FIGURE 3.

Endogenous molecules that impact sleep and the approaches that led to their discovery

Only mammalian molecules are listed. Red, promotes waking; blue, promotes sleep; purple, promotes waking and sleep; asterisk, regulates sleep timing. Not listed: components of metabolic pathways for neurotransmitters, neurotransmitter receptors, and transporters. ^‡A gain-of-function mutation in NALCN decreases REM sleep but has no effect on total sleep duration (44). Loss-of-function mutations in the fly ortholog of NALCN, called narrow abdomen, increase sleep (64). Therefore, NALCN has been provisionally assigned a wake-promoting function.