title: Endogenous adenosine induces NMDA receptor-independent persistent epileptiform discharges in dorsal and ventral hippocampus via activation of A2 receptors.
abstract: Although adenosine is widely assumed to be an endogenous anticonvulsant its role in epileptogenesis is still contradictory. Using slices from the dorsal (DH) and the vental (VH) rat hippocampus and extracellular recordings from the CA3 field we aimed to determine the effects of endogenous adenosine on the expression and long-term maintenance of epileptiform activity induced by blockade of adenosine receptors types A(1) (A(1)R) and A(2) (A(2)R) under conditions of low magnesium. We found that the A(1)Rs blockade induced persistent epileptiform discharges (PED) more frequently in VH (by 52%) than in DH (by 31%). The induction of PED upon an additional blockade of A(2)Rs increased in VH (by 48%) but decreased in DH (by 74%). Remarkably, the increment in VH was prevented by a blockade of NMDARs. A blockade of A(2)Rs increased the NMDAR-mediated component of evoked synaptic potential in both VH and DH (by ~100%) but suppressed the non-NMDAR-mediated component in DH but not VH. A blockade of A(1)Rs induced PED equally in DH (76%) and VH (80%) via a NMDAR-independent mechanism. A blockade of A(2)Rs under blockade of A(1)Rs and NMDARs reduced the PED to 17% in DH and to 38% in VH. These findings show that A(2)Rs play a different role in the long-term maintenance of epileptiform activity between DH and VH and suggest that endogenous activation of A(2)Rs facilitates NMDAR-independent induction of PED in both hippocampal poles, but suppresses NMDAR-dependent induction of PED in VH.
authors.affiliation: Laboratory of Physiology, Medical School, University of Patras, 26504 Rion, Greece.
authors.forename: Christos
authors.initials: C
authors.lastname: Moschovos
authors.forename: George
authors.initials: G
authors.lastname: Kostopoulos
authors.forename: Costas
authors.initials: C
authors.lastname: Papatheodoropoulos
mesh_terms: D000241:Adenosine / Q000502:physiology*; D058917:Adenosine A2 Receptor Antagonists / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D004827:Epilepsy / Q000378:metabolism* / Q000503:physiopathology / Q000517:prevention & control; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D043683:Receptors, Adenosine A2 / Q000378:metabolism* / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D055366:Synaptic Potentials / Q000502:physiology
chemical_list: D058917:Adenosine A2 Receptor Antagonists; D043683:Receptors, Adenosine A2; D016194:Receptors, N-Methyl-D-Aspartate; D000241:Adenosine