Fig. 1. Mechanical withdrawal threshold and response to inflammation at different developmental ages. The mechanical withdrawal threshold (von Frey hair number [vFH]) of the ipsilateral and contralateral paw is represented at baseline and 3 h after hind-paw injection of carrageenan (ipsilateral post carrageenan; contralateral post carrageenan). The withdrawal threshold increases with increasing postnatal age. At each age, the threshold of the ipsilateral injected paw after carrageenan was significantly lower than in all other groups.  Data points = mean ± SEM. **  P < 0.01, one-way analysis of variance with Tukey  post hoc comparison; n = 32–40 in all groups.