Physiological modulation by adenosine: selective blockade of A1-receptors with DPCPX enhances stimulus train-evoked neuronal Ca influx in rat hippocampal slices.

Decreases in the extracellular Ca2+ concentration (delta Ca) elicited by a 20 Hz/10 s orthodromic stimulus train were measured with combined ion sensitive/recording electrodes in the CA1 area of rat hippocampal slices. Addition of the selective adenosine A1-receptor antagonist, DPCPX, or adenosine deaminase increased evoked delta Ca in the synaptic and pyramidal cell soma layer by more than 100%. This was accompanied by an earlier generation of population spikes during the train. It is concluded that physiological adenosine concentrations of about 1 microM exert a depressive tonus on synaptic transmission and frequency potentiation and that this effect is mediated via A1-receptors.