Bangsheng Wu

Abstract Wakefulness produces sleep-promoting substances and the cerebrospinal fluid contains substances that reflect homeostatic sleep pressure. However, identities of such molecules, and the neural mechanisms for producing and sensing them, remain mysterious. Here we show that cerebrospinal fluid levels of tryptamine (TrpA) track homeostatic sleep pressure in nocturnal mice and diurnal pigs, reflecting physical activity history independently of light–dark cycles.