For fruit flies, sleep is induced by stress at the cellular level. When fruit flies are exposed to stressful conditions, such as heat or starvation, their cells produce a molecule called adenosine. Adenosine then binds to receptors in the brain, which signals the fly to fall asleep. This process is similar to how caffeine works in humans. Caffeine blocks the adenosine receptors in the brain, which prevents us from feeling tired.

Scientists have found that adenosine levels increase in fruit flies that are sleep-deprived. This suggests that adenosine plays a role in regulating sleep in fruit flies. In addition, fruit flies that are genetically modified to produce less adenosine have shorter sleep times than normal flies. This further supports the role of adenosine in sleep induction.

The discovery that adenosine induces sleep in fruit flies could have implications for understanding sleep in humans. It is possible that adenosine also plays a role in regulating sleep in humans. If this is the case, then it could lead to new treatments for sleep disorders.