ApoE4 TR animals show increased LTP induction without changes in synaptic transmission. A) Input-output curve generated from the slope fEPSP versus fiber volley amplitude measured at increasing stimulus intensities. B) Paired pulse facilitation. Second stimuli delivered at 20 ms intervals from 20 to 300 ms from first stimuli. Percent facilitation of fEPSP slope of second response as percentage of first response. C) Long-term potentation induced by 5 trains of theta-burst stimulation (arrow). Expressed as slope of fEPSP, standardized to the first 20 minutes of recording. Representative traces 5 minutes before (black lines) and 40 minutes after (colored lines) stimulation for apoE4 (red) and apoE2 TR (blue). Scale: 0.5 mV, 2 ms. D) Average potentiation of last 20 minutes of recording. C57BL/6J = WT, green diamond, n = 12; apoE-deficient = E0, Black circle, n = 12; apoE2 TR = E2, blue square, n = 17; apoE3 TR = E3, purple inverted triangle, n = 6; apoE4 TR = E4, red triangle, n = 14. Data expressed as mean ± SEM. *p < 0.05, ANOVA with Bonferroni's posttest.