2.6.1 Hot plate test
Heat thresholds were measured in the hot plate test. Animals were placed
in their home cages and allowed to acclimate for at least 30 min before
testing. After habituation, an unrestrained animal was placed on the
metal surface of the hot plate, which was maintained at a constant
temperature of 55℃. The response latency (i.e., the time before
nocifensive behavior was exhibited) was recorded. Nocifensive behaviors
included forepaw withdrawal or licking, hind paw withdrawal or licking,
stamping, leaning posture, and jumping. If no behavioral response was
elicited after 40 s (cutoff time), the animal was removed from the hot
plate to prevent tissue damage. This procedure was repeated three times
and the average across trials was used for data analysis.