Postischemic seizures and necrotizing ischemic brain damage: neuroprotective effect of postischemic diazepam and insulin. Insulin has recently been shown experimentally to modify ischemic brain damage when administered either before or after the episode of ischemia. In controlled studies in the rat, high doses of insulin (greater than or equal to 8 IU/kg) result in seizures and early death. The present study was undertaken to determine whether diazepam, a potent, centrally penetrating GABAmimetic, alone or in combination with insulin, could mitigate postischemic seizures or regional selective neuronal necrosis and infarction. Forebrain ischemia was induced in rats for 10 1/2 minutes by carotid clamping and hypotension. The animals were observed clinically until elective perfusion-fixation and quantitative pathologic examination at 1-week recovery. Diazepam, either alone or with insulin, reduced regional brain necrosis and reduced the seizure rate. Insulin alone also led to reduced regional necrosis. However, the combination of diazepam plus insulin yielded the greatest proportion of undamaged brains in the hippocampus, thalamus, and midbrain. In the neocortex, the diazepam-only group showed the greatest number of normal hemispheres. Hypothalamic infarction was eliminated by all three treatments. Seizures per se were associated with increased damage in the cerebral cortex, thalamus, and brainstem, irrespective of treatment group. The findings indicate that ischemic brain necrosis can be mitigated by diazepam and insulin treatment begun in the immediate postischemic period. 