The nerve cells, or neurons, in this part of the hypothalamus secrete substances known as hypocretins or orexins, which regulate the sleep/wake cycle in humans.
As of the early 2000s, narcolepsy is thought to be an orexin deficiency syndrome; that is, it develops when a person's hypothalamus does not secrete enough orexins to keep the person from falling asleep at inappropriate times.
Samples of cerebrospinal fluid taken from patients with narcolepsy contain little or no orexins.
MRI scans of these patients indicate that there is some loss of brain tissue in the hypothalamus itself, suggesting that the neurons responsible for secreting orexins have died.
Yanagisawa. "Orexins: From Neuropeptides to Energy Homeostasis and Sleep/Wake Regulation."
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