Fig. 5: A subset of vCA1–BA synapses was selectively strengthened in discriminative contextual fear conditioning.
From: Encoding of contextual fear memory in hippocampal–amygdala circuit
a Experimental setup for b–j. b After surgery, mice received three context labeling sessions with a 1-week interval to induce ChR2 expression in vCA1 neurons active in Context A. After a week, the mice received tamoxifen injection and were fear-conditioned in Context A on Day 1 for tdTomato (tdT) expression in BA fear neurons. On Days 2–5, mice were trained for discriminative fear in Context A as in Supplementary Fig. 1b. c Comparison of freezing responses in Contexts (Ctx) A vs. Context B on Day 5 (p = 0.001, two-sided paired t-test; n = 5 mice). d Images showing ChR2-eYFP-expressing vCA1 neurons (green, circles; left) and tdT-labeled BA neurons (red; right). e Traces of EPSCs recorded in tdT− and tdT+ BA neurons. tdT+ neurons were identified with red fluorescence within the BA (inset; scale bar, 10 μm). EPSCs were induced with photostimulation of Context A vCA1 inputs and recorded as in Fig. 4d. f Left: comparison of the AMPA/NMDA (A/N) ratios between tdT− and tdT+ BA neurons. Two-way ANOVA with post hoc comparisons was used to analyze combined data in f and n. Right: scatter plot of the A/N ratios in 18 pairs of tdT− (x-axis) and tdT+ BA neurons (y-axis) that were adjacent to each other. g Comparison of the amplitude of AMPAR EPSC (EPSCAMPAR) induced by photostimulation of the same intensity (6.4 mW/mm2) and recorded in tdT− vs. tdT+ BA neurons (two-sided paired t-test). h Traces of AP firing induced by depolarizing current injection (500 ms long) in tdT− and tdT+ BA neurons. Baseline membrane potential was adjusted to approximate −85 mV. i Comparison of AP firing in tdT− (18 cells) and tdT+ BA neurons (17 cells) (p = 0.67, two-way ANOVA). j Comparison of resting membrane potential (RMP, p = 0.45) and input resistance (Rin; p = 0.96, two-sided unpaired t-test) in tdT− (18 cells) and tdT+ BA neurons (17 cells). k Experimental setup for l–n. ChR2 was globally expressed in vCA1 neurons. BA fear neurons (tdT+) were labeled with tdT as in b. l Left: mice received three context labeling sessions and were then fear-conditioned in Context A on Day 1 for tdT expression in BA fear neurons as in b. On Days 2–5, the mice were trained for discriminative fear in Context A as in b. Right: quantification of freezing responses on Day 5. n = 5 mice. m Traces of EPSCs induced by global stimulation of vCA1 inputs and recorded in tdT− and tdT+ BA neurons as in e. n Left: comparison of the AMPA/NMDA ratios between tdT− and tdT+ BA neurons (p = 0.35, two-way ANOVA with post hoc comparisons). Right: scatter plot showing the AMPA/NMDA ratio in 10 pairs of tdT− and tdT+ BA neurons. Error bars represent the SEM. Source data are provided as a Source Data file. See also Supplementary Figs. 12–13.
