The larval zebrafish pineal gland, which produces the hormone melatonin, is shown colored in red for aanat2, a gene which is required for the natural production of melatonin, and in green for nitroreductase, an enzyme which can be used to ablate the pineal gland where the production of melatonin occurs. In studying this area of the brain and the effects of blocking the natural synthesis of melatonin in this region, Caltech researchers recently showed that melatonin normally plays an important role in sleep, helping zebrafish larvae to both fall asleep and stay asleep.

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