[Purinergic neuromodulation]

Adenosine and its nucleotides participate in the regulation of various functions in the nerve system and in some internal organs. These purines are released from a variety of nervous and non-nervous cellular sources. Adenosine receptors are situated extracellular; they mediate some effects of the adenosine and are coupled negatively (A1 adenosine receptors) and positively (A2 adenosine receptors) to adenylate cyclase. The physiological effects of adenosine are inhibitory; they are exerted synaptically and extrasynaptically. The main synaptic modulatory effect is the presynaptic inhibition of the excitatory and inhibitory neurotransmitters release. Postsynaptically adenosine modulate the answer to neurotransmitter effects. ATP functions probably as co-transmitter or transmitter in the non-adrenergic non-cholinergic autonomic neurons. Neuromodulatory and the majority of metabolic adenosine effects are antagonized by methylxanthines. Exogenous substances can influence the molecular mechanisms of adenosine systems; some of the induced pharmacodynamical effects could be of therapeutic interest. Drug-interactions with adenosine systems can cause side effects.