Global Ischemia Activates Nuclear Factor-κB in Forebrain Neurons of Rats

Abstract

Background and Purpose After global ischemia, brain levels of hydrogen peroxide, oxygen radicals, and the cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) are increased. Oxygen radicals, TNF-α, and IL-1β are known to activate nuclear factor-κB (NF-κB) in vitro. The present study was performed to determine whether NF-κB was activated in vivo by global ischemia in hippocampal CA1 neurons. Methods Adult male rats were subjected to 30 minutes of four-vessel occlusion and killed 72 hours later. Levels of NF-κB p50 and p65 subunits in hippocampus were determined by immunocytochemistry, Western blot, and gel-shift analysis. Specific labeling of DNA strand breaks was demonstrated by means of an Apoptag apoptosis detection kit. Results Labeling of DNA strand breaks was present at 72 hours. Chromatin compaction and segregation, a characteristic of apoptosis, was observed in sections stained with hematoxylin and eosin. NF-κB p50 and p65 immunoreactivity localized only to nuclei of CA1 neurons at 72 hours after reperfusion. Induction of the activated p50 and p65 subunits was confirmed by Western blot and electromobility shift analysis. The results demonstrate that NF-κB is activated selectively in hippocampal CA1 neurons at 72 hours after four-vessel occlusion, which is at the approximate time of CA1 neuronal cell death. Conclusions Transient forebrain ischemia resulted in a marked activation of nuclear NF-κB in the highly vulnerable CA1 sector. Intense nuclear localization of NF-κB was associated only with dying neurons; regions of the hippocampus that were not vulnerable to four-vessel occlusion did not exhibit nuclear NF-κB localization. The elevation of NF-κB in degenerating CA1 neurons may be associated mechanistically with apoptotic or necrotic cell death.