Electrophysiological recordings were used to investigate the effects of ATP analogues on θ-burst-induced long-term potentiation (LTP) in rat hippocampal slices. α,β-Methylene ATP (α,β-MeATP; 20 μM) decreased LTP from 36+/-9% to 17+/-5%, an effect prevented by adenosine A 1 receptor blockade in accordance with the localised catabolism of ATP analogues into adenosine, leading to adenosine A 1 receptor activation. Thus, to probe the role of extracellular ATP, all experiments were performed with the A 1 receptor selective antagonist, 1,3-dipropyl-8-cyclopentylxanthine (50 nM). In these conditions, α,β-MeATP or 5'-adenylylimido-diphosphate (β,γ-ImATP; 20 μM) facilitated LTP by 120%, an effect prevented by the P2 receptor antagonists, pyridoxalphosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS; 20 μM) or suramin (75 μM), as well as by the P2X 1 / 3 -selective antagonist 8-(benzamido)naphthalene-1,3,5-trisulfonate (10 μM). The facilitations of LTP by either α,β-MeATP or β,γ-ImATP (20 μM) were also prevented by both 4-(2-[7-amino-2-(2-furyl(1,2,4)-triazolo(2,3a)-(1,3,5)triazin-5-yl-amino]eth yl)phenol (50 nM) or 7-2(-phenylethyl)-5-amino-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo[1,5-c] pyrimidine (50 nM), antagonists of facilitatory adenosine A 2 A receptors, were occluded by the A 2 A receptor agonist, CGS 21680 (10 nM) and were prevented by the protein kinase C inhibitor, chelerythrine (6 μM) and unaffected by the protein kinase A inhibitor, H89 (1 μM). Furthermore, β,γ-ImATP (20 μM) enhanced [ 3 H]adenosine outflow from rat hippocampal slices by nearly 150%, an effect prevented by PPADS (20 μM) or suramin (75 μM). The adenosine transport inhibitors, nitrobenzylthioinosine (5 μM) and dipyridamole (10 μM) also prevented β,γ-ImATP (20 μM)-induced [ 3 H]adenosine outflow and facilitation of LTP. These results suggest that ATP analogues facilitate LTP through P2 receptor activation that mainly triggers adenosine release leading to the activation of adenosine A 2 A receptors.