Figure 1

Induction of transient pain by co-injection of PGE ₂ (0.5 μg) and bradykinin at different concentrations. (a) Primary mechanical hyperalgesia as assessed by ascending pressure applied to the knee joint. Here, the desired drop in mechanical thresholds from baseline (BL) of more than 30% was obvious starting from 0.75 μg bradykinin in an escalating dose design (n = 4). For the chosen dose of 182.25 μg, this was verified in bradykinin-naïve animals (n = 4). Furthermore, the pain-related behavior induced by this concentration could be reversed by morphine (Mo; n = 4). (b) Weight force on the injected hindpaw (as percentage of total weight on both hindpaws). Here, a significant effect was obvious for concentrations of 22.25 μg and higher. Again, this effect could be verified in bradykinin-naïve animals and morphine administration prevented weight shifting. Data are presented as mean ± standard error of the mean. * P < 0.05 as obtained using t-tests applying Bonferroni-Holm correction. PGE_2, prostaglandin E₂.