The anti-migraine agent sumatriptan induces a calcium-dependent discharge in meningeal sensory neurons

Sumatriptan activates TRPA1

Background:

Migraine therapy with sumatriptan may cause adverse side effects like pain at the injection site, muscle pain, and transient aggravation of headaches. In animal experiments, sumatriptan excited or sensitized slowly conducting meningeal afferents. We hypothesized that sumatriptan may activate transduction channels of the “irritant receptor,” the transient receptor potential ankyrin type (TRPA1) expressed in nociceptive neurons.

Methods:

Calcium microfluorometry was performed in HEK293t cells transfected with human TRPA1 (hTRPA1) or a mutated channel (TRPA1-3C) and in dissociated trigeminal ganglion neurons. Membrane currents were recorded in the whole-cell patch clamp configuration.

Results:

Sumatriptan (10 and 400 µM) evoked calcium transients in hTRPA1-expressing HEK293t cells also activated by the TRPA1 agonist carvacrol (100 µM). In TRPA1-3C-expressing HEK293t cells, sumatriptan had hardly any effect. In rat trigeminal ganglion neurons, sumatriptan, carvacrol, and the transient receptor potential vanillod type 1 agonist capsaicin (1 µM) generated robust calcium signals. All sumatriptan-sensitive neurons (8% of the sample) were also activated by carvacrol (14%) and capsaicin (48%). In HEK293-hTRPA1 cells, sumatriptan (100 µM) evoked outwardly rectifying currents, which were almost completely inhibited by the TRPA1 antagonist HC-030031 (10 µM).

Conclusion:

Sumatriptan activates TRPA1 channels inducing calcium inflow and membrane currents. TRPA1-dependent activation of primary afferents may explain the painful side effects of sumatriptan.

Sumatriptan improves postoperative quality of recovery and reduces postcraniotomy headache after cranial nerve decompression

BACKGROUND

Microvascular decompression (MVD) is a surgical treatment for cranial nerve disorders via a small craniotomy. The postoperative pain of this procedure can be classified as surgical site somatic pain and postcraniotomy headache similar in nature to a migraine, including its association with photophobia, nausea, and vomiting. This headache can be difficult to treat and can impact on postoperative recovery. Sumatriptan is used to treat migraine-like headaches in various settings. This single-centre randomized controlled trial investigated whether postoperative administration of sumatriptan after MVD surgery impacts the quality of postoperative recovery.

METHODS

Fifty patients who complained of postoperative headache after MVD were randomized to receive an s.c. injection of sumatriptan (6 mg) or saline. The primary outcome was quality of recovery as measured by the Quality of Recovery-40 (QoR-40) score at 24 h.

RESULTS

The QoR-40 scores were significantly higher in the sumatriptan group (median 184; interquartile range 169-196) than in the placebo group (133; 119-155; P<0.01), suggesting higher quality of recovery. The sumatriptan group also had significantly lower headache scores at 4, 12, and 24 h. There were no significant differences in other secondary outcomes.

CONCLUSIONS

Use of sumatriptan improved the quality of recovery as measured by the QoR-40 and reduction of headache at 24 h after surgery. Sumatriptan is a useful alternative treatment for postcraniotomy headache. The mechanism remains unknown but could be related to reduction in headache, mood modulation, or both, mediated by a serotonin effect.

CLINICAL TRIAL REGISTRATION

NCT01632657.

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.

Estrogen-Dependent Changes in Dura Mater Microvasculature Add New Insights to the Pathogenesis of Headache

The pathogenesis of headaches is a matter of ongoing discussion of two major theories describing it either as a vascular phenomenon resulting from vasodilation or primarily as a neurogenic process accompanied by secondary vasodilation associated with sterile neurogenic inflammation. While summarizing current views on neurogenic and vascular origins of headache, this mini review adds new insights regarding how smooth muscle-free microvascular networks, discovered within dura mater connective tissue stroma (previously thought to be “avascular”), may become a site of initial insult generating the background for the development of headache. Deficiencies in estrogen-dependent control of microvascular integrity leading to plasma protein extravasation, potential activation of perivascular and connective tissue stroma nociceptive neurons, and triggering of inflammatory responses are described. Finally, possible avenues for controlling and preventing these pathophysiological changes are discussed.

Mechanisms of glyceryl trinitrate provoked mast cell degranulation

BACKGROUND

Migraine patients develop attacks several hours after intravenous infusion of glyceryl trinitrate. Due to the short half-life of nitric oxide, this delayed migraine cannot be caused by a direct action of nitric oxide derived from glyceryl trinitrate. The involvement of meningeal inflammation and dural mast cell degranulation is supported by the effectiveness of prednisolone on glyceryl trinitrate-induced delayed headache.

METHODS

Using a newly developed rat model mimicking the human glyceryl trinitrate headache model, we have investigated the occurrence of dural mast cell degranulation after a clinically relevant dose of glyceryl trinitrate.

RESULTS

A 6-fold increase in degranulation was observed starting at 2 hours after glyceryl trinitrate infusion. Interestingly, pre-treatment with the effective anti-migraine substances L-nitro-arginine methyl ester and sumatriptan prevented glyceryl trinitrate-induced mast cell degranulation whereas the calcitonin gene-related peptide-receptor antagonist olcegepant and the substance P receptor antagonist L-733,060 did not affect mast cell degranulation. However, topical application of two different nitric oxide donors did not cause mast cell degranulation ex vivo.

CONCLUSIONS

Direct application of an exogenous nitric oxide donor on dural mast cells does not cause mast cell degranulation ex vivo. In vivo application of the nitric oxide donor glyceryl trinitrate leads to a prominent level of degranulation via a yet unknown mechanism. This effect can be completely blocked by inhibition of the endogenous nitric oxide production and by 5-HT1B/1D receptor agonists but is unaffected by calcitonin gene-related peptide and substance P receptor antagonists.

The complex actions of sumatriptan on rat dural afferents

AIM

To test the hypothesis that the clinical efficacy of triptans reflects convergent modulation of ion channels also involved in inflammatory mediator (IM)-induced sensitization of dural afferents.

METHODS

Acutely dissociated retrogradely labeled rat dural afferents were studied with whole cell and perforated patch techniques in the absence and presence of sumatriptan and/or IM (prostaglandin E2, bradykinin, and histamine).

RESULTS

Sumatriptan dose-dependently suppressed voltage-gated Ca²⁺ currents. Acute (2 min) sumatriptan application increased dural afferent excitability and occluded further IM-induced sensitization. In contrast, pre-incubation (30 min) with sumatriptan had no influence on dural afferent excitability and partially prevented IM-induced sensitization of dural afferents. The sumatriptan-induced suppression of voltage-gated Ca²⁺ currents and acute sensitization and pre-incubation-induced block of IM-induced sensitization were blocked by the 5-HT(1D) antagonist BRL 15572. Pre-incubation with sumatriptan failed to suppress the IM-induced decrease in action potential threshold and overshoot (which results from modulation of voltage-gated Na⁺ currents) and activation of Cl⁻ current, and had no influence on the Cl⁻ reversal potential. However, pre-incubation with sumatriptan caused a dramatic hyperpolarizing shift in the voltage dependence of K⁺ current activation.

DISCUSSION

These results indicate that although the actions of sumatriptan on dural afferents are complex, at least two distinct mechanisms underlie the antinociceptive actions of this compound. One of these mechanisms, the shift in the voltage dependence of K⁺ channel activation, may suggest a novel strategy for future development of anti-migraine agents.

Peripheral targets of 5-HT(1D) receptor immunoreactive trigeminal ganglion neurons

OBJECTIVE

The aim of the current study was to determine the proportion of trigeminal primary afferent neurons that innervate the intracranial vasculature, and other craniofacial tissues, that are also 5 hydroxy triptamine (5-HT)(1D) receptor immunoreactive.

METHODS

Retrograde tracing and immunohistochemistry was used to identify 5-HT(1D) receptor labeled trigeminal primary afferent neurons that innervate the lacrimal gland (n = 3 animals), nasal mucosa (n = 3 animals), and the intracranial vasculature (middle meningeal artery in the dura [n = 3 animals] and middle cerebral artery [n = 3 animals]).

RESULTS

The percentage of neurons that were 5-HT(1D) receptor immunoreactive was greater for primary afferent neurons innervating the middle meningeal artery (41.8 ± 1%) than those innervating the middle cerebral artery (28.4 ± 0.8%), nasal mucosa (25.6 ± 1%), or lacrimal gland (23.5 ± 3%). For each retrograde labeled population, the 5-HT(1D) receptor immunoreactive cells were among the smallest of the retrograde labeled cells.

CONCLUSIONS

These findings provide a basis for understanding the role of 5-HT(1D) receptor agonists (eg, triptans) in the treatment of primary vascular headaches and suggest that the selectivity of triptans in the treatment of these headaches does not appear to result from specific localization of the 5-HT(1D) receptor to trigeminovascular neurons alone.

Sustained morphine-induced sensitization and loss of diffuse noxious inhibitory controls in dura-sensitive medullary dorsal horn neurons

Overuse of medications used to treat migraine headache can produce a chronic daily headache, termed medication overuse headache (MOH). Although "overuse" of opioids, triptans, and over-the-counter analgesics can all produce MOH, the neuronal mechanisms remain unknown. Headache pain is likely to be produced by stimulation of primary afferent neurons that innervate the intracranial vasculature and the resulting activation of medullary dorsal horn (MDH) neurons. The present study compared the receptive field properties of MDH dura-sensitive neurons in rats treated with morphine to those given vehicle. Animals were implanted with osmotic minipumps or pellets for sustained subcutaneous administration of morphine or vehicle 6-7 d before recording from dura-sensitive neurons. Electrical and mechanical activation thresholds from the dura were significantly lower in chronic morphine-treated animals when compared to vehicle controls. In addition, sustained morphine increased the cutaneous receptive field sizes. The presence of diffuse noxious inhibitory controls (DNICs) was examined by placing the tail in 55 degrees C water during concomitant noxious thermal stimulation of the cutaneous receptive field, usually located in the ophthalmic region. The DNIC stimulus produced significant inhibition of heat-evoked activity in vehicle- but not chronic morphine-treated animals. Inactivation of the rostral ventromedial medulla with 4% lidocaine reinstated DNICs in chronic morphine-treated animals. These results are consistent with studies demonstrating a loss of DNICs in patients that suffer from chronic daily headache and may partially explain why overuse of medication used to treat migraine can induce headaches.

The blood-brain barrier in migraine treatment

Salient aspects of the anatomy and function of the blood-barrier barrier (BBB) are reviewed in relation to migraine pathophysiology and treatment. The main function of the BBB is to limit the access of circulating substances to the neuropile. Smaller lipophilic substances have some access to the central nervous system by diffusion, whereas other substances can cross the BBB by carrier-mediated influx transport, receptor-mediated transcytosis and absorptive-mediated transcytosis. Studies of drugs relevant to migraine pathophysiology and treatment have been examined with the pressurized arteriography method. The drugs, given both luminally and abluminally, provide important notions regarding antimigraine site of action, probably abluminal to the BBB. The problems with the BBB in animal models designed to study the pathophysiology, acute treatment models and preventive treatments are discussed with special emphasize on the triptans and calcitonin gene-related peptide (CGRP). The human experimental headache model, especially the use of glycerol trinitrate (the nitric oxide model), and experiences with CGRP administrations utilize the systemic administration of the agonists with effects on other vascular beds also. We discuss how this can be related to genuine migraine attacks. Our view is that there exists no clear proof of breakdown or leakage of the BBB during migraine attacks, and that antimigraine drugs need to pass the BBB for efficacy.

Sensitization and Activation of Intracranial Meningeal Nociceptors by Mast Cell Mediators

Intracranial headaches such as migraine are thought to result from activation of sensory trigeminal pain neurons that supply intracranial blood vessels and the meninges, also known as meningeal nociceptors. Although the mechanism underlying the triggering of such activation is not completely understood, our previous work indicates that the local activation of the inflammatory dural mast cells can provoke a persistent sensitization of meningeal nociceptors. Given the potential importance of mast cells to the pain of migraine it is important to understand which mast cell-derived mediators interact with meningeal nociceptors to promote their activation and sensitization. In the present study, we have used in vivo electrophysiological single-unit recording of meningeal nociceptors in the trigeminal ganglion of anesthetized rats to examine the effect of a number of mast cell mediators on the activity level and mechanosensitivity of meningeal nociceptors. We have found that that serotonin (5-HT), prostaglandin I(2) (PGI(2)), and to a lesser extent histamine can promote a robust sensitization and activation of meningeal nociceptors, whereas the inflammatory eicosanoids PGD(2) and leukotriene C(4) are largely ineffective. We propose that dural mast cells could promote headache by releasing 5-HT, PGI(2), and histamine.

Antimigraine drug, zolmitriptan, inhibits high-voltage activated calcium currents in a population of acutely dissociated rat trigeminal sensory neurons

Background

Triptans, 5-HT_1B/ID agonists, act on peripheral and/or central terminals of trigeminal ganglion neurons (TGNs) and inhibit the release of neurotransmitters to second-order neurons, which is considered as one of key mechanisms for pain relief by triptans as antimigraine drugs. Although high-voltage activated (HVA) Ca²⁺ channels contribute to the release of neurotransmitters from TGNs, electrical actions of triptans on the HVA Ca²⁺ channels are not yet documented.

Results

In the present study, actions of zolmitriptan, one of triptans, were examined on the HVA Ca²⁺ channels in acutely dissociated rat TGNs, by using whole-cell patch recording of Ba²⁺ currents (I_Ba) passing through Ca²⁺ channels. Zolmitriptan (0.1–100 μM) reduced the size of I_Ba in a concentration-dependent manner. This zolmitriptan-induced inhibitory action was blocked by GR127935, a 5-HT_1B/1D antagonist, and by overnight pretreatment with pertussis toxin (PTX). P/Q-type Ca²⁺ channel blockers inhibited the inhibitory action of zolmitriptan on I_Ba, compared to N- and L-type blockers, and R-type blocker did, compared to L-type blocker, respectively (p < 0.05). All of the present results indicated that zolmitriptan inhibited HVA P/Q- and possibly R-type channels by activating the 5-HT_1B/1D receptor linked to G_i/o pathway.

Conclusion

It is concluded that this zolmitriptan inhibition of HVA Ca²⁺ channels may explain the reduction in the release of neurotransmitters including CGRP, possibly leading to antimigraine effects of zolmitriptan.

Response Properties of Dural Nociceptors in Relation to Headache

Single-unit electrophysiological recording studies have examined the activity of sensory neurons in the trigeminal ganglion that innervate the intracranial meninges to better understand their possible role in headache. A key question is whether the meningeal sensory neurons are similar to nociceptive neurons in other tissues or, alternatively, whether they have unique properties that might be of significance for headache pathogenesis and drug therapy. Such studies have indeed found that the intracranial dura is innervated by neurons that exhibit properties characteristic of nociceptors in other tissues, including chemosensitivity and sensitization. This sensitization, consisting of an enhanced responsiveness to mechanical stimuli, might be relevant to symptoms that are characteristic of certain headaches that indicate the presence of an exaggerated intracranial mechanosensitivity. Studies that examined whether the anti-migraine agent sumatriptan might inhibit this sensitization (in addition to its well-known inhibition of neurotransmitter release) found that it had no inhibitory effect but rather produced a calcium-dependent discharge, which might account for the initial worsening of headache that can follow sumatriptan administration. In studies that examined the effects of vasodilator agents, nitroprusside produced mixed effects on mechanosensitivity, whereas calciton gene-related peptide (CGRP) had no effect on either spontaneous or mechanically evoked discharge. These results call into question the role of vasodilation in headache and suggest that the role of CGRP in headache may be through its action as a central neurotransmitter rather than through vasodilation and activation of meningeal nociceptors. In general, studies of meningeal sensory neurons have not found evidence of unique properties that distinguish them from nociceptive neurons in other tissues. Ultimately the distinctive clinical characteristics of headache may prove to be related not so much to any differences in the intrinsic molecular or cellular properties of the meningeal sensory neurons but rather to the distinctive properties of the tissue that they innervate.