Cesium prevents maintenance of long-term depression in rat hippocampal CA1 neurons

Long-term depression of field excitatory postsynaptic potentials (EPSP) in the CA1 region of hippocampal slices was evoked by delivering a 15 min train of pulses at 1 Hz to the Schaffer-commissural-CAl pathway, and prevented by adding an Af-methyl-D-aspartate (NMDA) receptor antagonist (AP-5,50 μM) to the perfusing medium. Superfusion of the slices with Cs (2 mM) during the 1 Hz stimulation period could both inhibit the maintenance phase of the depression itself and elicit spontaneous rhythmic activity. Cs had no effect on the postsynaptic response to the GAB A-B agonist, baclofen. As a major effect of Cs is a block of the hyperpolarization-activated current (I_h), these results suggest the possible involvement of I_h in the maintenance of long-term depression.