The role and regulation of adenosine in the central nervous system

Adenosine is a modulator that has a pervasive and generally inhibitory effe ct on neuronal activity. Tonic activation of adenosine receptors by adenosi ne that is normally present in the extracellular space in brain tissue lead s to inhibitory effects that appear to be mediated by both adenosine A(1) a nd A(2A) receptors. Relief from this tonic inhibition by receptor antagonis ts such as caffeine accounts for the excitatory actions of these agents. Ch aracterization of the effects of adenosine receptor agonists and antagonist s has led to numerous hypotheses concerning the role of this nucleoside. Pr evious work has established a role for adenosine in a diverse array of neur al phenomena, which include regulation of sleep and the level of arousal, n europrotection, regulation of seizure susceptibility, locomotor effects, an algesia, mediation of the effects of ethanol, and chronic drug use.