A novel G-protein-coupled receptor with adenine identified as the endogenous ligand has recently been described. In vivo electrophysiological techniques in the rat were used to record the response of dorsal horn neurones in response to transcutaneous electrical stimulation to the hindpaw receptive field. Spinal adenine (1-1000 microg) exerted facilitatory effects on the electrically-evoked neuronal responses, in a mildly dose-related manner. After establishment of carrageenan-induced inflammation to the hindpaw this excitatory effect of adenine was still apparent, yet reduced. C-fibre-evoked responses and other nociceptive related measures were most susceptible to the effects of adenine, whereas non-nociceptive Abeta-fibre evoked activity remained unaffected. Thus, activation of the adenine receptor site, via spinally applied adenine, suggests a pronociceptive role in nociceptive sensory transmission.