Migraine can be induced by sildenafil without changes in middle cerebral artery diameter

Effects of the PDE5-inhibitor vardenafil in a mouse stroke model

Recent experimental studies in rodents suggest that treatment with inhibitors of phosphodiesterase type 5 (PDE5) (tadalafil, sildenafil, zaprinast) not only increases cerebral blood flow but also improves functional recovery after stroke. Here, we investigated in a mouse model of stroke the effects of vardenafil on survival, functional outcome and lesion size after experimental stroke. Mice were subjected to experimental stroke by occlusion of the middle cerebral artery (MCAO) for 45 min. A group of mice received vardenafil (twice 10 mg/kg body weight per day orally over 14 days) starting 3 h after MCAO. Control animals received the vehicle only. Survival, body weight, and behavior were monitored over 4 weeks and brain lesions were measured by T2-weighted MRI, hematoxylin/eosin -- as well as GFAP-staining of cryostat sections, subsequently. The mortality in MCAO-operated animals amounted to 45% until day 10 after stroke and no significant difference in survival between the vardenafil- and vehicle-treatment groups was observed. Compared to sham-operated animals, MCAO-operated mice from both treatment groups demonstrated a significant weight loss until day 5 and regained their body weight by day 14 after ischemia. There was no significant difference between the vardenafil and vehicle-treated MCAO groups. In behavioral studies (sucrose consumption and pole test), analyzing sensorimotor functions as well as a parameter of depression-like symptoms, we observed no significant effect of vardenafil treatment on functional recovery in our model of stroke. Although we observed a trend towards less hemispherical atrophy in the vardenafil compared to the vehicle-treated group four weeks after MCAO our data do not suggest a functionally relevant CNS-tissue protective or regenerative effect in murine stroke.

The neurogenic basis of migraine

There is accumulating evidence of a neurogenic basis of migraine. This evidence arises from both the clinical and experimental domains. Many of the well known clinical features of migraine attacks including the prodrome are not explained by changes in vascular caliber. Despite the fact that ergotamines and triptans are vasoactive does not provide substantive proof that vasoconstriction is their most important mechanism of action. Several effective treatments for migraine, both old and new, do not affect vascular caliber. Experimental evidence from investigation of both the aura and headache phases of migraine clearly supports a neural basis of migraine. All genes thus far conclusively associated with hemiplegic migraine code for neural proteins.

Phosphodiesterase-5 inhibitors oppose hyperoxic vasoconstriction and accelerate seizure development in rats exposed to hyperbaric oxygen

Oxygen is a potent cerebral vasoconstrictor, but excessive exposure to hyperbaric oxygen (HBO(2)) can reverse this vasoconstriction by stimulating brain nitric oxide (NO) production, which increases cerebral blood flow (CBF)-a predictor of O(2) convulsions. We tested the hypothesis that phosphodiesterase (PDE)-5 blockers, specifically sildenafil and tadalafil, increase CBF in HBO(2) and accelerate seizure development. To estimate changes in cerebrovascular responses to hyperoxia, CBF was measured by hydrogen clearance in anesthetized rats, either control animals or those pretreated with one of these blockers, with the NO inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME), with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), or with a blocker combined with l-NAME. Animals were exposed to 30% O(2) at 1 atm absolute (ATA) ("air") or to 100% O(2) at 4 or 6 ATA. EEG spikes indicated central nervous system CNS O(2) toxicity. The effects of PDE-5 blockade varied as a positive function of ambient Po(2). In air, CBF did not increase significantly, except after pretreatment with SNAP. However, at 6 ATA O(2), mean values for CBF increased and values for seizure latency decreased, both significantly; pretreatment with l-NAME abolished these effects. Conscious rats treated with sildenafil before HBO(2) were also more susceptible to CNS O(2) toxicity, as demonstrated by significantly shortened convulsive latency. Decreases in regional CBF reflect net vasoconstriction in the brain regions studied, since mean arterial pressures remained constant or increased throughout. Thus PDE-5 blockers oppose the protective vasoconstriction that is the initial response to hyperbaric hyperoxia, decreasing the safety of HBO(2) by hastening onset of CNS O(2) toxicity.

Nitric oxide-induced headache may arise from extracerebral arteries as judged from tolerance to isosorbide-5-mononitrate

Long-term exposure to organic nitrates influences different sections of the vascular bed heterogeneously. Continuous dosage of nitrates leads to the development of tolerance both to the vascular effects and to the unwanted adverse effect, headache. Human data on the development of tolerance in different cranial arteries over more than 24 h are lacking. We compared the vascular changes of the middle cerebral, superficial temporal and radial arteries during oral administration of isosorbide-5-mononitrate (5-ISMN) 30 mg three times daily for 7 days in 11 healthy subjects in a double-blind, randomised, placebo controlled cross-over design. Blood velocity in the middle cerebral artery was measured with transcranial Doppler and the diameters of the temporal and radial arteries were measured with high frequency ultrasound. Headache recordings were compared to the observed vascular changes over time. Tolerance was complete within 24 h in the middle cerebral artery whilst in the superficial temporal and the radial arteries, tolerance was only partial and developed much more slowly, i.e. after 7 days correlating with the disappearance of NO-induced headache. The present study thus demonstrated the important differences in the time profiles of appearance of nitrate tolerance in arteries of different vascular beds in man. If vasodilatation is the cause of NO-induced headache the results point to extracerebral arteries as the locus of nociception. Due to a variety of other possible pain-inducing effects of nitric oxide our results do not exclude cerebral arteries.

Main anatomical features of the M1 segment of the middle cerebral artery: a 3D time-of-flight magnetic resonance angiography at 3 T study

The purpose of our study was to determine the main anatomical features of the M1 segment of middle cerebral artery (MRA) using a 3D TOF-MRA at 3 T. Reconstructed and post-processed MRA images were independently analysed by two anatomists in order to determine the course patterns, the division patterns and the early cortical branches patterns of the M1 segments. The division patterns were defined as bipode, tripode or other. The ECB were studied according to their number and their distance from the origin of the M1 segment. The interobserver agreement, to determine the division patterns of the M1 segment, was calculated. The division of the M1 segment was bipode in 73% of the MCAs, monopode in 17%, tripode in 9%, and fan-shaped in 1. In 46% of the cases no ECB was found. In the other cases, only 1 ECB was found and it arose from the medium part of the M1 segment. Our results confirm post-mortem microdissection studies and show that strict anatomical criteria may be applied to 3D TOF MRA at 3 T.

Intracranial hemodynamics during intravenous infusion of glyceryl trinitrate

The mechanisms of glyceryl trinitrate (GTN)-induced headache are not fully elucidated. In this study we administered GTN 0.5 μg/kg/min i.v. for 20 min in six healthy volunteers. Before, during and 60 min after the infusion, we investigated regional cerebral blood flow (rCBF), cerebral blood volume (CBV), both estimated with SPECT, and blood flow velocity (BFV) in the middle cerebral artery (MCA), measured with transcranial Doppler. Headache was scored on a numerical verbal rating (0–10) scale. rCBF was unchanged, CBV was slightly increased (13%) during GTN infusion, whereas BFV decreased both during (20%) and 60 min (15%) after GTN. Headache was short-lived and maximal during infusion. This discrepancy of time-effect curves for the effect of GTN on headache and dilatation of MCA indicates that MCA is most likely not the primary source of pain in GTN-induced headache. The time-effect curves for the effect of GTN on headache and on dilation of MCA differed markedly. This indicates that MCA is most likely not the primary source of pain in GTN-induced headache.

Familial hemiplegic migraine type 1 shows no hypersensitivity to nitric oxide

Familial hemiplegic migraine type 1 (FHM-1) is a dominantly inherited subtype of migraine with aura and transient hemiplegia associated with mutations in the CACNA1A gene. FHM-1 shares many phenotypical similarities with common types of migraine, indicating common neurobiological pathways. Experimental studies have established that activation of the nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway plays a crucial role in migraine pathophysiology. Therefore, we tested the hypothesis that CACNA1A mutations in patients with FHM-1 are associated with hypersensitivity to NO-cGMP pathway. We included eight FHM-1 patients with R583Q and C1369Y mutations and nine healthy controls, who received intravenous infusions of 0.5 microg kg(-1) min(-1) glyceryl trinitrate (GTN) over 20 min. We recorded: headache intensity on a verbal rating scale; mean flow velocity in the middle cerebral artery (V(meanMCA)) by transcranial Doppler; diameter of the superficial temporal artery (STA) by Dermascan. One patient reported migraine without aura 5 h after start of the GTN infusion. No aura was reported. The AUC(headache) in the immediate phase was more pronounced in patients than in controls (P = 0.01). In the 14 h following GTN infusion, there was no difference in the AUC(headache) between patients and controls (P = 0.17). We found no difference in the AUC(VmeanMCA) (P = 0.12) or AUC(STA) (P = 0.71) between FHM-1 patients and controls. None of the control persons reported migraine-like headache. FHM-1 patients do not show hypersensitivity of the NO-cGMP pathway, as characteristically seen in migraine patients with and without aura. This indicates that the pathophysiological pathways underlying migraine headache in FHM-1 may be different from the common types of migraine.

Vasoactive Intestinal Peptide Causes Marked Cephalic Vasodilation, but does not Induce Migraine

We hypothesized that intravenous infusion of the parasympathetic transmitter, vasoactive intestinal peptide (VIP), might induce migraine attacks in migraineurs. Twelve patients with migraine without aura were allocated to receive 8 pmol kg-1 min-1 VIP or placebo in a randomized, double-blind crossover study. Headache was scored on a verbal rating scale (VRS), mean blood flow velocity in the middle cerebral artery ( Vmean mca) was measured by transcranial Doppler ultrasonography, and diameter of the superficial temporal artery (STA) by high-frequency ultrasound. None of the subjects reported a migraine attack after VIP infusion. VIP induced a mild immediate headache (maximum 2 on VRS) compared with placebo ( P = 0.005). Three patients reported delayed headache (3-11 h after infusion) after VIP and two after placebo ( P = 0.89). Vmean mca decreased (16.3 ± 5.9%) and diameter of STA increased significantly after VIP (45.9 ± 13.9%). VIP mediates a marked dilation of cranial arteries, but does not trigger migraine attacks in migraineurs. These data provide further evidence against a purely vascular origin of migraine.

Protective effect of sildenafil (Viagra) in transient spinal cord ischemia

Prospective study of the neuroprotective activity of sildenafil in a rat spinal ischemia model. The present study involved 21 male Sprague-Dawley rats. The animals were divided into 3 groups. Physiological serum was administered intraperitoneally to the 8 rats in the control group at the beginning of reperfusion for a period of 20 min after abdominal aortal occlusion. Sildenafil (Viagra) was administered as a single 10-mg/kg/day intraperitoneal dose to the 8 rats in the sildenafil group at the beginning of reperfusion after 20 min of abdominal aortal occlusion. No occlusion was performed and no agent was administered to the 5 rats in the sham group, but the abdominal aorta was reached by means of surgical intervention. Before the animals were sacrificed, several physiological and biochemical parameters were investigated, preoperative and postoperative motor functions were also assessed, and somatosensory evoked potential (SEP) monitoring and histopathological examinations were carried out. No differences were found between the physiological and biochemical parameters in each of the 3 groups. Neurological scoring performed after reperfusion demonstrated a significant improvement in the neurological results relative to those of the control group over 48 h in subjects that received sildenafil. These animals also showed better 24-hour SEP results, measured in terms of extended latency and decreased amplitude, than the control animals. A histopathological study showed reduced ischemic symptoms in rats that received sildenafil compared with those in the control group. However, no anomalies were observed in the sham group with respect to the histopathological and neurological findings. These results indicate that neurological damage due to spinal-cord ischemia-reperfusion injury can be reduced by sildenafil.

Emerging therapies for migraine

Migraine is a common disabling brain disorder that--considering its clinical and economic impact--is understudied and in need of additional management options. Currently, treatments are classified as preventive or acute-attack therapies, although it is expected that this distinction will become blurred over time. The gap-junction blocker tonabersat, an inducible nitric oxide synthase (NOS) inhibitor and botulinum toxin A are all being investigated in clinical trials as preventive therapies. Device-based approaches using neurostimulation of the occipital nerve have provided promising results, whereas the first study of patent foramen ovale closure for migraine prevention produced disappointing results. Calcitonin gene-related peptide receptor antagonists, vanilloid TRPV1 receptor antagonists and NOS inhibitors are all being investigated in clinical trials for acute migraine. There is much cause for optimism in this area of neurology and considerable benefit awaits our patients.

Role of K+ and Ca2+ fluxes in the cerebroarterial vasoactive effects of sildenafil

The aim of this study was to assess the role of K(+) and Ca(2+) fluxes in the cerebroarterial vasoactive effects of the phosphodiesterase-5 inhibitor sildenafil. We used isolated rabbit basilar arteries to assess the effects of extracellular K(+) raising on sildenafil-induced vasodilatation, and studied the pharmacological interaction of sildenafil with selective modulators of membrane K(+) and Ca(2+) channels. Expression of Kv1 subunits of K(+) channels was assessed at messenger and protein levels. Parallel experiments were carried out with zaprinast for comparison. Sildenafil (10 nM-0.1 mM) induced concentration-dependent relaxation of endothelin-1 (10 nM)-precontracted arteries, which was partially inhibited by depolarization with KCl (50 mM), 3 mM tetraethylammonium (non-selective K(+) channel blocker) or 1 mM aminopyridine (inhibitor of K(v) channels), but not by 1 microM glibenclamide (inhibitor of K(ATP) channels) or 50 nM iberiotoxin (inhibitor of K(Ca) channels). Arterial smooth muscle expressed messengers for Kv1.2, Kv1.3, Kv1.4, Kv1.5 and Kv1.6, and proteins of Kv1.1, Kv1.2 and Kv1.4. CaCl(2) (10 microM- 10 mM) induced concentration-dependent contraction in Ca(2+)-free, depolarizing (50 mM KCl) medium. Sildenafil (0.1-100 microM) produced reversible concentration-dependent inhibition of the response to CaCl(2), which was completely abolished by the highest sildenafil concentration. By contrast, only 100 microM zaprinast inhibited the response to CaCl(2). The L-type Ca(2+) channel activator Bay K 8644 (0.1 nM-1 microM) induced concentration-dependent potentiation of the response to CaCl(2) inhibited by 100 microM sildenafil. Moreover, Bay K 8644 (0.1 nM-1 microM) induced concentration-dependent contraction in slightly depolarizing (15 mM) medium, which was inhibited to the same extent and in a concentration-dependent way by sildenafil (0.1-100 microM) and zaprinast (1 or 100 microM). These results show that sildenafil relaxes the rabbit basilar artery by increasing K(+) efflux through K(v) channels, which in turn may affect Ca(2+) signalling. Expression of Kv1 subunits involved in this pharmacological effect occurs at the messenger and, in some cases, at the protein level. In addition to this phosphodiesterase-5-related effect, sildenafil and zaprinast inhibit cerebroarterial vasoconstriction at least in part by directly blocking L-type Ca(2+) channels, although a decrease in the sensitivity of the contractile apparatus to Ca(2+) can not be discarded.

Effects of autogenic training on nitroglycerin-induced headaches

OBJECTIVES

To investigate the prophylactic and acute effects of autogenic training (AT) during a nitroglycerin-induced migraine attack.

METHODS

Thirty female migraineurs (without aura) and 11 controls participated in the study. Of these, 11 migraineurs and 5 controls practiced AT regularly for at least 6 months prior to and during the sublingual nitroglycerin test. Headache intensity and characteristics were recorded with a standardized method. During the nitroglycerin challenge, blood was collected for plasma cortisol determination and blood pressure and pulse rate were recorded.

RESULTS

As a long-term preventive treatment, AT significantly decreased the mean headache frequency and intensity (P = .001) compared to the pretreatment period in the migraineurs who regularly practiced AT (n = 11). During the nitroglycerin challenge, AT successfully attenuated the nitroglycerin-induced acute decrease in blood pressure and pulse rate (P = .013; n = 16 AT subjects vs n = 25 non-AT subjects). However, it was not effective in preventing immediate headache (P = .71), did not decrease the frequency of acute migraine attacks (P = .79), and could not alleviate acute migraine pain (P = .78; n = 16 AT subjects vs n = 25 non-AT subjects). Plasma cortisol concentration significantly increased (P = .003) during the acute migraine attack (n = 22), and migraine intensity correlated with plasma cortisol elevations (P < .001; n = 41) and showed a tendency of negative correlation with morning plasma cortisol concentration (P = .08; n = 41). However, AT did not alter plasma cortisol responses (P = .99; n = 16 AT subjects vs n = 25 non-AT subjects).

CONCLUSION

(1) The long-term AT therapy proved to be a significantly effective preventive intervention in migraine sufferers. We hypothesized that this long-term effect of AT is based on modulation of the pain anticipation system, which is strongly correlated with function of the anterior cingulate cortex. (2) We demonstrated that AT could not alter the nitroglycerin-induced acute migraine attacks, which are directly related to the dysfunctional brainstem activation according to previous studies. (3) Our results suggested that there are multiple, complex relationships between cortisol responses and migraine pain, which are possibly mediated by the brain serotonergic system. (4) In addition, our results provide further evidence that nitroglycerin-induced vasodilatation is not directly connected to either immediate headache or delayed migraine attack.

Magnetic resonance angiography shows dilatation of the middle cerebral artery after infusion of glyceryl trinitrate in healthy volunteers

Previous studies have reported dilatation of the middle cerebral artery (MCA) during acute glyceryl trinitrate (GTN)-induced headache, using imaging techniques such as transcranial Doppler (TCD), positron emission tomography (PET) and single photon emission computerized tomography (SPECT). In the present study we aimed to evaluate whether magnetic resonance angiography (MRA) may be used to examine the effect of GTN on the MCA, with respect to changes in diameter and cross-sectional area in healthy volunteers. In addition, we wanted to determine the intra- and inter-observer variation of the method. In a randomized, double blind, crossover study 12 healthy volunteers received intravenous infusion of GTN (0.5 microg/kg/min for 20 min) or placebo. Using 1.5 Tesla MRA, we recorded changes in the diameter and cross-sectional area of MCA before, during and after infusion of GTN. The MRA images were evaluated by two blinded, independent observers/neuroradiologists. The primary endpoints were the differences in the AUC for diameter and cross-sectional area of the MCA between the two experimental conditions and the intra- and inter-observer variation. The areas under the curve (AUC) of the MCA diameter and cross-sectional area were significantly greater after GTN than after placebo (P < 0.05). The intra-observer variation (day-to-day) at baseline was 8.3% and 10.9% for the two observers. The mean inter-observer variation of the cross-sectional MCA area was 15.5% and for the diameter measurements 8%. The present study shows that the MRA method gives a reliable semi-quantitative index of the vascular changes in the intra-cerebral arteries after infusion of GTN and may be useful for headache research.

Recurrent headache as the main symptom of acquired cerebral toxoplasmosis in nonhuman immunodeficiency virus-infected subjects with no lymphadenopathy: the parasite may be responsible for the neurogenic inflammation postulated as a cause of different types of headaches

Headache and/or migraine, a common problem in pediatrics and internal medicine, affect about 5% to 10% children and adolescents, and nearly 30% of middle-aged women. Headache is also one of the most common clinical manifestations of acquired Toxoplasma gondii infection of the central nervous system (CNS) in immunosuppressed subjects. We present 11 apparently nonhuman immunodeficiency virus-infected children aged 7 to 17 years (8 girls, 3 boys) and 1 adult woman with recurrent severe headaches in whom latent chronic CNS T. gondii infection not manifested by enlarged peripheral lymph nodes typical for toxoplasmosis, was found. In 7 patients, the mean serum IgG Toxoplasma antibodies concentration was 189 +/- 85 (SD) IU/mL (range 89 to 300 IU/mL), and in 5 other subjects, the indirect fluorescent antibody test titer ranged from 1:40 to 1:5120 IU/mL (n= <1:10 IU/mL). Some of the patients suffered also from atopic dermatitis (AD) and were exposed to cat and/or other pet allergens, associated with an increased IL-4 and decreased IFN-gamma production. These cytokine irregularities caused limited control of cerebral toxoplasmosis probably because IL-4 down-regulated both the production of IFN-gamma and its activity, and stimulated production of a low NO-producing population of monocytes, which allowed cysts rupture, increased parasite multiplication and finally reactivation of T. gondii infection. The immune studies performed in 4 subjects showed a decreased percentage of T lymphocytes, increased total number of lymphocytes B and serum IgM concentration, and impaired phagocytosis. In addition, few of them had also urinary tract diseases known to produce IL-6 that can mediate immunosuppressive functions, involving induction of the anti-inflammatory cytokine IL-10. These disturbances probably resulted from the host protective immune reactions associated with the chronic latent CNS T. gondii infection/inflammation. This is consistent with significantly lower enzyme indoleamine 2,3-dioxygenase (IDO) activity reported in atopic than in nonatopic individuals, and an important role that IDO and tryptophan degradation pathways plays in both, the host resistance to T. gondii infection and its reactivation. Analysis of literature information on the subjects with different types of headaches caused by foods, medications, and other substances, may suggest that their clinical symptoms and changes in laboratory data result at least in part from interference of these factors with dietary tryptophan biotransformation pathways. Several of these agents caused headache attacks through enhancing NO production via the conversion of arginine to citrulline and NO by the inducible nitric oxide synthase enzyme, which results in the high-output pathway of NO synthesis. This increased production of NO is, however, quickly down-regulated by NO itself because this biomolecule can directly inactivate NOS, may inhibit Ia expression on IFN-gamma-activated macrophages, which would limit antigen-presenting capability, and block T-cell proliferation, thus decreasing the antitoxoplasmatic activity. Moreover, NO inhibits IDO activity, thereby suppressing kynurenine formation, and at least one member of the kynurenine pathway, 3-hydroxyanthranilic acid, has been shown to inhibit NOS enzyme activity, the expression of NOS mRNA, and activation of the inflammatory transcription factor, nuclear factor-kB. In addition, the anti-inflammatory cytokines IL-4 and IL-10, TGF-beta, and a cytokine known as macrophage deactivating factor, have been shown to directly modulate NO production, sometimes expressing synergistic activity. On the other hand, IL-4 and TGF-beta can suppress IDO activity in some cells, for example human monocytes and fibroblasts, which is consistent with metabolic pathways controlled by IDO being a significant contributor to the proinflammatory system. Also, it seems that idiopathic intracranial hypertension, pseudotumor cerebri, and aseptic meningitis, induced by various factors, may result from their interference with IDO and inducible nitric oxide synthase activities, endogenous NO level, and cytokine irregularities which finally affect former T. gondii status 2mo in the brain. All these biochemical disturbances caused by the CNS T. gondii infection/inflammation may also be responsible for the relationship found between neurologic symptoms, such as headache, vertigo, and syncope observed in apparently immunocompetent children and adolescents, and physical and psychiatric symptoms in adulthood. We therefore believe that tests for T. gondii should be performed obligatorily in apparently immunocompetent patients with different types of headaches, even if they have no enlarged peripheral lymph nodes. This may help to avoid overlooking this treatable cause of the CNS disease, markedly reduce costs of hospitalization, diagnosis and treatment, and eventually prevent developing serious neurologic and psychiatric disorders.

Recent advances in understanding migraine mechanisms, molecules and therapeutics

Migraine is a complex, disabling disorder of the brain that manifests itself as attacks of often severe, throbbing head pain with sensory sensitivity to light, sound and head movement. There is a clear familial tendency to migraine, which has been well defined in a rare autosomal dominant form of familial hemiplegic migraine (FHM). FHM mutations so far identified include those in CACNA1A (P/Q voltage-gated Ca(2+) channel), ATP1A2 (N(+)-K(+)-ATPase) and SCN1A (Na(+) channel) genes. Physiological studies in humans and studies of the experimental correlate--cortical spreading depression (CSD)--provide understanding of aura, and have explored in recent years the effect of migraine preventives in CSD. Therapeutic developments in migraine have come by targeting the trigeminovascular system, with the most-recent being the proof-of-principle study of calcitonin gene-related peptide (CGRP) receptor antagonists in acute migraine. To understand the basic pathophysiology of migraine, brain imaging studies have firmly established reproducible changes in the brainstem in regions that include areas that are involved in sensory modulation. These data lead to the view that migraine is a form of sensory dysmodulatio--a system failure of normal sensory processing.

The headache-inducing effect of cilostazol in human volunteers

We have previously shown that nitric oxide (NO) and cyclic guanosine monophosphate (GMP) may cause headache and migraine. However, not all findings in previous studies can be explained by an activation of the NO-cGMP pathway. Calcitonin gene-related peptide (CGRP) causes headache and migraine in migraine patients, but CGRP receptor activation causes an increase in cyclic adenosine monophosphate (cAMP). In order to investigate the role of cAMP in vascular headache pathogenesis, we studied the effect of cilostazol, an inhibitor of cAMP degradation, in our human experimental headache model. Twelve healthy volunteers were included in a double-blind, randomized, crossover study. Placebo or cilostazol (200 mg p.o.) was administered on two separate study days. Headache was scored on a verbal rating scale (0-10) and mechanical pain thresholds were measured with von Frey hairs. The median peak headache score 0-16 h postdose was 0 (range 0-2) after placebo and 3.5 (range 0-7) after cilostazol (P = 0.003). The median headache curve peaked at 6-9 h postdose. The headaches induced were usually bilateral and pulsating. Nausea occurred in two volunteers, photo- and phonophobia were not seen. Two volunteers had a headache that fulfilled International Headache Society criteria for migraine without aura after cilostazol. No change in mechanical pain thresholds in the forehead was seen (P = 0.25). The headache after cilostazol was equal to or more severe than headache induced by glyceryl trinitrate in previous experiments. The present study thus indicates that increased levels of cAMP may play a role in headache and migraine pathogenesis.

Dipyridamole may induce migraine in patients with migraine without aura

Dipyridamole inhibits phosphodiesterase 5 (PDE5) and adenosine re-uptake. The most prominent side-effect is headache. We examined the migraine-generating effects of dipyridamole as well as the cerebral blood velocity response in a single-blind study, including 10 patients with migraine without aura and 10 healthy subjects. Dipyridamole 0.142 mg/kg per min was administered intravenously. Headache intensity was scored on a verbal rating scale along with pain characteristics and accompanying symptoms. Blood velocity in the middle cerebral artery (V(mca)), blood pressure and heart rate were recorded repeatedly. Headache was induced in all migraine patients and in eight of 10 healthy subjects (P = 0.47) with no significant difference in headache intensity (P = 0.53). However, five patients but only one healthy subject experienced the symptoms of migraine without aura, according to ICHD-2 criteria, within 12 h (P = 0.14). Four patients reported photophobia after dipyridamole compared with no healthy subjects (P = 0.087). V(mca) decreased (P < 0.001) during and after dipyridamole infusion with no difference between groups (P = 0.15) coinciding with initiation, but not cessation of immediate headache. Thus, dipyridamole induces symptoms of migraine and an initial decrease in V(mca) in migraine patients, but not significantly more than in healthy subjects. This relatively low frequency of migraine induction, compared with nitric oxide donors and sildenafil, is probably due to the less specific action of dipyridamole on the cGMP signalling pathway as well as a possible bidirectional effect of adenosine on migraine induction.

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Migraine: emerging treatment options for preventive and acute attack therapy

This review discusses emerging treatments of migraine in the context of what is now available. At present, patients are treated with a range of acute attack medicines or preventive treatments, with many having significant drawbacks. Important unmet needs are acute attack treatments that act by exclusively neural mechanisms with no vascular effects, and effective, well tolerated preventive medicines. Calcitonin gene-related peptide receptor antagonist, vanilloid receptor antagonists and nitric oxide synthase inhibitors are all in clinical trials for acute migraine. Tonaberset (a gap-junction blocker), an inducible nitric oxide synthase inhibitor and botulinum toxin A are in clinical trials for preventive therapy. Device-based approaches using neurostimulation of the occipital nerve are being studied, although the first study of patent foramen ovale closure for migraine prevention failed.

Pharmacology of erectile dysfunction in man

Erectile dysfunction (ED) is defined as the consistent or recurrent inability of a man to attain and/or maintain a penile erection sufficient for sexual activity (2nd International Consultation on Sexual Dysfunction-Paris, June 28th-July 1st, 2003). Following the discovery and introduction of sildenafil, research on the mechanisms underlying penile erection has had an enormous boost and many preclinical and clinical papers have been published in the last 5 years. This review is structured in order to give the reader an overview of the clinical and preclinical data available on the peripheral regulation of and the mediators involved in human penile erection. The most widely accepted risk factors for ED are discussed. The article is focused on human data, and the safety and effectiveness of the 3 commercially available Phosphodiesterase-5 (PDE5) inhibitors used to treat ED are also discussed.

Migraine: a review and future directions for treatment

Migraine is a chronic, neurological disorder generally manifesting itself in attacks with severe headache, nausea and an increased reactivity to sensory stimuli. A low migraine threshold is set by genetic factors, although the phenotype also modulates the manifestations. The 1-year prevalence is approximately 13% and is higher among women. Patients usually experience neuropsychological dysfunction, and sometimes also reversible focal neurological symptoms. The trajectories of the characteristic symptoms of acute migraine usually follow a similar time course, indicating a reciprocal underlying mechanism. A central nervous system hyperexcitability has been demonstrated in neurophysiological studies. The dibilitating effects of migraine are not confined to the attacks per se. Many individuals do not recover completely between the attacks and most report a negative impact on the most important life domains, and an interest in testing other treatments. Young persons have a higher frequency of attacks. Acute treatment should routinely be initiated with an analgesic plus a prokinetic anti-emetic. Triptans must not be provided early during the attack to ensure their efficacy. The natural course of attacks is commonly only temporarily altered by acute treatment. Non-pharmacological treatment and drugs may be equally viable in prophylaxis for migraine. In more complicated cases, conjoint therapy should be considered. New strategies to improve adherence with existing therapeutic regimens might yield greater benefits than will new pharmacological agents.

Migraine and Patent Foramen Ovale: A Residual Coincidence or a Pathophysiological Intrigue?

Migraine is one of the most common neurological disorders and one of the most frequent primary headaches. It imposes a significant burden on the affected individuals, society and health care system. As the etiology and pathophysiology of migraine are not well understood, treatment is largely symptomatic. Patent foramen ovale is a remnant of a fetal circulation and is highly prevalent in the general population. Its presence was linked to several disorders including migraine. The aim of this review was to search in the available data the answer to the question whether the link between migraine and patent foramen ovale is coincidental or whether they represent a pathophysiological entity.

Phosphodiesterase 3 and 5 and cyclic nucleotide-gated ion channel expression in rat trigeminovascular system

Activation of the trigeminovascular pain signalling system appears involved in migraine pathophysiology. However, the molecular mechanisms are only partially known. Stimulation of cAMP and cGMP production as well as inhibition of their breakdown induce migraine-like headache. Additionally, migraine may be associated with mutations in ion channels. The aim of the present study was to describe the expression of phosphodiesterase 3 (PDE3) and 5 (PDE5) and cyclic nucleotide-gated ion channels (CNG) in cerebral arteries, meninges, and the trigeminal ganglion. mRNA for PDE and CNG was determined in the rat middle cerebral artery, basilar artery, trigeminal ganglion, and dura mater using real-time PCR. PDE and CNG proteins were identified using Western blot. For comparison, rat aorta and mesenteric artery were analysed. PDE3A, PDE3B, and PDE5A mRNA were detected in all tissues examined except for PDE3A mRNA in dura mater and the trigeminal ganglion. PDE5A and PDE3A protein expression was present in both cerebral and peripheral arteries, whereas PDE3B protein was present only in the cerebral arteries. The CNGA4 and B1 subunit mRNAs were detected in cerebral arteries and CNGA2 also in the mesenteric artery. CNGA2 and A3 proteins were found in cerebral arteries and dura and CNGA1, CNGA2 and CNGA3 in the trigeminal ganglion. In conclusion, PDE3A, PDE3B, PDE5A, and five CNG subunits were expressed in several components of the trigeminovascular system of the rat. This suggests that modulation of cAMP and cGMP levels by PDE and activation of CNG may play a role in trigeminovascular pain signalling leading to migraine headache.

Sildenafil can trigger cluster headaches

Phosphodiesterase-5 inhibitors commonly trigger migraines but rarely trigger cluster headaches. Two cases of cluster headaches triggered by sildenafil are described.

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.

Sildenafil Improves Dynamic Vascular Function in the Brain: Studies in Patients with Pulmonary Hypertension

BACKGROUND

Prostaglandins and nitric oxide play a pivotal role in the regulation of macro- and microcirculatory blood flow distribution. Interference with both mediator systems have been implicated in cerebrovascular dysfunction. Inhaled iloprost (long-acting prostacyclin analogue) and the phosphodiesterase-5 inhibitor sildenafil have recently shown efficacy in the treatment of chronic pulmonary hypertension. We investigated the impact of these agents on cerebral microcirculatory regulation in patients suffering from this disease.

METHODS

In 11 patients suffering from severe pulmonary hypertension, a functional transcranial Doppler test utilizing a visual stimulation paradigm was undertaken to measure the evoked flow velocity in the posterior cerebral artery. Measurements were performed in parallel to right heart catheterization and pharmacological testing of the pulmonary vasoreactivity. After assessment of baseline measurements, inhaled iloprost and oral sildenafil were given consecutively for testing of cerebral and pulmonary vascular function. The data gained from the Doppler measurements were compared to data from 22 healthy volunteers.

RESULTS

Both substances provoked a significant reduction of pulmonary arterial pressure and vascular resistance, accompanied by minor changes in systemic vascular resistance. In contrast to these superimposable hemodynamic profiles opposite effects were observed regarding cerebral vascular tone: cerebral microvascular reactivity, as assessed by attenuation and time rate parameters, was significantly improved by sildenafil, but slightly worsened by iloprost.

CONCLUSIONS

Sildenafil has beneficial effects on cerebral vascular reactivity indicative of an improvement in neurovascular coupling in patients with pulmonary hypertension. These results warrant further investigations of the influence of sildenafil on dynamic vascular function in the brain independent of the underlying disease.

Relaxant effect of sildenafil in the rabbit basilar artery

We hypothesized that sildenafil, inhibitor of phosphodiesterase-5 (PDE-5), interacts with the nitric oxide (NO)-cGMP pathway in the cerebral arteries and shows vasoactive effects. To prove it in the isolated rabbit basilar artery, we compared the effects of sildenafil with other PDE-5 inhibitors, assessed the endothelial dependence of the vasoactive responses, and used modulators of the cGMP and cAMP signaling processes. Sildenafil (10 nM-0.1 mM) induced concentration-dependent relaxations of endothelin-1 (10 nM)-precontracted basilar artery, which were partially inhibited both in endothelium-denuded arteries and in arteries precontracted by depolarization with KCl (50 mM). Endothelin-1 (1 pM-30 nM) induced concentration-dependent contractions that were inhibited by sildenafil (0.1-100 microM). Zaprinast (10 nM-0.1 mM) and MBCQ (1 nM-0.1 mM), PDE-5 inhibitors, induced concentration-dependent relaxations with lower and higher potency than sildenafil, respectively. Sildenafil-induced relaxation was inhibited in arteries preincubated with the NO synthase inhibitor L-NAME (0.1 mM) or the soluble guanylyl cyclase inhibitor ODQ (10 microM). Preincubation with sildenafil (0.1 microM) enhanced the relaxations induced by acetylcholine (0.1 nM-0.1 mM) and the NO donor sodium nitroprusside (0.1 nM-0.1 mM), but not those induced by the cell-permeable cGMP analogue 8-Br-cGMP (1 nM-0.1 mM) and the adenylyl cyclase activator forskolin (0.1 nM-10 microM). These results show that sildenafil has vasoactive effects in isolated cerebral arteries. By enhancing the NO-cGMP signaling pathway in the cerebrovascular wall, sildenafil induces vasodilation, prevents vasoconstriction, and potentiates the effect of other NO-dependent vasodilators.

Phosphodiesterase 5 and effects of sildenafil on cerebral arteries of man and guinea pig

Sildenafil (Viagra), a selective inhibitor of phosphodiesterase 5 (PDE5), induces headache and migraine. Although previously supposed to be a "vascular" headache, no significant cerebral artery dilatation was found in vivo. Thus, we hypothesised that PDE5 may not be present or that sildenafil is less effective on the cGMP hydrolysis in cerebral arteries, and that sildenafil may not be an effective dilator of cerebral arteries under baseline conditions. We evaluated the presence of PDE5 mRNA and protein in human arteries. Furthermore, the effects of two selective PDE5 inhibitors, sildenafil and UK-114,542, and a PDE1 inhibitor UK-90,234 on cGMP hydrolysis were investigated in human and guinea pig cerebral arteries. The vasoactive responses of the compounds were evaluated in guinea pig basilar arteries in vitro, with concomitant measurements of cAMP and cGMP. PDE5 was found in human middle cerebral arteries. Sildenafil and UK-114,542 inhibited cGMP hydrolysis concentration-dependently in both species. In guinea pig arteries, sildenafil induced an endothelium-dependent vasodilatation only at concentrations above 10 nM, which was augmented by sodium nitroprusside and attenuated by reduction of cGMP, but was cGMP independent at high concentrations. UK-114,542 was more and UK-90,234 was less potent than sildenafil. In conclusion, PDE5 is present in human and guinea pig cerebral arteries, and is inhibited by sildenafil at micromolar levels. Sildenafil in vitro is a poor dilator of guinea pig cerebral arteries unless a nitric oxide donor is co-administered, corresponding to the previous findings in vivo.

Effect of sildenafil and acclimatization on cerebral oxygenation at altitude

Phosphodiesterase-5 inhibitors decrease hypoxic pulmonary vasoconstriction under hypobaric hypoxia, but are not known to affect cerebral blood flow or oxygenation. The present study was designed to evaluate the effect of sildenafil on cerebral haemodynamics during acute exposure to altitude and after acclimatization. Ten subjects were studied 1 and 3 days after rapid ascent to 3480 m before and for two consecutive hours after taking sildenafil (50 mg). Before acclimatization, HR (heart rate) rose at 1 h (76.3±1.0 beats/min compared with 72.5±1.5 beats/min at baseline; P<0.05) and had returned to baseline at 2 h (71.3±1.1 beats/min; P>0.05). Mean BP (blood pressure) fell from 96.0±2.0 mmHg at baseline to 91.7±2.5 (P<0.001) at 1 h and 89.8±1.8 mmHg (P<0.0001) at 2 h, whereas SaO2 (arterial oxygen saturation) increased from 83.9±0.5% at baseline to 85.3±0.4% (P<0.0001) at 1 h and 85.0±0.5% (P<0.01) at 2 h. MCAV [MCA (middle cerebral artery) velocity] and PETCO2 (end-tidal partial pressure of CO2) were unchanged, but rSO2 (regional cerebral oxygen saturation) rose progressively at 1 h (62.7±0.8%; P<0.05) and 2 h (65.3±0.9%; P<0.0001) compared with baseline (59.3±1.3%). After 3 days of acclimatization, resting rSO2 and RMCA (MCA resistance) increased and oxygen delivery fell. Changes in HR and mean BP after sildenafil were similar to day 1, but SaO2 did not change. However, rSO2 increased [61.7±0.9% at baseline to 65.0±1.0% (P<0.0001) at 1 h and 64.0±0.9% (P<0.001) at 2h], despite a reduction in MCAV [65.3±1.8 cm/s at baseline to 61.3±1.5 cm/s (P<0.01) at 1 h and 60.9±1.7 cm/s (P<0.0001) at 2 h] and PETCO2 [4.1±0.05 kPa at baseline to 4.0±0.04 kPa at 2 h (P<0.01)]. These observations suggest that sildenafil improves cerebral oxygenation at altitude. Whereas the early changes before acclimatization may be largely pulmonary in origin, the later observations may be a direct cerebral effect which warrants further study.

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.

The effect of circulating adenosine on cerebral haemodynamics and headache generation in healthy subjects

Adenosine is an endogenous neurotransmitter that is released from the brain during hypoxia and relaxes isolated human cerebral arteries. Many cerebral artery dilators cause migraine attacks. However, the effect of intravenous adenosine on headache and cerebral artery diameter has not previously been investigated in man and reports regarding the effect of intravenous adenosine on cerebral blood flow are conflicting. Twelve healthy participants received adenosine 80, 120 microg kg(-1) min(-1) and placebo intravenously for 20 min, in a double-blind, three-way, crossover, randomized design. Headache was rated on a verbal scale (0-10). Regional cerebral blood flow (rCBF) with 133Xe inhalation and single-photon emission computed tomography (SPECT) and MCA flow velocity (V(MCA)) with transcranial Doppler, were measured in direct sequence. Six participants developed headache during 80 microg kg(-1) min(-1) and six during 120 microg kg(-1) min(-1) compared with none on placebo (P = 0.006). The headache was very mild and predominantly described as a pressing sensation. When correcting data for adenosine-induced hyperventilation, no significant changes in rCBF (P = 0.22) or V(MCA) (P = 0.16) were found between treatments. A significant dilation of the superficial temporal artery (STA) was seen (P < 0.001). These results show that circulating adenosine has no effect on rCBF or V(MCA), while it dilates the STA and causes very mild headache.

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.

BIBN4096BS Antagonizes Human α-calcitonin Gene Related Peptide–induced Headache and Extracerebral Artery Dilatation*

BACKGROUND AND OBJECTIVE

Calcitonin gene-related peptide (CGRP) plays a pivotal role in migraine pathogenesis. BIBN4096BS is the first CGRP receptor antagonist available for human studies, and its efficacy in the acute treatment of migraine has been demonstrated. We investigated the ability of BIBN4096BS to inhibit human alphaCGRP (h-alphaCGRP)-induced headache and cerebral hemodynamic changes in healthy volunteers.

METHODS

Ten healthy volunteers completed this double-blind, placebo-controlled crossover study with 2.5 mg BIBN4096BS and placebo as pretreatments before a 20-minute intravenous infusion of h-alphaCGRP (1.5 microg/min). Transcranial Doppler ultrasonography was used to measure blood flow velocity in the middle cerebral artery (MCA); regional and global cerebral blood flow (CBF) was measured by xenon 133 inhalation single-photon emission computed tomography. The temporal and radial artery diameter was measured by high-frequency ultrasound. Systemic hemodynamics, end-tidal partial pressure of carbon dioxide (PETCO(2)), and headache were monitored.

RESULTS

Of the 10 volunteers, 6 had a CGRP-induced headache during the in-hospital phase after placebo pretreatment but none after BIBN4096BS (P = .031). BIBN4096BS did not affect changes in the diameter of the MCA or changes in CBF induced by h-alphaCGRP. Vasodilatation of the extracranial arteries was, however, significantly inhibited (P < .001 for temporal artery and P = .001 for radial artery).

CONCLUSIONS

These results show that BIBN4096BS effectively prevents CGRP-induced headache and extracerebral vasodilatation but does not significantly affect the induced cerebral hemodynamic changes.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computerized tomography, and functional magnetic resonance imaging, have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes, and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Sensory nitrergic meningeal vasodilatation and non-nitrergic plasma extravasation in anaesthesized rats

The aim of the present study was to evaluate the role of nitric oxide (NO) of sensory neural origin in neurogenic inflammatory response in the trigeminovascular system. Antidromic vasodilatation and plasma extravasation in response to electrical stimulation (15 V, 5 Hz, 0.5 ms, 100 impulses) of the trigeminal ganglion were investigated in the dura mater and nasal mucosa/upper eyelid by laser Doppler flowmetry and [(125)I]-labelled bovine serum albumin, respectively. Electrical stimulation of the trigeminal ganglion of rats elicited a reproducible ipsilateral enhancement of both meningeal and nasal mucosal blood flow. N(omega)-nitro-L-arginine (L-NNA; 4, 8, and 16 mg/kg, i.v.), a nonselective inhibitor of nitric oxide synthase (NOS), inhibited antidromic vasodilatation both in the dura mater (15.86+/-2.05%, 22.82+/-2.51%, and 36.28+/-4.37%) and nasal mucosa (35.46+/-8.57%, 58.72+/-9.2%, and 89.99+/-8.94%) in a dose-dependent manner. Specific inhibitors of neuronal NOS, 7-nitroindazole (7-NI; 20 mg/kg, i.v.) and 3-bromo-7-nitroindazole (3Br-7NI; 10 mg/kg, i.v.) were administered to assess the possible role of NO released from the trigeminal sensory fibres. The meningeal vasodilatation was inhibited by both 3Br-7NI and 7-NI (63.36+/-7.7% and 49+/-6.5%, respectively). The nasal hyperaemic response was also reduced by 3Br-7NI (78.26+/-8.7%). Plasma extravasation in the dura mater and upper eyelid evoked by electrical stimulation of the trigeminal ganglion (25 V, 5 Hz, 0,5 ms, 5 min), expressed as extravasation ratios (ERs) of the stimulated vs. nonstimulated sides, was 1.80+/-0.8 and 4.63+/-1.24, respectively. This neurogenic oedema formation was not inhibited by neither L-NNA nor 3Br-7NI. It is concluded that neural nitrergic mechanisms are involved in the meningeal vasodilatation evoked by electrical stimulation of the trigeminal ganglion.

Expression of PDE5 splice variants during ontogenesis of chick dorsal root ganglia

Cyclic GMP (cGMP)-binding cGMP-specific phosphodiesterase (PDE5) activity was found in chick dorsal root ganglia (DRG). PDE5 expression was studied at different stages of development: in embryonic day 10 (E10) and E18 embryos and in 5-day post-hatching chick (P5). The presence of PDE5 was suggested by the ion exchange chromatography elution profile in E18 DRG extracts, where cGMP-specific hydrolytic calmodulin-independent activity was found; in other stages, this activity coeluted with the PDE1 calmodulin-stimulated isoform characterized previously. Inhibition studies supported the hypothesis that the newly identified PDE activity belongs to the PDE5 isoform. Western blot analysis using a PDE5-specific antibody was also carried out and revealed the presence of three specific immunoreactive bands with apparent molecular weights of 98, 93, and 86 kDa, corresponding to the three described splice variants (PDE5A1, PDE5A2, and PDE5A3). The expression in DRG of the three PDE5 isoforms was also confirmed by RT-PCR. Developmental regulation of PDE5 was revealed by the immunoblot analysis at different stages; expression was very low at E10 but an overall substantial increase occurred between E10-18 (about 12-fold, considering the three PDE5 isoforms together). Differences were revealed, however, when a single PDE5 isoform was considered. PDE5A1 and PDE5A3 showed an increase at all stages although more pronounced between E10-18, whereas PDE5A2 underwent a marked increase (about 38-fold) in the first period and remained nearly constant between E18 and P5. This is the first evidence of PDE5 in sensory neurons, and the distinct temporal expression patterns of enzyme isoforms may indicate different physiologic roles in developing and mature chick DRG.

The phosphodiesterase 3 inhibitor cilostazol dilates large cerebral arteries in humans without affecting regional cerebral blood flow

Cilostazol, an inhibitor of phosphodiesterase (PDE) type 3, is used clinically in peripheral artery disease. PDE3 inhibitors may be clinically useful in the treatment of delayed cerebral vasospasm after subarachnoid hemorrhage. The authors present the first results on the effect of cilostazol on cerebral hemodynamics in normal participants. In this double-blind, randomized, crossover study, 200 mg cilostazol or placebo was administered orally to 12 healthy participants. Cerebral blood flow was measured using 133Xe inhalation and single photon emission computerized tomography. Mean flow velocity in the middle cerebral arteries (VMCA) was measured with transcranial Doppler, and the superficial temporal and radial arteries diameters were measured with ultrasonography. During the 4-hour observation period, there was no effect on systolic blood pressure (P = 0.28), but diastolic blood pressure decreased slightly compared with placebo (P = 0.04). VMCA decreased 21.5 +/- 5.7% after cilostazol and 5.5 +/- 12.2% after placebo (P = 0.02, vs. placebo), without any change in global or regional cerebral blood flow. The superficial temporal artery diameter increased 17.6 +/- 12.3% (P < 0.001 vs. baseline) and radial artery diameter increased 12.6 +/- 8.6% (P < 0.001 vs. baseline). Adverse events, especially headache, were common. The findings suggest that cilostazol is an interesting candidate for future clinical trials of delayed cerebral vasospasm.

Plasma levels of cAMP, cGMP and CGRP in sildenafil-induced headache

Sildenafil, a selective inhibitor of the cyclic guanosine monophosphate (cGMP) degrading phosphodiestrase 5 (PDE5), induced migraine without aura in 10 of 12 migraine patients and in healthy subjects it induced significantly more headache than placebo. The aim of the present study was to determine whether the pain-inducing effects of sildenafil would be reflected in plasma levels of important signalling molecules in migraine: cGMP, cyclic adenosine monophosphate (cAMP) and calcitonin gene-related peptide (CGRP). Ten healthy subjects (four women, six men) and 12 patients (12 women) suffering from migraine without aura were included in two separate double-blind, placebo-controlled, cross-over studies in which placebo or sildenafil 100 mg was administered orally. Plasma levels of CGRP, cAMP and cGMP were determined in blood from the antecubital vein. Despite the ability of sildenafil to induce headache and migraine, no significant differences in plasma levels of CGRP, cGMP and cAMP were detected after sildenafil compared with placebo. In conclusion, plasma levels of CGRP, cGMP and cAMP remain normal during sildenafil-induced headache or migraine. However, since previous studies indicate an important role of these signalling molecules, the present study questions whether cAMP and cGMP in peripheral blood can be used for monitoring pathophysiological events in headache and migraine mechanisms.

Drug-induced headache

Medication overuse headache is a common complex disorder with physical and psychologic elements. Treatment may be difficult but often is accomplished in an outpatient setting. Some patients require inpatient treatments. An option for some is day treatment with i.v medication in an infusion center over several consecutive days. The two most common classes of drugs that acutely induce headache are NO donors, typified by NTG, and PDE inhibitors, typified by sildenafil. NO donors cause a biphasic headache in migraineurs and PDE inhibitors a monophasic one.

Glyceryl trinitrate triggers premonitory symptoms in migraineurs

Studying attacks of migraine is considerably hampered by its fundamentally episodic nature. Developing approaches to triggering migraine reliably is important for advancing understanding of the disorder by facilitating its study. Based on the work of the Copenhagen Group we administered an intravenous infusion of 0.5 microg/kg/min glyceryl trinitrate (GTN) to 44 migraineurs, 23 migraine without aura, 21 migraine with aura, and to 12 healthy controls. We sought to characterise the GTN-induced migraine in terms of the clinical features of the attacks and reproducibility of triggering, and included a non-migraine control group for the purpose of comparing any effects to exclude an ordering effect. Of the 44 patients administered GTN, 33 had a migraine attack fulfilling International Headache Society criteria. Thirty-two attacks were of migraine without aura and one of migraine with aura. Twelve patients described typical premonitory symptoms, which have not been previously documented with GTN-induced migraine. A repeat attack was triggered in all subjects but one. In one case a visual aura was also triggered both times. Our study shows that GTN-induced triggering is common in our patients, and remarkably reproducible. The data will facilitate the use of the GTN model in studies requiring extensive planning, such as brain imaging, or where preventive questions are at issue. We also report the first patient with a reproducible GTN-triggered migraine with aura.

Modulation of Dural Nociceptor Mechanosensitivity by the Nitric Oxide-Cyclic GMP Signaling Cascade

The role of the nitric oxide (NO)-cGMP signaling cascade in modulation of peripheral nociception is controversial. Although behavioral studies have suggested both pro- and anti-nociceptive effects, little is known about the direct action of this signaling cascade on primary afferent nociceptive neurons that mediate these behaviors. Here, using single-unit recordings, we examined the direct effect of NO-cGMP signaling on spontaneous activity and mechanical responses of nociceptive afferents that innervate the dura mater. We found that the NO donor sodium nitroprusside (SNP), when applied topically to the neuronal receptive field, induced both sensitization and inhibition of the mechanical responses, albeit in different populations of neurons, which could be distinguished based on their baseline mechanical thresholds. SNP, however, did not change the level of spontaneous activity. Administration of the cGMP analogue 8-pCPT-cGMP mimicked only the inhibitory effect. When SNP was co-applied with either an inhibitor of guanylyl cyclase or a cGMP blocker, sensitization never occurred, and the inhibitory effect of SNP could also be blocked. Our findings suggest that NO can either increase or decrease the mechanical responsiveness of nociceptors and that its action might depend, in part, on the baseline level of neuronal excitability. Our results also implicate cGMP in mediating the inhibitory effect of NO.