Fig. 2. Log dose–response curves for the antinociceptive effects (percentage maximum possible effect) of intrathecally administered morphine (left ) or dexmedetomidine (right ), alone or with the addition of 30 or 100 μg racemic ketamine, R  (−)-ketamine, or S  (+)-ketamine. Each point represents the mean ± SEM of the data from 5–14 animals.