Persistent CREB phosphorylation with protection of hippocampal CA1 pyramidal neurons following temporary occlusion of the middle cerebral artery in the rat

Phosphorylation of the DNA-binding transcription factor, cyclic AMP respons e element binding protein (CREB), was immunohistochemically examined in rat brain hippocampal CA1 in order to examine the ischemic vulnerability of th is region from the viewpoint of CREB activation The rat brain had been subj ected to 90-min focal ischemia followed by various periods of recirculation . Focal ischemia was induced by occlusion of the middle cerebral artery usi ng the intraluminal suture method. CA1 pyramidal neurons in the sham animal s showed definite immunoreactivity with anti-CREB antibody, which binds to both unphosphorylated and phosphorylated CREB, while reactivity with anti-p hosphorylated CREB antibody was barely detectable in these neurons. In cont rast, at 3.5 h of recirculation, a significant increase in the number of ph osphorylated CREB-positive neurons was noted in the CA1 on both sides, and the increase continued until 48 h of recirculation with a tendency for grad ual decline. At each period, the ischemic side showed a more marked increas e in the number of immunoreactive cells as compared to the nonischemic side . Cresyl violet staining revealed CA1 pyramidal neurons to be maintained in tact until 14 day of recirculation, at which time CREB phosphorylation has returned to the control level. Transient global ischemia is known to induce only mild CREB phosphorylation in the CA1 followed by a frank neuronal los s in this region. These data suggest that CREB phosphorylation can be persi stently activated in CA1 neurons after focal ischemia and that this phenome non may be closely associated with protection of these neurons. (C) 2000 Ac ademic Press.