He said new therapies could be developed from orexin receptor agonists, which mimic the effect of orexin.

BBC: NEWS | Health | Brain chemical helps narcolepsy

"This is extremely important because it shows that these mice retain the ability to respond to orexin, " Dr Yanagisawa said.

BBC: NEWS | Health | Brain chemical helps narcolepsy

In humans narcolepsy is an autoimmune disorder that destroys the orexin neurons.

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"This new treatment is likely to be better, although current treatments are not curative, and it is unlikely that orexin would be curative, " he told BBC News Online.

BBC: NEWS | Health | Brain chemical helps narcolepsy

Instead, suvorexant turns off a different set of switches, known as orexin receptors, which are involved in waking people up and are only present in 70, 000 neurons in a particular place in the brain.

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These orexin cells were discovered from the study of narcolepsy, a disease in which people cannot stay awake, in the late 1990s by Emmanuel Mignot, a Stanford researcher, who found that dogs with a defective orexin receptor gene developed the condition.

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