Mechanical Sensitivity Testing With von Frey Filaments

On test days, rats were placed on an elevated mesh galvanized steel platform in individual chambers with a hinged lid and allowed to acclimate for at least 20 min before exposure to mechanical stimuli. Von Frey filaments (ranging from 0.4 to 15.0 g and increasing in ∼0.25 log increments; North Coast Medical, Morgan Hill, CA) were applied to the plantar surface of each hindpaw, and the threshold stimulus to elicit paw withdrawal was determined in log grams using the “up-down” method as previously described (Chaplan et al., 1994; Leitl et al., 2014b; Legakis et al., 2019). Filament forces greater than 15.0 g were not used because they physically lifted the paw, and as a result, paw movement could not be reliably attributed to a withdrawal response by the subject. For rats receiving Ipl CFA or saline, only data from the injected paw were subjected to data analysis; thresholds in the uninjected paw were nearly always at the cutoff value of 15.0 g (data not shown). For rats receiving paclitaxel or saline, data from both paws were averaged within a rat and then across rats for subsequent analysis.