Time course and dose response of DAMGO in hMOR-T and hMOR rats. (A) DAMGO (3 μg/10 μl) was given at time 0 (arrow) and PWLs were measured at various intervals. The DAMGO induced analgesia developed quickly, reached a maximum ~15 min and the response returned to the baseline ~ 60 min later. (B) The DAMGO ED50 (μg/10 μl) obtained from dose–response analyses were 0.15 ±0.02 ((hMOR), 0.38 ± 0.08 (hMOR-T) and 0.66 ± 0.13 (GFP). The Hill coefficients were 0.6 for hMOR, 0.6 for hMOR-T and 0.7 for GFP.