Glutamate ionotropic transmission from Schaffer collateral axons onto GABAergic interneurons differs from that on the principal CA1 pyramidal cells. For example, many glutamate synapses on interneurons contain postsynaptic kainate receptors and calcium permeable AMPA receptors. We have previously shown, in the developing (< 2 week old) rat, that many glutamate synapses on interneurons, like those on pyramidal neurons, exhibit AMPA silent synapses and activity-dependent AMPA silencing (Riebe et al SfN 2004, Xiao et al Nat Neurosci 7:236). In the present study we report that AMPA silencing is observed not only in interneurons in the developing brain, but also in interneurons from the adult (> 40 day old) animal. Stimulating the Schaffer collaterals with 0.2 Hz, while voltage-clamping the interneuron at -80 mV, resulted in a rapid decrease of the naïve AMPA EPSC magnitude, stabilizing at 48±12% (n=5) of the initial value. This decrease was similar to that obtained in developing animals (66±8%, n=9) and it was...