(A) Heat and mechanical sensitivity in WT and tPA−/− mice. n=5 mice. Heat and mechanical pain sensitivity was measured by radiant heat (Hargreaves) and von Frey hairs, respectively. (B) Acute morphine (10 mg/kg, s.c.)-induced analgesia in WT and tPA−/− mice. n=5 mice. Morphine analgesia was determined by tail flick latency in the hot water immersion test. (C) Chronic morphine (10 mg/kg, s.c., daily for 10 days)-induced antinociceptive tolerance in WT and tPA−/− mice. *P<0.05, compared with WT mice at the same time point, n=6 mice, t-test. Morphine analgesia was determined by tail flick latency at 30 min after the daily morphine injection.