Differences in infarct evolution between lipopolysaccharide-induced tolerant and nontolerant conditions to focal cerebral ischemia

Object. Although brain tissue may be protected by previous preconditioning, the temporal evolution of infarcts in such preconditioned brain tissue during focal cerebral ischemia is largely unknown. Therefore, in this study the authors engaged in long-term observation with magnetic resonance (MR) imaging to clarify the difference in lesion evolution between tolerant and nontolerant conditions. Methods. Bacterial lipopolysaccharide (LPS; 0.9 mg/kg) was administered intravenously to induce cross-ischemic tolerance. Focal cerebral ischemia was induced 72 hours later in spontaneously hypertensive rats. Serial brain MR images were obtained 6 hours, 24 hours, 4 days, 7 days, and 14 days after ischemia by using a 7.05-tesla unit. Lesion-reducing effects were evident 6 hours after ischemia in the LPS group. Preconditioning with LPS does not merely delay but prevents ischemic cell death by reducing lesion size. Lesion reduction was a sustained effect noted up to 14 days after ischemia. Reduction of local cerebral blood flow (ICBF) in the periinfarct area was significantly inhibited in the LPS group, which was correlated with endothelial nitric oxide synthase (eNOS) expression. Conclusions. Significant preservation of ICBF in the periinfarct area, which is relevant to sustained upregulation of eNOS, could be a candidate for the long-term inhibiting effect on infarct evolution in the LPS-induced tolerant state.