Figure 4. Paw withdrawal latency to radiant heat after capsaicin (10 [micro sign]g/20 [micro sign] l) or vehicle (20 [micro sign]l) injections. Preinjection withdrawal latencies were similar in NK-1 knockout (n = 10) and wild-type mice (n = 10). Capsaicin injection had no effect on the withdrawal latencies in the NK-1 knockout mice, whereas in the wild-type mice the withdrawal latencies were decreased (**P < 0.01 compared with the preinjection values; error bars = SD). Vehicle injections did not have an effect on the withdrawal latencies in NK-1 knockout (n = 7) or wild-type (n = 6) mice.