The Sources of Extracellular Adenosine in Hippocampus and Neostriatum of the Rat Brain

Endogenous adenosine can enter the extracellular space either by direct release or via formation from adenine nucleotides. We have compared the effects of substances blocking the ecto-5'-nucleotidase with α, β-methylene adenosine 5'-diphosphate (AOPCP) or adenosine kinase with iodotubercidin (Itu) on field potentials in the hippocampus and the neostriatum in vitro evoked by stimulation of the stratum radiatum or the cortico-striatal pathway respectively. AOPCP enhanced the amplitude of the population spikes by 34% in the hippocampus and by 26.5% in the neostriatum. DPCPX, a selective A1-receptor antagonist, increased the amplitude of the population spikes by 68% in the hippocampus and by 53.5% in the neostriatum. Thus both, release of adenosine from the intracellular space and, extracellular dephosphorylation of adenine nucleotides to a lesser extent, contribute to the effective levels of adenosine in the extracellular space in hippocampus and neostriatum.