Uridine is released by depolarization and inhibits unit activity in the rat hippocampus

PERFUSION of 5 mu M kainate through microdialysis probes:,induced >2-fold e levation of extracellular uridine and adenosine concentrations in the hippo campus and in the thalamus of anaesthetized rats. Administration: of uridin e via this route produced an estimated uridine:concentration of 50-100 mu M around the electrode surface. This markedly decreased the average firing r ate of neurones in the hippocampus, but not in the thalamus. Activity of se parated single hippocampal pyramidal cells was completely inhibited by urid ine. The same:amount of adenosine completely blocked neuronal activity in b oth hippocampus and thalamus. Uridine administration had no effect on extra cellular adenosine concentration. These findings suggest an important neuro modulatory role for depolarization-released uridine in the CNS. (C) 1999 Li ppincott Williams & Wilkins.