Fig. 3. K⁺-evoked (46 mM) glutamate release from perfused rat cerebrocortical slices was inhibited in a concentration-dependent manner by ketamine. Percent inhibition of release was calculated from the S²/S¹ratios obtained as shown in figure 1, and inhibition is denoted by a downward deflection in the concentration response curve (i.e. , 0 = no inhibition; −60 = 60% inhibition). Data are mean ± SEM (n ≥ 5). The estimated half-maximum inhibition of release value for thiopental was 18.2 μM.