Medical Health Encyclopedia

The hormone melatonin is also involved in the body's biologic rhythms.

Alterations in Serotonin. The brain chemical serotonin is of particular interest in the study of headaches, particularly migraine and cluster headaches. This neurotransmitter (chemical messenger) affects, among other functions, well being, sleep, and appetite. Some research has also suggested that serotonin may play an important role in the way circadian rhythms are expressed. There is some evidence of abnormal regulation of brain serotonin levels in cluster patients (although it is not as pronounced as in migraine patients).

Dilation of Blood Vessels

Cluster headaches are associated with dilation (widening) of blood vessels and inflammation of nerves behind the eye.

Cluster headaches may be caused by blood vessel dilation in the eye area. Inflammation of nearby nerves may give rise to the distinctive stabbing, throbbing pain usually felt in one eye. The trigeminal nerves branch off the brainstem behind the eyes and send impulses throughout the cranium and face.

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In both cluster and migraine headaches blood vessels dilate, but in cluster headaches only the blood vessels behind the eyes pulsate. What causes these events and how they relate to cluster headaches are still unclear:

• Because blood vessel dilation appears to follow, not precede, the pain, some action originating in the brain is likely to be part of the primary process.
• Some experts believe that at least some of the pain is caused by dilation in branches of the carotid artery (a major artery that supplies the brain with blood).
• Certain substances, such as histamine and a protein called endothelin-1 that widens blood vessels and are being investigated for a possible role in cluster headaches.

Other Factors

Nitric Oxide. Nitric oxide is a small molecular messenger that activates nerve pathways in the brain, muscles, or elsewhere. It may contribute to major primary headaches (tension-type, cluster, and migraines) by specifically triggering inflammation and overactivity in the trigeminal nerves. (This is a major nerve pathway that runs from the brain stem to the head and face.) However, other factors must be present that make cluster headache patients susceptible to the actions of nitric oxide.