Pre- and postsynaptic actions of adenosine in the in vitro rat hippocampus

The mechanisms underlying the depressant effect of adenosine on excitatory synaptic transmission were studied in rat hippocampus in vitro. The relative contribution of direct effects of adenosine upon CA1 pyramidal neurons (hyperpolarization, increased conductance) was evaluated by comparing the effects of superfused adenosine on EPSP amplitude, and on depolarizing responses to local application of glutamate. Adenosine depressed synaptic EPSPs to a greater extent than glutamate responses in 30 out of 32 cases, and its effects were independent of the site of glutamate application (somatic vs dendritic). Thus, the postsynaptic effects of adenosine, including a possible dendritic conductance that would be undetectable with somatic recordings, can only partially account for the depression of synaptic potentials observed with adenosine.