Melatonin promotes sleep-like state in zebrafish

The sleep-promoting effect of the pineal hormone melatonin in humans is known for decades. However, the mechanisms of this phenomenon remain obscure, mainly due to lack of a simple, genetically tractable, animal model. We now report that melatonin promotes sleep-like state in a diurnal lower vertebrate, zebrafish (Danio rerio), and this effect is mediated through activation of specific melatonin membrane receptors. Furthermore, our data show that the sleep-like state in zebrafish has fundamental similarities with sleep in mammals, including characteristic postures, elevated arousal threshold to sensory stimulation and a compensatory rest rebound following rest deprivation, and can be induced by conventional hypnotics, diazepam and sodium pentobarbital. Collectively, these data indicate that melatonin is evolutionary conserved sleep-promoting agent in diurnal species and suggest that zebrafish provide an efficient animal model for studying the molecular mechanisms of sleep regulation and for screening new types of hypnotic medications. (C) 2001 Published by Elsevier Science B.V.