Figure 1.

Repeated morphine induces pain sensitivity to mechanical stimuli. Measurements are taken 12 h after repeated saline (□) or morphine administration (▪). Values are expressed as mean %±SEM from baseline, set to 100 (a, b, d), except for the hot plate test, which shows raw data (c). (a) Mechanical paw thresholds measured with von Frey test, n=6. (b) Paw withdrawal latencies to heat stimulation, Hargreaves test, n=6.(c) Paw withdrawal latencies to heat stimulation, hot plate test, n=6–7. (d) tail-flick latencies to heat stimulation, hot tail immersion test, n=6–7. *P<0.05, saline vs morphine; unpaired t-test. ^#P<0.05, vs baseline, paired t-test.