Table 2.
Worms | Flies | Fish | Mammals | |
---|---|---|---|---|
Clock Genes | +1 | + | + | + |
Cyclic AMP | + | + | ? | + |
Cyclic GMP | + | + | ? | ? |
EGF | + | + | ? | + |
GABA | ? | + | + | + |
Adenosine | ? | + | + | + |
Dopamine | ? | + | ? | + |
Histamine | ? | + | + | + |
Melatonin | ? | ? | + | + |
Hypocretin/orexin | ? | ? | +2 | + |
Potassium channels | ? | + | ? | + |
Clock gene expression is associated with developmentally timed sleep.
The precise direction of hypocretin sleep regulation is under debate.