2.5. Nissl staining
The mice from each group were deeply anesthetized by intraperitoneal injection of 10% chloral hydrate and then subjected to transcardial perfusion with 0.9% NaCl, followed by fixation with 4% paraformaldehyde in 0.1 M phosphate buffer. Brain slices (5 μm) were deparaffinized and immersed in cresyl violet (C0117, Beyotime Biotechnology) for 10 min at room temperature. Brain sections were then dehydrated in graded alcohol, mounted with neutral balsam and observed under a light microscope. The hippocampal subregions including CA1, CA3 and DG were selected and viable neurons were calculated, respectively, from different groups.