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. 2020 Apr 18;23(5):101078. doi: 10.1016/j.isci.2020.101078

Figure 3.

Figure 3

Reduced Expression of Coherent Network Oscillations in CA3 Hippocampal Neurons of TrkbGad1-KO Mice

(A) GDPs recorded from P3 to P9 TrkbGad1-WT and TrkbGad1-KO mice. An expanded timescale for the GDPs marked with an asterisk is shown on the right.

(B) Summary plots showing the mean frequency and the mean area of GDPs obtained from TrkbGad1-WT and TrkbGad1-KO mice; GDPs (frequency: control 0.019 ± 0.003 Hz [n = 20 from 6 pups], TrkbGad1-KO 0.004 ± 0.001Hz [n = 14 from 3 pups], ∗∗∗p < 0.0001); area (control 0.024 ± 0.003 mVs−1, TrkbGad1-KO 0.015 ± 0.003 mVs−1, ∗p = 0.03).

(C) Spontaneous and miniature GPSCs recorded from CA3 principal cells in hippocampal slices from P3 to P9 in TrkbGad1-WT and TrkbGad1-KO mice.

(D) Summary plots showing the mean frequency and amplitude of sGPSCs obtained from TrkbGad1-WT (n = 15 from 3 pups) and TrkbGad1-KO (n = 18 from 6 pups) mice, respectively (sGPCSs frequency: TrkbGad1-WT 1.97 ± 0.2 Hz, TrkbGad1-KO 2.74 ± 0.2 Hz, ∗p = 0.03; sGPCSs amplitude: TrkbGad1-WT 50.3 ± 4 pA, TrkbGad1-KO 64 ± 6 pA, p = 0.09).

(E) Cumulative distributions of interevent interval (IEI) of sGPSCs and mGPSCs for cells shown in (C).

(F) Summary plots showing the mean frequency and amplitude of mGPSCs obtained from TrkbGad1-WT (n = 16 from 5 pups) and TrkbGad1-KO (n = 15 from 4 pups) mice, respectively (mGPSCs frequency: TrkbGad1-WT 0.97 ± 0.1 Hz, TrkbGad1-KO 1.39 ± 0.2 Hz, ∗p = 0.04; mGPSCs amplitude: TrkbGad1-WT 45.5 ± 2.2 pA, TrkbGad1-KO 39.5 ± 1.7 pA, p = 0.07). Values are mean ± SEM, p statistic from unpaired Student's t tests.

(G–L) Increased number of GABAergic synapses in the CA3 region of TrkbGad1-KO mice. Number of synapses in the CA3 hippocampal region/100 μm2 at P5, TrkbGad1-WT (n = 4 mice), TrkbGad1−KO (n = 3 mice). (G) Total, TrkbGad1-WT, 4.28 ± 0.25, TrkbGad1-KO, 4.07 ± 0.38, p > 0.05. (H) Symmetrical synapses, TrkbGad1-WT, 1.40 ± 0.09, TrkbGad1-KO, 2.06 ± 0.08, p = 0.003. (I) Asymmetrical synapses, control, 2.88 ± 0.25, TrkbGad1-KO, 2.01 ± 0.32, p = 0.04. (J and L) Representative electron micrographs of single symmetrical synapses (white arrows) from TrkbGad1-WT (J) and TrkbGad1-KO (K) mice at P5. (L) Representative electron micrograph showing one asymmetrical synapse (black arrow) and two neighboring symmetrical synapses (white arrows) in the CA3 region of a TrkbGad1-KO mouse at P5. Note the presence of a clear postsynaptic density at the asymmetric synapse that is lacking from the symmetric synapses. Values are mean ± SEM, p statistic from unpaired one-tailed Student's t tests. Scale bars: 0.5 μm in (J and K) and 500 μm in (L).

(M and N) No significant changes in the probability of GABA release at MF-CA3 synapses of TrkbGad1-KO mice. (M) Representative examples of synaptic currents evoked in CA3 principal cells by pair stimulation of MF (50-ms interval). (N) Summary plots showing the mean paired-pulse ratio (PPR) values obtained in TrkbGad1-WT (n = 7 from 5 pups), 1.91 ± 0.3, and in TrkbGad1-KO mice (n = 10 from 9 pups), 1.34 ± 0.1; p = 0.1.

See also Figures S3 and S4.