Fig. 1: Activity in the vCA1–BA pathway contributes to the acquisition of contextual fear memory.
From: Encoding of contextual fear memory in hippocampal–amygdala circuit
a Experimental setup for b. b Images showing eYFP expression in the vCA1 (left, green) and eYFP-labeled vCA1 axons in the amygdala (middle and right). Red, Nissl stain. LA, BLA, BMA, and CeA: lateral, basolateral, basomedial, and central nuclei of the amygdala, respectively. c Experimental setup for d. Top: vCA1 neurons projecting to the BA (vCA1: BA projectors) were retrogradely labeled with HSV-mCherry. Bottom: mice in FC group were fear conditioned in Context A as in Supplementary Fig. 1a. Mice in CTX group were exposed to Context A without a US. After 24 h, they were tested for freezing behavior in Context A. Brain tissues were then fixed 90 min later for c-Fos immunohistochemistry. Mice in HC group were left in their home cages until brain fixation. d Left: image showing vCA1: BA projectors (red) in the dorsal (dCA1), intermediate (iCA1), ventral CA1 hippocampus (vCA1), and ventral subiculum (vSub). vDG, ventral dentate gyrus. LEC, lateral entorhinal cortex. Middle: image showing c-Fos+ cells (green) and vCA1: BA projectors (mCherry+, red). A square indicates a c-Fos+ vCA1: BA projector. Right: quantification of c-Fos+ proportion among vCA1: BA projectors (6 mice per group). **p = 0.001, ***p < 0.001 (one-way ANOVA with post hoc comparisons). e Experimental setup for f–h. vCA1: BA projectors expressed hM4Di-mCherry or mCherry. We bilaterally injected retrograde CAV2-Cre into the BA and AAV-DIO-hM4Di-mCherry (hM4Di group) or AAV-DIO-mCherry (mCherry group) into the vCA1. f Images showing hM4Di-mCherry expression in vCA1: BA projectors (left and middle). Note no hM4Di-mCherry expression in the amygdala (right). g Behavioral training and testing protocols for h. h Quantification of freezing behavior on test days in the hM4Di (left, 10 mice) and mCherry groups (right, 8 mice) on test days. *p < 0.05, **p < 0.01 (two-way ANOVA with post hoc comparisons; group × treatment interaction, p < 0.05). Error bars indicate standard error of the mean (SEM). Source data are provided as a Source Data file. See also Supplementary Figs. 1 and 2.
