Fig. 1. Response to nociceptive testing before and after treatment with fentanyl, 320 μg subcutaneously on Day 0. Data are represented as withdrawal threshold to positive airway pressure (P^aw)(left ), withdrawal latency to radiant heat (middle ), or withdrawal threshold to punctate testing with von Frey filaments (right ). Each symbol represents the mean ± SE of 6 animals. *P < 0.05 versus  Day 0.