Priming of homosynaptic long-term depression in hippocampus by previous synaptic activity

Mechanisms regulating long-lasting, activity-dependent decreases in synaptic strength are poorly understood. Theoretical studies have suggested that the critical level (threshold) of synaptic activity needed to induce long-term depression (LTD) versus potentiation (LTP) of synaptic transmission should vary as a function of previous synaptic activity. In order to determine whether such a 'sliding threshold' is indeed a physiological phenomenon, we stimulated Schaffer collateral afferents in area CA1 of rat hippocampal slices at frequencies from 1 to 5 Hz before or after inducing LTP.