2.4.2. Von Frey Filament Test

Paw withdrawal threshold (PWT, in grams) in response to calibrated von Frey filaments (Stoelting, Wood Dale, IL, USA) was applied to the right hindpaw to assess mechanical hyperalgesia/allodynia as a positive sign of nociceptive behavior, as previously described [7,31]. The rats were placed in compartmentalized clear plastic chambers, which were set on an elevated metal mesh floor; we applied a series of von Frey filaments to the middle of the plantar region by Chaplan’s up–down method to determine the closest filament to the threshold of pain response (licking or withdrawal) [34]. PWT was also assessed from the average of three tests, separated by 3 min, by independent examiners.