Release of immunoreactive substance P in the brain stem upon stimulation of the cranial dura mater with low pH - inhibition by the serotonin (5-HT1) receptor agonist CP 93,129

The Anti-CGRP Antibody Fremanezumab Lowers CGRP Release from Rat Dura Mater and Meningeal Blood Flow

Monoclonal antibodies directed against the neuropeptide calcitonin gene-related peptide (CGRP) belong to a new generation of therapeutics that are effective in the prevention of migraine. CGRP, a potent vasodilator, is strongly implicated in the pathophysiology of migraine, but its role remains to be fully elucidated. The hemisected rat head preparation and laser Doppler flowmetry were used to examine the effects on CGRP release from the dura mater and meningeal blood flow of the subcutaneously injected anti-CGRP monoclonal antibody fremanezumab at 30 mg/kg, when compared to an isotype control antibody. Some rats were administered glycerol trinitrate (GTN) intraperitoneally to produce a migraine-like sensitized state. When compared to the control antibody, the fremanezumab injection was followed by reduced basal and capsaicin-evoked CGRP release from day 3 up to 30 days. The difference was enhanced after 4 h of GTN application. The samples from the female rats showed a higher CGRP release compared to that of the males. The increases in meningeal blood flow induced by acrolein (100 µM) and capsaicin (100 nM) were reduced 13–20 days after the fremanezumab injection, and the direct vasoconstrictor effect of high capsaicin (10 µM) was intensified. In conclusion, fremanezumab lowers the CGRP release and lasts up to four weeks, thereby lowering the CGRP-dependent meningeal blood flow. The antibody may not only prevent the released CGRP from binding but may also influence the CGRP release stimulated by noxious agents relevant for the generation of migraine pain.

Pain in NMOSD and MOGAD: A Systematic Literature Review of Pathophysiology, Symptoms, and Current Treatment Strategies

Neuromyelitis optica spectrum disorders (NMOSDs) and myelin oligodendrocyte glycoprotein-antibody-associated disease (MOGAD) are autoimmune inflammatory disorders of the central nervous system (CNS). Pain is highly prevalent and debilitating in NMOSD and MOGAD with a severe impact on quality of life, and there is a critical need for further studies to successfully treat and manage pain in these rare disorders. In NMOSD, pain has a prevalence of over 80%, and pain syndromes include neuropathic, nociceptive, and mixed pain, which can emerge in acute relapse or become chronic during the disease course. The impact of pain in MOGAD has only recently received increased attention, with an estimated prevalence of over 70%. These patients typically experience not only severe headache, retrobulbar pain, and/or pain on eye movement in optic neuritis but also neuropathic and nociceptive pain. Given the high relevance of pain in MOGAD and NMOSD, this article provides a systematic review of the current literature pertaining to pain in both disorders, focusing on the etiology of their respective pain syndromes and their pathophysiological background. Acknowledging the challenge and complexity of diagnosing pain, we also provide a mechanism-based classification of NMOSD- and MOGAD-related pain syndromes and summarize current treatment strategies.

Ultra-rapid brain uptake of subcutaneous sumatriptan in the rat: Implication for cluster headache treatment

BACKGROUND

In spite of the substantial therapeutic efficacy of triptans, their site of action is still debated. Subcutaneous sumatriptan is the most efficacious symptomatic treatment for cluster headache (CH) patients, showing therapeutic onset within a few minutes after injection even in migraine patients. However, whether subcutaneous sumatriptan is able to reach the CNS within this short time frame is currently unknown.

METHODS

Here, by means of liquid chromatography/mass spectrometry, we investigated peripheral and brain distribution of subcutaneous sumatriptan soon after injection in rats at a dose equivalent to that used in patients. Tissue sumatriptan contents were compared to those of oxazepam, a prototypical lipophilic, neuroactive drug.

RESULTS

We report that sumatriptan accumulated within brain regions of relevance to migraine and CH pathogenesis such as the hypothalamus and the brainstem as soon as 1 and 5 minutes after injection. Notably, sumatriptan brain distribution was faster than that of oxazepam, reaching concentrations exceeding its reported binding affinity for 5HT1_B/D receptors, and in the range of those able to inhibit neurotransmitter release in vivo.

CONCLUSION

Our findings indicate that sumatriptan distributes within the CNS soon after injection, and are in line with prompt pain relief by parenteral sumatriptan in CH patients.

Intracellular emetic signaling cascades by which the selective neurokinin type 1 receptor (NK1R) agonist GR73632 evokes vomiting in the least shrew (Cryptotis parva)

To characterize mechanisms involved in neurokinin type 1 receptor (NK₁R)-mediated emesis, we investigated the brainstem emetic signaling pathways following treating least shrews with the selective NK₁R agonist GR73632. In addition to episodes of vomiting over a 30-min observation period, a significant increase in substance P-immunoreactivity in the emetic brainstem dorsal motor nucleus of the vagus (DMNX) occurred at 15 min post an intraperitoneal (i.p.) injection GR73632 (5 mg/kg). In addition, time-dependent upregulation of phosphorylation of several emesis -associated protein kinases occurred in the brainstem. In fact, Western blots demonstrated significant phosphorylations of Ca²⁺/calmodulin kinase IIα (CaMKIIα), extracellular signal-regulated protein kinase1/2 (ERK1/2), protein kinase B (Akt) as well as α and βII isoforms of protein kinase C (PKCα/βII). Moreover, enhanced phospho-ERK1/2 immunoreactivity was also observed in both brainstem slices containing the dorsal vagal complex emetic nuclei as well as in jejunal sections from the shrew small intestine. Furthermore, our behavioral findings demonstrated that the following agents suppressed vomiting evoked by GR73632 in a dose-dependent manner: i) the NK₁R antagonist netupitant (i.p.); ii) the L-type Ca²⁺ channel (LTCC) antagonist nifedipine (subcutaneous, s.c.); iii) the inositol trisphosphate receptor (IP₃R) antagonist 2-APB (i.p.); iv) store-operated Ca²⁺ entry inhibitors YM-58483 and MRS-1845, (i.p.); v) the ERK1/2 pathway inhibitor U0126 (i.p.); vi) the PKC inhibitor GF109203X (i.p.); and vii) the inhibitor of phosphatidylinositol 3-kinase (PI3K)-Akt pathway LY294002 (i.p.). Moreover, NK₁R, LTCC, and IP₃R are required for GR73632-evoked CaMKIIα, ERK1/2, Akt and PKCα/βII phosphorylation. In addition, evoked ERK1/2 phosphorylation was sensitive to inhibitors of PKC and PI3K. These findings indicate that the LTCC/IP₃R-dependent PI3K/PKCα/βII-ERK1/2 signaling pathways are involved in NK₁R-mediated vomiting.

Fremanezumab-A Humanized Monoclonal Anti-CGRP Antibody-Inhibits Thinly Myelinated (Aδ) But Not Unmyelinated (C) Meningeal Nociceptors

Calcitonin gene-related peptide (CGRP), the most abundant neuropeptide in primary afferent sensory neurons, is strongly implicated in the pathophysiology of migraine headache, but its role in migraine is still equivocal. As a new approach to migraine treatment, humanized anti-CGRP monoclonal antibodies (CGRP-mAbs) were developed to reduce the availability of CGRP, and were found effective in reducing the frequency of chronic and episodic migraine. We recently tested the effect of fremanezumab (TEV-48125), a CGRP-mAb, on the activity of second-order trigeminovascular dorsal horn neurons that receive peripheral input from the cranial dura, and found a selective inhibition of high-threshold but not wide-dynamic range class of neurons. To investigate the basis for this selective inhibitory effect, and further explore the mechanism of action of CGRP-mAbs, we tested the effect of fremanezumab on the cortical spreading depression-evoked activation of mechanosensitive primary afferent meningeal nociceptors that innervate the cranial dura, using single-unit recording in the trigeminal ganglion of anesthetized male rats. Fremanezumab pretreatment selectively inhibited the responsiveness of Aδ neurons, but not C-fiber neurons, as reflected in a decrease in the percentage of neurons that showed activation by cortical spreading depression. These findings identify Aδ meningeal nociceptors as a likely site of action of fremanezumab in the prevention of headache. The selectivity in its peripheral inhibitory action may partly account for fremanezumab's selective inhibition of high-threshold, as a result of a predominant A-δ input to high-threshold neurons, but not wide dynamic-range dorsal horn neurons, and why it may not be effective in all migraine patients.SIGNIFICANCE STATEMENT Recently, we reported that humanized CGRP monoclonal antibodies (CGRP-mAbs) prevent activation and sensitization of high-threshold (HT) but not wide-dynamic range trigeminovascular neurons by cortical spreading depression (CSD). In the current paper, we report that CGRP-mAbs prevent the activation of Aδ but not C-type meningeal nociceptors by CSD. This is the first identification of an anti-migraine drug that appears to be selective for Aδ-fibers (peripherally) and HT neurons (centrally). As the main CGRP-mAb site of action appears to be situated outside the brain, we conclude that the initiation of the headache phase of migraine depends on activation of meningeal nociceptors, and that for selected patients, activation of the Aδ-HT pain pathway may be sufficient for the generation of headache perception.

Fos expression induced by activation of NMDA and neurokinin-1 receptors in the trigeminal subnucleus caudalis in vitro: role of protein kinases

Activity-induced neuronal plasticity is partly facilitated by the expression of the immediate-early gene c-fos and the resulting transcription factor Fos. Expression of Fos is associated with nociceptive afferent activation, but a detailed stimulation-transcription pathway for Fos expression has not yet been determined in the trigeminal system. This study utilized a novel in vitro model to determine whether Fos expression can be induced in trigeminal subnucleus caudalis by NMDA or neurokinin-1 receptor activation, and whether inhibition of intracellular kinases has any effect on Fos expression induced by activation of these receptors. Brainstems of male Wistar rats were excised and maintained in artificial cerebrospinal fluid at 37°C. NMDA or the specific neurokinin-1 receptor agonist [Sar(9),Met(O(2))(11)]-SP was applied. These agonists were subsequently tested in the presence of the protein kinase A inhibitor Rp-cAMP or protein kinase C inhibitor chelerythrine chloride. In all experiments the sodium channel blocker tetrodotoxin was used to prevent indirect neuronal activation. Brainstems were processed immunocytochemically for Fos expression, and positive cells were counted in the trigeminal subnucleus caudalis. NMDA and [Sar(9),Met(O(2))(11)]-SP significantly increased Fos expression, but these increases could be prevented by chelerythrine chloride. Rp-cAMP had no effect on Fos induced by NMDA but caused a significant reduction in Fos induced by [Sar(9),Met(O(2))(11)]-SP. These data demonstrate that in trigeminal subnucleus caudalis activation of either NK1 or NMDA receptors alone induces Fos expression; protein kinases A and C are involved in NK1R-induced Fos while protein kinase A is not required for NMDA receptor-induced Fos.

Headache and pregnancy

BACKGROUND

Many women who suffer from migraine and tension-type headaches (TTHs) have an improvement in the frequency of these headaches during pregnancy. At the same time pregnancy predisposes women to a number of potentially life-threatening conditions which can present with headache. Accurate diagnosis and treatment of headache during pregnancy is essential.

REVIEW SUMMARY

The primary objectives of this review are to: (1) Summarize the natural history of primary headache disorders, including migraine, tension-type, and cluster headaches during pregnancy, as well as the impact of migraine on pregnancy outcomes and complications.(2) Summarize the therapeutic options and strategies for managing headaches in pregnancy and (3) Discuss the causes of secondary headaches and the diagnostic evaluation for new onset headache during pregnancy.

CONCLUSION

Primary headache disorders, in particular TTHs and migraines, generally improve during pregnancy. However the frequency of improvement varies greatly. Because the pathophysiology of both migraines and TTHs is poorly understood, this limits our ability to predict improvement. Future research should be focused on headache pathophysiology and the effect of ovarian hormones and the pregnant state on headache pathogenesis.

Activation of the 5-HT1B/D receptor reduces hindlimb neurogenic inflammation caused by sensory nerve stimulation and capsaicin

Activation of the 5-HT(1B/D) receptor inhibits cerebrovascular neurogenic inflammation (NI). The aim of this study was to determine if the 5-HT(1B/D) receptor agonist sumatriptan can also inhibit NI in other regions of the body. NI was assessed by measuring plasma extravasation (PE) and changes in blood flow in the rat hindpaw. Sumatriptan was administered locally (20 microl, 50 or 100 nM, s.c.) into the dorso-medial region of one hindpaw. The other paw was pre-treated with vehicle (20 microl of 0.9% saline) and served as a control. NI was induced after treatment with sumatriptan/vehicle by injecting capsaicin (15 microl, 1%, s.c.) into each paw or by electrically stimulating the saphenous nerve (4 Hz, 30s). Sumatriptan administered locally or systemically (300 microg/kg, i.v.) significantly reduced saphenous nerve and capsaicin-induced PE and vasodilation. The systemic and local inhibitory actions of sumatriptan are mediated by the 5-HT(1B/D) receptor as pre-treatment with the 5-HT(1B/D) antagonist GR127935 (GR; 15 microl, 1 microM, s.c. or 0.2 micromol/kg, i.v.) completely blocked the inhibitory effect of sumatriptan on capsaicin-induced vasodilation and reduced the inhibitory effect of sumatriptan on capsaicin and electrically induced-PE. Neither PE induced by local injection of substance P (SP) (20 pmol, 20 microl, s.c.) nor vasodilation induced by local CGRP injection was affected by pre-treatment with sumatriptan. These findings indicate that both local and systemic activation of the 5-HT(1B/D) receptor by sumatriptan reduce NI induced by nerve stimulation or capsaicin presumably by inhibiting neuropeptide release. 5-HT(1B/D) receptor agonists may be useful for the treatment of non-trigeminal pain conditions involving NI.

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.

Selective 5-HT1B receptor agonist reduces serotonin synthesis following acute, and not chronic, drug administration: results of an autoradiographic study

The effects of acute and chronic administration of the serotonin (5-HT)1B agonist CP-93,129, on 5-HT synthesis rates were evaluated using the alpha-[14C]methyl-L-tryptophan (alpha-MTrp) autoradiographic method. In the acute treatment study, CP-93,129 (7 mg/kg) was injected intraperitoneally 30 min before the alpha-MTrp injection (30 microCi over 2 min). A single dose of CP-93,129 caused a significant increase in the synthesis in the median raphe nucleus (MR) without a significant influence on the dorsal raphe nucleus (DR). There was a reduction in 5-HT synthesis in almost all of the projection areas. In the chronic treatment study, CP-93,129 was administered continuously (7 mg/kg/day) for 14 days using an osmotic minipump implanted subcutaneously. The chronic treatment with CP-93,129 did not produce a significant change in 5-HT synthesis in the raphe nuclei nor in the nerve terminal structures, except for the medial frontal bundle and the visual and sensory-motor cortices. The unaltered 5-HT synthesis rates in the chronic treatment study probably reflect a normalization of the synthesis as a result of the desensitization of 5-HT1B autoreceptors and/or heteroreceptors.

Effects of sumatriptan on rat medullary dorsal horn neurons

This study examined the cellular actions of the anti-migraine drug sumatriptan, on neurons in the substantia gelatinosa of the spinal trigeminal nucleus pars caudalis. Sumatriptan inhibited the miniature EPSC (mEPSC) rate in a dose dependent fashion, with an EC(50) of 250 nM. Sumatriptan (3 microM) inhibited the mEPSC rate by 36%, without altering the mEPSC amplitude. This effect was partially reversed by the 5HT(1D) specific antagonist BRL15572 (10 microM). In contrast, the 5HT(1B) agonist CP93129 (10 microm) did not alter the mEPSC rate. Furthermore, sumatriptan (3 microM) decreased the amplitude of electrically evoked EPSCs (eEPSC) by 40%. After incubating the slices in ketanserin (an antagonist which shows selectivity for 5HT(1D) over 5HT(1B) receptors) sumatriptan had little effect on eEPSC amplitude. In control conditions paired stimuli resulted in paired pulse depression (PPD; the ratio eEPSC(2)/eEPSC(1)=0.7+/-0.01), whilst in the presence of sumatriptan the PPD was blocked (ratio eEPSC(2)/eEPSC(1)=0.9+/-0.1). Sumatriptan produced no post-synaptic membrane current and had no significant effect on membrane conductance over a range of membrane potentials (-60 to -130 mV). RT-PCR experiments revealed the presence of mRNA for both 5HT(1D) and 5HT(1B) receptor subtypes in the trigeminal ganglia and subnucleus caudalis. These data suggest that sumatriptan acts pre-synaptically on trigeminal primary afferent central terminals to reduce the probability of release of glutamate, and that this action is mediated through 5HT(1D) receptors.

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

The anti-migraine agent sumatriptan constricts cerebral blood vessels, and also blocks neuropeptide release from meningeal sensory neurons. We investigated whether sumatriptan can also affect neuronal discharge, by recording the activity of dural primary afferent neurons during dural application of sumatriptan in anesthetized rats. Sumatriptan (0.24-24 microM) induced a concentration-dependent increase in ongoing discharge. The discharge occurred only in the presence of calcium. The suppressive effect of calcium removal was not a result of a general decrease in excitability, because calcium removal produced a pronounced increase in mechanically evoked discharge. The excitatory effect on dural afferent discharge might underlie the initial worsening of the headache that can occur following sumatriptan administration, prior to the subsequent onset of headache relief.

Analgesic triptan action in an animal model of intracranial pain: a race against the development of central sensitization

We have shown that the development of cutaneous allodynia (exaggerated skin sensitivity) during migraine is detrimental to the anti-migraine action of the 5HT(IB/ID) receptor agonists known is triptans. Because cutaneous allodynia is a manifestation of sensitization of central trigeminovascular neurons, we examined whether triptan treatment can intercept such sensitization before its initiation or after its establishment in our rat model for cutaneous allodynia induced by intracranial pain. Single-unit recordings were obtained from spinal trigeminal neurons that proved to received convergent inputs from the dura and facial skin. The effects of sumatriptan (300 microg/kg i.v.) on central sensitization induced by topical application of inflammatory soup (IS) on the dura were determined when the drug was administered either 2 h after IS (late intervention) or at the same time as IS (early intervention). Late sumatriptan intervention counteracted two aspects of central sensitization: dural receptive fields, which initially expanded by IS, shrunk back after treatment; neuronal response threshold to dural indentation, which initially decreased after IS, increased after sumatriptan. On the other hand, late sumatriptan intervention did not reverse other aspects of central sensitization: spontaneous firing rate and neuronal response magnitude to skin brushing which initially increased after IS, remained elevated after sumatriptan; response threshold to heating of the skin, which initially dropped after IS, remained low after sumatriptan. Early sumatriptan intervention effectively blocked the development of all aspects of central sensitization expected to be induced 2 h after IS application: dural receptive fields did not expand; neuronal response threshold to dural indentation and skin stimulation did not decrease; spontaneous firing rate did not increase. The early treatment results suggest that triptan action provides a powerful means of preventing the initiation of central sensitization triggered by chemical stimulation of meningeal nociceptors. The late treatment results suggest that triptan action is insufficient to counteract an already established central sensitization. Thus, triptan action appears to be exerted directly on peripheral rather than central trigeminovascular neurons.

Disruption of communication between peripheral and central trigeminovascular neurons mediates the antimigraine action of 5HT 1B/1D receptor agonists

Triptans are 5HT(1B/1D) receptor agonists commonly prescribed for migraine headache. Although originally designed to constrict dilated intracranial blood vessels, the mechanism and site of action by which triptans abort the migraine pain remain unknown. We showed recently that sensitization of peripheral and central trigeminovascular neurons plays an important role in the pathophysiology of migraine pain. Here we examined whether the drug sumatriptan can prevent and/or suppress peripheral and central sensitization by using single-unit recording in our animal model of intracranial pain. We found that sumatriptan effectively prevented the induction of sensitization (i.e., increased spontaneous firing; increased neuronal sensitivity to intracranial mechanical stimuli) in central trigeminovascular neurons (recorded in the dorsal horn), but not in peripheral trigeminovascular neurons (recorded in the trigeminal ganglion). After sensitization was established in both types of neuron, sumatriptan effectively normalized intracranial mechanical sensitivity of central neurons, but failed to reverse such hypersensitivity in peripheral neurons. In both the peripheral and central neurons, the drug failed to attenuate the increased spontaneous activity established during sensitization. These results suggest that neither peripheral nor central trigeminovascular neurons are directly inhibited by sumatriptan. Rather, triptan action appears to be exerted through presynaptic 5HT(1B/1D) receptors in the dorsal horn to block synaptic transmission between axon terminals of the peripheral trigeminovascular neurons and cell bodies of their central counterparts. We therefore suggest that the analgesic action of triptan can be attained specifically in the absence, but not in the presence, of central sensitization.

Pharmacological opportunities and pitfalls in the therapy of migraine

The mild vasoconstrictor effects of modern antimigraine drugs, such as serotonin (5-HT; 5-hydroxytryptamine)1B/D agonists, have led to a search for nonvasoconstrictor approaches to therapy. Such approaches have included substance P (neurokinin I) antagonists, endothelin antagonists and highly specific 5HT1D agonists. All of these substances are effective in animal models and have no significant vasoconstrictive effects. However, all of them failed to demonstrate any antimigraine effects. Current clinical and experimental evidence therefore supports the view that isolated peripheral trigeminal nerve inhibition is insufficient to relieve acute migraine.

Meningeal nociception: electrophysiological studies related to headache and referred pain

Headaches, which are usually referred to characteristic sites of the skull, are believed to involve meningeal nociceptors located in the dura mater encephali. Animal experiments show that these meningeal nociceptors are polymodal and usually highly sensitive to mechanical stimulation. These properties are also characteristic for the second order neurons in the spinal trigeminal nucleus, most of which receive convergent input from facial receptive sites. Sensitization of primary and secondary neurons by chemical irritants to mechanical stimuli may be an important mechanism in the generation of headaches. The convergent input from extracranial structures, which seems to be differentially organized in rodents and man, may explain the typical features of referred headache. Targets for analgesics used in the therapy of headaches (non-steroidal antiinflammatory drugs, 5-HT(1) receptor agonists) are probably meningeal nociceptors and different sites of the central trigeminal nociceptive and antinociceptive pathways.

Physiology of meningeal innervation: aspects and consequences of chemosensitivity of meningeal nociceptors

Up to now, the cause of most types of headaches is unknown. Why headache starts or why it fades away during hours or a few days is still a mystery. This phenomenon makes headache unique compared to other pain states. For long it has been known that during headache sensory structures in the meninges are activated. But it was not until the last two decades that scientists investigated the physiology of the sensory innervation of the meninges. Animal models and in vitro preparations have been developed to get access to the meninges and to determine the response properties of meningeal afferents. Although animals hardly can tell their pain, blood pressure measurements and observations of behaviour in two models of headache suggest that such animal models are valid and may add remarkable information to our understanding of human headache. Since chemicals and endogenous inflammatory mediators may alter sensory thresholds and responsiveness of neurons, they are putative key molecules in triggering pathophysiological sensory processing. This review briefly summarizes what is known about the chemosensitivity of meningeal innervation.

Substance P receptor antagonists in the therapy of migraine

Clinical observations, the vascular component of migraine pain, its pulsating or throbbing pain character, have focused attention on the trigeminal innervation of pain-sensitive intracranial structures, such as the dura mater and large vessels. These intracranial structures are innervated by the ophthalmic branch of the trigeminal nerve, which is marked by the presence of vasoactive peptides, such as substance P and calcitonin gene-related peptide. Substance P is a mediator of the sterile inflammation of the dura mater, which has been considered to be the source of migraine pain. Modern antimigraine drugs, such as 5-HT(1B/D) agonists (triptans), block this dural neurogenic inflammation dose-dependently in an animal model but their vasoconstrictor effects have led to a search for non-vasoconstrictor approaches. One such approach has been substance P (neurokinin-1) antagonists. These are highly effective in animal models of dural inflammation and have no significant vasoconstrictive effect. However, several NK(1) antagonists failed to demonstrate any effect in acute migraine. Current clinical and experimental evidence therefore supports the view that NK(1) receptor antagonists may have no significant antimigraine properties.

alpha-eudesmol, a P/Q-type Ca(2+) channel blocker, inhibits neurogenic vasodilation and extravasation following electrical stimulation of trigeminal ganglion

In this study, we investigated the effect of alpha-eudesmol, which potently inhibits the presynaptic omega-agatoxin IVA-sensitive (P/Q-type) Ca(2+) channel, on neurogenic inflammation following electrical stimulation of rat trigeminal ganglion. Treatment with alpha-eudesmol (0.1-1 mg/kg. i.v.) dose-dependently attenuated neurogenic vasodilation in facial skin monitored by a laser Doppler flowmetry. In addition, alpha-eudesmol (1 mg/kg. i.v.) significantly decreased dural plasma extravasation in analysis using Evans blue as a plasma marker. On the other hand, alpha-eudesmol (1 mg/kg, i.v.) did not affect mean arterial blood pressure in rats. The calcitonin gene-related peptide (CGRP) and substance P (SP) released from activated sensory nerves have recently been suggested to be associated with the neurogenic inflammation. In this study, we also showed that alpha-eudesmol (0.45-45 microM) concentration-dependently inhibits the depolarization-evoked CGRP and SP release from sensory nerve terminals in spinal cord slices. These results indicate that the anti-neurogenic inflammation action of alpha-eudesmol, which does not affect the cardiovascular system, may be due to its presynaptic inhibition of the neuropeptide release from perivascular trigeminal terminals. We also suggest that the omega-agatoxin IVA-sensitive Ca(2+) channel blocker, alpha-eudesmol, may become useful for the treatment of the neurogenic inflammation in the trigemino-vascular system such as migraine.