Activin A or NGF injection induces tactile allodynia. Rats received a 20 μl injection of activin A, NGF, saline, or BSA solution under the skin of the left ankle. A, Leg withdrawal was assessed with von Frey filaments at 1-48 h after injection, and the number of animals with a response was scored in the table. B, The withdrawal threshold among responding animals was averaged and plotted in the bottom graph. One microgram of activin A induced tactile allodynia at 1 h that was still present at 48 h (*), and 300 ng of NGF induced allodynia and lasted at least 12 h after injection (#). Data from eight activin A, six NGF, six saline, or six BSA animals were analyzed by ANOVA followed by Fisher's PLSD. *,#p < 0.05 denotes the significance level.