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. 2021 Aug 16;131(16):e137221. doi: 10.1172/JCI137221

Figure 2. Potentiation in CA2 can be induced before PNN maturation.

Figure 2

(A) Staining for PNNs as defined by WFA is morphologically mature in CA2 at P14 (right) but not at P11 (left). Scale bars: 250 μm. (B) Representative image of a 300-μm-thick hippocampal slice showing the placement of a recording electrode in CA2 and a stimulating electrode in CA3 stratum radiatum. Scale bar: 100 μm. (C) In slices from WT mice, excitatory postsynaptic current (EPSC) amplitudes recorded in CA2 neurons increased in response to an LTP pairing protocol (270 pulses at 3 Hz paired with postsynaptic depolarization at time 0) at P8–11, but not in slices harvested at P14–18 (n = 8 for P14–18, in blue; n = 9 for P8–11, in purple). Top: Representative traces of EPSCs from CA2 neurons before and 25 minutes after the pairing protocol. Arrow indicates time of the pairing. Indicated are means ± SEM, normalized to baseline. Right: Normalized mean response amplitudes averaged over 25–30 minutes of recovery after pairing; *P = 0.0104, 2-tailed unpaired t test. (D) EPSC amplitudes in response to indicated stimulation intensities were larger at P11 compared with P14; **P = 0.0026 at 320 pA, 2-way ANOVA, Bonferroni’s post hoc test (n = 9 and 8, P8–11 and P14–18, respectively). Top: Representative traces from a CA2 neuron at P10 in response to increasing stimulation intensities. Inset displays responses at lower stimulation intensities, the range at which LTP experiments were performed. (E) Paired-pulse ratio was unchanged between P8–11 and P14–18 at CA2 synapses; P > 0.05. Top: Representative trace from WT CA2 P11 neuron in response to a 50-millisecond stimulus interval (S1, peak of first stimulus response; S2, peak of second stimulus response). (F) Action potential firing frequency of P14–18 CA2 neurons was greater compared with that at P8–11 at 180 pA of injected current; *P = 0.0185, 2-way ANOVA, Bonferroni’s post hoc test (n = 13 and 20, P8–11 and P14–18, respectively). Top: Representative traces of action potentials recorded in response to current injections from 0 to 180 pA in WT P11.