Migraine-relevant sex-dependent activation of mouse meningeal afferents by TRPM3 agonists

Background Migraine is a common brain disorder that predominantly affects women. Migraine pain seems mediated by the activation of mechanosensitive channels in meningeal afferents. Given the role of transient receptor potential melastatin 3 (TRPM3) channels in mechanical activation, as well as hormonal regulation, these channels may play a role in the sex difference in migraine. Therefore, we investigated whether nociceptive firing induced by TRPM3 channel agonists in meningeal afferents was different between male and female mice. In addition, we assessed the relative contribution of mechanosensitive TRPM3 channels and that of mechanosensitive Piezo1 channels and transient receptor potential vanilloid 1 (TRPV1) channels to nociceptive firing relevant to migraine in both sexes. Methods Ten- to 13-week-old male and female wildtype (WT) C57BL/6 J mice were used. Nociceptive spikes were recorded directly from nerve terminals in the meninges in the hemiskull preparations. Results Selective agonists of TRPM3 channels profoundly activated peripheral trigeminal nerve fibres in mouse meninges. A sex difference was observed for nociceptive firing induced by either PregS or CIM0216, both agonists of TRPM3 channels, with the induced firing being particularly prominent for female mice. Application of Yoda1, an agonist of Piezo1 channels, or capsaicin activating TRPV1 channels, although also leading to increased nociceptive firing of meningeal fibres, did not reveal a sex difference. Cluster analyses of spike activities indicated a massive and long-lasting activation of TRPM3 channels with preferential induction of large-amplitude spikes in female mice. Additional spectral analysis revealed ​a dominant contribution of spiking activity in the α- and β-ranges following TRPM3 agonists in female mice. Conclusions Together, we revealed a specific mechanosensitive profile of nociceptive firing in females and suggest TRPM3 channels as a potential novel candidate for the generation of migraine pain, with particular relevance to females.

PACAP-PAC1 Receptor Inhibition is Effective in Models of Opioid-Induced Medication Overuse Headache

Opioids are regularly prescribed for migraine and can result in medication overuse headache and dependence. We recently showed that pituitary adenylate cyclase activating polypeptide (PACAP) is upregulated following opioid administration or in a model of chronic migraine. The goal of this study was to determine if PACAP was a link between opioid use and headache chronification. We tested the effect of PACAP-PAC1 receptor inhibition in novel models of opioid-exacerbated migraine pain and aura; and examined the co-expression between mu opioid receptor (MOR), PAC1, and PACAP in headache-associated brain and peripheral regions.To model opioid exacerbated migraine pain, mice were injected daily with morphine (10 mg/kg) or vehicle for 11 days. On days 3,5,7,9, and 11 they also received the known human migraine trigger nitroglycerin (0.1 mg/kg) or vehicle. To model opioid exacerbated aura, mice were treated with vehicle or morphine twice daily for 4 days (20 mg/kg on days 1-3, 40 mg/kg on day 4), a well-established paradigm for causing opioid-induced hyperalgesia. On day 5 they underwent cortical spreading depression, a physiological correlate of migraine aura. The effect of the PAC1 inhibitor, M65 (0.1 mg/kg), was tested in these models. Fluorescent in situ hybridization was used to investigate the expression of MOR, PAC1, and PACAP.Only mice treated with combined morphine and nitroglycerin developed chronic cephalic allodynia (n=18/group). M65 reversed this hypersensitivity (n=9/group). Morphine significantly increased the number of CSD events (n=8-9/group); and M65 decreased this exacerbation by morphine (n=8-12/group). PAC1 and/or PACAP were highly co-expressed with MOR, and varied by region (n=6/group). MOR and PACAP were co-expressed in the trigeminal ganglia, while MOR and PAC1 receptor showed near complete overlap in the trigeminal nucleus caudalis and periaqueductal gray. The cortex showed similar cellular co-expression between MOR-PACAP and MOR-PAC1.These results show that opioids facilitate the transition to chronic headache through induction of PACAPergic mechanisms. Antibodies or pharmacological agents targeting PACAP or PAC1 receptor may be particularly beneficial for the treatment of opioid-induced medication overuse headache.

CGRP Signals from Endosomes of Schwann Cells to Elicit Migraine Pain

Efficacy of monoclonal antibodies against calcitonin gene-related peptide (CGRP) or its receptor (calcitonin receptor-like receptor/receptor activity modifying protein-1, CLR/RAMP1) implicates peripherally-released CGRP in migraine pain. However, the site and mechanism of CGRP-evoked migraine pain remain unknown. By cell-selective RAMP1 gene deletion, we reveal that CGRP released from mouse cutaneous trigeminal fibers targets CLR/RAMP1 on surrounding Schwann cells to evoke periorbital mechanical allodynia. CLR/RAMP1 activation in human and mouse Schwann cells generates long-lasting signals from endosomes that evoke cAMP-dependent formation of NO. NO, by gating Schwann cell transient receptor potential ankyrin 1 (TRPA1), releases ROS, which in a feed-forward manner sustain allodynia via nociceptor TRPA1. When encapsulated into nanoparticles that release cargo in acidified endosomes, a CLR/RAMP1 antagonist provides superior inhibition of CGRP signaling and allodynia in mice. The CGRP-mediated neuronal/Schwann cell pathway is critical to mediate allodynia associated with neurogenic inflammation, thus contributing to the pro-migraine action of CGRP.

Reduction in migraine pain intensity in patients treated with erenumab: A post hoc analysis of two pivotal randomized studies

Background Erenumab (erenumab-aooe in the US) effectively reduces monthly migraine days in episodic and chronic migraine. This traditional outcome does not capture the intensity of headache pain on days with migraine. Methods This post hoc analysis of two pivotal randomized, placebo-controlled studies in patients with episodic migraine and chronic migraine examined the effect of erenumab 70 and 140 mg on migraine pain. Cumulative monthly migraine pain intensity is the sum of the peak pain intensity scores (0 = no migraine to 3 = migraine day with severe pain) on migraine days. Change from baseline in cumulative monthly migraine pain and average monthly pain intensity was assessed over months 4 to 6 for episodic migraine and month 3 for chronic migraine; change in average monthly pain intensity was assessed among monthly migraine days responders/non-responders. Results Efficacy analysis included 946 patients for the episodic migraine study and 656 patients for the chronic migraine study. Cumulative monthly migraine pain decreased significantly with erenumab versus placebo ( p < 0.001, for episodic migraine and chronic migraine). In addition, monthly average migraine pain intensity decreased significantly with erenumab versus placebo for episodic migraine ( p < 0.01); decreases were non-significant for chronic migraine. In comparison with placebo-treated patients, a greater proportion of erenumab-treated patients were pain intensity responders regardless of threshold used. Episodic migraine and chronic migraine patients with a ≥50% reduction in monthly migraine days (responders) had a greater reduction in monthly average pain intensity than non-responders. Conclusions Erenumab reduced cumulative monthly migraine pain in episodic migraine and chronic migraine patients and significantly reduced monthly average migraine pain in episodic migraine, demonstrating treatment benefit beyond reduction in migraine frequency. Clinical Trial Registration: ClinicalTrials.gov, NCT02456740; ClinicalTrials.gov, NCT02066415

Migraine and neuroinflammation: the inflammasome perspective

Background Neuroinflammation has an important role in the pathophysiology of migraine, which is a complex neuro-glio-vascular disorder. The main aim of this review is to highlight findings of cortical spreading depolarization (CSD)-induced neuroinflammatory signaling in brain parenchyma from the inflammasome perspective. In addition, we discuss the limited data of the contribution of inflammasomes to other aspects of migraine pathophysiology, foremost the activation of the trigeminovascular system and thereby the generation of migraine pain. Main body Inflammasomes are signaling multiprotein complexes and key components of the innate immune system. Their activation causes the production of inflammatory cytokines that can stimulate trigeminal neurons and are thus relevant to the generation of migraine pain. The contribution of inflammasome activation to pain signaling has attracted considerable attention in recent years. Nucleotide-binding domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) is the best characterized inflammasome and there is emerging evidence of its role in a variety of inflammatory pain conditions, including migraine. In this review, we discuss, from an inflammasome point of view, cortical spreading depolarization (CSD)-induced neuroinflammatory signaling in brain parenchyma, the connection with genetic factors that make the brain vulnerable to CSD, and the relation of the inflammasome with diseases that are co-morbid with migraine, including stroke, epilepsy, and the possible links with COVID-19 infection. Conclusion Neuroinflammatory pathways, specifically those involving inflammasome proteins, seem promising candidates as treatment targets, and perhaps even biomarkers, in migraine.

Determining 5HT7R’s Involvement in Modifying the Antihyperalgesic Effects of Electroacupuncture on Rats With Recurrent Migraine

Electroacupuncture (EA) is widely used in clinical practice to relieve migraine pain. 5-HT7 receptor (5-HT7R) has been reported to play an excitatory role in neuronal systems and regulate hyperalgesic pain and neurogenic inflammation. 5-HT7R could influence phosphorylation of protein kinase A (PKA)- or extracellular signal-regulated kinase1/2 (ERK1/2)-mediated signaling pathways, which mediate sensitization of nociceptive neurons via interacting with cyclic adenosine monophosphate (cAMP). In this study, we evaluated the role of 5-HT7R in the antihyperalgesic effects of EA and the underlying mechanism through regulation of PKA and ERK1/2 in trigeminal ganglion (TG) and trigeminal nucleus caudalis (TNC). Hyperalgesia was induced in rats with dural injection of inflammatory soup (IS) to cause meningeal neurogenic inflammatory pain. Electroacupuncture was applied for 15 min every other day before IS injection. Von Frey filaments, tail-flick, hot-plate, and cold-plated tests were used to evaluate the mechanical and thermal hyperalgesia. Neuronal hyperexcitability in TNC was studied by an electrophysiological technique. The 5-HT7R antagonist (SB269970) or 5-HT7R agonist (AS19) was administered intrathecally before each IS application at 2-day intervals during the 7-day injection protocol. The changes in 5-HT7R and 5-HT7R-associated signaling pathway were examined by real-time polymerase chain reaction (RT-PCR), Western blot, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA) analyses. When compared with IS group, mechanical and thermal pain thresholds of the IS + EA group were significantly increased. Furthermore, EA prevented the enhancement of both spontaneous activity and evoked responses of second-order trigeminovascular neurons in TNC. Remarkable decreases in 5-HT7R mRNA expression and protein levels were detected in the IS + EA group. More importantly, 5-HT7R agonist AS19 impaired the antihyperalgesic effects of EA on p-PKA and p-ERK1/2. Injecting 5-HT7R antagonist SB-269970 into the intrathecal space of IS rats mimicked the effects of EA antihyperalgesia and inhibited p-PKA and p-ERK1/2. Our findings indicate that 5-HT7R mediates the antihyperalgesic effects of EA on IS-induced migraine pain by regulating PKA and ERK1/2 in TG and TNC.

Deciphering in silico the Role of Mutated NaV1.1 Sodium Channels in Enhancing Trigeminal Nociception in Familial Hemiplegic Migraine Type 3

Familial hemiplegic migraine type 3 (FHM3) is caused by gain-of-function mutations in the SCN1A gene that encodes the α1 subunit of voltage-gated NaV1.1 sodium channels. The high level of expression of NaV1.1 channels in peripheral trigeminal neurons may lead to abnormal nociceptive signaling thus contributing to migraine pain. NaV1.1 dysfunction is relevant also for other neurological disorders, foremost epilepsy and stroke that are comorbid with migraine. Here we used computer modeling to test the functional role of FHM3-mutated NaV1.1 channels in mechanisms of trigeminal pain. The activation of Aδ-fibers was studied for two algogens, ATP and 5-HT, operating through P2X3 and 5-HT3 receptors, respectively, at trigeminal nerve terminals. In WT Aδ-fibers of meningeal afferents, NaV1.1 channels efficiently participate in spike generation induced by ATP and 5-HT supported by NaV1.6 channels. Of the various FHM3 mutations tested, the L263V missense mutation, with a longer activation state and lower activation voltage, resulted in the most pronounced spiking activity. In contrast, mutations that result in a loss of NaV1.1 function largely reduced firing of trigeminal nerve fibers. The combined activation of P2X3 and 5-HT3 receptors and branching of nerve fibers resulted in very prolonged and high-frequency spiking activity in the mutants compared to WT. We identified, in silico, key determinants of long-lasting nociceptive activity in FHM3-mutated Aδ-fibers that naturally express P2X3 and 5-HT3 receptors and suggest mutant-specific correction options. Modeled trigeminal nerve firing was significantly higher for FHM3 mutations, compared to WT, suggesting that pronounced nociceptive signaling may contribute to migraine pain.

Intractable Migraine

Migraine pain, particularly if long-lasting and accompanied by nausea can be disabling. Effective acute therapy includes intravenous neuroleptics and other medications.