The effect of 5-HT receptor antagonists on the induction of LTP in the white matter-layer II/III pathway in the visual cortex slices obtained from 5-week-old rats. A, Time course of LTP. Tetanic stimulation was applied in the absence (▵) or presence (▴) of 50 μm methysergide.Insets are sample records at the times denoted by the numbers. Calibration: vertical, 0.5 mV; horizontal, 5 msec.B, Effects of 5-HT receptor antagonists, methysergide, NAN-190, and mesulergine, on the magnitude of LTP. Data are the means ± SEM (n = 5). *p< 0.05, **p < 0.01 versus control group; Tukey's test after ANOVA.