Impairment of LTP in hippocampal CA1 synapses of fBZ/fBZ and trkB CA1-KO mice. All data in this figure and Figure 7 are expressed as mean ± SEM.A, Time courses of synaptic potentiation induced by tetanic stimulation in CA1 synapses of hippocampal slices from different genotypes. Field EPSPs were recorded in the CA1 area, and tetanus (2 × 1 sec, 100 Hz, 20 sec apart) was applied to Schaffer collaterals at time 0. Synaptic efficacy (initial slope of EPSPs) is expressed as the percentage of baseline values recorded during the first 20 min before tetanus. Each data point represents the averaged values of recordings at that particular time point. Wild-type, n = 5 mice; fBZ/fBZ,n = 4 mice; trkB CA1-KO,n = 7 mice. B, Percentage of successful LTP recordings for wild-type, fBZ/fBZ, andtrkB CA1-KO mice. LTP was judged successful if, at 45 min after the tetanus, the slope of the EPSP was >125% of the baseline. Wild-type, n = 35 slices from eight mice;fBZ/fBZ, n = 34 slices from six mice; trkB CA1-KO, n = 50 slices from seven mice. C, Effect of p75NTR antibodies on LTP. Slices from wild-type animals were treated with or without p75NTR antibodies (50 μg/ml in ACSF). The magnitude of LTP was expressed as a percentage of the EPSP slopes before and 60 min after tetanus. The control and anti-p75NTR antibody-treated groups (n= 4 and 5 slices, respectively) are not statistically different (two-tailed t test, p = 0.6).D, Magnitude of LTP in slices from wild-type,fBZ/fBZ, and trkB CA1-KO mice andtrkB CA1-KO slices treated with TrkB-IgG. Synaptic efficacies 45 min after the tetanus from each animal are averaged and expressed as the percentage of baseline values. Wild-type,n = 8 mice; fBZ/fBZ,n = 6 mice; trkB CA1-KO,n = 7 mice; trkB CA1-KO + TrkB-IgG,n = 4 mice. *Significantly different from wild-type group, p < 0.01; ^#Significantly different from fBZ/fBZ and trkB CA1-KO groups, p < 0.05. E, Synaptic responses to HFS at CA1 synapses in fBZ/fBZ andtrkB CA1-KO mice. The slope of the 100th EPSP in the train is presented as the percentage of the first EPSP slope. *Significantly different from wild-type, Student's ttest, p < 0.001. F, Synaptic responses to HFS at CA1 synapses of wild-type hippocampal slices treated with or without anti-p75NTR IgG. The slope of the 100th EPSP in the train is presented as the percentage of the first EPSP slope. There is no difference between the two groups [n = 4 for wild-type and n = 5 for p75 antibody (Ab)-treated groups, two-tailed t test,p = 0.33].