LTP evaluation in hippocampal slices. LTP was reliably induced in both groups in CA1 hippocampus immediately after high frequency stimulation (HFS - black arrow). Early LTP time points (1, 2, and 3 hours - 5 min sampling intervals) show no significant difference in LTP responses between the two groups (P > 0.05). However, a significant decrease (*P < 0.05) was found in EPSP slope in the p50−/− hippocampal slices (triangles) vs. p50+/+ (circles) slices at 4, 5, and 6 hour time points (5 m sampling intervals) indicating deficits in late LTP. Scale bar: 2 mV, 10 ms.