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

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.

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.

Migraine: an ophthalmologist's perspective

PURPOSE OF REVIEW

Migraine is a common disorder with visual and neurologic manifestations. Many patients present to ophthalmologists without a previous diagnosis of migraine. It is therefore essential for the ophthalmologist to have a good understanding of migraine to appropriately help these patients. Neurologic syndromes with migraine and retinopathy are well known. Here again, the ophthalmologist may play a role in establishing the correct diagnosis.

RECENT FINDINGS

For long the initial changes during a migraine attack have been shown to occur in the occipital cortex. In the recent years, the understanding of migraine has advanced with the availability of functional neuroimaging. A possible role of brainstem structures in the initiation of migraine attacks has been proposed based on functional magnetic resonance imaging blood oxygenation level-dependent signals. Activation of brainstem structures preceded activation of occipital cortex. Our understanding of cortical spreading depression is also advancing. Using multiwavelength optical intrinsic imaging, cortical spreading depression has been shown to have a triphasic response in rats. For the first time it has been shown that the cortical spreading depression activated the trigeminovascular system, which is followed by a series of cortical meningeal and brainstem events that cause the migraine headache. Sildenafil has been shown to induce migraine attack without dilation of cerebral blood vessels, further confirming that Wolf's vasogenic theory may not be true. Several loci for migraine have been identified in recent years. A new locus for migraine with and without aura has been identified on chromosome 6, a locus for migraine without aura to chromosome 14, and a locus for migraine with aura on chromosome 4.

SUMMARY

Our understanding of migraine is rapidly evolving with functional neuroimaging. There are several unanswered questions. In this article, we will review the epidemiology, genetics, and clinical features of various forms of migraine with emphasis on ocular migraine, pathogenesis, and briefly the management of migraine.

Phosphodiesterase 5 inhibitors in male sexual dysfunction

PURPOSE OF REVIEW

Phosphodiesterase 5 inhibitors are preferred by most men for the oral treatment of erectile dysfunction. In many guidelines, this therapy is recommended as first-line therapy because of convenience, high efficacy, and low rates of side-effects. Sildenafil was the first drug for the treatment of erectile dysfunction, introduced in 1998. There are now two new phosphodiesterase 5 inhibitors, vardenafil and tadalafil, for which approval was recently given in the European Union and is expected this year in the United States.

RECENT FINDINGS

Sildenafil has proved to be a very effective medicinal product. According to initial studies, vardenafil and tadalafil have demonstrated efficacy comparable to that of sildenafil. However, fewer data are available evaluating the adverse effects of vardenafil and tadalafil, particularly on their long-term use and their use in high-risk groups. Interestingly, vardenafil and tadalafil have a higher potency than sildenafil. Moreover, the long life of tadalafil has been associated with an erectogenic potential of the drug lasting for more than 24 h. The advantage of this is the possibility of a patient engaging in sexual activity more than once after a single administration of the drug.

SUMMARY

In the future, in addition to sildenafil, the new phosphodiesterase 5 inhibitors vardenafil and tadalafil will play an important role in the management of erectile dysfunction, depending on the patient's health profile.