Fine-tuning neuromodulation by adenosine.

In addition to its direct pre- and postsynaptic actions on neurones, adenosine is rich in nuances of priming, triggering and inhibiting the action of several neurotransmitters and neuromodulators. These actions are mediated by membrane adenosine receptors (A1, A2 and A3) and involve receptor-receptor interactions, which require, in most cases, the formation of an intermediate second messenger. The harmonic way adenosine builds its influence at synapses to control neuronal communication is operated through fine-tuning, 'synchronizing' or 'desynchronizing' receptor activation for neuropeptides such as calcitonin gene-related peptide and vasoactive intestinal peptide, nicotinic acetylcholine autofacilitatory receptors, NMDA receptors, metabotropic glutamate receptors, as well as its own adenosine receptors.