Coach Bill:
Before answering your question, I think it is REALLY important to note that
1) the mechanism of action in cluster headaches is not known
2) All primary headaches had been thought to be caused by chemical factors alone ("The dogma is that primary headache, like cluster headaches and migraine, are due to abnormal brain function with completely normal brain structure," Dr. Goadsby), BUT
3) using a new scanning technique (in 1999) Dr. Goadsby has shown that cluster headaches are likely to be caused by excessive growth of grey cells in one part of the brain (the hypothalamus),
4) "Professor Goadsby said, 'We also found that the area of the brain where these structural abnormalities were seen, the hypothalamus, is the same area of the brain where the functional studies show that activity is abnormal during the headache state. This complete correlation of functional and structural abnormality is striking.' " Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

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When it comes to the functional abnormalities, most of the cluster headache treatments are actually treatments developed for Migraines: most of those act on serotonin receptors.
"The precise cause of migraine headaches is still not fully understood [either], but it is generally believed that the key element in understanding them has to do with the blood flow changes in the brain," ...which Rosa was addressing.
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[Some trigger] "creates a spasm in the nerve-rich arteries at the base of the brain. This spasm closes down or constricts several arteries supplying blood to the brain, thus reducing blood flow to the brain. Simultaneously, platelets clump together and are believed to release a chemical called serotonin. (The trigeminal [5th cranial] nerve has been implicated.)
The serotonin causes the blood vessels in the head to contract and lowers the pain threshold. Before a migraine episode, serotonin levels have been detected to be unusually high in the brain, lending weight to the previous explanation. During a migraine attack, serotonin levels become very low. The low amounts cause the blood vessels to be unusually large...."
It is this basic vasodilation that is addressed by the triptans (which cause vasoconstriction), caffeine (which causes vasoconstriction), and oxygen (which causes vasoconstriction). Obviously each has a different mechanism of action, which is why they work for some people and not for others.
It is because the indole-ring compounds (such as LSD, LSA, psilocybin, Kudzu, &etc) have very similar chemical structure to serotonin that those researching psychedelics in the treatment of cluster headaches decided to explore that avenue.
Rosa is pointing out that there appears to be a relationship between sleep & serotonin levels (and thus the issues of vasodilation at night) that indicates that especially those with primarily night-time hits may respond better to treatment with indole-ring type compounds than other types of treatment. (I think).
Laurie