INDUCTION OF HEME OXYGENASE-1 (HO-1) AFTER TRAUMATIC BRAIN INJURY IN THE RAT

The induction of heme oxygenase-1 (HO-1), the 32 kDa heat shock protei n, was examined in the traumatized rat brain. At 24 h after either mil d or severe brain injury or sham surgery, HO-1 was immunolocalized in fixed sections of brain. After mild brain injury, hemorrhage was appar ent in the subarachnoid space, external capsule and cerebellum. HO-1 w as induced in similar areas in macrophages in the subarachnoid space a nd in glia in the cortex adjacent to the site of impact, the ipsilater al hippocampus, external capsule and cerebellum. After severe brain in jury, extensive hemorrhage occurred in the external capsule, hippocamp us and cerebellum. HO-1 was induced in glia in these areas of hemorrha ge but was more extensive than that seen after mild injury and include d the contralateral external capsule and hippocampus. These findings d emonstrate remarkable induction of HO-1 in glia in the injured brain. Since heme is a potent inducer of HO-1, it is likely that the subarach noid and/or intraparenchymal blood induced HO-1 in the glia where the heme was metabolized to biliverdin, iron, and carbon monoxide.