Remifentanil (batch number: 120801, Ren Fu Co, China) and sevoflurane (batch number: 08100931, Heng Rui Co., China) were supplied by the Department of Anesthesiology of Drum Tower Hospital (Nanjing, China). Remifentanil (80 µg/kg) was dissolved in saline (NaCl 0.9%) and infused subcutaneously over a period of 30 min (rate, 0.8 mL/h) using an apparatus pump. Control animals (sham-operated rats) underwent a sham procedure that consisted of the administration of sevoflurane plus the same volume of saline in identical conditions. BDNF-sequester TrkB/Fc (Sigma, USA) of 5 µg was dissolved in 10 µL saline. PNU-120596 (Sigma Chemical Co., St. Louis, MI), an α7-nAChRs agonist, was dissolved in 5% DMSO. The intrathecal injection of TrkB/Fc (5 µg) or PNU-120596 (8 µg) was performed 15 min before remifentanil was subcutaneously infused. A KCC2 inhibitor VU0240551 (Sigma, USA) was dissolved in 10 µL 0.01% DMSO.9 (link),31 (link) An intrathecal dose of 0.8 µg VU0240551 was administered 15 min before surgery in rats given PNU-120596. The intrathecal injections were made into the subarachnoid space on the midline between the L5 and L6 vertebrae in unanesthetized mice, according to the method of Hylden and Wilcox.32 (link) A Hamilton microsyringe with a 30-gauge needle was used.