Dihydroergotamine and sumatriptan attenuate levels of CGRP in plasma in rat superior sagittal sinus during electrical stimulation of the trigeminal ganglion

Salivary levels of CGRP and VIP in rhinosinusitis and migraine patients

BACKGROUND

Secretion of calcitonin gene-related peptide (CGRP) from trigeminal nerves and vasoactive intestinal peptide (VIP) from parasympathetic nerves is involved in the pathophysiology of migraine and rhinosinusitis. Analysis of these neuropeptides in human saliva samples can be used as markers of trigeminal and parasympathetic nerve activity in patients between and during attacks as well as in response to specific treatments.

OBJECTIVE

To compare the amount of trigeminal sensory and parasympathetic nerve activation by measuring CGRP and VIP levels in the saliva of subjects experiencing noninfectious allergic rhinosinusitis, migraine with sinus symptoms, and no symptoms.

METHODS

Subjects were enrolled in three groups. Group A: subjects without a history of migraine, "sinus" headache, or allergic rhinosinusitis within the previous 6 months. Group B: subjects with chronic recurrent noninfectious rhinosinusitis and no history of migraine or "sinus" headache. Group C: subjects with self-described "sinus" headaches whose symptoms met International Headache Society diagnostic criteria (1.1 or 1.2) for migraine. The total amount of CGRP and VIP present in saliva collected under normal, pathological, and therapeutic conditions was determined by radioimmunoassay. Neuropeptide levels were normalized to total volume and amount of protein, and levels were correlated to onset and change in clinical symptoms.

RESULTS

Total volume, total protein, and CGRP and VIP levels did not significantly change in saliva collected on consecutive days in the clinic and at the subject's home, respectively. No appreciable change in baseline salivary levels of CGRP and VIP was detected in control subjects. However, baseline salivary levels of CGRP and VIP were significantly elevated between attacks in allergic rhinosinusitis and migraine subjects compared to control values. For rhinosinusitis subjects, the amount of CGRP and VIP during attacks returned to baseline values following treatment with pseudoephedrine and relief of symptoms. Similarly, CGRP and VIP levels during a migraine headache were significantly reduced within 2 hours after sumatriptan treatment and reported symptom relief.

CONCLUSION

Correlation of CGRP and VIP saliva levels observed in our study supports physiologically coordinated regulation of trigeminal and parasympathetic nerve activation in allergic rhinosinusitis and migraine patients between and during attacks as well as following treatment. Furthermore, our findings demonstrate that analysis of human saliva neuropeptides may provide a semiquantitative index of pathological and therapeutic states and, therefore, function as a clinical model for studying neuronal mechanisms involved in migraine and rhinosinusitis.

New targets in acute migraine treatment

Migraine is a common and highly disabling neurological problem, whose acute treatment was revolutionized by the triptans, serotonin 5-HT1B/1D receptor agonists. Some patients do not respond to triptans, while others are not suitable for them largely because of contraindications based on vascular disease. The exploration of nonvasoconstrictor treatments for acute migraine offers the prospect of dramatic improvements in patient care, as well as important insights into the mechanisms of migraine. Possibilities for such developments include, calcitonin gene-related peptide receptor antagonists, serotonin 5-HT1F and 5-HT1D receptor agonists, glutamate excitatory amino acid receptor antagonists, nitric oxide synthase inhibitors and adenosine A1 receptor agonists. Taken together, the future for migraine and affected patients is bright and promising.

Can we Develop Neurally Acting Drugs for the Treatment of Migraine?

Serotonin (5-HT)(1B/1D) receptor agonists, which are also known as triptans, represent the most important advance in migraine therapeutics in the four millennia that the condition has been recognized. The vasoconstrictive activity of triptans produced a small clinical penalty in terms of coronary vasoconstriction but also raised an enormous intellectual question: to what extent is migraine a vascular problem? Functional neuroimaging and neurophysiological studies have consistently developed the theme of migraine as a brain disorder and, therefore, demanded that the search for neurally acting antimigraine drugs should be undertaken. The prospect of non-vasoconstrictor acute migraine therapies, potential targets for which are discussed here, offers a real opportunity to patients and provides a therapeutic rationale that places migraine firmly in the brain as a neurological problem, where it undoubtedly belongs.

New targets in the acute treatment of headache

PURPOSE OF REVIEW

The aim of this article is to review recently identified targets for the acute treatment of primary headache disorders.

RECENT FINDINGS

Calcitonin gene-related peptide (CGRP) receptor blockade has been shown to be an effective acute anti-migraine strategy and is a non-vasoconstrictor in terms of the mechanism of action. It is likely that direct blockade of CGRP release by inhibition of trigeminal nerves would be similarly effective in both migraine and cluster headache. Options for acute treatment based on preclinical work and initial clinical studies include: serotonin 5HT1F and 5HT1D receptor agonists, glutamate excitatory amino acid receptor antagonists, nitric oxide synthase inhibitors and adenosine A1 receptor agonists. Proof of principle studies with octreotide, a somatostatin receptor agonist, demonstrated it to be better than placebo in the acute treatment of cluster headache but not in the acute management of migraine.

SUMMARY

The prospect of a non-vasoconstrictor acute migraine therapy offers a real opportunity to patients, and perhaps more importantly, provides a therapeutic rationale to plant migraine and cluster headache firmly in the brain as neurological problems.

Sumatriptan causes parallel decrease in plasma calcitonin gene-related peptide (CGRP) concentration and migraine headache during nitroglycerin induced migraine attack

Sumatriptan-induced changes in plasma calcitonin gene-related peptide (CGRP) concentration and headache intensity were investigated in 19 female migraineurs during nitroglycerin-induced migraine attack. Sumatriptan nasal spray was administered 120 min after the onset of the attack. Blood samples were obtained immediately before and 60 min after sumatriptan administration. In those subjects whose migraine attack improved considerably 60 min after the treatment the plasma CGRP concentration decreased significantly (P<0.05). In contrast, plasma CGRP concentration failed to change in patients whose headache did not improve. In addition, plasma CGRP concentrations showed significant positive correlations with the headache scores both 60 and 120 min after sumatriptan administration (P<0.05). According to our results plasma CGRP concentration decreases parallel to headache intensity during sumatriptan treatment and this decrease in CGRP predicts effectiveness of antimigraine drug therapy. This supports that one of the main effects of triptans is to decrease CGRP release.

Calcitonin Gene-Related Peptide Antagonists as Treatments of Migraine and Other Primary Headaches

Calcitonin gene-related peptide (CGRP) is a potent neuromodulator that is expressed in the trigeminovascular system and is released into the cranial circulation in various primary headaches. CGRP is released in migraine, cluster headache and paroxysmal hemicrania. The blockade of its release is associated with the successful treatment of acute migraine and cluster headache. CGRP receptor blockade has recently been shown to be an effective acute anti-migraine strategy and is non-vasoconstricting in terms of the mechanism of action. The prospect of a non-vasoconstricting therapy for acute migraine offers a real opportunity to patients, and perhaps more importantly, provides a therapeutic rationale to reinforce migraine as a neurological disorder.

Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

Emerging drugs in migraine treatment

Ergot alkaloids have been the mainstay of acute migraine therapy for most of the 20th century. They have been supplanted by sumatriptan-like drugs ('triptans'), which, while keeping some of the ergotś mechanisms of action, show improved safety profiles due to their increased receptor selectivity. However, triptans are still far from being perfect drugs: they can constrict human coronary arteries at therapeutic doses and, therefore, are contra-indicated in the presence of cardiovascular disease. Another problem with these agents is recurrence of moderate-to-severe pain within 24 h of initial headache relief. While mechanism-driven drug design has led to the development of various novel, albeit still imperfect, acute antimigraine medications, only a few new prophylactic agents have been made available to migraine clinicians. The efficacy of most, if not all of them has been discovered serendipitously. This is probably due to the fact that, while the pathophysiology of a migraine attack is now reasonably understood, the mechanisms leading to an attack are still mostly unknown. This update analyses the profile of some antimigraine drugs in clinical trials, their mode of action and their potential advantages or drawbacks over already available agents.

Effects of sumatriptan on capsaicin-induced carotid haemodynamic changes and CGRP release in anaesthetized pigs

It is suggested that during a migraine attack capsaicin-sensitive trigeminal sensory nerves release calcitonin gene related peptide (CGRP), resulting in cranial vasodilatation and central nociception. Hence, inhibition of trigeminal CGRP release may prevent the above vasodilatation and, accordingly, abort migraine headache. Therefore, this study investigated the effects of sumatriptan (100 and 300 microg/kg, i.v.) on capsaicin-induced carotid haemodynamic changes and on CGRP release. Intracarotid (i.c.) infusions of capsaicin (10 microg/kg/min, i.c.) increased total carotid, arteriovenous anastomotic and capillary conductances as well as carotid pulsations, but decreased the difference between arterial and jugular venous oxygen saturations. Except for some attenuation of arteriovenous anastomotic changes, the capsaicin-induced responses were not affected by sumatriptan. Moreover, i.c. infusions of capsaicin (0.3, 1, 3 and 10 microg/kg/min, i.c.) dose-dependently increased the jugular venous plasma concentrations of CGRP, which also remained unaffected by sumatriptan. The above results support the contention that the therapeutic action of sumatriptan is mainly due to cranial vasoconstriction rather than trigeminal (CGRP release) inhibition.

Nitrergic and glutamatergic neuronal mechanisms at the trigeminovascular first-order synapse

Nitric oxide (NO) donors such as glyceryl trinitrate cause headache, which suggests involvement of NO in trigeminovascular sensory processing. Sensory transmission at first-order synapses is believed to involve glutamate and the question arises as to whether it is also involved in trigeminovascular sensation and whether it might interact with nitrergic mechanisms. We investigated these questions at the first central synapse in the trigeminovascular sensory system of the cat. Neuronal action potentials in the trigeminal nucleus were recorded while the superior sagittal sinus (SSS) or facial receptive field (RF) were stimulated electrically. Drugs, including the neuronal excitant glutamate, were applied to neurons via microiontophoresis. Results were obtained from 152 neurons activated with A-delta latencies by SSS stimulation and by glutamate. The NO donor S-nitrosoglutathione (SNOG, 50 nA) was applied iontophoretically to 41 neurons during SSS stimulation and 13 neurons during pulsatile glutamate ejection. Responses to both modes of stimulation were enhanced by SNOG; the proportion of neurons enhanced was 56% to SSS stimulation and 59% to glutamate. The inhibitor of nitric oxide synthase (NOS), N(omega)-propyl-L-arginine (p-ARG, 50 nA) was applied iontophoretically to 17 neurons during stimulation of SSS and to 10 neurons during pulsatile glutamate ejection. Responses to both stimuli were suppressed by p-ARG: The proportion of neurons suppressed were: to SSS stimulation 59% and to glutamate 80%. Microiontophoretic ejection of eletriptan (50 nA) reversibly suppressed responses of neurons to SSS stimulation, to RF electrical stimulation and to pulsatile iontophoretic application of glutamate. This suppression of responses was antagonised by the concurrent local iontophoretic application of the 5-HT1B/1D receptor antagonist GR127935 or by concurrent iontophoretic application of the selective 5-HT1D receptor antagonist BRL155732. These results suggest that glutamatergic mechanisms are important in sensory transmission in the trigeminovascular system and that they can be modulated by nitrergic and serotonergic mechanisms.

Effects of acute or chronic administration of anti-migraine drugs sumatriptan and zolmitriptan on serotonin synthesis in the rat brain

Triptans are 5-HT1 receptor agonists used as anti-migraine drugs. They act primarily on meningeal blood vessels and on trigeminovascular afferents, but they may also exert central effects. We studied the regional effects of acute and chronic treatment with sumatriptan or zolmitriptan on the rate of serotonin (5-HT) synthesis in the rat brain, using the alpha-14C-methyl-L-tryptophan quantitative autoradiographic method. Sumatriptan at low (300 microg/kg, s.c.) and high (1 mg/kg) doses, as well as zolmitriptan (100 microg/kg), acutely decreased (15-40%, P < 0.05-0.001) 5-HT synthetic rate in many brain regions, including the dorsal raphe nucleus. Chronically, sumatriptan (21 days, approximately 300 microg/kg per day via osmotic minipumps) induced significant increases in the 5-HT synthesis rate in many projection areas but had no effect in the dorsal raphe nucleus. The acute effects on 5-HT synthesis rate would be compatible with activation of 5-HT1 autoreceptors that inhibit serotonin release. In contrast, the increased 5-HT synthesis rate observed after chronic sumatriptan might possibly result from a down-regulation/desensitization of 5-HT1 receptors and/or unmasking of excitatory triptan-sensitive 5-HT receptors. Overall, the present findings indicate that not only zolmitriptan but also sumatriptan affect brain serotonergic neurotransmission.

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.

Calcitonin gene-related peptide receptor antagonist BIBN 4096 BS for the acute treatment of migraine

BACKGROUND

Calcitonin gene-related peptide (CGRP) may have a causative role in migraine. We therefore hypothesized that a CGRP-receptor antagonist might be effective in the treatment of migraine attacks.

METHODS

In an international, multicenter, double-blind, randomized clinical trial of BIBN 4096 BS, a highly specific and potent nonpeptide CGRP-receptor antagonist, 126 patients with migraine received one of the following: placebo or 0.25, 0.5, 1, 2.5, 5, or 10 mg of BIBN 4096 BS intravenously over a period of 10 minutes. A group-sequential adaptive treatment-assignment design was used to minimize the number of patients exposed.

RESULTS

The 2.5-mg dose was selected, with a response rate of 66 percent, as compared with 27 percent for placebo (P=0.001). The BIBN 4096 BS group as a whole had a response rate of 60 percent. Significant superiority over placebo was also observed with respect to most secondary end points: the pain-free rate at 2 hours; the rate of sustained response over a period of 24 hours; the rate of recurrence of headache; improvement in nausea, photophobia, phonophobia, and functional capacity; and the time to meaningful relief. An effect was apparent after 30 minutes and increased over the next few hours. The overall rate of adverse events was 25 percent after the 2.5-mg dose of the drug and 20 percent for the BIBN 4096 BS group as a whole, as compared with 12 percent for placebo. The most frequent side effect was paresthesia. There were no serious adverse events.

CONCLUSIONS

The CGRP antagonist BIBN 4096 BS was effective in treating acute attacks of migraine.

Migraine

Migraine is a very common neurobiological headache disorder that is caused by increased excitability of the CNS. It ranks among the world's most disabling medical illnesses. Diagnosis is based on the headache's characteristics and associated symptoms. The economic and societal effect of migraine is substantial: it affects patients' quality of life and impairs work, social activities, and family life. There are many acute and preventive migraine treatments. Acute treatment is either specific (triptans and ergots) or non-specific (analgesics). Disabling migraine should be treated with triptans. Increased headache frequency is an indication for preventive treatment. Preventive treatment decreases migraine frequency and improves quality of life. More treatments are being developed, which provides hope to the many patients whose migraines remain uncontrolled.

EP4 prostanoid receptor-mediated vasodilatation of human middle cerebral arteries

1. Dilatation of the cerebral vasculature is recognised to be involved in the pathophysiology of migraine. Furthermore, elevated levels of prostaglandin E(2) (PGE(2)) occur in the blood, plasma and saliva of migraineurs during an attack, suggestive of a contributory role. In the present study, we have characterised the prostanoid receptors involved in the relaxation and contraction of human middle cerebral arteries in vitro. 2. In the presence of indomethacin (3 microm) and the TP receptor antagonist GR32191 (1 microM), PGE(2) was found to relax phenylephrine precontracted cerebral arterial rings in a concentration-dependent manner (mean pEC(50) 8.0+/-0.1, n=5). 3. Establishment of a rank order of potency using the EP(4)>EP(2) agonist 11-deoxy PGE(1), and the EP(2)>EP(4) agonist PGE(1)-OH (mean pEC(50) of 7.6+/-0.1 (n=6) and 6.4+/-0.1 (n=4), respectively), suggested the presence of functional EP(4) receptors. Furthermore, the selective EP(2) receptor agonist butaprost at concentrations <1 microM failed to relax the tissues. 4. Blockade of EP(4) receptors with the EP(4) receptor antagonists AH23848 and EP(4)A caused significant rightward displacements in PGE(2) concentration-response curves, exhibiting pA(2) and pK(B) values of 5.7+/-0.1, n=3, and 8.4, n=3, respectively. 5. The IP receptor agonists iloprost and cicaprost relaxed phenylephrine precontracted cerebral arterial rings (mean pEC(50) values 8.3+/-0.1 (n=4) and 8.1+/-0.1 (n=9), respectively). In contrast, the DP and FP receptor agonists PGD(2) and PGF(2 alpha) failed to cause appreciable relaxation or contraction at concentrations of up to 30 microm. In the absence of phenylephrine contraction and GR32191, the TP receptor agonist U46619 caused concentration-dependent contraction of cerebral artery (mean pEC(50) 7.4+/-0.3, n=3). 6. These data demonstrate the presence of prostanoid EP(4) receptors mediating PGE(2) vasodilatation of human middle cerebral artery. IP receptors mediating relaxation and TP receptors mediating contraction were also functionally demonstrated.

Peripheral and central activation of trigeminal pain pathways in migraine: data from experimental animal models

Animal models for migraine have provided substantial advances on the mechanisms and mediators underlying migraine attacks. The neurogenic inflammation model has helped understanding the perivascular mechanisms underlying the pathophysiology of migraine attacks, the receptors involved and the effect of specific antimigraine drugs. The model based on probing the neuronal effects of nitroglycerin--an organic nitrate known to induce spontaneous-like migraine attacks in predisposed subjects--in the rat has provided interesting insights into the neuroanatomic circuits and neuropharmacological mechanisms involved in the initiation and repetition of migraine attacks [corrected].

S+ -flurbiprofen but not 5-HT1 agonists suppress basal and stimulated CGRP and PGE2 release from isolated rat dura mater

Neurogenic inflammation of the meninges, expressed in plasma extravasation and vasodilatation, putatively contributes to certain types of headache. Both, non-steroidal antiinflammatory drugs (NSAIDs) and serotonin-1 (5-HT1) receptor agonists are similarly effective antimigraine drugs but their mechanism of action is unclear. The clinical observation that sumatriptan lowered plasma levels of calcitonin gene-related peptide (CGRP), found increased during migraine attacks, drew attention to a possible inhibition of pro-inflammatory neuropeptide release from trigeminal afferents. An isolated preparation of fluid-filled rat skull cavities was used to study effects of NSAIDs and 5-HT(1B/D) agonists on the dura stimulated by inflammatory mediators (bradykinin, histamine and serotonin, 10(-5)M each). The release of immunoreactive CGRP (iCGRP) and immunoreactive PGE(2) (iPGE(2)) was measured in 5-min samples of superfusates using enzyme immunoassays. S(+)-flurbiprofen (10(-6)M) strongly reduced the basal and stimulated iCGRP release and abolished iPGE(2) release; R(-)-flurbiprofen showed much less effect on iPGE(2) liberation and did not influence iCGRP release. The 5-HT(1B/D) agonists naratriptan and CP93,129 were ineffective on both iCGRP and iPGE(2) release. Inspite of its weak COX blocking effect, R(-)-flurbiprofen is reported to exert antinociceptive effects, although it has not been tested in migraine. Only the potent COX blocker S(+)-flurbiprofen also suppressed iCGRP release while the 5-HT(1B/D) agonists were ineffective. Thus, inhibition of meningeal neuropeptide secretion is not a common action principle of the drugs that could be essential for their antimigraine effects.

Dihydroergotamine and its metabolite, 8'-hydroxy-dihydroergotamine, as 5-HT1A receptor agonists in the rat brain

1 In addition to stopping migraine attacks, dihydroergotamine (DHE) is an efficient drug for migraine prophylaxis. Whether 5-HT(1A) receptors could contribute to the latter action was assessed by investigating the effects of DHE and its metabolite, 8'-OH-DHE, on these receptors in the rat brain. 2 Membrane binding assays with [(3)H]8-OH-DPAT and [(3)H]WAY 100635 as radioligands showed that both DHE (IC(50)=28-30 nM) and 8'-OH-DHE (IC(50)=8-11 nM) are high-affinity 5-HT(1A) receptor ligands. 3 Both DHE and 8'-OH-DHE enhanced the specific binding of [(35)S]GTP-gamma-S to the dorsal raphe nucleus and the hippocampus in brain sections, but to a lower extent than 5-carboxamido-tryptamine (5-CT) in the latter area. 4 Both DHE (EC(50)=10.9+/-0.3 nM) and 8'-OH-DHE (EC(50)=30.4+/-0.8 nM) inhibited the firing of serotoninergic neurons in the dorsal raphe nucleus within brain stem slices. 5 Intracellular recording showed that 8'-OH-DHE was more potent than DHE to hyperpolarize CA1 pyramidal cells in rat hippocampal slices. 6 Both the stimulatory effects of DHE and 8'-OH-DHE on [(35)S]GTP-gamma-S binding and their electrophysiological effects were completely prevented by the selective 5-HT(1A) receptor antagonist WAY 100635. 7 As expected of 5-HT(1A) receptor partial agonists, DHE and 8'-OH-DHE prevented any subsequent hyperpolarization of CA1 pyramidal cells by 5-HT or 5-CT. 8 Through their actions at 5-HT(1A) auto- (in the dorsal raphe nucleus) and hetero-(notably in the hippocampus) receptors, DHE, and even more its metabolite 8'-OH-DHE, can exert both an inhibitory influence on neuronal excitability and anxiolytic effects which might contribute to their antimigraine prophylactic efficiency.

Neurogenic dural protein extravasation induced by meta-chlorophenylpiperazine (mCPP) involves nitric oxide and 5-HT2B receptor activation

The compound m-chlorophenylpiperazine (mCPP), which is known to trigger migraine-like head pain in some subjects, was evaluated for its ability to induce dural plasma protein extravasation (PPE) in guinea pigs. Intravenous mCPP dose-dependently increased PPE. This effect was inhibited by non-selective 5-HT2 receptor antagonists (methysergide, LY53857, LY215840), by a peripherally restricted 5-HT2 receptor antagonist (xylamidine) and by a 5-HT2B selective receptor antagonist (LY202146). These data suggests that peripheral 5-HT2B receptors mediate mCPP-induced PPE. The nitric oxide synthase inhibitor L-NAME and 5-HT1 agonist sumatriptan also blocked mCPP-induced PPE, suggesting a role for nitric oxide (NO) and the trigeminal system, respectively. NO release has been linked to activation of the 5-HT2B receptor on the vascular endothelium. However, LY202146 did not block PPE induced by electrical stimulation of the trigeminal ganglion. These data are consistent with activation of peripheral 5-HT2B receptors initiating PPE and the theory that selective 5-HT2B antagonists might be effective prophylactic therapies for migraine.

Constitutive nitric oxide synthase inhibition combined with histamine and serotonin receptor blockade improves the initial ovalbumin-induced arterial hypotension but decreases the survival time in brown norway rats anaphylactic shock

Anaphylactic shock accidents after allergen exposure are frequent. After immunization with ovalbumin (OVA), a common dietary constituent, we evaluated the efficacy of pretreatment with histamine-receptor or serotonin-receptor blockers administered alone or in combination with a nitric oxide synthase inhibitor (L-NAME) on OVA-induced anaphylactic shock in Brown Norway rats. Animals were allocated to the following groups (n = 6 each): control (0.9% saline); diphenydramine (15 mg kg(-1)); cimetidine (20 mg kg(-1)); diphenydramine + cimetidine; dihydroergotamine (50 microg kg(-1)); diphenydramine + cimetidine + dihydroergotamine; L-NAME (100 mg/kg) alone or associated with diphenydramine, cimetidine, diphenydramine + cimetidine, dihydroergotamine, or diphenydramine + cimetidine + dihydroergotamine. Mean arterial blood pressure (MABP), heart rate (HR), and survival time were monitored for 60 min following treatment. The shock was initiated with i.v. OVA. The MABP drop after i.v. OVA was worsened by diphenydramine and was modestly attenuated by cimetidine, dihydroergotamine, or both together. L-NAME potentiated slightly the effects of cimetidine and dihydroergotamine by lessening the initial MABP decrease, but this transient effect was not sufficient to prevent the final collapse or to improve survival time. Decreased vasodilatory (prostaglandins E2), increased vasoconstrictory (thromboxane B2) prostaglandins, and unchanged leukotriene C4 concentrations were contributory to the overall hemodynamic changes. Thus, the combined blockade of vasodilator mediators (histamine, serotonin, and nitric oxide) slowed the MABP drop in anaphylactic shock, but did not improve survival. More studies are needed to understand these discordant effects.

Preclinical studies characterizing the anti-migraine and cardiovascular effects of the selective 5-HT1D receptor agonist PNU-142633

The present study describes the preclinical pharmacology of a highly selective 5-HT1D receptor agonist PNU-142633. PNU-142633 binds with a Ki of 6 nm at the human 5-HT1D receptor and a Ki of> 18 000 nm at the human 5-HT1B receptor. The intrinsic activity of PNU-142633 at the human 5-HT1D receptor was determined to be 70% that of 5-HT in a cytosensor cell-based assay compared with 84% for that of sumatriptan. PNU-142633 was equally effective as sumatriptan and a half-log more potent than sumatriptan in preventing plasma protein extravasation induced by electrical stimulation of the trigeminal ganglion. Like sumatriptan, PNU-142633 reduced the increase in cat nucleus trigeminal caudalis blood flow elicited by electrical stimulation of the trigeminal ganglion compared with the vehicle control. The direct vasoconstrictor potential of PNU-142633 was evaluated in vascular beds. Sumatriptan increased vascular resistance in carotid, meningeal and coronary arteries while PNU-142633 failed to alter resistance in these vascular beds. These data are discussed in relation to the clinical findings of PNU-142633 in a phase II acute migraine study.

Triptans reduce the inflammatory response in bacterial meningitis

Severe headache and meningism provide clear evidence for the activation of trigeminal neurotransmission in meningitis. The authors assessed the antiinflammatory potential of 5HT1B/D/F receptor agonists (triptans), which inhibit the release of proinflammatory neuropeptides from perivascular nerve fibers. In a 6-hour rat model of pneumococcal meningitis, zolmitriptan and naratriptan reduced the influx of leukocytes into the cerebrospinal fluid, and attenuated the increase of regional cerebral blood flow. Elevated intracranial pressure as well as the brain water content at 6 hours was reduced by triptans. These effects were partially reversed by a specific 5HT1D as well as by a specific 5HT1B receptor antagonist. Meningitis caused a depletion of calcitonin gene-related peptide (CGRP) and substance P from meningeal nerve fibers, which was prevented by zolmitriptan and naratriptan. In line with these findings, patients with bacterial meningitis had significantly elevated CGRP levels in the cerebrospinal fluid. In a mouse model of pneumococcal meningitis, survival and clinical score at 24 hours were significantly improved by triptan treatment. The findings suggest that, besides mediating meningeal nociception, meningeal nerve fibers contribute to the inflammatory cascade in the early phase of bacterial meningitis. Adjunctive treatment with triptans may open a new therapeutic approach in the acute phase of bacterial meningitis.

Adenosine A1 receptor agonists inhibit trigeminovascular nociceptive transmission

There is a considerable literature to suggest that adenosine A1 receptor agonists may have anti-nociceptive effects, and we sought to explore the role of adenosine A1 receptors in a model of trigeminovascular nociceptive transmission. Cats were anaesthetized (alpha-chloralose 60 mg/kg, intraperitoneally), and prepared for physiological monitoring. The superior sagittal sinus (SSS) was stimulated electrically, and linked units were recorded in the trigeminocervical complex. Post-stimulus histograms were constructed to analyse the responses and the effect of drug administration. Blood was sampled from the external jugular vein to determine levels of calcitonin gene-related peptide (CGRP) release before and after drug administration. Intravenous administration of the highly selective adenosine A1 receptor agonist, GR79236 (3-100 microg/kg) had a dose-dependent inhibitory effect on SSS-evoked trigeminal activity. The maximal effect (80 +/- 6% reduction in probability of firing) was seen at 100 microg/kg. The neuronal inhibitory effect of GR79236 could be inhibited by the selective adenosine A1 receptor antagonist DPCPX (300 microg/kg; P < 0.05). SSS stimulation increased cranial CGRP levels from 33 +/- 2 pmol/l (n = 6) to 64 +/- 3 pmol/l, an effect substantially reduced by pre-treatment with GR79236 (30 microg/kg; P < 0.01). The selective low efficacy adenosine A1 receptor agonist, GR190178 (30-1000 microg/kg i.v.), also inhibited SSS-evoked neuronal activity in a dose-dependent fashion. In this model of trigeminovascular nociception, adenosine A1 receptor activation leads to neuronal inhibition without concomitant vasoconstriction, suggesting a novel avenue for the treatment of migraine and cluster headache.

New insights into the molecular actions of serotonergic antimigraine drugs

Migraine is a painful and debilitating neurological disorder that affects approximately 10% of the adult population in Western countries. Sensitization and activation of the trigeminal ganglia nerves that innervate the meningeal blood vessels is believed to play an important role in the initiation and maintenance of migraine pain. In this capacity, release of the neuropeptide calcitonin gene-related peptide (CGRP) and the resultant neurogenic inflammation is thought to underlie the pathophysiology of migraine. Largely due to the success of the serotonin Type 1 migraine drugs such as sumatriptan, migraine pathology and therapy has become a focus of intensive clinical and physiological research during the past decade. The effectiveness of these drugs is thought to be due to their ability to block the stimulated secretion of neuropeptides from trigeminal nerves to break the vicious nociceptive cycle of migraine. A component of this nociceptive cycle involves activation of mitogen-activated protein kinase signaling pathways. Indeed, activation of mitogen-activated protein kinase pathways can increase CGRP neuropeptide synthesis and secretion. Recently, the serotonin Type 1 agonists have been shown to cause a prolonged increase in intracellular Ca(2+) in trigeminal ganglia neurons and an increased phosphatase activity that can repress stimulated CGRP secretion and transcription. Identification of molecular signaling events in migraine pathology and therapy has provided new insight into the pharmacology and signaling mechanisms of sumatriptan and related drugs, and may provide the foundation for development of novel treatments for migraine.

CGRP may play a causative role in migraine

Calcitonin gene-related peptide (CGRP) has been detected in increased amounts in external jugular venous blood during migraine attacks. However, it is unknown whether this is secondary to migraine or whether CGRP may cause headache. In a double-blind crossover study, the effect of human alphaCGRP (2 microg/min) or placebo infused intravenously for 20 min was studied in 12 patients suffering from migraine without aura. Headache intensity was scored on a scale from 0 to 10. Two patients were excluded due to severe hypotension and one because she had an infection. In the first hour median peak headache score was 1.0 in the halphaCGRP group vs. 0 in the placebo group (P < 0.01). During the following 11 h all patients experienced headaches after halphaCGRP vs. one patient after placebo (P = 0.0004). The median maximal headache score was 4 after CGRP and 0 after placebo (P = 0.006). In three patients after halphaCGRP, but in no patients after placebo, the delayed headache fulfilled the IHS criteria for migraine without aura. As intravenous administration of halphaCGRP causes headache and migraine in migraineurs, our study suggests that the increase in CGRP observed during spontaneous migraine attacks may play a causative role.

5-HT(1B) and 5-HT(1D) receptors in the human trigeminal ganglion: co-localization with calcitonin gene-related peptide, substance P and nitric oxide synthase

5-Hydroxytryptamine (5-HT) is implicated in migraine and agonist directed against 5-HT(1B) and 5-HT(1D) receptors are commonly used as effective therapies. The antimigraine mechanisms involve the inhibition of intracranial sensory neuropeptide release. In order to determine which 5-HT(1) receptor subtypes are involved we have by immunocytochemistry examined the distribution of 5-HT(1B) and 5-HT(1D) receptors in the human trigeminal ganglia, and addressed which of them colocalize with calcitonin gene-related peptide (CGRP), substance P (SP) or nitric oxide synthase (NOS). We detected that 5-HT(1D) receptor immunoreactivity (i.r.) was predominantly expressed in medium-sized cells (86% of positive cells, 30-60 microm). About 9% of the 5-HT(1D) receptor i.r. cells were large in size (> 60 microm) and 5% were small in size (< 30 microm). In a similar pattern, 5-HT(1B) receptor i.r. was mainly expressed in medium-sized cells (81% in 30-60 microm, 15% in > 60 microm and 4% in < 30 microm). Double immunostaining was used to determine whether the 5-HT(1B) or 5-HT(1D) receptor immunoreactive cells co-localized with either CGRP, SP or NOS. Thus, 89% of the CGRP i.r. cells expressed 5-HT(1D) receptor i.r. and 65% of the CGRP positive cells were 5-HT(1B) receptor positive. Most of the 5-HT(1D) (95%) and the 5-HT(1B) (94%) receptor i.r. cells showed SP immunostaining and 83% of 5-HT(1D) receptor and 86% of 5-HT(1B) receptor i.r. cells contained NOS. In conclusion, both 5-HT(1B) and 5-HT(1D) receptors are expressed in the human trigeminal ganglion and they are mainly localized in medium-sized cells and they seem to colocalize with CGRP, SP and NOS.

The effect of adrenergic compounds on neurogenic dural vasodilatation

The pharmacology of neurogenic trigeminovascular vasodilator responses in the dura mater is of interest for understanding the pathophysiology of migraine and to develop new therapies for this disabling common condition. Aminergic mechanisms have been implicated in migraine through direct study of amines in patients, and by inference from the pharmacology of many effective anti-migraine compounds, particularly preventative agents. This study used intravital microscopy to assess the role of aminergic transmission in neurogenic dural vasodilatation (NDV) by measuring directly the diameter of dural arteries in sodium pentobarbitone anaesthetised rats. Electrical stimulation of a closed cranial window produces, by local depolarisation of nerves, dural vessel dilation that is monitored continuously on-line using video-microscopy and a video dimension analyser. This dural vasodilatation was not affected by pre-treatment with an alpha1-adrenoceptor agonist (phenylephrine, 1 and 5 microg/kg), or antagonist (corynanthine, 1 and 2 mg/kg), nor by an alpha2-adrenoceptor agonist (UK14,304, 5 microg/kg) or antagonist (yohimbine, 1 and 3 mg/kg). Similarly, we saw no effect of beta-adrenoceptor blockade (propranolol, 1 and 3 mg/kg). The lack of an inhibitory effect of UK14,304 the model of neurogenic dural vasodilation contrasts with its effect in neurogenic dural plasma protein extravasation model. The lack of inhibition of beta-adrenoceptor antagonists in the neurogenic vasodilatation model contrasts with their usefulness as migraine prophylactics, and suggests that their mechanism of action in migraine is unlikely to be through sensory trigeminal fibre terminals at the neurovascular junction. Moreover, the data indicate that the adrenergic system does not play a significant role in neurogenic dural vasodilation.

Co-localization of 5-HT(1B/1D/1F) receptors and glutamate in trigeminal ganglia in rats

Anti-migraine triptan drugs are 5-HT(1B/1D) receptor agonists which are thought to block the neurotransmitter/neuropeptide release from sensory nerve terminals and directly constrict blood vessel smooth muscles. In the present study, we have investigated the anatomical basis for a possible modulation of glutamate release from trigeminal ganglion neurons by 5-HT(1B/1D) receptor agonists and by 5-HT1F receptor agonists, using double immunohistochemical staining technique in the rat. The majority of 5-HT1B, 5-HT1D or 5-HT1F receptor positive neurons were also glutamate positive, but both 5-HT1B, 5-HT1D or 5-HT1F receptor single-labeled and glutamate single-labeled neurons were observed. These results suggest that 5-HT(1B/1D/1F) receptor agonists may modulate glutamate release, and that one mechanism of their anti-migraine action could be the blockade of glutamate release.

Neuronal messengers in the human cerebral circulation

In recent years our knowledge of the nervous control of the cerebral circulation has increased. The use of denervations and retrograde tracing in combination with immunohistochemical techniques has demonstrated that cerebral vessels are supplied with sympathetic, parasympathetic, and sensory nerve fibers and possibly central pathways containing a multiplicity of new transmitter substances in addition to the classical transmitters. The majority of these transmitters are neuropeptides. More recently it has been suggested that a gaseous transmitter, nitric oxide (NO) also could participate in the neuronal regulation of cerebral blood flow. Although little is known about the physiological actions and inter-relationships among all these putative neurotransmitters, their presence within cerebrovascular nerve fibers will make it necessary to revise our view on the mechanisms of cerebrovascular neurotransmission.

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.

[Anti-migraine drug sumatriptan succinate, a 5-HT1B/1D-receptor agonist]

Sumatriptan succinate (SMT) was a highly specific 5-HT1-receptor agonist. It showed high affinity only for 5-HT but no affinity for other neurotransmitter receptors such as muscarinic, dopamine D1, D2, adrenergic alpha 1, alpha 2, and beta. Furthermore, it was highly selective for 5-HT1B/1D-receptor and showed no affinity for 5-HT2 and 5-HT3 receptors. SMT contracted isolated cranial arteries such as basilar, midcerebral, temporal arteries and large arteries in the dura matter, but did not contract coronary, femoral, mesenteric and other arteries. Reflecting these results, SMT induced vasoconstriction of carotid artery, but produced practically no contractile responses in the other arteries mentioned above in anaesthetized animals. These pharmacological characteristics of SMT were different from those of ergot alkaloids, current anti-migraine drugs, which contracted coronary, femoral and other arteries as well. SMT inhibited neurotransmitter release, including CGRP, from trigeminal nerve terminals. Consequently protein extravasation induced by CGRP was inhibited and neurogenic inflammation could be suppressed. It was believed that SMT showed its anti-migraine activity through cranial vasoconstriction via 5-HT1B/1D receptors, since it did not show any analgesic activities. Its clinical efficacy on migraine and cluster headache had been already confirmed in about 100 western countries. Its efficacy was also shown by open trials and placebo controlled double blind tests in Japan.

Neurogenic inflammation in the context of migraine

Despite considerable research into the pathogenesis of idiopathic headaches, such as migraine, the pathophysiological mechanisms underlying them remain poorly understood. Although it is well established that the trigeminal nerve becomes activated during migraine, the consequences of this activation remain controversial. One theory, based on preclinical observations, is that activation of trigeminal sensory fibers leads to a painful neurogenic inflammation within the meningeal (dural) vasculature mediated by neuropeptide release from trigeminal sensory fibres and characterized by plasma protein extravasation, vasodilation, and mast cell degranulation. Effective antimigraine agents such as ergots, triptans, opioids, and valproate inhibit preclinical neurogenic dural extravasation, suggesting that this activity may be a predictor of potential clinical efficacy of novel agents. However, several clinical trials with other agents that inhibit this process preclinically have failed to show efficacy in the acute treatment of migraine in man. Alternatively, it has been proposed that painful neurogenic vasodilation of meningeal blood vessels could be a key component of the inflammatory process during migraine headache. This view is supported by the observation that jugular plasma levels of the potent vasodilator, calcitonin gene-related peptide (CGRP) are elevated during the headache and normalized by successful sumatriptan treatment. Preclinically, activation of trigeminal sensory fibers evokes a CGRP-mediated neurogenic dural vasodilation, which is blocked by dihydroergotamine, triptans, and opioids but unaffected by NK1 receptor antagonists that failed in clinical trials. These observations suggest that CGRP release with associated neurogenic dural vasodilation may be important in the generation of migraine pain, a theory that would ultimately be tested by the clinical testing of a CGRP receptor antagonist.

An in vivo rat model to study calcitonin gene related peptide release following activation of the trigeminal vascular system

Calcitonin gene related peptide (CGRP) released from the C-fibers projecting from the trigeminal ganglion to the meninges has been suggested to play a crucial role in the pathophysiology of headache, particularly migraine. In humans it has been shown that CGRP is released during migraine-attacks, and this is attenuated by the administration of typical anti-migraine drugs such as dihydroergotamine or sumatriptan. We describe a new rat model which allows the study of CGRP release from the meninges into venous blood following activation of the trigeminal vascular system. The effects of classical and new anti-migraine drugs such as acetylsalicylic acid (ASA), sumatriptan and the new high efficacy 5-HT1B/1D agonist donitriptan (4-[4-[2-(2-aminoethyl)-1H-indol-5-yloxyl]acetyl]piperazinyl-1-yl]benzonitrile) were evaluated in comparison with the established model of neurogenic inflammation in the meninges. Sumatriptan and donitriptan inhibited CGRP release as well as neurogenic inflammation. ASA, however, attenuated neurogenic inflammation, but not CGRP release, confirming the concept of prejunctional inhibition of CGRP release by 5-HT1B/1D receptors. This new model allows the further study of prejunctional pharmacology and mechanisms of neuropeptide release in the trigeminal vascular system, which might be crucial for the further development of potent, more effective anti-migraine drugs.

Functional immunohistochemistry of neuropeptides and nitric oxide synthase in the nerve fibers of the supratentorial dura mater in an experimental migraine model

The supratentorial cerebral dura of the albino rat is equipped with a rich sensory innervation both in the connective tissue and around blood vessels, which includes nociceptive axons and their terminals; these display intense calcitonin gene-related peptide (CGRP) immunoreactivity. Stereotactic electrical stimulation of the trigeminal (Gasserian) ganglion, regarded as an experimental migraine model, caused marked increase and disintegration of club-like perivascular CGRP-immunopositive nerve endings in the dura mater and induced an apparent increase in the lengths of CGRP-immunoreactive axons. Intravenous administration of sumatriptan or eletriptan, prior to electrical stimulation, prevented disintegration of perivascular terminals and induced accumulation of CGRP in terminal and preterminal portions of peripheral sensory axons. Consequently, immunopositive terminals and varicosities increased in size; accumulation of axoplasmic organelles resulted in the "hollow" appearence of numerous varicosities. Since triptans exert their anti-migraine effect by virtue of agonist action on 5-HT(1D/B) receptors, we suggest that these drugs prevent the release of CGRP from perivascular nerve terminals in the dura mater by an action at 5-HT(1D/B) receptors. Nitroglycerine (NitroPOHL), given subcutaneously to rats, induces increased beading of nitric oxide synthase (NOS)-immunoreactive nerve fibers in the supratentorial cerebral dura mater, and an apparent increase in the number of NOS-immunoreactive nerve fibers in the dural areas supplied by the anterior and middle meningeal arteries, and the sinus sagittalis superior. Structural alterations of nitroxidergic axons innervating blood vessels of the dura mater support the idea that nitric oxide (NO) is involved in the induction of headache, a well-known side effect of coronary dilator agents.

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.

N- and L- but not P/Q-type calcium channels contribute to neuropeptide release from rat skin in vitro

Here we directly demonstrate the liberation of CGRP from rat skin in vitro induced by high extracellular concentrations of KCl. The EC50 was 52 mM KCl and saturation was reached from 80 mM KCl. The release was entirely dependent on the presence of extracellular calcium ions. It was reduced by nonsubtype selective inhibition of voltage-operated calcium channels (VOCCs). Application of selective antagonists suggest expression of L-type and N-type but not P/Q-type VOCCs in cutaneous nociceptive terminals. These may be activated by any suprathreshold depolarizing stimuli to induce neurogenic inflammation. The expression pattern greatly differs from central nociceptive terminals where, in addition, P/Q-type VOCC have been found.

Depletion of substance P, neurokinin A and calcitonin gene-related peptide from the contralateral and ipsilateral caudal trigeminal nucleus following unilateral electrical stimulation of the trigeminal ganglion; a possible neurophysiological and neuroanatomical link to generalized head pain

Primary trigeminal neurons of the trigeminal ganglion (TG) innervate major parts of the face and head, including the dura. Electrical stimulation of the TG at specific parameters, can activate its nociceptive neurons and may serve as an experimental pain model. Markowitz [J. Neurosci. 7 (1987) 4129] reported that electrical stimulation of the trigeminal ganglion (TG) causes extravasation of plasma proteins from venules of the trigeminally innervated domain possibly due to the release of vasoactive substances. Neurogenic inflammation (vasodilatation, plasma protein extravasation, release of vasoactive peptides) in dura may serve as one of the possible pathomechanisms underlying vascular head pain [Moskowitz, Ann. Neurol. 16 (1984) 157]. We performed a unilateral electrical stimulation (7.5 Hz, 5 ms, 0.8-1.4 mA for 5 min) of the TG in rat, to induce a neurogenic inflammation in the peripheral trigeminal domain including the dura, looking for calcitonin gene related peptide (CGRP), substance P (SP) and neurokinin A (NKA) immunoreactivity (IR) in the caudal trigeminal nucleus (CTN) into which massive central trigeminal processes terminate. Here, we show patchy depletion(s) of CGRP-, SP- and NKA-IRs in the contralateral CTN of the rat in addition to their ipsilateral depletion. Such depletion is due to the release of these neuropeptides in the CTN leading to the activation of bilateral trigeminal nociceptive pathway. These data afford the possibility that under specific frequencies (which may roughly correlate to the intensity of the painful stimulus) and/or specific intensities (may correlate to specific areas of the peripheral trigeminal domain) of stimulation, activation of one side of the TG may activate bilateral trigeminal nociceptive pathway leading to the perception of an ill localized/generalized pain or headache rather than a unilateral one.

Calcitonin gene-related peptide levels during nitric oxide-induced headache in patients with chronic tension-type headache

It has been proposed that nitric oxide (NO) induced headache in primary headaches may be associated with release of calcitonin gene-related peptide (CGRP). In the present study we aimed to investigate plasma levels of CGRP during headache induced by the NO donor glyceryl trinitrate (GTN) in 16 patients with chronic tension-type headache and 16 healthy controls. The subjects were randomly allocated to receive 0.5 microg/kg/min GTN or placebo over 20 min on two headache-free days. Blood samples were collected at baseline, 10, 20 and 60 min after start of infusion. Both patients and controls developed significantly stronger immediate headache on the GTN day than on the placebo day and the headache was significantly more pronounced in patients than in controls. There was no difference between the area under the CGRP curve (AUCCGRP) on GTN vs. placebo day in either patients (P=0.65) or controls (P=0.48). The AUCCGRP recorded on the GTN day did not differ between patients and controls (P=0.36). Both in patients and controls, CGRP levels changed significantly over time, on both the GTN and placebo days (P < 0.05). The present study indicates that NO-induced immediate headache is not associated with release of CGRP.

Treatment of childhood headaches

Migraine and tension-type headaches are two of the most common types of primary headache disorders in children. Migraine is a primary central nervous system disorder characterized by triggered or spontaneous episodes of activation of trigemino-vascular complex, neurogenic inflammation around vessels and meninges, and stimulation of the peripheral and central pain pathways of the trigemino-cervical complex. The triptans, by their selective agonistic action on 5-HT1B/1D receptors, are very effective in the treatment of migraine pain and associated symptoms. Early studies on the safety and efficacy of triptans in the management of childhood migraine show encouraging results. We propose a stratified-care model for the management of migraine in children, and discuss pharmacotherapy based on the pathophysiologic mechanisms of migraine pain. Management of tension-type headaches requires comprehensive medical and psychologic evaluation and an individualized approach for a successful outcome.

Pharmacological evidence for CGRP uptake into perivascular capsaicin sensitive nerve terminals

Specific mechanisms, providing reuptake of cathecholamine and amino acid neurotransmitters (e.g. serotonin and glutamate) into cells of the central nervous system are well known, whereas neuronal uptake of neuropeptide transmitters have not previously been reported. In the present study we present evidence for uptake of the 37 amino acid neuropeptide, calcitonin gene-related peptide (CGRP) into perivascular terminals of capsaicin sensitive nerve fibres, innervating the guinea-pig basilar artery. Release of CGRP from perivascular nerve terminals was obtained by capsaicin-induced vanilloid receptor-stimulation and detected as CGRP receptor-mediated dilation of isolated segments of the guinea-pig basilar artery. Following three repeated capsaicin challenges, CGRP-depleted segments were incubated with CGRP. This caused significant reappearance of capsaicin-induced vasodilatory responses. These responses were dependent on duration and concentration of the preceding CGRP incubation and were inhibited by the CGRP receptor antagonist, CGRP(8 - 37). The CGRP-re-depletion was significantly reduced when CGRP(8 - 37) was present during the preceding CGRP incubation. Thus, presynaptic CGRP receptors are likely to be involved in neuronal CGRP uptake. Incubating the artery segments with (125)I-CGRP allowed subsequent detection of capsaicin-induced (125)I-release. Immunohistochemical experiments showed that only terminal CGRP is subject to capsaicin-induced depletion in vitro, whereas CGRP-immunoreactivity endures in the nerve fibres.

4991W93 inhibits release of calcitonin gene-related peptide in the cat but only at doses with 5HT(1B/1D) receptor agonist activity?

Calcitonin gene-related peptide (CGRP) is a marker for trigeminovascular activation and is released during the headache phase of migraine and cluster headache. CGRP may have a role in migraine through its potent cranial vasodilator effects, or by an action on trigeminal nerve activity, both of which are targeted by 5HT(1B/1D) agonist drugs. CP122,288, a conformationally restricted analogue of sumatriptan that is a potent inhibitor of neurogenic plasma protein extravasation (PPE), was ineffective at inhibiting CGRP release at a single low dose; and is also ineffective as an acute anti-migraine compound. However, it remained unclear as to whether, as a class, the conformationally-restricted triptan analogues could have inhibitory effects on CGRP in higher doses. 4991W93, a conformationally restricted analogue of zolmitriptan, is also a potent inhibitor of PPE at doses without 5HT(1B/1D)-mediated effects, that was developed as an anti-migraine drug, and thus was suitable to test whether higher doses of such conformationally restricted triptan analogues could inhibit trigeminal-evoked CGRP release. The superior sagittal sinus (SSS) was stimulated in 14 anaesthetised cats and external jugular vein blood samples were analysed by radioimmunoassay for CGRP levels before, 1 min after SSS stimulation, and 1 min after SSS stimulation in the presence of 4991W93. Stimulation of the SSS resulted in release of CGRP from the external jugular vein. 4991W93 at a dose of 0.1 and 10 microg/kg, selected for maximal PPE blocking effects in rodents, was ineffective at inhibiting CGRP release, with an SSS stimulation level of 78+/-4 pmol/l compared to a post-4991W93 level of 79+/-3 pmol/l (n=4). In comparison CGRP release was inhibited after a dose of 100 microg/kg 4991W93 from 64+/-6 to 36+/-3 pmol/l (n=5). Given that 4991W93 is inactive clinically at non-vascular doses, it seems clear that the 5HT(1B/1D) agonist effects of the compound are necessary for blockade of CGRP release and thus any anti-migraine action. Taken with the clinical results, these data emphasise the importance of CGRP release in migraine, and suggest that other non-5HT-based pharmacological targets may account for PPE blockade in animal studies.

Cortical spreading depression produces increased cGMP levels in cortex and brain stem that is inhibited by tonabersat (SB-220453) but not sumatriptan

Migraine headache is proposed to be mediated by nitric oxide (NO). Suitable mechanisms for eliciting increases in brain NO concentration in migraineurs have not yet been identified, although, animal models highlight cortical spreading depression (CSD) as a potential candidate. These studies have focused on CSD-associated NO release at highly acute time points (min-hours) and have not employed markers of NO metabolism with direct clinical application e.g. cGMP. The current study evaluated changes in plasma cGMP concentrations 3 h, 24 h and 3 days post-CSD and compared these to cortical and brainstem cGMP concentrations at 3 days. Moreover, this study also examined the effect of sumatriptan, a clinically effective antimigraine agent, and tonabersat (SB-220453) a potential novel antimigraine agent, on any observed changes in cGMP. Following pre-treatment with vehicle (n=3), sumatriptan (300 microg kg(-1) i.v, n=3) or tonabersat (SB-220453 10 mg kg(-1) i.p., n=3), CSD was evoked in anaesthetised rats by a 6-min KCl application to the parietal cortex. In the vehicle-treated group a median of eight depolarisations, were observed. Sumatriptan had no effect on the number of depolarisations, whereas tonabersat significantly reduced the number of events (median=2). No depolarisation events were observed throughout the recording period in the sham group. Following KCl application plasma cGMP concentrations were reduced up to 24 h post-CSD, but not significantly different from sham animals at 3 days. CSD in vehicle-treated animals produced a highly significant elevation in cGMP concentration in the brain stem 3 days after application of KCl. cGMP concentration increased 2.3-fold from 68+/-8 fmol/mg in sham animals (n=3) to 158+/-28 fmol/mg in the vehicle group. This increase in brain stem cGMP was abolished by tonabersat pre-treatment but not by sumatriptan.

The pharmacology of headache

Headache is a common problem which besets most of us at some time or the other. The pharmacology of headache is complex in an overall sense but can be understood in terms of the anatomy and physiology of the pain-producing structures. Migraine can be used as a template to understand the activation of nociceptive systems in the head and thus their neurotransmitter mediation and modulation. In recent years, the role of serotonin (5-HT) in headache pharmacology has been unravelled in the context of both understanding its role in the nociceptive systems related to headache and by exploiting its 5-HT1 receptor subtypes in headache therapeutics. The pharmacology of the head pain systems, as they are known and as they might evolve, are explored in the context of both, the anatomy and physiology of trigeminovascular nociception and in the context of clinical questions, such as those of efficacy, headache recurrence and adverse events.

Effects of eletriptan on the peptidergic innervation of the cerebral dura mater and trigeminal ganglion, and on the expression of c-fos and c-jun in the trigeminal complex of the rat in an experimental migraine model

Nociceptive axons and terminals in the supratentorial cerebral dura mater display an intense calcitonin gene-related peptide (CGRP) immunoreactivity. In an experimental migraine model, it has been shown that electrical stimulation of the rat trigeminal ganglion induced an increase in the lengths of CGRP-immunoreactive axons, increased size and number of pleomorphic axonal varicosities in the dura mater, and an increased number of c-jun and c-fos protein-expressing nerve cells in the trigeminal complex. We demonstrate the effect of the highly specific and moderately lipophilic serotonin agonist eletriptan (Pfizer) which prevents the effects of electrical stimulation in the dura mater. Eletriptan also affected the caudal trigeminal complex; it markedly reduced the numbers of the oncoprotein-expressing cells, mainly after stimulation and to some extent also in nonstimulated animals. Eletriptan also affected expression of CGRP in perikarya of trigeminal ganglion cells, insofar as the number of small nerve cells exhibiting a compact CGRP immunoreaction was decreased to one quarter of the original value. In all these respects, eletriptan acted in a similar way to sumatriptan, with the notable exception that eletriptan also blocked the stimulation-induced effects in the nucleus caudalis trigemini and the upper cervical spinal cord (trigeminal complex), whereas sumatriptan did not. It is concluded that eletriptan, acting on perikarya and both the peripheral and the central axon terminals of primary sensory neurons, exerts its antimigraine effect by an agonist action on 5-HT1B/1D receptors throughout the entire trigeminal system, probably by passing the blood-brain-barrier because of its lipophilic character.

Release of calcitonin gene-related peptide (CGRP) from guinea pig dura mater in vitro is inhibited by sumatriptan but unaffected by nitric oxide

Migraine attacks can be provoked by administration of nitroglycerin, suggesting a role for nitric oxide (NO). The fact that release of the neuropeptide CGRP from trigeminal sensory nerves occurs during the pain phase of migraine and that NO can augment transmitter release prompted us to study CGRP release from the in situ dura mater in guinea pig skulls. Release of CGRP by capsaicin or by high potassium concentration was concentration-dependent and counteracted in calcium-free medium. The anti-migraine compound, sumatriptan, inhibited CGRP release via the 5-HT1-receptor. The NO donors, nitroglycerin, sodium nitroprusside and S-nitroso-N-acetylpenicillamine did not influence CGRP release, alone or together with the stimulants. We concluded that the skull preparation is well suited for scrutinizing CGRP release from dura mater. The fact that sumatriptan inhibits CGRP release as in migraine patients suggests a use for the present preparation in headache research.

Case reports: headache caused by a spinal cord stimulator in the upper cervical spine

We report persistent headaches developing in a patient subsequent to the placement of a spinal cord stimulator in the upper cervical spine. These persistent headaches responded to dihydroergotamine and sumatriptan. Headaches ceased upon repositioning of the stimulator lower in the cervical spine. We postulate an effect of the device on the trigeminovascular system via the nucleus caudalis trigeminalis and/or spinal trigeminal tract.

Different effects of GABAergic anticonvulsants on 4-aminopyridine-induced spontaneous GABAergic hyperpolarizations of hippocampal pyramidal cells--implication for their potency in migraine therapy

Clinical studies indicate anti-migrane efficacy of the probably GABAergic anticonvulsants valproate and gabapentin. For the GABAergic anticonvulsants vigabatrin and tiagabine, studies about antimigrane efficacy are missing. The aim of this study was to test the GABAergic potency of these drugs in vitro before further clinical studies. Intracellular recordings were obtained from hippocampal pyramidal cells. Spontaneous GABAergic hyperpolarizations (SGH) elicited by 75 microM 4-aminopyridine were used to test the effect of these drugs on GABA-dependent potentials. Tiagabine (0.1 mM) prolonged the duration of SGH. Furthermore, monophasic SGH turned over into triphasic typical GABAergic membrane potential fluctuations within 20 min. In contrast, valproate, gabapentin, and vigabatrin failed to affect SGH up to 60 min of application. The reason for the fast action of tiagabine on SGH may be caused by a faster increase of synaptic GABA levels compared with other drugs. As migraine therapy benefits from an augmentation of GABA activity, we recommend clinical studies of tiagabine as a fast-acting agent in migraine attacks.

Evidence for increased plasma levels of calcitonin gene-related peptide in migraine outside of attacks

Although calcitonin gene-related peptide (CGRP) has been shown to be elevated in jugular venous blood of adult migraineurs during acute migraine attacks, it remains unknown whether CGRP is increased outside of attacks in jugular or cubital venous blood. The aim of the present study was to compare interictal plasma levels of CGRP in adult migraine patients and in healthy controls. Twenty patients with a diagnosis of migraine with or without aura and 20 healthy controls were included. In blood from the cubital vein, CGRP levels were significantly higher in patients (75+/-8 pmol/l (mean+/-SEM)) than in controls (49+/-3 pmol/l) (P=0.005). The subgroup of patients suffering exclusively from migraine without aura (n=14) also had significantly higher levels of CGRP (82+/-10 pmol/l) than controls (n=20; 49+/-3 pmol/l) (P=0.001). The findings could not be explained by confounding factors such as age, sex or use of contraceptive pills. We therefore conclude that CGRP is increased in cubital venous blood of migraineurs outside of attack. It is hypothesized that this finding may reflect a long-lasting or permanent abnormal neurogenic vascular control in patients with migraine.

Simultaneous depletion of neurokinin A, substance P and calcitonin gene-related peptide from the caudal trigeminal nucleus of the rat during electrical stimulation of the trigeminal ganglion

The central terminals of the primary sensory trigeminal ganglion (TG) neurons projecting into the caudal trigeminal nucleus (CTN) of the rat exhibit neurokinin A (NKA)-, substance P (SP)-, and calcitonin gene-related peptide (CGRP)-immunoreactivities (IRs). We stimulated the TG in the rat to induce some of the alterations which might occur during migraine (neurogenic inflammation). Under a stereotaxic apparatus and by means of a bipolar electrode, one-side TG of the animals were electrically stimulated (7.5 Hz, 5 ms, 0.8-1. 4 mA) with square pulses for 5 min. Then, using immunohistochemical methods, the lower medulla of each rat was studied for NKA-, SP- and CGRP-IRs. Light microscopic examination of brain-stem sequencial sections revealed a simultaneous decrease in the immunoreactivities of all neuropeptides (NKA, SP and CGRP) in the CTN ipsilateral to TG stimulation in comparison with the other (not stimulated) side CTN. It is suggested that this decrease in immunoreactivity would be due to the co-release of neuropeptides following noxious stimuli and that NKA, SP and CGRP might therefore act as co-transmitters or co-modulators at the first central synapses of the trigeminal sensory pathway.

Effects of sumatriptan on nitric oxide and superoxide balance during glyceryl trinitrate infusion in the rat. Implications for antimigraine mechanisms

Infusion of glyceryl trinitrate (GTN) into patients with migraine precipitates the onset of a migraine attack several hours after completion of the infusion. Using an infusion of GTN into anaesthetised rats, this study investigates the relationship of regional cerebral blood flux rCBF(ldf), cortical nitric oxide (NO) and cortical superoxide concentrations and the effect of sumatriptan on each variable. In saline treated animals, a 30 min infusion of GTN (2 microgram kg(-1) min(-1), i.v.) was found to markedly increase cortical rCBF(ldf) (133+/-3% of baseline) and NO concentrations (141+/-13% of baseline). Superoxide levels exhibited an inverse relationship to NO levels, decreasing below basal to 48+/-14% of baseline. It is hypothesised that high NO levels during GTN infusion may decrease the detectable superoxide due to "leeching" of the superoxide into low level peroxynitrite formation. In the presence of sumatriptan, a decrease below baseline in cortical rCBF(ldf) (82+/-5% of baseline) and NO concentration (64+/-13% of baseline) was observed throughout GTN infusion, although superoxide levels significantly increased above baseline by 105+/-14 nM (p<0.05, ANOVA post hoc LSD test). The mechanism for this action of sumatriptan is unknown but may include; modulation of cell redox state, NO scavenging or direct manipulation of superoxide release.