Figure 1: Ketamine concentrations in plasma or brain and potential neurotoxicity following a 5-min, 2-, 4-, 6- or 18-h withdrawal period. Ketamine (20 mg/kg x 6 injections) was administered subcutaneously at 2-h intervals (n=5/group). Ketamine levels, both in plasma and brain, were relatively high after 5 min and then began to sharply decrease by 2-4 h, and reached approximately zero 6 h after ketamine administration (A). Quantitative analysis of ketamine-induced neurotoxicity as indicated by cell death detection ELISA is shown in B. For each condition, at least five animals (n=5/group) were assayed. The cell death ELISA data are presented as means ± SEM. A probability of *p<0.05 was considered significant (one-way ANOVA with Holm-Sidak test).