The CGRP receptor antagonist BIBN4096 inhibits prolonged meningeal afferent activation evoked by brief local K+ stimulation but not cortical spreading depression-induced afferent sensitization

Upregulation of the neuropeptide receptor calcitonin receptor-like in the spinal cord via MLL2 in a mouse model of paclitaxel-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a prevalent and severe side effect affecting cancer patients undergoing paclitaxel treatment. Growing evidence underscores the pivotal role of calcitonin-related peptide (CGRP) in the development of CIPN. Repeated administration of paclitaxel induces alterations in CGRP release from sensory neurons within the dorsal root ganglia (DRG). The density of the CGRP receptor is most prominent in the dorsal horn of the spinal cord, where it overlaps with the distribution of CGRP. However, the impact of chemotherapy treatment on expression of the CGRP receptor in the spinal cord remains unclear, as well as the potential therapeutic benefits of a CGRP receptor antagonist in an animal model of CIPN. Using a mouse model of paclitaxel-induced mechanical hypersensitivity, we show upregulation of Calcitonin receptor-like receptor (Calcrl) mRNA expression in the spinal cord, an event that occurred in association with upregulation of the H3K4 methyltransferase MLL2. This effect of repeated paclitaxel administration was also linked to an increase in the recruitment of MLL2, thereby enhancing levels of the active mark H3K4me2 at the Calcrl promoter. Furthermore, administration of the CGRP receptor antagonist BIBN4096 mitigated mechanical and cold hypersensitivity in paclitaxel-treated mice. Together, these observations suggest the CGRP receptor in the spinal cord as a potential target for reducing paclitaxel-induced neuropathic pain in animal models.

The Multi-targeted Effect of Fascaplysin on the Proliferation and Dedifferentiation of Schwann Cells Inhibits Peripheral Nerve Degeneration by Blocking CDK4/6 and Androgen Receptor

Peripheral neurodegenerative diseases induced by irreversible peripheral nerve degeneration (PND), such as diabetic peripheral neuropathy, have a high prevalence worldwide and reduce the quality of life. However, there is no agent effective against the irreversible PND. After peripheral nerve injury, Schwann cells play an important role in regulating PND. However, because PND involves multiple biochemical events in Schwann cells, a one-drug-single-target therapeutic strategy is not feasible for PND. Here, we suggested that fascaplysin (Fas), a compound with multiple targets (CDK4/6), could overcome these problems. Fas exerted a significant inhibitory effect on axonal degradation, demyelination, and Schwann cell proliferation and dedifferentiation during in vitro and ex vivo PND. To discover the most likely novel target for PND, a chemo-bioinformatics analysis predicted the other on-targets of Fas and identified androgen receptor (AR) which were involved in Schwann cell differentiation and proliferation. AR interacted with Fas, and nuclear import of the AR/Fas complex was inhibited in Schwann cells, altering the expression patterns of transcription factors during PND. Therefore, Fas may have therapeutic potential for irreversible peripheral neurodegenerative diseases.

Novel insight into atogepant mechanisms of action in migraine prevention

Recently, we showed that while atogepant-a small-molecule calcitonin gene-related peptide (CGRP) receptor antagonist-does not fully prevent activation of meningeal nociceptors, it significantly reduces a cortical spreading depression (CSD)-induced early response probability in C fibres and late response probability in Aδ fibres. The current study investigates atogepant effect on CSD-induced activation and sensitization of high threshold (HT) and wide dynamic range (WDR) central dura-sensitive trigeminovascular neurons. In anaesthetized male rats, single-unit recordings were used to assess effects of atogepant (5 mg/kg) versus vehicle on CSD-induced activation and sensitization of HT and WDR trigeminovascular neurons. Single cell analysis of atogepant pretreatment effects on CSD-induced activation and sensitization of central trigeminovascular neurons in the spinal trigeminal nucleus revealed the ability of this small molecule CGRP receptor antagonist to prevent activation and sensitization of nearly all HT neurons (8/10 versus 1/10 activated neurons in the control versus treated groups, P = 0.005). In contrast, atogepant pretreatment effects on CSD-induced activation and sensitization of WDR neurons revealed an overall inability to prevent their activation (7/10 versus 5/10 activated neurons in the control versus treated groups, P = 0.64). Unexpectedly however, in spite of atogepant's inability to prevent activation of WDR neurons, it prevented their sensitization (as reflected their responses to mechanical stimulation of the facial receptive field before and after the CSD). Atogepant' ability to prevent activation and sensitization of HT neurons is attributed to its preferential inhibitory effects on thinly myelinated Aδ fibres. Atogepant's inability to prevent activation of WDR neurons is attributed to its lesser inhibitory effects on the unmyelinated C fibres. Molecular and physiological processes that govern neuronal activation versus sensitization can explain how reduction in CGRP-mediated slow but not glutamate-mediated fast synaptic transmission between central branches of meningeal nociceptors and nociceptive neurons in the spinal trigeminal nucleus can prevent their sensitization but not activation.

Unraveling the interplay of neuroinflammatory signaling between parenchymal and meningeal cells in migraine headache

BACKGROUND

The initiation of migraine headaches and the involvement of neuroinflammatory signaling between parenchymal and meningeal cells remain unclear. Experimental evidence suggests that a cascade of inflammatory signaling originating from neurons may extend to the meninges, thereby inducing neurogenic inflammation and headache. This review explores the role of parenchymal inflammatory signaling in migraine headaches, drawing upon recent advancements. BODY: Studies in rodents have demonstrated that sterile meningeal inflammation can stimulate and sensitize meningeal nociceptors, culminating in headaches. The efficacy of relatively blood-brain barrier-impermeable anti-calcitonin gene-related peptide antibodies and triptans in treating migraine attacks, both with and without aura, supports the concept of migraine pain originating in meninges. Additionally, PET studies utilizing inflammation markers have revealed meningeal inflammatory activity in patients experiencing migraine with aura, particularly over the occipital cortex generating visual auras. The parenchymal neuroinflammatory signaling involving neurons, astrocytes, and microglia, which eventually extends to the meninges, can link non-homeostatic perturbations in the insensate brain to pain-sensitive meninges. Recent experimental research has brought deeper insight into parenchymal signaling mechanisms: Neuronal pannexin-1 channels act as stress sensors, initiating the inflammatory signaling by inflammasome formation and high-mobility group box-1 release in response to transient perturbations such as cortical spreading depolarization (CSD) or synaptic metabolic insufficiency caused by transcriptional changes induced by migraine triggers like sleep deprivation and stress. After a single CSD, astrocytes respond by upregulating the transcription of proinflammatory enzymes and mediators, while microglia are involved in restoring neuronal structural integrity; however, repeated CSDs may prompt microglia to adopt a pro-inflammatory state. Transcriptional changes from pro- to anti-inflammatory within 24 h may serve to dampen the inflammatory signaling. The extensive coverage of brain surface and perivascular areas by astrocyte endfeet suggests their role as an interface for transporting inflammatory mediators to the cerebrospinal fluid to contribute to meningeal nociception.

CONCLUSION

We propose that neuronal stress induced by CSD or synaptic activity-energy mismatch may initiate a parenchymal inflammatory signaling cascade, transmitted to the meninges, thereby triggering lasting headaches characteristic of migraine, with or without aura. This neuroinflammatory interplay between parenchymal and meningeal cells points to the potential for novel targets for migraine treatment and prophylaxis.

Meningeal P2X7 Signaling Mediates Migraine-Related Intracranial Mechanical Hypersensitivity

Cortical spreading depolarization (CSD) is a key pathophysiological event that underlies visual and sensory auras in migraine. CSD is also thought to drive the headache phase in migraine by promoting the activation and mechanical sensitization of trigeminal primary afferent nociceptive neurons that innervate the cranial meninges. The factors underlying meningeal nociception in the wake of CSD remain poorly understood but potentially involve the parenchymal release of algesic mediators and damage-associated molecular patterns, particularly ATP. Here, we explored the role of ATP-P2X purinergic receptor signaling in mediating CSD-evoked meningeal afferent activation and mechanical sensitization. Male rats were subjected to a single CSD episode. In vivo, extracellular single-unit recording was used to measure meningeal afferent ongoing activity changes. Quantitative mechanical stimuli using a servomotor force-controlled stimulator assessed changes in the afferent's mechanosensitivity. Manipulation of meningeal P2X receptors was achieved via local administration of pharmacological agents. Broad-spectrum P2X receptor inhibition, selective blockade of the P2X7 receptor, and its related Pannexin 1 channel suppressed CSD-evoked afferent mechanical sensitization but did not affect the accompanying afferent activation response. Surprisingly, inhibition of the pronociceptive P2X2/3 receptor did not affect the activation or sensitization of meningeal afferents post-CSD. P2X7 signaling underlying afferent mechanosensitization was localized to the meninges and did not affect CSD susceptibility. We propose that meningeal P2X7 and Pannexin 1 signaling, potentially in meningeal macrophages or neutrophils, mediates the mechanical sensitization of meningeal afferents, which contributes to migraine pain by exacerbating the headache during normally innocuous physical activities.SIGNIFICANCE STATEMENT Activation and sensitization of meningeal afferents play a key role in migraine headache, but the underlying mechanisms remain unclear. Here, using a rat model of migraine with aura involving cortical spreading depolarization (CSD), we demonstrate that meningeal purinergic P2X7 signaling and its related Pannexin 1 pore, but not nociceptive P2X2/3 receptors, mediate prolonged meningeal afferent sensitization. Additionally, we show that meningeal P2X signaling does not contribute to the increased afferent ongoing activity in the wake of CSD. Our finding points to meningeal P2X7 signaling as a critical mechanism underlying meningeal nociception in migraine, the presence of distinct mechanisms underlying the activation and sensitization of meningeal afferents in migraine, and highlight the need to target both processes for effective migraine therapy.

Meningeal Mechanisms and the Migraine Connection

Migraine is a complex neurovascular pain disorder linked to the meninges, a border tissue innervated by neuropeptide-containing primary afferent fibers chiefly from the trigeminal nerve. Electrical or mechanical stimulation of this nerve surrounding large blood vessels evokes headache patterns as in migraine, and the brain, blood, and meninges are likely sources of headache triggers. Cerebrospinal fluid may play a significant role in migraine by transferring signals released from the brain to overlying pain-sensitive meningeal tissues, including dura mater. Interactions between trigeminal afferents, neuropeptides, and adjacent meningeal cells and tissues cause neurogenic inflammation, a critical target for current prophylactic and abortive migraine therapies. Here we review the importance of the cranial meninges to migraine headaches, explore the properties of trigeminal meningeal afferents, and briefly review emerging concepts, such as meningeal neuroimmune interactions, that may one day prove therapeutically relevant.

Meningeal P2X7 signaling mediates migraine-related intracranial mechanical hypersensitivity

Cortical spreading depolarization (CSD) is a key pathophysiological event that underlies visual and sensory auras in migraine. CSD is also thought to drive the headache phase in migraine by promoting the activation and mechanical sensitization of trigeminal primary afferent nociceptive neurons that innervate the cranial meninges. The factors underlying meningeal nociception in the wake of CSD remain poorly understood but potentially involve the parenchymal release of algesic mediators and damage-associated molecular patterns, particularly ATP. Here, we explored the role of ATP-P2X purinergic receptor signaling in mediating CSD-evoked meningeal afferent activation and mechanical sensitization. Male rats were subjected to a single CSD episode. In vivo, extracellular single-unit recording was used to measure meningeal afferent ongoing activity changes. Quantitative mechanical stimuli using a servomotor force-controlled stimulator assessed changes in the afferent's mechanosensitivity. Manipulation of meningeal P2X receptors was achieved via local administration of pharmacological agents. Broad-spectrum P2X receptor inhibition, selective blockade of the P2X7 receptor, and its related pannexin 1 channel suppressed CSD-evoked afferent mechanical sensitization but did not affect the accompanying afferent activation response. Surprisingly, inhibition of the pronociceptive P2X2/3 receptor did not affect the activation or sensitization of meningeal afferents post-CSD. P2X7 signaling underlying afferent mechanosensitization was localized to the meninges and did not affect CSD susceptibility. We propose that meningeal P2X7 and Pannexin 1 signaling, potentially in meningeal macrophages or neutrophils, mediates the mechanical sensitization of meningeal afferents, which contributes to migraine pain by exacerbating the headache during normally innocuous physical activities.

Significance Statement

Activation and sensitization of meningeal afferents play a key role in migraine headache, but the underlying mechanisms remain unclear. Here, using a rat model of migraine with aura involving cortical spreading depolarization (CSD), we demonstrate that meningeal purinergic P2X7 signaling and its related Pannexin 1 pore, but not nociceptive P2X2/3 receptors, mediate prolonged meningeal afferent sensitization. Additionally, we show that meningeal P2X signaling does not contribute to the increased afferent ongoing activity in the wake of CSD. Our finding points to meningeal P2X7 signaling as a critical mechanism underlying meningeal nociception in migraine, the presence of distinct mechanisms underlying the activation and sensitization of meningeal afferents in migraine, and highlight the need to target both processes for effective migraine therapy.

Potent dual MAGL/FAAH inhibitor AKU-005 engages endocannabinoids to diminish meningeal nociception implicated in migraine pain

BACKGROUND

Engaging the endocannabinoid system through inhibition of monoacylglycerol lipase (MAGL) and fatty acid amide hydrolase (FAAH), degrading endocannabinoids (endoCBs) 2-arachidonoylglycerol (2-AG) and anandamide (AEA), was proposed as a promising approach to ameliorate migraine pain. However, the activity of MAGL and FAAH and action of endoCB on spiking activity of meningeal afferents, from which migraine pain originates, has not been explored thus far. Therefore, we here explored the analgesic effects of endoCB enhancement in rat and human meningeal tissues.

METHODS

Both MAGL and FAAH activity and local 2-AG and AEA levels were measured by activity-based protein profiling (ABPP) and LC-MS/MS, respectively, in rat meninges obtained from hemiskulls of P38-P40 Wistar rats and human meninges from elderly patients undergoing non-migraine related neurosurgery. The action on endoCBs upon administration of novel dual MAGL/FAAH inhibitor AKU-005 on meningeal afferents excitability was tested by investigating paired KCl-induced spiking and validation with local (co-)application of either AEA or 2-AG. Finally, the specific TRPV1 agonist capsaicin and blocker capsazepine were tested.

RESULTS

The basal level of 2-AG exceeded that of AEA in rat and human meninges. KCl-induced depolarization doubled the level of AEA. AKU-005 slightly increased spontaneous spiking activity whereas the dual MAGL/FAAH inhibitor significantly decreased excitation of nerve fibres induced by KCl. Similar inhibitory effects on meningeal afferents were observed with local applications of 2-AG or AEA. The action of AKU-005 was reversed by CB1 antagonist AM-251, implying CB1 receptor involvement in the anti-nociceptive effect. The inhibitory action of AEA was also reversed by AM-251, but not with the TRPV1 antagonist capsazepine. Data cluster analysis revealed that both AKU-005 and AEA largely increased long-term depression-like meningeal spiking activity upon paired KCl-induced spiking.

CONCLUSIONS

In the meninges, high anti-nociceptive 2-AG levels can tonically counteract meningeal signalling, whereas AEA can be engaged on demand by local depolarization. AEA-mediated anti-nociceptive effects through CB1 receptors have therapeutic potential. Together with previously detected MAGL activity in trigeminal ganglia, dual MAGL/FAAH inhibitor AKU-005 appears promising as migraine treatment.

Atogepant - an orally-administered CGRP antagonist - attenuates activation of meningeal nociceptors by CSD

BACKGROUND

This study investigated the mechanism of action of atogepant, a small-molecule CGRP receptor antagonist recently approved for the preventive treatment of episodic migraine, by assessing its effect on activation of mechanosensitive C- and Aδ-meningeal nociceptors following cortical spreading depression.

METHODS

Single-unit recordings of trigeminal ganglion neurons (32 Aδ and 20 C-fibers) innervating the dura was used to document effects of orally administered atogepant (5 mg/kg) or vehicle on cortical spreading depression-induced activation in anesthetized male rats.

RESULTS

Bayesian analysis of time effects found that atogepant did not completely prevent the activation of nociceptors at the tested dose, but it significantly reduced response amplitude and probability of response in both the C- and the Aδ-fibers at different time intervals following cortical spreading depression induction. For C-fibers, the reduction in responses was significant in the early phase (first hour), but not delayed phase of activation, whereas in Aδ-fibers, significant reduction in activation was apparent in the delayed phase (second and third hours) but not early phase of activation.

CONCLUSIONS

These findings identify differences between the actions of atogepant, a small molecule CGRP antagonist (partially inhibiting both Aδ and C-fibers) and those found previously for fremanezumab, a CGRP-targeted antibody (inhibiting Aδ fibers only) and onabotulinumtoxinA (inhibiting C-fibers only)- suggesting that these agents differ in their mechanisms for the preventive treatment of migraine.

Parenchymal neuroinflammatory signaling and dural neurogenic inflammation in migraine

Background

Pain is generally concomitant with an inflammatory reaction at the site where the nociceptive fibers are activated. Rodent studies suggest that a sterile meningeal inflammatory signaling cascade may play a role in migraine headache as well. Experimental studies also suggest that a parenchymal inflammatory signaling cascade may report the non-homeostatic conditions in brain to the meninges to induce headache. However, how these signaling mechanisms function in patients is unclear and debated. Our aim is to discuss the role of inflammatory signaling in migraine pathophysiology in light of recent developments.

Body

Rodent studies suggest that a sterile meningeal inflammatory reaction can be initiated by release of peptides from active trigeminocervical C-fibers and stimulation of resident macrophages and dendritic/mast cells. This inflammatory reaction might be needed for sustained stimulation and sensitization of meningeal nociceptors after initial activation along with ganglionic and central mechanisms. Most migraines likely have cerebral origin as suggested by prodromal neurologic symptoms. Based on rodent studies, a parenchymal inflammatory signaling cascade has been proposed as a potential mechanism linking cortical spreading depolarization (CSD) to meningeal nociception. A recent PET/MRI study using a sensitive inflammation marker showed the presence of meningeal inflammatory activity in migraine with aura patients over the occipital cortex generating the visual aura. These studies also suggest the presence of a parenchymal inflammatory activity, supporting the experimental findings. In rodents, parenchymal inflammatory signaling has also been shown to be activated by migraine triggers such as sleep deprivation without requiring a CSD because of the resultant transcriptional changes, predisposing to inadequate synaptic energy supply during intense excitatory transmission. Thus, it may be hypothesized that neuronal stress created by either CSD or synaptic activity-energy mismatch could both initiate a parenchymal inflammatory signaling cascade, propagating to the meninges, where it is converted to a lasting headache with or without aura.

Conclusion

Experimental studies in animals and emerging imaging findings from patients warrant further research to gain deeper insight to the complex role of inflammatory signaling in headache generation in migraine.

Astrocytes mediate migraine-related intracranial meningeal mechanical hypersensitivity

ABSTRACT

The genesis of the headache phase in migraine with aura is thought to be mediated by cortical spreading depression (CSD) and the subsequent activation and sensitization of primary afferent neurons that innervate the intracranial meninges and their related large vessels. Yet, the exact mechanisms underlying this peripheral meningeal nociceptive response remain poorly understood. We investigated the relative contribution of cortical astrocytes to CSD-evoked meningeal nociception using extracellular single-unit recording of meningeal afferent activity and 2-photon imaging of cortical astrocyte calcium activity, in combination with 2 pharmacological approaches to inhibit astrocytic function. We found that fluoroacetate and l-α-aminoadipate, which inhibit astrocytes through distinct mechanisms, suppressed CSD-evoked afferent mechanical sensitization, but did not affect afferent activation. Pharmacological inhibition of astrocytic function, which ameliorated meningeal afferents' sensitization, reduced basal astrocyte calcium activity but had a minimal effect on the astrocytic calcium wave during CSD. We propose that calcium-independent signaling in cortical astrocytes plays an important role in driving the sensitization of meningeal afferents and the ensuing intracranial mechanical hypersensitivity in migraine with aura.

Combined onabotulinumtoxinA/atogepant treatment blocks activation/sensitization of high-threshold and wide-dynamic range neurons

Background

OnabotulinumtoxinA and agents that block calcitonin gene‒receptor peptide action have both been found to have anti-migraine effects, but they inhibit different populations of meningeal nociceptors. We therefore tested the effects of combined treatment with onabotulinumtoxinA and the calcitonin gene‒receptor peptide antagonist atogepant on activation/sensitization of trigeminovascular neurons by cortical spreading depression.

Material and methods

Single-unit recordings were obtained of high-threshold and wide-dynamic-range neurons in the spinal trigeminal nucleus, and cortical spreading depression was then induced in anesthetized rats that had received scalp injections of onabotulinumtoxinA 7 days earlier and intravenous atogepant infusion 1 h earlier. The control group received scalp saline injections and intravenous vehicle infusion.

Results

OnabotulinumtoxinA/atogepant pretreatment prevented cortical spreading depression-induced activation and sensitization in both populations (control: Activation in 80% of high-threshold and 70% of wide-dynamic-range neurons, sensitization in 80% of high-threshold and 60% of wide-dynamic-range neurons; treatment: activation in 10% of high-threshold and 0% of wide-dynamic-range neurons, sensitization in 0% of high-threshold and 5% of wide-dynamic-range neurons).

Discussion

We propose that the robust inhibition of high-threshold and wide-dynamic-range neurons by the combination treatment was achieved through dual blockade of the Aδ and C classes of meningeal nociceptors. Combination therapy that inhibits meningeal C-fibers and prevents calcitonin gene‒receptor peptide from activating its receptors on Aδ-meningeal nociceptors may be more effective than a monotherapy in reducing migraine days per month in patients with chronic migraine.

Activation of Peripheral and Central Trigeminovascular Neurons by Seizure: Implications for Ictal and Postictal Headache

An epileptic seizure can trigger a headache during (ictal) or after (postictal) the termination of the event. Little is known about the pathophysiology of seizure-induced headaches. In the current study, we determined whether a seizure can activate nociceptive pathways that carry pain signals from the meninges to the spinal cord, and if so, to what extent and through which classes of peripheral and central neurons. To achieve these goals, we used single-unit recording techniques and an established animal model of seizure (picrotoxin) to determine the effects of epileptic seizure on the activity of trigeminovascular Aδ-, C-, wide-dynamic range, and high-threshold neurons in male and female rats. Occurrence of seizure activated 54%, 50%, 68%, and 39% of the Aδ-, C-, wide-dynamic range, and high-threshold neurons, respectively. Regardless of their class, activated neurons exhibited a twofold to fourfold increase in their firing, which started immediately (1 min) or up to 90 min after seizure initiation, and lasted as short as 10 min or as long as 120 min. Administration of lidocaine to the dura prevented activation of all neuronal classes but not the initiation or maintenance of the seizure. These findings suggest that all neuronal classes may be involved in the initiation and maintenance of seizure-induced headache, and that their activation patterns can provide a neural substrate for explaining the timing and duration of ictal and possibly postictal headaches. By using seizure, which is evident in humans, this study bypasses controversies associated with cortical spreading depression, which is less readily observed in humans.SIGNIFICANCE STATEMENT This preclinical study provides a neural substrate for ictal and postictal headache. By studying seizure effects on the activity of peripheral (C and Aδ) and central (wide dynamic range and high-threshold) trigeminovascular neurons in intact and anesthetized dura, the findings help resolve two outstanding questions about the pathophysiology of headaches of intracranial origin. The first is that abnormal brain activity (i.e., seizure) that is evident in human (unlike cortical spreading depression) gives rise to specific and selective activation of the different components of the trigeminovascular system, and the second is that the activation of all components of the trigeminovascular pathway (i.e., peripheral and central neurons) depends on activation of the meningeal nociceptors from their receptors in the dura.

New discoveries in migraine mechanisms and therapeutic targets

Migraine is among the most common and most disabling disorders worldwide, yet its underlying pathophysiology is among the most poorly understood. New information continues to emerge on mechanisms within the central and peripheral nervous systems that may contribute to migraine attacks. Additionally, new therapeutics have recently become available and along with much needed relief for many patients, these drugs provide insight into the disorder based on their mechanism of action. This review will cover new findings within the last several years that add to the understanding of migraine pathophysiology, including those related to the vasculature, calcitonin gene-related peptide (CGRP), and mechanisms within the cortex and meninges that may contribute to attacks. Discussion will also cover recent findings on novel therapeutic targets, several of which continue to show promise in new preclinical studies, including acid-sensing ion channels (ASICs) and the delta-opioid receptor (DOR).

Exploring the effects of extracranial injections of botulinum toxin type A on prolonged intracranial meningeal nociceptors responses to cortical spreading depression in female rats

Background

Botulinum neurotoxin type A, an FDA-approved prophylactic drug for chronic migraine, is thought to achieve its therapeutic effect through blocking activation of unmyelinated meningeal nociceptors and their downstream communications with myelinated nociceptors and potentially the vasculature and immune cells. Prior investigations to determine botulinum neurotoxin type A effects on meningeal nociceptors were carried out in male rats and tested with stimuli that act outside the blood brain barrier. Here, we sought to explore the effects of extracranial injections of botulinum neurotoxin type A on activation of meningeal nociceptors by cortical spreading depression, an event which occurs inside the blood brain barrier, in female rats.

Material and methods

Using single-unit recording, we studied myelinated C- and unmyelinated Aδ-meningeal nociceptors' responses to cortical spreading depression 7–14 days after injection of botulinum neurotoxin type A or saline along calvarial sutures.

Results

In female rats, responses to cortical spreading depression were typically more prolonged and, in some cases, began at relatively longer latencies post-cortical spreading depression, than had been observed in previous studies in male rats. Extracranial administration of botulinum neurotoxin type A reduced significantly the prolonged firing of the meningeal nociceptors, in the combined sample of Aδ- and C-fiber, but not their response probability.

Discussion

The findings suggest that the mechanism of action by which botulinum neurotoxin type A prevents migraine differ from the one by which calcitonin gene-related peptide monoclonal antibodies prevent migraine and that even when the origin of migraine is central (i.e. in the cortex), a peripherally acting drug can intercept/prevent the headache.

Cranial Osteopathy: Obscurantism and Enlightenment

The application of cranial osteopathic manipulative medicine (OMM) is always controversial in the literature. Primary respiration related to the movement of spheno-basilar synchondrosis in the adult goes against the knowledge of complete ossification that occurs at this articulation after the pubertal phase. The idea that the operator's hands can communicate with the meninges is difficult to accept. The anatomy shows us that the fascial system involves the meninges and that from the microcellular point of view there are no layers that divide one tissue from another. The backing of new sciences, such as quantum physics, suggest that cranial palpation allows the osteopath to come into contact with the meninges. Recent scientific evidence shows that meningeal afferents can affect extracranial areas and that the pericranial musculature itself is able to influence these afferents. The article highlights some reflections in support of cranial osteopathy, based on scientific information that could help the osteopath to improve clinical work.

Spreading depression as a preclinical model of migraine

Spreading depression (SD) is a slowly propagating wave of near-complete depolarization of neurons and glial cells across the cortex. SD is thought to contribute to the underlying pathophysiology of migraine aura, and possibly also an intrinsic brain activity causing migraine headache. Experimental models of SD have recapitulated multiple migraine-related phenomena and are considered highly translational. In this review, we summarize conventional and novel methods to trigger SD, with specific focus on optogenetic methods. We outline physiological triggers that might affect SD susceptibility, review a multitude of physiological, biochemical, and behavioral consequences of SD, and elaborate their relevance to migraine pathophysiology. The possibility of constructing a recurrent episodic or chronic migraine model using SD is also discussed.

Calcitonin Gene-Related Peptide Modulators - The History and Renaissance of a New Migraine Drug Class

Several lines of evidence pointed to an important role for CGRP in migraine. These included the anatomic colocalization of CGRP and its receptor in sensory fibers innervating pain-producing meningeal blood vessels, its release by trigeminal stimulation, the observation of elevated CGRP in the cranial circulation during migraine with normalization concomitant with headache relief by sumatriptan, and translational studies with intravenous (IV) CGRP that evoked migraine only in migraineurs. The development of small molecule CGRP receptor antagonists (CGRP-RAs) that showed clinical antimigraine efficacy acutely and prophylactically in randomized placebo-controlled clinical trials subsequently gave definitive pharmacological proof of the importance of CGRP in migraine. More recently, CGRP target engagement imaging studies using a CGRP receptor PET ligand [¹¹ C]MK-4232 demonstrated that there was no brain CGRP receptor occupancy at clinically effective antimigraine doses of telcagepant, a prototypic CGRP-RA. Taken together, these data indicated that (1) the therapeutic site of action of the CGRP-RAs was peripheral not central; (2) that IV CGRP had most likely evoked migraine through an action at sites outside the blood-brain barrier; and (3) that migraine pain was therefore, at least in part, peripheral in origin. The evolution of CGRP migraine science gave impetus to the development of peripherally acting drugs that could modulate CGRP chronically to prevent frequent episodic and chronic migraine. Large molecule biologic antibody (mAb) approaches that are given subcutaneously to neutralize circulating CGRP peptide (fremanezumab, galcanezumab) or block CGRP receptors (erenumab) have shown consistent efficacy and tolerability in multicenter migraine prevention trials and are now approved for clinical use. Eptinezumab, a CGRP neutralizing antibody given IV, shows promise in late stage clinical development. Recently, orally administered next-generation small molecule CGRP-RAs have been shown to have safety and efficacy in acute treatment (ubrogepant and rimegepant) and prevention (atogepant) of migraine, giving additional CGRP-based therapeutic options for migraine patients.

Neuroimaging clues of migraine aura

While migraine headaches can be provoked, or predicted by the presence of an aura or premonitory symptoms, the prediction or elicitation of the aura itself is more problematic. Therefore, imaging studies directly examining the aura phenomenon are sparse. There are however interictal imaging studies that can shed light on the pathophysiology of the migraine with aura (MWA) cascade. Here, we review findings pointing to the involvement of cortical spreading depression (CSD) and neuroinflammation in MWA. Whether asymptomatic CSD also happens in some migraine without aura is still under debate. In addition, new evidence points to glial activation in MWA, indicating the involvement of astrocytes in the neuroinflammatory cascade that follows CSD, as well as dural macrophages, supporting the involvement of the trigeminovascular system in migraine pain.

Current understanding of meningeal and cerebral vascular function underlying migraine headache

BACKGROUND

The exact mechanisms underlying the onset of a migraine attack are not completely understood. It is, however, now well accepted that the onset of the excruciating throbbing headache of migraine is mediated by the activation and increased mechanosensitivity (i.e. sensitization) of trigeminal nociceptive afferents that innervate the cranial meninges and their related large blood vessels.

OBJECTIVES

To provide a critical summary of current understanding of the role that the cranial meninges, their associated vasculature, and immune cells play in meningeal nociception and the ensuing migraine headache.

METHODS

We discuss the anatomy of the cranial meninges, their associated vasculature, innervation and immune cell population. We then debate the meningeal neurogenic inflammation hypothesis of migraine and its putative contribution to migraine pain. Finally, we provide insights into potential sources of meningeal inflammation and nociception beyond neurogenic inflammation, and their potential contribution to migraine headache.

Dissociation between CSD-Evoked Metabolic Perturbations and Meningeal Afferent Activation and Sensitization: Implications for Mechanisms of Migraine Headache Onset

The onset of the headache phase during attacks of migraine with aura, which occur in ∼30% of migraineurs, is believed to involve cortical spreading depression (CSD) and the ensuing activation and sensitization of primary afferent neurons that innervate the intracranial meninges, and their related large vessels. The mechanism by which CSD enhances the activity and mechanosensitivity of meningeal afferents remains poorly understood, but may involve cortical metabolic perturbations. We used extracellular single-unit recording of meningeal afferent activity and monitored changes in cortical blood flow and tissue partial pressure of oxygen (tpO₂) in anesthetized male rats to test whether the prolonged cortical hypoperfusion and reduction in tissue oxygenation that occur in the wake of CSD contribute to meningeal nociception. Suppression of CSD-evoked cortical hypoperfusion with the cyclooxygenase inhibitor naproxen blocked the reduction in cortical tpO₂, but had no effect on the activation of meningeal afferents. Naproxen, however, distinctly prevented CSD-induced afferent mechanical sensitization. Counteracting the CSD-evoked persistent hypoperfusion and reduced tpO₂ by preemptively increasing cortical blood flow using the ATP-sensitive potassium [K(ATP)] channel opener levcromakalim did not inhibit the sensitization of meningeal afferents, but prevented their activation. Our data show that the cortical hypoperfusion and reduction in tpO₂ that occur in the wake of CSD can be dissociated from the activation and mechanical sensitization of meningeal afferent responses, suggesting that the metabolic changes do not contribute directly to these neuronal nociceptive responses.SIGNIFICANCE STATEMENT Cortical spreading depression (CSD)-evoked activation and mechanical sensitization of meningeal afferents is thought to mediate the headache phase in migraine with aura. We report that blocking the CSD-evoked cortical hypoperfusion and reduced tissue partial pressure of oxygen by cyclooxygenase inhibition is associated with the inhibition of the afferent sensitization, but not their activation. Normalization of these CSD-evoked metabolic perturbations by activating K(ATP) channels is, however, associated with the inhibition of afferent activation but not sensitization. These results question the contribution of cortical metabolic perturbations to the triggering mechanism underlying meningeal nociception and the ensuing headache in migraine with aura, further point to distinct mechanisms underlying the activation and sensitization of meningeal afferents in migraine, and highlight the need to target both processes for an effective migraine therapy.