Male C57BL/6 mice were obtained from Beijing HFK Bioscience Co., Ltd., China. The mice were then randomly separated into sham and sevoflurane administrated (SEV) groups, with each group containing 20 animals. In SEV groups, mice were placed in an anesthetizing chamber and exposed to 2.5% sevoflurane (CAS No. 28523-86-6, no. S2464, Selleck, Shanghai, China) with complete oxygen for 2 h, and sham group mice were conducted with the same procedure without sevoflurane exposure.

The Sprague-Dawley rats (male, 20-month-old, 550-700 g, n = 6 per group) were obtained from the Beijing Vital River Laboratory Animal Technology Co., Ltd. (Beijng, China). A total of 78 rats were used in animal experiments. Rats were allocated into the following five experimental groups: control, Sev, Sev + Ech (L), Sev + Ech (M), and Sev + Ech (H). Ech (Sigma-Aldrich; purity 98%) was given to rats by intraperitoneal injection as a single dose of 20 (L), 40 (M), or 80 mg/kg (H) at 1 h before Sev exposure. The injection volume of each rat was 5 mL. For control and Sev groups, an equal volume of vehicle was intraperitoneally injected into rats. Then, rats except for the control group were anaesthetised with 2% Sev (Sigma-Aldrich) for 5 h. The histological and biochemical analysis of the hippocampus was done 48 h later after the rats were sacrificed and the brains were removed.