Fig. 4. The effects of DL-2-amino-5-phosphonovaleric acid (AP-5; 10−4m) on the relations between extracellular Mg2+concentration ([Mg2+]o) and isoflurane (0.7 vol%)-induced inhibition of population spikes (PSs). Open circles = the artificial cerebrospinal fluid (no antagonist); closed circles = AP-5. Data points (mean ± SD) are expressed as percent of control (normalized to the value in the absence of anesthetic at each [Mg2+]o) for five determinations from separate slices. Data points were fitted to a linear function (continuous lines).