Adenosine and Sleep-Wake Regulation
腺苷和睡眠觉醒调节

Adenosine may function as a neuromodulator in the central nervous system. The extracellular concentration of adenosine increases in the brain during prolonged wakefulness and decreases during the sleep recovery period. Therefore, adenosine is proposed to act as one of homeostatic regulators of sleep. There are four adenosine receptor subtypes, adenosine A1 receptor (A1R), A2AR, A2BR and A3R. Both the adenosine A1R and A2AR are demonstrated to be involved in sleep induction. Inhibition of wake-promoting neurons via the A1R mediates the sleep-inducing effects of adenosine, whereas activation of A1R in sleep-promoting neurons induces wakefulness, suggesting that A1R regulates the sleep-wake cycle in a site-dependent manner. On the other hand, the A2AR mediates the somnogenic effects of endogenous PGD2. A2AR agonist induces the most potent sleep similar to physiological sleep among somnogens reported so far, whereas blockade of A2AR induces wakefulness. Among adenosine receptors responsible for sleep induction, the role of A2AR is predominant. This paper presents an overview of the current knowledge about the role of adenosine in the sleep-wake regulation and briefly discusses the potential therapeutic applications of agonists and antagonists of these receptors in sleep disorders.