Corticosterone (CORT, 235135) was purchased from sigma, nor-Binaltorphimine dihydrochloride (nor-BNI, ab120078) and anti-dynorphin A17 antibody (DYN A17, ab82509) were purchased from Abcam, Anti-oprk 1 antibody (A14035) was purchased from Wuhan ABclonal, magnolol (M111378) was purchased from aladdin, uoxetine (HY-B0102) was purchased from MCE. Magnolol (25/50/100 mg/kg/day), nor-BNI (10 mg/kg/day) and uoxetine (10 mg/kg/day) were uniformly dispersed in 1% Tween 80 and then dissolved in distilled water. All drugs were administered in an injection volume of 4 mL/ kg - 1 (i.p.). All drugs were dispensed on the spot [34] .