Animals were acclimated on a glass plate held at 30°C (model 390 series 8, IITC Life Science Inc.). A radiant heat source was applied to the hindpaw, and latency to paw withdrawal was recorded (46). Three trials were conducted on each paw, with at least 5 min between testing the opposite paw and at least 10 min between testing the same paw. To avoid tissue damage, a cutoff latency of 20 s was set. Values from each paw were averaged to determine withdrawal latency.