Paw withdrawal thresholds to mechanical stimulation were measured using an electronic von Frey anesthesiometer (IITC model Alemo 2390–5, Woodland Hills, CA) as described previously.24 (link) Mice were placed on an elevated metal mesh table where they were habituated under individual, inverted plastic cages for at least 20 min until exploratory behavior had ceased. After the habituation period, a force was applied to the midplantar region of the hind paw with a semiflexible tip connected to the anesthesiometer. Mechanical stimulation was terminated when the animal withdrew its paw and the value of the applied force was recorded in grams. Mechanical paw withdrawal thresholds were obtained twice for each paw, and are reported as the mean of two duplicate determinations obtained from each animal, averaged across subjects. Mechanical thresholds were taken at 5, 30, 60, and 120 min post-capsaicin injection. AM251 (3 mg/kg), AMG9810 (3 mg/kg), or vehicle were administered 30 min prior to i.pl. capsaicin or vehicle injection.