Toll-like receptor 4 is associated with seizures following ischemia with hyperglycemia

Seizures are a common sequel of cerebral ischemia, and hyperglycemia markedly increases the onset of seizures following an ischemic insult. However, the underlying mechanism of seizures is unclear. The toll-like receptor 4 (TLR4) pathway is known to be involved in temporal lobe epilepsy. The present study investigated the potential involvement of TLR4 in the pathogenesis of seizures following cerebral ischemia with hyperglycemia. Fifteen minutes of global ischemia was produced in adult Wistar rats using a 4-vessel occlusion method. Hyperglycemia was induced via an intraperitoneal injection of glucose 15 min prior to ischemia. We determined that 56.7% of the hyperglycemic rats, but none of the normoglycemic rats, developed tonic-clonic seizures within 12h after ischemia. TLR4 was mildly expressed in a few cells in the control hippocampus, primarily in interneurons, and was localized in the cytoplasm. The TLR4-positive cells were significantly increased 3-12h after ischemia. In the hyperglycemic ischemia group, TLR4-positive cells were further increased in quantity and intensity, with a peak at 3h after ischemia relative to the normoglycemic group. There was no difference in the expression of TLR4 between the hyperglycemic ischemia and LPS groups or between the hyperglycemic non-ischemia and control groups. Western blot analysis consistently exhibited an increase in TLR4 protein levels in the CA3 region 3h after hyperglycemic ischemia. High mobility group box 1 (HMGB1) (an endogenous ligand of TLR4) was localized in the nucleus of neuronal cells throughout the hippocampus in the control animals. We observed a dramatic decrease in HMGB1 immunostaining at 3h after hyperglycemic ischemia that gradually returned to control levels. These results suggest that the TLR4 pathway is associated with seizures following global ischemia with hyperglycemia, which provides a new direction for the study of the pathogenesis of seizures that result from hyperglycemic ischemia.