What tells the brain that it is time to sleep?

Chinese scientists have made an important discovery regarding how sleep is regulated. According to a study published in the journal Nature Neuroscience, the previously understudied molecule tryptamine may be one of the key mechanisms signaling the body that it is time to sleep.

Researchers studied the homeostatic pressure of sleep—meaning that the longer a person stays awake, the greater the need for sleep increases. Experiments were conducted on mice and pigs. Previously, adenosine was considered the main chemical signal for this process, but it could not fully explain how the brain "understands" that it is time to sleep.

The new study found that the amount of tryptamine gradually increases during wakefulness. Scientists revealed that this molecule acts on the GPR139 receptor in the hypothalamus, activating neurons responsible for sleep.

During experiments, when tryptamine synthesis or the GPR139 receptor was blocked, the animals had difficulty recovering sleep after sleep deprivation. Conversely, drugs that activate this receptor increased sleep duration and improved its quality in both animal species.

According to the authors, tryptamine could become an important target for developing new medications against insomnia in the future. However, they emphasize that it is still too early to apply these conclusions to humans, as the studies were conducted only on animals and clinical trials involving humans have not yet begun.

Scientists also noted that tryptamine is not the only molecule regulating sleep and may work in conjunction with adenosine and other biological substances.