Behavioural tests
All behavioural tests were performed 24 h after administration (days 2,
5, 9, 12, 16, 19, 23, and 26). The thermal nociceptive threshold was
assessed using the ZH-6C cold-plate (Anhui Zhenghua Biological
Instrument Equipment Co., Ltd.). The mice were placed on the cold-plate
floor. The temperature of the cold plate was kept constant at 4.0-4.2
°C. After allowing the mice to adapt for 1 min, the frequency of
hind-paw licking by the mice was recorded for 2 min.