Following behavioral testing, mice were returned to their home cages. After 2 h, mice were deeply anesthetized with isoflurane and sacrificed. The mouse skull was opened and whole brain was removed. Fresh tissues of BLA, vHIP and mPFC were isolated from the corresponding coronal sections under the stereomicroscope. Total RNA was extracted from the BLA, vHIP or mPFC using RNAiso plus reagent (Takara Biotech, Co., Ltd., Dalian, China) in accordance with the manufacturer’s instructions. DNA contamination was removed with RNase-free DNase. cDNA was synthesized from 1 µg of RNA with M-MuLV reverse transcriptase and random hexamer following the manufacturer’s instructions (Fermentas, Burlington, Canada). Quantitative real-time PCR (Q-RT-PCR) was performed using PIKoREAl96 detector (Thermo Scientific, USA). The mRNA levels of zif268 and arc in triplicate samples of reverse-transcribed cDNA were checked with SYBR Green PCR Master Kit (Promega Corporation, USA) in accordance with the manufacturer’s instructions. The primers for mouse zif268 were 5′-CGAACAACCCTATGAGCACCTG-3′ (forward) and 5′-GGCTGGGATAACTCGTCTCCAC-3′ (reverse). The primers for mouse arc were 5′-GCCAAACCCAATGTGATCCTG-3′ (forward) and 5′-CTGCTTGGACACTTCGGTCAAC-3′ (reverse). The mouse gapdh primers were 5′-GCGAGACCCCACTAACATCAA-3′ (forward) and 5′-GTGGTTCACACCCATCACAAA-3′ (reverse). The assays were initiated for 5 min at 95 °C, 40 cycles of 15 s at 94 °C, and 1 min at 60 °C. The threshold cycles of the target gene and gapdh were calculated. The amplification of zif268 and arc cDNA was normalized to the expression of gapdh. The relative mRNA expression levels of zif268 and arc were calculated using the 2ΔCT method.