The von Frey Test.

The von Frey test was performed as previously described (41). C57BL/6 mice (male, weighing 22–30 g at the time of the test) were acclimatized to an elevated metal mesh floor chamber (10.0 × 16.0 × 9.0 cm) for 60 min before the von Frey test. Mechanical hyperalgesia was assessed by measuring the left hind-paw withdrawal response to stimulation with a series of von Frey filaments (0.04–2.0 g; Aesthesio) presented perpendicular to the plantar surface. We determined the 50% paw withdrawal threshold using Dixon’s up-down method (42). Clodronate was injected i.v. via the tail vein 60 min before the von Frey test in a volume of 100 μL per 10 g of body weight.