N2A-FmK6H cells were treated with vehicle or 1 μM norBNI for 1 h followed by 30-minute treatment with vehicle or 10 μM U50,488H. Cells were lysed and receptors were partially purified. The eluted samples were used for immunoblotting with indicated phospho-specific antibodies. Staining intensity of each phosphorylated KOPR was normalized against that of the total KOPR in the same lane. Data were then normalized against those of 10 μM U50,488H-treated group and each value represents the mean ± S.E.M of 4–6 independent experiments. Data were analyzed by one-way ANOVA followed by Newman-Keuls post hoc test. (***:p<0.001, compared to untreated group; ###:p<0.001, compared to U50,488H-treated group).