MK-801 preconditioning offers protection against a wide range of (A) NMDA and (B) staurosporine concentrations. Cortical cultures were pretreated with 1 μm MK-801 or vehicle for 30 min and returned to drug-free CM for 48 hr before being exposed to NMDA for 5 min or staurosporine for 6 hr as described in the legend to Figure 1. Dishes were then washed once in CSS buffer, and saved conditioned medium was returned to the cultures for 24 hr, at which time cell viability was assessed by PI exclusion described in the legend to Figure 1. Results are presented as percent viable cell counts in quadruplicate dishes. InA, values are means ± SEM of at least four separate determinations, and values in B are of two separate experiments. *p < 0.01 compared with non-MK-801-treated conditions.