Fig. 2. Stress-induced hyperalgesia in α-2A knockout (KO) mice. (A ) Paw withdrawal latencies from a 50°C hotplate in wild-type (WT) and α-2A KO mice after no stress (red bars , n = 6) or ultrasonic stress (blue bars , n = 12). (B ) Paw withdrawal latencies in WT mice (n = 11) and α-2A KO mice (n = 5) tested once on a hotplate at various times after the initiation of 10-min ultrasonic stress. (C ) Paw withdrawal latencies in α-2A KO mice after no stress (red bars , n = 6) or ultrasonic stress (blue bars , n = 6) on 3 consecutive days. The α-2A KO mice exhibit a prolonged nonhabituating hyperalgesia instead of analgesia in response to ultrasonic stress. *=P < 0.05; ***=P < 0.001, increase in latency versus no stress (analgesia); +=P < 0.05; +++=P < 0.001, decrease in latency versus no stress (hyperalgesia). Data are expressed as mean ± SEM.