Mechanical allodynia of rats in repetitive-crossover carrageenan injection with a 2-week interval. Rats of each group were tested for mechanical allodynia of bilateral hind paws at time points of before (Base), and 4 h, 24 h, 48 h, 72 h after carrageenan-injection. The first injection was administered into the plantar surface of the right paw (a and b); the second injection was administered into the left paw 2 weeks later (c and d). The results showed a sustained decrease of mechanical threshold in the initial injected paw (d). Error bars indicated standard error of the mean. Ten rats for each group. ** p < 0.01, vs. the control group; # p < 0.05, ## p < 0.01, vs. the model group.