MODULATION OF ORNITHINE DECARBOXYLASE MESSENGER-RNA FOLLOWING TRANSIENT ISCHEMIA IN THE GERBIL BRAIN

Ornithine decarboxylase (ODC) is the rate-limiting enzyme that catalyzes the synthesis of polyamines from ornithine and is thought to be involved in the cellular response to growth, differentiation, and stress. Previous studies have demonstrated that transient cerebral ischemia results in an increase in ODC activity and polyamine synthesis. We have used the Mongolian gerbil as a model system to test the hypothesis that the cellular response to ischemia induces a distinct pattern of ODC gene expression. Our results indicate that transient ischemia, induced by bilateral carotid occlusion, elevates ODC mRNA within 1-4 h after reperfusion, which correlates with increased ODC activity and polyamine synthesis. Increased ODC mRNA can be detected in the forebrain, striatum, hippocampus, and midbrain but not the cerebellum, which is not subject to ischemic injury. In contrast, c-fos mRNA increased by 15 min after reperfusion and actin mRNA did not demonstrate alterations in level after ischemia. Pentobarbital prevented the increase in ODC mRNA, whereas the glutamate antagonist MK-801 had no effect on the elevation of ODC gene expression after ischemia. We conclude that the ischemia-induced increase in ODC enzyme activity may be attributed in part to transcriptional activation of the ODC gene.