The inducible isoform of the enzyme cyclooxygenase-2 (COX2) is an immediate early gene induced by synaptic activity in the brain. COX2 activity is an important mediator of inflammation, but it is not known whether COX2 activity is pathogenic in brain. To study the role of COX2 activity in ischemic injury in brain, expression of COX2 mRNA and protein and the effect of treatment with a COX2 inhibitor on neuronal survival in a rat model of global ischemia were determined. Expression of both COX2 mRNA and protein was increased after ischemia in CA1 hippocampal neurons before their death. There was increased survival of CA1 neurons in rats treated with the COX2-selective inhibitor SC58125 {1-[(4-methylsulfonyl) phenyl]-3-trifluoro-methyl-5-[(4-fluoro)phenyl] pyrazole} before or after global ischemia compared with vehicle controls. Furthermore, hippocampal prostaglandin E 2 concentrations 24 h after global ischemia were decreased in drug-treated animals compared with vehicle-treated controls. These results suggest that COX2 activity contributes to CA1 neuronal death after global ischemia.Cyclooxygenase (prostaglandin G͞H synthase) is the first committed step in the production of prostaglandins and thromboxanes. Two forms of the cyclooxygenase enzyme have been cloned. Cyclooxygenase-1 (COX1) is constitutively expressed in many tissues including platelets, gastrointestinal mucosa, and kidney (1-3). The inducible form, cyclooxygenase-2 (COX2), is primarily expressed in leukocytes and brain (4). Its expression is induced by cytokines and inhibited by glucocorticoids, and it is an important mediator of cell injury in inflammation (5-7). Transcription of COX2 mRNA does not require new protein synthesis; therefore, it is an immediate early gene (6). The rat brain COX2 is identical to the nonnervous system COX2 (8). Its mRNA expression is rapidly induced by synaptic activity but blocked by the N-methyl-Daspartate receptor antagonist MK801 (8). This finding suggests that COX2 transcription is induced by increased intraneuronal Ca 2ϩ . COX2 is found in dendrites of neurons that receive excitatory input (9). Thus, COX2 may produce rapid neuronal responses to synaptic activity.Neuronal excitation and increased intracellular calcium, two stimuli that induce expression of COX2, are also important in the pathophysiology of neuronal death in ischemia and a variety of neurodegenerative diseases (10, 11). In nonneural cells, COX2 activity mediates inflammatory injury (12); however, COX2 overexpression may prevent apoptosis in intestinal epithelium (13). What role COX2 expression and activity have in mediating injury after global ischemia in brain is unknown. To address this question, the expression of COX2 mRNA and protein was studied in rat brain after global ischemia, and the effect of treatment with a selective inhibitor of COX2 {SC58125; 1-[(4-methylsulfonyl)phenyl]-3-trifluoro-methyl-5-[(4-fluoro)phenyl] pyrazole} on hippocampal neuronal survival and prostaglandin E 2 (PGE 2 ) concentrations was determined. METHODSAnimal M...

Using in situ hybridization, Northern blot analysis, Western blot analysis, and immunocytochemistry, mRNA and protein expression of the novel DNA damage-inducible gene GADD45 was examined in the rat brain at 0.5, 2, 4, 8, 16, 24, 48, and 72 hours after 15 minutes of transient global ischemia. Transient ischemia produced by the four-vessel occlusion method resulted in DNA double-strand breaks and delayed neuronal cell death in vulnerable neurons of the hippocampal CA1 sector, the hilus, dorsal caudate-putamen, and thalamus, as shown by in situ DNA nick end-labeling and histologic staining. GADD45 mRNA was transiently increased in less-vulnerable regions such as the parietal cortex (up to 8 hours after ischemia) and dentate granule cells (up to 24 hours after ischemia) but was persistently increased in vulnerable neurons such as CA1 pyramidal neurons (up to 48 hours). GADD45 immunoreactivity was increased in both vulnerable and less-vulnerable regions at earlier reperfusion periods (4 to 16 hours), but thereafter immunoreactivity was decreased below control levels in most vulnerable regions before delayed cell death and DNA double-strand breaks. At 72 hours after transient ischemia, a moderate increase in GADD45 immunoreactivity was still detectable in some CA3 neurons and in a few surviving neurons in the CA1 region. Double staining performed at 16 to 72 hours after ischemia revealed that GADD45 immunoreactivity was persistently increased in neurons that did not develop DNA damage. Because GADD45 protein may participate in the DNA excision repair process and because it has been shown that this protein is also overexpressed in neurons that survive focal ischemia and kainate-induced epileptic seizures, the results reported here support the hypothesis that GADD45 could have a protective role in neuronal injury.

Recent advances in magnetic resonance spectroscopy permit noninvasive study of brain metabolism in vivo, 31P spectroscopic imaging being the method for evaluation of localized phosphorous metabolism. Experimentally, an ischemic-hypoxic brain insult is characterized by depletion of high energy metabolites. These changes are seen immediately after an ischemic insult. We had the opportunity of carrying out 31P spectroscopic imaging of hyperacute cerebral infarction, while MRI and CT were negative. Cerebral infarction of the middle cerebral artery territory was suggested by 31P spectroscopic imaging, which was closely consistent with a later-developing region of low density on CT. In cerebral infarction, early detection of the lesion is a useful pointer to the patient's prognosis, making 31P spectroscopic imaging a potential tool.

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