Fig. 2. Response to mechanical stimulation with von Frey filaments in the sural skin territory for bupivacaine-loaded microspheres (BLM)–treated group (n = 12) and spared nerve injury (SNI) control animals (n = 11). The control animals demonstrated a marked decrease in mechanical withdrawal threshold after SNI surgery (P < 0.01 compared with baseline). The treated group showed an increase in threshold (corresponding to the weight of the paw passively lifted by the von Frey filament) while all animals were blocked (dark gray zone ), a mean intermediate response when some animals lost their block (light gray zone ), and marked hypersensitivity when all blocks faded (P < 0.001 compared with baseline). No statistically significant difference was observed between the control and bupivacaine-treated groups after day 10 (P > 0.05).