Measurement of mechanical allodynia
Mechanical allodynia was assessed by measuring rats’ paw withdrawal threshold in response to probing with a series of fine calibrated filaments (von Frey, Stoelting, Wood Dale, IL). Rats were placed in suspended plastic cages with wire mesh floor, and each von Frey filament was applied perpendicularly to the plantar surface of the paw. The “up-and-down” method (sequential increase and decrease of the stimulus strength) was used to determine the withdrawal threshold Dixon’s nonparametric method was used for data analysis, as described by Chaplan et al (Chaplan, Bach, Pogrel, Chung & Yaksh, 1994). Data were expressed as the mean withdrawal threshold.