in women than in men, the authors delve into sex hormone-related events in migraine patients. A comprehensive overview is given of existing hormonal therapies, including oral contraceptives, intrauterine devices, transdermal and subcutaneous estradiol patches, gnRH-agonists, oral testosterone, and 5α reductase inhibitors. The authors discuss their effectiveness and risks, noting their suitability for different patient profiles. Next, novel evolving hormonal treatments, such as oxytocin and prolactin, are explored. Lastly, the authors cover hormonal conditions associated with migraine, such as polycystic ovary syndrome, endometriosis, and transgender persons receiving gender affirming hormone therapy, aiming to provide more personalized and effective solutions for migraine management.

EXPERT OPINION

Rigorous research into both existing and new hormonal targets, as well as the underlying pathophysiology, is needed to support a tailored approach in migraine treatment, in an ongoing effort to alleviate the impact of migraine on individuals and society.

Mechanisms and treatments of chronic pain after traumatic brain injury

While pain after trauma generally resolves, some trauma patients experience pain for months to years after injury. An example, relevant to both combat and civilian settings, is chronic pain after traumatic brain injury (TBI). Headache as well as pain in the back and extremities are common locations for TBI-related chronic pain to be experienced. TBI-related pain can exist alone or can exacerbate pain from other injuries long after healing has occurred. Consequences of chronic pain in these settings include increased suffering, higher levels of disability, serious emotional problems, and worsened cognitive deficits. The current review will examine recent evidence regarding dysfunction of endogenous pain modulatory mechanisms, neuroplastic changes in the trigeminal circuitry and alterations in spinal nociceptive processing as contributors to TBI-related chronic pain. Key pain modulatory centers including the locus coeruleus, periaqueductal grey matter, and rostroventromedial medulla are vulnerable to TBI. Both the rationales and existing evidence for the use of monoamine reuptake inhibitors, CGRP antagonists, CXCR2 chemokine receptor antagonists, and interventional therapies will be presented. While consensus guidelines for the management of chronic post-traumatic TBI-related pain are lacking, several approaches to this clinically challenging situation deserve focused evaluation and may prove to be viable therapeutic options.

Oxytocin as neuro-hormone and neuro-regulator exert neuroprotective properties: A mechanistic graphical review

BACKGROUND

Neurodegeneration is progressive cell loss in specific neuronal populations, often resulting in clinical consequences with significant medical, societal, and economic implications. Because of its antioxidant, anti-inflammatory, and anti-apoptotic properties, oxytocin has been proposed as a potential neuroprotective and neurobehavioral therapeutic agent, including modulating mood disturbances and cognitive enchantment.

METHODS

Literature searches were conducted using the following databases Web of Science, PubMed, Elsevier Science Direct, Google Scholar, the Core Collection, and Cochrane from January 2000 to February 2023 for articles dealing with oxytocin neuroprotective properties in preventing or treating neurodegenerative disorders and diseases with a focus on oxidative stress, inflammation, and apoptosis/cell death.

RESULTS

The neuroprotective effects of oxytocin appears to be mediated by its anti-inflammatory properties, inhibition of neuro inflammation, activation of several antioxidant enzymes, inhibition of oxidative stress and free radical formation, activation of free radical scavengers, prevent of mitochondrial dysfunction, and inhibition of apoptosis.

CONCLUSION

Oxytocin acts as a neuroprotective agent by preventing neuro-apoptosis, neuro-inflammation, and neuronal oxidative stress, and by restoring mitochondrial function.

Inflammatory Orofacial Pain Activates Peptidergic Neurons and Upregulates the Oxytocin Receptor Expression in Trigeminal Ganglion

The majority of orofacial pain is caused by musculoskeletal and neuropathological diseases related to inflammatory processes that lead even to transcriptional alterations in the trigeminal ganglion (TG) neurons. The hypothalamic nonapeptide oxytocin has been reported to modulate nociception via binding and activating its receptor in primary sensory neurons. The purpose of this study was to analyze the gene expression of the oxytocin receptor (OTR), c-Fos, an indicator of neuronal activity, and α-calcitonin gene-related peptide (αCGRP), a characteristic neurotransmitter of the peptidergic trigeminal primary afferents in an animal model of inflammation-induced orofacial pain. Carrageenan was unilaterally injected into the vibrissal pads of male and female adult Wistar rats. RT-qPCR was performed to analyze the levels of mRNA expression in TGs 24 h after injection. The gene expression analysis revealed higher fold changes regarding the c-Fos (mean ± S.E: ♀: 3.9 ± 0.19; ♂: 3.55 ± 0.18) and αCGRP (♀: 2.84 ± 0.13; ♂: 3.39 ± 0.47) expression levels of mRNA, and a moderate rise in the expression of the OTR mRNA (♀: 1.52 ± 0.07; ♂: 1.49 ± 0.07) was observed in comparison to both vehicle(saline)-treated and untreated controls. Our results furnish evidence for inflammation-induced activation of peptidergic neurons, and it is suggested that oxytocin modulates inflammation-induced nociception by enhancing their signaling capacity due to its elevated expression in the sensory ganglion cells, thus providing new therapies for orofacial pain relief that target the OTRs.

Evaluating the efficacy of oxytocin for pain management: An updated systematic review and meta-analysis of randomized clinical trials and observational studies

Background

There is a need for novel analgesics with favorable risk to benefit profiles. Oxytocin has recently gained attention for its potential analgesic properties.

Aim

The aim of this study was to perform an updated systematic review and meta-analysis evaluating the effect of oxytocin for pain management.

Method

Ovid MEDLINE, Embase, PsycINFO, CINAHL, and Clinicaltrials.gov were searched for articles reporting on associations between oxytocin and chronic pain management from January 2012 to February 2022. Studies published before 2012 that were identified in our previous systematic review were also eligible. Risk of bias of included studies was assessed. Synthesis of results was performed using meta-analysis and narrative synthesis.

Results

Searches returned 2087 unique citations. In total, 14 articles were included that reported on 1504 people living with pain. Results from meta-analysis and narrative review were mixed. Meta-analysis of three studies indicated that exogenous oxytocin administration did not result in a significant reduction in pain intensity relative to placebo (N = 3; n = 95; g = 0.31; 95% confidence interval [CI] -0.10, 0.73). Narrative review provided encouraging evidence that exogenous oxytocin administration reduced pain sensitivity among individuals with back pain, abdominal pain, and migraines. Results suggested that individual difference factors (e.g., sex and chronic pain condition) may influence oxytocin-induced nociception, but the heterogeneity and limited number of studies identified precluded further investigation.

Discussion

There is equipoise for the benefit of oxytocin for pain management. Future studies are imperative and should undertake more precise exploration of potential confounds and mechanisms of analgesic action to clarify inconsistency in the literature.

CGRP physiology, pharmacology, and therapeutic targets: migraine and beyond

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse physiological functions. Its two isoforms (α and β) are widely expressed throughout the body in sensory neurons as well as in other cell types, such as motor neurons and neuroendocrine cells. CGRP acts via at least two G protein-coupled receptors that form unusual complexes with receptor activity-modifying proteins. These are the CGRP receptor and the AMY1 receptor; in rodents, additional receptors come into play. Although CGRP is known to produce many effects, the precise molecular identity of the receptor(s) that mediates CGRP effects is seldom clear. Despite the many enigmas still in CGRP biology, therapeutics that target the CGRP axis to treat or prevent migraine are a bench-to-bedside success story. This review provides a contextual background on the regulation and sites of CGRP expression and CGRP receptor pharmacology. The physiological actions of CGRP in the nervous system are discussed, along with updates on CGRP actions in the cardiovascular, pulmonary, gastrointestinal, immune, hematopoietic, and reproductive systems and metabolic effects of CGRP in muscle and adipose tissues. We cover how CGRP in these systems is associated with disease states, most notably migraine. In this context, we discuss how CGRP actions in both the peripheral and central nervous systems provide a basis for therapeutic targeting of CGRP in migraine. Finally, we highlight potentially fertile ground for the development of additional therapeutics and combinatorial strategies that could be designed to modulate CGRP signaling for migraine and other diseases.

Prolactin and oxytocin: potential targets for migraine treatment

Migraine is a severe neurovascular disorder of which the pathophysiology is not yet fully understood. Besides the role of inflammatory mediators that interact with the trigeminovascular system, cyclic fluctuations in sex steroid hormones are involved in the sex dimorphism of migraine attacks. In addition, the pituitary-derived hormone prolactin and the hypothalamic neuropeptide oxytocin have been reported to play a modulating role in migraine and contribute to its sex-dependent differences. The current narrative review explores the relationship between these two hormones and the pathophysiology of migraine. We describe the physiological role of prolactin and oxytocin, its relationship to migraine and pain, and potential therapies targeting these hormones or their receptors.In summary, oxytocin and prolactin are involved in nociception in opposite ways. Both operate at peripheral and central levels, however, prolactin has a pronociceptive effect, while oxytocin appears to have an antinociceptive effect. Therefore, migraine treatment targeting prolactin should aim to block its effects using prolactin receptor antagonists or monoclonal antibodies specifically acting at migraine-pain related structures. This action should be local in order to avoid a decrease in prolactin levels throughout the body and associated adverse effects. In contrast, treatment targeting oxytocin should enhance its signalling and antinociceptive effects, for example using intranasal administration of oxytocin, or possibly other oxytocin receptor agonists. Interestingly, the prolactin receptor and oxytocin receptor are co-localized with estrogen receptors as well as calcitonin gene-related peptide and its receptor, providing a positive perspective on the possibilities for an adequate pharmacological treatment of these nociceptive pathways. Nevertheless, many questions remain to be answered. More particularly, there is insufficient data on the role of sex hormones in men and the correct dosing according to sex differences, hormonal changes and comorbidities. The above remains a major challenge for future development.

Current and Emerging Pharmacotherapy for Menstrual Migraine: A Narrative Review

INTRODUCTION

In this article, we discuss menstrual migraine (MM), which can be categorized as menstrually related migraine (MRM) or pure menstrual migraine (PMM). MM attacks are often longer, more severe, and harder to treat than other migraine attacks. Appropriate treatment strategies include acute treatment, short term preventive treatment, and daily preventive treatment, depending on the patient's pattern of migraine and occurrence of migraine outside the menstrual period.

AREAS COVERED

A PubMed, Cochrane Library, Medline, and Ovid search from inception to October 2022 provided articles relating to MM pathophysiology and treatment.

EXPERT OPINION

In patients for whom standard acute therapy is inadequate, short term or daily preventive treatment should be considered. Patients with PMM may be adequately managed with short term preventive treatment started 2 days prior to the onset of migraine and continued for 5-6 days. Frovatriptan is the mainstay of short-term prevention. Patients who experience additional attacks outside the menstrual period may benefit from daily preventive treatment. Estrogen-containing contraceptive treatment may be effective in appropriately selected patients. Emerging research on the pathophysiology of MM indicates that oxytocin agonists and CGRP antagonists may prove to be effective treatment options.

Highly Specific Detection of Oxytocin in Saliva

Oxytocin is a peptide neurophysin hormone made up of nine amino acids and is used in induction of one in four births worldwide (more than 13 percent in the United States). Herein, we have developed an antibody alternative aptamer-based electrochemical assay for real-time and point-of-care detection of oxytocin in non-invasive saliva samples. This assay approach is rapid, highly sensitive, specific, and cost-effective. Our aptamer-based electrochemical assay can detect as little as 1 pg/mL of oxytocin in less than 2 min in commercially available pooled saliva samples. Additionally, we did not observe any false positive or false negative signals. This electrochemical assay has the potential to be utilized as a point-of-care monitor for rapid and real-time oxytocin detection in various biological samples such as saliva, blood, and hair extracts.

A study of differential microRNA expression profile in migraine: the microMIG exploratory study

BACKGROUND

Several studies have described potential microRNA (miRNA) biomarkers associated with migraine, but studies are scarcely reproducible primarily due to the heterogeneous variability of participants. Increasing evidence shows that disease-related intrinsic factors together with lifestyle (environmental factors), influence epigenetic mechanisms and in turn, diseases. Hence, the main objective of this exploratory study was to find differentially expressed miRNAs (DE miRNA) in peripheral blood mononuclear cells (PBMC) of patients with migraine compared to healthy controls in a well-controlled homogeneous cohort of non-menopausal women.

METHODS

Patients diagnosed with migraine according to the International Classification of Headache Disorders (ICHD-3) and healthy controls without familial history of headache disorders were recruited. All participants completed a very thorough questionnaire and structured-interview in order to control for environmental factors. RNA was extracted from PBMC and a microarray system (GeneChip miRNA 4.1 Array chip, Affymetrix) was used to determine the miRNA profiles between study groups. Principal components analysis and hierarchical clustering analysis were performed to study samples distribution and random forest (RF) algorithms were computed for the classification task. To evaluate the stability of the results and the prediction error rate, a bootstrap (.632 + rule) was run through all the procedure. Finally, a functional enrichment analysis of selected targets was computed through protein-protein interaction networks.

RESULTS

After RF classification, three DE miRNA distinguished study groups in a very homogeneous female cohort, controlled by factors such as demographics (age and BMI), life-habits (physical activity, caffeine and alcohol consumptions), comorbidities and clinical features associated to the disease: miR-342-3p, miR-532-3p and miR-758-5p. Sixty-eight target genes were predicted which were linked mainly to enriched ion channels and signaling pathways, neurotransmitter and hormone homeostasis, infectious diseases and circadian entrainment.

CONCLUSIONS

A 3-miRNA (miR-342-3p, miR-532-3p and miR-758-5p) novel signature has been found differentially expressed between controls and patients with migraine. Enrichment analysis showed that these pathways are closely associated with known migraine pathophysiology, which could lead to the first reliable epigenetic biomarker set. Further studies should be performed to validate these findings in a larger and more heterogeneous sample.

Expression of vasopressin and its receptors in migraine-related regions in CNS and the trigeminal system: influence of sex

BACKGROUND

Hypothalamus is a key region in migraine attacks. In addition, women are disproportionately affected by migraine. The calcitonin gene-related peptide (CGRP) system is an important key player in migraine pathophysiology. CGRP signaling could be a target of hormones that influence migraine. Our aim is to identify the expression of vasopressin and its receptors in the brain and in the trigeminovascular system with focus on the migraine-related regions and, furthermore, to examine the role of sex on the expression of neurohormones in the trigeminal ganglion.

METHODS

Rat brain and trigeminal ganglia were carefully harvested, and protein and mRNA levels were analyzed by immunohistochemistry and real-time PCR, respectively.

RESULTS

Vasopressin and its receptors immunoreactivity were found in migraine-related areas within the brain and, in the trigeminal ganglion, predominantly in neuronal cytoplasm. There were no differences in the number of positive immunoreactivity cells expression of CGRP and vasopressin in the trigeminal ganglion between male and female rats. In contrast, the number of RAMP1 (CGRP receptor), oxytocin (molecular relative to vasopressin), oxytocin receptor and vasopressin receptors (V1aR and V1bR) immunoreactive cells were higher in female compared to male rats. Vasopressin and its receptors mRNA were expressed in both hypothalamus and trigeminal ganglion; however, the vasopressin mRNA level was significantly higher in the hypothalamus.

CONCLUSIONS

A better understanding of potential hormonal influences on migraine mechanisms is needed to improve treatment of female migraineurs. It is intriguing that vasopressin is an output of hypothalamic neurons that influences areas associated with migraine. Therefore, vasopressin and the closely related oxytocin might be important hypothalamic components that contribute to migraine pathophysiology.

Oxytocin and secretin receptors - implications for dry eye syndrome and ocular pain

Dry eye syndrome, a form of ocular surface inflammation, and chronic ocular pain are common conditions impacting activities of daily living and quality of life. Oxytocin and secretin are peptide hormones that have been shown to synergistically reduce inflammation in various tissues and attenuate the pain response at both the neuron and brain level. The oxytocin receptor (OXTR) and secretin receptor (SCTR) have been found in a wide variety of tissues and organs, including the eye. We reviewed the current literature of in vitro experiments, animal models, and human studies that examine the anti-inflammatory and anti-nociceptive roles of oxytocin and secretin. This review provides an overview of the evidence supporting oxytocin and secretin as the basis for novel treatments of dry eye and ocular pain syndromes.

Impact of Magnesium on Oxytocin Receptor Function

BACKGROUND AND PURPOSE

The intranasal administration of oxytocin (OT) reduces migraine headaches through activation of the oxytocin receptor (OTR). Magnesium ion (Mg2+) concentration is critical to the activation of the OTR, and a low serum Mg2+ concentration is predictive of a migraine headache. We, therefore, examined the functional impact of Mg2+ concentration on OT-OTR binding efficacy using two complimentary bioassays.

EXPERIMENTAL APPROACH

Current clamp recordings of rat trigeminal ganglia (TG) neurons measured the impact of Mg2+ on an OT-induced reduction in excitability. In addition, we assessed the impact of Mg2+ on intranasal OT-induced craniofacial analgesia in rats.

KEY RESULTS

While OT alone dose-dependently hyperpolarized TG neurons, decreasing their excitability, the addition of 1.75 mM Mg2+ significantly enhanced this effect. Similarly, while the intranasal application of OT produced dose-dependent craniofacial analgesia, Mg2+ significantly enhanced these effects.

CONCLUSIONS AND IMPLICATIONS

OT efficacy may be limited by low ambient Mg2+ levels. The addition of Mg2+ to OT formulations may improve its efficacy in reducing headache pain as well as for other OT-dependent processes.

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.

"Less is more": a dose-response account of intranasal oxytocin pharmacodynamics in the human brain

Intranasal oxytocin is attracting attention as a potential treatment for several brain disorders due to promising preclinical results. However, translating findings to humans has been hampered by remaining uncertainties about its pharmacodynamics and the methods used to probe its effects in the human brain. Using a dose-response design (9, 18 and 36 IU), we demonstrate that intranasal oxytocin-induced changes in local regional cerebral blood flow (rCBF) in the amygdala at rest, and in the covariance between rCBF in the amygdala and other key hubs of the brain oxytocin system, follow a dose-response curve with maximal effects for lower doses. Yet, the effects on local rCBF might vary by amygdala subdivision, highlighting the need to qualify dose-response curves within subregion. We further link physiological changes with the density of the oxytocin receptor gene mRNA across brain regions, strengthening our confidence in intranasal oxytocin as a valid approach to engage central targets. Finally, we demonstrate that intranasal oxytocin does not disrupt cerebrovascular reactivity, which corroborates the validity of haemodynamic neuroimaging to probe the effects of intranasal oxytocin in the human brain. DATA AVAILABILITY: Participants did not consent for open sharing of the data. Therefore, data can only be accessed from the corresponding author upon reasonable request.

Role of Oxytocin in Different Neuropsychiatric, Neurodegenerative, and Neurodevelopmental Disorders

Oxytocin has recently gained significant attention because of its role in the pathophysiology and management of dominant neuropsychiatric disorders. Oxytocin, a peptide hormone synthesized in the hypothalamus, is released into different brain regions, acting as a neurotransmitter. Receptors for oxytocin are present in many areas of the brain, including the hypothalamus, amygdala, and nucleus accumbens, which have been involved in the pathophysiology of depression, anxiety, schizophrenia, autism, Alzheimer's disease, Parkinson's disease, and attention deficit hyperactivity disorder. Animal studies have spotlighted the role of oxytocin in social, behavioral, pair bonding, and mother-infant bonding. Furthermore, oxytocin protects fetal neurons against injury during childbirth and affects various behaviors, assuming its possible neuroprotective characteristics. In this review, we discuss some of the concepts and mechanisms related to the role of oxytocin in the pathophysiology and management of some neuropsychiatric, neurodegenerative, and neurodevelopmental disorders.

Neural Functions of Hypothalamic Oxytocin and its Regulation

Oxytocin (OT), a nonapeptide, has a variety of functions. Despite extensive studies on OT over past decades, our understanding of its neural functions and their regulation remains incomplete. OT is mainly produced in OT neurons in the supraoptic nucleus (SON), paraventricular nucleus (PVN) and accessory nuclei between the SON and PVN. OT exerts neuromodulatory effects in the brain and spinal cord. While magnocellular OT neurons in the SON and PVN mainly innervate the pituitary and forebrain regions, and parvocellular OT neurons in the PVN innervate brainstem and spinal cord, the two sets of OT neurons have close interactions histologically and functionally. OT expression occurs at early life to promote mental and physical development, while its subsequent decrease in expression in later life stage accompanies aging and diseases. Adaptive changes in this OT system, however, take place under different conditions and upon the maturation of OT release machinery. OT can modulate social recognition and behaviors, learning and memory, emotion, reward, and other higher brain functions. OT also regulates eating and drinking, sleep and wakefulness, nociception and analgesia, sexual behavior, parturition, lactation and other instinctive behaviors. OT regulates the autonomic nervous system, and somatic and specialized senses. Notably, OT can have different modulatory effects on the same function under different conditions. Such divergence may derive from different neural connections, OT receptor gene dimorphism and methylation, and complex interactions with other hormones. In this review, brain functions of OT and their underlying neural mechanisms as well as the perspectives of their clinical usage are presented.

Roles of Oxytocin in Stress Responses, Allostasis and Resilience

Oxytocin has been revealed to work for anxiety suppression and anti-stress as well as for psychosocial behavior and reproductive functions. Oxytocin neurons are activated by various stressful stimuli. The oxytocin receptor is widely distributed within the brain, and oxytocin that is released or diffused affects behavioral and neuroendocrine stress responses. On the other hand, there has been an increasing number of reports on the role of oxytocin in allostasis and resilience. It has been shown that oxytocin maintains homeostasis, shifts the set point for adaptation to a changing environment (allostasis) and contributes to recovery from the shifted set point by inducing active coping responses to stressful stimuli (resilience). Recent studies have suggested that oxytocin is also involved in stress-related disorders, and it has been shown in clinical trials that oxytocin provides therapeutic benefits for patients diagnosed with stress-related disorders. This review includes the latest information on the role of oxytocin in stress responses and adaptation.

Hormonal influences in migraine - interactions of oestrogen, oxytocin and CGRP

Migraine is ranked as the second highest cause of disability worldwide and the first among women aged 15-49 years. Overall, the incidence of migraine is threefold higher among women than men, though the frequency and severity of attacks varies during puberty, the menstrual cycle, pregnancy, the postpartum period and menopause. Reproductive hormones are clearly a key influence in the susceptibility of women to migraine. A fall in plasma oestrogen levels can trigger attacks of migraine without aura, whereas higher oestrogen levels seem to be protective. The basis of these effects is unknown. In this Review, we discuss what is known about sex hormones and their receptors in migraine-related areas in the CNS and the peripheral trigeminovascular pathway. We consider the actions of oestrogen via its multiple receptor subtypes and the involvement of oxytocin, which has been shown to prevent migraine attacks. We also discuss possible interactions of these hormones with the calcitonin gene-related peptide (CGRP) system in light of the success of anti-CGRP treatments. We propose a simple model to explain the hormone withdrawal trigger in menstrual migraine, which could provide a foundation for improved management and therapy for hormone-related migraine in women.

The locus of Action of CGRPergic Monoclonal Antibodies Against Migraine: Peripheral Over Central Mechanisms

Migraine is a complex neurovascular disorder characterized by attacks of moderate to severe unilateral headache, accompanied by photophobia among other neurological signs. Although an arsenal of antimigraine agents is currently available in the market, not all patients respond to them. As Calcitonin Gene-Related Peptide (CGRP) plays a key role in the pathophysiology of migraine, CGRP receptor antagonists (gepants) have been developed. Unfortunately, further pharmaceutical development (for olcegepant and telcagepant) was interrupted due to pharmacokinetic issues observed during the Randomized Clinical Trials (RCT). On this basis, the use of monoclonal antibodies (mAbs; immunoglobulins) against CGRP or its receptor has recently emerged as a novel pharmacotherapy to treat migraines. RCT showed that these mAbs are effective against migraines producing fewer adverse events. Presently, the U.S. Food and Drug Administration approved four mAbs, namely: (i) erenumab; (ii) fremanezumab; (iii) galcanezumab; and (iv) eptinezumab. In general, specific antimigraine compounds exert their action in the trigeminovascular system, but the locus of action (peripheral vs. central) of the mAbs remains elusive. Since these mAbs have a molecular weight of ∼150 kDa, some studies rule out the relevance of their central actions as they seem unlikely to cross the Blood-Brain Barrier (BBB). Considering the therapeutic relevance of this new class of antimigraine compounds, the present review has attempted to summarize and discuss the current evidence on the probable sites of action of these mAbs.

Kamikihito, a traditional Japanese Kampo medicine, increases the secretion of oxytocin in rats with acute stress

ETHNOPHARMACOLOGICAL RELEVANCE

Kamikihito (KKT) is a Kampo medicine that is prescribed in Japan for the treatment of anemia, insomnia and mental anxiety in Japan. However, its precise mechanism of action remains unclear.

AIM OF THE STUDY

This study aimed to evaluate the possible antistress effect of KKT in rats with acute stress and the contribution of oxytocin to the process.

MATERIALS AND METHODS

Acute immobilization stress (AIS; for 90 min) was used to assess the effect of KKT on acute stress. Male Wistar rats were orally treated with KKT. Parameters of stress were evaluated, and concentrations of oxytocin in plasma and cerebrospinal fluid (CSF) were measured.

RESULTS

AIS-induced defecation and fecal weight were significantly decreased because of treatment with KKT. The plasma levels of stress-related hormones following AIS were investigated. The pre-administration of KKT significantly increased adrenocorticotrophic hormone (ACTH) and corticosterone (CORT) levels following AIS. Conversely, there was no significant change in the plasma oxytocin level. Microdialysis and hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS) were used to monitor the oxytocin secretion in CSF. Oxytocin level increased during AIS following the treatment of KKT. At 30 min after AIS, the level remained higher than before AIS. Furthermore, using an open field test, the locomotion (exploratory behavior) immediately after AIS was examined. The total traveled distance decreased after AIS; however, the decrease was significantly inhibited by the treatment of KKT. However, the effect of KKT was obstructed by the pre-administration of the oxytocin receptor antagonist.

CONCLUSIONS

These results suggest that KKT has antistress activity and increased oxytocin secretion may be a mechanism underlying this phenomenon.

Repeated oxytocin prevents central sensitization by regulating synaptic plasticity via oxytocin receptor in a chronic migraine mouse model

BACKGROUND

Central sensitization is one of the characters of chronic migraine (CM). Aberrant synaptic plasticity can induce central sensitization. Oxytocin (OT), which is a hypothalamic hormone, plays an important antinociceptive role. However, the antinociceptive effect of OT and the underlying mechanism in CM remains unclear. Therefore, we explored the effect of OT on central sensitization in CM and its implying mechanism, focusing on synaptic plasticity.

METHODS

A CM mouse model was established by repeated intraperitoneal injection of nitroglycerin (NTG). Von Frey filaments and radiant heat were used to measure the nociceptive threshold. Repeated intranasal OT and intraperitoneal L368,899, an oxytocin receptor (OTR) antagonist, were administered to investigate the effect of OT and the role of OTR. The expression of calcitonin gene-related peptide (CGRP) and c-fos were measured to assess central sensitization. N-methyl D-aspartate receptor subtype 2B (NR2B)-regulated synaptic-associated proteins and synaptic plasticity were explored by western blot (WB), transmission electron microscope (TEM), and Golgi-Cox staining.

RESULTS

Our results showed that the OTR expression in the trigeminal nucleus caudalis (TNC) of CM mouse was significantly increased, and OTR was colocalized with the postsynaptic density protein 95 (PSD-95) in neurons. Repeated intranasal OT alleviated the NTG-induced hyperalgesia and prevented central sensitization in CM mouse. Additionally, the OT treatment inhibited the overexpression of phosphorylated NR2B and synaptic-associated proteins including PSD-95, synaptophysin-1 (syt-1), and synaptosomal-associated protein 25 (snap25) in the TNC of CM mouse and restored the abnormal synaptic structure. The protective effect of OT was prevented by L368,899. Furthermore, the expression of adenylyl cyclase 1 (AC1)/ protein kinase A (PKA)/ phosphorylation of cyclic adenosine monophosphate response element-binding protein (pCREB) pathway was depressed by OT and restored by L368,899.

CONCLUSIONS

Our findings demonstrate that repeated intranasal OT eliminates central sensitization by regulating synaptic plasticity via OTR in CM. The effect of OT has closely associated with the down-regulation of AC1/PKA/pCREB signaling pathway, which is activated in CM model. Repeated intranasal OT may be a potential candidate for CM prevention.

Intranasal Administration for Pain: Oxytocin and Other Polypeptides

Pain, particularly chronic pain, remains one of the most debilitating and difficult-to-treat conditions in medicine. Chronic pain is difficult to treat, in part because it is associated with plastic changes in the peripheral and central nervous systems. Polypeptides are linear organic polymers that are highly selective molecules for neurotransmitter and other nervous system receptors sites, including those associated with pain and analgesia, and so have tremendous potential in pain therapeutics. However, delivery of polypeptides to the nervous system is largely limited due to rapid degradation within the peripheral circulation as well as the blood–brain barrier. One strategy that has been shown to be successful in nervous system deposition of polypeptides is intranasal (IN) delivery. In this narrative review, we discuss the delivery of polypeptides to the peripheral and central nervous systems following IN administration. We briefly discuss the mechanism of delivery via the nasal–cerebral pathway. We review recent studies that demonstrate that polypeptides such as oxytocin, delivered IN, not only reach key pain-modulating regions in the nervous system but, in doing so, evoke significant analgesic effects. IN administration of polypeptides has tremendous potential to provide a non-invasive, rapid and effective method of delivery to the nervous system for chronic pain treatment and management.

Nasal oxytocin for the treatment of psychiatric disorders and pain: achieving meaningful brain concentrations

There is evidence of the therapeutic potential of intranasal oxytocin for the treatment of pain and various psychiatric disorders, however, there is scant evidence that oxytocin reaches the brain. We quantified the concentration and distribution pattern of [¹²⁵I]-radiolabeled oxytocin in the brains and peripheral tissues of rats after intranasal delivery using gamma counting and autoradiography, respectively. Radiolabel was detected in high concentrations in the trigeminal and olfactory nerves as well as in brain regions along their trajectories. Considerable concentrations were observed in the blood, however, relatively low levels of radiolabel were measured in peripheral tissues. The addition of a mucoadhesive did not enhance brain concentrations. These results provide support for intranasal OT reaching the brain via the olfactory and trigeminal neural pathways. These findings will inform the design and interpretation of clinical studies with intranasal oxytocin.

Can intranasal oxytocin reduce craving in automated addictive behaviours? A systematic review

Existing pharmacotherapies for managing craving, a strong predictor of relapse to automated addictive behaviours, are limited in efficacy and characterised by increased health risks associated with their pharmacological profile. Preclinical studies have identified oxytocin as a promising pharmacotherapy with anticraving properties for addictive behaviours. Here, we provide the first systematic review of 17 human studies (n = 722; 30% female) investigating the efficacy of intranasal oxytocin to reduce craving or consumption in addictive behaviours. We identify intranasal oxytocin as a method that warrants further investigation regarding its capacity to decrease cue-induced, acute stress-induced or withdrawal-related craving and relapse related to alcohol, cannabis, opioids, cocaine or nicotine, including a potential role as ad hoc medication following exposure to drug-related cues. Future studies should investigate the role of factors such as treatment regimens and sample characteristics, including the role of the amygdala, which we propose as a distinct mechanism mediating oxytocin's anticraving properties.

A new hypothesis linking oxytocin to menstrual migraine

OBJECTIVE

To highlight the emerging understanding of oxytocin (OT) and oxytocin receptors (OTRs) in modulating menstrual-related migraine (MRM).

BACKGROUND

MRM is highly debilitating and less responsive to therapy, and attacks are of longer duration than nonmenstrually related migraine. A clear understanding of the mechanisms underlying MRM is lacking.

METHODS

We present a narrative literature review on the developing understanding of the role of OT and the OTR in MRM. Literature on MRM on PubMed/MEDLINE database including clinical trials and basic science publications was reviewed using specific keywords.

RESULTS

OT is a cyclically released hypothalamic hormone/neurotransmitter that binds to the OTR resulting in inhibition of trigeminal neuronal excitability that can promote migraine pain including that of MRM. Estrogen regulates OT release as well as expression of the OTR. Coincident with menstruation, levels of both estrogen and OT decrease. Additionally, other serum biochemical factors, including magnesium and cholesterol, which positively modulate the affinity of OT for OTRs, both decrease during menstruation. Thus, during menstruation, multiple menstrually associated factors may lead to decreased circulating OT levels, decreased OT affinity for OTR, and decreased expression of the trigeminal OTR. Consistent with the view of migraine as a threshold disorder, these events may collectively result in decreased inhibition promoting lower thresholds for activation of meningeal trigeminal nociceptors and increasing the likelihood of an MRM attack.

CONCLUSION

Trigeminal OTR may thus be a novel target for the development of MRM therapeutics.

Acute and Preventive Management of Migraine during Menstruation and Menopause

Migraine course is influenced by female reproductive milestones, including menstruation and perimenopause; menstrual migraine (MM) represents a distinct clinical entity. Increased susceptibility to migraine during menstruation and in perimenopause is probably due to fluctuations in estrogen levels. The present review provides suggestions for the treatment of MM and perimenopausal migraine. MM is characterized by long, severe, and poorly treatable headaches, for which the use of long-acting triptans and/or combined treatment with triptans and common analgesics is advisable. Short-term prophylaxis with triptans and/or estrogen treatment is another viable option in women with regular menstrual cycles or treated with combined hormonal contraceptives; conventional prevention may also be considered depending on the attack-related disability and the presence of attacks unrelated to menstruation. In women with perimenopausal migraine, hormonal treatments should aim at avoiding estrogen fluctuations. Future research on migraine treatments will benefit from the ascertainment of the interplay between female sex hormones and the mechanisms of migraine pathogenesis, including the calcitonin gene-related peptide pathway.

Oxytocin modulates local topography of human functional connectome in healthy men at rest

Oxytocin has recently received remarkable attention for its role as a modulator of human behaviour. Here, we aimed to expand our knowledge of the neural circuits engaged by oxytocin by investigating the effects of intranasal and intravenous oxytocin on the functional connectome at rest in 16 healthy men. Oxytocin modulates the functional connectome within discrete neural systems, but does not affect the global capacity for information transfer. These local effects encompass key hubs of the oxytocin system (e.g. amygdala) but also regions overlooked in previous hypothesis-driven research (i.e. the visual circuits, temporal lobe and cerebellum). Increases in levels of oxytocin in systemic circulation induce broad effects on the functional connectome, yet we provide indirect evidence supporting the involvement of nose-to-brain pathways in at least some of the observed changes after intranasal oxytocin. Together, our results suggest that oxytocin effects on human behaviour entail modulation of multiple levels of brain processing distributed across different systems.

Brain oxytocin: how puzzle stones from animal studies translate into psychiatry

The neuropeptide oxytocin has attracted great attention of the general public, basic neuroscience researchers, psychologists, and psychiatrists due to its profound pro-social, anxiolytic, and "anti-stress" behavioral and physiological effects, and its potential application for treatment of mental diseases associated with altered socio-emotional competence. During the last decade, substantial progress has been achieved in understanding the complex neurobiology of the oxytocin system, including oxytocinergic pathways, local release patterns, and oxytocin receptor distribution in the brain, as well as intraneuronal oxytocin receptor signaling. However, the picture of oxytocin actions remains far from being complete, and the central question remains: "How does a single neuropeptide exert such pleotropic actions?" Although this phenomenon, typical for many of about 100 identified neuropeptides, may emerge from the anatomical divergence of oxytocin neurons, their multiple central projections, distinct oxytocin-sensitive cell types in different brain regions, and multiple intraneuronal signaling pathways determining the specific cellular response, further basic studies are required. In conjunction, numerous reports on positive effects of intranasal application of oxytocin on human brain networks controlling socio-emotional behavior in health and disease require harmonic tandems of basic researchers and clinicians. During the COVID-19 crisis in 2020, oxytocin research seems central as question of social isolation-induced inactivation of the oxytocin system, and buffering effects of either activation of the endogenous system or intranasal application of synthetic oxytocin need to be thoroughly investigated.

Activation of oxytocin receptor in the trigeminal ganglion attenuates orofacial ectopic pain attributed to inferior alveolar nerve injury

This study explores the effects of oxytocin receptor (OXTR) in the trigeminal ganglion (TG) on orofacial neuropathic pain. We demonstrate that OXTR activation in the TG relieves the orofacial ectopic pain as well as inhibits the upregulated expression of calcitonin gene-related peptide (CGRP), IL-1β, and TNFα in the TG and spinal trigeminal nucleus caudalis (SpVc) of rats with inferior alveolar nerve transection. OXTR, a G protein-coupled receptor, has been demonstrated to play a significant role in analgesia after activation by its canonical agonist oxytocin (OXT) in the dorsal root ganglion. However, the role of OXTR in the trigeminal nervous system on the orofacial neuropathic pain is still little known. In the present study, we aimed to investigate the regulation effect and mechanism of OXTR in the TG) and SpVc) on orofacial ectopic pain induced by trigeminal nerve injury. The inferior alveolar nerve (IAN) was transected to establish a ectopic pain model. A behavioral test with electronic von Frey filament demonstrated IAN transection (IANX) evoked mechanical hypersensitivity in the whisker pad from day 1 to at least day 14 after surgery. In addition, administration of OXT (50 and 100 μM) into the TG attenuated the mechanical hypersensitivity induced by IANX, which was reversed by pretreatment with L-368,899 (a selective antagonist of OXTR) into the TG. In addition, immunofluorescence showed the expression of OXTR in neurons in the TG and SpVc. Furthermore, Western blot analysis indicated that the upregulated expression of OXTR, CGRP, IL-1β, and TNFα in the TG and SpVc after IANX was inhibited by the administration of OXT into the TG. And the inhibition effect of OXT on the expression of CGRP, IL-1β, and TNFα was abolished by preapplication of OXTR antagonist L-368,899 into the TG.NEW & NOTEWORTHY This study explores the effects of oxytocin receptor (OXTR) in the trigeminal ganglion (TG) on orofacial neuropathic pain. We demonstrate that OXTR activation in the TG relieves the orofacial ectopic pain as well as inhibits the upregulated expression of calcitonin gene-related peptide, IL-1β, and TNF-α in the TG and spinal trigeminal nucleus caudalis of rats with inferior alveolar nerve transection.

Intranasal oxytocin as a treatment for chronic pelvic pain: A randomized controlled feasibility study

OBJECTIVE

To investigate the effect of intranasal oxytocin on chronic pelvic pain in a randomized, double-blind, within-subject crossover trial. Aims included: (1) determine intranasal oxytocin's effect on pain intensity and pain interference relative to placebo; (2) assess feasibility and acceptability.

METHODS

Women with chronic pelvic pain were recruited from chronic pain and gynecology clinics between September 2017 and December 2018. Pain was recorded at pre-trial screening, and while administering intranasal oxytocin and placebo. Pain and pain-related interference were measured using the Brief Pain Inventory - Short Form. Feasibility and acceptability were measured using validated measures and interviews.

RESULTS

Twenty-one women were randomized with sufficient data available from 12 to permit analyses. Relative to placebo, a 2-week course of oxytocin administration resulted in improvement in pain severity with no effect on pain-related interference. This effect was driven by four women who demonstrated a minimal clinically significant improvement in pain following intranasal oxytocin (no women met this threshold for placebo). Adherence to dosing was excellent and occurrence of adverse effects did not differ between oxytocin and placebo.

CONCLUSION

Intranasal oxytocin may represent an adjuvant analgesic that could result in a minimal clinically significant improvement in pain among one in three women with chronic pelvic pain. Registration: ClinicalTrials.gov (Registration# NCT02888574).

Functional gene networks reveal distinct mechanisms segregating in migraine families

Migraine is the most common neurological disorder worldwide and it has been shown to have complex polygenic origins with a heritability of estimated 40-70%. Both common and rare genetic variants are believed to underlie the pathophysiology of the prevalent types of migraine, migraine with typical aura and migraine without aura. However, only common variants have been identified so far. Here we identify for the first time a gene module with rare mutations through a systems genetics approach integrating RNA sequencing data from brain and vascular tissues likely to be involved in migraine pathology in combination with whole genome sequencing of 117 migraine families. We found a gene module in the visual cortex, based on single nuclei RNA sequencing data, that had increased rare mutations in the migraine families and replicated this in a second independent cohort of 1930 patients. This module was mainly expressed by interneurons, pyramidal CA1, and pyramidal SS cells, and pathway analysis showed association with hormonal signalling (thyrotropin-releasing hormone receptor and oxytocin receptor signalling pathways), Alzheimer's disease pathway, serotonin receptor pathway and general heterotrimeric G-protein signalling pathways. Our results demonstrate that rare functional gene variants are strongly implicated in the pathophysiology of migraine. Furthermore, we anticipate that the results can be used to explain the critical mechanisms behind migraine and potentially improving the treatment regime for migraine patients.

Natural Products and their (Semi-)Synthetic Forms in the Treatment of Migraine: History and Current Status

BACKGROUND

Migraine may be described as a headache with moderate to extreme pain that is often accompanied by incapacitating neurological symptoms. It is estimated that 12% of the world population suffers from migraine. Although a number of drugs have been used for treatment of migraine, most of these are not effective for every patient and may have undesirable side-effects. Thus, there is an enormous unmet need in current migraine therapy for discovering safer and more effective agents.

METHODS

The information summarized in this review was obtained through extensive literature review and search of relevant books and articles with the use of Web of Knowledge and SciVerse Scopus databases.

RESULTS

Greater understanding of the molecular mechanisms underlying the etiopathogenesis of migraine is helpful in identifying novel targets for antimigraine drugs such as cannabinoid, histamine, and melatonin receptors. In the past, natural product-derived constituents have served as an invaluable source of numerous medicinally useful antimigraine agents and it may be expected that further promising drug candidates from natural products will be discovered for antimigraine pharmacotherapy with better efficacy and fewer adverse-effects.

CONCLUSION

The discovery of novel targets in migraine therapy has opened new horizons for compounds that have not been clinically tested or that previously failed in clinical trials as potential antimigraine drugs. Ginkgolide B, melatonin, histamine, oxytocin, various ribosomal peptide toxins, kavalactones, devil's claw-derived compounds, salvinorin A and petasin are among those agents that show considerable promise as novel drugs in migraine prevention and treatment. It is necessary to conduct more research to better understand their antimigraine action, to confirm their effectiveness and safety, and to introduce them into clinical practice.

Oxytocin as a regulatory neuropeptide in the trigeminovascular system: Localization, expression and function of oxytocin and oxytocin receptors

BACKGROUND

Recent clinical findings suggest that oxytocin could be a novel treatment for migraine. However, little is known about the role of this neuropeptide/hormone and its receptor in the trigeminovascular pathway. Here we determine expression, localization, and function of oxytocin and oxytocin receptors in rat trigeminal ganglia and targets of peripheral (dura mater and cranial arteries) and central (trigeminal nucleus caudalis) afferents.

METHODS

The methods include immunohistochemistry, messenger RNA measurements, quantitative PCR, release of calcitonin gene-related peptide and myography of arterial segments.

RESULTS

Oxytocin receptor mRNA was expressed in rat trigeminal ganglia and the receptor protein was localized in numerous small to medium-sized neurons and thick axons characteristic of A∂ sensory fibers. Double immunohistochemistry revealed only a small number of neurons expressing both oxytocin receptors and calcitonin gene-related peptide. In contrast, double immunostaining showed expression of the calcitonin gene-related peptide receptor component receptor activity-modifying protein 1 and oxytocin receptors in 23% of the small cells and in 47% of the medium-sized cells. Oxytocin immunofluorescence was observed only in trigeminal ganglia satellite glial cells. Oxytocin mRNA was below detection limit in the trigeminal ganglia. The trigeminal nucleus caudalis expressed mRNA for both oxytocin and its receptor. K⁺-evoked calcitonin gene-related peptide release from either isolated trigeminal ganglia or dura mater and it was not significantly affected by oxytocin (10 µM). Oxytocin directly constricted cranial arteries ex vivo (pEC₅₀ ∼ 7); however, these effects were inhibited by the vasopressin V_1A antagonist SR49059.

CONCLUSION

Oxytocin receptors are extensively expressed throughout the rat trigeminovascular system and in particular in trigeminal ganglia A∂ neurons and fibers, but no functional oxytocin receptors were demonstrated in the dura and cranial arteries. Thus, circulating oxytocin may act on oxytocin receptors in the trigeminal ganglia to affect nociception transmission. These effects may help explain hormonal influences in migraine and offer a novel way for treatment.

Metabolic Effects of Oxytocin

There is growing evidence that oxytocin (OXT), a hypothalamic hormone well recognized for its effects in inducing parturition and lactation, has important metabolic effects in both sexes. The purpose of this review is to summarize the physiologic effects of OXT on metabolism and to explore its therapeutic potential for metabolic disorders. In model systems, OXT promotes weight loss by decreasing energy intake. Pair-feeding studies suggest that OXT-induced weight loss may also be partly due to increased energy expenditure and/or lipolysis. In humans, OXT appears to modulate both homeostatic and reward-driven food intake, although the observed response depends on nutrient milieu (eg, obese vs. nonobese), clinical characteristics (eg, sex), and experimental paradigm. In animal models, OXT is anabolic to muscle and bone, which is consistent with OXT-induced weight loss occurring primarily via fat loss. In some human observational studies, circulating OXT concentrations are also positively associated with lean mass and bone mineral density. The impact of exogenous OXT on human obesity is the focus of ongoing investigation. Future randomized, placebo-controlled clinical trials in humans should include rigorous, standardized, and detailed assessments of adherence, adverse effects, pharmacokinetics/pharmacodynamics, and efficacy in the diverse populations that may benefit from OXT, in particular those in whom hypothalamic OXT signaling may be abnormal or impaired (eg, individuals with Sim1 deficiency, Prader-Willi syndrome, or craniopharyngioma). Future studies will also have the opportunity to investigate the characteristics of new OXT mimetic peptides and the obligation to consider long-term effects, especially when OXT is given to children and adolescents. (Endocrine Reviews XX: XX - XX, 2020).

Effects of route of administration on oxytocin-induced changes in regional cerebral blood flow in humans

Could nose-to-brain pathways mediate the effects of peptides such as oxytocin (OT) on brain physiology when delivered intranasally? We address this question by contrasting two methods of intranasal administration (a standard nasal spray, and a nebulizer expected to improve OT deposition in nasal areas putatively involved in direct nose-to-brain transport) to intravenous administration in terms of effects on regional cerebral blood flow during two hours post-dosing. We demonstrate that OT-induced decreases in amygdala perfusion, a key hub of the OT central circuitry, are explained entirely by OT increases in systemic circulation following both intranasal and intravenous OT administration. Yet we also provide robust evidence confirming the validity of the intranasal route to target specific brain regions. Our work has important translational implications and demonstrates the need to carefully consider the method of administration in our efforts to engage specific central oxytocinergic targets for the treatment of neuropsychiatric disorders.

The distribution of oxytocin and the oxytocin receptor in rat brain: relation to regions active in migraine

BACKGROUND

Recent work, both clinical and experimental, suggests that the hypothalamic hormone oxytocin (OT) and its receptor (OTR) may be involved in migraine pathophysiology. In order to better understand possible central actions of OT in migraine/headache pathogenesis, we mapped the distribution of OT and OTR in nerve cells and fibers in rat brain with a focus on areas related to migraine attacks and/or shown previously to contain calcitonin gene related peptide (CGRP), another neuropeptide involved in migraine.

METHODS

Distribution of OT and OTR in the adult, rat brain was qualitatively examined with immunohistochemistry using a series of well characterized specific antibodies.

RESULTS

As expected, OT was extensively localized in the cell somas of two hypothalamic nuclei, the supraoptic (SO or SON) and paraventricular nuclei (Pa or PVN). OT also was found in many other regions of the brain where it was localized mainly in nerve fibers. In contrast, OTR staining in the brain was mainly observed in cell somas with very little expression in fibers. The most distinct OTR expression was found in the hippocampus, the pons and the substantia nigra. In some regions of the brain (e.g. the amygdala and the hypothalamus), both OT and OTR were expressed (match). Mismatch between the peptide and its receptor was primarily observed in the cerebral and cerebellar cortex (OT expression) and hippocampus (OTR expression).

CONCLUSIONS

We compared OT/OTR distribution in the CNS with that of CGRP and identified regions related to migraine. In particular, regions suggested as "migraine generators", showed correspondence among the three mappings. These findings suggest central OT pathways may contribute to the role of the hypothalamus in migraine attacks.

Orally administered oxytocin alters brain activation and behaviors of pre-weaning mice

Oxytocin (OXT) regulates adult social behavior and has been implicated in its development. Because mammalian milk contains OXT and we have recently identified OXT receptors (OXTR) in the face and oronasal cavity of pre-weaning mice, we hypothesize that orally applied OXT may impact brain activity and acute behavior in developing mice. Oral OXT may have effects in the absence of sensory stimulation or perhaps by modulating sensory input, such as whisker stimulation. The present study investigates the acute c-Fos response in the paraventricular nucleus of the hypothalamus (PVN) and along whisker sensory processing brain regions (trigeminothalamocortical circuit) to orally applied OXT, compared to saline, with and without whisker stimulation in postnatal day (P) 14 and P21 male and female mice. Acute behavioral responses were also quantified after oral OXT with whisker stimulation in a non-social context. Oral OXT with and without whisker stimulation increased c-Fos activity in the PVN of males and decreased c-Fos in the ventroposterior medial thalamus in both males and females compared to saline. Additionally, oral OXT with whisker stimulation decreased c-Fos activity across whisker sensory processing brain regions in males and females and decreased c-Fos activity in the trigeminal motor nucleus of females. Lastly, oral OXT with whisker stimulation increased males' locomotor behavior and decreased females' oromotor behavior compared to saline-treated controls. These data indicate that orally applied OXT has acute brain and behavioral effects on developing mice. OXT-modulated sensory signals may bias brain and behavior development toward the social world.

Migraine: navigating the hormonal minefield

Migraine affects 959 million people worldwide,1 with the highest prevalence being in women of childbearing age. The interplay between female hormones and migraine can be a challenging area to navigate since issues relating to pregnancy, contraception and the menopause are often out of the neurology comfort zone. This review aims to help the neurologist to manage women with migraine, from menarche to menopause.

Inhibition of nociceptive dural input to the trigeminocervical complex through oxytocinergic transmission

Migraine is a complex brain disorder that involves abnormal activation of the trigeminocervical complex (TCC). Since an increase of oxytocin concentration has been found in cerebrospinal fluid in migrainous patients and intranasal oxytocin seems to relieve migrainous pain, some studies suggest that the hypothalamic neuropeptide oxytocin may play a role in migraine pathophysiology. However, it remains unknown whether oxytocin can interact with the trigeminovascular system at TCC level. The present study was designed to test the above hypothesis in a well-established electrophysiological model of migraine. Using anesthetized rats, we evaluated the effect of oxytocin on TCC neuronal activity in response to dural nociceptive trigeminovascular activation. We found that spinal oxytocin significantly reduced TCC neuronal firing evoked by meningeal electrical stimulation. Furthermore, pretreatment with L-368,899 (a selective oxytocin receptor antagonist, OTR) abolished the oxytocin-induced inhibition of trigeminovascular neuronal responses. This study provides the first direct evidence that oxytocin, probably by OTR activation at TCC level inhibited dural nociceptive-evoked action potential in this complex. Thus, targeting OTR at TCC could represent a new avenue to treat migraine.

Leptin and Associated Mediators of Immunometabolic Signaling: Novel Molecular Outcome Measures for Neurostimulation to Treat Chronic Pain

Chronic pain is a devastating condition affecting the physical, psychological, and socioeconomic status of the patient. Inflammation and immunometabolism play roles in the pathophysiology of chronic pain disorders. Electrical neuromodulation approaches have shown a meaningful success in otherwise drug-resistant chronic pain conditions, including failed back surgery, neuropathic pain, and migraine. A literature review (PubMed, MEDLINE/OVID, SCOPUS, and manual searches of the bibliographies of known primary and review articles) was performed using the following search terms: chronic pain disorders, systemic inflammation, immunometabolism, prediction, biomarkers, metabolic disorders, and neuromodulation for chronic pain. Experimental studies indicate a relationship between the development and maintenance of chronic pain conditions and a deteriorated immunometabolic state mediated by circulating cytokines, chemokines, and cellular components. A few uncontrolled in-human studies found increased levels of pro-inflammatory cytokines known to drive metabolic disorders in chronic pain patients undergoing neurostimulation therapies. In this narrative review, we summarize the current knowledge and possible relationships of available neurostimulation therapies for chronic pain with mediators of central and peripheral neuroinflammation and immunometabolism on a molecular level. However, to address the needs for predictive factors and biomarkers, large-scale databank driven clinical trials are needed to determine the clinical value of molecular profiling.

[New horizons for acute and prophylactic treatments of migraine]

The current treatment of migraine attacks is triptans and NSAIDs, but the calcitonin gene-related peptide (CGRP) has emerged as a key neuropeptide target for migraine therapy. Despite an off target class effect on liver enzymes, two CGRP receptor antagonists, ubrogepant and rimegepant, remain in development, together with a 5-HT_1F receptor agonist (lasmiditan), for which cardiovascular contraindications that limit the utility of triptans do not exist. Importantly, to avoid an excessive use of acute medication with the risk of medication overuse, prophylactic therapeutics are the best choice. To date, monoclonal antibodies which block CGRP actions are on the market all over the world but not yet in France. The research is very active in different directions and targets notably hypothalamic neuropeptides because the hypothalamus hosts many key neuropeptide systems that seem to play a role in migraine physiopathology. These neuropeptides include orexins, oxytocin, neuropeptide Y (NPY) and pituitary adenylate cyclase-activating polypeptide (PACAP). In addition, other promising drugs for the treatment of migraine are nitric oxide synthase inhibitors and acid-sensing ion channel (ASIC) blockers.

Volume of Hypothalamus as a Diagnostic Biomarker of Chronic Migraine

It is believed than hypothalamus (HTH) might be involved in generation of migraine, and evidence from high resolution fMRI reported that the more anterior part of HTH seemed to play an important role in migraine chronification. The current study was aimed to identify the alteration of morphology and resting-state functional connectivity (FC) of the hypothalamus (HTH) in interictal episodic migraine (EM) and chronic migraine (CM). High-resolution structural and resting-state functional magnetic resonance images were acquired in 18 EM patients, 16 CM patients, and 21 normal controls (NC). The volume of HTH was calculated and voxel-based morphometry (VBM) was performed over the whole HTH. Receiver operating characteristics (ROC) curve analysis was applied to evaluate the diagnostic efficacy of HTH volume. Correlation analyses with clinical variables were performed and FC maps were generated for positive HTH regions according to VBM comparison. The volume of the HTH significantly decreased in both EM and CM patients compared with NC. The cut-off volume of HTH as 1.429 ml had a good diagnostic accuracy for CM with sensitivity of 81.25% and specificity of 100%. VBM analyses identified volume reduction of posterior HTH in EM vs. NC which was negatively correlated with headache frequency. The posterior HTH presented decreased FC with the left inferior temporal gyrus (Brodmann area 20) in EM. Decreased volume of anterior HTH was identified in CM vs. NC and CM vs. EM which was positively correlated with headache frequency in CM. The anterior HTH presented increased FC with the right anterior orbital gyrus (AOrG) (Brodmann area 11) in CM compared with NC and increased FC with the right medial orbital gyrus (MOrG) (Brodmann area 11) in CM compared with EM. Our study provided evidence of structural plasticity and FC changes of HTH in the pathogensis of migraine generation and chronification, supporting potential therapeutic target toward the HTH and its peptide.