The document describes experiments evaluating the effects of Compound X, a NMDA modulator, on long-term potentiation (LTP) and depression (LTD) in rat hippocampal slices. First, the LTP/LTD crossover point of about 50 Hz is determined. Compound X concentration-dependently decreases NMDA-mediated EPSP, with an IC50 of 3.6 μM. Compound X at concentrations of 0.3-3 μM slightly decreases the amplitude of LTP induced by 100 Hz stimulation compared to controls.