[Adenosine.amino acid].

Somnogenic effect of adenosine came to be widely known by experiments of the central administration of fowls and dogs in the early 1970s. This effect was subsequently confirmed in rats by the use of metabolically stable analogues of adenosine. Now, there is a hypothesis that adenosine, which is a metabolite of adenosine triphosphate (ATP) and the main source of energy, conveys a feedback signal to check the rise in the consumption of ATP, and then induces the state of sleep with low consumption of energy. Based on the pharmacological and structural characteristics, the receptors for adenosine are now divided into A1, A2a, A2b, and A3. Cholinergic neurons in DBH, PPT, and LDT which are involved in the promotion of wakefulness, are presumed to be the target structure of adenosine to promote sleep by causing a depressant effect on the neuronal excitation through A1 adenosine receptor. On the other hand, it is becoming apparent that A2a adenosine receptors located in the ventral and rostral part of the basal forebrain are also involved in the promotion of SWS and PS with different mechanisms mediated by A1 adenosine receptor.