Figure 3. Maximal rate of force development, +dF/dt and maximal rate of relaxation, -dF/dt with increasing concentrations of racemic ketamine (shaded square, n = 12), S(+)-ketamine (black square, n = 12) and R(-)-ketamine (open square, n = 11); mean values +/- SD. Significant differences of the comparison between increasing concentrations of either the isomers or the racemat with the initial control are shown (*P < 0.05).