Animals

Male Sprague-Dawley (SD) rats aged 5–6 weeks, weighing 240–250 g, were purchased from Beijing Huafukang Bioscience Co. Ltd (Beijing, China). The rats were given water and food ad libitum and were housed in conditions of constant temperature (22 ± 2°C) and humidity (50 ± 15%) with a 12-h light/dark cycle. All animals were adapted to the laboratory environment for at least 3 days before the experiment. This study was approved by the Animal Welfare and Ethics Committee of China-Japan Friendship Hospital (No. zyrhyy21-20-01-4). All experimental procedures were performed in accordance with the guidelines of the Animal Welfare and Ethics Committee of China-Japan Friendship Hospital and the International Association for the Study of Pain.