NMDA-independent induction of transsynaptic LTP. Pressure ejection of the NMDA receptor antagonist d-APV (100 μm; ∼70 nl/min for 15–30 min) into the apical dendrites of the CA3 and the dentate gyrus before theta burst stimulation blocked the induction of perforant path (pp) LTP (for both monosynaptic input to CA3 and the dentate) but not transsynaptic mossy fiber (mf) LTP (waveforms are averages of responses collected during last 5 min of a given sample period). Calibration bars, 1 mV and 5 msec.