Fig. 4. Raising divalent cation concentration to 1.6 mM Mg²⁺/2.0 mM Ca²⁺ after complete 4-AP washout reduced but usually did not block ictal-like activity.

A: Recording from entorhinal cortex in 0.6 mM Mg²⁺/1.2 mM Ca²⁺ solution in 4-AP (top), after 4-AP washout for 32 min (middle) and after 31 min in 1.6 mM Mg²⁺/2.0 mM Ca²⁺ solution (bottom). B: % time spent in SE + ictal-like events after 4-AP washout fell upon raising the divalent cation concentration (n = 8, measured for the 10 min period immediately prior to initiation of the solution change and for the 10 min period between 30 and 40 min following initiation of the solution change). Triangles represent the slice in A. C: Longest epileptiform event in 4-AP washout in each slice before and after raising the divalent cation concentration. Three of eight slices had no ictal-length events after raising divalent cation concentration. The unpaired point represents the slice that had only SE-like activity before the divalent cation concentration was raised. Excluding unpaired point, P = 0.237, n = 7 (Wilcoxon).