Antinociceptive effect of morphine in MOR-KO mice determined using tail-flick tests before and after they had been transfected with the dsAAV2-MORS196A-EGFP gene. (A) The time-response curves for saline and 10 mg/kg of morphine before (0 day M10) and 21 days (21 days M10) after transfection. ***P < 0.001 (vs. saline). (B) The mean AUC (area under curve) values for each treatment in Fig. 3A (n = 12). ***P < 0.001 (vs. saline).