Fig. 2. Pain behavior and hyperalgesia induced by intraplantar capsaicin in wild-type (WT) and α2A-adrenoceptor knockout (KO) mice. ( A ) Duration of licking behavior in the first 10 min after administration. ( B ) Responses to mechanical stimulation of the hind paw with von Frey hairs in the baseline condition (pre) and 10 min after injection of capsaicin (Caps). ( C ) Responses to mechanical stimulation of the hind paw 10 and 30 min after capsaicin ipsilateral (left) and contralateral (right) to the injection. In B , data are shown as mean percent response frequency at each stimulus intensity. In C , response frequencies at all stimulus intensities in each condition are pooled, and the differences between the pooled data obtained after and before capsaicin treatment are shown (score > 0 represents hyperalgesia). n =6/group. The error bars represent SEMs. ** P < 0.01 ( t test).