(2R,6R)-HNK produced delayed antinociception (Panel B), while ketamine produced rapid and short-lived antinociception (Panel A). (2S,6S)-HNK did not produce antinociception at any time point (Panel B). The data were analyzed together using a repeated measures two-way ANOVA but are shown in two separate graphs for clarity. The error bars represent group means ± S.D. Comparisons are made between drug/dose and saline at the same time point: **P < 0.01, ***P < 0.001. N = 20 for saline control, N = 21 for ketamine 10 mg/kg, N = 10 for ketamine 30 mg/kg, and N = 22 for both HNK groups.