Normal LTP in CA1 of Smad4 mutants with different protocols and configuration. A, In a submerged recording chamber, one train of TBS induced similar levels of LTP from two groups. Mean amplitudes of fEPSPs recorded 0–20 min before induction of LTP were set as a baseline. B, A single train of 100 Hz protocol induced a similar level of LTP in Smad4 KO and control slices from interface chamber. C, A train of 100 Hz in 1 s given four times with 5 min interval induces late-phase LTP at the same level in both Smad4 KO and control slices. Averaged sweeps of baseline and 3 h after induction are shown above the accumulated plot.