Comparison of antinociceptive effects of KGOP01 and
OP-NT hybrids 7 and PK20 in the tail-flick
test in mice after sc administration. Groups of mice were treated
with KGOP01 (1.82 μmol/kg), 7 (2.64
μmol/kg), PK20 (5.52 μmol/kg), or saline
(control), and tail-withdrawal latencies were measured at different
time points after drug administration. Data are shown as means ±
SEM (n = 5 to 6 mice per group). **P < 0.01 and ***P < 0.001 vs saline group; #P < 0.05, ##P < 0.01, and ###P < 0.001 hybrid 7 vs PK20; §§P < 0.01 and §§§P <
0.001 hybrid 7 vs KGOP01; two-way ANOVA
with the Bonferroni post hoc test.