A'-Methyl-D-aspartate (NMDA) has been implicated in a number of pathophysiologic conditions, including seizures. Magnesium is a physiologic blocker of the NMDA receptor. As magnesium sulfate (MgSO4) is currently used as a treatment for eclamptic seizures in North America, we examined the anticonvulsant effects of MgSO4 on central NMDA-induced seizures. Forty-one female rats were surgically anesthetized and a bipolar recording electrode was stereotaxically implanted into the dorsal hippocampus, while a cannula was implanted into the lateral cerebral ventricle for drug injection. Following 1-week recovery, baseline behavior and electrical activity were recorded. Two treatment protocols were examined: (a) chronic–intraperitoneal injection of 270 mg/kg MgSO4, followed every 20 min with 27 mg/kg MgSO4 for a total of 2 h; and (b) acute—intravenous injection of MgSO4 (30, 60, or 90 mg/kg) in a volume of 1.5 mL/kg via the tail vein. Following either treatment protocol, rats received 1 µ;L of 20 mg/mL NMDA via the...