Figure 5.

Morphological Alterations of CA3 Principal Cells and Impaired Hippocampal LTP at MF-CA3 Synapses in Adult Trkb^Gad1-KO Mice

(A) Representative images of Golgi-stained (left) and neurolucida tracings (right) of CA3 principal cells from young adult control (Trkb^Gad1-WT) and Trkb^Gad1-KO mice.

(B) Quantitative analysis of dendritic length of CA3 principal neurons in Trkb^Gad1-WT and in Trkb^Gad1-KO mice. Total dendritic length, proximal 1–100 μm from soma (Trkb^Gad1-WT, 362.32 ± 65.51; Trkb^Gad1-KO, 203.75 ± 23.78, Student's t test: t₍₁₉₎ = 2.59; ∗p = 0.017), and distal 100–300 μm from soma (Trkb^Gad1-WT, 358.13 ± 94.33; Trkb^Gad1-KO, 369.82 ± 107.61, Student's t test: t₍₁₈₎ = 0.26; p = 0.79).

(C) Sholl analysis of principal neurons in Trkb^Gad1-WT and Trkb^Gad1-KO mice. Statistically significant differences across the dendritic trees between genotypes are marked by a vertical line (Trkb^Gad1-WT, 5.77 ± 1.0; Trkb^Gad1-KO, 2.63 ± 0.4, Student's t test: t₍₁₈₎ = 2.93; ∗p = 0.008); values are mean ± SEM. Trkb^Gad1-WT, n = 9 neurons from 4 mice; Trkb^Gad1-KO, n = 12 neurons from 3 mice.

(D) Representative images of Timm stain per genotype showing similar MF pattern in the CA3 target region of 2M-old mice (n = 3 each group).

(E) LTP at MF-CA3 synapses. Cartoon illustrating the experimental paradigm.

(F) Sample traces of paired field (f) EPSPs (50-ms interval) evoked in CA3 stratum radiatum (sr) upon stimulation of MF in stratum lucidum (sl) in the presence of DL-AP5 (100 μM).

(G) Each column represents the mean value of the paired-pulse ratio (PPR, 50-ms interval) obtained from Trkb^Gad1-WT (1.35% ± 9%, n = 7 slices from 4 mice) and from Trkb^Gad1-KO mice (1.33% ± 6%, n = 8 slices from 3 mice), p = 0.92.

(H) Input-output relationship of fEPSP responses evoked in CA3 stratum radiatum by MFs stimulation in the stratum lucidum of Trkb^Gad1-WT (n = 9 slices from 5 mice) and Trkb^Gad1-KO mice (n = 5 slices from 5 mice), Kolmogorov-Smirnov test, p = 0.998. Each point represents the mean ± SEM.

(I) The amplitudes of MF-fEPSPs recorded from Trkb^Gad1-WT (n = 4 slices from 3 mice) and Trkb^Gad1-KO mice (n = 5 slices from 4 mice) before and after theta-bursts stimulation (arrow, 10 trains 200 Hz, 50 ms each, repeated twice at 0.1 Hz) of MF was normalized to baseline values and plotted against time. Mean amplitude values of fEPSPs evoked 10 min before and 30 min after LTP induction (30 min, fEPSPs amplitude, Trkb^Gad1-WT, 160% ± 2.1%, n = 4 slices from 3 mice; Trkb^Gad1-KO, 116.1% ± 0.52%, n = 5 slices from 4 mice, p < 0.001). The insets above the graph show two superimposed average traces of fEPSPs obtained from Trkb^Gad1-WT and Trkb^Gad1-KO mice before and 30 min after LTP induction.

Scale bars: 500 μm in (A) and 100 μm in (D).