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. Author manuscript; available in PMC: 2010 Jul 8.
Published in final edited form as: Curr Biol. 2008 Aug 5;18(15):R670–R679. doi: 10.1016/j.cub.2008.06.033

Table 2.

Conserved sleep mechanisms.

Worms Flies Fish Mammals
Clock Genes +1 + + +
Cyclic AMP + + ? +
Cyclic GMP + + ? ?
EGF + + ? +
GABA ? + + +
Adenosine ? + + +
Dopamine ? + ? +
Histamine ? + + +
Melatonin ? ? + +
Hypocretin/orexin ? ? +2 +
Potassium channels ? + ? +
1

Clock gene expression is associated with developmentally timed sleep.

2

The precise direction of hypocretin sleep regulation is under debate.