2.5 Response to mechanical stimuli
We evaluated mechanical hypersensitivity by measuring the hind paw
withdrawal response to von Frey filament stimulation. Mice were placed
individually in Plexiglas cages positioned on a wire‐mesh stand. Mice
were allowed to acclimate to the environment for approximately 30 min
before testing. Low force (0.07 g) and high force (0.45 g) monofilaments
(Stoelting Co., Wood Dale, IL) were applied to a fixed point on the
midplantar surface of each hind paw (Guan,
Liu, Tang, Raja, Anderson & Dong, 2010). Each von Frey filament was
applied 10 times successively at approximately l–2-s intervals.
Vertical elevation of the paw and licking associated with the mechanical
application were considered withdrawal responses. Paw withdrawal
frequencies (PWF) were calculated for both hind paws.